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We are pleased to announce the call of “Late News” as poster presentations. The latest research topics newly found and/or achieved after the ordinary deadline of abstract submission can be accepted. The content of the abstract should be less than 300 words (or 2,000 characters) addressing magnet technology research and development (see the Submission Categories of MT27: https://csj.or.jp/MT27/scope/) The deadline of the abstract submission for the “Late News” is September 15, 2021. Please submit your “Late News” abstract through "Abstract Submission (and Your Submitted Abstract)" in the left menu or from the button "Submit new abstract" at the bottom (if the button, please use a browser other than Internet Explorer).
The conference information can be found at https://www.csj.or.jp/MT27/.
Fast ramping magnets are important accelerator components in several areas. In High Energy Physics they are needed in an accelerator ring for a Muon Collider, in booster accelerators for other colliders, and for production of high-intensity proton beams for high intensity targets. In the Basic Energy Sciences and the Department of Defense there is considerable need for intense levels of irradiation for material science and single-event effects component testing, which is critical for establishing hardware reliability in satellites. For applications such as accelerator driven modular nuclear reactors in Fusion Energy Sciences, a compact accelerator technology would enable either or both multiple accelerators and multiple beam ports into the core mitigating the difficult ultra-reliability requirement. A fast-cycling superconducting compact accelerator technology is also a critical and disruptive technology for commercial and medical applications. In this paper the performance of hyperconductors and high purity aluminum Litz cables is compared with those of fine filament LTS and HTS superconductors based on AC loss calculations. Suitability of each conductor is established on the basis of fast ramping magnet specifications for different accelerator applications. As an example, we consider concepts for muon beam acceleration to TeV-scale beam energies, which utilize fast ramping magnets in hybrid rapid cycling synchrotrons and recirculating linac designs. These concepts utilize lattices with fast-ramping normal conducting iron or superferric HTS-based dipoles interleaved with high field superconducting dipoles1,2,3. To minimize muon decays during the ramping cycle, these magnets would ideally provide peak ramp rates >1000 T/s with roughly ± 2T peak-to-peak magnetic field excursions. Finally, for suitable conductors, cable design for various accelerator magnet applications is explored.
As part of the FAIR project, the heavy-ion synchrotron SIS100 is currently under construction at GSI in Darmstadt. As a german in-kind contribution, GSI is delivering all superconducting modules for SIS100. This includes 108 dipole modules as well as 83 highly integrated quadrupole doublet modules. One quadrupole doublet module consists of two quadrupoles, one nested steering magnet, containing a vertical and a horizontal steerer, beam instrumentation, and depending on the position in the ring additional corrector magnets such as chromaticity sextupole or combined corrector magnets.
While the dipole production has been finished at the end of 2020, the quadrupole doublet module series manufacturing has just recently started after the First-of-series quadrupole doublet module has been delivered at the end of 2019 and undergone an extensive testing campaign until summer 2020.
The main features of the different module types will be presented as well as the results of the ongoing site acceptance tests. This includes results of the thermal evaluation, the evaluation of the magnetic field quality as well as mechanical stability of the cold mass during operation.
Recently, a domestic project for the construction of a 4th generation light source, Ochang Advanced Synchrotron for Industry and Science(OASIS), is embarked by the Ministry of Science and ICT in Korea. To increase the performance of the next generation storage ring, Seoul National University in collaboration with Pohang Accelerator Laboratory started a feasibility study on no-insulation(NI) HTS undulator magnet. We designed, constructed, and tested NI HTS undulator coil with 1.5 periods, 14 mm periodic length, and 6 mm magnetic gap. Performance and characteristic parameters of the coil are evaluated at different operating temperature ranges in a conduction cooling circumference: (1) maximum achievable magnetic field; (2) critical current; (3) characteristic resistance; and (4) joint resistivity. Based on the test results, we present preliminary design sets of undulator magnets with different specifications: (1) operating temperature; (2) periodic length; and (3) conductor specification.
Acknowledgment
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249). This work was also supported in part by MSIT and POSTECH.
Design and fabrication of a new Nb3Sn-based superconducting undulator (SCU) are underway at the Advanced Photon Source (APS) of Argonne National Laboratory in collaboration with Fermilab and Lawrence Berkeley National Laboratory. This device will be installed on APS’s storage ring and will deliver a wide range of hard x-rays to APS users. To develop a robust and reliable fabrication process, the magnet development consists of several steps. First, magnetic and mechanical simulations were performed to optimize the magnet design; then the design matured further by fabricating and testing a series of very short prototypes, ~8 cm long with a period length of 18 mm. These short prototype studies were previously reported [1, 2]. Second, the design was scaled to an intermediate length of 0.5 m. These two steps led to the final design of 1.1-m-long magnets, which are currently being fabricated. The quench behavior of each 0.5-m-long undulator magnet, as well as undulator assemblies from these magnets, was studied. The first SCU assembly did not meet the design specifications due to breakdown of the insulation. The second SCU assembly, with an improved design and fabrication process based on lessons learned, achieved the design undulator field of 1.2 T. The design was further optimized, and a third set of magnets was fabricated and successfully tested. Design features of the magnets, fabrication steps, and test results will be discussed in more detail.
[1] I. Kesgin et al., IEEE Trans. on Appl. Supercond., vol. 30, no. 4, pp. 1-5, 2020.
[2] I. Kesgin et al., IEEE Trans. on Appl. Supercond., vol. 29, no. 5, pp. 1-4, 2019.
The Fermilab Mu2e experiment is currently being built at Fermilab to search for evidence of charged lepton flavor violation through the direct conversion of muons into electrons. The experiment comprises three large superconducting solenoids; the transport solenoid consists of 52 superconducting coils arranged in an s-shaped pattern in order to guide muons from the source to the stopping target. The Transport Solenoid system is made of two independently powered and independently cryostated magnets, referred to as Transport Solenoid Upstream (TSU) and Downstream (TSD). Each TS superconducting coil is wound using NbTi superconducting cables stabilized with pure Aluminum. The impregnated coils are machined and subsequently assembled into Aluminum housing shells via a shrink fit process to form a total of 27 modules, which are then bolted together and electrically and cryogenically connected. Each shell is machined from a large forged billet to the precision needed to achieve the proper coil-shell interference as well as to preserve the spatial orientation of the 52 coils needed to satisfy the magnetic field requirements set by the mu2e experiment. The manufacturing of the Transport Solenoid cold mass is now concluded. This work summarizes the main aspects of the TS cold mass design, describes the manufacturing and assembly processes and discusses lesson learned from the fabrication.
As part of the European Strategy for Particle Physics there is an ongoing development towards a Future Circular Collider (FCC) where electron-positron collisions could produce Higgs particles in a low background environment due to the high center-of-mass energy and the leptonic nature of the collisions. Particle detectors are used to study these collisions and a strong magnetic field is required inside the detector volume to measure the particles’ momenta.
In the Innovative Detector for Electron-positron Accelerators (IDEA) concept a 6 m long solenoid is placed in between a tracker detector and the calorimeters. Since the superconducting solenoid is placed inside the calorimeter it needs to be as transparent as possible to particles that are produced in the collisions. This transparency is usually expressed in the number of radiation lengths, the length a particle travels through a medium before losing a certain amount of energy. For the IDEA detector the transparency of the magnet should be below one radiation length. This poses challenges for the superconducting magnet design, because a reduction in the amount of material naturally leads to a more challenging quench protection and higher stresses in the coil mass.
This paper compares different design options for the IDEA detector magnet, towards a design that combines the requirement of maximum particle transparency with suitable quench protection and mechanics. The goal is to design a 2 T magnet with a bore radius of 2.2 m. The stored energy of the magnet system will be around 160 MJ. This includes the iron yoke on the outside of the detectors. In this paper the transparency of the coil, support structure, quench protection, winding layout, conductor, mechanics, and current supply are discussed.
The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which provides external and in-house researchers with the possibility to perform a broad range of experiments in pulsed magnetic fields [1]. Being a member of the European Magnetic Field Laboratory (EMFL), HLD provides access and supports more than 100 scientific projects annually. At the HLD, such diverse high-resolution experimental techniques as electrical transport, magnetization, ultrasound, magnetostriction, magnetic resonance (ESR and NMR), permittivity, magnetocaloric effect, and high-field infrared spectroscopy in pulsed magnetic fields are available for users.
The Dresden High Magnetic Field Laboratory operates ten experimental cells equipped with a variety of pulsed magnets energized by two independent, modular capacitor banks with maximum stored energies of 50 and 14 MJ at 24 kV maximum operational voltage. The pulsed magnets at the HLD are subject of permanent improvements in terms of peak field, reliability, noise level, cooling time, and longevity. A number of pulsed-field magnets specialized for needs of some advanced experimental techniques are under design now. We discuss current pulsed-magnet upgrades, design improvements, and our operational experience obtained with the pulsed magnets at the HLD. We report the status of a triple-coil magnet, designed to reach repeatedly 100 T.
We acknowledge the support of the HLD at HZDR, a member of the European Magnetic Field Laboratory (EMFL), the DFG via SFB 1143, and the BMBF via DAAD (project-id 57457940).
[1] http://www.hzdr.de/hld
The Laboratoire National des Champs Magnétiques Intenses (LNCMI) is a French host facility for experiments in high magnetic fields. LNCMI is a member of the European Magnetic Field Laboratory (EMFL) with the Hochfeld-Magnetlabor in Dresden (HLD) and the High Field Magnet Laboratory in Nijmegen (HFML). The Toulouse facility is dedicated to the generation of pulsed magnetic fields. It offers 98.8 T nondestructively and 209 T with a semi destructive Megagauss installation. We focus here on the nondestructive activities. All the electromagnets that generate these high fields and their associated capacitor banks are developed in the laboratory. We present here some recent developments, as the operation of a 100 T magnet, the design of new capacitor banks and some ways to push the limits of nondestructive pulsed magnetic field above the actual 100.75 T world record.
Driven by the 1.4 GW generator, the 60TCW magnet was the most powerful controlled waveform system in the world and had always been one of most important magnets to the NHMFL and high-field research community because of its following unique features: (1) quasi-static field up to 60 T with 100 ms flat-top and total pulse-length of 2000 ms, (2) variable magnetic field waveforms such as staircase and triangle with flat-top (3) relative large bore (32 mm) and (4) very fast cooling time (20 minutes) between pulses. The magnet is composed of nine concentric coils, with each coil consisting of several conductor winding layers reinforced by a high-strength metallic shell. In late 2014 the magnet failed in coil 7 where the stress level was the highest. The simulations that followed indicated that the overall strength of the coil would increase by replacing a section of the reinforcing shell with Zylon fiber-epoxy composite. This reduces the stress and thus significantly lowers the level of plastic deformation in the windings. The role of the metal and Zylon fiber reinforcing layers in bearing the axial and radial Lorentz forces has been studied to optimize the magnet design. The results of the optimization will be discussed as well as challenges that have been presented in rebuilding the individual coils of the magnet.
High magnetic fields allow for the stabilization of otherwise inaccessible new quantum states of matter. A scattering technique is imperative for a deep and thorough microscopic understanding of these exotic high field phases in correlated electron systems. We report pulsed magnetic field installation for x-ray scattering experiments, aiming up to 60 T, within an international user consortium called HiBEF (Helmholtz International Beamline for Extreme Fields). The pulsed-field setup will be combined with the High Energy Density instruments at the European X-ray Free Electron Laser (XFEL) facility, covered x-ray energies from 5-25 keV. The European XFEL provides a unique time structure with bunch trains consisting of up to 2700 bunches separated by 220 ns. The pulse length of our high field magnet matches the length of the X-ray bunch train, 0.6 ms. This offers the opportunity to measure the field dependence of fundamental and/or superlattice diffraction intensities in a single magnetic-field pulse. We have developed a 750 kJ/24 kV capacitor bank with the peak current of 100 kA for energizing a horizontal bi-conical solenoid with 60 (20) degree opening at the outgoing (incoming) side of the XFEL pulses. This coil system integrates an eddy-current shield in order to minimize stray fields and vibrations due to interactions with the environment. We present the status of the project, including the coil design, magnet and sample cryo environment, as well as the X-ray goniometer.
We acknowledge the support of the HLD at HZDR, member of the European Magnetic Field Laboratory (EMFL).
We report on recent progress regarding the practical use and characterisation of fields in the 100-200T range with microsecond-duration at the LNCMI high-field magnet facility. Our Megagauss platform makes use of single-turn coils with 8-15mm diameter that are destroyed in the process, albeit with a close-to-100% chance of survival for scientific equipment in the bore. The setup permits several shots per day and is mainly used for experiments in condensed matter physics by LNCMI scientists and external users. In this context, our technical objectives are: firstly, a better characterisation of the generated field with respect to homogeneity requirements taking into account the coil deformation and asymmetry; and secondly, a better control of destructive effects associated with the explosive sublimation of conductor material at the highest fields. For this purpose both experimental and theoretical studies have been performed. A computer code has been developed that uses a multi-filamentary approach to first simulate the coil expansion, local heating and dynamic current distribution during a shot. The result is used to map out the field profile and to identify conductor regions with substantial sublimation. These hot-spots can then be treated by considering appropriate changes of the conductor's cross-sectional geometry. Originally based on circular current loops, we have also extended our approach to 3 dimensions using polygonal filaments to simulate the current feed-gap, i.e. the point where the current enters and leaves the coil, and its effect on field homogeneity. Experimentally, our principal tool are precise field and field-distribution measurements using pick-up and gradient coils as well as Faraday rotation imaging. Destructive effects at the highest fields are evaluated based on the post-mortem analysis of coil fragments, damage suffered by plastic tubes placed inside the bore and impact traces on protective elements.
We achieved both high electric conductivity and optimum strength in Cu-0.54Cr-0.046Zr alloy (wt%), and firstly characterized their properties at cryogenic temperature, which was comparable to those of Al60 both at 295K and 77K. Ordered clustering of solute atoms was revealed to be uniformly distributed in solution-treated samples. During deformation, those clusters became the heterogenous nucleation sites for precipitates growing in 2-D layer structure. 2-D layered precipitation had no evident influence on improving the conductivity. Aging treatment led to precipitates growing in 3-D particle shape. And due to the size in a couple of nanometer, aging-induced particle most maintained a coherency relationship with matrix. 3-D clustering had a relative high Cr (1~8 wt%) content, and played a crucial role on doubling the conductivity.
For high magnetic field, the pulsed magnets are normally designed with multiple coils. However, the magnetic field produced by the outer coil starts to drop at the moment when the inner coil starts working due to the electromagnetic coupling. Simulations show that the field drop is as much as 30% if the outer coil is driven by pulsed generator, with the result that the coil has to be designed to endure the magnetic force at the peak field but it contributes 30% less field. A novel scheme is proposed to eliminate the field drop by introducing compensation electromotive force in the coils. A triple-coil pulsed magnet and triple-coil transformer have been designed and manufactured. The inner, middle and outer coils of the magnet are connected in series with the inner, middle and outer windings of the transformer, and are energized with capacitor banks and pulsed generator. Experimental results show that the magnetic field produced increases from 8 T to 15 T with increasing the magnetic force in the outer coil, which proves the feasibility of the new scheme and the potential to produce 100 T.
State-of-the-art future lepton colliders, such as SuperKEKB, CLIC, FCC-ee or ILC require high quality positron sources. Positrons are created after the collision of electrons on a tungsten target and then focused to match the emittance of the injector chains within an Adiabatic Matching Device. This contains a Flux concentrator (FC), a magnet that produces the positrons yield. The FC is a tapered solenoid powered with fast pulses (microsecond) of high current (kiloamperes) at high repetition rates (hundreds Hz). The current pulse produces a strong magnetic field (3-8 T) at the magnet entrance that rapidly decays (over few cm) to zero. This paper describes the finite element model of the FC and the transient electromagnetic simulation capable of describing experimental data in terms of current, field and voltage. The computed field map is transferred into particle tracking code to compute the positron yield. The coil configuration is optimized to minimise the voltage and Lorentz forces and to maximise the yield. Three optimized designs are intended to be tested at the KEK test bench.
Fujikura Ltd. has developed REBa2Cu3Oy (REBCO) high temperature superconductors (HTS) for various applications. Recently, Fujikura has manufactured uniform and long-length REBCO HTS tapes over 600m for several applications. It is important for the designs of the applications to use the REBCO HTS tapes with high uniformity of in-field critical current (Ic) of HTS tapes. Therefore, Fujikura has focused on manufacturing the REBCO HTS tapes with high uniformity of in-field Ic in order to reduce the margin of the magnet design. And then, it is essential for the coil protection of the magnet to adapt thick copper stabilizer of the REBCO HTS tapes. Therefore, the prototype of 4mm-wide HTS tapes with laminated copper tapes have evaluated for the REBCO HTS magnets at Fujikura. In this work, recent status and activities of REBCO HTS tapes at Fujikura are presented.
In the past 2 years SuperOx has invested significant resources into developing the next generation 2G-HTS wires for high magnetic field applications and created state-of-the-art production facilities in Japan and Russia, aiming at the fusion, MRI, accelerator magnets and motors markets.
Our current major product is based on the novel YBCO composition fabricated by PLD process on the Hastelloy substrate with IBAD-MgO based buffer. It allows for producing wires with very high critical current at low temperature and high magnetic field. In the typical process, wires of 350-600m with the Ic of 160-230A/4mm at 20K and 20T (B//c) and 400-500 A/4mm at 4.2K can be fabricated. The important structural feature of these wires is an absence of the correlated columnar defects, which are usually perceived as necessary condition for strong pinning under the specified conditions. In contrast, the developed HTS wire contains randomly placed nano-sized Y2O3 particles with a uniform size distribution, and it seems to be a peculiar feature of the materials fabricated by highly non-equilibrium PLD process. Further modification of the base YBCO composition can provide HTS wires with better performance in moderate magnetic field (e.g. 30K and 5T) and at high temperature and low magnetic field (of 65-70K and 0.5-1T) that will be also reviewed in this presentation.
The combination of the 40 um thin substrate and 5 um copper top layer allows achieving Je values of over 1000 A/mm2 at 20K and 2000 A/mm2 at 4.2K and 20T. It should be emphasized that such properties are demonstrated for over thousand commercially produced wires rather than for a short laboratory scale sample.
The overall production capacity of two companies is approaching 2,000 km of 4mm HTS wires in 2021. The large volume of acquired statistical data helps to conclude that developed manufacturing process is robust and reproducible.
Advancements in 2G HTS conductor performance continue to drive the operating limits for a broad range of demanding applications. The design, testing and fabrication technology of 2G HTS (RE)BCO conductors is presented, highlighting the ability of 2G HTS wire to function under a wide range of operating conditions. SuperPower continues to focus on process improvement to achieve high uniformity of wire performance, long piece length and high repeatability in wire production. In particular, extensive studies on wire properties have been carried out and processing upgrades implemented to improve both the base performance of the conductor, as well as its functionality by enhancing key characteristics such as piece length, mechanical properties, uniformity of critical current and lift factor. Updated measurements on recent production material are presented and plans for future performance targets discussed.
At SuNAM, we set up a new RCE-DR(Reactive Co-Evaporation – Deposition and Reaction) system employing a 100 kW electron-gun for superconducting layer deposition. Using the new system, with higher power and enhanced beam stability, we co-evaporated APC generating materials such as Hf and Zr. We also tried rare earth(RE) elements other than currently used Gd, and mixtures of REs to get enhanced pinning. We observed increase of IC in mid-temperature(20~40 K) and mid-field(< 5 T) range, and are in the process of further optimization for higher fields.
Improved e-beam stability and beam controllability let us make more uniform tapes in our conventional formula for electric power applications such as cables, and fault current limiters. These features, together with higher deposition rates enabled by more powerful e-gun let us well positioned for new cable projects in Korea following the 1st commercial installation a couple of years ago.
We had also developed high field magnets with the center field higher than 20 Tesla, and also tested various cable designs mainly based on stacked-tape type with a plan to applying them in our magnet manufacturing. In this conference, the recent activities and achievements in SuNAM will be presented.
In recent years, a huge demand for HTS tape to be used in future commercial fusion reactors has emerged. High requirements on the mechanical properties and the tape performance in high magnetic fields for this market and other high-field magnet applications led to several developments at THEVA that are now transferred to regular production. Major improvements to the engineering critical current density have been achieved by reducing the substrate thickness from 100µm to 50µm and by introducing artificial pinning centers. We will present performance of this new product and compare it to the standard HTS tape highlighting the improvements at low temperatures and high magnetic fields.
Additionally, the quality of the copper surround coating was improved by a new PVD process by replacing the previously used electrochemical deposition. This allows a significantly more homogeneous thickness of the copper coating avoiding the typical dog boning effect of the electrochemical process and thus a more reliable and compact stacking of the tapes. Furthermore, a laser slitting method will be presented that allows to produce narrow tapes without burr and significantly reduced damage of the superconducting layer at the slitting edge.
The critical current density (Jc(θ,B,T)) of ReBa2Cu3Oy¬ (ReBCO) coated conductors is essential knowledge for the safe design of high field superconducting ReBCO magnets. However, though the ReBCO windings in a real coil are oriented such that B is applied typically at a range of 0-18° from the tape plane depending on position in the winding, coated conductors are most often characterized with BꞱtape at either 77K or in-field at 4.2K. Due to the intrinsic electronic anisotropy of ReBCO coated conductors and the extra complications induced by non-isotopic artificial pinning center (APC) arrays and their strain-induced weak uncorrelated pinning below 45K, Jc becomes highly anisotropic. This complex pinning landscape makes it difficult to predict the angular dependence of Jc from tape to tape, especially as the dominant pinning type changes with increasing T and B. We recently reported the Jc(BꞱtape,T) results on 4 tapes representative of those used in the 32T all-superconducting magnet at the NHMFL that were all purchased to the same advanced pinning specification. Applying a Ginzburg-Landau model for vortex pinning and correlating its predictions with TEM images of the nanorod pins, we found that APC size, volume fraction and density varied significantly across the 4 conductors studied and correlated with the large variation seen in the Jc(B,T) properties and the characteristic pinning energies. We here extend that study to investigate the Jc(B,T) properties at 18° from the tape plane. In this case the nanorods are no longer parallel to B and we observe significant changes in the Jc properties compared to the BꞱtape orientation. Using an inductive method, we also report the results of Jc(B,T) over the full angular range in 4.2K<T<40K and B<30T. We report on the way that the pinning landscape changes at varying field and temperature ranges as the angle θ is varied.
A future accelerator facility to open up a new frontier will require a superconducting magnet with high radiation resistance. A construction plan of a second target staiton of materials and life science experimental facility is proposed as one of the future plans of J-PARC. At the facility, superconducting solenoids are placed just behind the target to maximize the production of secondary particles. The absorbed dose of the superconducting magnet reaches 130 MGy in 10 years and the heating radiation is roughly estimated to be 650 W. In case of conventional NbTi based coils, it is difficult to keep the coil at superconducting temperature lower than 6.5 K due to heat load by the extremely high radiation. Therefore, research and development of superconducting magnets based on REBCO coated conductors have been performed to establish technology for a next generation radiation resistant superconducting magnet. As one of the research subjects, we have been studying the irradiation effect on REBCO coated conductors. Effect of gamma ray irradiation by Cobalt-60 source on critical current of REBCO and superconductivity vanishment of REBCO irradiated above neutron fluence of $1.8\times10^{22}$ $n/m^{2}$ will be reported in this contribution.
We have been developing the SCSC cable (or double “SC” cable, standing for Spiral Copper-plated Striated Coated-conductor cable), in which we wind copper-plated striated (multifilament) coated conductors spirally around a round core. In the SCSC cable, its spiral geometry decouples filaments against transverse AC magnetic fields to reduce its AC loss while the plated copper allowing current sharing among filaments enhances the robustness against normal transition.
In order to verify the effect of the spiral geometry to decouple filaments, we prepared the following three samples: a 150 mm long straight monofilament coated conductor; a 150 mm long straight 5-filament coated conductor; a 174 mm long 5-filament coated conductor wound spirally around a GFRP core with a diameter of 5 mm. The conductor width and the copper thickness per side were 4 mm and 0.02 mm, respectively, in all samples. We measured the magnetization losses of these samples in the transverse AC magnetic field with a frequency of 65.44 Hz. The measured magnetization loss of the straight 5-filament coated conductor was almost same as that of the straight monofilament one. These results are understandable, because the filaments could couple at 65.44 Hz, when the coupling current expands to the entire length of 150 mm long 5-filament coated conductor. Meanwhile, the magnetization loss of the spiral 5-filament coated conductor was much smaller than that of straight one, even though the former was longer than the latter. We also measured the magnetization losses of various samples made with narrower filaments (0.4 mm), a narrower core (3 mm), and various copper thicknesses at various frequencies. We compare the comprehensive set of experimental data and discuss the potential of the SCSC cable in the operating conditions in various practical applications.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
The muon g-2/EDM experiment, which aims at the ultra-precise measurement of muon anomalous magnetic moment (g-2) and electric dipole moment (EDM), is now under planning at J-PARC. For muon g-2, there is a discrepancy of more than 3-σ between the theoretical calculation in the Standard Model and the experimental results in the preceding experiment. Therefore, muon g-2 is one of the promising physics quantities to search for new physics beyond the Standard Model by ultra-precise measurements. Also, the EDM measurements of muons may be the first experimental detection of the time reversal symmetry breaking.
To realize these ultra-precise measurements, muon beams will be injected and stored in a solenoid-type magnet with a diameter of 66 cm, which is based on a medical MRI magnet. At this time, an unprecedented beam injection method called 3-D spiral injection is adopted, and the demonstration experiment is being carried out at KEK.
For successful 3D spiral injection of the beam, correlation of phase spaces of horizontal and vertical directions (so-called “X-Y coupling”) should be controlled appropriately. This X-Y coupling can be adjusted by the rotation angles and current values of quadrupole magnets in the beamline. To precisely adjust this rotation angles and ensure the reproducibility of the experiment, we are planning to use remote mechanical control device.
In this presentation, we will estimate expected beam phase space controlled by ideal rotating quadrupoles, and we will compare with measured values in our beam line. Required accuracy for the rotation angle will be determined. Status of the design and fabrication of the rotation mechanism will be reported, too. In addition, dedicated pole shape study of the bending magnet is also discussed to avoid strong horizontal focusing effect on the beam. This study will allow as to accomplish very precise control of the X-Y coupling.
Design of a beam transport line for a newly developed three-dimensional spiral injection scheme is discussed. This transport line is unique and one of key equipment for a new experiment at J-PARC, which measures a muon anomalous magnetic moment (g-2) and electric dipole moment (EDM) to explore a new physics beyond the standard model. Very precise measurement on spin precession angular momentum of a muon in a high uniformity magnetic field will allow us to obtain these two fundamental physics values: g-2 and EDM. We apply medical MRI type superconducting magnet technology to perform +/-0.1ppm of high uniformity of three Tesla magnetic field. Relativistic energy of muon beam injection into such MRI sized magnetic field is the world first attempt. Because of axial symmetric field shape of a solenoid magnet, the beam phase-space should be strongly coupled in vertically (=solenoid axis) and radially (so called X-Y coupling), otherwise the stored beam diverges in vertically immediately. In order to avoid vertical dispersion of the stored beam, dedicated beam transport line is designed which realizes required X-Y coupling.
In this poster, we introduce (1) a transfer matrix of the entire beam transport line to meet required X-Y coupling, (2) arbitrarily angle rotating quadrupole magnets to realize X-Y coupling. We also discuss other challenges due to installation of the storage magnet (three Tesla superconducting magnet); (3) dedicated support system for arbitrary angle rotating quadrupoles on the 25-degrees tilted transport line with respect to the horizontal plane, (4) active shield steering magnets at the end of the transport line with connection to the storage magnet point. Finally, we will summarize specifications of all devices along the entire beam transport line and strategy of the beam commissioning of the muon beam injection into the MRI sized compact storage magnet.
X-ray Free Electron Laser (XFEL) facility based on electron linear accelerator (LINAC) is regarded as one kind of the fourth-generation light source with the characteristics of high intensity, exceptional brightness, ultrashort pulse duration, and spatial coherence. Shanghai high repetition-rate XFEL and extreme light facility (SHINE) is the first hard XFEL based on a superconducting accelerated structure in China, is now under development at the Shanghai Advanced Research Institute, Chinese Academy of Sciences. Beam distribution switchyard is located midway between the endpoint of linear accelerator (LINAC) and the entrance of undulator lines for distributing electron beams within specified mode. The kicker-septum section is used for distributing electron bunches to three different undulator lines. Kicker magnets are the key components to distribute the beam into the different undulator beam lines. For more flexible distribution among the three undulator lines, the kicker should be able to perform bunch-by-bunch kick to the electron beam and, what’s more, should also be programmable for arbitrary distribution patterns. In order to reduce power consumption, an inductance-type single-turn coil magnet in a vacuum chamber is adopted for beam distribution. The design considerations of single-turn coil kicker magnet are described. This study presents the design considerations of the single-turn coil kicker magnet. The design considerations of choice for material of iron core, thermal analysis and structure design are described. Simulation results of Opera and Flotherm show that the magnetic field and thermal distribution can meet the requirement. Theoretically analysis and program simulation have verified the feasibility of the kicker magnet basic structure. At the end, relevant experimental results are also presented. The experiment results show that we have developed a kicker magnet mostly satisfying our requirements for the SHINE project.
The J-PARC muon g-2/EDM experiment aims to perform ultra-precise measurements of anomalous magnetic moments (g-2) and electric dipole moments (EDM) from the spin precession of muons in a precise magnetic field, and to explore new physics beyond the Standard Model. On experimental requirements, the beam must be stored in a compact storage orbit with a diameter of 66 cm, which is about 1/20th smaller than that of the previous experiment. To be realized, we adopt an unprecedented injection technique called three-dimensional spiral injection scheme. In this scheme, the beam is injected from upward of the solenoidal storage magnet. The vertical beam motion along the solenoid axis is controlled by a pulse kicker of a few 100 ns time duration. Once the beam is guided into the center fiducial storage volume, the muon beam is stored by the weak focusing magnetic field. Therefore, a stable and accurate control of the pulse kicker is one of the major technical challenges to realize ultra-precise measurement of the muon spin precession. From feedback knowledges of the stand-alone operation of the prototype pulse kicker device, we realize several issues which should be considered for actual operation.
In this presentation, we discuss about detailed studies of those matters firstly. And the required accuracy of the weak focusing magnetic field, as well as kicker fields. Adjustments of these parameters are highly coupled. These studies will reflect actual design of the kicker coil system for the production experiment at J-PARC. We will also report on the future prospects for that.
A Cos-theta type fast cycling dipole model for synchrotron is being developed at IMP. The magnetic field of the dipole is 6 T with maximum ramp rate is 1 T/s. The coil inner diameter is 80 mm and two-layer coils are used to produce accelerator field quality in two third of coil aperture. Rutherford cable with 316L stainless steel core is used to reduce the inter-strand couple loss. Low loss NbTi wire with 2~3 um filament diameter and CuMn/ CuNi matrix has been chosen for the magnet. This paper will report the Rutherford cable design, 2D cross section magnetic field optimization and coil end design.
The paper presents a description of the magnets for transfer line to transport ions from the Booster to the Nuclotron at the NICA project.
The transfer line has a complex three-dimensional structure because of the Booster and the Nuclotron are located in two levels. To realize complicated geometry of the transfer line necessary to reduce the magnets weight. Due to this they are made pulsed. The magnetic field duration is 10 ms; the uniformity of the magnetic fiel integral dB/B is less than 10-3 and ΔG/G is less than 2*10-3.
The magnetic field measurements were carried out by combined method: using point search coils and pulsed Hall sensors. The structure of a three-dimensional transfer line, magnetic field calculation and measurement results of the pulsed magnets are presented.
As one of the key components of synchrotron injection and extraction system, the septum magnet not only needs to produce a strong magnetic field to deflect the injection/ extraction beam, but also cannot affect the circulating beam passing by it. Otherwise, the disturbance of the leakage magnetic field to the circulating beam will affect the beam loss. Based on the theory of electromagnetic field, the magnetic field design and leakage field analysis of septum magnet are carried out by using the electromagnetic field analysis software-Opera. On this basis, different shielding measures are proposed to reduce the loss caused by leakage magnetic field. Based on the factor analysis method, the models of different shielding modes are simulated, and the variation of leakage magnetic field in the circulating beam pipe area with different shielding structures and parameters is analyzed. According to the analysis results of the influencing factors, the septum magnet is optimized design and manufactured. Through the test of the magnetic field, the experimental results and the numerical simulation results are compared to verify the correctness of the numerical simulation and the rationality of the shielding structure.
The Future Circular Collider would require a high-field septum magnet with a possibly thin blade for the extraction of the 50 TeV proton beam from the ring. One of the two baseline concepts in the conceptual design report is the "superconducting shield" (nicknamed as SuShi) septum, utilizing a zero field cooled, passive superconducting shield in order to create a zero-field channel inside the bore of a canted cosine theta (CCT) type superconducting magnet producing about 3 Tesla field outside of the shield. The optimization of the magnet and shield geometry, estimations of field quality, engineering design, and progress with the construction of the prototype will be presented.
In September 2018, China Spallation Neutron Source (CSNS) passed the national acceptance and started stable operation. Many scientific achievements have been made, but more and more experiments require accelerators with higher beam quality. Based on the current Lattice layout and further research, an alternative upgrade plan is proposed for RCS, which will become the formal design scheme of CSNSII after gradual improvement. As the initial start-up project of CSNSII, the trim quadrupole magnet and the AC sextupole magnet will be developed first. Both types of magnets are pulse AC magnets, and the number is 16 respectively. The trim quadrupole magnet and the main quadrupole magnet with the same aperture are putted together. Every two sextupole magnets and the main quadrupole magnet with another aperture are combined into a focusing unit. This article introduces the dynamic magnetic field simulation of the two types of magnets, fringe field interference analysis, the key technologies in fabrication, magnetic field measurements and physical effects.
Conventional design of a septum magnet is based on combination of C-shape iron, which forms decent dipole magnetic field, and a coil. Due to saturation of magnetic induction of the iron yoke, the maximum magnetic field of such a kind of septum magnets is limited about 2 T. However, a higher magnetic field of septum magnets is required for next generation high energy accelerators. Truncated-cosine-theta (TCT) design enables to overcome the 2 T limitation and reach a higher magnetic field strength.
For Future Circular Collider (FCC) at CERN and a future heavy ion synchrotron at FAIR/GSI, design studies of superconducting septum magnets with TCT aimed at a field strength about 4 T is ongoing. Due to high rigidity of the beam of FCC, high field septum magnet is required to minimise the extraction beam line length. A future heavy ion synchrotron will be assembled above the other synchrotron SIS100 currently being constructed for FAIR. Due to limitation on space for the beam extraction, which is commonly used with SIS100, a high field septum magnet is considered.
In this presentation, the design principle of a TCT magnet will be described and status of the design studies will be presented.
The cyclotron CYCIAE-100, the driving accelerator of the Beijing Radioactive Ion-beam Facility (BRIF), was completed successfully to provide up to 52 kW proton beams with energy range from 70 to 100MeV continuously for researches of nuclear physics, material and life science, also for medical isotope production in 2014. Although the design is ‘compact’, the total weight of CYCIAE-100 is still up to 435 ton, which limits the further applications. In order to reduce the weight significantly of high power cyclotrons, an ironless superconducting cyclotron CYCIAE-100B is proposed by China Institute of Atomic Energy (CIAE). To improve thermal stability and simplify the cryogenic system, 2G HTS tapes are used to wind the sector coils, shimming coils and main coils, and the first two of which are the replacement of iron poles. The operating temperature is below 30K. The practical production of the field with complicated distribution for beam dynamics had been explored. In order to obtain the isochronous field with strong focusing, a peak-valley staggered arrangement for sector coils and trim coils, and the corresponding mechanical structure are designed. Due to the limitation on the minimum bending radius of the HTS coil and the difficulty of precise positioning of the coils, we have to use few iron in the design: 1) an iron central plug to produce a field bump for the lack of flutter in the center region; 2) a H-shaped iron scheme for magnetic shimming at the room temperature side, which is particularly beneficial for the shimming quality and efficiency. The 110 MHz waveguide cavity and its induced magnetic field, cryogenic and vacuum system, quench protection and power supply system will be also presented in this paper.
To study the properties of the Higgs, scientists from the Institute of High Energy Physics have proposed to build the Circle Electron Positron Collider (CEPC) and published a conceptual design report in 2018. In order to improve the luminosity of the CEPC, the final focus system in the interaction region is continuously upgraded. According to the latest physical requirements of superconducting magnets in the CEPC interaction region, a high gradient, double aperture quadrupole magnet Q1a is required, which is 1.9 m from the collision point. The gradient of the superconducting magnet Q1a is 141 T/m and the magnetic length is 1.21 m. In this paper, we discuss the advantages and disadvantages of the three kinds of quadrupole coil structures, including cos2θ coil, CCT coil, and racetrack coil. High-temperature superconducting materials and low-temperature superconducting materials are used in our magnet design. In addition to completing the design of the superconducting quadrupole magnet Q1a, design optimization is needed to greatly reduce the weight of the magnet.
A 1.5 T high-temperature superconducting dipole magnet for the heavy ion spectrometer has been fabricated and tested. It mainly consists of four double pancake HTS coils and a warm iron yoke with two cylindrical poles. The gap between the poles is 120 mm. The HTS coils wound with a 12 mm wide and 0.28 mm thick HTS tape have an inner diameter of 480 mm. They will be cooled down below 20 K by a GM cryocooler and generate a central field of 1.5 T at an operation current of 280 A. In this paper, the design and construction of the HTS magnet are described and the test results are reported and discussed.
A new solution for cost effective, high average power (2 GeV, 6 MW) proton accelerator has been proposed and studied since 2013. The energy limit of isochronous accelerator has been successfully increased from 1GeV to 2GeV. In 2019, China Institute of Atomic Energy (CIAE) started the design of a 2 GeV FFAG accelerator and launched the preliminary study on the design of a high-temperature superconducting magnet and several other key components, e.g. the high power cavity. In order to carry out a further study for the thermal stability and the electromagnetic characteristics during the excitation of the none insulation HTS coil, and more importantly for the manufacturing process of the spiral-shaped magnet with concave edges, a 1:4 scaled HTS model magnet is being developed. We will first describe in detail the design scheme of the 1:4 scale model and the winding process of the concave coil. Then, simulations of the terminal voltage variation and the magnetic field variation of a double pancake coil during magnetic excitation are performed through a reasonable improvement of an equivalent circuit network model and the test results of single double-pancake coil are also outlined. These results are much helpful for the manufacture of the final full size superconducting magnets of the 2 GeV FFAG accelerator.
Recent advances in the fabrication of high-temperature superconducting (HTS) coils allow the design of superconducting accelerator magnets working in a persistent current mode. There are many various rather low field magnets in the particle accelerators which operated in the DC current mode. At Fermilab was designed, fabricated, and tested the HTS dipole magnet model having 20 mm air gap and the magnetic field up to 1 T. The magnet has a primary copper coil which works a short period of time to pump the energy in the short-circuited secondary HTS coil. In the paper presented design, fabrication, and test of this magnet at the liquid nitrogen temperature.
Racetrack model coils (RMC) have been built at CERN during the past decade, as a R&D tool to qualify conductors and technologies developed for high field superconducting magnets. Racetrack model coils, assembled in a dipole magnet configuration, proved to be an efficient instrument reducing cost and feed-back time while developing new magnets. In a similar way as for the HL-LHC project, CERN has designed the enhanced RMC (eRMC) made of two flat coils using 40 (1 mm diameter) Nb3Sn strand cable produced with RRP technology. This conductor geometry, originally designed and produced to build the FRESCA2 magnet, was chosen to reduce the production time and shorten the road towards the feasibility demonstration to reach 16-18 T magnetic fields in a dipolar configuration. As previous model coils built at CERN (SMC & RMC), eRMC1 has been built using the “bladders and keys” type mechanical structure. This paper describes the main construction steps and the powering test results. The magnet produced a 16.5 T field at 1.9 K, the highest ever for a dipole magnet of this configuration.
CERN is currently investigating the feasibility of a future collider - the Future Circular Collider (FCC)- as a potential successor of the Large Hardon Collider (LHC), providing scientists in the field of high energy physics with a powerful discovery tool. A 100 km tunnel hosting a circular electron–positron collider as a first stage towards a 100 TeV proton–proton collider would probe new phenomena coupled to the Higgs and electroweak sectors with unparalleled precision.
To construct such a high center-of-mass energy HC in a tunnel of ~100km in length, dipole magnets with a nominal operation field of ~16T and ~15% margin are necessary. At the state of current available technology, only coil strands made of Nb3Sn can provide such nominal field levels. Key requirements for the realization of an accelerator of this magnitude are the ability to demonstrate that accelerator-quality magnets can indeed produce such a magnetic field and a substantial reduction of the costs of building and operating superconducting magnets to produce a cost-effective design. INFN developed the main 16T Nb3Sn dipole of the FCC based on the cos-theta coil design. The baseline design of the superconducting magnet includes a welded stainless-steel skin based on the bladder-and-key concept.
The scope of this work is FEAC, as a third-party, to validate and further study the baseline design in collaboration with INFN and CERN. This paper describes the design concept and the fully parametric multi-physics finite & boundary element (FEM & BEM) model used in the detailed design optimization. The optimized assembly parameters are presented, and the effect of the manufacturing tolerances are studied via a sensitivity analysis performed on geometrical, material and assembly parameters.
We present the design of a four-layer, Canted Cosine Theta (CCT) Nb3Sn dipole magnet as part of the general R&D program for high field superconducting magnets supported by the US Magnet Development Program (US-MDP). Future testing with HTS inserts in a hybrid configuration motivates the design’s large clear aperture of 120 mm and target operating dipole field of 12 T. First, we show results from a 2D scaling study leading to the selection of an initial cable and cross-section that reaches design targets. Then, a 3D magnetic and mechanical design study around this point is described, which leads to a final design satisfying short-sample margin and conductor stress criteria in 3D. We explore the implications of this design for fabrication of the magnet winding mandrels, and present initial prototyping results along this direction. Finally, we demonstrate compatibility of the CCT6 design with a large utility structure, based on key and bladder technology, currently considered for use within multiple US-MDP high-field magnet programs.
Large-aperture high-field magnets based on Nb3Sn superconductor are needed for various accelerator systems of future hadron and muon colliders. High level of magnetic field and large aperture lead to significant Lorentz forces and mechanical strains and stresses, which can degrade or even permanently damage brittle Nb3Sn coils. This paper describes a 120-mm-aperture two-layer dipole coil developed at Fermilab based on cos-theta coil geometry with stress management and Nb3Sn Rutherford cable. The design and main parameters of the superconducting wire and cable, the coil stress management structure design and the coil FEA in the dipole mirror and dipole test configurations are presented and discussed. A plastic model of the coil support structure was printed using 3D printing technology and used for practice coil winding. The real coil support structure was printed using 316 stainless steel. The key fabrication steps of the Nb3Sn coil, coil instrumentation, and assembly in a four-layer dipole mirror configuration with an additional 60-mm aperture Nb3Sn insert coil are reported in the paper.
The future of the particle accelerators points to a new CERN’s circular collider with an order of magnitude increase in the center-of-mass energy compared to the Large Hadron Collider (LHC). To achieve this increase from 14 TeV to 100 TeV a 100 km tunnel will be required to host the collider. This particle accelerators requires a new generation of double aperture superconducting magnets, capable of generating a high quality, stable 16 T magnetic field in a 50 mm bore. To manage this challenging task a roadmap, including several intermediate steps, was planned in the development of accelerator-grade Nb3Sn magnets under a specific four-year CERN-INFN agreement. The first of these steps will be the construction of a short, single aperture cosθ dipole, with a target magnetic field of 12 T and an ultimate field of 14 T. In this contribution, the design of this short model, called Falcon Dipole (Future Accelerator post-LHC Cosθ Optimised Nb3Sn Dipole) will be presented. To generate the required field, this magnet will feature a two-layer design, with state-of-art Nb3Sn conductor. This work is focused on the mechanical analysis of this short model. To cope with the intense magnetic forces that are generated in the magnet during operation and to ensure the integrity of the conductor, a novel mechanical structure has been identified, the so-called "bladder and key", a technique that has never been used in cosθ dipoles and needs to be validated. In conclusion, this paper presents 2D and 3D finite element analyses able to describe all the constructive steps that meet the requirements imposed by the project to ensure the correct operation of this magnet.
The new HEL (Hollow Electron Lens) units are part of the upgrade baseline of the High-Luminosity LHC accelerator (HL-LHC) will be installed in the machine ring at point P4 on each counter-rotating LHC proton beamline during a long shutdown in 2025-2027 at CERN. The main goal is to achieve active control of the proton beam halo as a robust solution of risk mitigation to improve the collimation system performance by controlling beam energy loss in the beam halo.
The magnet system consists of two main 1.5 m long split 5 T superconducting solenoids equipped with steering dipole correctors and fringe field coils which compress the annular low energy e-beam (15 keV) generated from the e- gun cathode and provide a stable interaction region with the high energy proton beam (7 TeV). Other sets of superconducting solenoids up to 4.0 T are used for fine-tuning and guiding the electron beam at the extremities of the interaction region on both the gun and the collector side. A standalone dipole compensator is included to correct the net transverse field components up to 0.5 T.m responsible for a vertical kick onto the main proton beam.
The compact design of the cryostat operating at 4.5 K is challenging, and the quench protection scheme is complex as it houses multiple coils assembly with large inductances and mutual coupling. An essential feature of the main solenoid's system performances is the field quality requirements defined, in line with selected measurement technology options. In this paper, the design progress of the HEL magnet system is presented and discussed.
The High Luminosity LHC requires dipole orbit correctors grouped in double aperture magnet assemblies. They provide a field of 3.1 T at 100 A in an aperture of 70 mm. The current standard design is a classical cosine-theta layout made with ribbon cable. However, the electric insulation of the ribbon cable is however not radiation-resistant enough to withstand the radiation load expected in the coming years of LHC operation. A new design is needed based on a radiation-resistant polyimide insulated cable that can replace the existing orbit correctors when they reach their end-of-life due to radiation damage. The challenge is to design a magnet that simply plugs into the existing positions and re-uses bus-bars, passive quench protection, and power supplies. We propose a self-protected canted-cosine-theta (CCT) design. We take the opportunity to explore new concepts for the CCT design to produce a cost-effective and high-quality design with a more sustainable use of resources. The new orbit corrector’s design must fit with tight field quality requirements while keeping within the same mechanical volume and maximum excitation current.
A collaboration of Swedish universities, Swedish industry, and CERN has started to develop a prototype following concurrent engineering (CE) methodology to reduce the time needed to deploy functional CCT magnet. The magnet will have a 1m long CCT dipole layout consisting of two coils. The superconductor is a commercially available 0.33mm strand with polyimide insulation in 6-around-1 cabling. The channels in the coil formers, that determine the CCT layout, allow for 2x5 cable-layers. A total of 70 windings makes that the coil current can be kept below 100 A. We will present the detailed design and quench simulations.
A beam separation dipole of the High-Luminosity LHC, known as MBXF, is a 7-m NbTi magnet, which is designed to generate 35 Tm at the operating condition of 1.9 K. The magnet has a collared yoke structure with a 150-mm-aperture single-layer coil. The dipole field is 5.6 T at nominal operating current while a b3 integral is required to be within 2.9 units. The target pre-load is set to 115 MPa to increase mechanical reinforcement against the high Lorentz force. The High Energy Accelerator Research Organization, KEK, has developed three 2-m model magnets in collaboration with CERN and has evaluated those field qualities. The last two model magnets have shown anomalous b3 which was higher than expectations by 16-18 units and this is mainly due to incorrect cable thickness assumed during the magnetic design stage. In addition, the coil is known to be deformed ovally because of large pre-loads, giving an additional offset to b3. The complexity of design problem is overcome by starting optimization of two dimensional coil cross section from the lower current where we can eliminate effects from magnetization of other components such as an iron yoke. After then necessary corrections are considered to estimate a three dimensional b3 distributions at the nominal operating current. The magnetic design of the first MBXF prototype (MBXFP1) was considered by following the above methodology. Even though the two dimensional coil cross section of MBXFP1 is not fully optimized due to a limited span of time, it is quite important to evaluate our methodology and to check if further iterations are possible for series production of MBXF magnets. In this presentation we first review field qualities of the model magnets and then report results from magnetic measurement of MBXFP1. Finally, final magnetic design of series production magnets is presented.
The Large Hadron Collider (LHC) upgrade, called High Luminosity LHC (HL-LHC) is planned for the next decade. A set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS & CMS experiments will be developed. Tow institutes IHEP (Institute of High Energy Physics), IMP (Institute of Modern Physics), and one company in China will work on the magnet R&D and series production. IMP in charge of the performance test both at ambient and cryogenic temperatures, the first China-Built model (MCBRDP2) has been tested recently. In this paper, the test setup for magnetic measurements, the 2.3m-long rotating coil probe, and the instrumentation being used at IMP are presented. The measurement results, in terms of field quality, effects of iron saturation, as well as magnetic cross-talk are discussed.
The HL-LHC upgrade requires installation of eight, 105 mm diameter, double aperture dipole correctors (MCBRD) on both sides of ATLAS and CMS, each side with a horizontal and a vertical dipole. A Canted Cos-Theta (CCT) design was selected by CERN in 2015 and a development of the MCBRD magnet followed. Since then, a prototype (P01) has been built and measured at CERN, and quench results agree with simulations. In 2017, the programme has been joined with in-kind contribution of one prototype (P02) and twelve (four spare) series magnets with efforts by WST, IMP, IHEP, BAMA, all in China.
The MCBRD comprises two tilted Nb-Ti solenoids wound on aluminium formers, with opposite inclination and operating at nominal 394 A and 1.9 K with a peak field of 2.94 T. Due to winding proximity to the metal formers and selected impregnation method, the allowed voltage to ground and hot-spot temperature were limited to 500 V and 200 K, respectively.
Based on simulations using the code STEAM-ProteCCT, developed at CERN, energy extraction was selected as the most promising method to protect the magnet against overheating in case of a quench. Simulations showed that high magnetic-field change rate during the magnet discharge causes substantial quench-back due to the heat generated by the eddy currents in the formers, hence increasing the discharge rate and reducing the hot-spot temperature.
The P01 and P02 prototypes use strands with different Cu:SC ratio and aluminium formers with different electrical and thermal conductivity. This altered the quench behaviour of P02 which was recently measured at CERN. A quench simulation study was launched, and additional material properties were measured. This contribution presents the results and elaborates on to what degree the quench behaviour change can be accounted for by wire and formers properties.
The High-Luminosity LHC project is an upgrade of the Large Hadron Collider (LHC) and comprises the installation of two Hollow Electron Lens (HEL) systems, each on one beam on each side of LHC point 4. The system allows for a controlled depletion of hadron beam tails and an enhanced hadron beam halo collimation.
The system consists of 22 magnets with independently powered circuits, among which are seven solenoid magnets of five types. The largest solenoid is 1.6 m long, with 180 mm bore diameter and central field of 5 T at 330 A and 4.5 K.
The energy stored in each solenoid magnet ranges from 0.3 kJ to 495 kJ, with the total of 1.2 MJ, representing the majority of the total system stored energy. This contribution focuses on the quench protection of these seven solenoid magnets. All the magnets use the same Nb Ti/Cu rectangular wire with enamel insulation and are resin impregnated with pre preg between layers.
Based on STEAM-LEDET simulations, a quench protection scheme is devised, with focus on minimizing complexity and cost and respecting the limits of maximum peak voltage-to-ground and hot spot temperature of 500 V and 120 K, respectively. An energy-extraction-based quench protection is implemented for the two largest magnets to reduce recovery time after quench, whereas the other magnets are self-protected upon timely switch-off of the power converter. Active quench detection is based on voltage taps and relies on CERN’s Universal Quench Detection System. Several quench scenarios are considered and presented, considering various wire and coils impregnation characteristics, induced eddy currents in the conducting cryoshields, and the effect of possible quench-back due to AC loss.
For the HL-LHC project, a 90 mm NbTi cos (2θ) quadrupole magnet with an operating gradient of 120 T/m at 1.9 K is being developed as an option to replace the 70 mm aperture LHC quadrupole MQY. CEA in collaboration with CERN designed and manufactured a single aperture short model magnet with a magnetic length of 1.211 m at 1.9K called MQYYM. The MQYYM cold test occurred at CEA at 4.2 K in a vertical cryogenic station. During the power test, the operating gradient at 1.9 K has been reached at 4.2K after two training quenches. All along the test, magnetic measurements were done using a rotating probe.
This paper describes the performance of the MQYYM and proposes an analysis of the data acquired during the test including training behavior, quench detection, protection and magnetic field quality measurements.
The next upgrade for the Large Hadron Collider (LHC), called High-Luminosity LHC, has the aim of increasing the rate of collisions of the accelerator by a factor of ten. To achieve this goal, the dipoles and quadrupoles before and after the interaction region of the ATLAS and CMS experiments will be replaced. One of these is the separation-recombination dipole MBRD, which features a target integral magnetic field of 35 T⋅m in a double aperture of 105 mm, obtained with a magnetic field of 4.5 T along a magnetic length of 7.78 m. One of the main challenges in the development of this magnet is the fact that the two apertures must have the same polarity and this causes a magnetic cross-talk between the two apertures. Because of this, it has been necessary to develop a left/right asymmetric design for the coils to compensate this effect, that would have generated unwanted multipoles. Another issue related to the heavy cross-talk is a repulsive Lorentz force between apertures, which has been managed through the implementation of Al alloy sleeves assembled around the two collared apertures. The design was carried out in the framework of a CERN-INFN Genova agreement and the construction is ongoing in the industry ASG Superconductors. The 1.6 m long model was built and successfully cold tested, followed by the construction of a full-length prototype, which is currently on-going, while the construction of the series of 6 magnets is foreseen to be started on May 2021. This contribution will describe the prototype assembly status, also covering the field quality aspect, discussing the results of the warm magnetic measurements at ASG and their implication on the design of the series in terms of harmonic content.
Abstract
A cryogenic permanent-magnet undulator (CPMU) with a period of 18mm and a magnetic length of 2m is being constructed for the Taiwan Photon Source (TPS). The CPMU with a gap of 5.5 mm can generate an effective magnetic field of 1.2 T at 150 K. When the field measurement, the temperature of hall probe will be drop at cryogenic temperature. Therefore, a field strength calibration and thermostatic temperature control system is necessary. The range of field strength calibration is from 5.5 to ±1.5T at a homemade dipole electromagnet. A 2-axis compact SENIS hall probe is mounted on homemade copper plate in vacuum chamber. The temperature control system consists of a cryocooler、PT100 sensor and a heater to control the Hall probe temperature. Finally, a higher-order polynomial surface fitting to analysis measurement data from calibration system. The field strength maximum error is < 0.2 G at fitting surface. The detailed temperature dependent calibration system is presented in this poster.
Space charge compensation technology using multiple multipolar magnetic field components has been applied to high intensity beam transport. In order to realize this compensation technology in a limited space, we devised a compact size permanent hybrid multi-pole magnet. This magnet can produce two or more adjustable multi-pole components at the same location. In this presentation, we will discuss the design of magnets for the simultaneous production of quadrupole and adjustable octupole components using permanent magnet materials and the manufactured prototypes of magnet systems.
A prototype bipolar correction magnet with permanent magnets, which is realized by rotatable permanent magnet rods, was fabricated and magnetic field measurements were performed. Based on the evaluation, improvement on the magnet structure is under study. The new design will be discussed here.
High-field magnets are often demanded for advanced scientific studies. Although a hybrid coil design comprising Nb-Ti, Nb3Sn, and HTS (High Temperature Superconductors) are potential candidates for such application, the costs of Nb3Sn and HTS are expensive compared with Nb-Ti. Permanent magnet can join hybrid magnets. By generating additional field about 1 T by permanent magnets, required amounts of superconducting material may be reduced. Magnetic properties of some magnetic materials have been studied by other work at temperature as low as 100 K. The remanent field of conventional NdFeB magnets decreases at 100 K due to spin reorientation. PrFeB magnets consisting of praseodymium (Pr) instead of neodymium (Nd) do not show such degradation and the coercivity of PrFeB at 100 K is 7 T. The coercivity at 4 K would be estimated as 10 T by a naive extrapolation. Therefore, PrFeB magnets may be applicable as the field booster in the high-field hybrid magnets. In this study, B-H curve, as a primary magnetic property, of a PrFeB magnet sample was measured in the temperature range down to 4 K. Based on the experimental result, magnet configuration for an accelerator dipole magnet is also studied as an example of application.
Permanent magnets are necessary materials for particle accelerator components. As the beam intensity of the accelerator increases, demagnetization effects in permanent magnet materials is becoming one of the important issues. In order to measure the demagnetization rate of the magnet materials such as NdFeB, SmCo, and Ferrite magnets, a neutron irradiation experiment in Kyoto University Research Reactor was carried out. By comparing the magnetization before and after the irradiation, relation between the demagnetization rate and irradiated dose were studied. In this presentation, results of the experiment will be presented.
The ITER Central Solenoid (CS) will be realized by assembling a stack of six modules. Each module is a solenoid consisting of 40 pancakes wound with a Nb3Sn Cable in Conduit Conductor (CICC). The tests of the second module (CSM#2) are ongoing at the General Atomics (GA) facility in San Diego (US). During the test campaign, the CS Module is submitted to dumps of the transport current from different initial values (10, 15, 20, 25, 30, 35, 40 kA) to 0 kA, which allow measuring the AC losses in the coil.
In this paper we present the results on AC losses in the dumps as computed through two different methods. The first method is based on the observation that the dumps determine a very fast pressure rise of the supercritical helium embedded in the module, which undergoes an isochoric transformation. The method is therefore based on the computation of the variation of internal energy of the helium during the pressure rise itself. The second method is based instead on a calorimetric procedure aimed at estimating the enthalpy variation of the supercritical helium due to the thermal power deposited during the current dumps. A validated thermohydraulic model is also applied to a thorough analysis of the experimental results.
The results of AC loss tests performed with different decay time constants of the dumps are also presented. Since the transport current dumps are performed both in virgin conditions and after cyclic loading of the CS Module, the evolution of losses during the test campaign is finally discussed.
Two out of six Poloidal Field Coils (PFC) are already delivered to the ITER Organization. The PFC are built winding, impregnating and vertically stacking double pancakes (DPs) of NbTi Cable-in-Conduit conductors into a Winding Pack (WP). Later, the Winding Pack (WP) is impregnated for ground insulation and clamping devices are installed for structural support and interface with the rest of the ITER machine. Four of the five coils are manufactured at ITER site by European companies under Fusion For Energy (F4E) management, PF06 was manufactured in China, in a collaboration agreement between the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and F4E.
One of the main parameters characterizing the PFCs is the Current Centre Line (CCL), defined as the barycentre of its WP conductors. Ideally, the CCL would be in the WP’s symmetry plane but due to solutions in the construction design and manufacturing deviations, it may vary. Double Pancakes (DPs) may be wound with different dimensions, or a deviation during their stacking would cause a misalignment of all the conductors contained in that ill-positioned DP, affecting the CCL. Based on the method developed for the Toroidal Field Coils but considering their specific architecture and particularities, F4E calculated the PF CCL for the two first coils in a joint CAD, metrology and manufacturing engineering effort. Data used are geometric measurements taken during the Double Pancakes (DP) and WP manufacturing, and the process is divided in three main phases: DP modelling, Virtual Stacking and WP global alignment.
This paper explains the process to calculate the Current Centre Line (CCL) of the two first PF Coils using manufacturing data, defining the uncertainty associated to the calculation and comparing against the target tolerances defined for the proper ITER machine operation.
In April 2021, four Toroidal Field Coil (TFC) built by European industries are already delivered to the ITER Organization. The TFC are composed mainly by a superconducting Winding Pack (WP), and the enclosing Coil Cases (TFCC).
One of the main parameters characterizing the TFCs is the Current Centre Line, defined as the barycentre of the WP conductors. The CCL has been initially calculated for all the TFCs, and Fusion for Energy (F4E) developed a methodology to monitor and control the CCL during the subsequent manufacturing processes, including WP insertion, TFCC welding, preparation for machining and final measurements. The method is based on detailed laser measurements, CAE models and data processing, and it provides one of the main inputs to be considered when defining the final machining of the component. The final CCL position after machining can be further used as input parameter during the machine assembly and it is useful to understand important aspects for the operation of ITER reactor such as the Error Field.
This paper presents the results of the abovementioned strategy for the coils completed so far, during the different manufacturing phases, and the intermediate results of the remaining coils under construction. It focuses on the similarities and differences obtained comparing the TFCs, and it assesses the correspondence of the CCL data with other parameters related to the magnet.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
AC loss is a major heat load in the fast-pulsed, superconducting ITER coils, and thus a design driver for the cryo-system and superconductor. Given the importance of AC loss, extensive AC loss characterization of the components of the ITER coils, from the superconducting strands, cables and insert-coils to the completed coils, were conducted over the past years.
Following factory cold testing of the first Central Solenoid (CS) modules, AC loss data are now available for some as-built coils, providing a fully consistent set, fully representative of the operational conditions. The comparison with experimental data is essential for the validation of the computer models. The model validation and as-built coil performance assessment are both critical steps for the preparation of ITER Tokamak operation and commissioning.
The following describes the AC loss computer models for the ITER CS modules, including its validation for the different stages, from conductor to coil. Such a model needs to be simple to implement and fast to execute to allow simulation of the long ITER plasma scenarios. The paper will explains the simplifications applied and discuss the implications. Predictions of the AC loss during ITER plasma scenarios will also be briefly discussed.
The ITER Central Solenoid (CS) consists of a stack of six independent coil packs called modules. It features a total height of 18 m and a diameter of over 4 m. The modules are in an advanced stage of fabrication by the US ITER Project Office (USIPO) and its subcontractor General Atomics (GA). A qualification module mock-up at one to one scale but of reduced height was wound and Vacuum Pressure Impregnated (VPI) by GA to validate final manufacturing, using tooling and processes fully representative of a series module. The module was submitted to a thermal cycle down to the temperature of 4.5 K at which the coils will be cooled by supercritical helium. During plasma operation, the CS modules are subjected to a complex combination of static and dynamic forces. The understanding of the mechanical behaviour of the CS module coils is of paramount importance to analyse and predict the overall response of the CS stack. To this purpose, an extensive programme of investigation of the module mock-up has been defined and applied. This allowed assessing, through examination and testing of a large number of VPI conductor array samples extracted from the mock-up, the soundness of the coil through advanced non-destructive examination techniques including X-ray micro-tomography, dimensional metrology measurements and micro-optical observations. Moreover, additional testing of physical and mechanical properties carried out at room and cryogenic temperature allowed the behaviour of the conductor stacks to be assessed. The paper summarises the results of these investigations and their interpretation through mechanical analyses based on the individual properties of the coil constituents.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
Fusion for Energy (F4E), the European Domestic Agency for the International Thermonuclear Experimental Reactor (ITER), is responsible for the supply of 5 out of the 6 Poloidal Field (PF) Coils: PF2-PF6. While the 9 meter diameter PF6 was manufactured by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and tested in the cold test facility at Cadarache under a collaboration agreement with F4E; coils PF2-PF5 are currently being manufactured on site, close to the Tokamak building, their size ranging from 17 to 24 meters diameter and weights from 200 to 400 tons.
This article describes the final acceptance tests performed on the coils PF5 and PF6, the testing setup, paying special attention to the tests performed before, after and during the cooldown at 80K. The tests cover a wide range of aspects of the operation at cryogenic temperatures: ranging from the high voltage electrical insulation performance during the potential fault conditions during plasma operation, leak tightness under vacuum and its pressure drop behaviour of its hydraulic system during operation with forced flow helium.
In addition, we will describe the final preparation activities for the delivery to ITER that mainly focus in the metrology measurement of the most important interfaces of the coils inside the tokamak cryostat. From the location of the coil clamps which fix together the PF coils to the toroidal field coils, to the coil electrical and hydraulic interfaces that will connect the coil electrical 55kA joints and cooling supply manifold systems of the machine, to the installation of the protection covers which constitute the most external part of the coil assembly.
Feasibility study of ITER In-vessel coils bracket manufacture and integration had been developed in Institute of Plasma Physics, Chinese Academy of Sciences. The ITER In-Vessel Coil system is comprised of Edge-Localized Mode (ELM) and Vertical Stabilization (VS) coils. The ELM coils are used to mitigate the Edge Localized Modes and the VS coils are used to provide Vertical Stabilization of the plasma. Designed bracket for IVC coils is a kind of building block type three or four stacked components with arcuate groove matching with round conductor. This paper describes structure design, manufacture and integration process of the ELM and VS bracket. R&D of bracket weld and assembly sequence optimization are carried out to determine the welding and assembly process. At last, three brackets are integrated in ASIPP.
Index Terms—ITER IVC bracket, structure design, manufacture and integration, welding technology
As the experimental ITER fusion reactor faces its final construction phase, design activities of the next reactor DEMO that will supply net electrical energy to the grid are being conducted in Europe. DEMO will be significantly larger than ITER, and its magnet system will be key to confine the plasma and control its shape. In particular, the Toroidal Field (TF) Coils are necessary to generate the closed toroidal field lines that confine the plasma in a tokamak fusion reactor. The interaction of the current in these coils with the magnetic field produced by the poloidal magnet system induces out-of-plane forces that make unavoidable a three-dimensional structural assessment of the TF magnet structure. Moreover, Poloidal Field (PF) Coils are supported by the TF Coil casings and are to be included in the analysis of a global model of the magnet system. Nevertheless, Winding Packs (WP) in Fusion magnet coils are heterogeneous and rather complex structures, hence accounting for a detailed model of the WP with a fine mesh in a 3-D analysis of the magnet system can become extremely costly. Homogenization techniques are therefore commonly used to model the WP by means of a uniform elastic block with orthotropic thermo-mechanical properties. Several techniques exist for this purpose and indeed a variety of approaches are in use in the fusion magnet community yielding different values for the effective properties. This work describes homogenization techniques stemming from an energetic criterion and presents a comparison between them with the goal to contribute to the founded standardization of the structural analysis procedures in the fusion magnet field, with special emphasis in the challenging DEMO magnet coils. The mentioned standardizations are crucial if the design and construction of Fusion Magnets are to become widespread activities in the future.
The ITER PF system consists of 6 ring coils and it provides magnetic field for plasma shaping and position control together with the Central Solenoid (CS) coils. It needs to operate in a fast pulse mode, leading to induced voltages of up to 14 kV on the coil terminals during operation. The cable-in-conduit conductors (CICC) with Niobium-Titanium (NbTi) superconducting material are used in the coils. All coils are fabricated by stacking 6 to 9 double-pancakes wound by two-in-hand winding scheme.
ITER PF magnets are supplied in-kind by Domestic Agencies (DAs) and PF2~6 will be procured by European Domestic Agency (EUDA). Regarding PF6 coil, EUDA has decided to outsource the manufacture of PF6, which, as the smallest of the coils, could be transported along the ITER itinerary with only a minor widening of the original route. Finally, it was decided to construct PF6 in the Chinese Academy of Science Institute ASIPP with an International cooperation agreement.
Since the PF coil design review for PF2-6 coil in 2009, the new design inputs have been requested to increase the reliability of the PF coil components such as helium inlet, the terminal and joints of the PF coils. As a qualification activity, the component qualification has been carried with corresponding mechanical and the electric tests at room temperature, 77 K and 4.2 K. In addition, the PF dummy double pancakes and winding pack mock ups are fabricated to demonstrate the preliminary manufacturing process. Finally, PF5 and PF6 coils have been successfully manufactured and the performance of the coils are demonstrated by the cold tests.
This paper presents the fabrication of PF magnet components as well as manufacturing process and cold test of ITER PF5 and PF6 Coil.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
To guarantee the required performances stringent dimensional requirements have been defined for the ITER TF coils.
The assembly of the European magnets from its components, the Winding Pack (WP) and the stainless steel Coil Cases (CC), is currently under responsibility of SIMIC SpA in the framework of a Fusion For Energy contract.
The process has been divided in the following stages: reception of the parts, insertion of the WP into the CC, closure welding, gap filling and final machining.
At each of the production stages, metrological surveys are carried out in order to check the compliance with the defined requirements: fiducials positions, gap evaluation, virtual fit, welding distortion.
In particular, one of the key elements of the magnets is the position of the Current Center Line (CCL), the coil theoretical representation of the magnetic field.
The CCL has to be kept under control during the production and linked to the external TF coil case interfaces.
A rigid metrology process has been put in place, assuring reliable results in terms of repeatability and accuracy of the measurement. Laser tracking, sided when possible by photogrammetry technologies, have been chosen for the scope.
This article aims at introducing the main metrology controls and analyses in the manufacturing process, giving an overview of the technology adopted together with the procedures deployed to cope with requirements.
During the years of ITER conductors qualification phases, samples from all domestic agencies were tested. Some of these tests were focused on characterizing the AC losses properties of the ITER conductors. The data produced originate from various facilities (SULTAN, University of Twente, CERN…), using different experimental protocols, for a large number of samples. The result is thus a considerate amount of information with a wide spread in the properties.
The need for a reduced set of parameters describing the AC losses properties of the ITER conductors is now becoming urgent in order to permit consistent analysis of the coils heat loads in commissioning and operation.
This paper will try to summarize the conductor choices, the models and the parameters that emerge from the extensive experimental characterizations, hoping to give a strong baseline for analysts investigating AC losses in ITER conductors.
Fusion for Energy (F4E), the European Domestic Agency for ITER, is responsible for the supply of ten out of 18 Toroidal Field Coils installed in the ITER machine. This article gives an update of the status of the cold test of the winding packs and their insertion into the Coil Cases being the last work package of the TF magnet production performed under the framework of an F4E contract assigned to SIMIC SpA. We report on production details like items acceptance, welding, casting, geometrical surveys, machining, and main non-conformities; using optimized production indexes, analysis of key production activities like cold tests, acceptance tests, insertion, welding, gap filling, and final machining will be discussed.
9 ITER TF coils are being manufactured in Japan for ITER project. Each TF coil consists of 7 Nb3Sn conductor double-pancakes (DP). In heat treatment of DP, strand witness samples are heat-treated with DP simultaneously and then their critical current (Ic) is measured to confirm soundness of the heat treatment. Recently, heat treatment of all of 63 DPs has been successfully completed under proper process control. The result are reported in the paper. On the other hand, there was a risk of disturbance, which is unpredictable such as sudden temperature deviation and interruption, due to unavoidable trouble (blackout etc.,) during heat treatment. In such a case, the strand performance may be degraded, especially in internal-tin Nb3Sn strand. Therefore, to clarify an influence of the heat treatment disturbance on strand performance, authors prepared witness samples heat-treated with artificial disturbance and the Ic were measured. As a result, it was revealed that influence of temperature deviation appeared on strand performance while influence of temperature interruption was sufficiently small. The details is also described in the paper.
As a part of a conceptual design study for developing more higher magnetic field hybrid magnet, an outsert low temperature superconducting coils which can generate about 14 T magnetic field is being developed at the High Magnetic Field Laboratory of the Chinese Academy of Sciences. The superconducting outsert with a room temperature bore diameter of 1800 mm is composed of Nb3Sn coils and NbTi coils wound from four grades of cable-in-conduit conductor cooled with forced-flow supercritical helium at an inlet temperature of 4.5 K. This work presents the magnetic and the structural assessment of the performance of the superconducting outsert. The objective of the design process is to obtain a coil that is capable of providing the required magnetic performance while being structurally compliant. The overall design concept and preliminary results of electro-magnetic, structural, and thermo-hydraulic analysis are presented.
A conceptual design study of superconducting toroidal field (TF) magnet for a steady-state Korean fusion demonstration reactor (K-DEMO) was done in 2015. Through some minor design modifications of the K-DEMO TF magnet, the maximum toroidal field strength of the K-DEMO is expected to be about 16 T. In order to test a Cable-In-Conduit Conductor (CICC) of the K-DEMO TF magnet, a conductor test facility which can provide over 16 T magnetic field is required. Those test facility magnets, so called PUMA (Pulsed MAgnet) and SUCCEX (SUperConducting Conductor EXperiment), have been already reported on our previous conceptual design papers. However PUMA has only 12 T maximum field and SUCCEX is specialized on a U-shaped conductor samples and has short high field zone for SULTAN (SUpraLeiter TestANlage) -like straight samples. AS an alternative design for over 16 T conductor test facility magnet, racetrack dipole magnet design is proposed in this work. A specification of winding pack and magnetic field design which can offer the EDIPO(European DIPole)-like high field zone are considered. In addition, possible upgrade of magnet with high temperature superconductor (HTS) insert is also considered in design of magnet bore.
Acknowledgement
This work was supported by R&D program of “code No. CN2101” through the Korea institute of Fusion Energy(KFE) funded by the Government funds.
Abstract: A closed-loop high temperature superconducting (HTS) magnet with thermal switch, wound by REBCO wire, is proposed, which can be magnetized by flux pump and operated in persistent current mode. In this paper, the structure, fabrication and principle of the magnet is explained. Because the magnet has the structure of thermal switch, it can be excited to saturation efficiently. Numerical analysis is carried out to investigate the excitation process of the magnet. Experiment is also applied on the model magnet to verify the feasibility of the model magnet. The result confirms that the suggested magnet can be operated in persistent current mode and the principles of the magnet and the flux pump are reasonable.
REBCO with its high-strength substrate is the preferred superconductor for high-field applications and is the choice for the NHMFL’s 40 T all-superconducting magnet. Many electromechanical characterizations of this conductor have been performed in its longitudinal direction which is its primary load path. Little has been reported on structural limits in its transverse, narrow edge, direction or axial with respect to a solenoid’s coordinates. This is becoming more important as the axial pressure at the coil’s mid-plane of high-field magnets can be on the order of 100 MPa. In addition, many magnet systems put into service, such as the NHMFL’s 40 T, will be exposed to cyclic operations necessitating the determination of cyclic load limit data. A study has been conducted and results will be presented on small REBCO double pancakes wound with stainless steel co-wind with various geometries and with the conductor wound as a single tape or two-in-hand. The coils were loaded to pressures of 100 MPa and 150 MPa and cycled up to 50,000 times in a bath of liquid nitrogen. Periodically during the load sequence, critical current measurements were made to evaluate the level of degradation.
Acknowledgement
This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and DMR-1839796, and the State of Florida.
High Temperature Superconductor (HTS) based magnets are potential candidate for the future fusion reactors and electrical industries due to its compact size and operational economy. A SS laminated BSCCO-2223 HTS tape based and double pancake wound compact solenoid coil with an inter-double pancake joint of bore diameter 50 mm with 24 nos. of turns has been fabricated and tested at LN2 temperature. This coil has been charged up to 2.1 kA with maximum current ramp rate per turn of about 8.5 MA/s and generated axial magnetic field of 1.1 T at 77 K, self-field. The estimated axial magnetic field ramp rate of this coil is greater than 4 kT/s. This has inter-turn Kapton insulation. In order to study the effect of inter-turn electrical insulation on the current ramp rate, double pancake based solenoid coils with and without inter-turn Kapton insulation of similar dimensions have also been fabricated and tested up to 10 K using Cryo-cooler. The differences in the current and voltage profiles during current ramp up and ramp down observed for coil with and without electrical insulation. These coils were charged up to 440 A at 10 K and produced magnetic field up to 2 kG. The inter-double pancake joint resistance with overlap length of 100 mm is measured around 48 nΩ at 10 K, self-field. The first coil was operated in pulsed mode for about one millisecond up to the current 20 times higher than the critical current without any thermal damage at 77 K. I-V characteristics for all three coils, joint resistance, and axial magnetic field measurement results and analysis will be reported in this presentation.
Canted-Cosine-theta (CCT) magnet is an excellent dipole magnet structure design for developing high-field accelerator magnets, because of its modular construction and the prevention of the Lorentz-force-induced conductor stress accumulations. Although REBCO tapes can maintain a relatively higher engineering current density than other superconducting conductors in the high field environment, it is not easy to apply REBCO tapes in CCT magnets directly. The stress challenge and the large tilt angle of the flat REBCO tapes demand to optimize the conductor structure for the practical application. In the previous work, Narrow-Stacked (NS) wire has been confirmed as a novel REBCO conductor structure with many advantages, such as low AC loss, small screening current induced field (SCIF) and available no-insulation technique. Owing to the 1-mm width of NS wire, the minimum tilt angle can be reduced effectively to avoid the superconducting characteristic being degraded during slantwise winding. NS wire has a smaller limit than original REBCO tape in HTS magnet applications. Therefore, NS wire is a suitable method to use the REBCO tape in CCT magnet. In this paper, a small CCT prototype based on NS wire was designed and fabricated, then it was also tested at 77K to verify the feasibility of the CCT magnet based on NS wire. This paper result will provide a new way to apply REBCO tapes in CCT magnet.
AC losses in stacked bundle conductors exposed to external magnetic fields are numerically evaluated by means of a two-dimensional finite element method formulated using a self-magnetic field due to currents induced in an analysis region. The bundle conductor is composed of two pieces of rare-earth-based coated conductors without electrical insulation to improve the thermal stability. In the analysis models, an idealized copper layer is sandwiched by a pair of superconducting layers in every bundle conductor. The external magnetic fields are increased monotonically from zero so as to simulate the electromagnetic responses in several typical parts inside a pancake coil for high field magnet. In order to understand only the geometrical effects on the AC losses, the superconductors are assumed to be subject to the Bean model, in which the critical current density is independent of the local magnetic field. The influences of the numbers of bundle conductors, the gaps between bundle conductors and the angles of applied magnetic fields on the AC losses are investigated numerically.
This work was supported by JSPS KAKENHI Grant Number JP18H0528.
For mechanical reinforcement against the huge Lorentz forces in high magnetic fields, epoxy resins are commonly used to impregnate the high temperature superconducting (HTS) coils. However, performance degradation of the epoxy impregnated HTS coils is inevitable due to different thermal expansion coefficients between the epoxy resin and the HTS tape. The ice impregnation technique of pulsed magnets was applied to HTS coils for the first time in our previous study. Compared with the epoxy impregnated HTS coils, ice impregnated HTS coils showed almost no degradation in critical current after several thermal cycles. Besides, the ice impregnated coils had better thermal stability than that of the epoxy impregnated coils. The mechanical properties of ice were very important for studying the application of ice in the HTS magnets and rarely studied at 77 K. In this paper, uniaxial tension test, compression test and crack detection test of the ice specimens were conducted at 77 K. And ice mixed with substances such as, glassfiber and alcohol, were used to improve performance of ice. Thermal properties of ice were also measured in this paper. The results showed that ice had superior mechanical strength and thermal properties in the HTS coils.
During the NHMFL 32 T magnet project, a program to develop a reliable method for making soldered lap joints between REBCO tape conductors was initiated. Several combinations of solder, flux and process were tried and then tested in liquid nitrogen. A standard process was adopted from the findings of that study. For each unique REBCO conductor piece procured for the 32 T project, a lap solder joint was made using the standard process and tested for resistance in liquid nitrogen. A total of 211 lap joints were made and tested. For the NHMFL 40 T magnet project, a similar study was performed using the same standard process on conductors procured for test coils. A total of 22 lap joints were made and tested. Results from both data sets are reported, and compared with findings from the initial study and published findings by others.
In the stacked double-pancake construction adopted by the NHMFL for REBCO coils, each double-pancake is connected in series to adjacent modules with a crossover connection, made from an assembly of several REBCO tapes placed in parallel and soldered across the terminal ends of each adjacent module. Resistances of the crossovers in a 32 T test coil, from test articles and test coils made during the 40 T project, are reported here. The resistances of the crossovers do not scale inversely with area in the same manner as lap joints. A test of the current distribution in a crossover joint was performed in liquid nitrogen. Findings from this test are reported, and an improved predictive model for the resistance of a crossover connection is given.
A proton therapy equipment named SC200 is developing in the Institute of Plasma Physics Chinese Academy of Sciences (IPP, CAS) and Heifei CAS Ion Medical and Technical Devices company. In order to develop a light weight gantry for proton therapy, the Canted Cosine theta (CCT) superconducting magnet technology was considered to apply in the superconducting gantry development. The designs of two curved CCT dipole magnets with the physical angles of 90 º and 135 º will be designed in this study. The formers of the two CCT magnets will be fabricated with different technical methods. Firstly, the magnetic fields and harmonic components of the curved CCT coils and the straight CCT coils were compared and analyzed. The effects of the curved CCT magnet design parameters on harmonic components were analyzed. Secondly, a harmonic optimized method for the curved CCT dipole magnets was approached. The designs of the two curved CCT dipole with a field quality requirement of 10-4 were presented. Finally, the mechanical structure of the magnet and error analysis on field quality were presented in this study.
Proton therapy (PT) is a precise and efficient radiotherapy method in modern medical treatment, which can be focused on the lesion location to kill the tumor cells with little affection on the normal tissues and thus largely reduce the potential side effects. However, the proton therapy instrument is usually very huge with a large occupation in the space. In order to reduce the instrument scale, a petawatt level laser proton accelerator project is being conducted in China. This paper will report a bended Canted-Cosine-Theta (CCT) magnet which is a critical component in the proposed laser proton accelerator system. The CCT superconducting magnet was designed with a bended dipole magnet that had an equivalent arc π/4 with radius 1m, and two short quadrupole magnets were nested symmetrically at the dipole magnet ends. The warm bore of the magnet was 72mm, where a homogeneous transverse magnetic field that amounted to 2.5 T was required along the magnet bore and homogeneous magnetic field gradients 25 T/m were required at the magnet inlet and outlet. NbTi superconducting wire will be used on the coil winding and immersed in liquid helium environment. The magnet fabrication process will be presented in terms of the CCT mandrel manufacturing, winding, and assembling and the performance test will also be reported.
Index Terms— Superconducting magnet, proton accelerator, CCT magnet
A project to develop a compact heavy-ion therapy device has been initiated at the National Institutes for Quantum and Radiological Science and Technology. The therapy device uses a 430-MeV/u synchrotron with superconducting bending magnets as a main accelerator. In order to reach the required output of the heavy-ion beam, the bending magnets have been designed to be operated alternately from 0.3 T (for injection) to 3.5 T maximum (for extraction) at the ramping rate of 0.6 T/s. The 3D electromagnetic design of the synchrotron bending magnet has been performed. The magnetic length is 1.49 m for 45-degree bending angle, and curvature radius is 1.89 m. The superconducting coil consists of a low-loss NbTi wire with a 1-mm diameter, and the maximum operating current is 265A. To suppress the magnetomotive force, the cross-sectional coil design adopted an elliptical-shaped arrangement. The coil and iron yoke designs were optimized for the uniformity of the magnetic field in the required area. In addition, a short-straight model with a magnetic length of 400 mm was fabricated for the feasibility demonstration. The results of the excitation test as well as the electromagnetic design will be reported.
In heavy particle radiotherapy, a rotating gantry enables charged particles to be delivered to a tumor with great accuracy. Therefore, cancer therapy that minimizes unnecessary damage to a patient can be realized by using the rotating gantry. The world’s first rotating gantry composed of superconducting magnets was developed in Japan. Using superconducting magnets instead of conventional magnets, it became possible to make a smaller, lighter gantry.
A superconducting magnet for the rotating gantry is composed of a cosine-theta superconducting coil surrounded with an iron yoke which is the heaviest part of the magnet’s weight. The weight of one superconducting magnet reaches several tons, and the rotating gantry is equipped with ten superconducting magnets. Precise rotation control is required under the condition that several ten tons are mounted on the frame of the rotating gantry. In this study, a superconducting magnet composed of an active shield coil for the gantry has been proposed to simplify the control system and the frame structure of the rotating gantry by reducing its weight. Using an active shield coil instead of an iron yoke to shield the stray magnetic field, the magnet’s weight can be reduced.
The previous study indicated the possibility that the superconducting magnet with active shielding can significantly reduce the magnet weight compared to the superconducting magnet with an iron yoke. However, the support structure of the superconducting magnet with active shielding was not taken into account in the previous study. Considering the coil support structure, hence, the design study of the superconducting magnet with active shielding was conducted based on the coil cross-section designed in the previous study. In this paper, the electrical-structural analysis of the superconducting magnet with active shielding is described. Additionally, the weight of the magnet is evaluated.
For effective induction heating properties of cancer therapy, the high-frequency electromagnet system's target specifications are 0.06 T of the peak magnetic flux density with 114 kHz of the operating frequency at the center of the used space. Generally, the electromagnet with a narrow air-gap can be designed by the magnetic circuit. However, the electromagnet for magnetic hyperthermia requires a wide air-gap to use the high-frequency spatial magnetic field. In this case, the magnetic flux in the air-gap will spread. Then, it becomes difficult to estimate the self-inductance and magnetic flux density distribution of the electromagnet. Moreover, the electromagnet's power loss becomes difficult to calculate due to the coil windings' current sharing problem and the core loss of the magnetic core. This work aims to carry out a high precision design method for magnetic Hyperthermia high-frequency electromagnet. The high-frequency design method includes the self-inductance calculation model, the center magnetic flux density calculation model, and power loss analysis. In addition to this, the proposed design method was tested compared to the experimental results using a magnet prototype. Basing on the scaling law, the authors summarize the final design of the real-scale high-frequency electromagnet for magnetic hyperthermia. From the results, the electromagnet is designed using 120-A Litz wires coil windings and a magnetic core created with TPW33 core material. The power loss and one-turn voltage of the coil windings are 59.8 kW and 31.9 kV, respectively. It suggests that the coolant of the electromagnet cooling system requires high specific heat and high dielectric strength when the electromagnet is operating.
The last bending section of a proton therapy beam line is mounted on a rotating gantry to target the cancerous cells of the patients from all possible angles. Such capability can increase the effectiveness of cancer treatment as the tumors would receive the appropriate amount of radiation dose with a minimum impact on the surrounding healthy tissue. Superconducting magnets with their high energy density can provide a large reduction in weight and some reduction in size for the components that need to be installed on the rotatory gantry. In the following work, a magnet configuration is presented using combined function magnets. It includes two conventional electromagnets and three superconducting magnets operated at 4.2 K. For such assembly, an alignment procedure is carried out to guaranty a large beam momentum acceptance. Furthermore, 3D mechanical Finite Element analysis was conducted to check that the structural support of the superconducting magnets and their thermal shields could handle their weigh as well as the momentum due to the rotation.
This paper describes the design and the test result of the world’s most compact rotating gantry for heavy ion therapy system mounted with superconducting bending and focusing magnets that is successfully installed in East Japan Heavy Ion Center Faculty of Medicine, Yamagata University, Japan. Rotating gantry is a cylindrical irradiation equipment with magnets for beam transport and beam scanning that delivers energetic carbon ions up to 430 MeV/u precisely to a tumor from any direction without changing the posture of the patient. On the other hand, because of the high magnetic rigidity of therapeutic carbon ions, the size of rotating gantry was too huge to install in general hospitals. Therefore, the first superconducting rotating gantry had been developed and installed in collaboration with QST-NIRS. At Yamagata University, a project to construct a heavy ion therapy facility has been started from 2015, which includes a rotating gantry port with superconducting magnets in addition to the fixed horizontal port. In the project of Yamagata University, to achieve further downsizing of the rotating gantry, the length of scanning irradiation system is shortened and the magnetic field of the superconducting magnet is increased from the first superconducting gantry at QST-NIRS. As a result, the gantry is downsized to 2/3 of the first superconducting rotating gantry. This next generation small superconducting rotating gantry has already been installed and is working for preclinical commissioning at Yamagata University. In this study, we will report this next generation small superconducting rotating gantry and its superconducting magnet.
SIGRUM (Superconducting Ion Gantry with Riboni’s Unconventional Mechanics) project comes from the strong collaboration between ‘Centro Nazionale di Adroterapia Oncologica’ (CNAO), in Pavia, Italy, and CERN. This centre, relying on CERN experience in accelerator particles, wants to improve cancer treatments with a novel superconducting ion gantry structure.
The magnet is operated at a temperature of 4.5 [K] and a nominal current of 2144 [A] generating a 3.3 [T] magnetic field in magnet aperture. For this magnet design, at nominal current the current-sharing temperature is about 6 [K].
Above this value the magnet quenches, losing its superconducting properties, with the subsequently magnetic field drop and losing the control on the beam.
The project wants to assess the impact of transitory losses on the magnet thermal transient, proving that the actual magnet design does not need any special features to improve the cooling in order to limit the coil peak temperature below 6 [K].
A thermal transient analysis has been performed with a COMSOL© model generated by STEAM-SIGMA in order to investigate on the temperature increase in the whole superconducting combined function magnet during repetitive triangular 60 seconds-long power cycles (0.1 [T/s]).
The thermal analysis has proved that, in the reference operating condition, and even under conservative assumptions (both for the losses and cooling features), repetitive magnetic cycling does not result in excessive temperature (below 6 [K]) during repetitive power cycles.
Furthermore, a parametric analysis has been performed to investigate on worse scenarios than the reference one, changing the cooling features and the transitory losses amplitude, in order to understand in which scenarios the quench may occur.
Finally, a quench protection system based on the energy-extraction has been proposed. The quench transient has been simulated using STEAM-LEDET. The magnet self-protectability has been evaluated.
Heavy-ion radiotherapy has a high curative effect and low burden on patients, so it has been spreading in recent year. On the other hand, since heavy-ion radiotherapy system have large apparatuses such as injector, synchrotron, and rotating gantry, it is necessary to downsize these apparatuses in order to further wide spreading. Therefore, a project to develop a next generation small facility for heavy-ion radiotherapy called quantum scalpel has been started from 2016 at National Institutes for Quantum and radiological Science and Technology (QST). One of the aim of this project is to significantly downsize the synchrotron by applying superconducting technology, and we have been developing a superconducting magnet for a compact heavy-ion synchrotron. This superconducting magnet can generate a dipole field of 3.5 T with operating current of 265 A, and it’s designed to be able to raise the magnetic field from 0.3 T to 3.5 T in a 5 second while adopting conduction cooling with GM-cryocoolers. Such high-speed excitation causes AC loss in the superconducting coil. The thermal design result including this AC loss will be reported. In addition, a short model with the same cross section as the designed coil were fabricated and excitation test was carried out. The test result will be also reported.
In this paper, a laboratory electromagnet utilizing high temperature superconducting (HTS) coils is designed and analyzed. The laboratory electromagnet is applied to excitate high magnetic fields compared with the conventional laboratory electromagnet with copper coils. The proposed electromagnet was composed of iron-core, HTS coils, and cryostat for the HTS coils. The components are designed using numerical calculation and finite element analysis. The electromagnet is based around a compact iron-core with HTS double pancake coils, and the electromagnetic design is carried out to take into account magnetic properties of the iron-core material and the Ic-B performance of the HTS conductor. Based on the design results, characteristics of the laboratory HTS electromagnet are analyzed.
In the magnetic Czochralski crystal growth (MCZ) process, a Lorentz force that influences the flow and tends to reduce the amplitude of the melt fluctuations by applying a magnetic field outside the furnace body. It is a main method to suppress the uneven distribution of impurities and reduce the density of crystal defects. The strong magnetic field provided by superconducting magnet is a feasible way to prepare larger than 12-inch semiconductor grade monocrystalline silicon wafer. In this paper, the electromagnetic structure of MCZ superconducting magnet with four-solenoid type is designed. In the cylindrical space region of 800 mm in diameter and 400 mm in height, the magnetic field intensity reaches 0.4 T, the magnetic field inhomogeneity is about ±18%. The superconducting magnet is cooled by conduction cooling mode using GM type refrigerators. By optimizing the low temperature structure of superconducting magnet, the magnet cooling down duration is estimated about 10 days. The magnet is subjected to cooling-down and energizing experiments. The performance of the magnet meets the design requirements.
Key words: superconducting magnet; conduction cooling; crystal growth; MCZ
We proposed the novel separation method, which is the combination of magnetic separation and selection tube, aiming at more precise and easier separation for the paramagnetic substances than the conventional High Gradient Magnetic Separation (HGMS). In order to control and separate the paramagnetic substances with magnetic force, the magnetic field of higher than 5T and high gradient magnetic field are inevitable. This means high gradient superconducting magnetic separation system is needed. In this study, we aim to apply a lower magnetic field for magnetic separation of paramagnetic substances.
Selection tube can separate particle mixture in a suspension into each component of particles by the balancing the drag force, buoyancy and gravity. The drag force and buoyancy depends on flow velocity, particle size, shape and specific weight. By controlling the flow velocity we can separate particles precisely depending the size. Since the particles are apparent weightless state in balanced condition, even the paramagnetic particles can be captured with a relatively small magnetic force.
Firstly, we showed the effectiveness of the developed system using the imitated substance, colored glass. The 1.3T Open Gradient Magnetic Separation and the selection tube were employed. The experimental results were found to shows good separation efficiency. Eventually, we tested the system using HGMS instead of OGMS whether the separation efficiency could be improved at lower magnetic field. The SUS 430 magnetic filters which was 0.8mm in diameter and 15mesh were installed in the selection tube and the magnetic field of 0.5T was applied. The effective separation of paramagnetic glass (volume magnetic susceptibility: +3.17×10-4) was performed successfully by the developed system.
Magneto plasma sail is a space propulsion system with a higher fuel efficiency for future deep space explorations. The thrust to power ratio of the magneto plasma sail can be greatly improved with a superconducting magnet by generating a larger magnetic field with less power consumption. The thrust of the magneto plasma sail is produced by the transfer of momentum from a solar wind plasma to a magnetic field generated by a High Temperature Superconducting (HTS) magnet in the spacecraft, and proportional to the magnetic moment of the magnet (current × magnet area). To obtain a large thrust to mass ratio, or acceleration, enough for space missions, our target is to develop a lightweight HTS magnet system with a large magnetic moment. However, as the magnetic moment or current increases, the electromagnetic force applied to the magnet, such as a hoop stress and axial compressive stress, increases, and a reinforcement structure for the magnet is required. We investigated a suitable reinforcement structure for the HTS magnet to maximize its magnetic moment within the capacity of a space vehicle.
We analyzed the mechanical stresses applied to HTS magnets with a variety of reinforcement structure during the excitation to clarify a suitable reinforcement structure of the HTS magnet for use in space. The suitable configuration of the HTS magnet was investigated to maximize its magnetic moment within an outer diameter of 5 m and total mass of 400 kg. As a result, we showed that a “ladder-type” reinforcement structure can greatly reduce the axial compressive stress as well as the hoop stress by preventing the transmission of force through magnets and maximize the magnetic moment.
This study proved the possibility to increase the thrust of the magneto plasma sail and leads to realizing a space propulsion system using the HTS magnet.
Introduction
Iron oxide scale removal from boiler feed water was studied to suppress the deterioration of power generation efficiency of the thermal power plants adopting oxygenated treatment (OT), by using high gradient magnetic separation (HGMS). Since the magnetic susceptibility and secondary particle size of the target particles have large effects on the magnetic separation efficiency, we focused on the surface charges and the aggregation state of the scale particles. The objective of this study is to clarify the relation among pH, surface charge, particle aggregation and magnetic separation efficiency.
Experimental methods
The mixtures of ferromagnetic magnetite and paramagnetic hematite or goethite were respectively prepared as simulated scales, the capture target. The ratio of each mixture was based on that of the collected scale in low-pressure feed-water heater drain, where the system is planned to be introduced. The pH of each mixture was adjusted to change the surface charge, and then magnetic separation was conducted. After this, the weight and magnetic susceptibility of the particles were measured.
Results and discussions
Both the mixtures showed highest separation rate in neutral pH. This is due to heterogeneous aggregation caused by low surface charge. However, the separation ratio of goethite component in neutral pH was lower than other pH. This is considered to be due to the homogeneous aggregation of goethite by hydroxyl groups at neutral pH. The HGMS is to be installed in the feed-water system of thermal power plant or in the chemical cleaning line, which are respectively basic and acidic to neutral pH. Hence, it is necessary to construct magnetic separation system that is the most suitable for each condition.
Acknowledgment
This research was partly supported by “Advanced Low Carbon Technology Research and Development Program (ALCA)” of Japan Science and Technology Agency (JST) Grant Number: JPMJAL1304.
Removal of magnetic fine particles from a non-magnetic fine powder by high gradient magnetic separation under dry condition was studied. The dry magnetic separation has been partially put to practical use in the separation of iron from waste, the mining field, the food industry and so on. However, in the application of high-gradient magnetic separation (HGMS) with a stronger magnetic force, there is a troublesome problem of clogging of the magnetic filter due to aggregation and deposition of non-magnetic fine powder. In this research, we have developed a new magnetic filtering system in which magnetic thin wires arranged in one direction with regular intervals were layered perpendicularly to the magnetic field direction. This makes it possible to reliably capture the magnetic fine particles while avoiding the filter clogging due to the powder. The capture rate of the proposed magnetic filter was investigated by a magnetic separation experiment and a three-dimensional FEM particle trajectory simulation. The magnetic wire size, spacing, and number of layers were changed, and the capture rate was investigated. As a result, by reducing the magnetic wire size and spacing and increasing the number of layers, the capture rate was improved without blockage of the filter, and its effectiveness was clarified.
A method of removing microplastics from seawater using electromagnetic force was devised and its feasibility was demonstrated by calculation. Plastic is difficult to decompose and puts a heavy load on the marine environment. In particular, plastics smaller than 5 mm are defined as microplastics, which are carried over long distances by ocean currents and cause global pollution. The development of technology to remove microplastics from the ocean is an urgent issue.
The developed method is to induce Lorentz force in seawater and applying the reaction force to microplastic. The substances calculated was polyethylene as microplastic. A square pipe with a cross section of 35 mm x 35 mm is placed in a room temperature bore 50 mm of superconducting magnet, and seawater in which polyethylene is dispersed flows vertically upward. On the facing wall two electrodes were placed in the region where the external magnetic field is 3T and then the directions of the current and the magnetic field are vertical. When an electric current is passed, Lorentz force is induced in seawater and a reaction force in the opposite direction apply to the polyethylene. This reaction force can be used to accumulate the polyethylene particles.
The length of the electrode was 40 mm, and the microplastic was considered to be spherical, and the diameter was changed to 1, 3, and 5 mm. The current density was changed so as to JxB are from 2.8x103 to 2.8x104 (N / m2). The average flow velocity was set at 1 m / s, and a parabolic flow velocity distribution was assumed. The calculation results showed that 95% recovery is possible with polyethylene with a diameter of 1 mm. The results suggest that the possibility of separation of microplastics from seawater was shown.
This paper describes a design of a Vertical-ring High Gradient Superconducting Magnetic Separation (VHGMS) magnet for recovery of the magnetic ore and purification of non-metallic minerals. Compared to the conventional design which uses copper wires, using superconducting magnet can help reduce the energy consumption and increase the magnetic field. The first part of this paper introduces the operation margin design of the superconducting magnet. This magnet is wound with NbTi wires and its temperature margin is designed to be higher than 1K.It generates an average magnetic field above 2T in the filtering area. The second part of this paper introduces a quench protection circuit implemented in this magnet and post-quench analysis is also presented. Simulation results show that maximum temperature and terminal voltage are within the safe limits of 270K and 1000V, respectively. So the superconducting magnet can be effectively protected from burning-out during a quench. The third part of this paper analyzes the stresses during magnet charging and quench process. The hoop stress of the coil is limited to be less than conductor’s yield stress.
A quasi-microgravity space, exploiting a large magnetic field in combination with a large field gradient, is considered for potential applications such as protein crystallization and cell culture without natural convection caused by gravity. To provide a high magnetic field in a more cost-effective way, large-single grain bulk superconductors – such as the RE-Ba-Cu-O (RE: rare earth element or Y) family of materials – have shown promising potential for generating magnetic fields over several tesla as so-called trapped field magnets (TFM). Compatibility between the magnetic performance and flexibility in operation is required to realize a practical TFM device that can provide such high magnetic fields in an open space outside the vacuum chamber. The authors recently proposed a new concept of a high-gradient trapped field magnet (HG-TFM), which consists of slit ring bulks that can generate a downward-oriented magnetic field, are tightly stacked with conventional TFM cylinders [1]. It has been estimated numerically that a magnetic field gradient product over 3000 T^2/m could be realized by field-cooled magnetization (FCM) of such a device, even with a relatively small external field of 9 T at 40 K. This is comparable with the performance of conventional, large-scale hybrid magnets with 20 T.
In this paper, to realize the HG-TFM concept experimentally, we report the design of an HG-TFM apparatus with an open bore and confirm the expected magnetic properties experimentally. As the next step, magnetic levitation would be performed for any fundamental, diamagnetic materials to observe the corresponding levitation position and compare these with the numerical results. The extensibility of the proposed HG-TFM device for magnetic levitation will be discussed.
[1] K Takahashi, H Fujishiro and M D Ainslie, Supercond. Sci. Technol., 34 035001, 2021.
Acknowledgements
• Engineering and Physical Sciences Research Council (EPSRC) UK, Early Career Fellowship, EP/P020313/1
In many industrial applications, there has been a growing need for electrical motors having high performance such as high power density and high efficiency. An electrical motor with high temperature superconducting (HTS) coils allows to offer those advantages due to the very high current density compared with conventional superconducting motors. HTS motors can be divided into an inner rotor type in which the HTS coil is located in the inner rotor and an outer rotor type in which the HTS coil in the outer rotor. Since each type has advantages and disadvantages in motor characteristics, a design comparison between each type is necessary. Therefore, in this paper, we report a design comparison between an inner and outer rotor type for an HTS synchronous motor based on a multi-objective optimization. First of all, the HTS synchronous motors with the inner and outer rotor type are respectively optimized by a multi-objective optimization which considers three characteristics; power density, efficiency, and HTS tape consumption simultaneously. At this time, the performance of each design is evaluated through the electromagnetic finite element method. Finally, the results obtained by optimization are compared between the inner and outer rotor type.
Acknowledgement
This work was supported by the R&D Collaboration Programs of Hyundai Motor Company. This work was also partly supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249).
The concept of an electric aircraft and ship implies the development of an entirely new electric propulsion system. Among the key technologies of these systems, electric motors and generators are required for high performances such as high efficiency and high specific power. In this paper, a study on the electromagnetic design of the MW class superconducting (SC) machine according to electromagnetic structure was carried out. The structure of a partially SC machine has a three-phase copper coil on the inner rotor and a shield coil or magnetic core in the outermost structure for magnetic shielding. To improve the power density, the weight of the system, and the shielding capability, the electromagnetic field analysis of SC machine is very important in the design stage. To establish the design process of the SC machine, an analytical method considering shielding conditions and type of armature core was proposed. The proposed analytical method is to calculate the analytical solution by deriving the governing equation and general solution for each domain based on Maxwell's equation and electromagnetic field theory and applying appropriate boundary conditions. The magnetic permeability of the air core is the same as that of the vacuum, and the magnetic permeability of the electrical steel core can be calculated using the iteration method based on magnetic field analysis. In addition, the active shield and the passive shield were selected to have the same magnetic field at the outermost shell. The electromagnetic performances obtained using the analytical method were compared with those obtained using finite element (FE) analysis, and the validity of the analytical method presented in this paper was verified through comparison of the analysis results. The analytical modeling, analysis results, performance rating, and discussion according to the core type and shielding conditions of SC machines will be presented in the full paper.
Recently, as interest in high-efficiency motors has increased, motors of various structures have been developed. In particular, the axial flux motor has a relatively low leakage flux, so the power density, output torque, and efficiency are high. High-temperature superconducting (HTS) coils have a higher magnetic flux density than permanent magnets. Therefore, by applying HTS coil to the existing axial type motor, the advantages of weight reduction, miniaturization and high efficiency can be maximized.
This paper deals with a revolving armature type axial flux HTS motor design, fabrication, and its performance analysis.
Using HTS wire, a 2 kW axial flux motor was designed that operates at a temperature of 77 K and a rotational speed of 400 rpm at a rated voltage of 100 V. This axial flux HTS motor, a revolving armature was selected because a solid vacuum condition must be maintained for stable cooling of the HTS field coil.
A 3D finite element method (FEM) simulation was performed to analyze the electromagnetic properties and the thermal characteristics of this motor.
The critical current of the field coil made for the HTS axial flux motor was 65 A at the operating temperature, and the operating current taking into account the cooling margin was 35 A. The output torque and the mechanical power of the motor were 55 Nm and 2 kW, respectively. The magnetic field at the air-gap was 0.4 T. The measured data of the critical currents and the inductances agreed well with the results calculated in the simulation. The results of this study can be effectively used to design various types of HTS axial flux motors in the future.
Since the late 2000s, research on electric turbo engine propulsion aircraft is being actively conducted in the aircraft industry to reduce environmental pollution and increase energy use efficiency. The electric propulsion aircraft will be equipped with a large-capacity, high-power density electric motor and generator with superconducting technology. In order to develop superconducting electric machines with high specific power, research on the development of partial superconducting (only field coils use superconductors) and fully superconducting (both fields and armatures use superconductors) electric machines are being actively studied. According to previous studies, when a fully superconducting electric machine is applied, it is possible to develop a device that is 3.5 times lighter than a partial superconducting electric machine, and when calculating the specific power including all the cooling devices, it is possible to achieve 30 kW/kg or more. It is explained that a fully superconducting electric machine is the most appropriate concept applicable to the electric propulsion aircraft of the N3-X (NASA) concept [1]. In this paper, as another candidate model applicable to electric propulsion aircraft, a rotating armature partial superconducting air core generator is proposed, and a conceptual design of a 10MW 3000rpm class generator is performed. The validity of the design was verified through finite element analysis (FEA). As a result of the analysis, it was confirmed that the design target 10MW output power was satisfied, and the specific output was about 11.4kW/kg. The actual performances are verified through a static superconducting magnet force measurement and a lab-scale rotating armature superconducting generator experiment.
[1] M. Corduan, M. Boll, R. Bause, M. P. Oomen, M. Filpenko, and M. Noe, “Topology comparison of superconducting AC machines for hybrid electric aircraft,” IEEE Trans. Appl. Supercond., vol.30, no.2, March 2020.
Large-scale high temperature superconducting (HTS) wind power generators suffer from the high electromagnetic force and high torque due to their high current density and low rotational speed. Therefore, to maintain the mechanical strength of the HTS coil, the torque and Lorentz force of the HTS wind power generator must be carefully investigated. This paper deals with the experimental test and characteristic analysis results of a real scale HTS coil for a 10 MW HTS generator using a performance evaluation system (PES). We have proposed a method to evaluate the characteristics of large-scale HTS wind turbine generators using a PES. The PES is designed and manufactured to examine the electromagnetic properties, stability and cooling performance of a full-scale 10 MW HTS coil. Three HTS coils and corresponding armature modules were designed and manufactured to confirm the characteristics of a real-scale generator using the PES. The system was assembled to withstand the force equivalent to one pole of a 10 MW HTS wind turbine under load conditions. The HTS coil was cooled to 30 K through a neon helium cooling system. The HTS coil operates at a rated field current of 221 A, and generates the same force by flowing a DC current through the armature, which corresponds to the rated armature current of a 10MW generator. As a result, the no-load temperature of the HTS coil operating at 221 A increased by about 2 K. The force on one pole of the wind turbine was measured with a strain gauge attached to the HTS coil under the condition of applying the load current to the three-phase armature coil, and through this, the magnetic field stability, mechanical strength, and thermal conditions of the HTS coil of a 10 MW class wind turbine were able to confirm.
The distributed electric propulsion system with superconducting synchronous motors with lightweight and high power density is a promising technology to reduce CO2 emissions. REBa2Cu3Oy (RE = Y, Eu, Gd, etc., REBCO) superconducting tapes have an advantage of higher critical current density even in high magnetic field at a liquid nitrogen temperature. Then fully superconducting motors with REBCO tapes have an advantage in power density as compared with partially superconducting motors. However the REBCO superconducting tapes have complicated AC loss properties. In addition, we plan to cool the REBCO superconducting field winding by helium gas in near future for the reduction of windage loss. In the actual situation in the future, hydrogen gas will be adopted as well as the present power generators. As well known, the cooling capacity of gas is not so high as compared with liquid. So it is necessary to reduce the AC loss in the field winding induced due to the variation of applied magnetic field. The magnetic field applied to the field winding is composed of DC field by field winding itself and AC field by armature windings. The AC loss properties of the REBCO superconducting tapes in such a situation have not cleared yet. In this paper, the AC losses in the field winding were investigated in order to find out the optimum winding design from the viewpoint of loss reduction. First the AC loss of REBCO superconducting tapes was measured under DC and AC magnetic fields by the pickup coil method. Next, by making a numerical calculation of magnetic field distribution in a motor operation, the AC losses in field winding were estimated. Finally the optimum winding design was proposed. The details will be presented in MT27.
2G high temperature superconducting (HTS) coil working in persistent current mode (PCM) has shown a superior potential in linear motor applications. While due to the external magnetic field, specifically, the harmonic field component generated by the ground coils, the HTS coil used in synchronous motor suffers inevitable current decay resulting from dynamic resistance, which is usually much larger than joint resistance. To predict this behavior, it is preferable to take investigation numerically, since it costs a lot experimentally. In this work, based on a real scale HTS coil used in synchronous motor, we have built a finite element model by H-formulation and kim model. To promote the calculation speed, a homogenous method was adopted for the modelling of HTS coil, and the expression of the harmonic magnetic field was deduced as the boundary condition of the model as well. We firstly obtained the critical current of the coil by load-line method, and then compared the decay curves of different carried current ratio (I/Ic). The results indicate that with a high current ratio, the load current is more vulnerable to AC non-uniform field and the decay rate will be obviously accelerated, furthermore, dynamic resistance mainly occurs at the edge of HTS coil.
This paper deals with the fabrication and preliminary rotational test of an high-temperature superconducting (HTS) synchronous motor with linear-motor type flux pump exciters. This HTS synchronous motor is composed of copper armature windings, HTS field windings, linear-motor type flux pump exciters, vacuum chamber, cryogenic cooling system, etc.The various core components were manufactured, assembled, and tested to configure the high-temperature superconducting synchronous motor. We manufactured a linear-motor type flux pump as a DC power supply to charge the racetrack coil without contact, which avoids thermal load from current leads. The double racetrack-type HTS field coils are wound with YBCO tapes and cooled directly by the cold heads. The designed operation temperature is about 30 K. The generator operation mode was employed to configure the test environment, including no-load characteristics, load characteristics, full-load efficiency are introduced. The test results are presented in this paper.
To prevent global warming, CO2 emission by aircrafts is required reduction. For that purpose, the electric propulsion system is focused on as a promising technology. That system enables the aircraft to adopt distributed propulsors which have a great advantage from the viewpoint of aerodynamics. That system contains rotating machines; however, the conventional ones cannot satisfy the stringent weight requirement of aircraft applications. The superconducting rotating machines can be designed as compact and lightweight because of no iron core and the shorter windings than conventional ones. Our research group investigated the fully-superconducting synchronous generator with 10 MW output power for electric aircrafts. We reported the result of simple thermal-electromagnetic coupled analysis focusing on only the temperature rise by the losses. In this study, to obtain the detailed property, we will conduct the thermal-electromagnetic coupled analysis considering the interaction between the temperature rise and the temperature dependence of the losses. The superconducting windings are composed of REBa2Cu3Oy (REBCO) superconducting tapes. The AC loss of them depends on the temperature and the amplitude of magnetic field. In case of armature windings, i.e. large field amplitude, such as > 0.1 T, the AC loss decreases as increasing temperature. In contrast, in case of field windings, i.e. small field, such as < 0.1 T, the AC loss increases as increasing temperature. Considering such complicated property of the losses, the analysis using FEM software will be conducted for 2D models. Conducting analysis for various generator models, for instance, its armature windings with ducts for efficient cooling, the optimal winding structure will be proposed from the viewpoint of cooling. The coolant for the armature windings and the field ones are liquid nitrogen and gas helium, respectively, and the temperature of both coolants is 65 K. The detailed results will be reported in MT27.
With the Meissner effect and flux pinning, high temperature superconducting (HTS) bulk can levitate with “self-stable” property above a magnetic guideway, integrating levitation and guidance functions in one. Generally, the propulsion function of an HTS maglev transportation is realized by another independent system, which has complicated the entire train system. Lately, according to the previous study of force between an HTS bulk and a reversed excitation electromagnetic guideway (EMG), it is found that the reversed excitation mode can introduce propulsion force in an HTS maglev system. However, the levitation and guidance performances of a single HTS bulk will also be affected synchronously. In this paper, the propulsion-function method is proposed with a multi HTS bulk arrangement and an exciting current regulation strategy in a straight EMG segment. Two HTS bulk arrangements are tested and the propulsion force is measured and analyzed firstly. Afterward, the levitation and guidance force variations during the propulsion stage are analyzed and optimized by using different excitation current switching methods. At the end, the advantages of the propulsion-function integrated HTS maglev system are summarized. This work will bring in new operation method in HTS maglev and provide basis for relative studies in the future.
A prototype racetrack high temperature superconducting (HTS) magnet used for high-speed superconducting maglev has been in progress at Institute of Electrical Engineering, Chinese Academy of Sciences. The dynamic thermal and mechanical characteristics of the racetrack HTS coil is affected by multiple factors while it is accelerating, which has an effect on the operating margin inversely. To design a reliable HTS coil of superconducting maglev, it is essential to analyze the dynamic thermal and mechanical behaviors in HTS magnet accurately. In this paper, the AC losses induced by the rapidly changed magnetic field originated from levitation planes and guidance coils were analyzed, and the temperature fluctuation inside the HTS coil was calculated furthermore based on the cooling method and heating power. A refined finite element method was proposed to analyze the mechanical behaviors of HTS coil with considering the combined effects of winding, bands, cooling method, ac losses, and electromagnetic force. To increase the analyzing accuracy, the screening current induced by the coupling magnetic field from levitation planes and guidance coils is also taken into considerations to calculate the stress/strain in the HTS coil. The experimental data and simulation results will be compared and discussed detailed in the paper.
Index Terms— HTS magnet, racetrack coil, superconducting maglev, thermal behavior, mechanical behavior
INTRODUCTION
Recently, magnetic levitation techniques have been developed for various fields such as magnetically levitated vehicles and energy storage flywheels. Thus, there are many reports about levitation techniques using high critical temperature (Tc) superconducting magnetic bearings (SMBs) composed of superconducting (SC) bulk and permanent magnet (PM). However, there are not so many reports about levitation techniques using SC coils and PMs. In this paper, a new magnetically levitated mover (MAGLEM) using SC coils running on PM guideway is discussed.
STRUCTURE OF MAGLEM
Our group has made a MAGLEM composed of an aluminum body with four SC coils. The MAGLEM runs on the guideway composed of PMs. The MAGLEM measures 0.57 kg in weight, 223 mm in length, 168 mm in width and 67 mm in height. The MAGLEM is composed of four SC coils with 25 mm in inner diameter, 49 mm in outer diameter and 20 turns. The guideway is composed of two railways with an arrangement of alternating polarity PMs. In order to get the speed of the MAGLEM, it is forced to push after the SC coils cooled down.
EXPERIMENTS AND DISCUSSIONS
In the experiments, various speeds are performed. This paper discusses the levitation force, the dynamic characteristics during the running, etc. Each speed gradually decreases with increasing time. This is because there are energy losses in the SC coils. It is found that the levitation force is periodical depending on the speed.
SUMMARY
A new MGLEM is proposed. The mover is composed of four SC coils. The guideway is composed of two railways with an arrangement of alternating polarity PMs. Several experiments are performed to verify the levitation principle.
High-temperature superconductors have significant potential for application in systems based on magnetic levitation: levitation bearings, magnetically suspended transport, flywheel energy storage devices, motors and generators. Bulk REBCO (where RE stands for rare earth elements) is currently a widely used material. However, the widespread use of coated conductors tapes (CC-tapes) allows to use them as an alternative to bulk superconductors. However, the majority of researches on the magnetic transport focuses on the study of stacked arrays of tapes. But the good flexibility of CC-tapes makes it possible to create more complex configurations on their basis. One of the possible options is CC-tape windings.
In this paper, we present new experimental results on the study of the magnetic force interaction of CC-tape windings with a permanent magnet guideway. For measurements, a commercially available 4 and 12 mm wide CC-tape produced by SuperOx was used. On the basis of the tape, windings of various shapes with a different number of layers were made. An assembly of permanent magnets in the form of a Halbach array was used as a guideway. Both the vertical levitation force and the lateral restoring force were measured. The measurements were carried out both in field cooling and in zero field cooling modes. The levitation characteristics are compared with CC-tapes stacks . It is shown that CC-tape windings can exhibit greater lateral stability in comparison with stacks. This may be relevant for the development of hybrid levitation systems using permanent magnets to increase the levitation force.
Numerical simulation of levitation force and restoring force by the finite element method has been carried out in the Comsol Multiphysics simulation environment. The calculation results are in a good agreement with the experimental data.
This work was supported by a grant from Russian Science Foundation (Project 17-19-01527).
Permanent magnet guideway (PMG) has commonly been used for an HTS maglev system so far. In some previous studies, electromagnetic guideway (EMG) was proved to have some advantages in a practical HTS maglev construction.
EMGs with different geometries produce different magnetic field distributions and have different performance characteristics in a HTS maglev system. In this study, comparative experiments of E-Shaped and Fan-Shaped EMG specimens have been conducted under the comparable conditions of vertical direction component of magnetic flux density, power input, magnetic potential and magnetic potential per unit length along the direction of the travelling. The experimental results were compared and discussed combined with the results of 2D numerical simulations. The results may be helpful for further development of EMGs for HTS maglev applications.
The wireless power transfer (WPT) using magnetic resonance coupling method has been known to have the advantage of being able to transfer power across large air gap with considerably high efficiency. As well as, as such a method can eliminate the physical contact loss in the system, it provides an ideal solution for the problem of contact losses in the power applications. From these reasons, WPT technology has started to be applied to the wireless charging for various power applications such as transportations (electric vehicle, high speed MAGLEV train, capsule train with subsonic speed etc.). In the high speed superconducting magnetic levitation (MAGLEV) train, the antenna (Tx) coils, which are installed both sides of train, are placed on the guidance rail, as well as, superconducting receiver (Rx) coils can be installed in traveling train. In the superconducting system, a cooling vessel, which is made by steel materials, is a requisite subsystem. However, since the steel materials can shield electromagnetic field, the structure design of cooling vessel can affect the transfer efficiency. The inserted resonance coupling coils in wireless power charging system of MAGLEV magnet can be one of resonable options for the shielding of electromagnetic field since the inserted coupling coils can accomplish strong resonance coupling between Tx and Rx, which derives improved transfer power, compared with the surroundings of non-inserted resonance coils. In this study, authors present the design and performance of multi copper Tx coils for superconducting Rx coils under different inserted HTS resonance coils at 150, 370 and 750 kHz . Addtionally, authors evaluate operating characteristics for inserted resonators under the shielding surroundings of cooling vessel structure.
In conventional transport systems using wheels and belts, there are friction that generates wear of mechanical parts and consequently reduces the whole system efficiency and this a problem, especially when using it in special environments such as clean room. As a way to solve this problem, a magnetic levitation system was developed using magnetic levitation as main technology. Called Hybrid Magnetic Levitation System, this system combines the superconducting levitation, which has high stability but low levitation force, and levitation between permanent magnets, which has low stability but high repulse force. Moreover, the rails of this system are made of permanent magnets in Halbach Array to enhance the magnetic field on the upper side of the rail.
Because of superconducting levitation stability, stable levitation and guidance is given without control. For propulsion system, air core coils have been assembled on the rail along its length so that when it is excited by a current, the generated magnetic field drives the system efficiently. Interaction between the propulsion coils and the HTS that pins flux from the magnetic rail generates propulsion force.
The principle of propulsion method consists of magnetizing the back region of the superconductor and demagnetizing the front region of the superconductor.
In this paper, propulsion method is studied. The experimental device is developed. The propulsion coil installed on the magnetic rail acts the permanent magnet and HTS on the carrier. The effective excitation method of the propulsion coil is shown, and propulsion force increases. As the flux of the propulsion coil acts on the HTS on the carrier, influence on the HTS is investigated. From the results, there is little influence on the HTS, and stability of the levitation and guidance is confirmed.
We have been studying a magnetic levitation system using a magnetic shielding effect of HTS bulks. The analysis method is numerical simulation utilizing the 2D and 3D finite element method software, COMSOL Multiphysics. This system consists of three items which are an iron rail, the HTS bulks, and the magnet. In the former work using a permanent magnet, the peak levitation force was smaller than 1 kilogram. To increase a magnetic field generated by the magnet, we replaced the permanent magnet to a HTS solenoid magnet. In the modified system, the peak levitation force increased and was 2 or 3 kg. In the present study, we designed a racetrack magnet whose volume were same as the solenoid magnet’s volume, and changed the solenoid magnet to the racetrack magnet in the levitation system. This change makes the field generated by the magnet reach effectively to the rail. According to the analytical results, the levitation force using the racetrack magnet increased by a few percent compared with that using the solenoid magnet. Next, we extended the strait section in the racetrack magnet. From the simulation results using the long racetrack magnet, the levitation force strongly increased and was approximately 20 kg. We think that the racetrack magnet is effective to gain the large levitation force in this levitation system.
With the merits of passive stability, energy-saved and environment-friendly, high-temperature superconductor (HTS) magnetic levitation (Maglev) is regarded as a promising candidate for the future high-speed transit. Amont the two main HTS maglev methods the bulk-type and stack-type, the stack-type HTS maglev is of the merits of larger engineering current density, larger loading potential and flexible size. In recent years the dynamic characteristics of bulk-type HTS maglev system has been well studied, however, there is little researches about the dynamic characteristics of stack-type HTS maglev system to our best knowledge. Limited by the experimental conditions, numerical methods are generally employed in most of the current research on dynamic charactristics of HTS Maglev. Thus the ultimate goal of this paper is to build a numerical model to advance the understanding of the dynamic charactristics of stack-type HTS Maglev system. A strong-coupled electromagnetic-thermal-mechanical model based on H-formulation was built to study the dynamic response, in which the non-linear electromagnetic characteristics and the thermal characteristics of the HTS tape were taken into consideration. To predict the dynamics of the system, the relative movement between the HTS and the permanent magnet (PM) is modeled using time-dependent Dirichlet boundary conditions, while the position is obtained by solving the equation of motion. The dynamics and temperature rise of the stack-type HTS maglev system were studied, with the different time-varying external magnetic fields imposed on the stack magnet of the HTS tape, which refer to the guideway irregularity. The influences of guideway irregularity were studied to restrain vibration, so as to improve the system stability. The results of this paper will play a positive role to suggest the viable measures for improving the stability of the stack-type HTS maglev system.
By the merits of self-stable levitation, low energy cost and no-contact friction, high-temperature-superconducting (HTS) pinning maglev system has a great potential to become an ultra-high-speed transportation. Recently, with the mature of the HTS pining maglev technology, the first HTS maglev engineering prototype vehicle was successfully established in our group. As the most important factor in engineering, operation stability and safety reflected by the monitoring of vehicle running state is significant. In the previous research, the detection of HTS pinning maglev running state is usually calculated by the mathematical interaction among mass, levitation force, guidance force, and vehicle stiffness matrix. However, with the growing data dimension, large-scale stiffness matrix operation has high computational and time complexity. And the large quantity of being processed data and low accuracy of state detection will also hinder the real-time monitoring of the HTS vehicle operational state. But the high efficiency of deep learning can well solve this problem. Hence, this paper proposes a way for HTS state detection based on deep learning. Initially, accelerometers and levitation gap sensors are placed on the testing apparatus, respectively. Secondly, the data under different operational conditions is collected. Then, these aggregated data with features are denoised. Next, four mainstream deep learning clustering methods are selected to distinguish the maglev vehicle operational states based on the above dataset. Finally, the detection accuracy and calculation time for deep learning method are compared with traditional stiffness matrix calculation approach. And the results verify the effectiveness and applicability of deep learning algorithms. This hybrid application can realize the real-time monitoring of HTS vehicle operational states which will facilitate control system to adjust strategy based on the running conditions in future engineering application as well.
This paper will discuss the combination and application of superconductivity technology and magnetic levitation technology, and study the current rapidly developing technology of superconducting magnetic levitation suspension system. The magnetic levitation force of the superconducting magnetic levitation suspension system will be analyzed and calculated. By building a simulation model, the operation process of the superconducting magnetic levitation suspension system and the parameter variation characteristics of the magnetic levitation force will be investigated. Meanwhile, a physical model of the superconducting magnetic levitation suspension system will be made and used for experimental studies to obtain relevant data for comparison and validation with the simulation model.
A 12 T REBCO solenoid with a 192 mm wide inner bore tapes was designed in the framework of the BOSSE Project, using 12 mm-wide isolated tape as conductor. This 814 mm high coil can be used as a compact 1 MJ – 2 MW inductive energy storage, with an 850 A rated current. One of the objectives was to overcome the present record of mass energy density, held by a NbTi coil (13 kJ/kg), and reach 20 kJ/kg of self-supporting winding.
This solenoid is composed of 21 double-pancakes with a soldered inner joint. The successful test of a first full scale prototype double-pancakes reached its limiting critical current (972 A) in standalone with no damage. This result was possible thanks to a sensitive (100 µV range) quench detection system. This prototype was also tested up to 625 A under background field up to 6 T in a resistive large bore magnet, in order to validate the mechanical design, reaching 400 MPa.
Our approach to safely operate this magnet in spite of the high operating current density (530 A/mm²) is to protect each double-pancakes independently. Several partial assemblies are currently being tested in order to configure and validate the simultaneous protection of a growing number of double-pancakes. During these tests, the transient voltage is carefully monitored to detect dissipation. The various phenomena contributing to this transient voltage will be discussed with the help of detailed electromagnetic modelling results. We will present here the results of these tests for stacks of 3 and 5 double pancakes, in terms of energy storage and efficiency for the future use of the coil as energy storage. We will also present the results of field linearity and stability and discuss them for the use of single tape isolated REBCO coils as ultra-compact high field magnets.
Double pancake (DP) coils for a SMES coil have been developed using MgB2 Rutherford type superconductor. The DP coils are indirectly cooled in liquid hydrogen in order that the current carrying region such as conductors and leads cannot contact directly with the liquid hydrogen. However the cooling efficiency of the indirect cooling system is less than that of the direct immersed cooling system. It is important for cooling system design to estimate AC loss of the SMES. The DP coils with 400 mm ID and 600 mm OD are wound with Rutherford type conductor composed of MgB2 multifilament strands. The coils were electrically connected in series and the resultant storage capacity was about 10 kJ. Various triangular current waveforms up to 600 A were supplied to the coils and the AC losses of the coils were measured by calorimetric method under various conditions. In this paper the measurements of AC losses are described and the results are compared with the theoretical values.
A 6.5 MVA/25 kV high temperature superconducting (HTS) traction transformer for the Chinese high-speed train was proposed in earlier works aiming to replace the oil-based transformers while achieve higher efficiency, lighter weight, and minimized volume. The high targeted efficiency of the transformer (> 99%) makes AC loss reduction a vital issue. HTS coated conductors generally exhibit asymmetric Ic (B, θ), where θ is the angle between the magnetic field and normal component of the conductor face, leading to a non-trivial influence on the AC loss of coil windings. Meanwhile, commercial HTS conductors from different manufacturers may have distinctive characteristics in their critical currents. AC loss reduction of the 6.5 MVA transformer windings by exploiting asymmetric conductor critical current is essential to achieve the efficiency target.
In this work, we carried out AC loss simulations on the HV and LV windings of the 6.5 MVA transformer through combination of two-dimensional axisymmetric T-A formulation and homogenization method. The HV windings are wound with HTS coated conductors, whereas the LV windings are wound with Roebel cables. In our simulation, the measured Ic (B, θ) curves of HTS conductors from different manufacturers are used as the input for the simulation. The simulated AC loss values in HTS transformers wound with coated conductors from different manufacturers are compared. The simulation results clearly show that AC loss reduction can be achieved by exploiting the asymmetric conductor critical current, and this can be used to improve the efficiency of the 6.5 MVA traction transformer.
This work was partially supported by the Chinese Ministry of Science and Technology through the National Key Research and Development Program of China under Grant No. 2016YFE0201200. This work was also partially supported by the New Zealand Ministry of Business, Innovation and Employment Contract No. RTVU1707.
A floating offshore wind power generation has been investigated to reduce the greenhouse gas emissions in Japan. When the floating offshore wind farm transmits AC electric power to the commercial power system on the land using a copper cable, it is necessary to increase the voltage by an offshore transformer facility in order to reduce the transmission loss of the copper cable. However, it is difficult to install the offshore transformer facility because the seabed around Japan is deep. Thus, a high-temperature superconducting (HTS) cable with the high capacity and the low loss has been investigated. On the other hand, the HTS cable termination has a mechanical connection between the HTS wire and the copper wire. Therefore, there are some problems with the HTS cable termination: the mechanical degradation due to heat intrusion from the normal temperature part, heat generation by the contact resistance, and heat shrinkage. We devised a coil structure for the HTS cable termination applying a wireless power transmission system, and mechanically separated the HTS cable (low temperature part) from the copper cable (normal temperature part). In this study, we investigated the coil structure suitable for the HTS cable termination from the experiments and the electromagnetic field analysis using finite element method. As a result, we found that the coil structure for the HTS cable termination is more suitable for a solenoid coil structure than a spiral coil structure. This is because the coupling coefficient between the HTS solenoid coil and the copper solenoid coil was higher than that fabricated with the spiral coil structure. Also, we found that the high-efficiency HTS cable termination is possible by providing a larger inductance of the HTS coil side than that of the copper coil side.
With the increase of the permeability of renewable energy, the equivalent inertia and damping of the power system gradually decrease, which makes the power system stability problem more and more prominent. By emulating the electromechanical transient characteristics of synchronous generators, the virtual synchronous generator (VSG) technology enables the renewable power generator to have the same external characteristics of synchronous generators, such as inertia, damping, frequency and voltage regulation. This paper proposed a novel current source (CS) photovoltaic synchronous generator (PVSG) topology incorporated with a superconducting magnetic energy storage system (SMES). The SMES has the advantage of high efficiency, quick response, and infinite cycling capability and is an ideal energy storage device for high power application. The CS-PVSG utilizes the SMES as an energy buffering device to provide inertial and frequency support to the grid, which makes the photovoltaic generator behave as a synchronous generator. Compared with voltage source PVSG, the CS-PVSG has the advantage of low cost, high stability margin. The parameter design method and control strategy are presented. The feasibility of the proposed CS-PVSG is verified by simulation results.
The composite method is an effective way to obtain superconductors with better performance. Through the combination of the first and second generation high temperature superconductors, the stability of superconductors can be improved, the engineering current density can be increased, and the AC loss of superconductors can be reduced. In this paper, a HTS transformer with first and second generation HTS tapes is designed. The distributions of magnetic field and current, AC loss are simulated. The results show that the application of hybrid superconductors can increase the critical current, reduce the AC loss, and get a better cost performance of HTS transformers.
Abstract—Superconducting magnetic energy storage system (SMES) has the advantages of fast response, four quadrant adjustable active and reactive power. It can improve the stability of power system, improve power quality, be used as distributed power system and energy management in power system. The research and development of large capacity energy storage magnet is an important development direction of SMES. SMES can be divided into low temperature SMES and high temperature SMES according to different superconducting materials. Because cryogenic magnets need to be cooled by soaking in liquid helium, its application is limited to a certain extent, so it is difficult to be widely used. With the development of high temperature superconducting tape preparation technology and the improvement of tape performance, high temperature superconducting magnets have broad application prospects in SMES and other electromagnetic devices. The components of SMES include superconducting magnet, refrigeration system, power regulating system and monitoring system. The high temperature superconducting magnet is the core component of SMES. In this paper, the toroidal field D-type magnet is selected as the energy storage magnet of 10MJ SMES. Based on the electromagnetic optimization design, the thermal analysis and force analysis of the magnet are completed, and the performance parameters of the magnet and the toroidal magnet are compared.
Index Terms—SMES, high temperature superconducting magnet, toroidal field D-type magnet, thermal analysis, force analysis
We propose the electric propulsion system which are composed of 10 MW superconducting generators, superconducting transformers, superconducting cables, and 2 MW superconducting motors. The design study of 2 MW fully superconducting motors with a rated voltage of 1 kV is being conducted. On the other hand, the 10 MW fully superconducting synchronous generators were designed so as to operate at a rated voltage of 6.9 kV from the viewpoint of a current capacity of the armature windings. Therefore, 6.9/1.0 kV-10 MVA transformers with lightweight are required. We have already designed a 66/6.9 kV-20 MVA superconducting transformer cooled with subcooled liquid nitrogen at 65 to 70K and successfully fabricated the 1/10 model. Here transposed parallel conductors which were composed of laser-scribed multifilamentary REBCO tapes were adopted to realize a high current capacity and low AC loss. In this paper, we designed a lightweight 6.9/1.0 kV-10 MVA superconducting transformer with REBCO tapes for e-aircrafts so that the transformer had a current-limiting function for early recovery from the quench due to fault excess current. By making a numerical simulation of sudden short-circuit, the current limiting behavior of the superconducting windings was investigated quantitatively. In this paper, it is demonstrated that the temperature rise of the superconducting windings can be suppressed by designing the current limiting function properly.
Acknowledgments
This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO), the Japan Science and
Technology Agency (JST): Advanced Low Carbon Technology Research and
Development Program (JPMJAL1405), and the Japan Society for the Promotion
of Science (JSPS): Grant-in-Aid-for Scientific Research (JP18H03783 and JP19K14964).
Superconducting magnetic energy storage (SMES) has the advantages of high efficiency, longevity, and excellent instantaneous response with high power. However, it has the disadvantage that its storage density is extremely small compared to other power storage devices. The no-insulation coil (hereinafter referred to as "NI coil") is expected to be a winding method that can achieve both high current density and high thermal stability. It is thought that if this NI coil technology can be applied to SMES, it will be possible to improve energy storage density by achieving higher current density. Because SMES is power devices, it is generally desirable for coils to be designed with high current and low inductance. Therefore, in this study, we considered adopting the winding method in which a bundle conductor consisting of multiple no-insulation REBCO tapes is wound without electrical insulation (hereinafter referred to as "bundle NI coil") for SMES coils. However, since the REBCO tapes in the bundle conductors are not electrically insulated each other and the bundles also have no electrical insulation between themselves, the time variation of the current distribution in the bundle NI coil becomes very complicated. Therefore, we developed a computer program to analyze and evaluate the current distribution in a bundle NI coil, and for application to SMES, we numerically investigated the behavior during excitation and demagnetization of a coil wound with a no-insulation bundle conductor composed of two no-insulation REBCO tapes. In addition, a small bundle NI coil was fabricated and tested to confirm the validity of the developed computer program, and the time variation of the current distribution in the bundle conductor was clarified from the analysis results.
LN2/CF4 mixture would be an effective coolant and insulating medium of high-temperature superconducting (HTS) magnets and power devices, which could provide a cryogenic environment in the temperature range of 50 to 100 K and serve as a liquid dielectric. In this paper, recent progress concerning the LN2/CF4-cooled HTS power devices including superconducting fault current limiter (SFCL) and superconducting magnetic energy storage (SMES) is presented with the emphasis focused on their improved electromagnetic characteristics and thermal stability compared with those devices immersed in liquid nitrogen. In addition, the characteristics of SFCL and SMES prototypes immersed in the LN2/CF4 mixture are further analyzed from the aspect of thermal and electrical properties of LN2/CF4 medium.
With ever-increasing requirements in a wide area of detection and high accuracy of measurement, it is necessary for the sensor networks to be built with extensive coverage and often installed in some places that are tough to be reached, such as underground or underwater. Under these circumstances, the costs of periodical maintenance can be extremely high. To solve this problem, a multi-input, high-temperature superconductor (HTS) based wireless charging system has been proposed for undersea sensor networks. With proper current control of multiple transmitters and the use of HTS coils, the wireless power transfer distance can be over 10 times longer than that of the existing system. Consequently, the proposed system makes it possible for the undersea sensor networks with a depth of over 200 m to be recharged with both convenience and flexibility.
In the proposed system, the transmitter currents can be synchronously overlaid for the concerning target. Not only the resonant voltages can be effectively dropped, but the allowable transmitter current will also be increased, and thus the output power can reach the satisfied level. On the other hand, the proposed current control strategy can also meet the requirement of great fault tolerance ability in long-range wireless charging procedures.
Hence, it is particularly attractive to install the proposed system in one or several working ships to remotely charge a large area of undersea sensor networks. Both finite element analysis of the full-scale system and practical experimentation of the reduced-scale system are conducted to evaluate the viability of the proposed system. The proposed system can tremendously reduce the cost for undersea operation of battery replacement for the sensor nodes. This work was fully supported by a grant (Project No. T23-701/20-R) from RGC, Hong Kong, China.
Our research has shown that an energy conversion/storage device composed of a permanent magnet and a superconductor coil has superior performance. In order to improve the conversion efficiency and energy storage capacity of this device. An effective method to enhance the interaction behavior between a permanent magnet and a closed superconductor coil is proposed in this paper. The functions that determine the induced current in the superconductor coil and the interaction force between the coil and the external magnetic field are derived in principle. Three experiments are composed to verify the proposed method. The results indicate that the calculation formulas and the enhancement method proposed in this paper have guiding significance for the study of the interaction between permanent magnets and closed superconducting coils. In addition, this method is of great significance to our study of the energy conversion/storage device.
A Wireless Power Transmission (WPT) system for a railway vehicle has been investigating to reduce the greenhouse gas emissions in a diesel vehicle. Since the WPT system for the railway vehicle is required to transmit the electric power of several hundred kW in a short time, it is difficult to suppress heat generation by the internal resistance of a copper coil. Therefore, we have investigated the WPT system using a high-temperature superconducting (HTS) coil for the railway vehicle. On the other hand, in order to reduce the AC loss of the HTS coils in the conceptual design of the WPT system for the railway vehicle, and it was necessary to install multiple HTS coils in parallel on the vehicle and ground sides. Also, the increase in size of the HTS coils and cooling system was a problem, and it is necessary to increase the transmission power density per the HTS coil. Therefore, we focused on narrow REBCO wire arranged in parallel to achieve the low loss coil structure for high energy density. In this study, we measured the AC loss characteristics of the HTS coil using parallelized REBCO wires. Also, we clarify the low loss coil structure for high energy density, and evaluated the power transmission characteristics of the WPT system using the low loss HTS coil for the railway vehicle. As a results, the low loss coil structure for high energy density can be achieved by a single pancake coil structure with the parallelization of the narrow REBCO wire in the radial direction. We clarified the WPT system using the low loss HTS coil can perform more rapid charging and the high-efficiency transmission than that using the copper coils.
In recent years, the application of superconducting technology in electrical field is becoming more and more popular and the HTS transformer has become a hot topic because of its small size, light weight and low loss. The thermal stability is a critical issue for the application of the HTS transformer. In order to study the temperature characteristic, a 500 kVA HTS transformers is designed. Firstly, we design a two-dimensional axisymmetric model of the HTS transformer and the current distribution and temperature distribution of the transformer winding are simulated based on finite element method (FEM). A thermal disturbance is then applied to the transformer and study the minimum quench energy (MQE) and the quench propagation velocity (QPV) of the HTS transformer. The thermal stability of transformer is studied by changing thermal disturbance and applied current.
Superconducting Magnetic Energy Storage (SMES) has the advantages of fast response speed, large energy storage density and low loss, which is suitable for dynamic power compensation of power systems. During operation, the superconducting magnet exchanges power with the AC grid through the power conditioning system (PCS). The PCS generally adopts a PWM converter based on a high-frequency switching device, and its output PWM pulse voltage with a steep rising / falling edge is transmitted to the superconducting magnet through a cable and a current lead. A peak overvoltage is generated at the terminal of the superconducting magnet, which in turn causes the voltage distribution inside the magnet winding to become uneven, threatening the safety of the magnet operation.
In this paper, when the SMES magnet is subjected to high-frequency PWM pulse voltage, simulations were conducted on the overvoltage distribution characteristics in the superconducting magnet. From the perspective of optimizing magnet operation parameters, the relationship between operation mode and voltage distribution characteristics is studied. And the optimization design method of operation mode to reduce the unevenness of voltage distribution is explored. The design scheme of 3.8MJ SMES in microgrid was corrected and modified, and the feasibility of the optimized design of operation mode was verified.
For fluctuation suppression and energy compensation of the power system of the particle accelerators Booster and Nuclotron of NICA complex at JINR, 3 inductively coupled SMES coils are adopted. ASIPP is responsible for one of the three coils with 1 MJ energy storage. The inner diameter of the SMES coil is optimized to be 680 mm. The operating current is about 6 kA level and the pulse period is 4 s. which means that the rate of current changing is about 1.5 kA/s. The maximum magnetic field in the coil region is about 5.1 T. For realizing high safety margin and reducing local performance degradation points caused by manufacturing, the 1MJ SMES coil is composed of multiple identical double pancake coils in series. Each pancake coil is cooled by an individual liquid neon forced flow circuit to guarantee the fluid pressure while all the pancake coils are connected electrically in series. So, the terminal of the superconducting cable is specially designed to realize the separation of cooling and electrical connection. The superconducting cable is helically wound with high-performance thin YBCO tape. For ensuring the bending performance, the spiral angle of each layer is different, which varies from 25-degree to 40-degree. The preparation of the single double pancake coil is underway. The excitation test will be finished in June 2021 to validate the performance.
The intermittent characteristics and low system inertial are two major problems for the renewable energy sources (RESs) dominated power system. This paper proposes the novel idea of integrating the wind and photovoltaic power generators with a superconducting magnetic system (SMES) as a whole to behave as a grid-forming renewable energy system. The proposed grid forming system can provide inertial and frequency for the grid and smooth the renewable power output. The fluctuation characteristics of wind and solar are complementary to some extend, which reduces the energy storage capability requirement of SMES. The Wind, photovoltaic, and SMES share the same power converter, which also reduces the investment cost. It is therefore more economic than the stand-alone wind, photovoltaic, and SMES system. Simulation model of a 1MW prototype is set up. Simulation results verify the efficacy of the proposed approaches.
High current superconducting CORC® cable or wire is composed of spiraled HTS REBCO tapes in multiple layers. Multilayered CORC® wires can carry very high currents in background magnetic fields up to 20 T. The cable combines isotropic flexibility and high resilience to electromagnetic and thermal loads. The flexibility of the cable is limited by the critical strain value damaging the REBCO layer in the tape. Mechanical stresses during operation can result in irreversible degradation in the CORC® wires/cables' performance. Different mechanical loads acting on CORC® cable during production, winding, assembly, and electromagnetic operation are bending, axial and transverse loads. The tape’s helical shape around the central core allows tapes to experience only a fraction of the total axial strain applied to the entire cable in the case of tensile loads. The winding angle is the main cabling parameter that influences the tensile strain limit of the CORC® cable. The radial contraction of the tape depends on Poisson’s ratio of the central core and winding angle. An analytical model is proposed to estimate the tensile strain in CORC® wires and cables. With optimized cabling parameters, the irreversible strain limit of CORC® cables and wires can be as high as 7%, which is 10 to 12 times higher than the irreversible strain limit of single REBCO tapes. The axile strain tolerance of optimized CORC® cables and wires far exceeds that of highest performing single NbTi strands.
Authors: Keyang Wang, V A Anvar, Yuanwen Gao, Danko van der Laan, Jeremy Weiss, Arend Nijhuis
The Conductor on Round Core (CORC®) cable or wire comprises several layers of helically wound HTS tapes on a round core with the winding direction reversed in each successive layer. This configuration can significantly reduce the AC loss while improving the bending flexibility. However, compared with traditional multi-filament cables, this structure also brings new challenges for predicting the CORC® mechanical behavior since it will be subjected to radial extrusion and circumferential stretching due to the electromagnetic force's action during operation. In this study, starting with the cabling process, the deformation of the tape, the normal contact force and friction distribution between the tapes are described. The effect of different winding parameters, such as core radius and winding helix angle, is obtained by combining theory and Finite Element Method (FEM) simulation. Detailed FEM and theoretical modeling of the REBCO tape strain state and the contact behavior between tape and core are performed to analyze the mechanical behavior of CORC® cables and wires, supported by experiments. The results describe the interaction between tapes in the cabling process, and when the contact is intensified during axial and transverse loading. The interlayer tapes are extruded and friction is generated, which affects the critical current degradation. The developed analytical and FEM models can predict the mechanical and electrical properties of CORC® cables and form a unique basis for CORC® optimization depending on its application.
Research and development of large-current High-Temperature Superconducting (HTS) conductors toward the application to magnets of experimental nuclear fusion devices are in progress at NIFS. As a candidate, the FAIR conductor [1] has been developed. Using a number of HTS REBCO tapes, we have been optimizing the manufacturing process of the conductor by repeating current-transport tests in liquid nitrogen with no external magnetic field. As the next step, the characteristics in variable temperatures at high magnetic field are being examined. In this study, we fabricated current-feeding terminals using a new fabrication method and performed current transport experiments of the FAIR conductor at variable temperatures in magnetic field using a variable-temperature insert. For the terminals, we cut the REBCO tapes into stepwise shapes, sandwiched halved cylindrical copper blocks, and jointed two conductors using low-melting-temperature solder. By measuring the joint resistance of the prototype terminal in liquid nitrogen, it was confirmed that the connection had low resistance to be applied. Moreover, we have introduced variable-temperature insert to adjust the sample temperature by flowing coolant helium gas from the variable-temperature cryogenic system installed in the superconducting magnet research laboratory in NIFS. The variable temperature insert is mounted in the split coil which can generate magnetic field up to 9 T. The transport current can be applied to the testing conductor up to 20 kA. The details of the experimental results will be discussed.
[1] Toshiyuki Mito et al 2020 J. Phys. Commun. 4 035009
In order to meet the requirements of the large HTS solenoid detector magnet for Circular Electron Positron Collider (CEPC), a new high temperature superconducting cable, Aluminum stabilized Stack ReBCO Tape Cable (ASTC) has been proposed and developed. The HTS conductor is one of the promising options for the large solenoid applications. In this study, a 20 layers ASTC sample has been fabricated and tested in liquid nitrogen. To verify the self-field effect of the sample, a numerical analysis was performed by considering the current and magnetic field distribution using self-consistently model. In addition ASTC could be used as basic units to fabricated more complicated cable modus, such as CICC and Rutherford cables. The main parameters, analysis and test results of the ASTC sample will be presented.
Applications for coated conductors, such as fusion magnets, power transmission and generator windings, require high current-carrying capacity. This requirement can be fulfilled by various cable concepts using commercial lengths of REBCO coated conductors with high current-carrying properties, such as Rutherford cables. In the past few years, our group has successfully developed Quasi-isotropic strands (QI-S) which consisit of 72 symmetrically assembled by second generation (2G) high temperature superconducting (HTS) conductors that are attractive for low temperature high field magnet applications.In this work, we investigated the critical current evaluation process of Rutherford cables made of quasi-isotropic strands.The Rutherford cable prototype was determined, and the critical current of the dummy cable was calculated by the finite element method (FEM)based on a self-consistent model, and then measured experimentally.Their conclusions are in general agreement. Then,the method was extended to the evaluation calculation of the critical current of the fully superconducting Rutherford cable. Finally, the critical current values of Rutherford cables made of quasi-isotropic strands were obtained by simulation calculations, which will be useful for future experimental validation and engineering applications.
For high field accelerator magnets, it is more attractive to wind the coils with a compact high current-carrying capacity cable, which is composed of tens or even hundreds of superconductors. In the last decades, various ReBCO cable conceptions have been proposed, but only a few cables, such as Roebel cable, can achieve a current density as high as single tapes. However, the high performance of the Roebel cable is at the expense of losing almost half of the original REBCO tapes, resulting in high costs. Herein, we are developing a novel high-current-density and low-cost cable with a Roebel-like structure, but is implemented by directly bending ReBCO coated conductors to realize the transposition and reduce the dynamic losses. Recently, some prototype cables have been manufactured and successfully tested. The main parameters, fabrication process and experimental results of those prototype cables will be presented.
Quench detection is an indispensable part of the superconducting electrical device to ensure its safe and stable operation. For HTS cables with a length of several kilometers, Distributed Temperature Sensing (DTS) based on Raman Optical Time Domain Reflection (R-OTDR) has irreplaceable capacity such as continuous spatial measurement and long sensing distance, but the optical fiber needs to endure the long-term challenge of the harsh environment to prove its reliability. In this paper, the fatigue characteristics of different types of optical fiber under long-term impact of liquid nitrogen was discussed. The fatigue characteristics was characterized by the loss value of the optical fiber and the temperature measurement was also observed as a reference basis.
This presentation shows the effect of soldering between YBCO tapes on the inter-tape resistances in the stacked cables composing of dozens of YBCO tapes. The research and developments of a stacked cable with multiple YBCO tapes are ongoing as a candidate for large-scale conductors for fusion experimental devices. In this study, the inter-tape coupling losses in the cable composing of stacked 50 YBCO tapes were measured under external ac magnetic fields in liquid nitrogen. Inter-tape resistances are estimated through comparison with measured and calculated coupling losses. The measurements were carried out on two samples with and without soldering between tapes in samples composed of YBCO tapes with a copper layer. The soldered sample is stacked solder-plated YBCO tapes and then spirally wrapped in a 4-mm wide copper tape to hold them; furthermore, the whole sample is soldered. No soldered sample is composed of the same YBCO tapes without solder plating. The tapes were stacked in the air and then held with the polyimide tape. Both sample lengths were about 100 mm and non-twisted. Therefore, the inter-tape coupling current in the sample flowed around the whole sample length during experiments. The effects of soldered tapes on the resistances are discussed from the difference between coupling losses in both samples.
High field superconducting magnets require a large number of ampere-turn in their windings. To avoid large self-inductances in such magnets they must be wound using superconducting cables. Compared to other currently available HTS cables REBCO Roebel and CORC cables have their strands transposed or twisted which reduces both their ac losses as well as magnetization. This improves field homogeneity and makes the magnets less ramp rate sensitive. Stability and current sharing is crucial in these cables. Here we present FEM modeling results on isothermal as well as non-isothermal current sharing in Roebel and CORC cables containing broken elements of different size and intensity located in different places of the cables. CORC cables have an advantage of rather simple control of their stability via modifying the size of their cores. Conclusions on stability and quench of these cables in magnet windings are made.
Acknowledgements: This work was supported by the U. S. Department of Energy, Office of Science, Division of High Energy Physics, under grant DE-SC0011721
REBCO coated conductors are expected to apply high field superconducting magnets since they have high critical currents and excellent mechanical properties. It is well known that REBCO coated conductors have angular dependence and strain dependence of the critical current in magnetic field. However, there are few experimental results of angular dependence of critical current under strains. Especially, the mechanism of the strain effect for REBCO has not been clear. In this study, the angular dependence of critical current of REBCO coated conductors under bending strains are investigated. A critical current measurement apparatus at various temperature, field, field angle and bending strains is developed. REBCO coated conductors with and without artificial pinning centers were prepared. The angular dependence of critical currents for the samples with micro-bridge of ~0.1 mm width and 2 mm length were measured at 77 K, 0.4 T and bending strains of 0, 0.2 and 0.4%. We found that the difference of the critical currents at field angles of 0º and 90º is appeared under bending strains. The difference of the critical current behaviors between the samples with and without artificial pinning centers under bending strains are not observed.
With the development of REBCO high-temperature superconductor (HTS), many structures of superconducting strand/conductor stacked with REBCO tapes were proposed in past years. The Quasi-isotropic superconducting strand made by stacked REBCO tapes and copper tapes was proved to have excellent performance in critical current at liquid nitrogen temperatures. In this paper, the critical current of QI-S strand is simulated based on H-formulation at 4.2 K and 77 K. And the bending and twisting properties of QI-S strand are studied based on laminate theory at 4.2 K. The results indicate that QI-S strand has better performance in application fields at low temperatures such as power transmission, large superconducting magnets and fusion industry.
The high-temperature superconductor REBa2Cu3Oy (REBCO) is expected to be applied to fusion magnets because of its high critical current density at 20 K [1]. Various kinds of REBCO conductors with a large current capacity have been developed for the fusion magnets by stacking the REBCO tapes such as FAIR conductor [1]. A drawback of REBCO conductors is that the buffer layer prevents current sharing between the tapes, causing reduced conductor stability. We propose a conductive micro-paths to improve conductor stability where current is shared between the REBCO tapes. In this study, we fabricated the conductive micro-paths in REBCO tapes to investigate the current sharing in the REBCO tapes.
Blind holes were made on REBCO tapes as non-conductive micro-paths by using a Nd:YAG laser. Additional Ag films were deposited on the tapes by sputtering method to make the micro-paths conductive. We observed the microscopic structure of the blind holes and conductive micro-paths by SEM microscopy. As a result, the blind holes reached substrates of the REBCO tapes and the holes were filled by the deposited Ag films.
Two REBCO tapes, one with degradation intentionally introduced, were prepared and stacked to investigate current sharing between the tapes. Partial voltage in the tapes were measured with some voltage taps with sweeped current at 77 K. As a result, the current was shared between the REBCO tapes and successfully bypassed the damaged part. We will discuss improved stability of the REBCO conductors with the conductive micro-paths.
This work was partly supported by the NIFS Collaboration Research Program (NIFS21KECA090, NIFS21KOBA034), JSPS-KAKENHI (20K15217, 20H02682), JST-A-STEP, and NEDO.
[1] T. Mito et al.: J. Phys. Commun. 4, 035009 (2020).
REBCO coated conductors have a high critical current density in a high magnetic field at low temperature. Therefore, the research and development of REBCO coated conductors have proceeded for high magnetic field applications. A critical current of REBCO coated conductor shows field angular dependence and strain dependence. Especially, the mechanism of the strain effect for REBCO coated conductor is not clear. In our laboratory, the relationship between the strain and other environment for REBCO is studied to understand the strain effect of REBCO. In this study, the angular dependences of critical current for REBCO coated conductors under various tensile strains were investigated. A small tensile test apparatus for large transport current measurement was developed. The field angular dependence of the critical current of REBCO coated conductors was measured at 77 K, 0.4 T and several tensile strain. As a result, we found that the difference of the critical current at field B // c-axis and B // ab-plane is increased with increasing tensile strain.
Currently, the development of superconducting magnetic energy storage devices (SMES) based on the cables from high-temperature superconducting tapes of the second generation are carried out. Such SMES will be used, for example, in the NIKA project to power the pulsed magnets of Booster and Nuclotron accelerators. Similar cables may be used in accelerating magnets as well. The number of working cycles of current pulses can be more than several million. So the important issue is the stability of HTS tape under both multiple pulsed current loads and long-term current loads that typical for the frozen magnetic field mode.
In this report we present the results of the study of stability of industrial samples of 2G HTSC tapes based on REBCO, carried out in three modes of current load.
In the first mode a direct current of I1 = 0.9Ic, I2 = 1.1Ic were passed through the sample. The duration of exposure was up to 350 hours. It was observed that under long-term exposure to high current density, the value of the critical current remains within acceptable limits.
In the second mode, simulating a possible quench, HTSC tapes were exposed by pulsed current actions with a current density exceeding the critical current density and duration from 10 μs to 250 μs. We found the parameters at which irreversible changes in the critical current were observed.
In the third mode, that simulates multiply periodical current loads in SMES or an accelerating magnet, HTS tapes were subjected to multiple (more than 1 million times) cyclic changes in the current in the range from 0.5Ic to 0.8Ic with a cycle duration of 1s. We report the results of such load current studies that were obtained by means of transport measurements, Hall scanning magnetometry and magneto-optical imaging.
In the case of a REBCO superconducting coil, the coated conductors endure both tensile and bending strain. Therefore, the mechanical behavior of REBCO coated conductors and its effect on the critical current under combined tensile-bending deformation should be revealed. In this study a mixed-dimensional laminated composite finite element model (FEM) for REBCO conductor is developed for stress and strain analyses in the processes of fabricating and cooling, as well as tensile and bending test. The model includes all the major constituent layers of a typical REBCO conductor and is experimentally validated. First, the thermal residual stresses and strains accumulated during the fabrication and cooling processes are analyzed. Then, with the residual stresses and strains as initial stresses and strains, the mechanical behavior under tensile, bending and their combined strain state is studied. Lastly, a phenomenological critical current-strain model based on the Ekin power-law formula and the Weibull distribution function is combined with the FEM to predict the strain dependence of critical current under the combined tensile-bending deformation. The calculations show that a proper compressive pre-bending can improve the tensile strain tolerance of the conductors. While an exaggerated compressive pre-bending can reduce the initial critical current, even cause the irreversible degradation. It indicates that reasonable arrangement of bending and tensile strains is very important for the extremely high field operation of a superconducting coil.
In this paper, a REBCO thin film superconducting wire was fabricated by depositing materials with different specific resistance values (Ag) on REBCO superconducting wire, using the “RF Sputtering Deposition Method” with micro-range thicknesses to form the outer layer. Then the fabricated REBCO superconducting wire were subjected to basic characteristics tests (measurement of their temperature distribution according to their changing resistance) and over-current transport-current tests to investigate their phase transition. Finally, the results of the basic characteristics tests and the over-current transport-current tests were analyzed to present the applications of superconducting power application devices of the REBCO superconducting wire according to the thickness and properties of the wire’s stabilization layer.
The superconducting tape stack has increasing impact on the applied superconductivity community due to the high field and current applications such as plasma confining magnets. The interlayer resistance of the stack, however remains a problem for the Coated Conductors (CCs) due to the ceramic buffer layer, which causes totally different behavior of the stack of CCs and the traditional low temperature superconducting cables. The main scope of this paper is to clarify the transient process of overheat or overcurrent focusing on electromagnetic and thermal characteristics of interlayer contact surfaces. A finite element method (FEM) model is established in this paper to reveal the overheat and/or overcurrent process of the stacked CCs. The FEM model for numerical simulation is coupled to calculate the heat, current, and magnetic field distribution during the stacked CCs’ quenching and recovery process. The interlayer resistance is emphatically investigated and discussed by setting different boundary constrains and assumptions to answer the question how low should the interlayer resistance be for certain applications. An optimal range of the stacked CCs’ turn-to-turn contact resistance for manufacture is proposed referring to numerical simulation results and analyses. This FEM model can also be applied to analyze the transient quenching process of no-insulation coils.
Since the 2G HTS tapes are made by a multi-layered thin film process, delamination occurs easily when stress is applied in the vertical direction of the tape. That is, in the cooling process of the superconducting coil, delaminations occur in the multi-layered HTS tapes when the stress value due to the difference in the thermal contraction rate of each material constituting the HTS tape is greater than the bonding strength of the superconducting layer. The same problem arises in the hoop stress that occurs in the superconducting coil. When delamination occurs, the characteristics of the superconducting tape are deteriorated. To improve this problem, we developed a ‘holing and hole filling process’ in which holes are processed using a laser in the vertical direction of a HTS tape and then filled with metal such as copper or solder. The metal substrate is evaporated by the heat of the laser, and the evaporated metal is coated on the hole wall that is to fix the superconducting layer. The the hole walls coated with metal prevents delamination of HTS tapes
In this study, it is suggested that not only the mechanical properties of HTS tapes can be improved by the holing and hole filling process, but also the electromagnetic properties of the coil can be improved. The current distribution and heat flow around the artificially made hole were calculated, and the effect on the stability of the superconducting coil was investigated. It can be seen that the magnetic field decreases faster than the metal-insulation coil because of the rapid current distribution after quenching at hole and hole filling processed coil.
Ceramic powders A1-xSrxTiO3 (where x = 0.02, and A=Ba2+, Pr3+, Sm3+, Eu3+, and Er3+) were synthesized by solid-state reaction method and sintered at up to 1400 °C. The phase formation, elemental composition, and microstructure of the sintered samples were investigated by TGA, XRD, EDX and SEM techniques, respectively. The results of the partial substitution of Ba ions by other rare earth ions (Pr, Sm, Eu and Er) showed an improved on piezoelectric and electrical properties of A1-xSrxTiO3 system. This work will provide a relationship between the structural and physical properties of the A1-xSrxTiO3 through doping of various rare earth elements.
High tensile strength and fracture toughness at 4 K are required on structural materials for ITER Toroidal Field Coil (TFC) cases to withstand huge electromagnetic forces generated on TFC. However, hence there were no standard materials satisfying ITER requirements, QST developed new cryogenic structural material of JJ1 (0.03C-12Cr-12Ni-10Mn-5Mo-0.24N), and optimized nitrogen contents of 316LN to strengthen tensile strengths according to ITER requirements through trials since 1980s. These trial results served the basis to develop the material section of “Codes for Fusion Facilities -Rules on Superconducting Magnet Structure (2008)” issued by the Japan Society of Mechanical Engineers in October 2008 (JSME code). One of unique points of JSME code is that satisfaction of tensile test result at room temperature also guarantee results at 4 K. This JSME code was basis on material specification for ITER TFC cases’ materials, and material manufacturing started from 2012. Totally over 2000 materials (over 5000 tons) have been manufactured by 6 fabricators and it was completed successfully in 2020. Material properties, e.g. chemical composition, grain size, tensile test at room temperature, Charpy impact test at 77K, were obtained as quality control test for all materials. In addition, around 600 tensile tests at 4K and 77K were performed as sampling test to confirm cryogenic tensile properties by QST. Those material properties and mechanical test results were stored in data base established by QST and correlation between mechanical properties and material properties were evaluated to optimize material specification for future superconducting magnets. This paper will show summary and evaluation results of the material properties of mass production for ITER TFC cases.
The Chinese Fusion Engineering Testing Reactor (CFETR) is aiming to bridge the gap between the ITER and the first commercial fusion power plant, a necessary complement of the ITER. The requirement for sustaining long burn duration as specified in the duty time CFETR mission necessitates the use of
superconducting magnets. Totally 16 TF D-shaped (six arcs and a straight leg) coils which are of cable-in-conduit conductor type are designed. All the subcomponets have very demanding requiremnt to withstand the severe enviroments. This paper give the the nondestructive test (NDT) method developed for th (TF) coil conductor jackets made of 316L stainless steel.Based on the linear elastic fracture mechanics, maximum acceptable defect sizes in the TF jacket material have been defined. PAUT method and ECT method were devloped for the circular-in-square jacket inspection . For PAUT method , foculs laws are calucated and optimized. for ECT method, specific ECT probe was designed and manufatured. Benchmark experiments were carried out to study the NDT reliability.
A commercial micrometric Cu powder is mixed with Ag nanowires (diameter 0.2 µm, length 30 µm) synthesized in-house, in order to prepare a powder with a Ag content of 1 vol. %. Two powder batches are prepared for consolidation into cylinders (diameter 8 mm, length 33 mm) by spark plasma sintering.
One cylinder is sintered at 400 °C, where the solubility of Ag in Cu is below 0.1 vol. %, which allows one to obtain a composite microstructure with pure Ag nanowires dispersed in a pure Cu matrix. The other cylinder is sintered at 600 °C, where the solubility of Ag in Cu is equal to about 2.4 vol. %, which allows the Ag nanowires to dissolve into the surrounding Cu volume to form Cu/Ag alloy nanowires.
The diameter of the cylinders is reduced by wire-drawing, in several passes, thus producing progressively finer wires (diameter in the range 1-0.2 mm). Wires with ultrafine Cu grains (200-700 nm for a 0.5 mm diameter wire) elongated along the drawing axis are prepared. The nanowires (pure Ag or Cu/Ag alloy) are dispersed along the Cu grain boundaries.
Both kind of wires show a similar ultimate tensile strength (1100 MPa at 77 K), reflecting an equivalent strengthening effect provided by the pure Ag and Cu/Ag alloy nanowires.
However, the electrical resistivity of the Cu/Ag-Cu wires (0.56 µΩ.cm at 77 K) is significantly higher compared to that of the Ag-Cu wires (0.49 µΩ.cm at 77 K). This shows that despite the very local nature of the Cu/Ag alloy, its formation is to be avoided by controlling the sintering conditions, which thus have to be changed depending on the chosen Ag content.
Pure Ag nanowires - Cu composites wires are to be preferred in order to obtain the most suitable properties for high magnetic fields.
High Temperature Superconductors (HTS) is a promising option for high current Cable-In-Conduit Conductors (CICC) for large high-field magnets. CICC are often constructed from several HTS strands which themselves are formed from individual HTS tapes. Quench propagation is CICCs is currently under intensive investigation, and it can be predicted by modelling the entire structure. However, for the modelling heat transfer problems, along with thermal material properties, the thermal properties of contact interfaces between structural materials are highly needed. So far, a lack of such data in the literature made the analysis of quench propagation very difficult.
Thermal resistance of copper-copper and copper-stainless steel interfaces were characterized for different pressure and temperature ranges. Therefore, thermal conductivity was measured with the axial heat flow method within the Physical Property Measurement System (PPMS) of Quantum Design using a Thermal Transport Option (TTO) in the steady-state measurement mode in the temperature range from 4 K to 300 K. For the required investigation, the TTO option was extended: the TTO sample puck was equipped with additional copper frame allowing measuring a thermal conductivity of stack of metallic plates pressurized by a screw. The method was further extended to allow the measurement of thermal conductivity at different pressure values. For this, the copper frame was equipped with strain gauges, and calibrated for measuring the pressure applied to the stack at different temperatures. Further step included the systematic measurement of thermal conductivity versus temperature of the stacks for a range of contact pressure values in PPMS. Different stacks geometries and different compositions were investigated.
After completing the 32T all-superconducting user magnet, development of magnets of this class with a noticeably higher field has begun: the NHMFL 40T magnet is the immediate target. The next generation of high temperature superconductor (HTS) high-field user magnets demands the next generation of quench protection systems. Previously, a bank of batteries was employed to power the quench protection heaters, but safety considerations have driven the development of alternatives. One such alternative is a pulse forming network (PFN). A PFN is a specially tuned RLC circuit designed to deliver a pulse of current of a specific shape. It can be designed to deliver a large variety of pulse shapes and can therefore be tuned to the specific needs of the current generation of quench protection systems. A PFN is simpler to maintain and has fewer safety considerations than a battery bank, making them ideal choices for user magnets that will likely see many years of service. We will discuss the development, construction, and testing of the first quench protection system to make use of a PFN. This unique application was realized using the design and manufacturing expertise available at the Mag Lab to construct a test scale system for use in the development of the all-superconducting 40T project.
Quench protection is one of the key issues for superconducting magnets with high energy storage, especially for those wound with superconducting cables, which have low thermal conductivity between each turns. Thermal quench-back induced by a co-wound heater wire is an available quench protection scheme for the magnets wound with 6+1 type cables (6 superconducting wires wound with 1 heater wire). In the present paper, an electro-thermal coupling model is developed to deal with the dynamic coupling behaviors of electrical and temperature field inside the superconducting magnets during quench protection process based on the nonlinear quench-back. The transient evolutions of current, voltage and temperature are numerically obtained and analyzed by finite element method, which show observable quench-back features. The model is verified by comparing the numerical results with experimental measurements of a small scale model canted-cosine-theta (CCT) magnets. Furthermore, the influences of the coil inductance, operating current and dump resistor on hot-spot temperature are systematically analyzed and the relations between the quench protection parameters and peak values of terminal voltage and temperature are revealed, which are significant to the design of quench protection scheme for superconducting magnets further.
Use of 2G HTS superconductors in magnet applications allows creating compact magnets with large magnetic fields due to many times higher current density of superconductors in comparison with traditional metal wires. At the same time, 2G HTS tapes make the design of magnet special and require choosing 2G HTS tape parameters suitable to each magnet design. The unique properties of 2G HTS tapes are possible current transport in parallel in the superconducting and normal conducting layers, non-uniform critical current distribution by length of 2G HTS tape, strong correlation of heating of the tape with the thickness of the thin stabilizer layers and the non-linear behavior in external magnetic field. All factors have an impact on the quench detection of magnets and have to be taken into consideration to prevent overheating of local hot-spots. This paper describes a method for selecting the 2G HTS tape geometry for magnet design by calculation of quench protection properties in accordance with current sharing between layers of 2G HTS tapes in the external magnetic field and with deviation of critical current values by length. Analysis of quench in 2G HTS tape with realistic critical current distribution by length allows predicting behavior of temperature and voltage in each point of tape and provides specifications for creating an effective quench protection system.
Protecting a high temperature superconducting (HTS) magnet from a quench event is a challenging task, especially in the case of accelerator magnets where current density is usually very high. Because of the slow normal zone propagation velocity, the long reliable quench detection method by coil voltage may not be timely for HTS anymore, leaving HTS magnets under danger of overheating. Many new quench detection approaches have been proposed, such as optical fiber, hall sensor, acoustic MEMS sensor, by RF wave, by stray-capacitance, and most interestingly by another superconductor. Using low temperature superconducting (LTS) wires to detect quench in HTS conductors have recently been experimentally proved by different groups, yet a theoretical study is still needed to further develop this technique and make it prepared to be applied more generally. Here we try to figure out how LTS wires can work as quench detectors for HTS conductors by theoretical discussion and numerical analysis. The efficiency is also compared with quench detection simply by coil voltage.
The authors’ group is investigating a quench protection method for HTS coils that use Cu tape co-wound with HTS tape. In this method, the voltage $V_s$ across the resistive zone in the HTS coil is monitored by measuring the voltage difference between the HTS coil and the co-wound Cu tape coil in normal operation. When $V_s$ exceeds the quench detection voltage, the HTS coil is disconnected from the power supply and the energy stored in the HTS coil is dumped into a dump resistor $R_1$. At the same time, a voltage is induced in the co-wound Cu coil and a switch to connect the co-wound coil to a resister $R_2$ is closed to induce a current in the co-wound coil. Then, a part of the currents of the HTS coil is quickly transferred to the co-wound Cu tape coil because of the tight magnetic coupling of the both coils, and the HTS coil current is decreased rapidly to a certain value just after the quench protection sequence starts. Thus, the hot spot temperature is reduced. In the authors’ previous work, effectiveness of the quench protection method was shown by a numerical simulation analysis. In this work, the method was investigated by simulation experiments using small scale test pancake coils co-wound with YBCO wire and Cu tape. Current patterns of the YBCO coil and co-wound Cu coil of a model magnet at a quench event were calculated for the case that this quench protection method was applied. In the experiment, the same patterns of the currents were applied to the quenching test coils by controllable current supplies. Experimental results showed that the quench protection method was effective to reduce the hot-spot temperature, when a proper value of $α = R_1/R_2$ was selected.
In the framework of a joint collaboration funded by US Department of Energy (DOE), a large bore “Cable Test Facility Magnet” is under development. This is a joint effort between the Office of High Energy Physics (HEP) and the Office of Fusion Energy Sciences (FES). A 15 T Nb3Sn dipole magnet is being developed at Lawrence Berkley National Laboratory (LBNL). The magnet will produce the background field needed test advanced superconducting cables and inserts in large field. The test facility will be located at Fermi National Accelerator Laboratory, that is also developing the cryostat.
Due to the large field and stored energy (> 12 MJ), the quench protection is one of the challenges of the magnet design. In this paper we present how an active protection system based on dump resistor can keep the magnet hot spot temperature within Nb3Sn limits, and peak voltages within insulation sustain level, and how a CLIQ unit can be used in order to make the system more robust, efficient and redundant. We show also how the magnet interact with inserts during a quench.
We have been developing the Frequency Loss Induced Quench (FLIQ) protection system for high-temperature superconducting magnets. We have studied the sensitivities of the various FLIQ system parameters to understand the design of an effective quench protection system. FLIQ drives AC current in the magnet coil and generates AC losses. The heating associated with the losses quenches the HTS magnet safely. This distributed heating of the magnet will cause the field energy to dissipate over the entire volume of the magnet to minimize peak hot spot temperatures and compensate for the thermal margin caused by the normalized region.
Due to the uncertainty and complexity of AC Loss calculations during the quenching process at high frequencies, we conducted a series of tests of the FLIQ system on 2G HTS pancake coils in liquid nitrogen to study the dynamics of quench and the energies involved in the quenching process. Liquid nitrogen boil-off measurements were used to measure the heat energy deposited. The paper will present the experimental results and an analysis of the results concerning the FLIQ design parameters.
Here we have studied the performance and quench properties of a large (outer diameter: 901 mm; winding pack: 44 mm thick × 50.6 mm high) conduction-cooled, react-and-wind, MgB2 superconducting coil. Minimum quench energy (MQE) values were measured at several coil operating DC currents (Iop ), and distinguished from the minimum energy needed to generate a normal zone (MGE). During these measurements, normal zone propagation velocities (NZPV) were also determined using multiple voltage taps placed around the heater zone. The conduction cooled coil obtained a critical current (Ic ) of 186 A at 15 K. Two kinds of heater were involved in this study: (1) a localized heater ('test heater') used to initiate the quench, and (2) a larger 'protection heater' used to protect the coil by distributing the normal zone after a quench was detected. The protection heater was placed on the outside surface of the coil winding. We explored two different protection modes via both experiment and simulation. In the first, a DC power supply was used to energize the protection heater (attached to the coil surface) once a quench was detected. In the second, AC was injected into the windings once a quench was detected, quenching the coil with AC heating generated by hysteretic and coupling losses in the conductors. Simulations of the energy needed from the AC power supply and thermal heating from AC excitation are performed. Different heating mechanisms and protection rates were compared for the two modes (i) pulse provided to external heater, and (ii) AC injection into the windings. The implications of this comparison are then discussed.
Superconducting magnet protection must address two main areas of the magnet and circuit performance, namely Conductor Hot-Spots and Circuit Voltages. Both hot spot and voltage operational maximums are during the superconductor's transition called a Quench. Historically high voltages have resulted in many damaged and destroyed magnet coils so reducing voltages is a preferred direction for designs. In an ideal design the Hot Spots should be limited to a level below the point where the thermal expansion starts to develop shear and direct stresses: this is at about 100 K for most materials. For magnets that use energy extraction to external loads, either fixed to the cold coil or at room temperature outside the cryostat, for a given magnet current the value of the maximum allowed voltage imposes the value of the energy extraction resistor. This determines, together with the magnet inductance, the time the energy is removed and thus the hot spot.
If we simply replace the resistor with a high-energy voltage-dependent resistor (varistor), we can extract more energy for the same maximum voltage because the self-adjusting resistance of the varistor reduces the extraction time.
This paper presents: the Varistor’s warm and cold designs, the variety of possible protection circuits, and many test event data from several superconducting magnet cold tests.
The main challenges to implementing HTS in ultra-high field are management of stress and quench, due to intrinsic strain limits and lower normal zone propagation velocities than LTS magnets. While Bi-2212 magnets can be considered comparatively easier to protect than ReBCO coils due to Bi-2212’s more moderate margin and high silver stabilizer fraction, quench management is critical when moving towards larger volume magnets with higher stored energies. While evaluating the mechanical and quench limits of several Bi-2212 test solenoids including one wound from Rutherford cable, we implemented alternative quench management methods. Among these were the installation of capacitance sensor arrays for rapid heat/quench detection, implementing varistor energy extraction to validate predicted improvements to quench protection, as well as demonstrating the benefits of Rutherford cable solenoids for rapid detection and protection (lower inductance and voltage tap section length). An analysis of the quench data from these test coils will be presented.
Acknowledgements: This work is funded by the DOE (HEP Award No. 227011-520-032288), the NSF (Award No. DMR-1157490), and by the State of Florida. This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program.
Metal plates are applied in high-temperature superconducting (HTS) magnet to provide a mechanical support and conduction cooling. The electromagnetic coupling between the metal plates and HTS coils has a considerable influence on the discharge operation of HTS coils during quench protection. In this paper, a multi-physics model is developed using circuit- field coupling method to study the effect of the metal plates on the quench protection operation of the HTS coil. An experimental platform is built to verify the simulation model, which includes dump resistors, HTS double-pancake coil, switch and DC power supply. The central magnetic field, coil voltage and current are measured and analyzed during a series of discharging operations. The HTS coil is carried out at 77K (in liquid nitrogen). The effects of initial transport current, size of metal plates, martials on the discharging process during quench protection are studied by experiments and simulations. Using the simulation model, the temperature of the HTS coil and metal plates is analyzed, and the effect of the initial temperature o is studied. The results show that the metal plates can lead to a sharp current drop in the early stage of coil discharging process, the thickness and quantity of metal plates can significantly accelerate current dropping. Furthermore, the metal plates can keep the temperature evenly distributed in the HTS coil during quench protection, which can significantly reduce the risk of coil damage.
The major difficulty of the quench detection of the superconducting magnetic system (SMES) is that the pulsating voltage of the converter is much larger than the local normal-zone voltage of the HTS coils. It is therefore difficult to detect the quench of the superconducting coil (SC) with the voltage measurement method. This paper presents a novel quench detection method without additional sensors. The proposed method directly utilizes the converter voltage and current to identify the resistance of SC. The steepest descent method is proposed to estimate the SC resistance on line. And the online identification method is embedded in the controller of the SMES. It is therefore able to make the SMES respond to protect the SC instantaneously upon quench detection. Simulation result verifies the efficacy of the proposed approach.
During 2020, the SULTAN test facility was upgraded to host Quench Experiments on HTS conductors. In the frame of the EUROfusion program, few cables based on the Swiss Plasma Center (SPC) Twisted Stack-Tapes design have been manufactured and successfully tested. Each conductor addresses a specific design parameter. For the first time, it was possible to observe the quench evolution and propagation (maximum current 15 kA, maximum magnetic field 9 T) in a sub-size HTS conductor for fusion applications, reaching high temperature (above 200 K) and electric field (above 10 mV/cm). The goal of the experiment was to study how the different design parameters affect the quench evolution and the temperature distribution among different regions (cable, helium, jacket). The presented outcomes shall support the design of HTS cables for fusion. The experimental results are compared to the model of the HTS conductor build by the multi-physics code THEA.
High–temperature superconductors (HTSs) still hold some unignorable issues, such as AC losses and its poor robustness against normal transition. For HTS tapes, dividing superconducting layer into filaments by striation shows remarkable effects on reducing AC losses. However, it could deteriorate robustness due to blocking a current sharing among filaments. Thus, plating copper on the entire group of superconductor filaments plays an important role in improving the robustness.
Quench characteristics of copper–plated multifilament coated conductors are so complicated that we hardly can understand it from experiments. In order to evaluate the robustness of such conductors and design the conductors with high robustness, the numerical analysis is a powerful tool. We are developing the quench analysis model of the copper–plated multifilament coated conductors. This model consists of thermal and electric circuit analysis. To simplify the analysis, we model the conductor as a two dimensional object neglecting its thickness. For the thermal analysis, heat capacity and thermal conductivity are averaged in the direction of the thickness of the conductor. We also develop the model of the electric circuit analysis for the copper–plated multifilament coated conductors considering non-linear resistivity of superconductors. Since heat conduction is significantly slow compared to the time evolution of current, the temperature and the current can be calculated separately although they are dependent to each other.
We apply a thermal disturbance to a multifilament conductor and, then, examine the time–dependent current and temperature profiles. Also, we analyze a multifilament conductor having a local low critical current region while the current is ramped up.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
Nb3Sn conductors are prone to quench due to deposition of heat energy from disturbances such as flux jumps and cracking of nearby epoxy, which push the conductor into the normal state. In Nb3Sn magnets, this manifests as training, wherein the magnet can reach a progressively higher current after a succession of quenches. By incorporating substances with a higher heat capacity at cryogenic temperatures, the amount of energy needed to increase temperature and cause a quench can be increased. Here we report on the results from several 36/61-restack experimental tube-type strands made by Hyper Tech, each with different high heat capacity additions mixed into the center region of the Cu matrix. We attached a resistor to a strand and, after applying a constant transport current to the strand at 4.2 K, applied increasing amounts of energy to the resistor until the strand quenched. It is shown that wires with high-heat capacity additions can absorb more energy from a heat pulse before quenching than a control wire with a Cu-only matrix. Magnets made from this wire design should be more resistant to quenching, especially at currents approaching Ic.
Due to the normal zone propagation velocity (NZPV) of a high temperature superconductor (HTS) being about 100-1000 times slower than that of a low-temperature superconductor (LTS), the quench detection is a difficult challenge for HTS structures so far. To propose more effective quench detecting methods and criterion, it is necessary to reveal the mechanism and multi-field coupling behavior during a quench for a HTS. In this work, a two-dimensional thermoelastic coupling model is developed to deal with the quench occurrence and normal zone propagation behaviors as well as the transient thermoelastic responses of HTS stacks. The evolutions of temperature, strain and strain-rate are numerically obtained by homogenized and layered finite element models for REBCO composite stacks during a quench triggered by a heater respectively. There shows a good agreement between the predicted NZPVs by the present model and the existing experimental results. The inherent relation between the thermoelastic response and the quench event is determined by the evolution of strain and strain-rate associated with the temperature. At locations far away the heater, the strain and strain-rate curves show observable decreasing behaviors and extreme points before normal zone arrives. And inflection points are also observed on the strain-rate curve which precisely correspond to the critical temperature values, showing the occurrence of a quench. Thus, the strain and strain-rate decreasing behaviors may be used to detect a quench earlier and the corresponding extreme points could be effective mechanical criterion for quench detection in HTS structures.
For future larger and higher energy particle accelerator, the Fourth superconducting electron cyclotron resonance ion source (FECR) is building in Institute of Modern Physics, Chinese Academy of Science. In order to verify the technology of the Nb¬3Sn superconducting magnet for FECR, a prototype which consists of two axis solenoid coils and six sextupole coils with cold iron yoke has been fabricated. A three-dimensional quench simulation of the magnet has been carried out in OPERA-quench and ANSYS, the quench process of the magnet without protection circuit and iron yoke is first performed and the protection circuit is designed based on the analysis result. Then the experiment had been carried by the protection circuit. Finally, the difference between simulation results and experiment is discussed.
The 9.4-T whole-body MRI superconducting magnet system with a warm bore of 800mm in diameter has been designed and fabricated in the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS) for bioscience research applications. A passive quench protection system with the coil subdivisions and the heater network to accelerate quench propagation has been employed to avoid the damage of the magnet. Recently, the magnet system was tested successively and the magnet underwent two premature quenches at the operating current of 172.6 and 174.7 A respectively. In this paper, the test quench results have been analyzed. The quench behaviors including time-dependent current decay, voltages and hot-spot temperatures during aforementioned quenches are calculated in full by means of two quench numerical simulation codes based separately on anisotropic continuum model and finite difference model. The simulation results of the two numerical methods have been analyzed and compared to the test quench results and the performance of the two numerical methods has been discussed.
Key Words—MRI, superconducting magnets, quench protection, numerical simulation.
VIPER cable is a high-current and high-field capable high temperature superconducting (HTS) cable designed by MIT and Commonwealth Fusion Systems (CFS) for large scale superconducting magnet system applications. The VIPER cable design is based on the high-temperature superconductor cable architecture known as Twisted Stacked Tape Conductor (TSTC) first proposed by Takayasu et al. [1]. Several VIPER cable prototypes (name Alpha, Bravo, Charlie, and Delta) were instrumented and tested at the SULTAN facility to qualify the mechanical strength, fatigue cycling, and quench stability at fusion-relevant conditions. This poster will cover the quench tests results and COMSOL simulation modelling of the VIPER Delta test campaign. The VIPER Delta cable was tested at fields up to 10.9T, currents up to 50 kA, and operating base temperatures ranging from 4.5 K to 20 K. Experimental results show quench propagation velocities (QPV) on the order of 0.1 m/s with QPV increasing with operating current and decreasing with operating temperature. 3D COMSOL models were created to simulate the quench dynamics, such as QPV changing with temperature, of the VIPER Delta cable at Sultan. The cryostability, quench temperature thresholds, and normal zone propagation will be simulated with the 3D COMSOL model and compared to experimental data. In addition, sensitivity studies will show how important accurate REBCO tape characterization (Ic vs. angle, temperature, and magnetic field), HTS stack assumptions, and cable material property data (thermal and electrical properties) translate to the accuracy of the model compared to experimental results.
This research is supported by Commonwealth Fusion Systems. The authors appreciate the testing support by the SULTAN team at PSI; and the authors thank the MIT PSFC team and the CFS team who worked on designing and manufacturing the VIPER cable.
[1] M. Takayasu, et al., “HTS twisted stacked-tape cable conductor,” Supercond. Sci. Technol., 2011.
This paper studied the alternating current (AC) loss of stacked high-temperature superconducting (HTS) tapes based on the finite-element method (FEM). By solving the partial differential equation (PDE) of H formulation, this research analyzed the effects of the frequency, amplitude and phase of the current and magnetic field on the AC loss of the three-layer stacked HTS tapes which works under AC transmission current and AC external magnetic field. To fully understand the AC loss distribution in the HTS tapes, the total loss in the stacked tapes was investigated and the difference in loss between the middle tape and the end tape were highlighted. The results shows that the AC loss of the tapes at both ends is always greater than that of the tape in the middle, and the total AC loss of the tapes varies linearly with frequency, symmetrically with phase. Over all, The characteristic parameters of current and magnetic field are quantitatively studied to find the optimal solution of AC loss under the coordination of all parameters, which plays a key role in the subsequent optimization of flux pump system.
AC loss reduction in HTS coils can help reduce the cryogenic demands and increase the performance of HTS machines. In an HTS coil, most AC loss is generated in the end windings due to the large radial magnetic field in these parts. Therefore, one of the effective methods to reduce AC loss in HTS coils is using ferromagnetic flux diverters to reduce the radial components of the magnetic field in the end windings. In this work, measurement and numerical simulation results of AC loss in an HTS coil assembly comprising four REBCO double-pancake coils with two types of low-loss magnetic flux diverters (MFDs) are presented. One is molypermalloy-powder (MPP) MFD which has a saturation magnetic field of 0.8 T and the other is high flux MFD which has a 1.5 T saturation field. Numerical models for the HTS coil assemblies with the MFDs are built based on the T-A formulation. Experimental results and numerical simulation show that both MFDs can significantly reduce the AC loss in the HTS coil assembly while generating negligible AC loss in themselves. AC loss results in the coil assemblies using both MFDs are compared and discussed.
Electric machines have been applied to every industrial and transport applications today and are required to realize high-output density.
Superconducting technology is one of the most effective methods for realizing the high-output density motors. The superconducting coils at ultra-low temperature can energize several hundred times higher current density in comparison with copper wires; it directly leads to the realization of high current density coil, while reducing the weight of field coils and armature windings at rotor and stator.
AC losses occur, however, by applying alternating magnetic field or current to superconductors; the losses mainly consist of hysteresis and coupling losses and are often technical problems for the superconducting applications. One of the effective methods to reduce the AC losses is the employment of the multi filament wire structures. MgB2 wire, which has multi filament structure and can be used at liquid hydrogen temperature (20 K), is one of optional materials for superconducting motor coils.
We have been designing and constructing an AC loss measurement device using PM rotor; in this device, rotating magnetic field is applied to the MgB2 superconducting coil. The PM rotor employs Halbach structure to apply rotating magnetic field of over 0.1 T to the MgB2 superconducting coil. The MgB2 superconducting coil stored within the cryostat is to be cooled at 20 K with refrigerator. By using this AC loss measurement device, the AC loss of MgB2 superconducting coil in rotating field is measured from the torque change. This change can be considered as the loss of the whole rotation system. In this presentation, we will report the AC loss measurement results of the MgB2 superconducting coils, by using the constructed device.
Rare earth barium copper oxide (REBCO) coated conductors (CC) have high thermal stability and high current density. REBCO CCs are suitable for generating high magnetic fields. It is expected that magnets wound with REBCO CCs are utilized for high magnetic field applications, such as magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR), medical-use accelerators, and compact fusion. In recent years, REBCO magnets have been also developed for high-performance motors of electric aircraft and ship propulsion. REBCO magnets may be also suitable for armature windings of such high-performance synchronous motors because they can generate high DC magnetic fields. One of major problems to apply REBCO armature magnets is quench protection. As known well, when REBCO magnets are transitioned into a normal state, they often burn out in case without good protection, because it is difficult to detect a quench due to slow normal-state propagation.
In 2011, the no-insulation (NI) winding technique was proposed as a quench protection. NI REBCO coils can be avoided from burning-out in an event of normal-state transition, by removing insulation between turns. Hence, NI REBCO coils are getting a lot of attention. Moreover, the high performances of NI REBCO pancake coils containing multiple defects (defect irrelevant winding; DIW) were shown. The DIW NI REBCO coils could generate a high field with high current, without quench, despite some defects. This feature is very attractive for aircraft- or ship-propulsion motors, because it is undesired to stop motors during operation due to local hot spots or defects. Meanwhile, armature coils are exposed to external small AC magnetic fields with low frequency. When applying AC magnetic fields, NI REBCO pancake coils easily produce AC losses. The characteristics of NI REBCO pancake coils in AC magnetic fields is still not clarified, therefore, we need to clarify and evaluate them by numerical simulation.
No-insulation (NI) high-Tc superconducting (HTS) coils process much higher thermal and electrical stability than the conventional insulated coils. In some rotating machines and Maglev trains, HTS coils carry persistent current and serve as the permanent magnets. For these applications, the main issue is that the demagnetization of HTS coils caused by the local external alternating fields. This paper established an effective simulation that coupling the circuit and T-A formulation models to study the demagnetization behavior of a NI coil in alternating fields that transverse to its axis. The simulation results indicate that after the application of AC fields, screening current is induced in the outermost turns. The persistent current in the outermost turns of the coil is transferred to the inner turns via the turn-to-turn paths. Compared to its insulated counterpart, the NI coil exhibits a better magnetization stability, since the persistent currents are to flow in the shielded inner turns of the coil.
As is well known all types of superconductors are affected by AC losses.
Those losses occur when a time varying current flows in a superconductor or when it’s subjected to a variable magnetic field.
The main effect of these losses on the conductor is temperature rise due to the energy dissipation within the superconductor. Many methods were previously studied in order to reduce the magnitude of this loss.
The main task of superconductor manufacturers is to optimize the design of the wire in order to reduce AC losses according to the
magnet requirements.
This paper presents experiemental results of an empiric experiment designed to demonstrate the theoretical benefit of MgB2, with respect to standard NbTi, in low-field/fast-ramped applications.
High temperature superconductor (HTS) coil has superior current-carrying ability, and can trap higher magnetic fields, thus shows a promising application on machines with super high power density. Winding coils with bare tapes without any insulation, which is called no-insulation (NI) coil, can significantly enhance the thermal stability and reliability of HTS coils. However, in many applications, such as rotating machines and maglev trains, NI HTS coils are inevitably exposed to a background AC magnetic field. Thus, eddy transport current is induced, which can lead to more magnetization loss in superconductors. This paper provides a detailed study on the magnetization loss of NI coils exposed to AC magnetic fields. A circuit-field critical model is developed for NI HTS coils by coupling an equivalent circuit network model and a finite element method (FEM) T-A formulation model. The network model calculates current distribution, and the FEM model calculates magnetization loss. The influence of transport current, turn-to-turn resistivity, field frequency and amplitude is studied using the model. Results show that coil parameters and working conditions have a significant influence on this external loss. This paper aims to provide valuable knowledge for the development and design of NI HTS machines.
In order to examine the applicability of superconducting technology to fields of industrial applications such as linear conveyor, transfer, and transport systems, we investigated AC loss characteristics of HTS sample coils under conditions assumed for use in power electronics devices. Since inverters are used in the drive circuit of power electronics devices in a linear transfer system and so on, the drive current contains harmonic components, and then it is expected that AC losses increase. In this study, we measured AC loss characteristics of the HTS sample coil by the nitrogen boil-off method under various conditions in which the amplitude and frequency of the harmonic current were changed. The HTS sample coils were wound by a Bi-2223 tape. The outer diameter of sample coil is about 60 mm, and the height is about 25 mm. As the results of the measurement, AC losses increased in proportion to the square of the harmonic current amplitude and increased in proportion to the square of the harmonic frequency. Based on the measured results, the factors of the increase of AC losses due to the harmonic current component were discussed.
Nb3Al has better the strain properties than that of Nb3Sn, but it is difficult to manufacture as a wire. In recent years, a research group of the National Institute for Materials Science (NIMS) in Japan has developed a new shape of ultra-fine and flexible Nb3Al superconducting. Jelly-rolled Nb/Al composite monofilamentary wires with an outer diameter of 30 m, and multi-strand wires were successfully fabricated. In this jelly-roll process, Ta or Nb core is wrapped by a thin foil of Nb and Al and then inserted into a copper tube. The copper tube was drawn and then annealed at below 1000℃. The critical temperature of fabricated Nb3Al wire is higher than that of NbTi wire, and it has an excellent flexibility that allows winding by React & Wind method, so it can be expected to be applied to the superconducting applications cooled by conduction cooling method.
On the other hand, the heat transfer and cooling capacity characteristics by conduction cooling are significantly different from the pool cooling method by liquid helium. Therefore, in order to apply the developed Nb3Al superconducting wire to superconducting applications cooled by the conduction cooling method, it is necessary to evaluate the critical properties and the AC loss characteristics under conduction cooling operation. In this study, we have developed a measurement method that can accurately measure the critical properties considering the heat transfer characteristics of the Nb3Al sample wire in the conduction cooling operation. We prepared the single and multi-strand Nb3Al sample wires with different outer diameter (30 - 80 m) and number of strand (7 -19 strand). The temperature (4.5 K -14 K) and magnetic field (0 T -6 T) dependence of the critical current of developed Nb3Al sample wires were experimentally examined and measured the AC loss characteristics in the conduction cooling will be presented.
In this paper we show that the design of specialized rotating coil system to measure magnetic Axis of the triplet quadrupoles whose magnetic axis deviation are less than 0.1mm and angle deviation are less than 1mrad between them, built for DTL of a Linear accelerators. In this paper we describe the design of the rotating coils canceling the first two field harmonics, and the process of the measurement. Based on the results obtained on the two Triplets, we show that this system meets the requirements.
We have been developing a no-insulation (NI) REBCO coil system for medical accelerators and high-field magnetic resonance imaging (MRI). There are increasing attempts to apply NI winding technology to achieve both high current density and high thermal stabilization of REBCO coils. However, REBCO coated conductor has a tape shape, and when a magnetic field is applied vertically to the tape surface, a shielding current is induced, and an irregular magnetic field (shielding current induced magnetic field: SCIF) is generated. In addition, when NI winding technology is applied, an excitation delay occurs because current flows not only in the circumferential direction but also in the radial direction. In our previous study, we have investigated the influence of the SCIF on magnetic field accuracy when the excitation delay occurs in NI-REBCO coil system by newly developed computer program, and confirmed that a current control by overshoot with plateau improves the temporal stability of the magnetic field. The current control adopting plateau is a method of maintaining the demagnetization effect by waiting for a certain period for the "delay of the circumferential current due to the excitation delay" generated in NI coil winding. However, there is a demerit that the excitation time becomes long. In this study, to improve the temporal stability of the generated magnetic field, we attempted to optimize the energizing current waveform to suppress the effect of SCIF and excitation delay in NI-REBCO coil by considering the ratio of overshoot and the temporal length of plateau as parameters.
This work was supported by JSPS Grant-in-Aid for Scientific Research (S) from the Ministry of Education, Science, Sports, and Culture (No. 18H05244).
The U.S. High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) is developing MQXFA magnets, a series of 4.5 m long 150 mm aperture high-field Nb$_3$Sn quadrupole magnet for the Hi-Luminosity LHC upgrade at CERN. Five Pre-Series magnets, MQXFA03 through MQXFA07, have been developed. During the magnet assembly stage, we perform magnetic measurements of the coil packs and magnets to track the field quality for two purposes. First, it serves as a quality assurance tool to check if the magnet field quality meets the acceptance criteria. Magnetic measurements are used to understand if/how magnetic shims are needed to compensate low-order field errors and to meet the field quality targets. Second, the measurements during the assembly stage can also help understand the field quality, in particular the geometric field errors for Nb$_3$Sn accelerator magnets. Here we summarize the measurement results of the pre-series MQXFA magnets, including the magnetic axis and twist angle. We also report the correlation between the coil geometry and the observed field errors. The results will provide useful feedback for the series magnet production and on the optimization of field quality of accelerator magnets based on wind-and-react Nb$_3$Sn technology.
This work was supported in part by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US HL-LHC Accelerator Upgrade Project, and in part by the High Luminosity LHC project at CERN.
Bi:2212 superconducting cables are being considered for use in high field magnets such as those in the next generation of particle accelerators. However, a comprehensive understanding of their behavior is necessary before full-scale magnets can be constructed. The magnetization and flux creep in the superconductor can lead to significant field errors which need to be compensated. To study this, a 28-mm long segment containing two 17-strand cables was extracted from the RC5 racetrack coil made at LBNL. The cable was made from Bruker OST PMM170123 non-twisted Bi:2212 wire. Using a Hall probe calibrated by (a) flux exclusion and (b) Ni replacement, we report on the cable’s temporal decay characteristics. In addition, the effect on magnetization and decay of adjusting the cycling of the magnetic field was studied to simulate the preinjection cycles of an accelerator magnet.
LQXFA/B production series cryogenic assemblies are being built for the LHC upgrade by the HL-LHC Accelerator Upgrade Project (AUP). These contain a pair of MQXFA quadrupole magnets combined as a cold mass installed within a vacuum vessel, and are to be installed in the IR regions of the LHC. The LQXFA/B are being tested at 1.9 K to assess alignment and magnetic performance at Fermilab’s horizontal test facility. The ~10 m - long assembly must meet stringent specifications for quadrupole strength and harmonic field integrals determination, magnetic axis location, and for variations in axis position and local field profile. A multi-probe, PCB-based rotating coil and Single Stretched Wire system are employed for these measurements. Magnetic measurements are confined to be within the 100 mm diameter of the anti-cryostat used for cold testing, but the aperture is reduced to 46 mm at the cryogenic feed box of the test stand – further complicating both the alignment and rotating coil measurements. To accurately determine rotating coil location and angles within the cold mass, a laser tracker is employed to record multiple targets at one end of the probe, deep within the anti-cryostat.
This paper describes the measurements, probes/equipment, and techniques used to perform the necessary characterization of the cold mass.
Targeted alpha-particle therapy is a cancer treatment method using alpha-emitting radioisotope (RI), and is expected as a treatment method for progressive cancer. We are conducting research toward the development of a High-temperature-superconducting Skeleton Cyclotron (HTS-SC), which is an ultra-compact and high-intensity accelerator capable of stably producing the alpha-emitting radioisotope, 211At used in targeted alpha-particle therapy. In the HTS-SC, the high magnetic field and high precision magnetic field required for particle acceleration is generated only by air-core REBCO coil system without the use of iron cores. For cyclotron, high-precision magnetic field distribution and temporal stability of the magnetic field are required on the particle acceleration surface, but the magnetic field caused by the screening current induced in the REBCO coated conductor deteriorates the quality of the generated magnetic field spatially and temporally. Therefore, we plan to conduct experiments scheduled for 2022 to investigate the electromagnetic, thermal, and mechanical behavior of the Ultra-Baby-Skeleton-Cyclotron (UBSC), which is a small demonstration model of REBCO coil system for HTS-SC. So far, we have numerically analyzed and evaluated the effect of the screening current induced magnetic field (SCIF) on the generated magnetic field for UBSC. It has been confirmed that the influence of the SCIF can be suppressed by controlling the energization pattern. We are aiming to realize a multifunctional accelerator that can produce 211At for targeted alpha-particle therapy as well as RI for positron emission tomography (PET) and neutron irradiation for boron neutron capture therapy (BNCT). In this study, we evaluated the effect of SCIF when changing the output energy for multi-functionality and investigated the reduction method of the effect of SCIF by optimizing the excitation pattern for a full-scale HTS-SC for these actual applications.
It has been fifty years since the first papers on the effects of magnetization in the superconductor in an accelerator magnet field quality were measured. The effects of conductor magnetization are most pronounced at low fields. By late 1971, a reliable method for estimating the effects of superconductor magnetization on the field quality in accelerator magnets was developed. A review of this method is presented in this paper. The model included unsaturated iron. The effect of filament proximity was modeled in the late 1980's. A simple in-magnet correction system was demonstrated in the early 1990's. The problem that remained was the effect of strand-to strand circulating currents in magnet cables. These currents decay with time for magnets made with cables made with almost any conductor. Accelerator magnets made with wide ReBCO tapes in place of cables are not expected to exhibit any magnetization current decay. Calculation methods developed before 1990 can lead to solutions for reducing the effects of conductor magnetization in HTS magnets as well as LTS magnets. This will be discussed in this paper.
The magnetic center alignment is extraordinarily important before put a new ion-source into operation. Misalignment of ion-source may cause arc chamber destroyed. We take two methods to measure and align the ion-source superconducting magnet based on the cryostat bore in IMP. The required offset between ion-source magnetic center and mechanical center of warm bore is less than 0.5mm.
The FECR superconducting magnet consists of a sextupole magnet and four solenoid magnets. All of these component magnets are required to installed and aligned precisely based on the same mechanical axis. We set an adjustment unit to correct the position of ion-source magnet constitution in the cryostat after integral installation.
Two different measurement methods are adopted for the alignment of two kinds of coils. The harmonic coil is taken to measure the offset in the X and Y direction of sextupole. And the Hall sensor is used to measure the offset of four solenoids. Both the harmonic coil and Hall probe are mechanically related to the warm bore of cryostat. Compared result of these offset measurements, we choose a best correction scheme to adjust the magnet constitution to fit the mechanical axis of cryostat bore.
In recent year, there has been remarkable progress in the use of high-field rare-earth barium copper oxide (REBCO) coils in NMR, MRI, and accelerator applications. No-insulation (NI) winding techniques are adopted to achieve high thermal stability and high current density. Thus, each winding in a non-impregnated NI REBCO coil can deform separately and move freely because of the thermal strain and electromagnetic force. The additional force and stress due to a screening current has also become an issue in REBCO coils. The screening current leads to a non-uniform force distribution in REBCO tapes and forces exceeding an acceptable value. It has been reported that REBCO coils have experienced mechanical deterioration or damage when operating under high magnetic fields. However, the detailed mechanism for this damage or deterioration has not been clarified. In order to clarify the detailed mechanism of this damage to a REBCO coil, the stress and strain during the winding, cooling down, charging, and discharging processes need to be evaluated. Furthermore, in NI REBCO coils, the turn-to-turn contact configurations are very important for the current bypassing, the thermal and mechanical stability. In previous studies, we have developed the numerical simulation code on the electromagnetic behavior of screening current and mechanical behavior of the turn-to-turn contact state. This study evaluated the deformation and stress in REBCO tape and the turn-to-turn contact in NI REBCO coils.
The high-field magnets experience the large amount of mechanical stress as a result of Lorentz forces. During the magnetization of the coil, strong Lorentz forces give rise to hoop stress, which can cause mechanical failure, resulting in the degradation of the coil performance. A recent study led to the discovery that scratching the GdBCO-coated conductor (CC) tapes ameliorated the degradation of the superconducting properties of the coil caused by Lorentz forces as a result of the friction between successive turns. Therefore, it is necessary to consider the frictional force between the superconducting tapes when calculating the hoop stress. In this study, the effect of the variation in the frictional force between successive turns of the coil on the stress-strain was investigated using intentionally scratched stainless-steel tape co-wound with GdBCO CC tape. The changes in the strain resulting from the Lorentz force were examined on the basis of the applied external force. Moreover, sudden-discharge, overcurrent, and charging-discharging tests were conducted and the charge/discharge characteristics during quenching were examined to evaluate the thermal and electrical stability of the coil.
< Acknowledgment>
This work was supported by the Korea Basic Science Institute under Grant D110200
REBCO wires have high thermal stability and high current density, therefore, it is expected to be applied to high magnetic field magnet for NMR, MRI, and accelerators. On the other hand, there is the problem such as mechanically deteriorations and damages of REBCO coils. Because REBCO wires are tape shape, when charging and discharging, screening currents are induced to circulate in the windings. Screening currents lead to not only the irregular magnetic field but also the additional force and stress. It has been reported that REBCO coils have experienced mechanical deteriorations or damages when operating under high magnetic fields. In previous study, we showed that the mechanical deformations of REBCO coils due to screening-current-induced force are remarkably different from those of conventional coils.
In this study, reinforcement effects against electromagnetic and thermal stresses in insert REBCO coils of high field magnet are numerically evaluated. In this simulation, we evaluate stress and deformation of REBCO coils taking mechanical stress during winding process, thermal stress during cooling down and electromagnetic stress including the screening-current-induced stress during charging and discharging processes by using the our developed 3D electromagnetic numerical simulation code. And we investigate the reinforcement effect of over-banding, frame-reinforced structure such as YOROI structure, and hybrid structure combining these., and discuss the relationship between the stresses in REBCO coil and the limitation of the tensile stress in the longitudinal and width direction, the compressive stress in transverse direction of REBCO tape.
In recent years, the no-insulation REBCO (NI-REBCO) coils show remarkable attraction and potential in high field areas. For a REBCO coil, the stress generated by screening current under high magnetic field is a crucial concern for the magnet operating performance. Therefore, how to effectively reduce strain created by screening current is a key challenge in the NI-REBCO coil magnet’s mechanical design. In this study, we developed a numerical model to analyze the mechanical behavior including screening current influence of NI-REBCO coil, and its validation was realized by comparing numerical results with corresponding experimental data. In order to evaluate effective methods of reducing the impact of screening current induced stress, we design a NI-REBCO coil magnet as a benchmark model. Then, we mainly focus on three potential methods to reduce screening current induced stress: winding tension and over-band in the fabrication process, monofilament and multifilament REBCO tape, co-winding metal tape. By comparing the mechanical response during charging of benchmark REBCO coil and coils with the three aforementioned methods, we quantitatively analyze the effects of these potential methods separately. Based on the numerical results, we present a series of NI-REBCO coil magnet design suggestions to reduce screening current induced stress.
High-temperature superconducting (HTS) magnets have been widely used in the fields of electricity, transportation, medicine, and scientific experiment. However, HTS magnets generally suffer from the thermal stress and electromagnetic stress during manufacture and operation, deteriorating its mechanical properties as well as restricting its further development. This study is aimed at improving the mechanical properties of HTS magnets by applied multi-thickness armored REBCO tapes. The electrical and mechanical properties of short REBCO samples with multi-thickness armor were measured firstly. Then, we have built a finite element model to calculate the stress of the HTS magnet from various sources, in which the properties of the superconducting material are described by the measured data with an interpolation approach. Based on this model, the highest stress position of the HTS magnet has been revealed, and we have optimized the magnet by utilizing multi-thickness armored REBCO tapes to prevent the possible mechanical failure. The result shows that the design of utilizing multi-thickness armored tapes can improve the mechanical properties of superconducting magnets, and provide a reference for the design of HTS magnets in the future.
Stress managed magnet designs are being developed to limit the strain and stresses applied to the conductor during powering. The canted cos $\theta$ (CCT) design is one of the proposed solutions. In this design, the conductor is wound around a mandrel: the impregnation process creates a bonding between the two, that can fail when the magnet is powered. The energy releases consequent to the debonding are a potential cause of training quenches. In this study, we model the mandrel-conductor interfaces using cohesive zone material models. The material properties were calibrated by means of measurements, performed on representative interfaces. The models were used to investigate the interfacial failure during the magnet life of CCT magnets built for the Magnet Development Program. The model results were then used to predict potential quenches and investigate the effect of structural modifications on magnet performances.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program.
A combined superconducting magnet on six sextupole coils and four solenoids are currently developed by the Institute of modern physics of Chinese Academy of Sciences (IMPCAS). As a prototype for the fourth-generation ECR ion source operating at frequency of 45 GHz, each coil is made of a single and brittle Nb3Sn wire. To effectively prevent the wires motion from performance degradations and a quench, a pre-stress is essential for the combined superconducting magnet during its assembly using bladder-key technology. Thus, their strains behaviors were also focused during its assembly and excitation, indicating that operation of the combined superconducting magnet. In this paper, the mechanical behaviors of the combined superconducting magnet during assembly and operation were evaluated by detecting its external support structure. Several low-temperature resistance strain gauges and their compensations were affixed directly on its external support structure. Many groups of wireless strain acquisition system were used for the strain measurements of the combined superconducting magnet. It is shown that the strains measured in the superconducting magnet give much valuable information characterizing the deformation and the stress state during the assembly, cooling down and excitation. Finally, the combined superconducting magnet with the combined support structure were tested successfully for excitation. The strain measurements of external support structure were almost unchanged. It was proved that the support structure with the aluminum shell can hold well the combined coil.
Abstract: The YBCO superconducting coils will cause complex deformation, and even moving between layers under the large Lorentz forces during energization. These will further disturb the magnetic field quality and the operating safety and stability. A more accurate estimation of the magneto-mechanical behaviors of YBCO coil during excitation is a crucial one. However, the conventional finite element modeling (FEM) no considering friction effects between the layers of coils based on the isotropic homogenized approach, which is difficult to predict accurately the magneto-mechanical behaviors of YBCO superconducting magnet, due to the heterogeneous and multilayer structure characteristics of YBCO superconducting coil. In this paper, the magneto-mechanical behaviors of YBCO superconducting magnet was numerically analyzed by using FEM with friction effect between the layers of coils. To give a more accurate prediction on the composite structure of coil, the FEM utilized an orthotropic homogenized approach to connect the micro-scale of YBCO superconducting composite tapes to the macro-scale of YBCO superconducting coil based on RVE method. The simulations show that the FEM with friction effect between the layers of coils predictions on magneto-mechanical behaviors of the YBCO superconducting coils are in better agreement with the experimental data compared to the model without friction effect.
As a preparation towards the final fabrication of China Fusion Engineering Test Reactor (CFETR) central solenoid coil, the Central Solenoid Model Coil (CSMC) is designed in advance. In order to save the manufacturing cost, the hybrid superconducting magnet is adopted. The coil is comprised of five magnet modules, namely the inner and outer Nb3Sn coils, the top, medium and bottom NbTi coils. Once CSMC is energized, huge electromagnetic force is generated, which will result in the misalignment of the coil modules. To maintain the integrity of CSMC, the pre-compression load should be applied. While the pre-compression load is affected by the thermal contraction load and electromagnetic force. Different preload application schemes are compared and the variation of preload under different load cases are analyzed in the paper, which are helpful to obtain the optimized pre-compression method.
The INFN-LASA laboratory (Milano, Italy) is involved in the High-Luminosity LHC program for the design, construction, and test of 54 superconducting high-order corrector magnets. One of the challenging project stages was the transition from the construction of prototype magnets to the series production, awarded to industries with the demanding requirement of maintaining high-quality production standards during the production of a relatively high number of components, e.g. almost 500 superconducting coils.
This paper reports on the advanced quality assurance methods implemented at the manufacturer premises for the test of the coils electrical characteristics: the electrical insulation towards ground (measured through standards methods), the number of turns, and the internal turn-to-turn insulation.
The consistency of the number of turns during production is verified by a dedicated electromagnetic setup designed and built at LASA. It consists of a ferromagnetic yoke coupling two superconducting coils fed by alternating currents with opposite signs. A pickup coil is mounted on the yoke to measure the magnetic flux that for a perfectly balanced system is equal to zero. The design of the setup is optimized through finite element models to improve the signal-to-noise ratio, i.e. the measurement of the flux due to an unbalanced number of turns with respect to the flux due to geometrical imperfections, and make it high enough for its application in an industrial environment.
The quality of the coils internal insulation is assessed through a surge test with a capacitor bank generating an AC voltage. The data shows that the conventional numerical method used for the analysis leads to several false positives and, therefore, a dedicated numerical method with higher specificity is implemented.
The data collected on about 80% of the total coil production shows the effectiveness of the adopted methods, which in some cases allowed for early defect detection.
A combined method was used for mapping the fields in the pulsed bending magnets of the Booster-Nuclotron transfer line of the NICA complex. In the measurements, an array of “point” search coils was used together with Hall sensors. Signals from coils were processed by digital integrators, and a specially designed fast precision ADC was used in Hall measurements. The paper presents the results obtained and compares the capabilities of both measurement methods.
Accelerator magnet test facilities frequently need to measure different magnets on differently equipped test stands and with different instrumentation. Designing a modular and highly reusable system that combines flexibility built-in at the architectural level as well as on the component level addresses this need. Specification of the backbone of the system- the interfaces and dataflow for software components and core hardware modules - serves as a basis for building such a system. The design process and implementation of an extensible magnetic measurement data acquisition and control system are described, including techniques for maximizing the reuse of software. The discussion is supported by showing the application of this methodology to constructing two dissimilar systems for rotating coil measurements, based on the same architecture and sharing core hardware modules and many software components. The first system is for production testing 10 m long cryo-assemblies containing two MQXFA quadrupole magnets for the High Luminosity LHC (HL-LHC) upgrade and the second for testing one-of-a-kind conventional chicane magnets built for the ORNL Proton Power Upgrade project.
Two types of nested orbit combined correctors are necessary for LHC upgrade, so called MCBXFA and MCBXFB. They shared the same cross section, but feature different lengths, 2.5 and 1.5 m, respectively. The power tests performed on two prototypes showed an excellent performance when individually powered, but the training to reach nominal torque in combined operation was very long. Moreover, memory was lost after torque direction reversal.
A detailed analysis of the power test results concluded that the origin of the problem was an insufficient support for the torque at the inner dipole coil ends. A fine tuning of the inner dipole design is proposed to improve the performance of both types of magnets. This paper describes the analytical and numerical models developed to analyse the problem and their results.
Abstract — This work investigates the effect of rotor eccentricity and current harmonics on the performance of high-speed permanent magnet (PM) generators (HSPMG) with multi-physical analysis. First, the effect of rotor eccentricity in the no-load and load conditions on the distributions of magnetic flux density and electromagnetic force in the generator is studied and the allowed tolerance of rotor eccentricity is determined. Then, the current harmonics generated by the rectifier are injected into the generator armature to study the distribution of core loss, eddy current loss, and temperature rise (particularly on the rotor). Moreover, the resonance impact of rotor eccentricity and current harmonics on the electromagnetic force distribution is also evaluated. The results show that the increase of losses, temperature, vibration, and mechanical strength in HSPMG depends on the amplitude and percentage of total current harmonic distortion injected into the HSPMG under an allowable rotor eccentricity. Finally, the performance of the generator in multi-physical fields is validated through experimental studies.
Model and Analysis Method — A 200kW high-speed generator is studied here and the current harmonics (with 16.8% THD) generated due to the rectifier that is connected to a load of 375A output current is injected when the generator reached the peak power at the 45000 rpm speed. FEA is utilized to comprehensively evaluate the impact of rotor eccentricity and current harmonics on the electromagnetic field, loss distribution, temperature field, vibration, and mechanical strength of the high-speed generator.
Conclusion — This effect of rotor eccentricity and current harmonics on the performance of a high-speed generator has been analyzed, and the results show that the iron loss and temperature of the generator are worsened with the effect of current harmonics. The detail analysis and experimental results will be reported in the full paper.
Abstract: The segmented core reactor is small in size and low in cost. It not only has good electromagnetic compatibility, but also has a larger inductance value due to the multi-section air gap structure. However, under the interaction of electromagnetic force and magnetostriction at the air gap, the reactor core is deformed, causing vibration and generating louder noise than other ordinary reactors. An optimization method based on topology optimization and genetic algorithm is proposed in this paper to reduce the segmented core reactor's vibration during operation. In this method, a novel reactor design is obtained using topology optimization, besides the inductance value is ensured. Firstly, the electromagnetic-mechanical coupling model of the reactor is established to analyze the vibration and deformation of the reactor. Secondly, topology optimization is performed to make strain energy reach the minimum, now the deformation of the reactor core is minimized to realize the optimal design of noise reduction and vibration reduction of the reactor. Thirdly, since the change of the air gap structure will affect the inductance value, the genetic algorithm is combined to keep the inductance value of the reactor. Finally, the finite element numerical method is used to calculate the optimized parameter values before and after the optimization. The results show that the deformation of the air gap and the vibration acceleration of the reactor has been significantly reduced, which provide theoretical support for the design of lower noise reactor.
Acknowledgments
This work was supported by the National Natural Science Foundation of China under Grant Nos. 51777054 and 52007102, Natural Science Foundation of Hubei Province (2020CFB212).
Keywords: reactor; electromagnetic-mechanical coupled model; electromagnetic vibration; topology optimization
In the framework of the 40 T all superconducting SuperEMFL magnet, we investigated the metal-as-insulation (MI) winding technique for use in the insert part. This winding technique enhances the thermal stability of High Temperature Superconductor (HTS) coils without the drawback of long charging times, providing a self-protecting behavior.
We have then developed a unique numerical model to study the behavior of MI coils made of HTS tapes. The multi-physics model comprises an electric network model, taking into account the contact resistance between turns, coupled to a two-dimensional thermal coil model and a three-dimensional magnetic field coil model. The novelty is the integration of the non-uniform distribution of the current density within each conductor (i.e screening currents) assuming the well-known power law for the E(J) relation.
We present the behavior of a small MI solenoid made of several pancakes in two situations, the discharge of an external outsert and the case of a quench occurring in one of its pancakes. Finally, we compare the results against our PEEC model assuming a uniform current distribution.
In this contribution the magnetic modelling and experimental validation of a superconducting degaussing system for maritime vessels is discussed. Degaussing coils compensate for the distortion in the earths’ magnetic field by the magnetized steel hull of a ship, thus rendering it ‘invisible’ for magnetic field sensors. Whereas typical power requirements with copper coils are of the order of 100 kW, an HTS degaussing system in principle allows to reduce this by an order of magnitude. In order to validate such efficiency estimates and to demonstrate the required hardware, a table-top test set-up was realized with magnetic ship steel. The vessel imitating cylindrical demonstrator is equipped with six degaussing coils, grouped in three sets that act in two different directions, with each set consisting of one copper and one ReBCO coil, the latter one equipped with a sub-cooled liquid nitrogen system. Static and dynamic magnetic field measurements are reported and compared to both analytical and numeric finite element models. The results illustrate how even relatively simple analytical models can be used as a powerful tool to extrapolate design parameters and thus to predict the power requirements of large-scale degaussing systems.
No-insulation (NI) winding method has been widely used in the fabrication of superconducting coils due to its excellent thermal stability and mechanical stiffness. In the NI coil, there is a charging delay and heat loss due to leakage current and metal insulated (MI) winding method has been proposed to reduce the charging delay and the heat loss by the leakage current due to the increased contact resistance by the metal tape. However, it is difficult to quantify the contact resistance between turns of the coil at the design stage. To resolve this problem, a new winding method named as SMI (Soldered Metal Insulation) was proposed by the authors, the electrical properties were evaluated in the bath of liquid nitrogen.
As a follow-up to the previous research, experimental investigations are conducted in a conduction cooling test apparatus to investigate electrical and thermal characteristics of the SMI coil below 77 K. The electric contact resistances are evaluated through sudden discharging experiments. Then, the thermal contact resistances are also measured using a heater installed on the outer turn of the coil. The experimental results are compared with that of the expected values and the discrepancy is investigated through a precise inspection of the cutting cross section of the SMI coil. It is believed that the SMI winding technique can be applied to fabricate REBCO coils with the predictable contact resistance.
*Acknowledgement
This work was supported by the Korea Institute of National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019R1A5A8083201) and the Korea Medical Device Development Fund grant funded by the Korea government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety) (Project Number: 202011C21)
This paper presents the results about analysis and experiment on the electrical and thermal characteristics of metal insulation (MI) REBCO racetrack coil wound with stainless steel (SS) tape under rotating magnetic field. The field windings of synchronous rotating machine can be occasionally operated under time-varying magnetic field due to the unsynchronized armature windings during electrical or mechanical load fluctuations. Therefore, the transient operation reliability of SS MI coil should be examined and investigated under unsynchronized operation environment to confirm the applicability of SS tape on the turn-to-turn insulator of REBCO field winding. In this study a characteristic evaluation device to apply asynchronous rotating magnetic field was firstly designed and developed. The system is divided into two parts. One is cryostat part to test the REBCO racetrack coil, the other is three phase armature winding part to generate the rotating magnetic field. Then, the electrical and thermal characteristics of SS-MI REBCO racetrack coil installed on salient pole are experimentally investigated according to changes in the operation temperatures at the test coil and strengths and frequencies of the injected rotating magnetic field from the armature winding at the most outer part of the characteristic evaluation system.
Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT). (Nos. 2021R1C1C2003235 and 2019R1A2C1004715)
Abstract:
High-temperature superconducting (HTS) magnet is a promising candidate for transportation systems and power systems, such as ultra-high field magnet, electrodynamic suspension (EDS) train, magnetic resonance imaging (MRI), due to its large current-carrying capacity and low power loss. The critical current of the HTS magnet depending on magnetic flux density is an essential factor assessing its application performance. Normally, the HTS magnet is wound into rectangular cross-section, which results in magnetic field concentration. By contrast, the HTS magnet with stepped cross-section can alleviate the magnetic field concentration, and improve the critical current accordingly. From this point, this paper will design an HTS magnet with stepped cross-section to maximum the critical current. Firstly, a homogenized self-consistent model is established for assessing the critical current of HTS magnet. Then the geometry parameters of the HTS magnet are designed and optimized with the self-consistent model. Eventually, based on the design results, an HTS magnet with stepped cross-section is wound. The magnetic field distribution and critical current were experimentally measured to verify the calculated results.
Keywords: HTS magnet, stepped cross-section shape, optimization, critical current
We aim to develop a persistent-mode 1.3 GHz (30.5 T) LTS/HTS NMR magnet. For protecting the layer-wound REBCO innermost coil from quench, we have proposed the intra-Layer No-Insulation (LNI) method. This winding technique employs single-sided insulated copper sheets as inter-layer materials to provide the no-insulation state within each layer. For quench protection, the most influential parameter is the contact resistivity (ρct) between the conductors and the copper sheets. In previous work, an LNI-REBCO coil was protected from a 31.4 T quench, owing to a high ρct value of 10,000 µΩcm2. Thus, achieving the desired ρct of a coil is of great importance for designing and fabricating a magnet. In this light, we investigated the effects of winding tension and thermal cycles on the ρct value of LNI-REBCO coils.
We fabricated 8-layer LNI-REBCO coils (Coils A, B, and C) wound under winding tensions of 49 MPa, 98 MPa, and 147 MPa, respectively. Each coil was 50 mm in inner diameter and 41 mm in height. For these coils, we repeated the sequence of cooling to 77 K, charging, power supply shutdown, and warm-up. In each thermal cycle, the values of ρct were obtained from field decay curves after power supply shutdown.
In the first cooling tests, ρct of Coils A, B, and C were 1,750 µΩcm², 600 µΩcm², and 180 µΩcm², respectively; a lower winding tension gave a higher ρct. Along with the thermal cycles, ρct increased and saturated at high values of 16,000µΩcm², 6,500µΩcm², and 2,500µΩcm², respectively. We believe that this unique behavior is produced through stabilizing the winding contact condition by thermal cycling. For establishing a method to implement a desired ρct value, we will make a contact model experiment and structural analysis to better understand the phenomenon.
This work was supported by the JST Mirai-Program Grant Number JPMJMI17A2.
REBCO tapes have good critical current characteristics under high magnetic fields. Their application to superconducting magnets generating above 25 T is under active study. However, performance inhomogeneity along their length can cause damaging hotspots. Adapted winding technologies are needed to mitigate this phenomenon. One of such winding techniques is the two-tape bundle co-winding method, where two REBCO tapes are co-wound along with an isolating tape to form the conductor. To test this solution, a double pancake coil was wound with an artificially degraded short section on one of the tapes. We previously reported its current-carrying capability, showing the gain in reliability. We now study its behavior in terms of field hysteresis and dynamic, at various temperatures (20-65Ｋ).
In two-tape co-winding HTS coil, in addition to the shielding current flowing in the width of the tape, there are coupling current flowing between the two tapes. The axial field contribution of screening currents is in opposition to the field generated by the coil driving current, while the coupling current contribution is in the same direction. These two phenomena are thus in competition, the resulting overall field hysteresis depending on their relative amplitude and their decay dynamics.
For our test coil, the hysteresis behavior is strongly dominated by coupling effect during continuous ramping at all temperatures, contrary to other similar experiments conducted previously. This is due to the face-to-back configuration used for this co-wound conductor, which increase the distance between the REBCO layers and thus the coupling current flow path. The field transient at plateau show the decay of coupling currents, the field hysteresis being then dominated by screening current effect. The electromagnetic dynamic properties of this coil are presented with the temperature influence and compared with 2D axisymmetric modelling.
The no-insulation (NI) winding technique provides high stability of HTS pancake coils and a high magnetic field NI HTS magnet was developed. On the other hand, the balance between the turn-to-turn contact resistance and the coil inductance is an important factor to characterize the thermal stability and charging delay of NI HTS coils. So, it is very important to accurately measure and evaluate the contact resistance of NI HTS coils. Although the conventional sudden-discharging method is widely used to measure the turn-to-turn contact resistance, it is not applicable to various conditions and its use is limited. Therefore, we have previously proposed a low-frequency-AC-current (LFAC) method to measure the turn-to-turn contact resistance of the NI HTS coils. In the LFCA method, the contact resistance and inductance of the HTS coil were measured at the total voltage of the NI HTS coil using a lock-in amplifier, and the phase of the AC current was detected by the Rogowski coil. In the proposed LFCA method, the contact resistance between windings is accurately evaluated when all AC currents flow in the radial direction in the NI HTS coil. However, the distribution ratio of the AC current between the radial direction and the circumferential direction in the NI HTS coil is expected to depend on the contact conditions between the windings and the frequency and magnitude of the transported AC current. In this study, in order to demonstrate the measurement accuracy of the proposed LFCA method, we prepared several test coils with slightly different contact resistance between windings. Specifically, several test coils wound with REBCO wire with different surface roughness and different winding tensions were prepared, and the accuracy of the proposed LFCA method will be reported.
Three racetrack type double-pancake coils were wound and assembled in a certain sequence to form a module. To improve the anisotropism between the straight sections and circular sections, the bobbin was designed and some clamping fixtures were added on both sides and on the straight sections. By investigating the viscosity and torque of rotor, the optimum range of temperature for impregnating the coils was confirmed. After the assembly of the coils, the module of coils was whole sucked in liquid paraffin. Then the whole module was fixed in a dewar which filled with liquid nitrogen to cool the coils. The coils with dewar were tested the mechanical shock resistance dynamically. From the results, after paraffin impregnation, the characteristics of the coils did not change. With increasing value of acceleration up to 30g every 5g interval in X direction dynamically, the voltage and magnetic field were almost unaffected. Thus this method of construction and paraffin impregnation and fixtures can be used in this racetrack type double-pancakes coils.
Keywords YBCO ·Racetrack Type·Vacuum Impregnation·Mechanical Shock Test
In this study, the quench initiation and propagation characteristics of REBCO coil, which was electrically and thermally insulated by a vanadium III oxide (V2O3), were investigated under internal heater activation. When the quench occurs in REBCO coil, V2O3 insulator can enhance the thermal stability of REBCO coil due to its automatically and remarkably switched from high to low turn-to-turn contact resistances depending on its temperature rising. This special ability allowing the REBCO coil operates as an insulated and non-insulated coil under the steady and transient states, respectively. First, thermal quench tests were performed on a single pancake REBCO coil heated by heater activation to investigate the current bypass behavior based on the resistance switching feature of V2O3 insulator as well as the heat transfer behavior in terms of the minimum quench energy and normal zone propagation velocity. Then, the thermal transient characteristics were analyzed and compared with that of conventional counterpart insulated by Kapton polyimide film.
Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT). (Nos. 2021R1C1C2003235 and 2019R1A2C1004715)
The REBCO coil, which was electrically insulated using a metal-insulator transition (MIT) material between turn-to-turn contact layers, can achieve high stability in the transient operation as well as fast response of magnetic field in the normal operation due to its automatically switched electrical resistivity of MIT material according to the temperature changes. Among of MIT materials, A vanadium III oxide (V2O3) has the transition temperature of approximately 150 K to switch from high to low levels in turn-to-turn contact resistance. Thus, the V2O3 REBCO coils can be operated as an insulated coil without charge-discharge delay at normal operation below 150 K and as a non-insulated coil with the high stability above 150 K depending on the absence or presence of current bypass phenomenon, respectively. In this paper, a small pancake REBCO coil was co-wound with a V2O3 paste between turn-to-turn layers. Then, the normal and transient characteristic tests were performed in a 77 K liquid nitrogen bath to investigate the feasibility and the repeatability of resistivity switching feature of V2O3 insulator under the various extreme operational environments, such as internal heat generation, continuous overcurrent and pulse overcurrent, and mechanical vibration.
Acknowledgment: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT). (Nos. 2021R1C1C2003235 and 2019R1A2C1004715)
We propose a new active feedback control method to quickly charge no-insulation(NI) magnets, as well as sustaining thermal stability. The main feature of our suggested method is controlling ramping rate of the magnet to minimize consecutive Joule heating induced by the radial leakage current and resistive joint. The suggested method to be applicable for the iron core NI coils, dynamic inductance variation due to iron saturation is taken into account in the feedback diagram. With a constraint of maximum allowable Joule heating and power supply current, charging protocol is automatically decided by the designed feedback loop. To validate our suggested method, we fabricated an NI coil wound on the iron bobbin, and tested the coil in a conduction cooler. Measured temperature and magnetic field data are compared between two different ramping scenarios: (1) a linear ramping; and (2) a ramping with our suggested method. Finally, we demonstrate the effectiveness of our suggested method on reducing total charging time of both air and iron core NI coils.
Acknowledgement
This work was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-09" to "This work was supported by the Korea Medical Device Development Fund grant funded by the Korea government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety) (Project Number: 1711138068, KMDF_PR_20200901_0063)".
No-insulation (NI) winding technique shows superior electrical and thermal performance for high temperature superconducting (HTS) coils compared with the insulation winding technique. However, the NI HTS winding technique is uncertain about the thermal contact resistance between winding turns because the HTS wire has various surface conditions such as roughness and oxidation. In this paper, the diffusion bonding technique is applied to make expectable contact resistance between turns of the NI HTS coil. In order to examine the electrical and thermal characteristics of NI HTS coils, two kinds of NI coils are fabricated by using conventional NI HTS winding and diffusion bonding techniques. The thermal contact resistances of the NI coils are measured in a conduction cooling experimental apparatus applying a heat load to the outside the coil. Then, the electrical contact resistances of the NI coils are evaluated by sudden discharge experiments compared to the expected values at the various temperature from 20 K to 77 K.
[Acknowledgement] This research was supported by Korea Electrotechnology Research Institute(KERI) Primary research program through the National Research Council of Science & Technology(NST) funded by the Ministry of Science and ICT (MSIT) (No. 21A01019) and This work was supported by the Korea Institute of National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2019R1A5A8083201)
The linear-motor type high temperature superconducting (HTS) flux pump is a wireless charger which can pump DC current into the second-generation (2G) HTS tapes without the physical contact. In addition ,the flux pump has the smaller volume than the traditional power supply for the same output current. So it is very convenient to charge HTS tapes by utilizing the flux pump which has a compact structure. More importantly, it avoids the serious disadvantage of heating leakage by current leads. In order to make the HTS flux pump better be used in nuclear magnetic resonance(NMR), magnetic resonance imaging(MRI), motors and other equipment that requires a strong magnetic field, we have further improved its structure so that the superconducting coil can be pumped into a larger current to generate a stronger magnetic field. In this paper, we optimized the design of the linear-motor type flux pump by reducing its AC traveling wave length and tested it. The test result shows that the total output current of the flux pump can exceed 1000A in the cryogenic environment of 77K.
The flux pumping devices attract a lot of attention for the excitation of superconducting magnets or the compensation of the field decay. A carefully designed linear flux pump is presented in this work, the dimension of which is smaller than a 5 cm cube. The key part of the device is the magnetic circuit which guarantees the optimized flux pumping performance in terms of operation current, output voltage and the power efficiency. The performance of the device is tested at different driving current waveform and operation conditions of the external circuit (the superconducting magnet).
The presented flux pump is especially promising for sustaining the magnetic field of portable superconducting magnets where not only the size and weight of the power supply but also the conduction heating through the current lead is concerned.
High temperature superconducting (HTS) magnets have many potential applications, for instance, NMR/MRI, levitation systems, and high field applications. HTS magnets require a constant external current source to operate in CC mode. Flux pumps provide an alternative contact-less charging source that can inject flux into a closed-loop superconducting circuit. The simplicity of the rotating type flux pump makes it a popular choice. The rotating type flux pump operates as a DC voltage source with inherent resistance, Rd. From the literature review, it is evident that a lot of aspects of the HTS rotating type permanent magnet-based flux pump have been studied and certain aspects require further research.
The literature review shows that the design of the stator has major implications on the output capability of the flux pump. In this study, we have carried out the optimization of the rotating type flux pump by focusing on the stator design. Different stator designs have been studied. Factors, such as the number of stator tapes and the gap between the stator tapes, and their impact on the output capability of the rotating type flux pump have been analysed. Moreover, the open-circuit output voltage (Vdc), inherent resistance (Rd), and short circuit output current (Isc) have been analysed and compared for each design of the stator. We found that paralleling more stator tapes with appropriate gaps can be a promising design strategy to maximize the output capability for HTS rotating permanent magnets-based flux pump.
Superconducting materials have a high current-carrying capacity and direct current(DC) lossless characteristics. The linear-motor type flux pump is a wireless DC power source for high-temperature superconducting coils.In the control process of outputting DC current to the superconductor coil.Except for an uncontrollable parameter λ,which length is depended on the length of the teeth and slots of the phase windings,there are three controllable parameters such as DC-bias field, amplitude of the AC travelling wave, and the field frequency (travelling speed). By changing those parameters, we change the applied fields and its DC output current into superconducting coils. In this paper, we will use a LabView program to control three controllable parameters.By changing the direction of DC bias magnetic field and the magnitude of DC bias magnetic field, AC wave amplitude and magnetic field frequency，the fast response of the system and the high precision control of the output current are realized.The error between the actual output current and the expected output current is greatly reduced and the output current can reach the specified value in a short time.
The flux pump technology is bale to output ultra high current for the High temperature superconducting (HTS) magnets without the copper current leads. This can make the HTS magnets system more compact and save more energy. Currently, the flux pump technology is moving forwards to high current level up to 1-2 kA. But there are still mane components to be optimized and studied, and the HTS switch is one of them. This study will present a experimental study on the AC field controlled HTS switch made by ReBCO coated conductor, based on our experience from previous research work of multi-physics simulation. The experimental results will be compared with simulations, and will find out an optimized switch design based on experiments and with the help of simulations.
This paper studies the principle of direct current and DC bias voltage induced by superconducting tape in a linear magnetic flux pump system. The external magnetic field is a comprehensive magnetic field composed of a bias magnetic field and a traveling wave magnetic field. An experimental platform for linear magnetic flux pumps was built. Using a combination of simulation and experiment, the induction of superconducting tape under a single magnetic field was measured, and the effects of different magnetic fields in the system were discussed. Furthermore, the characteristic parameters of the bias magnetic field and the traveling wave magnetic field were modified under the simultaneous application of the magnetic field, and the mechanism of the magnetic flux quantum coupling effect in the system was analyzed.
In this article, we proposed a method of using multiple linear flux pumps to charge an HTS magnet and set up an experimental system. The system mainly includes three linear-motor flux pumps and five HTS double pancake coils, of which the five coils form an HTS magnet. Each linear-motor flux pump adopts an independent inverter and a DC power supply for cluster control. In order to obtain the maximum central magnetic field of the HTS magnet, we explored a method of optimizing the excitation sequences, that is, collecting certain sorted data and using the genetic algorithm of machine learning to preliminarily explore the effect of different excitation sequences on improving the central magnetic field of the HTS magnet. The results showed that this method can effectively improve the central magnetic field of the HTS magnet compared with single power supply excitation.
High Temperature Superconductor (HTS) are one of the most promising applications of HTSs as they offer a means of charging magnetic loads without the need for physical current leads. Flux pumps have been generally built using Low Temperature Superconductors (LTSs), although their implementation using HTSs has been the subject of recent research interest owing to their lower cryogenic requirement. Despite their promise, research is still being done to better understand their operating behavior to facilitate further design optimizations. This work proposes a novel simulation method of HTS Transformer-Rectifier flux pumps using HTS dynamic voltage switches with varying arrangements that better matches the observed properties of the device. The proposed simulations are compared with the simulation methods that are currently used to show their benefit.
The superconducting electrical machines are going to be widely used in many modern transport applications in near future. In fact, their great features such as high efficiency, high torque density, high power density, and lighter weight make them an excellent fit for electric aircraft and marine applications. The fully superconducting machines built with superconducting magnets requires a current carrying leads which increases not only losses due to copper conductor also complicate the insulations.
Flux pumps are the promising means of energising closed superconducting magnets without direct electrical contact. By doing so we can opt out the resistive heating of the leads carrying the current to the cryogenic magnet coil from the current source at room temperature. In this work, we developed the self-rectifying flux pump device to deliver a maximum of direct current greater than 1 kA to the HTS coil with minimised heat loss. A passive self-switching flux pump is achieved by applying asymmetric current waveform to the primary windings, instead of any active switching component, reducing the complexity of the system significantly comparing to the other flux pump architectures and removes the need for dissipative electronics components in the cryogenic environment.
We explore methods for stabilization and control of persistent currents in high-temperature superconducting Bi-2223 coils. Several different techniques are considered, including flux transfer through inductive coupling as well as other novel approaches. These different methods are tested at 77 K using an experimental setup with a closed loop of Bi-2223 conductor powering two iron-dominated magnets. Cryogenic hall probes characterize the effectiveness of stabilization techniques to prevent field decay, as well as the extent to which general control over the persistent current magnitude and waveform is achieved. The roles of conductor magnetization and path dependence of the persistent current initialization are studied numerically and then compared to experimental results. Finally, we describe the relevance of this work for full size Bi-2223 coils operating in persistent current mode.
HTS flux pumps enable superconducting currents to be directly injected into a magnet coil without the requirement for thermally inefficient current leads. As exciter of high temperature superconducting synchronous motor, HTS flux pumps will reduce the cryogenic volume and improve the efficiency of the HTS machine. With the air gap between the flux pump and the HTS stator increases, the effective magnetic field acting on the superconducting stator becomes smaller. But too small an air gap will limit the application of flux pumps. Therefore, based on the stingy gap (1mm) linear flux pump previously used in the laboratory, the air gap of linear-motor type flux pump is optimized in this paper, so that it can charge the HTS racetrack coil at a larger air gap. Firstly, we simulate the air gap magnetic field when the air gap is changed between 1-12mm with the COMSOL Multiphysics. Secondly, we use the optimized linear-motor type flux pump to carry out charging experiments on the HTS racetrack coils under different air gaps. The results of this experiments are instructive for the further optimization of the HTS flux pump and the application of the flux pump to the 16.9kW HTS synchronous motor built in the laboratory. The linear flux pump can be used to charge the superconducting coil across the wall of the cryostat, which greatly simplifies the complex structure of the cryostat and is easy to install.
In order to enhance the quality of measurement results of a Physical Property measurement System using a superconducting magnet, spatially uniform magnetic field is required at the magnet center. However, measured field uniformity is usually worse than that of design result due to manufacturing errors of a magnet system. Therefore, spatial field uniformity compensation is needed to reduce effect of the manufacturing errors on field uniformity. The conventional field compensation methods require recursive routines of field mapping and compensation coil current adjustment, which lead to less effective time-consuming process. In this study, a newly-developed active field compensation algorithm employing Pattern Search, which is one of the optimization theories will be introduced. An active compensation coil channel currents calculation MATLAB code with the pattern search was developed. And the six compensation coil designs and the field distributions calculations with and without the proposed method were also carried out to compare the results. The test results demonstrate feasibility of the proposed field compensation method.
A lightweight superconducting gantry with large momentum acceptance is under development at Huazhong University of Science and Technology (HUST), which is based on strong focusing and local achromatic technology. The essential component of this superconducting gantry is the curved alternating gradient canted-cosine-theta (AG-CCT) magnet. This paper introduces the study on coil error analysis of the curved CCT magnet. Based on single line model using Biot-Savart law, a coil model built with manufacturing error and coil winding error is developed. A comparative study on the different error levels is carried out to determine the limit of the magnet parameters. In addition, the influence on the proton beam is also discussed.
Sirius is a 4th generation light source with a sub-nm.rad horizontal emittance currently under commissioning in Brazil. The Sirius beamlines will mainly use insertion devices as the source of synchrotron light, and some of the beamlines will use the currently installed central dipole magnets (permanent magnets) of 3.2 T. However, there is a demand for a high-energy x-ray tomography beamline that requires photons with a critical energy higher than 40 keV, which is not achieved with the current dipoles. In this sense, a dipole magnet with a magnetic field higher than 6 T would be of great interest. A conceptual design for a superconducting dipole magnet of 6.4 T, based on conduction cooled NbTi coils and Holmium poles, has been proposed and will be presented, emphasizing the first ideas of the electromagnetic, mechanical, cryogenic and quench protection designs.
With 3 GeV electron beam energy for the National Synchrotron Light Source II (NSLS-II) ring, only superconducting wiggler (SCW) producing greater than 4T peak field can cover photon energy range of 20keV and 200keV with sufficient number of photons. The High energy Engineering X-ray (HEX) Diffraction beamline, which is primarily funded by the New York State Energy Research and Development Authority (NYSERDA) and NSLS-II, will be equipped with 1.2m-long SCW with 70mm period length and 4.3T on-axis field. This SCW is free from liquid Helium and is cooled only with cryo-coolers. Electron Beam Chamber (EBC) with vertical aperture of 8mm is made from 316LN stainless steel and copper plating is applied both entire upper surface and +- 12.5mm wide from the center in the inner surface. The expected heat load from the electron beam of the NSLS-II ring is estimated to 10W/m. This paper describes the design principles and engineering challenges for the device.
If filaments in a multifilament coated conductor are insulated electrically one another, the current carried by each filament could be restricted by its lowest local critical current along its length. The critical current of such a multifilament coated conductor could be the sum of the lowest local critical currents of all filaments. Considering a longitudinal variation in local critical current of each filament is unavoidable, the critical current of a multifilament coated conductor consisting of insulated filaments might be degraded substantially with increasing its length. If we plate copper over the entire group of filaments, because the overlaid copper allows current sharing to detour any section of a filament where its local critical current is low, longitudinal variations in local critical currents of filaments do not directly lead to the degradation of the critical current of the entire multifilament coated conductor. We prepared short pieces of copper-plated multifilament coated conductors and measured their voltage – current curves using a comprehensive system of voltage taps. We attached series of voltage taps on both side edges of a copper-plated multifilament coated conductor (longitudinal voltage-tap series) and pairs of voltage taps across its width (transverse voltage-tap pairs). When we increased the current supplied to the sample gradually, a voltage appeared in a section of the longitudinal voltage-tape series on one side of the conductor: the local critical currents of the filaments near the series could be low. Voltages in different directions appeared in the transverse-tap pairs: it indicates the current flow detouring the low-critical-current section through the plated copper. Although such a current sharing helps to avoid the degradation of a long multifilament coated conductor, the n value might degrade, because a part of the current flows through the copper.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
A lightweight superconducting (SC) gantry with large momentum acceptance is under development at Huazhong University of Science and Technology (HUST). Three types of combined-function quadrupole-sextupole (QS) magnets are used to suppress the chromatic dispersion for the large momentum acceptance. Moreover, the size and weight of the gantry can be further reduced. This paper introduces the design and optimization of the QS magnets with an adjustable sextupole to quadrupole (S/Q) field ratio. A comparative study on the pole shaping and asymmetric excitation method is performed. Considering the magnetic field quality deterioration caused by the asymmetry of the pole face, the contour of the pole face and the pole end chamfer are optimized to minimize the harmonics of the QS magnets. After several iterations, the maximum harmonics of the QS2 magnet can be reduced to 1E-03. In addition, we investigate different S/Q ratios as well as the magnetic center shift caused by the asymmetric excitation.
Rotating coil magnetic field measurement system is an essential component to achieve the multipole harmonic fields measurement in accelerator quadruple magnets. The fundamental requirement for the coils are accuracy, easy fabrication and low-cost, so that the coil parameters can be customized to the magnet requiring test. This paper introduces the application of PCB technique on rotating magnetic field measurement system. After an introduction on the design considerations of the coil parameters and bucking method, we describe the manufacture details of the coil, required by HUST-PTF quadrupoles. Compared to the traditional hand winding coil, the weight and cost of the complete coil is drastically reduced. Finally, the measurement result of a quadrupole is present, which demonstrates high repeatability.
Sigmaphi participated to QUACO PCP whose objective was to propose an innovative solution for MQYY superconducting quadrupole magnets of HL-LHC Insertion Region. QUACO project was divided in three phases: a feasibility study, a detailed study including mock-ups and the manufacturing of a MQYY first-of-a-kind based on an innovative concept.
The innovation proposed by Sigmaphi concerns the collaring which is based on thick half aluminum collars assembled around the coils thanks to a press. The azimuthal stress through the coils is applied by stainless steel pole parts inserted in coil poles with a second press and maintained in position thanks to the aluminum collars. This collaring concept presents the main advantage to maintain the azimuthal stress through the coils during cool-down: it makes unnecessary to apply a large azimuthal stress at room temperature. This collaring solution might be particularly interesting for superconducting magnets made of conductor much more sensitive to stress than Nb-Ti such as Nb3Sn or HTS.
Sigmaphi manufactured successfully nine superconducting coils and performed modulus measurements on these coils. Two quadrupole apertures have then been collared according to the process defined by Sigmaphi thanks to an intensive mock-up program. The azimuthal stress through the coils is measured with 120 cryogenic strain gauges and the target of 55 MPa is reached on both apertures. The two apertures have finally been surrounded by iron yoke laminations and the MQYY magnet has been delivered at CERN in mid-June 2021. The magnetic performances at warm and low current have been checked by CERN. The next step consists in cooling down and energizing at nominal current this MQYY prototype in CEA’s test station.
This success story has been possible thanks to Sigmaphi’s strong investment in design and prototyping and thanks to the intensive and pertinent implication of QUACO’s technical experts at Sigmaphi’s side.
In the quest of higher field accelerator superconducting magnets, essential parts of their design are the so called yokes, which are traditionally made of low – carbon magnetic steel. In currently used magnets, they are typically found in the form of fine – blanked laminations, or machined from laminated heavy plates. The material’s choice is made based on a compromise between the high saturation field, providing a return path for the magnetic flux, and the mechanical robustness conferred to the magnets’ cold masses.
This paper describes the mechanical characterization of low – carbon steel, and applies several approaches for the design and validation of the material from the structural point of view, applicable to a Nb3Sn quadrupole: MQXF. Tensile tests at room and cryogenic temperature, together with fatigue and fracture toughness at cryogenic temperature have been performed. Calculations based on the obtained material properties and results of extensive non-destructive examination (ultrasonic testing) have been implemented in order to ascertain the structural limits of low – carbon steel for its use in the fabrication of high field accelerator superconducting magnets.
Field shaper is a powerful supplement for the magnetic field generator (namely, the driving coil) in electromagnetic forming (a high velocity manufacturing technology), which utilizes the magnetic shielding effect of deticated-shaped electrical-conductor to alter the path of the pulsed magnetic field, so as to obtain the desired spatial distribution for the magnetic field as well as the pulsed Lorentz force induced on the metal workpiece, thus shaping the metal workpiece into targeted geometry. In addition, the introduction of the field shaper may also essentially relieve the mechanical and thermal loadings on the driving coil, which is a critical issue for high performance life for the field generator.
This paper shall give an overview for the design and utilization of the field shaper. Adopting one type of most commonly-used field shaper, namely, the field shaper for tubular metal workpiece, as example, we shall discuss how to balance the trade-off of the energy efficiency, the targeted magnetic field distribution, and the thermal-mechanical loadings on the coil, thus targeting an optimum performance. And we shall validate our deduction by a combinations of experiment and simulation. While the paper is mainly focused on the applications of pulsed magnetic field in manufacturing industries, we think the content may stimulate a wide interest for the researchers in other area, especially for research area needing a flexible spatial pattern for the high pulsed magnetic field.
We report on power test of a rapid-cycling superconducting accelerator magnet. The dual-bore magnetic core of 0.5 m length and two 10 mm (vertical x 100 mm (horizontal) beam gaps arranged in vertical plane is energized with HTS-based power cable. The 3-turn magnet cable is placed within magnetic core space where core descending magnetic field is strongly suppressed minimizing ramping B-field induced eddy and hysteresis losses for the cable. The conductor cable is formed of 2 sub-cables each using 2 HTS strands (2.5 mm x 0.1 mm) helically wound on the supporting SS pipe (8 mm x 0.1 mm) which also serves as liquid helium conduit. The strands are firmly secured on the pipe surface with a single wrap of 12.5 mm x 0.1 mm Cu tape. Conventional current leads are used to connect power supply to magnet conductor coil. Magnet coil and leads are separately cooled with flow of supercritical helium (6 K, 2.5 bar). The current discharge capacitor bank is used to energize magnet. The sine -wave-like conductor current of 1 kA at 14 Hz generated 0.52 T B-field variation in magnet beam gaps with maximum ramping rate of 289 T/s. The liquid helium temperature does not show increase between the off/on power cycles within +/- 0.003 K measurement error indicating cryogenic power loss possibly less than 0.1 W. An upgrade of magnet design to higher B- fields in the 20 mm beam gaps, as considered for the muon collider accelerator, is discussed.
An infiltration and reaction (IR) process realizes the dense MgB$_2$ bulk without the external physical pressure. The trapped field, $B_{\rm T}$, of MgB$_2$ bulk prepared by the IR process was 2.4 T at 15.9 K, which was as high as that of MgB$_2$ bulk prepared by in-situ hot isostatic pressing method [1]. However, we found quite a large amount of unreacted micrometric B particles due to the incomplete diffusion of liquid Mg into a B precursor [2]. Therefore, overcoming this problem should give a further enhanced $B_{\rm T}$ for the IR-processed MgB$_2$ bulks. In this paper, we report the refining effects of B powder on the formation of MgB$_2$ and the trapped field properties. Crystalline B powder was refined by ball-milling at various rotation speeds up to 600 rpm for 1 h. The Mg pellet was placed on the B pellet in a stainless steel container and heat-treated at 900 $^\circ$C for 24 h. The $B_{\rm T}$ of the IR-processed MgB$_2$ bulk increased with reducing the grain size of starting B powder, which originated mainly from the increase of the grain boundaries in the MgB$_2$ bulks. Moreover, the volume fraction of MgB$_2$ using ball-milled B powder is larger than that of MgB$_2$ using as-purchased B powder, which also contributes to the enhancement of $B_{\rm T}$. We also attempted to fabricate the IR-processed MgB$_2$ bulks using the ball-milled amorphous B powders, however, the MgB$_2$ bulks were not created. We discuss the relationship of the creation of MgB$_2$ with the grain size and crystallinity of B.
References
[1] T. Naito et al., Supercond. Sci. Technol. 29 (2016) 115003.
[2] A. Ogino et al., IEEE Trans. Appl. Supercond. 27 (2016) 6800905.
Since the beginnings of NMR spectroscopy, the exceptionally successful method to analyze the chemical structure of solids and molecules in solution, experimentalists requested ever larger magnetic fields for their instruments, primarily to improve their resolution and their signal-to-noise ratio. While a succession of low-Tc superconductors – NbTi and a range of Nb3Sn wire types – were the base of a remarkable development from 4.7 T (200 MHz) in 1964 to 23.5 T (1.0 GHz) in 2009, only the use of high-Tc superconductors (HTS), discovered in the 1980s, held the promise to generate even higher fields. However, practical HTS conductors of sufficient unit length and quality were made only during the last decade, enabling the development and construction of ultra-high-field NMR magnets that reach fields beyond 1 GHz and meet further demanding requirements.
Bruker BioSpin, a leading supplier of complete NMR spectrometers with its own magnet R&D and production, followed the evolution of HTS conductors closely with a program to develop HTS coil technologies, quench protection schemes, homogenization methods and jointing techniques. Realizing its potential and trying to leverage expertise and manufacturing capabilities available in the company, the focus soon was on ReBCO coated conductors. After many tests on individual components and coil prototypes confidence in the developed technologies was sufficient to design and build 1.1 GHz and 1.2 GHz NMR LTS-HTS hybrid magnets, the first of which were installed at customer sites in 2019 and 2020 respectively. Four more systems followed since.
After a brief overview of the historic development of UHF magnets, this presentation discusses some of their challenging requirements (homogeneity, drift, force management and quench protection) and how they are met in LTS-HTS hybrid magnets. Following a review of the achieved NMR performance it concludes with the practical needs that commercial NMR systems must also satisfy.
See the online poster session at 7:00 a.m. for presentation details
This summer the US HL-LHC Accelerator Upgrade Project (AUP) reached an important milestone by completing 50% coil fabrication. AUP is fabricating half of the low beta quadrupoles (MQXFA) for the High Luminosity LHC (HL-LHC) at CERN. These magnets will be used in Q1 and Q3 Inner Triplet (IT) elements of HL-LHC. CERN is fabrication the magnets for Q2a and Q2b IT elements. The AUP effort is shared by BNL, Fermilab and LBNL, with strand QC verification tests at NHMFL.
At the time of this conference, conductor procurement is almost complete, cable fabrication is ~75% complete, 50% coils have been completed, 8 magnets have been assembled and some of them tested.
In this paper we are going to discuss achievements, challenges and lessons learned up to this point of production. Plans up to end of production will also be presented and discussed.
New high field and large-aperture quadrupole magnets for the low-beta inner triplets (Q1, Q2, Q3) are being built as part of the high-luminosity upgrade of the Large Hadron Collider (HL-LHC). These new quadrupole magnets are based on Nb3Sn superconducting technology. US Accelerator Upgrade Project (US-AUP) is producing the Q1 and Q3 cryo-assemblies; a pair of ~ 5 m long magnet structures installed in a stainless-steel helium vessel (cold mass) and surrounded by cryostat shields, piping, and vacuum vessel is the Q1/Q3 cryo-assembly. This paper gives an overview of the design, production and the results of the horizontal test of the first pre-series Q1/Q3 cryo-assembly.
The High-Luminosity project (HL-LHC) of the CERN Large Hadron Collider (LHC), requires low β* quadrupole magnets in Nb3Sn technology that will be installed on each side of the ATLAS and CMS experiments. After a successful short-model magnet manufacture and test campaign, the project has advanced with the production, assembly, and test of full-size magnets. In the last two years, two CERN-built prototypes (MQXFBP1 and MQXFBP2) have been tested and magnetically measured at the CERN SM18 test facility. These are the longest accelerator magnets based on Nb3Sn technology built and tested to date. In this paper, we present the test and analysis results of these two magnets, with emphasis on quenches and training, the quench localization with voltage taps and a new quench antenna, as well as voltage-current measurements.
In a dipole or quadrupole accelerator magnet the electromagnetic forces in the coil are azimuthally directed towards the mid plane and radially outwards. Displacement of the turns at powering could compromise field quality and cause releases of frictional energy, which could trigger a quench. To avoid movements of the conductors, preload is applied to the coil in the azimuthal direction. The design criteria used in accelerator magnets aim in the design phase at a preload providing contact between pole and coil at nominal current. This requirement was set at the beginning of the accelerator magnet era. On the other hand, accelerator magnets had shown that good magnet performance can be reached with only a partial preload, i.e. that coil unloading during the ramp does not prevent reaching higher currents. This issue is particularly relevant for Nb3Sn magnets, where the loads applied to the Nb3Sn filaments can reduce and/or permanently degrade their critical current. In order to investigate the impact of mechanical stress on the quench performance, the MQXFS6 short model quadrupole for the High Luminosity Upgrade was tested under an azimuthal pre-load ranging from 50 % to 100 % of the electromagnetic forces at nominal current. This paper presents the assembly details, quench performance, and describes the mechanical behavior of the magnet under the different stress conditions. The magnetic measurements of the first allowed multipole are also analyzed and compared to simulation results, to see if any evidence of coil unloading can be seen from the harmonics.
INFN is developing at the LASA lab (Milano, Italy) the High Order (HO) corrector magnets for the High Luminosity-LHC (HL-LHC) project, which will equip the new interaction regions. All the HO correctors, from skew quadrupole to dodecapole, are based on a novel superferric design, never used so far in high energy colliders, which allows a relatively simple, modular, and easy way to construct a magnet. The series production is ongoing after the completion of the five prototypes program; half of the 54 series magnets have been produced in the industry and the testing at LASA is ongoing. The delivery to CERN also started. We discuss the design optimizations introduced and the lessons learned during the first half of the series production. We also focus on the quality assurance plan, which allowed us to early detect non-conformities and monitor the learning curve. The testing station at LASA is fully operational, four magnets per cool down are tested. Each magnet is powered individually, and the magnetic measurement system, supplied by CERN, provides both field quality and transfer function. We provide an overview of the performed tests and measurements, focusing on test station’s performance and quality of the measurements. Finally, we provide an outlook of the production completion, test plan and delivery to CERN.
Large aperture beam separation dipole (MBXF) will be constructed as a Japanese contribution for the High-Luminosity LHC upgrade. Those magnets will be installed at both sides of two interaction points, ATLAS and CMS. The required field integral is 35 Tm with the coil aperture of 150 mm. Nominal dipole field of 5.6 T at the nominal current of 12 kA is produced at 1.9 K by Nb-Ti based technology. Magnetic length of this magnet is 6.3 m. KEK is responsible for delivery of seven cold masses including one prototype and six series production magnets within the framework of CERN–KEK collaboration. Since 2020, Hitachi has been constructing a full-scale prototype (MBXFP1). Magnet test will be conducted by KEK to validate that magnet performance fulfills acceptance criteria.
This paper reports a summary of the test results of MQXFP1, including training, mechanical performance, field quality and protection studies.
MCBXFB magnets are nested orbit combined correctors for the upgrade of the LHC. The first three magnets have been manufactured at CIEMAT and assembled at CERN, in the framework of the HL-LHC project. The power tests performed on the first prototype showed that the behaviour when the dipoles were individually powered was excellent, but the training to reach nominal currents in combined operation was very long. Memory was lost when the torque direction changed. A similar behaviour was found in the first power test of the second prototype described elsewhere. The origin of the problem has been identified as insufficient mechanical support at the inner dipole coil ends.
This paper depicts the results of the power test after the reassembly of the second magnet with increased pre-stress on the coils. Shimming plan is discussed. Furthermore, a fine tuning of the inner dipole design has been introduced in the third magnet. The results of the power tests on that magnet are also included.
We present the operation result of a liquid-helium-free 23.5-T/φ12.5-mm-cold-bore magnet prototype composed of a stack of 10 no-insulation (NI) REBCO double-pancake (DP) coils: eight middle coils of 6-mm wide and two end coils of 8-mm wide tape. All the tapes have only 1-µm-thick copper layer on each side to overcome the conductor thickness uniformity issue and enhance the mechanical strength within the winding. With this small-scale prototype towards a tabletop liquid-helium-free 1-GHz microcoil NMR magnet, we validate our coil design issues that include conductor performance, screening-current-induced field and stresses, and conduction-cooling cryogenics. We have applied additional electrical shunting by thin layers of solder on the top and bottom surfaces of the 10 NI DP coils for effective cooling and quench protection. Included in the paper are: 1) summary of construction and conduction-cooling; 2) charging and operating test results in the temperature range 10–30 K; 3) examination of screening-current effects by experimental and analytical methods; and 4) quench-protection heater performance. The paper concludes with a summary of enabling features to be used for subsequent development of the 23.5-T/φ25-mm-RT-bore microcoil NMR magnet.
Acknowledgement: The research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R21GM129688.
As a sequel to our previous report on in-field performance estimation of a 38 mm cold bore metal-as-insulation (MI) HTS insert after quench event of 32.5 T, this paper presents repairment process and test results of the insert. Although the insert had survived against insert quench and fault events of background magnet, the resistances of the insert increased because the inner as well as the outer junctions were kinked and the REBCO tapes of the last single pancake coil at the top and bottom of the stack were mechanically deformed. For this reason, 7 MI DP coils were re-wound with used REBCO tapes to just replace damaged HTS pieces by new ones for inner junctions. 2 DP coils were manufactured using new REBCO tapes as well as new inner junctions. During repairing process, a sapphire plate was used for electrical insulation between the SP coils to enhance the cooling condition inside each DP coil. The coils were tested in a bath of LN2 at 77 K to compare critical current, coil constant and resistance values of original, damaged and repaired DP coils. After assembly of DP coils, the 9 DP stacked insert was installed in a newly made probe with a 34 mm bore size tube to access to the center of the coil allowing further in situ characterizations of the coil and future experiments by end users. The insert was tested under various background magnetic fields (Bext) in a bath of LHe at 4.2 K. The key focuses of this paper are: 1) characteristics resistance change of the insert; 2) resistance value of each DP coil; 3) temperature change of the insert during operation; 4) the magnetic field induction rate of the insert under various Bext; and 5) field homogeneity of the insert through field mapping.
Towards a persistent-mode 1.3 GHz (30.5 T) LTS/HTS NMR magnet, quench protection of a layer-wound HTS inner coil is of great importance. The intra-layer no-insulation (LNI) method we recently proposed can be effective in protecting such a layer-wound HTS coil. In fact, we demonstrated an LNI-REBCO coil was protected from a self-quench at a center field of >30 T under a background field. However, its behavior under an LTS outer coil’s quench, a major quench scenario of the 1.3 GHz-NMR magnet, has been unclear. As a model experiment, we conducted a quench test on LTS/HTS small coils comprising a 90 mm-diameter NbTi outer coil and an 18 mm-diameter 24-layer LNI-REBCO inner coil.
We charged the LNI-REBCO coil to 368 A in liquid helium under a 5.5 T background field of the NbTi coil. In this state, we quenched the NbTi coil at t = 0 s. The REBCO coil voltage (Vre) started to decrease, while the measured center field (B0) remained constant for t < 0.15 s. At t = 0.15 s, Vre increased and B0 started to decrease, resulting in full discharge of both coils in 1 s. The peak of the REBCO coil current was estimated to be 848 A. These data show that the NbTi coil’s quench induced large currents in the REBCO coil and it suffered a quench due to an overcurrent. After the test, we charged the REBCO coil in a self-field in liquid helium and observed that the voltage-current curve agreed with that before the quench, i.e., the LNI-REBCO coil was self-protected from the NbTi coil’s quench.
We will conduct a numerical simulation on the detailed behavior of the LNI-REBCO coil and further experiments on a larger LNI-REBCO coil.
This work was supported by the JST Mirai-Program Grant Number JPMJMI17A2 and SPRP in RIKEN.
The high-strength substrate within REBCO contributes to its selection for use in the NHMFL 40 T all-superconducting magnet. To confidently scale up to a 40 T user magnet, both quench protection and cyclic fatigue are among the technologies that require successful demonstration. Here, numerous test and simulation results from two-in-hand wound, double-pancake stacked, insulated mid-scale test coils are shared and discussed. The two-in-hand winding method is known to provide resilience against single tape defects via the parallel superconducting paths, hence the technology descriptor - multitape insulated, or MTI. These MTI mid-scale coils were wound with >1.2 km of conductor and generated an additional ~15 T inside of 12 T LTS magnets. Designed to reach very high hoop strains (>0.5 %), the test coils were cycled (~1 kcycle) to evaluate the longevity of the various magnet components, as well as the REBCO tapes. Additionally, the test coil designs balance compact size against the amount of stabilizing conductive material, albeit resistive, available for energy extraction in the event of a protected quench. Here we demonstrate the feasibility of safely protecting a REBCO-tape wound, insulated coil with a designed Jcu of about 700 A/mm2.
Acknowledgement
This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and DMR-1839796, and the State of Florida.
We have succeeded in operating a 25 T cryogen-free superconducting magnet (25T-CSM), which consists of LTS outsert coils and Bi2223 insert pancake coils. As a next step, an upgrading of 25T-CSM to 30T-class CSM is considered by replacing the Bi2223 insert coils with REBCO coils, since REBCO tapes have better mechanical and in-field critical current properties. In a design of the 30T-CSM, the two-ply co-winding with a face-to-back configuration will be adopted so that current sharing is expected in the event of local degradation. In order to confirm the validity of our coil design, we investigate electromagnetic and mechanical properties of four-stacked two-ply REBCO pancake coils. The coils were fabricated with a Fujikura EuBCO tape with artificial pinning centers, which had a dimension of 4 mm width and 0.15 mm thickness. The inner and outer diameters of each coil were 68 and 268 mm, respectively. Several strain gauges were attached to the innermost and outermost surface of the windings to measure the hoop strain. The coil voltages and strains were measured at about 20 K cooled by the GM cryocooler under a background field of 11 T generated by the large-bore superconducting magnet at the HFLSM, IMR, Tohoku University. The maxim hoop stress was estimated to be about 480 MPa by the BJR relation for the operating current of 500 A in 11 T. Observed averaged strains on the outermost winding of each coil were approximately 0.2-0.3%. In the presentation, the I-V properties, measured strains, and the stress distribution in the coils by an FEM analysis will be reported and discussed.
This work was supported by JSPS KAKENHI Grant Number 18H05248.
Due to the combined superior electrical and mechanical performance, ReBCO tapes are considered as a candidate material for application of high current carrying magnets operation under high magnetic field. However, the high aspect ratio and multilayer structure of the tape complicate its cable and CICC conductor design and manufacturing. It is therefore important to carry out activities to investigate its high field application performance. Thus, ReBCO insert solenoids are taken as prototypes and have been developed in ASIPP, which were wound from ReBCO cables. Afterwards, the critical current of the manufactured solenoids were measured at 77 K, self-field and 4.2 K, a background field of 10 T and 19 T. Effects from the developed manufacturing technologies, electromagnetic and thermal loads during operation on the current carrying stability were assessed and summarized here. The results show that the manufactured solenoids critical currents are stable over dozens of electromagnetic and thermal cycles, which represent a key milestone in next step HTS magnet technology development for high field application.
Advanced Conductor Technologies has been developing high-temperature superconducting (HTS) Conductor on Round Core (CORC®) cables and wires wound from ReBa2Cu3O7- coated conductors for use in high-field magnets that would ultimately operate at fields exceeding 20 T. CORC® cables and wires have matured into practical high-current and high-current density magnet conductors that are being produced at long length and high quality. To demonstrate the maturity of CORC® cables for use in high-field magnets, a CORC® cable insert solenoid was developed and successfully tested in a 14 T background magnetic field. The CORC® cable solenoid was designed to operate at high current, high current density, and high Hoop stress; a combination that is essential in the development of low-inductance high-field cable magnets.
The 4-layer, 45-turn, CORC® cable insert solenoid was wound from a 19 meter long CORC® cable, containing 28 tapes of 3 mm width, and had an inner diameter of 100 mm. The CORC® solenoid was successfully tested in liquid helium in background magnetic fields of up to 14 T. The highly stable operation of the CORC® solenoid allowed for current to be increased into the superconducting transition, followed by a slow current ramp down, without causing a quench. The CORC® insert solenoid demonstrated a critical current of 4,404 A in a 14 T background field, resulting in a combined central magnetic field of 15.86 T and a peak magnetic field on the conductor of 16.77 T. The winding current density was 169 A/mm2, while the engineering current density was 282 A/mm2, which would result in a peak Hoop stress of 275 MPa. No significant degradation in critical current was measured after 16 high-current tests in high magnetic field, clearly demonstrating the robustness of the CORC® cable in high-field magnet applications.
From a magnet designer’s point of view Bi-2212 round conductor is, in many aspects, the ideal candidate for high field magnets. Besides very high critical current densities that exceed specification for conductor of the Future Circular Collider (FCC) of 1500 A/mm2 in 16 T background, it offers two particular advantages over other HTS conductors, namely that it is available as an up to one mile long round wire, that it has many finely distributed filaments, which can be twisted to reduce AC losses, that it behaves electromagnetically isotropic thus eliminating the need of distributing graded conductor throughout a coil, that it offers a very flexible and adaptable architecture, and that it can be cabled easily to provide conductor for high current carrying coils with low inductance. These advantages, however, come at the cost of low mechanical properties of the bare conductor, which are similar to Nb3Sn strand. In very high field magnet systems above 30 T extremely high stresses will have to be mitigated and a thorough understanding and control of the coil mechanics is paramount. In this presentation we will present an update of our coil R&D efforts with a focus on coil reinforcement.
This work is supported by the US DOE Office of High Energy Physics under grant number DE-SC0010421 and DE-SC0018683, and by the National Science Foundation under NSF/DMR-1644779 and by the State of Florida. Collaborations within the US Magnet Development Program supported by DOE-OHEP, especially with LBNL are gratefully acknowledged.
Korea Medical Device Development Fund (KMDF) launched a national project to develop a high-temperature superconductor magnet for magnetic resonance imaging (MRI) in 2020. This project's ultimate target is to develop a 6 T 320 mm high temperature superconductor (HTS) magnet. Major concerns in developing the MRI magnet in terms of electromagnetic dynamics are the time-varying field uniformity due to screening current-induced field (SCF) and turn-to-turn leak current relaxation and the consequent temporal field instability in a target diameter spherical volume (DSV) space. Unfortunately, few studies have been conducted to investigate real-time SCF relaxation and the consequent spatial and temporal magnetic field variation with a real-time monitoring approach. Thus, this paper provides real-time monitoring results using a Hall sensor array to investigate the spatial and temporal magnetic field variation induced by SCF in a no-insulation (NI) HTS test coil. Design, fabrication, and operation of an NI HTS test coil were performed. A Hall sensor array was attached to the test coil surface to measure the axial magnetic field's temporal variation and the consequent harmonic coefficient. Calculation with a finite element method (FEM) based simulation model is conducted to compare results with measurements. We provide discussions that include comparison results between calculation and measurement.
This work was supported by the Korea Medical Device Development Fund grant funded by the Korea government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety) (Project Number: 202011C21)
This work concerns the development of non-insulated (NI) HTS magnets at the Paul Scherrer Institute (PSI), Switzerland.
The Swiss Light Source (SLS) synchrotron at PSI uses superbend magnets as a brilliant source of X-rays. As part of an upgrade of the SLS, two LTS superbends are being constructed. These NbTi-based magnets will each consist of a pair of racetracks to generate the desired peak magnetic field, and a pair of Helmholtz coils to satisfy the required magnetic field integral.
To keep the SLS in a leading position in the future, PSI is currently investigating superbend magnets made from ReBCO-based NI coils, pushing to higher peak magnetic fields. The high current density, high stability, and relatively straightforward cooling at 10-20 K make NI coils ideally suited for this DC application.
The presented work focuses on the manufacturing, testing, and modeling of NI test magnets at PSI. The first test magnets consist of ReBCO-based pancake solenoids wound in-house, stacked together using a modular approach to generate a bore magnetic field of up to 14 T. Testing is performed in a cryocooled set-up. Results are compared with a coupled thermo-electromagnetic FEM model. The solenoid test program serves as a stepping stone to NI HTS superbends, and lessons learned will be applicable to racetrack-based NI magnets in general.
In recent years, remarkable progresses have been made in the R&D efforts for HTS high-field magnets. The screening-current-induced magnetic field (SCIF) and mechanical stress/strain (SCIS) in REBCO coils are raising growing concerns. This study presents experimental and theoretical analyses on the SCIS in two REBCO coils, with and without over-banding structures, as inserts in an LTS background field magnet.
The coupled electromagnetic-mechanical model, which takes into account the tilting angles of the superconducting tapes and the strain dependency of the critical currents, were developed. Three modelling strategies, the discrete-coupled model with turn-to-turn contacts, the discrete-sequential model and the block model, are implemented and compared against measured data. The block model, which presumes strong turn-to-turn interaction, underestimates the deformation of a dry-wound coil. Simulations with the discrete-coupled model are in better agreement with the experiments in most cases, in comparison with overestimation using the sequential model. It is demonstrated that the coupling of the electromagnetic field and the displacement field through the tilting angle and $\varepsilon$-$J_c$ relationship can significantly influence the magnetization process, especially with a large $B_z$/$B_r$ ratio.
In order to mechanically protect dry-wound REBCO coils against the concentrated Lorentz force, studies on the effects of over-banding and edge-bonding are carried out. The method of over-banding is proven efficacious in mitigating the SCIS, although it shows a different pattern compared to conclusions with uniform current distribution assumption. Edge-bonding with Stycast 2850 can reduce the hoop strains along the axially outer side of the pancake coil, but with increasing applied forces, it was no longer effective as the bonding materials eventually failed in our experiment.
This work could be useful for the design and analyses of future high-field REBCO magnets.
HTS is valuable for future detector magnets as it allows operation at elevated temperatures and magnetic fields. However, due to slow propagation of normal-zones, quench protection remains a challenge. Non-insulated coil technology offers a potential way forward, but controlling the associated ramping time constant is still an unresolved challenge. This study offers a potential way to have non-insulated coil technology with a desirable low time constant.
The radial resistance of a no-insulation pancake coil depends on many factors. The most important factors are the thickness of copper stabilizer, the thickness of the substrate and if- or if not the turns of the coil are soldered together. The oxide buffer layers between the substrate and ReBCO layer are insulators in bulk and have a high resistance as thin layers. Consequently, the path with the lowest resistance from one turn to the next turn is through the copper channels on the edges of the tapes. This bypass provides a low resistance passage in case of quench, but it increases the practical ramp-time of such coils drastically. A compromise can be made between the added protection and the ramp-time by fully soldering the coil pack and afterwards physically removing the copper and solder channels on the sides of the tapes. Now, the radial turn-to-turn resistance is dominated by the resistance of the substrate and buffer layers, which significantly reduces the time constant.
Three compact ReBCO HTS pancake coils were prepared using this preparation technique. Their time constants were reduced by a factor of 500 from around one hundred seconds to only a few hundred milliseconds by removing these copper channels. Tests were performed both in LN2 and in vacuum in a temperature range of 55 to 80 K. An overview of the preparation procedure, demonstrator coils and the test results will be presented.
High-temperature superconducting (RE)Ba2Cu3O7-x (REBCO) coated conductor (CC) tapes are known for their capacity to tolerate high tensile stress under applied uniaxial tension, typically in the range of 600-700 MPa at 77 K, while mediocre level under pure bending (a.k.a., easy bending). Once utilized in coil, however, there is a limit to the value of the allowed strain/stress before degradation of the critical current (Ic) occurs, which is mainly attributed to the combined twisting and axial tension. These strains or stresses will affect considerably the irreversible strain limits of Ic due to added strain along the CC tape’s edgewise direction (a.k.a., hard bending strain) even under static loading. With such conditions, degradation of the REBCO coil performance can be expected. So far, the systematic investigations of the mechanism for such Ic degradation in REBCO coil have not been clearly considered, therefore the current study aims to investigate the fundamentals of such degradation. Here, the linear superposition of strains induced in different modes such as pure tensile, easy and hard bendings, etc., are tackled analytically and experimentally. The Ic degradation behaviors of IBAD/REBCO CC tapes in windings with different pitches on a large diameter former are examined at 77 K and self-field, using a modified static fatigue tester designed for coil testing. The coil bend strain parameters, such as the radius of curvature, pitch between turns, etc., are analyzed. Through the linear superposition of strains induced in the REBCO coil, the appropriate approach to effectively suppress the Ic degradation while under static loading was suggested, and the static fatigue endurances were also determined.
This research was supported by a grant from the National Research Foundation of Korea (2020-R1I1A-3058389), funded by the Ministry of Education (MOE), Republic of Korea. Special thanks to SuNAM Co. for the supplied CC tapes.
In order to achieve high intensity and compact multifunctional cyclotron, the behavior of the non-circular coil in a high magnetic field at 4.2 K, and the reinforcement of it have been investigated. Two types of isosceles triangle shaped double-pancake coils; a coil with reinforcement due to Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure and a coil without reinforcement, were manufactured and observed their behaviors when current was applied to the each coil in a high magnetic field. The latter examination without reinforcement in 10 T external magnetic field showed that the superconducting property of the coil was lost and the flow resistance was observed when the applied current exceeded 160 A. Unbalanced and non-uniform electromagnetic stress affects the superconductor in the non-circular coil because the radius of the triangle shaped coil varies. The coil was disassembled after the hoop stress test, and it was found that the superconducting tape was plastically deformed and bent at the apexes of the triangle by the strong stress. The reinforced coil by Yoroi-coil structure was applied up to 300 A in a magnetic field of 14T. A voltage of 0.3 mV was observed when the coil current was 277 A, and excitation was terminated when voltage reached 0.6 mV at 300 A. The coil windings after the test were also observed, and the turbulence of the windings was significantly smaller than that of the coil without reinforcement. It was clarified that the Yoroi-coil structure has the effect of reducing the electromagnetic force affecting a coil winding even in a non-circular coil. Details of the experimental results will be reported.
A 14 T whole-body MRI superconducting magnet is currently being designed at the Institute of Plasma Physics Chinese Academy of Sciences. The main coils will be wound with the Nb3Sn Rutherford cable-in-channel conductors, actively shielded, and operate at 1634 A to produce a central field of 14 T in an 840 mm warm bore. The magnetic field homogeneity is 5 ppm in a 45cm DSV. The inductance is 441 H and the stored energy is 615 MJ. To generate such a high-field in a large warm bore, the Nb3Sn conductors will experience significant magnetic stress and strain, which may lead to irreversible degradation of critical current. Therefore, mechanical analyses are conducted to assess the mechanical behaviour of the 14 T MRI magnet, at the following load conditions: room-temperature preloading, cool-down from RT to 4.5 K, and operating conditions. Several approaches are being considered to reduce the hoop strain of the Nb3Sn conductors, which will be compared with the experimental result of the tensile strain irreversibility limit.
The U.S. Magnet Development Program (USMDP) is developing Canted-Cosine-Theta (CCT) magnet technology for future high field accelerator magnets. The CCT concept limits Lorentz force accumulation by placing turns within precision-machined grooves that are separated by ribs and a spar that intercept forces, substantially reducing the stress in the conductor. CCT technology has been advanced through the fabrication and testing of three Nb3Sn CCT (CCT3/4/5) dipole magnets, with the final magnet reaching 88% of short sample current and more than 9.1 T field in a 90 mm aperture. A subscale CCT magnet program has been initiated in order to better understand and reduce training in this type of magnet. The goal of the nominal subscale design is to reach a similar stress state as for the CCT3/4/5 series at the short sample limit, with a reduced coil size in order to achieve reduced fabrication and testing time for dedicated training studies. The stress state in the CCT magnets can be modified by the choice of design parameters and configurations. The test results for various subscale magnets with different design configurations will be presented.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program.
A project aiming to fabricate an operational Nb3Sn superconducting undulator for the storage ring of the Advanced Photon Source at Argonne National Laboratory is under way. The Nb3Sn undulator has a design magnetic field of 1.2 T and a nominal operation current of 850 A. The maximum magnetic field on the conductor is about 5 T. With large critical current densities, the 35 µm subelement size of the 0.6 mm Restacked Rod Processed wires with 144 superconducting subelements over 169 total is at the very limit of magnetic stability. The heat treatment has therefore been studied and optimized to obtain parameters within operation specifications. In this paper we show performance results on wires and coils from different heat treatments.
Superconducting undulator (SCU) technology has been in use at the Advanced Photon Source since 2013. Due to the successful and reliable operation of the existing SCUs, the Advanced Photon Source upgrade project has decided to expand the use of NbTi-based SCUs. The first new magnets to be designed and fabricated are 1.9 m long with a period length of 16.5 mm. NbTi superconductor is used for coil winding and there are four separate coils wound on the mandrel to produce the main undulator field along with end compensation and distributed dipole compensation. The magnetic design, fabrication details, assembly, and testing are described in detail.
A phasing magnet has been developed at National Synchrotron Light Source II (NSLS-II) for the Coherent Soft X-ray Scattering (CSX) beamline. The phasing magnet will be located at the center of the straight section in between two identical and independent variably polarized APPLE-II devices. Based on Permanent Magnet technology, the phasing magnet has been designed to achieve the required electron beam delay in order to properly adjust the phase matching of these two consecutive EPUs (Elliptically Polarizing Undulators) and ensure a positive interference between the photon beam emitted in each device. This paper will describe the mechanical and magnetic design together with the final field measurements and magnetic tuning results. Also, the spectral performance of the two EPUs and the method used to properly set the field strength of the phasing magnet for any given radiation wavelength and polarization mode will be presented as well.
Sirius is a 3 GeV 4th generation synchrotron light source located in Campinas, Brazil. Sirius first delta undulator is currently being built. It is a 1.2m long permanent magnet structure with 21 periods with a lengh of 52.5mm and 13.6mm gap. This paper provides an overview of the current status of the delta undulator regarding development, construction, measurements and correction of the insertion devide, briefly describing some of the most relevant challanges faced in the project and installation of the equipment in the Sirius storage ring.
Superconducting racetrack shaped magnet has been fabricated successfully aiming at its application to superconducting undulator. The magnet was wound with NbTi superconducting wires by a method of dry winding followed by the vaccum pressure impregnation. First the single coil was fabricated and the critical current was tested in liquid helium. The critical currents of the six coils tested were in the range of 475A to 483A. Then the coil module which was connected in series was wound and tested in dewar in a method of conduction cooling. The coil module was charged to 400A and did not quench. From the results, the single coil and coil module connected in series have reached the designed operating current.
Keywords Superconducting Undulator·Racetrack-type magnet· Niobium titanium·Critical Currents·
A new PrFeB cryogenic permanent magnet undulator (CPMU) prototype with 12mm period length is being constructed for High Energy Photon Source (HEPS) at IHEP. HEPS is a new 6 GeV synchrotron radiation light source. Insertion devices play a significant role in achieving the high performance of the photons. The magnetic field performance of the CPMU must be measured in the vacuum chamber and cooled to cryogenic temperature. A dedicated magnetic measurement system including Hall probe measurment bench and stretch wire device has been developed to perform magnetic field measurements of CPMU. This paper describes details of development and improvement of the measurement system.
Thermal effect on the magnet materials and magnetic structure plays an important role in the performance of the insertion devices such as the in-vacuum undulator. By cooling the magnetic structure to low temperature to achieve higher peak magnetic field and higher resistance to demagnetization, cryogenic permanent magnet undulator (CPMU) developed from the conventional in-vacuum undulator has complicated thermal effect on the magnetic performance including the RMS phase error. Temperature difference along the magnets array and the thermal deformation of the magnetic structure can cause a deterioration of the RMS phase error during cool down process. Shanghai Synchrotron Radiation Facility (SSRF) developed a NdFeB based CPMU prototype in 2016. This paper presents the analyses of the relation between the temperature distribution and thermal deformation of the magnets array and girders. Furthermore, the analyses of the thermal effect on the magnetic performance can provide guidance for optimizing the mechanical design and cryogenic cooling strategy to reduce the deterioration of the performance caused by sophisticated dynamic heat load.
Particle spin physics research at Nica collider deals with polarized proton and deuterium beams. Special solenoids are proposed to control the spin direction of the polarized beams in NICA. Spin direction can be controlled by adjusting the integral of axial magnetic field of the solenoids. We present design results for 6T polarization control superconducting magnets for NICA collider. The maximal integral of static field is 50 T∙m. The polarization control magnet system is composed of several identical stand-alone units. Each unit has a warm bore or two warm bores connected to the collider vacuum ring. An active study of the dynamics of the spin of a relativistic particle made it possible to detect a wide range of instabilities of spin motion. The instabilities of spin motion (depolarizing resonances) lead to a rapid loss of beam polarization upon acceleration and is the main problem in obtaining a polarized beam of high-energy protons. Active interest in solving this problem is due to a wide range of spin phenomena found in the high-energy region. Magnet design, field maps are calculated and the optimal solenoid configuration is discussed. This paper is dedicated to memory of professor Kovalenko A.D. , who recently passed away. The authors thank the Russian Foundation for Basic Research (RFBR) for the financial support of the project № 19-29-10007.
Large aperture superconducting combined function magnets with the magnetic rigidity of 13Tm will be utilized in the Spectrometer-Ring for the HIAF (High Intensity heavy-ion Accelerator Facility) project. The magnet is designed to provide a dipole field of 3.0 T and a quadrupole field of 11.3 T/m in a large aperture of 240 mm. The Canted Cosine Theta (CCT) superconducting magnet had been well developed recently in particle accelerators and proton therapy facility with the advantages of low higher-order harmonics (quadrupole, sextupole, etc.) and the low cost. However, the large aperture and curved structure make it difficult to guarantee the field quality for the combined function magnet. Additionally, due to large aperture, the Lorentz forces cause more structure problem on superconducting coil which has negative effects. To overcome the problems above, the optimal design of combined function CCT magnet has been presented in this paper. Based on finite element method (FEM) in OPERA and ANSYS, the electromagnetic and structure optimal design have been finished with new structure of superconducting cable and bobbin. Then, the tested coil winding and bobbin manufacture are under the way.
The Facility for Rare Isotopes Beams (FRIB) employs an advanced fragment separator for the efficient production and purification of the in-flight rare isotope beams. At the first stage, the incoming primary beam from a production target experiences an initial separation from the products of interest. A large phase secondary beam needs to be purified and focused with magnetic multipole elements having up to third-order image aberration correctors. Therefore, cold iron quadrupole triplet (CIQT), in which sextupoles and octupoles are nested and independently operated, have been designed and built for use in a vertical pre-separator that is followed by post-separator stages and beam distribution system for experiments. In this paper, we present the results of cooldown, energization, and field mapping of CIQT for the pre-separator. Based on the test results, the magnetic field gradient and effective length were calculated and compared with the simulation results. Harmonic analysis was also carried out to evaluate the magnetic field quality and compare to the requirements. Discussion includes the premature quench behavior and training process comparison between as-individual and as-assembled CIQT.
Bilfinger NOELL GmbH is the contractor of GSI for main SIS100 magnets.
The production of the 111 SIS100 Dipoles is completed and all dipoles are delivered to GSI. We will give a summary on the production of these magnets highlighting some of the major challenges. Production workflow, individual production steps and results from quality measurements at Bilfinger Noell are presented.
In the frame of contract for the 83 Quadrupole Doublet Magnets (QDM) we have delivered the First of Series (FoS) QDM in November 2019 and it was tested at GSI successfully. We will give an overview on test results during production as well the special challenges of this first QDM. Meanwhile we have started with the series production of the QDMs. While the SIS100 Dipole production was a real series production of magnets, the challenge of the QDM productions are linked to the high degree of variations between the individual QDMs and the necessary additional logistics.
Bilfinger Noell also currently manufactures the 12 so called Missing Dipoles (MDP). These systems are similar to the SIS100 Dipoles and we will report on the status of this production here, too.
Magnetic fields occupy an important position in many physics studies, and control of minute magnetic fields is important for measurement items in many physics experiments. Superconducting accelerating cavities can generate high electric fields with a small amount of high frequency power. However, the material niobium is a type-II superconductor, which traps the environmental magnetic flux in the material during the superconducting transition, resulting in loss during operation. Shielding from a weak magnetic field is essential. However, high magnetic permeability magnetic materials for very low temperatures are expensive, not easy to handle, and increase costs. Therefore, we are proceeding with research focusing on magnetic shields that utilize the diamagnetism of superconducting materials, rather than the magnetic flux absorption phenomenon caused by high magnetic permeability materials.
This solenoid will be used in new spectroscopy method in less researched THz range. The method is founded on using of a free electron laser with high spectral power radiation which can be smoothly tuned in desirable range of spectrum. The objects of research of this method are fast processes in physics, chemical and biological reactions. Uniform magnetic field of ~ 6 T value in the research area can considerably increase possibilities of this method. The magnetic field will modulate free induction decay radiation of molecules on characteristic frequencies of the Zeeman splitting that gives more possibilities of identification of molecules having even weak magnetic momentum.
The superconducting solenoid was designed to have 6.5 T in with diameter of 102 mm and with length of 0.5 m. The warm access diameter is 80 mm. The SC wire with Cu/NbTi = 1.4 was used. The passive quench protection methods were realized in the design. The uniformity of the field was obtained by using the iron yoke and by additional side windings. The cryogenics of the solenoid is based on two Sumitomo HI cryocoolers. It is a dry design.
The solenoid was tested up to 7.5 T in the cryostat. The result is higher due to 3.6 K operating temperature. Magnetic field was measured as in bath cryostat as in the design cryostat – the results were according design calculations. The more details will be presented in the poster.
The ISOLDE facility at CERN delivers the largest range of low-energy radioactive beams, exploited by several detector systems to investigate nuclear properties from the stable isotopes to the very exotic systems close to the neutron or proton drip lines. These studies can largely benefit from the use of a high-resolution fragment separator. To achieve this goal, an innovative spectrometer based on a compact superconducting (SC) ring, the Isolde Superconducting Recoil Separator (ISRS), is being studied. The ring will operate as an isochronous non-scaling fixed-field alternating-gradient (FFAG) system based on Canted-Cosine-Theta (CCT) magnets. These multifunction magnets have two alternating-gradient quadrupoles nested inside an outer dipole. According to preliminary beam dynamics studies, the dipole must sustain a maximum field of 2.2 T. A maximum quadrupole gradient of approximately 14 T/m will guarantee orbit stability for heavy ions with a maximum kinetic energy of 10 MeV/u. Fine tuning of the CCT magnets and the FFAG optics will provide very large solid angles > 100 msr and momentum acceptances Δp/p > 20%.
In this paper we present, the magnet designs and their optimisation.
A cost reducing active stray field superconducting coil shield design has been introduced to be able to remove approximate 4000 kg of yoke iron and the complexity of building a tightly curved yoke.
Future high energy particle colliders are under study, with a first goal of 16 T dipoles, which is believed to be the practical limit of $Nb_3Sn$ magnets. Another more ambitious goal is to aim for 20 T dipoles. This very high field would require High Temperature Superconductors (HTS), such as Bi2212 or REBCO. Their substantially higher cost necessitate anyways the use of Nb3Sn for an affordable accelerator application. Therefore, hybrid designs can be proposed, where the HTS are used in the high field (16-20 T) area, and $Nb_3Sn$ are used in the low field (<16T) area. Rectangular block-coil designs are particularly well adapted to this concept, since the separation between high field and low field can be made parallel to the cable turns, inside each layer of the coil. However, the large forces accumulating on the cable turns generate a high transverse stress detrimental to the coil. The paper presents a conceptual Hybrid Nb3Sn-HTS design generating 20 T in the bore with margin, using a block-coil concept. Several conductor options are discussed. The design also proposes stress-management solutions to deal with the large stress developing in the coils.
R2D2, the Research Racetrack Dipole Demonstrator, is a short model being developed within a collaboration between CEA Paris-Saclay and CERN aimed at developing key technologies for future high field 16 T $Nb_3Sn$ magnets for particle colliders. In the particular case of block-coil designs, two different cable grades are wound in the same coil layer, in order to maximize the current density, therefore to minimize the size of the magnet and the use of superconductor. One of the most challenging technologies with this grading concept, is the connection between two cables grades. CEA Paris-Saclay has proposed a concept of external joints, for which the cable exits are guided outside of the coil to perform the connections between the cable grades. The R2D2 project is aimed at demonstrating this technology in a representative demonstrator magnet, while simplifying and reducing the risks when possible, as an intermediate step towards 16 T magnets. In particular, the magnet is composed of single-layer racetrack coils, mainly to reduce the use of conductor and simplify some fabrication steps. However, the complexity inherent to the external joints requires a special focus in the design of the coil ends. To do so, the design of the magnet has been performed using a combination of CAD (Computer Aided Design), magnetic and mechanical 3D FEM (Finite-Elements Models). This paper will explain the design choices leading to a safe operation of the magnet in terms of peak fields and peak stresses. In particular, different strategies for the mechanical support of the coil-ends will be presented.
For future 20+ T accelerator type magnets, ReBCO tape based conductors are ideal for their capability of carrying high current densities in high magnetic field. At CERN, demonstrator dipole magnets using ReBCO conductor are being developed in order to study the feasibility of this technology. A key problem in such magnets is how to realize the coil ends when using ReBCO tape conductor without causing degradation due to coil winding, coil processing, cool down and operation. Here, the design of a new short racetrack magnet is presented, comprising two poles equipped with so-called Cloverleaf coil ends. Essentially the Cloverleaf geometry allows the tape to be passed over the particle beam pipe without any hard-way bending to avoid tape damage. An additional advantage is the relatively short length of the coil end sections when compared to so-called flared ends. The ReBCO coil is wound with a stack-cable comprising two ReBCO tapes by which the ReBCO layers are facing each other. For quench protection, the coils use non-insulated winding technology, allowing the coil current at quench to bypass local hot spots by flowing transversally through the winding pack. Progress on the electromagnetic and mechanical design of the magnet is reported in this paper.
High energy physics research will need more and more powerful circular accelerators in the next decades, in order to explore unknown regions of particle physics. It is therefore desirable to have dipole magnets able to produce the largest possible magnetic field, in order to keep the machine diameter within reasonable size. A 20 T dipole is considered a desired achievement, since it would allow the construction of an 80 km machine, able to circulate 100 TeV proton beams.
In order to reach 20 T, a hybrid Low Temperature Superconductor (LTS) - High Temperature Superconductor (HTS) magnet is needed, since LTS technology is presently limited to ~16 T regarding accelerator magnet design. In this paper, we present the design of 6 layers 20 T hybrid dipole magnets using Nb3Sn (LTS) and Bi2212 (HTS). We show what different design choices can be done to optimize the size, the cost, the performance, the mechanic and the protection of the magnet, presenting different cross-sections that are focused on the optimization of a specific parameter.
Recent years have seen significant development of high-temperature superconducting Bi-2212 wires and magnets in the US with record critical current density, record wire lengths and record performance model magnets. A dozen racetrack coils have been produced within the LBNL subscale accelerator magnet program using Bi-2212 Rutherford cables, including the record performance of RC6, which carried 8.6 kA and operated safely at a wire engineering current density of 1000 A/mm2. In addition, a 4.7 T common coil dipole magnet RC7n8 was made from twisted industrial wires. In this talk, we will examine coil fabrication technology based on a canted-cosine-theta magnet technology with stress management capability for achieving dipole fields greater than 15 T, and present results of prototype dipole magnets including quench characteristics and field quality. Performance will be examined in the larger context of applicability of Bi-2212 for the next generation high energy physics colliders and other applications. We will also discuss the efforts to increase the Bi-2212 coil length to ~1 m long using the overpressure processing heat treatment for the first time.
The cross-section design of cos $\theta$ superconducting magnets is historically developed in a two-step process: initially, the coil geometry is defined on the basis of magnetic optimizations; then, the structure is designed around the coil. The first step searches for the best coil cross-section maximizing the magnetic field, margin, field quality and conductor efficiency. The latter step aims at limiting the coil stresses and deformations. However, the coil design, defined with the initial magnetic optimization, can influence the mechanical behavior of the magnet, altering, for example, the peak stress during operation. As the critical current is a function of the applied strain, the mechanical implications of the coil cross-section design can limit the achievable performance. In this paper we propose an integrated optimization process that targets the peak stress on the conductor in addition to the magnetic objectives. The results are presented for two sample cos $\theta$ dipoles: a 2 layer and a 4 layer Nb3Sn magnet design aiming at ultimate conductor performance.
This paper presents the basic engineering design, analysis, and plan to build and test a “Proof-of-Principle” overpass/underpass (also called cloverleaf) high field block coil dipole. Block coil configurations are appealing for their simplicity in the body of a magnet, but less so in the ends of the blocks that must be lifted to clear the beam tube. This lifting —which typically is in the hard direction of the broad cable — must be very gradual, to avoid conductor degradation (especially Nb3Sn or HTS) from excessive strain, making for ends that are undesirably long. The overpass/underpass or cloverleaf end geometry is designed to overcome the above-mentioned shortcomings. The conductor clears the bore tube at the ends by replacing the hard-way bends by a gentle twist in a 270° turn. The design produces ends that are shorter in length as compared to those with lifted end designs. Moreover, the strain on the cable in the ends also remains low, although the geometry of the ends becomes more complex.
This work has been carried out under a Phase I Small Business Technology Transfer (STTR) program between the Particle Beam Lasers, Inc. (PBL) and the Brookhaven National Laboratory (BNL). A specific proof-of-principle demonstration will be carried out in Phase II for the pole coils in a 2-in-1 common coil dipole reaching ~11 T. The dipole DCC017 has a large, easily accessible open space in which the new coils can be inserted and tested as an integral part of the magnet without any need to disassemble and reassemble the original magnet. Once the design is successfully demonstrated, the overpass/underpass end geometry is likely to be used in other block coil designs besides the common coil. In fact, the present 20 T HTS dipole program at CERN is based on the overpass/underpass or cloverleaf design.
The Deep Underground Neutrino Experiment (DUNE) at Fermilab is one the most challenging next-generation experiments in the field of neutrino physics. It will feature two detectors for a detailed study of neutrino oscillations using an unprecedentedly intense neutrino beam. The two detectors are a Near Detector located on the Fermilab site, 574 m away from the neutrino generation, and a Far Detector in South Dakota, 1300 km away. Among the three elements of the Near Detector, designed for the best understanding of the neutrino beam and neutrino interactions on argon, ND-GAr is a High-Pressure gaseous Argon TPC surrounded by a calorimeter, in a 0.5 T magnetic field. The needed magnetic field is transverse to the neutrino beam direction and the solenoid will have a 7 m diameter, 8 m long warm bore. To minimise the material budget along the particle path a thin superconducting solenoid with a partial yoke has been designed. The design of this magnet is tightly bond with the mechanics of the detector, resulting in an unprecedented design. In this paper we present the up-to-date magnetic design and a detailed study for the mechanical integration for this magnet.
The CERN EP department has launched an R&D program on the next generation particle detectors and magnets. In this context a superconducting magnet is designed for a multi-purpose beam test facility to be used for detector prototype testing. The facility will serve as a replacement of the existing M1 and Morpurgo magnets that have been in operation since the late 70s in the experimental north area at CERN. The facility is envisioned to serve all the testing requirements for the following 50 years.
The magnet will have a central field of 4 Tesla with a free-bore diameter of 1.4 meters. The magnet will take either the form of a split solenoid, allowing dual use as a dipole or solenoid, or a skateboard tilted racetrack design, allowing dipole function. It is envisioned to use Niobium Titanium Rutherford cables with a Nickel-Aluminium stabiliser. The operation temperature will be 4.5 K with liquid Helium cooling. The stray fields are being minimised to stay below 15 mT at a distance of 5 m from the central point. The magnet will also incorporate bespoke Persistent Current Switches studied and developed in-house and well as possible inclusion of cryo-coolers.
The North Area Superconducting Magnet facility is an important project for the testing and development of future detectors and electronics at CERN, specifically components that will be utilised in the Future Circular Collider (FCC), the new 100 km collider to be built at CERN. This innovative facility therefore will serve as an important step for the future activities of CERN and High Energy Physics.
In the framework of the consolidation of the Antiproton Decelerator (AD) Target Area it was decided to replace the two original normal conducting quadrupoles used for the final focussing of the proton beam before the target by two 1-m-long quadrupoles based on permanent magnet technology. Their gradient is adjustable from 35 to 45 T/m inside an aperture of 60 mm in diameter. This paper describes the design, manufacture, assembly and magnetic measurements results of these high gradient quadrupoles.
The CSR external-target experiment (CEE) will be China’s first self-developed nuclear research experimental facility operating in the GeV regime based on the large-scale scientific facilities HIRFL-CSR. One of its core components is a dipole magnet with a large gap and wide acceptance. Unlike traditional large spectrometer magnets, the physical target of the CEE requires a highly stable, large-scale, uniform magnetic field. To achieve this design goal, the study introduces a 9-parameter model of the iron yoke structure. Multiple methods are employed to optimize both the air trim slot structure and the shimming structure. After several rounds of optimization, a design which can provides field uniformity less than ±0.6% within a region of 0.9 × 1.0 ×0.8 m (length × width × height) is proposed. The overall size of the magnet will be around 3.2 m long, 4.4m width and 2.9 m high. The aperture in the beam direction measures 2 × 1.2 m. The gap of the magnet is 1.3 m, and the yoke weighs 185 t in total.
The magnet system of the Muon to electron (Mu2e) experiment at Fermilab consists of three solenoid magnets: the Production Solenoid (PS), the Transport Solenoid (TS), and the Detector Solenoid (DS). The s-shaped TS consists of 52 superconducting coils which are grouped in units of 2-5 coils. The units undergo an acceptance testing campaign which includes a liquid helium temperature cold test and room-temperature magnetic axis measurements using a vibrating stretched wire. In the cold test, units are energized to 120% of nominal current to study quench performance and splice resistance. The magnetic axis measurements ensure the coils are aligned within the tolerances required for efficient muon transmission through the TS. The TS magnetic model is updated with the as-built coil positions to ensure the magnetic requirements for the experiment are met. Results from all units and the as-built magnetic model will be presented.
PERC is a novel experiment in the field of low energy particle physics under construction at the FRM II in Garching, Germany. The project aims to investigate angular correlations and energy spectra in the β-decay of free cold neutrons.
PERC consists of 13 superconducting solenoid coils. In a 6 m section of the 8 m long decay solenoid e- & p+ form neutron decay are accumulated. At the end of the long solenoid, a set of tilted coils (bending coils) separates the e- & p+ from the residual uncharged neutrons, which are absorbed by a beam stop. Downstream of the bending coils, several coils producing a higher and tunable magnetic field in the range from 3 T to 6 T act as magnetic filter on the angle of the e- & p+. Downstream of these selector coils, another tilted coil guides the e- & p+ back to the original horizontal axis and further to the detection area by a solenoid creating a lower magnetic field. The novel design and the high magnetic field of PERC are the basis to improve measurement accuracy by an order of magnitude. PERC is supported by the Priority Program SPP 1491 of the DFG.
In addition to the superconducting coils, the PERC system consists of the cryostat, the central warm bore (an ultra-high vacuum chamber to house the neutron guide and beam stop) and several auxiliaries such as power supplies and cryogenic feeding turret.
The system has a total length of ~ 12 m and weighs 15 tons, the cold mass weighs 6 tons. It contains about 50 km of NbTi wire and is cooled by liquid Helium. The design and manufacture of the PERC system has been commissioned from the PERC collaboration (TUM/DFG) to BNG. This document presents the manufacture of the superconducting coil-systems.
The Mu2e field mapping system is designed to produce high accuracy field maps of the detector solenoid used in the experiment. The data acquisition system is mobile and uses a self-propelled mapper with rotating arms equipped with 3D Hall probes. The measurements require not only accurate readouts of magnetic field, but also accurate location of all the Hall probes when taking data. The latter is accomplished by using the laser tracker to measure positions of several retroreflectors on the field mapper during data acquisition. The measurement process requires scanning the whole space inside the large solenoid and takes many hours to complete, which necessitates its full automation. The automation software includes control of the mapper, readout of Hall and NMR probes and control of a laser tracker, including prediction of retroreflector positions and execution of quality control checks. The software architecture and data acquisition hardware of the field mapping system are described, with special attention to control of the laser tracker and its integration with the system.
Bilfinger NOELL GmbH is active in the field of superconducting magnets for particle traps. We report on two types of traps: a magnet for a neutron trap and several magnets for antiproton traps.
Bilfinger NOELL has developed, manufactured and delivered a large volume magnetic storage device for ultra-cold neutrons to Technical University of Munich in June 2020. The magnet of PENeLOPE (Precision Experiment on the Neutron Lifetime Operating with Proton Extraction) serves to measure the lifetime of the free neutron with unprecedented accuracy. The magnetic and mechanical design as well as the manufacturing and testing is described. The NbTi superconductor coils are cooled with liquid helium and the magnet provides high magnetic field gradients at high field levels, built into a complex cryogenic structure as the neutrons are trapped in vacuum.
The magnets for antimatter-traps, usually Penning traps, request in particular a high homogeneity in a long cylindrical volume. The magnets designed and built throughout the last few years all have been “cryogen-free”, i.e. with G-M or pulse-tube cryocoolers and conduction cooling. There are two magnets that allow being transported while operating at full field. Therefore, active and passive magnetic shielding is foreseen to reduce magnetic fringe field to a very low level.
GSI (Darmstadt) together with a large international scientific community, among the members of which is the Budker Institute of Nuclear Physics, are engaged in the development of equipment and the construction of the CR (Collector Ring), which is part of the FAIR project.
Detailed calculations of CR in the isochronous mode show that the inhomogeneity of magnetic fields in dipole magnets leads to a deviation of the time of flight of particles by almost the same relative value. The quality of the field in CR dipole magnets, at best, can be improved to a level dB/(B(x))~2·10^(-4). In general, there is no need for the field quality of each dipole to reach such a high level, since the field integral must be compensated for over a full revolution in CR.
The most critical are the deflections of particles with different momentum. The effect introduced by different multipole distributions at different heights in a dipole magnet will be averaged by vertical betatron oscillations. But, in the case of a closed dispersion line, purely longitudinal contributions will not be averaged, and therefore they will be the largest. This means that the integral of the multipole component in one complete revolution must be corrected with high accuracy.
The sextupole and octupole correctors are already included in the CR. But the typical field distribution in an H-type magnet is characterized by a strong decapole component. However, the value of this component cannot be calculated in advance with the required accuracy, since it will change when the magnet is turned on. Therefore, a decapole corrector is required in CR. Otherwise, it will not be possible to achieve the required level of isochronism.
It was decided to use free-standing decapole magnets with a gradient integral of 182.33 T/m^2 and an integral decapole harmonic of -6.75·10^(-4).
Construction of a new primary proton beam line, which is called B-line, started in 2013 at the J-PARC Hadron Experimental Facility. The B-line is branched at the middle of an existing primary proton beam line (A-line) in the beam switching yard (SY), which is the connecting tunnel between the Main Ring (MR) and the Hadron experimental hall (HD-hall). At the branching point, about 0.1% of the primary beam is kicked off at 5 degrees using a Lambertson magnet and two septum magnets. The Lambertson magnet has a field free hole in its yoke. The proton beam that goes through a field region is separated from the A-line is extracted to the B-line. The rest of the beam that goes through the field free hole is transported through the existing primary beam line. Since a significant beam loss as much as 420W occurs at the edge of field free hole, the magnets near the Lambertson magnet are operated under a very high radioactive environment.
We have developed a “mini-chimney system” regarding easy maintenance of those magnets more than 1mSv/h on contact. The mini-chimney means a vertical tower of approximately 1 m in height. The tower is comprised of water pipes, power electrodes, and signal cables for safety interlock. Those can be easily connected and disconnected at the top of the chimney on the ceiling iron shields. In this paper, we summarize the maintenance scheme developed for the B-line, as well as the design of B-line.
In May 2020, the first proton beam was successfully extracted to the B-line by means of the Lambertson and the septum magnets. Up to now, the 1010 protons per 5.2 sec accelerator cycle shot have been available.
Abastract: Currently, a new gas-filled recoil separator Spectrometer for Heavy Atoms and Nuclear Structure 2 (SHANS2) is being developed and designed at IMP (Institute of Modern Physics, Chinese Academy of Sciences). It will be used to synthesize and study the superheavy elements, including their physical and chemical properties. The SHANS2 include two dipole magnets and three quadrupole magnets. The big gap/ aperture, wide good field regions, high magnetic field and high integral field homogeneity give rise to a big challenge for the design and measurement of these magnets. In this paper, the optimal design and magnetic field calculation of the SHANS2 magnets are performed by using the code OPERA based on the pole ends chamfering and pole face shimming approaches, and measured the magnetic field distribution and integral field homogeneity in the range of good field regions by using Hall sensors under room temperature. The simulation results show that the optimization results of these magnets satisfy the design requirements, and well agree with the measurement results.
FASER, the ForwArd Search ExpeRiment, is designed to search for new, yet undiscovered, light and weakly-interacting particles and study the interactions of high-energy neutrinos. Three dipoles are required to achieve sufficient separation of pairs of oppositely charged, high-energy Standard Model particles originating from decays of new physics particles. The first magnet is 1.5-m-long and surrounds a decay volume in the upstream part of the detector, the following two magnets are 1-m-long each.
The dipoles are of Halbach array type, and have an aperture of 200 mm in diameter with a minimum required magnetic field at the centre of 0.55 T. Due to tight space constraints, a design based on permanent magnet technology was proposed. This paper describes the design, manufacture, assembly, magnetic measurement and installation in the LHC of these large dipoles.
We have been developing radiation-resistant warm magnets insulated by a Cyanate ester resin. We developed a glass fiber cloth prepreg tape using Cyanate-ester pre-polymers supplied by Mitsubishi Gas Chemical Corporation INC. The proton beam irradiation test was carried out for the evaluation of the radiation hardness. We prepared cured resin samples of Cyanate ester, Bismaleimide Triazine (BT), and epoxy resins using a same glass fiber cloth. The 70 MeV proton beam was irradiated to the resin samples up to $10^9$ Gy at Cyclotron and Radioisotope Center, Tohoku University. The result of the tensile test after the irradiation showed that the radiation resistance of the Cyanate ester resin was almost same as that of the BT resin and more than 10 times as high as that of the epoxy resin. We also developed a Cyanate-ester putty to use in a coil molding. We performed a curing test of a coil mock up made of stacked hollow conductors insulated with the Cyanate-ester prepreg tape and putty. We successfully cured the coil mock up without causing thermal runaway.
The storage ring of Hefei Advanced Light Facility(HALF) will employ high-gradient quadrupoles for the sake of diffraction limit, the typical gradient values of them arrive at 60-80 T/m, the saturation on the pole tip is very serious. Moreover, the gap between two adjacent poles should have a certain interval to accommodate light box, which is equal to reduce the pole width. All the cases increase the designing difficulty of quadrupoles. In this paper, the Non-dominated Sorting Genetic Algorithm(NSGA-2) and Gauss-Newton algorithm(GN) are both adopted to find a proper pole tip profile, the typical multipole components reach the order of 1.0E-6.
The construction of European demonstration power plant (DEMO) aims to employ high temperature superconductors (HTS) as the main magnets to avoid the requirement of large amounts of helium for the cooling system. The central solenoid coils which is transported with AC current in the reactor should be ensured of their operation condition to avoid quench phenomenon under a high temperature environment. In this case, an HTS central solenoid winding pack which consists of (RE)BCO coated conductors has been designed. AC loss characteristics of the winding pack have been analyzed by using the finite element method which is based on the T-A formulation and the integration approach J-model. Outcomes calculated by the two methods show a better consistency. The results also indicate that eddy-current loss in the silver layers and copper layers of coated conductors in the winding pack has exceeded the hysteresis loss in superconducting tapes, which is of great significance to the design of HTS central solenoid coils for the EU-DEMO fusion reactor.
Keywords: AC Loss, CS winding pack, fusion magnets, HTS modelling
Recently, the development of the concept project of the high magnetic field (HMF) tokamak continues in the Russian Federation. The value of the magnetic field on the plasma axis in the device is about 8 T. The maximum field on the winding of the toroidal field coils is about 16 T. The generation of a high magnetic field in a limited space of tokamak-type device with a given aspect ratio-R/a≈3.77 (R=2.15 m - the big radius of the tokamak, and a=0.57 m - the plasma "radius") leads to a significant increase in the engineering current density in the toroidal field coils. The mechanical stresses in the magnet increase accordingly. The balance between the required amounts of superconductor (HTS tape), construction material (steel), stabilizing material (copper, aluminum) and refrigerant (helium), which can be achieved in devices with a lower maximum field on the winding – Bmax≤12 T (ITER, DTT,...) becomes difficult to achieve. At the same time acceptable parameters of protective energy output should ensures, namely the maximum electrical voltage Umax≤+/-5 kV and the temperature in the "hot spot" - Tmax≤200 K. In addition, it is necessary to minimize heat losses in the stationary operation mode of the tokamak, which significantly depend on the number of current leads used in the toroidal magnet. Obviously, in each particular case, this task solves individually. In this paper, we propose original possible solutions of the problems listed above. A "cable-in-conduit" type of conductor (CICC) uses in the TRT toroidal magnetic system. The HTS cable consict of parallel non-twisted tapes, which are oriented mainly parallel to the vector of the toroidal magnetic field. The design of the conductor is developed accordance to the requirements for a real device and differs from the previously proposed by more compact dimensions.
Compared to low temperature superconductor (LTS) based fusion conductors, the use of high temperature superconductors (HTS) offers the possibility to increase the magnetic field strength in future fusion reactors, allowing higher flux swing or even more compact fusion reactors. REBCO, the most promising HTS material, is commercially available as coated conductor tape. Opposed to LTS wires, HTS “macro strands” are formed from HTS tapes. One such macro strand is the HTS CrossConductor (HTS CroCo), in which HTS and intercalated copper tapes of two different widths are combined to a cross-shaped stack embedded in a round solder matrix. Several of those macro strands are assembled to a HTS cable in conduit conductor (CICC).
Due to the fundamentally different geometry of HTS cables and the temperature dependency of material parameters, the electrical, thermal and mechanical properties differ between HTS and LTS CICC. This leads to a drastically different behavior during quench incidents, e.g. a slower normal zone propagation velocity. Through this, local hot spots can develop, which may not be detectable with common voltage-based quench detection devices. Therefore, investigations on the quench behavior of HTS CICC are of great interest for future HTS-based fusion magnet concepts.
This work describes the sample design, manufacturing procedure and pre-test results of the KIT sample for a Quench Experiment on HTS CICC. The Helium-cooled conductor consists of a copper stabilized HTS CroCo triplet, targeting for operation around 15 kA at 6 K in a magnetic background field of 11 T. It features multiple sensors to record voltage drop, as well as the coolant, jacket and strand temperatures. The purpose of this sample is to observe and understand quench propagation in HTS fusion conductors and to provide experimental data to qualify and improve thermal-hydraulic models of quench in HTS CICC for fusion applications.
Significant progress has been made recently in the U.S. Fusion community to develop a strategic plan to enable engineering design and construction of a Fusion Pilot Plant (FPP). Princeton Plasma Physics Laboratory (PPPL) is working on developing high performance HTS conductors for fusion, and partnering with the U.S. industry, we are evaluating feasibility and affordability of cable on round core (CORC) that can be used for next-step compact fusion tokamak facility. High current density achieved by CORC cable based model coil recently tested at NHMFL motivated its consideration for low cost, reduced size fusion magnet application. This is of interest to PPPL because it is directly scalable to tokamak central solenoids in terms of required double flux swing for plasma startup operations. Working with Advanced Conductor Technologies, we design and build a two-layer CS model coil using CORC cable to demonstrate its direct applicability for Compact Tokamak Test Facility such as the Fusion Nuclear Science Facility and the U.S. Sustained high-power density tokamak facility. The 250 mm diameter CS model coil will be wound by a two layer CORC cable and can generate 6 T at 4.2 K when operated at 28 kA.
Nuclear fusion, regarded as a promising and infinite energy resource, is under rapid development. Associated with multiple essential advantages, such as carbon free, low land use, unlimited fuel and very low manageable waste, a number of high quality and multinational fusion projects are under construction. Tokamak, as an essential device for plasma confinement, is a key focus investigated globally. Designs of tokamak are various and they are mainly made of normal conductor (e.g. copper), low temperature superconductor (LTS) and high temperature superconductor (HTS). The tokamaks made of normal conductors are used for research, since high energy loss and heat only allows operations to last few seconds. LTS and HTS tokamaks are expected to be able to operate commercially in steady consistent operations, including ITER, DEMO, EAST, KSTAR for LTS and SPARC, CRAFT, Tokamak Energy for HTS.
This paper would focus on HTS tokamak magnets and present a novel design for the spherical tokamak developed for commercial operations. The novel design will solve several ground challenges including HTS-HTS joints for demountable structure, magnet control for auto plasma confinement, demand for high power supplies, and reliability monitoring.
Over the past decade High Temperature Superconductors (HTS) have gained interest for use in large scale coils for fusion applications. It is necessary to use a cable consisting of multiple parallel tapes in order to reduce the coil's inductance and to mitigate point defects. In many fusion and also non-fusion cable concepts the tapes are often transposed to reduce AC-losses. However, it has been theorized that this is not needed from an AC-loss perspective. Since this unnecessarily complicates coil manufacturing, it has been proposed at Tokamak Energy (TE) to use a non-twisted stack of tapes, a technique which has already been successfully applied to smaller solenoids. As a step towards larger more fusion relevant coils, a toroidal magnet named Demo4 is currently under construction at TE, using a similar stacked tape approach. To perform an in-depth analysis of AC-losses in Demo4 and future magnets, a new electro-magnetic and thermal network model named Raccoon was developed at Little Beast Engineering. This model is capable of calculating 3-dimensional screening current, coupling current and transport current effects at tape level detail in a full-scale magnet. Raccoon can also be used for quench analyses. In this paper the calculated time-dependent current distribution and corresponding losses in the Demo4 coil-set will be presented, and the effects of the non-transposed cable will be investigated.
High temperature superconductor (HTS) technology has been widely studied for various superconducting devices due to the capability of high magnetic field generation and its relatively strong strain resistance. Fusion magnet engineers also have made efforts to employ the HTS technology to their magnets, especially focused on the development of HTS cable-in-conduit conductor (CICC) such as twisted stacked tape conductor (TSTC) and conductor on round core (CORC) cables. Both cable schemes are based on the twisting of HTS tapes to reduce inductance variation and AC losses within magnet. In recent study, however, it was shown that twisted conductor decrease inductance variation only a few percent compared to the non-twisted counterpart, lower AC losses even up to half but still in the same high order of magnitude. In this study, we suggest an alternative solution that uses a long copper tape laminated with several HTS tapes, having three main advantages of: 1) mechanical robustness without the inherent mechanical issues resulted from the residual bending strain in the twisted HTS cables; 2) no limitation of winding length despite the relatively short piece length of HTS tapes; and 3) high thermal conductivity that can minimize the temperature gradient within the entire magnet even in conduction cooling condition. Technical issues for the development of HTS TF coils using the proposed copper-laminated long length HTS tapes and cables will be discussed in detail.
Acknowledgement
This work was supported by R&D program of “code No. CN2101” through the Korea institute of Fusion Energy (KFE) funded by the Government funds.
Tokamak is a feasible device to keep the fusion reaction by magnetic confinement method. The high DC current is loaded on toroidal field (TF) magnets to generate high field for plasma confinement. However, this load may also bring heat loss for normal conductor and the risk of melting. High temperature superconductor has great potential for TF magnets due to its zero resistance and high current density under high field. No-insulation (NI) coil without turn-to-turn insulation allows current flowing thorough turns, which leads to excellent electromagnetic and thermal stability. In this article, we present a scheme of HTS NI coil for TF magnets manufacturing. The tension controlling[1] method is used during winding process for better performance. Then, a charging test is carried out with TF magnets immersed by liquid nitrogen (LN2). The calorimetric method is selected to measure the excitation loss by the boil-off rate of LN2[2]. After that, a 3D finite element model with rotated anisotropic resistivity[3] is established to analysis charging process. Both excitation loss and charging time will be discussed. The conclusion of this article will help the design and optimization of cryogenic system.
Key words: TF magnets, No-insulation Coil, Calorimetric method, Excitation loss, finite element model.
[1] Zhang Y., Tang Y., et al. 2018 Investigation on performance of no-insulation coil considering the influence of stress distribution on radial characteristic resistivity IEEE Transactions on Applied Superconductivity 28 1
[2] Weng F., Zhang M., et al. 2020 Fully superconducting machine for electric aircraft propulsion: Study of ac loss for hts stator Superconductor Science and Technology 33 104002
[3] Mataira R.C., Ainslie M.D., Badcock R.A., and Bumby C.W. 2020 Finite-element modelling of no-insulation hts coils using rotated anisotropic resistivity Superconductor Science and Technology 33 08lt01
This paper describes a simple, compact and cost-effective capacitor pulse power supply, which only uses a single magnet coil and two capacitors of different voltage and capacity levels to form a special circuit structure. It can realize the pulse magnetic field similar to the flat top wave, so as to meet some scientific experiments that require higher magnetic field strength and stability. Through the reasonable design, the rising edge of the magnetic field waveform is accelerated, the stability of the waveform top is maintained for a relatively long time, and the energy of the magnet is rapidly transferred and released by controlling in the falling stage of the magnetic field. This design reduces the heating of the magnet due to heat accumulation, thus shortening the cooling waiting time of the magnet and improving the service life of the magnet.
Flat-top high magnetic field (FTMF) is a significant research method for physics, chemistry, biology and other scientific fields with the demands for higher magnetic intensity, longer flat-top pulsed width and a lower ripple. To meet these demands, a new FTMF system based on multiple-capacitors power supply has been realized at the Wuhan National High Magnetic Field Center in March 2021. However, the ripple of the magnetic field was 3000 ppm. In order to reduce the ripple of the FTMF, an active power compensator consists of lead-acid battery power supply, active power filter and compensatory magnetic coil is designed in this paper. A self-adaptive PI controller with the fuzzy control method is adopted to improve the controlling accuracy. The MATLAB/Simulink platform is used to establish the model of FTMF system and the preconceived 60T/70ms flat-top pulse with ripple less than 200 ppm is generated.
Large-size aluminum alloy rings are widely used as connector, transition ring and reinforcing structure in aerospace and other fields. Their performance determine the service life, assembly accuracy and reliability of the equipment directly. However, the residual stress introduced during the manufacturing process lead to the structural instability and poor mechanical properties of the aluminum alloy rings. In this paper, pulsed electromagnetic force is used to deform the aluminum alloy rings into plastic state and eliminate the residual stress in the workpieces. Compared with common methods of eliminating residual stress such as mechanical methods and aging methods, this method possesses many advantages. The electromagnetic drive force is a kind of body force and can be controlled flexibly, and its distribution is uniform and unlikely cause the stress concentration of the contact surface. Different from thin-walled tubes used in the traditional electromagnetic bulging process, the size of aluminum alloy rings studied in this paper are much larger and require high machining uniformity. Therefore, higher performance requirements of voltage insulation, inner support and outer reinforcement are put forward for pulsed magnets. Firstly, this paper uses the finite element simulation software COMSOL Multiphysics to design the electromagnetic bulging magnet of large-size aluminum alloy rings with an outer diameter of 720mm, a wall thickness of 60mm, and a height of 60mm. The influence of the number of turns and layers, and the size of the coil wire on the deformation of the workpiece and the stress field distribution of the ring was analyzed. Subsequently, by optimizing the position, thickness, shape and other parameters of the internal epoxy skeleton and the steel support ring, it can meet the requirements of magnet strength. Finally, the designed pulsed magnet can achieve the 2% plastic deformation that is required to eliminate the residual stress of the target rings.
The design and operation of resistive high field magnets require research and development in materials science, power supply engineering and instrumentation. Additionally, their energy efficient operation has become a growing constraint. The French National High Magnetic Field laboratory at Grenoble (LNCMI) is continuously improving its high magnetic field platform in order to satisfy the demands of the user community and to use the high electric power resource in the most efficient way.
We report on recent advances on an energy efficient use of the LNCMI resistive magnets that can reduce energy consumption by up to 20%, for a given user experiment. This saving is possible due to a special architecture of the LNCMI high field magnets: they consist of two independent concentric sub magnets exhibiting different field characteristics, i.e. absolute field value for a given current and spatial field distribution. Both sub-magnets can be powered in an independent way. Thus, the current in each sub-magnet can be tuned to minimize the total electrical power for a target magnetic field requested by the user. This enables energy efficient operation. However, the consequences of strain enhancement on magnet safety and life time due to higher current densities in the inner sub magnet have to be considered.
LNCMI magnet design, power supply and instrumentation teams have recently implemented this innovative operation mode in a collaborative project. We will present its technical realization including electrical power modelling, magnet parameter simulations as well as first benchmark experiments including NMR. Finally, we will discuss the benefits, risks and perspectives in terms of energy efficiency, versatility, field quality and sustainable magnet operation.
The long time thermal stability and radiation resistance of micro composite wires based on Cu-Nb alloy intended for use in devices with high neutron fluxes has been studied. We have demonstrated that for a given niobium content in the alloy (6%), it is possible to keep the ultimate tensile strength higher than 375 MPa after exposed to annealing vacuum treatment at 450 °C up to 3000 hours.
The highly developed interface of FCC(111) and BCC(110) phases in strongly deformed Cu / Nb wires ensures its radiation resistance under irradiation conditions in the range from 1017 to 1020 n/cm2, which is experimentally revealed due to the invariability of the specific electrical resistance of the irradiated samples.
SEM studies of the morphology of niobium fibers at various stages of annealing at 450o C demonstrated the absence of niobium fibers coagulation process, that was initially expected by calculations of the kinetics of this process.
X-ray diffraction revealed the transformation of microstructure that is characterized by the changes in crystallography lattices of the components in the area of interphase surfaces which is caused by the changes in the level of high micro stresses that are a peculiar feature of nanostructured micro composite materials.
Glidcop® is an alumina-particle dispersion-strengthened copper that has good properties combing high mechanical strength and high electrical conductivity. Therefore it has been used as a conductor for ultrahigh field pulsed magnets by the National High Magnetic Field Laboratory (NHMFL). Glidcop® is manufactured by powder metallurgy where powder of Cu-Al alloy and oxidant powder are mixed and heat treated. The heat treatment results in fine alumina particles in copper matrix. Glidcop® is commercially available with three grades, AL15, AL25, and AL60 with increasing Al2O3 content and highest strength.
There are evidences that the alumina particle size and density distributions determine its strength and ductility, which in turn determines its ability of cold forming such as wire drawing. If particle size is large or not evenly distributed, serious issue such as internal cracks or so-called ‘chevron’ cracks could be developed in the wire drawing process. The chevron crack causes wire breakage and, as a result, a very poor production yield. If undetected, these internal cracks may cause premature magnet failure.
In this work, we study the microstructure of Glidcop® materials by electron microscopy and correlate the microstructure with its performance. We identified the aluminum oxide particles to be -Al2O3. We found significant non-uniform distribution of these particles. In addition, the particle size varies widely from a few nanometers to a few microns. We will discuss the implication of these findings.
High-speed forming can greatly improve the forming performance of lightweight sheet and tube components, and has broad application prospects in aerospace and automobile manufacturing. Electro-hydraulic forming (EHF) and electromagnetic forming (EMF) are two common high-speed forming processes. EHF utilizes the underwater discharge to produce a shock pressure as the driving force, while EMF utilizes the pulsed Lorentz force induced in the workpiece as the driving force. In previous studies, these two types of forming processes are typically adopted independently to form lightweight components.
In this work, the two high-speed forming processes were combined to improve the forming capability of aluminum tubes furtherly. Specifically, during the EHF process, additional axial Lorentz forces were generated by the EMF process to control the material flow of the tube, which was achieved by placing two coils at the end of the tube. A coupled numerical model was established to design the system parameters and understand the composite forming process. On this basis, an EMF system with high-strength coils and adjustable pulse width was established, which can provide sufficient and flexible controlled axial Lorentz forces during the EHF process. Then the effectiveness of the developed forming method was verified by conducting a series of experiments on annealed state 6061 aluminum tubes. It was found that compared with the single EHF process, when the composite process of electromagnetic and electro-hydraulic tube forming was used, the bulging depth of the tube was improved by about 25%, while the wall thickness reduction was reduced by more than 30%. Furthermore, the underlying mechanism of the new forming process for improving the forming peformance of tubes was also revealed by numerical simulations.
Aluminum alloy rings are the key component to realize the lightweight and improve the mechanical properties of aerospace vehicles and devices. However, the residual stress is inevitably introduced by uneven heating and mechanical load having a negative effect on the dimensional accuracy and performance of the rings. Therefore, the elimination of residual stress is of great significance to improve the dimensional stability and fatigue strength of the alloy rings. The common methods to relieve the residual stress are mainly annealing treatment and mechanical method. But these methods have some shortages, as their machining ranges are limited, contact stress is too concentrated, and the temperature rise may soften the strength of components. To avoid the above disadvantages, a novel method using electromagnetic driving force to bulge the alloy ring into the plastic phase and eliminate the residual stress is proposed by this paper. Compared with traditional mechanical force, the spatiotemporal distribution and working area of electromagnetic force can be controlled by high field magnets flexibly. The target of this paper is relieving the residual stress of 2 and 5 series aluminum alloy rings with 720mm external diameter, 60mm thickness and 60mm height by pulsed electromagnetic force. Firstly, a high-performance magnet was designed and produced to generate a strong enough electromagnetic force. And it can provide about 2%-3% plastic deformation to the rings after electromagnetic bulging. On this basis, by changing the time constant and damping factor of the circuit, the effect of joule temperature rise and periodic vibration on the relaxation of residual stress are studied. Finally, to verify the effect of this method, hole-drilling method and x-ray diffraction were used to measure the changes of residual stress field in the rings. Moreover, the shape and size of lattice were studied by EBSD to explore the elimination mechanisms from microcosmic perspective.
Abstract: A special necking morphology was observed on Cu-Nb composites after the thermal compression. During the compression process under the heating temperature above 700℃, the nanofibers recrystallized rapidly, and the properties of Cu-Nb composites rapidly attenuated in the dynamic instabilty, and it was difficult to observe the rheological area. During the compression process below 700℃, the strain rate increased at first and reached the peak value, then rapidly dropped. The flow stress was tended to be stable, and the dynamic equilibrium was stable by the dislocation adjustment. Based on the modified Arrhenius-type hyperbolic sine constitutive model, the thermal compression constitutive relationship of Cu-Nb material was established, and the overlap between model calculation and experimental data was higher than 90%. The dynamic material model (DMM) was adopted, and the thermal processing maps of Cu-Nb composites with the strain of 0.2 and the strain of 0.6 were plotted. Based on these maps, materials with the strain of 0.6 prefers to a higher strain rate in the 620℃-750℃ region. However, lower strain rate was beneficial to a better deformability and good hot workability in the 650℃-730℃ region with the strain of 0.2.
Keywords: Pulse magnet, Cu-Nb composites, thermal deformation, constitutive relationship, thermal processing map
Electromagnetic forming (EMF) is an important application of pulsed magnetic field technology, which uses a pulsed magnetic field to induce a Lorentz force on a metal workpiece, thus shaping the workpiece into desired geometry. Compared to conventional forming processes, EMF can significantly enhance the formability of materials, making it a promising option for high strength metal alloys which generally have poor plasticity. However, due to severe mechanical and thermal loadings, the coil shall face a critical concern on its performance life when used for forming high strength metals.
One feasible method to overcome this barrier is using multi-step forming strategy, which replaces a single high energy discharge with multiple successive low energy discharges, thus incrementally shaping the metal workpiece into desired geometry. By using much lower discharge energy, this strategy significantly reduces the coil’s loadings, thus effectively improving its performance life. However, for conventional coil design, the multi-step forming strategy could lead to a very low energy-efficiency, because the in-consistent geometries between the deformed workpiece and the coil would result in a weak electromagnetic coupling between them.
This paper shall overcome the above problem by using a novel field generator, which consists of a solenoid coil coupled with a curved field shaper made of conductive materials. While the solenoid coil creates a primary pulsed magnetic field, the dedicated field shaper further reshapes its spatial distribution toward maintaining a strong electromagnetic coupling between the coil and the deformed workpiece. To validate the effectiveness of the proposed process, we developed a prototype for the process, experimentally characterized its magnetic field distribution, and performed a series of multi-step EMF experiments on aluminum alloy 5083 sheet workpieces.
Electromagnetic forming (EMF) is a metal forming process based on pulsed magnetic field. Instead of using mechanical force as in conventional forming process, EMF shall reshape metal workpiece by using a pulsed Lorentz force which is induced by a pulsed magnetic field. By adjusting the geometry configuration of the field generator (namely, coil), the Lorentz force with manifold spatial patterns can be generated, providing a high design freedom for diverse forming missions. And the introducing new spatial pattern for the Lorentz force by novel coil design is amongst the fundamental problems in EMF research.
In this paper, we introduce a new coil design for EMF process, which could be simultaneously used for the forming mission of both sheet and tubular metal workpieces. To be specific, the proposed design could be used to reshape the local geometry features for a circular hole in sheet metal workpiece, as well as the local geometry feature for the end of tubular metal workpiece. The proposed coil design consists a solenoid coil and a field shaper. While the solenoid coil is the primary field generator, the field shaper is a dedicated tool made from highly conductive materials, which is used to further reshape the spatial pattern of the magnetic field. And the core of the design is to optimize the geometry of the field shaper. We shall firstly detail the design procedure, including an illustration on process principle and an optimization on the system parameter. And then, we shall validate the feasibility of the proposed process by experiments on the developed protype.
Rapid-cycling synchrotrons (RCSs) are desired as the main component of radiotherapy facilities for cancer treatment in order to meet growing patient numbers. Superferric magnets consisting of high temperature superconducting (HTS) coil windings and iron cores are considered to be an effective solution for reducing construction cost and electricity consumption for RCSs. However, superferric magnets generate AC loss in their HTS coil windings when carrying AC current. The leakage magnetic field from the iron core also directly affects the AC loss of HTS windings. It is desirable to develop design methodologies for superferric magnets with minimized AC loss. FEM (Finite element method) is a powerful tool to develop the design methodologies for RSC magnets.
In this work, we carry out 3D FEM AC loss simulations in HTS coil assemblies coupled with an iron core using the T-A formulation. The dimensions of the iron core are based on our earlier published work. The HTS coil assemblies comprise double pancake coils (DPCs) wound with coated conductors manufactured by Shanghai Superconductor Co. with an average self-field Ic of 193 A. The number of DPCs and the distance between the iron core and the inner-turn of the DPCs are varied to investigate AC loss dependence on coil geometry and the influence of leakage magnetic field from the iron core on AC loss of the HTS windings, respectively. It is worth noting that the iron core geometry kept the same for all the simulated cases. The magnetic field and current density distributions of different parts of the HTS coil assemblies are compared to help understand the AC loss generation mechanism of the HTS coils coupled with the iron core.
A 14T physical property measurement system (PPMS) magnet with cryogen free is being developed in Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). Unlike steady-state magnets such as NMR, MRI, the PPMS magnet is required to be excited frequently and the excitation rate usually needs very high, for example in 30min to reach the full magnet field. The fast excitation rate accompanying with cryogen-free cooling method is a great challenge for the stability of the superconducting magnet. The magnet design adopted a combination of Nb3Sn and NbTi superconducting materials to reach the target magnetic field strength 14T within a cold bore 50mm. In order to raise the safety margin, the innermost magnet coil used high-Jc Nb3Sn superconducting wire, and the maximum magnetic field strength in the outside NbTi magnet coils was strictly restrained to be a much low level, for example, less than 5.5 T. With a series of balance, the final critical temperature was at 6.3K, which corresponds to a large power output of the refrigerator about 5W. Another rigorous requirement of the magnet design is a relatively larger homogeneous area 5cm (z)×1cm (d) with homogeneity 0.1% than a common demand Φ1cm, upon which the magnet must use compensating solenoids to elevate the magnetic field homogeneity of the main coils. The overall magnet design pursued a compact coil structure in order to reduce the inductance and thus increase the excitation rate as well. The magnet will be fabricated and assembled into the PPMS system in the future.
We are developing a high-Tc superconducting (HTS) air-core compact cyclotron, named Skeleton Cyclotron, that can accelerate various particles and variable energy for radio isotope (RI) production. The coil system of Skeleton Cyclotron consists of circular and noncircular REBCO coils for high magnetic field strength and high current density. However, the higher operating current density leads to lower thermal stability. No-insulation (NI) winding technique have been proposed as a technology to enable both high current densities and high thermal stabilities. The multiple REBCO coils in Skeleton Cyclotron are applied NI winding technique. The electromagnetic and thermal behaviors in NI coil differs from those in conventional insulated coils during charging, discharging, and quenching. In NI coils, the current flows not only in the circumferential direction of the winding but also in the inter-turn direction. As a result, the current distribution and electromagnetic stress is expected to be more complicated than that of conventional coils. The additional force and stress due to a screening current, which leads to non-uniform current distributions in the REBCO tape, has become issues. In addition, the thermal deformations and stresses are induced in REBCO coils of Skeleton Cyclotron with cryocooler conduction cooling. Each winding in NI coils can deform separately and move freely by the thermal strain and electromagnetic force. The thermal and electromagnetic stress, results in the coil experiencing more complex deformations and stress distributions. Therefore, it is necessary to investigate the mechanical behavior of multiple NI coils and reinforcement structure in Skeleton Cyclotron. In this study, we report on the numerical evaluation of mechanical properties of NI REBCO coils in Skeleton Cyclotron taking into account both the complex electromagnetic stresses unique to NI coils and thermal stresses.
In recent years, advanced cancer treatment technologies have been required to deal with cancer patients with various disease sites and stages. Especially, targeted alpha-particle therapy is expected. In targeted alpha-particle therapy, a targeted drug labelled by alpha-emitting-RI is administered in a cancer patient. Therefore, nuclide production facilities are required, and alpha-emitting-RI must be produced in a facility close to the hospital because of short-lived nuclide. Accelerators are promising device to solve these problems. However, reducing the operation cost and miniaturization for easy installation are essential to widely use accelerator for medical application. Therefore, in order to further promote the use of medical accelerators, we have proposed Skeleton Cyclotron applied high temperature superconducting (HTS) coils with non-insulation (NI) winding technique. The NI HTS coil can make both high current density and high magnetic field, so it can achieve miniaturization of its size and high intensity beams. Furthermore, in NI coils, the current flows not only in the coil winding direction but also in the radial direction. Therefore, even if the local normal transition occurs in the coil windings, the current can bypass into the neighboring wires and thermal stability can be improved. On the other hand, when the normal transition and quench occur, the electromagnetic and mechanical behaviors in NI coils are different from those of conventional insulated coil. Therefore, we developed a current distribution analysis code for non-insulation HTS coils, and simulated the current, magnetic field, electromagnetic force distributions, and evaluated its electromagnetic and mechanical properties during the normal transition and quench in NI REBCO coil system for Skeleton Cyclotron.
The part of this work was supported by Grant-in-Aid for Scientific Research (S) Grant Number 18H05244.
The traditional endoscope mainly relies on the operation of the operator. The intestinal wall is often deformed and bent when pushed the operator pushed endoscope in, which increases the probability of damage to the intestinal tissue. Here, a flexible endoscope (FE) is developed that overcomes the shortcomings of traditional endoscopes. In order to improve maneuverability, a permanent magnet ring is placed on the tip of the FE, and an external magnetic field generated by a magnetic navigation system composed of eight electromagnetic coils is used to guide it. The FE is made by transforming the traditional endoscope，and the number, position, and size of the permanent magnet ring at its tip are optimized through the finite element model(FEM). Since the endoscope is made of deformable material, it can be guided to the small intestine farther away using an external magnetic field. Experiments are conducted on various angles of the FE in the deformation angle range of 0 to 180° under various magnetic fields and found that these angles can be accurately estimated by the FEM. To verify the feasibility of magnetic navigation driving the FE for intestinal inspection further, the experiments are conducted in the intestinal model and the isolated intestine respectively use the magnetic navigation equipment to control the FE, and the performance of the optimized FE was evaluated by the X-ray machine imaging system.
Index Terms— Magnetic navigation, Flexible endoscope, Permanent magnets
Transcranial magnetic stimulation has important applications in clinical diagnosis, clinical treatment and scientific research. In transcranial magnetic stimulation, the geometric configuration of the coil is particularly important, which determines the stimulation intensity and focalization. To improve these two indicators of transcranial magnetic stimulation, a novel coil is proposed in this paper, namely semiellipse coil pair with eccentric windings(SEPEW). SEPEW adopts a semi-elliptical coil structure with eccentric windings. Different from the traditional planar coil, SEPEW adopts a curved structure, which is more ergonomic. The geometric parameters of SEPEW are optimized through the finite-element method by analyzing the spatial distributions of the intracranial induced electrical field generated by SEPEW with different geometric structure. Results prove that by designing and optimizing the geometric structure of SEPEW, the SEPEW coil can obtain better stimulation intensity and focalization in comparison to the traditional figure of eight coil under the same coil power loss.
Magnetic drug delivery system (MDDS) can deliver the magnetic drug to a specific area and reduce the side effect on healthy tissues. To improve its delivery efficacy, the high magnetic field strength and gradient are required. In order to understand the motion of the magnetic drugs under high magnetic field, this study established a multi-physics simulation model (including: magnetic force, drag force, and buoyancy-gravity), and the flow trajectory of ferromagnetic particles in the microfluidic channel were validated by microscopic observation. The main assumption was that the permanent magnet attracted the magnetic drug in the vein. The Nd-Fe-B permanent magnet was used as the magnetic source with a surface magnetic field of 0.35T. The strength of the magnetic field can be changed by controlling the distance from the microfluidic setup. In addition, both static and laminar flow conditions were studied. In the microfluidic validation experiment, the flow rate (1-15 mm/sec), channel width (~ 2 mm), density (~1060 kg/m^3), and viscosity (~0.0032 kg/m*sec) referred to the vein conditions were considered. Our preliminary flow simulation results were validated with the microfluidic experimental observations that magnetic particles larger than ~ 8 um will be captured on the wall of channel under 1 mm/sec flow rate and magnet distance ~ 20 mm. And the particle trajectory shown error less than 0.012 mm over 1.5 mm flow distance. In addition to the fluid mechanism, effect of the distance from a particle to a magnetic source, flow rates, viscosity, and particle sizes will also be discussed. Moreover, the simulation results will be used to predict the minimum captured particle size under a specific flow and magnetic strength characteristics for MDDS applications.
A 240 MeV proton cyclotron is under-development in Hefei for proton medical application. Two double-split HTS superconducting coils are designed to generate max. 5 T magnetic fields which are used to confine the proton beam revolving around the median plane. In the past experience, low temperature superconducting coils are classic design, but people have to face lower operating temperature and higher operating cost. The HTS material is becoming cheaper and cheaper in industrial market. In order to improve the superconducting magnet, we start to upgrade the magnet design from Low temperature superconducting technology to high temperature superconducting technology. The HTS superconducting magnet contains total magnetic storage energy of ~ 4 MJ. Magnet will generate possible killo-voltage during the quench. In order to reduce the impact of the high voltage, the coil is spitted into a few parts. This article will study thermal-electrical property of the coil quench based on the different electrical-diagram. The temperature hotspot, quench resistance and voltage are calculated and presented in the paper.
There are demands for mobile microwave power sources for different applications, such as the rock melting and drilling, for example. The 28 GHz gyrotron has been proposed as radiation source for such purpose [1]. For frequency ~ 28-30 GHz or more magnetic field ~1-3 T are needed for resonance interaction of the electron beam with eigenmodes of a circular waveguide at gyrodevices. Magnetic fields ~1 T could be realized with usual copper magnets or with permanent magnets but for higher fields superconducting magnets should be necessary. In this paper we consider development of superconducting magnet with ~3 T field along with the mobile cryostat for it. Approaches with high temperature and low temperature superconductors are compared. The design of the possible mobile cryostat is presented and discussed.
1. Paul P. Woskov, Herbert H. Einstein and Kenneth D. Oglesby, Conceptual design of the magnet for millimeter waves rock melts, 2014 39th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), DOI: 10.1109/IRMMW-THz.2014.6955993
In the aluminum industry, development of highly efficient and fast heating methods of aluminum billets is expected. The induction heating by rotating the aluminum billet in strong DC magnetic field generated by HTS coils is one of the candidates for the heating methods in the aluminum extrusion processes, since this method has the large heating capacity with higher energy efficiency and faster heating than the conventional high frequency induction heating method. In our R&D, an aluminum billet heater using a high temperature superconducting (HTS) magnet has been being developed. The target heating capacity is 400 kW to heat a 6-inch x 500 mm aluminum billet from 20 degrees Celsius to about 500 degrees Celsius within 60 seconds. The R&D has been being conducted in three steps. Firstly, the HTS magnet have been developed. For the purpose of cost reduction towards commercial production, we chose the HTS magnet with iron cores to reduce the amount of HTS wire, since the necessary magnetic field is about 1 T around the aluminum billet. The cool-down and the current charging tests for the developed HTS magnet have been successfully finished. It was confirmed that the agreement of the measured magnetic field generated by the HTS magnet in the region for aluminum heating with the design value was sufficient. Secondly, the mechanism for grasping and rotating the aluminum billet in the magnetic field generated by the HTS magnet has also been developed. We confirmed that the grasping force control corresponding to the temperature dependence of mechanical properties of aluminum well worked. Based on these developments, currently, we are assembling the test apparatus for the aluminum billet heating demonstration. In the presentation, the detail of the design and fabrication of our test apparatus is summarized and the results of the heating demonstration tests are reported.
It is expected to build a sustainable social system that uses "hydrogen" as a fuel to generate electricity without emitting CO2. To realize this, technology for storing a large amount of hydrogen is indispensable, and storage as liquid hydrogen is ideal. However, the efficiency of the cooling device in the temperature range around 20 K required for long-term storage with liquid hydrogen is low, and the equipment is huge and expensive, so it has not been established as a widely used technology.
Magnetic refrigeration is expected to be a highly efficient refrigerator in the temperature range of around 20 K because it can realize an ideal refrigeration cycle. However, in magnetic refrigeration, it is necessary to give a magnetic field change to the magnetic material. Further, in order to perform cooling with a large capacity and extremely low temperature by magnetic refrigeration, the magnetic field strength of a permanent magnet is insufficient, and it is indispensable to use a superconducting coil capable of generating a strong magnetic field with low power consumption.
This study aims to develop a static magnetic refrigeration system using multiple high-temperature superconducting coils. By utilizing the energy storage characteristics of the superconducting coil, we are considering a magnetic refrigeration system that can repeatedly generate magnetic field changes to save energy without the need for large amounts of energy to be taken in and out of the outside. The results of analyzing the behavior of magnetic field changes due to coil arrangement, such as reversing the magnetic poles of multiple coils next to each other, and the trial design of coils using FAIR conductors, which are under development, and the loss evaluation due to magnetic field changes were performed. We report on the technical feasibility of a static magnetic refrigeration system using multiple HTS coils.
Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing for metal parts. The raw material (metal powder or wire) is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.
For industries such as healthcare and aerospace, this creates new opportunities for both prototyping and low volume production of titanium parts. The time cost, and challenges of machining or investment casting are eliminated, which makes titanium parts readily available for functional testing or installation on the aircraft. Additionally, the additive process opens the door to new design configurations and weight-reduction alternatives.
In EBM, to precisely control the focused electron-beam on a spot within hundreds of microns in diameter over a large build plane requires different types of magnets that are similar as those used in accelerators to some extents. While special design requirements must be meet for EBM which includes but not limited to focus strength, deflection strength, field homogeneity, multi-pole harmonics, stray field, total power losses, eddy current compensation and etc.
This paper compared different design options for focusing magnet used in EBM and selected two of the best options for beam optics simulation and tests. Simulation results and some experimental data will be presented in this paper.
In industries, there are many issues against the implementation of conventional heating furnaces. First, the government recently executed an environmental protection policy that requires industries to use better technologies against low efficiency and CO2 emissions, etc. Second, industries use old and inefficient technologies for heating metals with large capacity and low efficiency. Also, the work space is sometimes large, dirty, dangerous, and dull. Finally, engineers with various skills are required to operate advanced heating furnaces.
As one of the solutions to resolve these issues, the superconducting induction heater (SIH) with high efficiency has been developed using MgB2 magnets manufacturing technologies. These technologies include: applying superconducting wires to the magnet for SIH, securing the thermal stability of superconducting magnets, and fabricating large bore magnets for industrial applications, which would yield many positive contributions to metal processing industries.
In this paper, the recent development trends of a 1.2 MW SIH using MgB2 NI magnets described. And the novel design and experimental test results of MgB2 magnets were presented and discussed. Large bore MgB2 magnets were designed newly. The heating capacity was decided and the target magnetic flux density of the HTS magnets with iron cores selected for 1,200 kW heating power for an iron metal billets. The simulation results of the MgB2 magnet were analysed through the FEM analysis models. The experimental test and results of the MgB2 magnets were presented in detailed.
The largest MgB2 magnets in the world were fabricated and tested with outstanding operational results. These test process will be helpful for heating characteristics analysis of the various MgB2 magnets for commercialization. The related research will get the reference information of this study.
The purpose of applying electromagnetic stirring was to change the flow field of molten steel in crystallizer during the solidification of casting blank, ultimately improving the quality of the steel. The strong static magnetic field was generated by the high-temperature superconducting magnets and rotated outside the crystallizer. The molten steel cut the magnetic line in the crystallizer to form eddy current and Lorentz force which could exert high magnetic binding force, high stirring force and high damping force on the molten steel. The superconducting electromagnetic stirring technology could constrain the form of molten steel and reduce contacts between the molten steel and the crystallizer. Using the high-temperature superconducting electromagnetic stirring device can reduce the center segregation, the loose and the shrinkage of the steel and improve the quality of the steel. This paper used the finite element software to calculate the distribution of the magnetic field and the electromagnetic force. The molten steel which could flow in the crystallizer because of cutting the magnetic line and forming the torque, the whole process was calculated.
The high-temperature superconducting induction heating technology could widely use in industrial production such as penetrating heating, quenching heating, welding and melting of steel. The steel uses the strong static magnetic field generated by the superconducting magnets of the high-temperature superconducting induction heating device. The steel rotate in the air gap and cut magnetic lines to produce the eddy current losses which can produce the Joule heats and heat the steel. Comparing with the tradition AC induction heating device, the high-temperature superconducting induction heating device can increase the heating speed of the steel and improve the uniformity of the heating effect. The heating depth is 10-20cm. This paper using the finite element software to calculate the distribution of the magnetic field, eddy current losses and the temperature of the steel in the heating area. The influence of the different rotate speeds of the steel on heating time is discussed. And the heating time of the steel with different diameters is calculated. It takes no more than 432 seconds to heat the steel to 1500°C when the steel rotates at 500rpm. And using AC induction heating device to heat the steel takes at least 1800 seconds to 1500°C. The comparison between the high temperature superconducting induction heating device and the AC induction heating device shows the advantages of the high temperature superconducting induction heating device.
Double-Stator-Single-Rotor (DSSR) surface mounted Permanent Magnet Synchronous Motor (PMSM) has the advantages of small size, light weight and high reliability. However, there are problems of large torque ripple and abundant back-EMF harmonic content. In order to improve the electromagnetic performance of the motor, a double-stator single-rotor field modulated motor (DSSR FMM) with high temperature superconductor (HTS) bulks is proposed in this paper. The motor is based on the operating principle of magnetic field modulation and uses a magnetic regulating ring with unequal width structure to adjust the internal and external air gap magnetic fields. In this model, the epoxy resin is replaced by superconducting materials, and the Meissner effect of superconducting materials is used to enhance the effect of magnetic flux regulation. Moreover, the auxiliary slot is opened in the outer stator of the motor model, which can not only reduce the cogging torque of the motor, but also improve the back EMF waveform. Finally, a motor model with an outer stator of 36 slots and 22 poles and an inner stator of 24 slots and 8 poles was established, and the electromagnetic properties of the motor such as air gap magnetic field, back EMF, torque and torque ripple were calculated. Compared with a DSSR PMSM, the results show that the back-EMF amplitude of the model is large and sinusoidal, the output torque is increased by 3.86%, and the torque ripple is reduced by 3.71%. It is proved that this topology can weaken the torque ripple and increase the electromagnetic torque of the double-stator single-rotor synchronous motor.
Magnetic gear (MG), as a kind of non-contact transmission component, has many advantages, such as no friction, oil-pollution free, low maintenance and easy installation, and so on.This paper proposes a novel coaxial magnetic gear (CMG) with eccentric permanent magnet structure and unequal Halbach arrays for achieving sinusoidal air-gap flux density and high output torque. The proposed model has a high temperature superconducting (HTS) bulks to replace the epoxy resin in the conventional stationary ring. According to the Meissner effect and one-sided field, the HTS bulks could enhance the modulation effect. The permanent magnets (PMs) on the inner and outer rotors are distributed in Halbach array, in which the PMs are arranged regularly on the outer rotor and the inner rotor is eccentric structure. So the inner non-uniform air gap can be obtained. The proposed model with the pole pairs of 4 and 17 for the inner and outer rotors is established, using finite element analysis (FEA) a calculated torque is up to 350.8N·m. It is 2.16 times the torque of conventional CMG.
The magnetic field modulation type magnetic gear composite motor is a new type of motor integrating magnetic gear and permanent magnet brushless motor. Its advantage is that it has higher torque density and efficiency, and has a good application prospect in the field of low speed and large torque. According to the principle of magnetic field modulation, the air gap magnetic field of the magnetic gear composite motor is complex and the harmonic content is rich. In order to improve the air-gap magnetic field distribution and increase the torque density, this paper proposes a magnetic-gear composite motor with irregular Halbach array and superconducting magnetic ring. The permanent magnets of the motor are magnetized by an irregular Halbach array, and the unilateral magnetization effect can strengthen the magnetic field at the air gap side and weaken the magnetic field at the core yoke. Using superconducting modules to replace the epoxy resin in the conventional magnetic tuning ring can enhance the magnetic tuning effect of the magnetic tuning ring. Finally, a finite element model with the pole pairs of 4 and 18 for the inner and outer rotors is established. By comparing with the conventional magnetic gear compound motor, it was found that the air gap magnetic density and back EMF of the motor were high in sine, the torque increased by 30.12%, and the torque ripple was reduced by 20.64%.
There is a huge energetic potential associated to ocean waves, expressed in terms of the power per wave meter length that can be harvested, up to 60-80 kW/m in many areas near to the shore of populated areas. Among the different devices proposed to extract that power, the most extended ones are the Point Absorbers, based on the linear displacement between two bodies for which the use of electric linear generators is the best option since the conversion is done in a single-stage process. Nevertheless, the generation is done at low speed and hence big forces are required. Having actuators capable of exerting big forces also allows the Point Absorber to modify its natural frequency of oscillation and to better adapt to different sea states increasing its energy extraction capability.
Unfortunately, high forces are associated to high Joule losses which must be limited oversizing the generator. In this regard, the use of a superconducting actuator becomes especially convenient since it can handle very high currents with restricted losses and a small volume.
Previous considerations led different partners to present the SEA TITAN project to the H2020 LCE Call, which was finally granted. One of the aims of the project consisted in developing a non-superconducting machine while a second one was to perform a conceptual design of a superconducting novel actuator which is the subject of this paper.
The actuator is a reciprocating Cylindrical Switched Reluctance Machine based on MgB2 superconductor and a novel refrigeration system which includes an expandible cryostat and a Cryogenic System based on recirculating a flow of helium which is cooled down using a two-stage cryocooler.
The paper includes the calculations of the machine and the description of how the principal components have been conceived.
Characteristics of fly-wheel type uninterrupted power supply (FW-USP) using superconducting induction machine (SIM) is analytically studied. In the study, it is assumed that the SIM is iron-cored and composed of Cu wire stator windings and HTS rotor windings. The rotor windings are made with HTS wires embedded in an iron rotor core and connected to HTS end-rings. The whole assemble of the rotor windings are placed in a rotor cryostat and cooled at cryogenic temperature, and there are no electric connections to the outside of the rotor. The stator is at room temperature. When AC currents are applied to the stator windings by an AC power supply to start the SIM, the HTS rotor windings are subject to AC magnetic field. At the beginning, rotating torque is not generated, because the rotor windings are superconductive and the AC shielding currents is induced to expel the magnetic flux. After that, the HTS wires becomes resistive due to the temperature rise caused by the AC losses in the wires, and the magnetic fluxes penetrate in the rotor windings for the rotating torque to be generated. When the revolution speed of the rotor becomes close to the synchronous speed, the temperature of HTS wires of the rotor decreases due to the decreasing losses and the wires become superconductive again. Then, the rotor is pulled into the synchronous state due to the trapped magnetic fluxes in the rotor windings. The back electromotive voltages induced in the stator windings due to the trapped magnetic flux in the rotor windings are kept even when the SIM is disconnected from the power supply. Therefore, by inserting a SIM combined with a fly-wheel between a power line and electric loads, electric power to the load is sustained even when the power from the line is lost.
Abstract:
Dynamo-type high-temperature superconducting (HTS) flux pump has been verified to be a practical method for the charge of HTS magnet, due to its simple structure and low cost. The nonlinear properties of HTS stator which is influenced by its substrate magnetism, play an important role on the charging performance of the dynamo-type HTS flux pump. Generally, there are three kinds of substrates being used in HTS coated conductors, e.g., non-magnetic substrates, weak-magnetic substrates and strong-magnetic substrates. In this study, we have compared the charging performance of dynamo-type HTS flux pump with different type of HTS stators numerically and experimentally. A finite-element model was established firstly, in which the nonlinear properties of the superconducting material are described by the E-J power law in conjunction with an H-formulation framework. Then, corresponding experiments were carried out to verify the simulated findings. According to the results of simulations and experiments, compared to the coated conductor without magnetic substrate, when the magnetic substrate was under the superconducting layer, the saturated current and the charging speed of the stator with magnetic substrate had been promoted obviously.
Key words: flux pump, finite-element simulation, magnetic substrate, charging performance
With recent progress of fabrication technology of long length and high critical current high temperature superconducting (HTS) wires, the application of HTS wires to the windings in rotational machines becomes feasible. In most current research and development of HTS rotational machines such as large scale wind turbine generators and ship propulsion motors, the HTS wires are applied only to the DC field windings. However, there are continuing interests in the development of fully superconducting rotating machines, since it is considered that the fully HTS rotating machines with HTS armature windings expand the application range of the HTS technology to middle size AC rotating machines. We have been developing the fully HTS induction/synchronous motor utilizing for transportation apparatuses such as electric vehicles. As a part of this R&D, we have developed a model armature for a 50 kW-class induction/synchronous motor using HTS coils. In this model armature, a toroidal type winding composed of 24 HTS coils and an iron core was used. The HTS coil used in the model armature was the race track double pancake coil wound by the parallel conductor with three REBCO tapes. The iron core of the armature was split into 24 parts made of laminated silicon steel sheets. Each REBCO coil was combined with the split iron core and these were assembled in the toroidal structure. The AC losses in the developed armature REBCO winding in 3-pahse AC condition were investigated. In the presentation, the electric design and the detailed specification of the stator winding using REBCO coils is summarized and its AC loss characteristics in the 3-phase AC condition are reported.
More attention is focused on high temperature superconducting (HTS) machines due to lighter weight, smaller size, higher power density and torque than conventional counterparts. An axial-type synchronous motor with Gd-123 bulk as field poles has been manufactured and tested successfully in Tokyo University of Marine Science and Technology. The rated output power of the HTS motor is 30 kW at a rotating speed of 720 min-1. Besides, it has eight HTS field poles and three-phase symmetrical copper armature windings. The performance of the prototype HTS motor is expected to be improved and optimized based on the below study.
Several axial-type synchronous motors are modeled based on the above HTS prototype, which include the bulk HTS motor model with the stator back-iron, the motor model with the permanent magnet (PM) rotor and the bulk HTS motor model with both air-core stator and rotor. The nonlinear constitutive law of the bulk HTS is included in the developed motor model through a treatment of the power law. Based on the motor models, a set of transient studies are completed, which includes the distribution of the magnetic flux, the output torque characteristics of the different type motors with the rotating speeds. In addition, we carried out and discussed the output torque of the bulk HTS motor with both air-core stator and rotor at different rotating speeds, air gap lengths, maximum excitation fields and armature coil currents. Finally, the performance of different type motors is estimated, and the optimal model and operating conditions are determined.
Our research group has developed a High Temperature Superconducting Induction/Synchronous Motor (HTS-ISM) for next-generation transportation equipment. It was clarified based on the experimental and the analytical studies that the fabricated HTS-ISM possesses not only the excellent steady performances such as high torque density, high efficiency, but also the novel transient characteristics such as autonomous stability, hysteretic rotating characteristics. In order to start the HTS-ISM, however, it is necessary to break the magnetic shield of the HTS cage winding loop and interlink the magnetic flux. Since the starting current for the above process is much larger than the driving current, its starting time needs to be as short as possible. In order to realize the above requirements, we proposed the new starting method[1], in which input rms voltage was changed as single square pulse wave while starting and afterwards kept stable at driving voltage (Zero voltage → Highest voltage → Driving voltage).
In this presentation, we report on the parametric study on the pulse waveform(pulse width, voltage level, voltage-rising or falling time) of the input rms voltage in the new method. This study was examined with model-based analysis for 20 kW class prototype HTS-ISM, which consists of BSCCO rotor and copper stator and under fixed driving voltage (80 Vrms), fixed frequency (60 Hz) and 10 kW load (= half load) conditions. We found that results can be classified into 4 types in terms of whether rotational speed reached or not to synchronous speed before voltage dropped to driving voltage, and whether the motor finally kept rotating or stopped. We also try to give the explanation on the behavior of the motor in these results. These results would be important in fast acceleration and operation of HTS-ISM. Details will be reported on the day.
We report the current state of research and development to realize a new design theory of High Temperature Superconducting (HTS) armatures that achieve both robustness and low-loss characteristics. In order to realize it, the self-organizing design method, which is the first-principles design method [1], and the Face-to-Face Double Stacked (FFDS) conductor technique [2] are effectively combined with each other.
A fully superconducting AC rotating machine, in which both the field and armature are composed of superconducting windings, is considered to be the ultimate low-dissipation as well as high-power (and/or- torque) density machine. However, the HTS conductor has a non-linear magnetic flux-flow resistance that depends on the current and the local magnetic field vector. In a rotating machine whose essence of energy conversion is modulation of a rotating magnetic field, it is essential to study the effect of the spatially distributed magnetic field on the non-linear resistance for realizing precise design.
In this study, we design a three-phase armature winding for a 150 kW-class rotating machine by means of the self-organizing method that can uniquely determine the detailed shape of the stator slot without a rule of thumb, based on the results of the 50 kW-class fully superconducting induction/synchronous motor [3]. Furthermore, by taking into account the mechanical and electrical characteristics of the FFDS conductor that joins two REBCO tapes with low resistance, a stator structure capable of increasing power density while maintaining low-loss is realized. The designed armature also show for the first time a robust structure that is stable even when an overcurrent exceeding the critical current is applied.
This work was supported by JST A-STEP Grant Number JPMJTR201A and JSPS KAKENHI Grant Number 19H05617.
[1] unpublished
[2] T. Kiss et al., 30th ISS, WB6-6-INV, 2017
[3] T. Nakamura et al., IEEE Trans. Appl. Supercond., 29(5) (2019) 5203005
Superconducting motors have been studied for electric vehicles, airplanes, and so on in the world. Therefore, superconducting motors become lightweight and have a high-power density. Since REBCO superconducting tapes have tape-shapes, motors with racetrack coils as armature windings have been studied. However, racetrack coils are inferiority in the respect of increasing interlinkage flux to rotor than distributed windings. In this study, considering characteristics of REBCO tapes, we proposed trapezoidal coils for armature windings to become shapes like distributed windings. Then, 2 kW-class induction motors used two-types coils were designed in order to compare two motors’ characteristics. JMAG Designer executed electromagnetic simulations about two models. As a result, the motor with trapezoidal coils used less REBCO tapes and indicated less amount of the vertical component of magnetic flux density than racetrack coils. For these reasons, the AC loss of trapezoidal coils become smaller than racetrack coils and the weight of trapezoidal coils are lighter than racetrack coils.
There are already a wide variety of medical mixers used in the pharmaceutical manufacturing process, and they have contributed greatly to many people suffering from diseases. However, most of the rotating machine used in current medical mixers adopt the mechanical bearing system, and dust is generated by friction with the rotating shaft. In addition, the contact rotating system has disadvantages of low energy efficiency and maintenance of the connecting part is required. On the other hand, although the controlled magnetic bearing allowed non-contact rotation is applied in some cases, it cannot get high torque since its very small load capacity. Therefore, we have been investigating the development of non-contact rotating machine using high temperature superconducting (HTS) bulks to enable the agitation process in clean circumstances. The non-contact rotating machine combined with ring-shaped HTS bulks and permanent magnet was proposed and investigated experimentally. The permanent magnet was arranged between HTS bulks and it is integrated with the rotor shaft. The HTS bulks were magnetized by the permanent magnet with field cooling method by liquid nitrogen. Therefore, the permanent magnet played a role of magnetic source. Since our current research aims to develop a medical mixer with a capacity of 600L to 1,000L, the proposed medical mixer using the HTS bulks requires not only high-speed rotation but also high torque. Therefore, in this study, we investigated the structure of a non-contact rotating machine that can achieve both high-speed rotation and high torque. Until now, only HTS bulks have been used as magnetic bearings for levitation, but in this study, we propose a structure that combines a superconducting coil and HTS bulks. The trapped field properties in HTS bulks by superconducting coil are analytically investigated using based on FEM analysis and optimized structure of magnetic bearing part will be reported.
The demand for high power density motors for electric propulsion aircraft demands conductors capable of withstanding high frequencies (i.e., 300-1kHz), but also capable of high current density. This is because motor power increases with B, J, and w. Superconductors are attractive because of their high J which can lead also to high B, but they are presently limited to f < 300 Hz. One alternative to superconductors is cryogenic hyperconducting Aluminum (HPAL). HPAL has very high RRR, and thus very low ohmic losses at cryogenic temperatures, and if made with very fine filaments, or as Litz cable, can have very low eddy current losses as well. One of the drawbacks of hyperconducting aluminum is an anomalous magnetoresistance. For B< 2 T, this contribution is minor. In addition, certain composite designs can make this contribution small even at high B. In this work we compare the current densities and AC losses of several different designs of HPAL conductors to superconductors at a variety of temperatures, frequencies, and field amplitudes, specifically for T = 20 and T = 120 K, the regimes of liquid hydrogen and LNG. The level of segmentation and the use of composite vs Litz cable is discussed, as well as the matrix/sheath material. The suitability for use in synchronous induction type propulsion motors is then compared in different regimes.
Based on the designed field current of an high temperature superconducting (HTS) synchronous motor and the cooling temperature at 30K in our laboratory,this article introduces the structure and fabrication of a novel cryostat suitable for a linear-motor type flux pump used on an synchronous motor, and reports the charging test of the HTS no-insulated (NI) double racetrack coil used in the rotor field winding of the 16.9 kW HTS synchronous motor at 30K in the cryostat .The machine technically employs an HTS contactless static excitation device (CSED), the so-called linear-motor type flux pump, to charge the HTS field winding through a non-contact and the thermal shielded wall in the cryostat excitation method. We show that the device can inject a large current into the HTS NI double racetrack coil at 30 K, and is capable of operating at flux gaps greater than the thickness of the thermal shield. The results of this work have practical guiding significance for the next step of the 16.9KW synchronous motor rotor field excitation and accommodating a cryostat wall within this flux gap will enable future flux pump designs, which is helpful to realize the application of linear-motor type flux pump for HTS motor rotor excitation.
The onboard high temperature superconducting (HTS) magnet of electrodynamic suspension (EDS) train suffers from the external magnetic fields generated by the ground coils including the suspension coils, propulsion coils and even generator coils. In such case, the ac losses will be produced in the HTS magnet and lead to a rise in temperature, possibly affecting the operation stability of the EDS train. Hence, it is necessary to estimate the ac losses in onboard HTS magnet. The goal of this paper is to present a finite el-ement method (FEM) model to calculate the ac losses of onboard HTS magnet under the magnetic excita-tion of the ground coils. The FEM model, based on the vector magnetic potential method, includes the HTS magnet composed of the HTS coil and its cryogenic vessel, suspension coils, and propulsion coils. Taking advantage of the magnetic potential boundary condition, the moving mesh of the onboard HTS magnet is not required, therefore significantly reducing the computing time. An experimental platform is established to measure the temperature rise and ac losses of HTS magnet subjected to the travelling mag-netic field from propulsion coils, and the calculated results are compared with the measured ones to vali-date the FEM model. The ac losses of the onboard HTS magnet under the external magnetic field from the ground coils of EDS train will be studied with the validated FEM model.
Coated superconductor magnets have already proved their feasibility in electrodynamic suspension (EDS) application as the on-board magnet, making the liquid-helium-free EDS train become possible. This paper designs a racetrack REBCO magnet served as the on-board magnet of EDS train, including the designs of both the REBCO coil composed of eight double pancake (DP) coils and the tailored cryogenic vessel us-ing conduction cooling. The REBCO magnet is designed to be detachable such that the REBCO coil can be taken out and put in the cryogenic vessel without breaking the REBCO magnet. Then, eight DP coils are wound and their critical currents are measured at liquid nitrogen temperature to assess their perfor-mances and accordingly determine their locations in the REBCO coil with the magnetic field distribution considered. Lastly, the key parameters of the REBCO magnet, such as the coil voltages, power losses, magnetic field distribution, and temperature distribution, are measured under the conduction-cooled con-dition. The safety margin of REBCO magnet operated at the designed current is predicted according to the measured voltage-current curve of the most dangerous DP coil as well as the critical current of the super-conducting current lead.
The world’s first full-sized high-temperature superconducting (HTS) Pinning magnetic levitation (maglev) engineering prototype train was officially launched in SWJTU, Chengdu, China in 2021. This prototype provides strong proof for the feasibility of engineering application of HTS pinning maglev in civil train. This prototype shows the basic load and low speed operation capability of HTS pinning maglev train, and the next important issue should be its levitation stability and dynamic behaviors. Unlike traditional vehicle system which most focus on the low frequency excitation due to its low natural frequency and usually ignore the influence of high frequency excitation on the train dynamics, the unique phenomenon of flux flow and flux creep inside the superconducting bulks complicates this case for HTS pinning maglev system, especially for the ultra-high speed this prototype aimed to achieve. To study the dynamic response and levitation stability of the HTS pinning maglev under high frequency, a series of experiments have been carried out. Firstly, the vertical and lateral levitation stiffnesses of a HTS pinning system were measured by static experiment. Secondly, the external excitations with different frequencies, intensities and directions were added to the system by a vibration table, and the dynamic response signals were collected. Finally, the effects of high frequency excitation on the dynamics response and levitation stability of the HTS pinning maglev system were gained by signal analysis. The result verified that the HTS pinning maglev can effectively isolate the high frequency vibration, but some excitations can affect the dynamic performance of the system. This study suggests the smoothness requirement of the operating line and the limitation of the operating speed, as well as providing references for future dynamic studies of HTS pinning maglev system.
Null-flux Electro-dynamic suspension (EDS) system promises to be one of the feasible high-speed maglev systems above 600 km/h. Due to its greater current-carrying capacity, superconducting magnet can provide super-magnetomotive force that is required for null-flux EDS system and cannot be provided by electromagnets and permanent magnets. There is already a relatively mature high-speed maglev technology with low temperature superconducting (LTS) magnets as the core, which work in the liquid helium temperature region (T≤4.2 K). 2-Generation high temperature superconducting (HTS) magnet winded by REBa2Cu3O7−δ (REBCO, RE=rare earth) tapes works above 20 K region，and can get rid of the dependence on liquid helium which is rare on earth. This paper designed HTS no-insulation closed-loop coils applied for EDS system and energized with persistent current switch. The coils can work at persistent current model and has premier thermal quench self-protection. Besides, a full size double-pancake module was designed and manufactured in this paper, and it was tested in liquid nitrogen. The double-pancake module’s critical current is about 54 A and it is capable of working at persistent current model, whose average decay rate measured in 12 hours is 0.58%/day.
Abstract: High temperature superconducting (HTS) maglev, which uses the magnetic flux pinning effect to realize the suspension and guidance, has attracted wide attention in the field of transportation due to its advantages of self-stabilizing suspension, high efficiency, and energy saving. As the connection components between the bogie and car body, and the transmission components of traction and brake power, traction rods not only satisfy the relative motion between car body and the bogie, but withstand the pounding of bogie relative to body as well. There is a great need to study the influence of traction rod parameters on its dynamic performance, includes its length, stiffness and arrangement, which can prolong the life of the traction device and running stability. In this paper, a rigid-flexible coupled dynamics model of the maglev vehicle, considering the traction rod as a flexible body, is established by means of multi-body dynamics software Universal Mechanism (UM). And the influence of the traction bar on the dynamic performance of the vehicle on straight line and curve line is analyzed. The analysis results provide a theoretical basis for improving the arrangement form and parameter selection scheme of the traction rod.
Key Words: HTS Maglev；traction rod；rigid-flexible coupled simulation；dynamic performance；curve passing performance
In order to increase the diversity of people's travel mode and fill the blank of the travel speed between the aircraft (900km/h) and the high-speed train (300km/h), the high-temperature superconductor magnetic levitation train still needs to be developed. The conventional magnetic rail used for levitation mainly adopts the isometric magnets. Advanced solution uses Halbach Array, which can increase the single-side magnetic density (increase levitation force) and improve sinusoidal distribution (increase the guiding force) of the magnetic field[1-3]. A fact that is easy to neglect is the different widths of the horizontal and vertical permanent magnets (PM) in Halbach array can affect the magnetic density significantly[3-5]. So that in Halbach array application, the structure topology of the PMs can be optimized in order to achieve a better magnetic performance.
In Halbach maglev rail topology optimization, a 2D model has been applied. The magneto-static energy is controlled to be the same, which means the total surface of the PMs section is the same. After the topology optimization by finite element method, when the width ratio between the horizontal and the vertical PMs is 3.182, the improvement of the surface magnetic flux density is the best, and in our research it’s about 20% augmentation. A section of the 10:1 suspension rail has been fabricated in order to measure the spatial magnetic flux density and the levitation force distribution, to compared with the mathematical model deduced based on Biot-Savart Law and method of equivalent current sheet.
By presenting the process of our research in detail, we hope to provide positive influence to follow-up scholars who carry out similar works.
High-temperature superconducting (HTS) maglev has good application prospects due to its passive stability. There are many researches on the levitation characteristics of a single bulk HTS in applied magnetic field. However, the bulks are usually arranged in an array in practical applications. In addition, experiments proved that levitation force and guidance force of the system with two bulks is not simply equal to that of the linear superposition of those two bulks. Therefore, it is interesting to further study the law of interaction between bulks with simulation methods quantitatively. In this paper, firstly, a three-dimensional (3D) model of the HTS maglev system with a square bulk HTS is established to simulate levitation characteristics based on COMSOL Multiphysics. Secondly, the influences of the seed-face orientation and the placement direction on the levitation characteristics of the maglev system are simulated and analyzed based on the 3D model. Finally, the interaction law between multiple bulks in a combination is studied. The simulation results are in good agreement with the experiments, which have reference value for the design and prediction on the levitation and guidance performance of the HTS maglev system with a combination of multiple HTS bulks.
The high-temperature superconducting (HTS) maglev system has tremendous possibilities for future high-speed transportation owing to its salient superiorities of self-stable. However, previous study had indicated that the relatively low damping of HTS maglev system may cause the undesired large-amplitude nonlinear vibration in system. To solve that, electromagnetic shunt damper (EMSD), which usually consists of electromagnets, permanent magnets and shunt impedance connected to the terminals of the coils, was introduced for damping improvement in HTS maglev system and had shown its effectiveness in vibration suppression. But EMSD has its limits, it only works most effectively in a narrow bandwidth near the natural frequency in a single mode due to the fixed and unchanged parameter value of shunted branch. Hence, a new negative resistance electromagnetic shunt damper (NR-EMSD) is employed to improve the vibration suppression performance of HTS maglev system. The negative resistance offsets the inherent resistance of the electromagnet coils and as a result the induced current of the circuit would increase, which will significantly enhance the performance of vibration suppression. And the change of resistance of closed circuit makes it feasible to suppress the multi-mode vibration. In this paper, mathematical model of NR-EMSD and governing equation of the HTS maglev system are established. The stability analysis is investigated to determine the design rules of negative resistance. And experiments are carried out using EMSD method and NR-EMSD method respectively for contrast. The results shows that the NR-EMSD can not only increase the damping of the system notably, but also has a better performance than passive EMSD. And multi-mode vibration suppression could be achieved simultaneously. This work may provide references for further practical application in HTS maglev system.
The superconducting magnets (SCMs) and figure-eight coils (FECs) are core components for the null-flux superconducting electrodynamic suspension (NFSEDS). In this paper, the multi-objective optimization design of NFSEDS is investigated to decrease the size of SCM and FEC based on Non-dominated Sorting Genetic Algorithm-II (NSGA-II). Twelve design variables are selected including the size of the FEC and SCM, and the mass of the FEC and SCM are considered as the optimization objectives on the basis of ensuring the original suspension force and the ratio of levitation force to drag force (drag ratio). Meanwhile, the comprehensive sensitive analysis is carried out to stratify the design variables into nonsensitive or sensitive levels on the basis of experiment of design (DOE). Afterwards, the optimized scheme is selected from the Pareto front combined NSGA-II and response surface method, which greatly increased the optimize efficiency. The coupling relationship between the size of the superconducting magnet and its critical current is considered to avoid the quench of superconducting magnet. Finally, the authenticity of optimized results is verified by finite element simulation. The result shows that the mass of the FECs and SCM reduce 12.07% and 33.85% while the suspension force and drag ratio of the NFSEDS increase 20.23% and 7.05%. The optimal method can greatly reduce the mass of the FEC and SCM，and has great significance for design of NFSEDS.
HTS magnets with magnetomotive force >360 kA and off-power operation time longer than 1 hour have been achieved for a prototype Maglev train. Off-power operation means no power source, no cryocooler, no vacuum pump and no more cryogen supply in the vehicle, like permanent magnets. Such operation mode was realized based on the following techniques: (1) persistent current mode (PCM) operation of HTS poles which are serial connected stacks of HTS coils; (2) solid nitrogen which serves as the so-called “thermal battery”; (3) coupled optimization of electromagnetic-mechanical-thermal design of the magnet structure.
Off-power operation provides the feasibility of levitating a small (<3 tons) prototype vehicle with no on-board power. And it also enhances the operation reliability for commercial running of real-scale maglev trains during fault conditions.
These magnets are conduction-cooled by GM cryocoolers in current project for a 200-meter test track. Each magnet contains two independent magnetic poles. And intrinsic decay rates around 1%/day has been realized. Turn-to-turn resistance of coils is 2-5 μΩ·cm2. This is a compromise of self-protection ability and potential eddy-current loss. Consequently, the initial energization time is several tens of hours. This is proposed to be acceptable by the authors since the recharging period is about 1 week and several hours are sufficient to finish the recharging process.
These magnets are produced for studying electrodynamic suspended (EDS) Maglev trains. In this route, the biggest achievement has been accomplished in Yamanashi test line. This type of maglev is promising for future high-speed train system, especially with the speed higher than 600 km/h and even 1000 km/h.
The presented activity of EDS Maglev based on HTS magnets is sponsored by CRRC Changchun Railway Vehicles Co., Ltd, Science and Technology Commission of Shanghai Municipality, Shanghai Superconductor Co., Ltd. and Shanghai Jiao Tong University.
Elevated bridge is applied widely in maglev railway systems for high-speed ground passenger transportation. But the vibration of vehicle and bridge is essentially coupled with each other and there is a strong problem of vehicle-bridge coupled vibration. Therefore, it is necessary to investigate the vertical dynamic characteristics of superconducting electrodynamic suspension (EDS) train vehicle-bridge coupled systems, which is currently the only through 600 kilometers speed domain application feasibility of rail transit vehicles. Firstly, based on Fourier inverse transformation, the guideway irregularity time domain series are obtained by numerical simulation, which is used as external excitation input to the superconducting EDS train. Then the superconducting EDS train dynamic model is built in Simpack, which is viewed as a model considering rigid bridge. The bridge finite element model is built in ANSYS and the modal state of the bridge is calculated to form a modal file into Simpack, which is viewed as a model considering flexible bridge. At the same time, to verify the reliability of the vehicle-bridge coupled model, the 22 degree of freedom (DOF) vertical analytical dynamic model is established with the vehicle-bridge coupled based on the Euler-Bemoulli model in Matlab/Simulink. Meanwhile, vertical dynamic response of flexible bridge is developed and evaluated. Subsequently, the vertical displacement and acceleration of the superconducting EDS train considering flexible bridge and rigid bridge are compared at different speeds. The results show that the vertical vehicle-bridge coupled systems can get more accurate vertical vibration performance of EDS train; key dynamic indexs of the bridge meet the relevant requirement. These results can provide a useful reference for the further research and practical application of the superconducting EDS train.
Whole body ultra-magnetic field 14 T magnetic resonance imag-ing (MRI) magnet is now under design at Institute of Plasma Physics, Chinese Academy of Sciences, the main coil based on the preliminary designed of Nb3Sn Rutherford cable in Channel Conductor (RICC). Rutherford cable is a core components of the conductor. During the fabrication process of Rutherford cable, the strands were subject to server deformation, these deformation can result in significant reduction of the critical current and the Residual Resistivity Ration (RRR). A Rutherford cabling ma-chine has been purchased which consists of 20 spools, Turks head, caterpillar, and take-up facility. Rectangular cables without a stainless steel core were developed and three types of mixed ca-ble using 1.0 mm Nb3Sn strand and copper strand were fabricat-ed. Two measurements method were adopt to evaluate the critical current degradation after cabling. The first one is to measure the critical current of the strands extracted from the cable, the second method is to measure the performance of the cable. In this paper, the results of measurements of critical current are presented.
The brittle intermetallic Nb3Sn superconductor is currently being used to develop high field magnets in the framework of the Hi-Luminosity upgrade of the Large Hadron Collider at CERN. Despite its excellent superconductive properties, Nb3Sn wires suffer from significant critical current Ic reduction due to the transverse load applied during the magnets’ assembly and energization.
A dedicated FEM 3D numerical model coupled with a Jc scaling law has been developed to predict the electro-mechanical behaviour of RRP and PIT wires under transverse loads. By using this model, the effects of different geometrical factors have been studied to identify the keys parameters that allow limiting the effect of transverse loads on the Ic reduction under transverse load. In particular, this paper deals with the role of the: 1) wire twist pitch, shape (round or rolled), diameter and copper to no copper ratio; 2) sub-elements numbers, disposition, shape (round or hexagonal) composition.
The accelerator magnets for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) use $\mathrm{Nb_3Sn}$ conductor to achieve in-field performance exceeding Nb-Ti based technologies. To sustain the Lorentz forces during operation, a pre-compression is applied to the conductor during the fabrication of the magnet. This can lead to an irreversible degradation due to the mechanical sensitivity of the $\mathrm{Nb_3Sn}$ material.
In this study, the impact of the pre-compression is investigated using a reacted double-stack of Rutherford cables. The stack is submitted to transverse stress at room temperature. The critical current is then measured in liquid helium and in a background field of up to 11.5 T in the FRESCA test station at CERN. The pressure applied at room temperature covers the range from 130 MPa to 190 MPa with a 10 MPa step increase.
Monotonic and cumulated pressures were applied to analyze the impact of the cyclic loading. Microscopic analysis of cross-sections were performed following procedures specifically developed to minimize surface damage during samples’ preparation. These observations were used to correlate the irreversible effect of the transverse pressure to the A15 damage in the cross section.
As known, the cold-rolled thin Nb-Ti tapes demonstrates very strong anisotropy of pinning force regarding rolling direction and external magnetic field because of dense anisotropic grain boundary structure. This leads in particular to form of “fish-tail” feature in low-field area of magnetization loops in inclined field due to competition of self-field and small external field in media with anisotropic critical current [1]. After heat treatment in vacuum (385°C, 25 h) a large number of additional pinning centers appears in form of small (15-40 nm) particles of α-Ti phase mainly located on grain boundaries, which increase critical current density measured by transport method. We carried out comparative magnetization measurements of both (cold-rolled sample cut along tape rolling direction and heat treated sample cut across tape rolling direction) Nb-Ti tape with the same anisotropy factor (Jmax/Jmin) in relation to magnetic field inclination. In contrast to magnetization loops of cold-rolled samples there are no pronounced “fish-tail” features on magnetization loops of heat treated samples. In our opinion, this may be due to the reversible flux motion within quite large and isotropic α-Ti participates which size significantly exceed the Nb-Ti coherence length (and flux core diameter).
Ti doping to Nb$_3$Sn wire is well known as one of the effective ways for improving the superconducting characteristics such as $B_\mathrm{c2}$ and $J_\mathrm{c}$. Early studies on Ti doping show that Ti doping to Nb$_3$Sn improve the microstructure, namely, decreasing the average grain size, promoting the Nb$_3$Sn layer formation, and normal state resistivity $\rho_\mathrm{n}$. Moreover, recent studies on Ti doping to bronze processed Nb$_3$Sn wire show that the microstructure such as Nb$_3$Sn grain morphology strongly depends on where Ti is doped, that is, to Cu-Sn matrix or Nb core.For example, thicker Nb$_3$Sn layer is formed in the case of Ti doping to Cu-Sn matrix, rather than to Nb core. Therefore, Ti doping to the matrix should be better to improve the superconducting characteristics.
In internal-tin processed wire, Ti can be doped to 3 positions, which are Sn cores, Cu matrix, and Nb cores. Based on previous studies on the bronze processed wire structure, Ti doping to the matrix side (Sn cores or Cu matrix) would be appropriate for improving the microstructure also in the internal-tin structure. However, in the case of Ti doping to Sn cores, Sn-Ti compounds are reportedly formed at the subelement boundaries, which prevent uniform Sn and Ti diffusion. The Sn-Ti compound formation would affect to the Nb$_3$Sn layer formation, however, the detail have still been unclear.
In this study, we investigated the microstructure and superconducting characteristic on the simple diffusion couple specimens with bronze processed and internal-tin processed structure with Ti doping to the various position, to reveal the effect of Ti doping position on the microstructure. In addition, we also examined an additional elemental doping with Ti to Nb$_3$Sn wire.
New generation accelerators, such as future circular collider (FCC), require superconducting dipole magnets with non-copper $J_c$ of 1500 A/mm$^2$ at 16 T, 4.2 K. Nb$_3$Sn is the only proven superconductor with large-scale industrial production. Still, present Nb$_3$Sn wires can not meet the required conditions, and improvement in the fabrication is needed. Kobe Steel Ltd. has developed Nb$_3$Sn wire by brass matrix distributed-tin (DT) method to achieve high $J_c$ and high mechanical strength.
The elemental addition approach to the Cu matrix was opted to enhance the Nb$_3$Sn formation and contribute to improving the mechanical properties of the matrix. A heat-treated helical sample soldered on the Walters spring (WASP) to measure the strain dependence of critical current with relatively long length and lower electric field criterion. Axial strain is applied to the wire by applying torque on the WASP at 16 T, 4.2 K.
In this paper, the $I_c$ –strain characteristics of Nb$_3$Sn conductor, with and without Zn addition in Cu matrix at 16 T, 4.2 K, and S-S behavior at RT and 77 K is presented, and the impact of the findings on the Nb$_3$Sn conductor development to achieve the FCC target is discussed.
Typical Cable In Conduit (CIC) typed Nb3Sn conductor applied for the fusion magnets are manufactured by twisting multiple Nb3Sn strands based on the current-carrying specification. Jc degradation by the cyclic loading in the CIC conductors was confirmed. This is caused by the Nb3Sn filament breakage by applying the huge electromagnetic force (i.e. transverse compressive load). Therefore, the mechanical strength improvement of Nb3Sn strand will become a critical issue to realize a future CIC conductor.
We approached the bronze matrix reinforcement using the Cu-Sn-Zn and Cu-Sn-In ternary bronze alloy. The Zn and In elements of the ternary bronze alloy remained in the matrix material after Nb3Sn synthesis heat treatment, and the bronze matrix after Nb3Sn formation was transformed to the solid solutions containing Zn or In elements. These solid solutions improved the mechanical strength of the Nb3Sn wire.
We evaluated the Jc performance under the transverse compressive stress on the bronze matrix reinforced Nb3Sn multifilamentary wires, and the effects of the solute elements on the Jc property under compressive stress was investigated.
On the conventional bronze processed Nb3Sn wire, Jc property was decreased monotonously around 30 MPa. In the case of the bronze matrix reinforced Nb3Sn wire using Cu-Sn-Zn alloy, however, no Jc deterioration was observed within 100 MPa. The irreversible compressive stress (σirr), which is defined as the stress that maintains the initial Jc value after unloading the compressive stress, was estimated to be approximately 160 MPa. This value was almost corresponded to the yield stress of Nb3Sn wire using Cu-Sn-Zn ternary alloy matrix after heat treatment. This suggested that the (Cu, Zn) solid solution transformed from the Cu-Sn-Zn ternary alloy acted as a protective material for the Nb3Sn filaments. The comparisons between Zn and In solute elements on the Jc performance under the compressive stress were also investigated.
In this work, we summarize the results of an experimental campaign of inductive and transport measurements aimed at the evaluation of the electromechanical performances of a 0.85 mm diameter RRP® wire relevant for the HiLumi LHC project. SEM micrographs have been used to evaluate the sub-element diameter and Cu/non-Cu ratio, whereas the chemical composition across the sub-element sections has been studied via energy dispersive X-rays spectroscopy. The critical current dependence on the magnetic field and uniaxial applied strain (between -0.2% and 0.5%) has been investigated in a temperature range comprised between 4.5 K and 10 K. Furthermore, the strand magnetization up to 12 T has been measured at different temperatures (4.3 K-14 K) to determine the strand’s effective filament diameter and to assess the critical current density in the temperature and field range where transport current measurements were not available. The experimental results have been analysed in the framework of a scaling law model, by using two different approaches for the data fitting. These results provide an accurate parameterization of the critical surface in terms of field, temperature and strain, to be used as a general reference for all purposes aimed at realizing a magnet sound design.
Nb3Al superconducting wires have high critical current and low strain sensitivity of the superconducting properties. Therefore, many Nb3Al wires were developed for accelerator or fusion magnets. In this study, critical current and mechanical properties of various Nb3Al wires were investigated. Some kinds of rapid heating, quenching and transformation (RHQT) processed Nb3Al wires were prepared. Young’s modulus and tensile strain dependence of critical current for the Nb3Al wires were measured at 4.2 K and 18 T by the transport current measurement apparatus under tensile load. The strain was measured by the two-strain gauge method. The results show that the residual strains of Nb3Al wires are less than 0.1%. The strain sensitivity of Nb3Al wires were estimated by the power law. We found that the wires with small fracture strain have large strain sensitivity.
Hf addition together with Ta to the Nb cores results in significant refinement of the Nb3Sn grain morphology, leading to large enhancement of flux pinning characteristics. That is why it attracts much interest in the field of Nb3Sn wire development. This effect has been confirmed so far for the internal tin Nb3Sn wires. However, this effect should be naturally expected also for the bronze route Nb3Sn wires. Especially in the application to the next generation fusion magnet DEMO that requires high stress tolerance as well as good critical current density for the strand, the Nb3Sn strand with Hf addition can be a better candidate for DEMO magnet.
In this work, we prepared and tested bronze route Nb3Sn wires with single core configuration to investigate fundamental effects of Hf addition on the microstructure and superconducting properties of bronze route Nb3Sn wires. Nb-4at%Ta-1at%Hf was used as parent Nb core, which was made by arc-melting. Cu-14wt%Sn was made by an induction heating furnace and used as the matrix. As a reference sample, we also prepared a wire with configuration of Cu-14wt%Sn-0.2wt%Ti/Nb. As a result, refinement of grain morphology of Nb3Sn layer was confirmed in the sample with Hf and Ta addition.
Using magnetization techniques to determine the temperature dependence of critical current in Nb3Sn wires is attractive. However, there is a known mismatch in the temperature scaling characterizations when using magnetization data compared to transport data. From a practical stand point, it is the latter that matters, as performance prediction, margin calculations, and other aspects of magnet designs rely on the knowledge of the amount of transport current the superconductor can carry in a magnetic field. In this paper, we will identify some of the underlying issues and propose procedural solutions for determining the temperature dependence of transport critical current in Nb3Sn superconducting wires using magnetization measurements. This way, it becomes possible to combine the simplicity and economy of quick magnetization measurements at different temperatures with accurate prediction of transport properties in extrapolated temperature ranges.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program. The work performed at Lawrence Berkeley National Laboratory was supported by the Office of High Energy and Nuclear Physics, U. S. Department of Energy, under contract No. DE-AC02-05CH11231.
Nb3Sn wires are wildly used in high-field (> 10 T) magnets and have great potential value in the next 20 years. Internal-tin Nb3Sn strand has been developed by many methods for the future fusion reactor, high energy accelerator and so on. Increasing the critical current density of Nb3Sn wire, reducing the use amount of wire in magnets and reducing the price are important ways to promote the industrialization and mass application of Nb3Sn wire. The Optimum Microstructure of High Jc Nb3Sn Wire after medium heat treatment is: (1) there is no Cu6Sn5 phase in the center of the sub-element; (2) there is no Cu-Nb-Sn phase near the inner Nb filament layer; (3) Cu-Nb-Sn phase is uniformly distributed in the all areas between Nb filaments. The above microstructure state is critical to improve the current density of the wire. After medium heat treatment, morphology of wire is improved obviously. The diffusion of Sn reaches 100% and there is no obvious Cu-Nb-Sn phase aggregation. The content of Cu6Sn5 phase decreased to 20%. Thus, in the wire after final heat treatment, there is no coarse grain in the sub-elements. The critical current of the wire increases from 540A to 623A and the residual resistance ratio increases from 66 to 139.
For the High Luminosity upgrade of the Large Hadron Collider (HL-LHC), CERN has procured about 20 tons of high critical current density Jc (>1200 A/mm2 at 15 T, 4.22 K) and high RRR (>150) wire from Bruker-EAS and Bruker-OST (1135 km of the 0.7 mm 108/127 RRP wire; 590 km of the 0.85 mm 192 bundle-barrier PIT wire and; 2180 km of the 0.85 mm 108/127 RRP wire). This conductor has been used for 11 T dipoles (0.7 mm wire) and for the low-beta quadrupoles (0.85 mm wire) of the new HL-LHC interaction regions. For the low-beta quadrupoles, the US-AUP collaboration is also procuring about 2000 km of the same 0.85 mm RRP wire . This is the first large procurement of high-Jc Nb3Sn conductor for accelerator type magnets. The wire was produced in 50 kg billets each resulting in approximately 12 km of the 0.7 mm wire and 9 km of the 0.85 mm wire. To qualify the material produced, for each billet about four critical current and four RRR measurements were performed both by the suppliers and by CERN in addition to copper to non-copper, geometrical and mechanical measurements. The Ic measurements were performed between 12 T and 15 T at 4.22 K. In the paper, a statistical analysis of the procured wire properties is reported and discussed.
In the industry for Nb3Sn conductors at the moment, it is considered that 16 mass% is a limit of the tin content for the bronze process as well as a limit of the critical current density (Jc). Because the mechanical performance of the bronze dramatically changes from ductile to brittle with increasing the thin concentration over 16 mass%. Therefore, the internal tin process using pure tin rod is adopted at predominant companies in the world for producing Nb3Sn wires having large Jc. However, some problems on the internal tin process, such as a tin leakage, low RRR, SC filament merging, large effective filament size, formation of large voids, less mechanical strength, dielectric breakdown, and etc., are of concern.
This brittleness of the high tin bronze over 16 mass%Sn is originated from the precipitation of the coarse delta phase. In conjunction with titanium additives, the coarse delta phase disappeared perfectly and replaced amazingly finer Cu-Sn-Ti ternary precipitates. Eventually we have developed the special bronze with 17.5-18.5 mass%Sn. These super-high tin bronze showed a good ductility at room temperature, and it was successfully fabricated 1,615 multifilamentary wires. In addition, we also studied a simultaneous addition of Ti and Hf to the super-high tin bronze alloys, and tried to fabricate multifilamentary wires as well. In this paper, we will report superconducting properties and microstructures of those unique and novel bronze alloys and Nb3Sn multifilamentary wires.
Development of high temperature superconducting REBa2Cu3Oy (REBCO, RE: Y and rare earth) coated conductors (CCs) would enable cost-effective magnet applications in rotation machines, generators for wind turbine and magnet use in medical imaging machines. To use for these applications, precipitates and structural defects with nano-meter size have been introduced in REBCO films to enhance vortex pinning, resulting in an increase of Jc in magnetic fields. Recently, a low-energy ion irradiation received a renewed interest as a practical method for improving Jc in magnetic fields in REBCO tapes. Low energy systems can be relatively inexpensively implemented for economic large-scale irradiation of REBCO tapes. We have demonstrated an enhancement of Jc by using low-energy ion irradiation, in which we created small cascade and cluster-like defects in iron-chalcogenide superconducting films.[1]
In this talk, we present comparative study of superconducting properties and damage structures in GdBCO CCs irradiated with 2 and 10 MeV Au-ions. In the both irradiation energies, The Tc of the GdBCO CCs gradually decreased with increasing irradiation dose, and started to drop sharply at around 8.0×1011 Au cm–2. As for the critical current properties calculated from magnetization measurement, over 70% Jc enhancement was achieved around 3 T at 30 K after 10 MeV Au-ion irradiations, indicative of effective pinning defects by the irradiation. We also observed a clear decrease in Jc near H//ab in Jc(θ) measurement after the irradiation. This would be attributed to the the damage of stacking faults and intrinsic pinning upon the irradiation. We will also compare superconducting properties in GdBCO films irradiated with differenct energy and dose.
1) T. Ozaki et al., Supercond. Sci. Technol. 33, 094008 (2020).
In high-temperature superconducting films and tapes, optical switching are complex and are determined not only by the laser pulse energy, but mainly by its duration. Thermal processes play the main role at durations from tens to hundreds of ps. To study the physical processes occurring in an HTS tape under ultrashort laser irradiation, using the Comsol Multiphysics software, a multiphysics FEM model of the dynamic description of the system was developed based on the phase field approach. In view of the complexity of the processes occurring during the interaction of laser radiation with matter, when implementing the model, the processes of current flow through the HTS tape and the heat release associated with it, phase transitions, processes of melting, solidification, evaporation, and thermal decomposition of matter under the action of laser radiation were considered. The governing equation of the model is reduced to the thermal equation of the two-phase zone model. The liquid phase is limited by surface tension, and the solid phase is described as a highly viscous liquid whose speed is limited to zero. The cases of a Gaussian laser beam, as well as a beam with a uniform distribution of the laser radiation intensity along the radius, are considered. The limiting regimes of laser action that do not damage the material when a transport current of different magnitude flows, as well as regimes of action that lead to a short-term complete or partial thermal transition of a superconductor to the normal state are estimated, switching times are calculated for different durations and powers of laser radiation, and also at different amplitudes of the transport current flowing through the superconductor.
The reported study was funded by RFBR, project number 20-08-00811
GdBa2Cu3Oy (GdBCO) coated conductors is one of the most promising candidates due to its high critical temperature over 90 K and high critical current density of the order of 1 106 A/cm2 at 77 K. The presences of a-axis-oriented grains has been known to cause the worsening current characteristics, so that it is important to investigate the formation mechanism of a-axis-oriented grains. In this study, the influence of film growth factor on a-axis grains in the GdBCO film was investigated. GdBCO films were deposited on CeO2/Gd2Zr2O7/Hastelloy substrates by a pulsed laser deposition (PLD) technique. Substrate temperature was varied from 700C to 800C at a constant oxygen pressure condition. The proportions of a-axis grains were estimated by the peak intensity ratio in XRD measurement. It was found that the proportions of a-axis grains were influenced greatly by the substrate temperature, 71% at 700C and 3.0% at 760C. Furthermore, XRD analysis revealed the presence of Gd2CuO4 (Gd214) in the film with high proportions of a-axis grains. Then, we assumed that GdBCO grain grows on Gd214 grain in the film and considered the orientation of GdBCO crystal grains in viewpoint of Gibbs free energy for the nucleation. As a result, a-axis grains tend to form at any substrate temperature when GdBCO grain grows on Gd214 grain. Also, a-axis grains tend to form at lower temperature than 740C when GdBCO grain grows on GdBCO grain. It was found that it is essential to suppress the formation of Gd214 to prevent the formation of a-axis grains of GdBCO.
The effect of the magnetic flux trapping in normal-phase fractal clusters on critical currents in percolative HTS composites is studied. The normal-phase clusters are united by the common trapped flux and surrounded by the filling superconducting phase. The superconducting phase fraction is above the percolation threshold so there is a superconducting percolation cluster which is carrying a transport current. The normal-phase clusters have fractal boundaries so their structural irregularities span a wide range of geometric sizes, up to the vortex core diameter. The latter feature makes pinning on such defects effective. Since any motion of magnetic flux causes energy dissipation in superconductors, a method to suppress such motion is of prime practical importance. The effect of flux creep on the critical currents for different values of fractal dimension of normal-phase cluster is analyzed. The modes of collective creep as well as Anderson-Kim creep are considered. The current-voltage and resistive characteristics of percolative superconductors in the presence of the flux creep are obtained, and the critical current values are estimated. The dependence of the resistive characteristics of superconducting composites containing normal-phase fractal clusters on the pinning barrier biasing by the transport current has been established. It is found that the existence of fractal boundaries between normal and superconducting phases intensifies the magnetic flux trapping and suppresses the electric field induced by creep. This feature enhances the current-carrying capability of a superconducting wire. Results apply to YBCO coated conductors for use in superconducting magnet windings.
Columnar defects (CDs) are useful pinning centers (PCs) not only to improve the absolute value of critical current density Jc in a magnetic field (B) but also to modify the anisotropy of Jc of high Tc superconductors: the modification of Jc by installing CDs in a controlled manner can be one of key technologies for superconducting magnet applications using REBa2Cu3Oy coated conductors. Swift-heavy-ion irradiation to high-Tc superconductors can be an effective method to control the CD morphologies by tuning the directions and the energies. In this work, we systematically investigated the morphologies of CDs in different directions in GdBCO coated conductors irradiated with 80 MeV Xe ions by using a transmission electron microscopy. The irradiation with 80 MeV Xe ions produced shortly segmented (discontinuous) CDs along the c-axis. When the irradiation angle were tilted by 20 degrees relative to the c-axis, the morphology of CDs became continuous despite the same irradiation energy. The morphologies of CDs produced by the ion-beams tilted off the c-axis, on the other hand, turned into discontinuous shape from continuous one along the depth direction from the surface. We also investigated the Jc properties of YBCO thin films irradiated with 50 MeV Kr ions and 200 MeV Xe ions respectively, where CDs were installed at various irradiation angles. The values of Jc for the 200 MeV Xe ion irradiated films irradiated were higher than those for the 50 MeV Kr ion irradiated ones regardless of the irradiation directions. When the directions of CDs were dispersed, on the other hand, the Jc was more enhanced both for the 50 MeV Kr and the 200 MeV Xe irradiated samples. These results suggest that the supreme pinning landscape can be provided by further tuning the morphologies of CDs such as discontinuity and direction-dispersion.
We have fabricated Ce and La co-doped Gd123 thin films on LaAlO3 single crystal substrates by the fluorine free metal organic deposition method (FF-MOD). From our previous study, it is confirmed that Ce doping is effective in introducing artificial pinning centers (APCs) into GdBa2Cu3Oy coated conductors. In addition, La doping promotes crystallization and crystal growth of the superconducting phase. By possessing both advantages, Ce 2.0 mol% and La 1.0 mol% co-doped Gd123 film achieved high critical current densities of 0.267 MA cm-2 at 1.0 T, 77.3 K. This improved by about 84% than that for non-doped one. To investigate the effectiveness by other rare earth doping, we also have replaced Gd to them and evaluated those superconducting properties.
We performed characterization of superconducting properties of production 2G HTS wires based on YBCO with Y2O3 nanoparticles, which were developed recently specifically for application in high magnetic field [1], including magnets for compact fusion reactors and particle accelerators. We measured magnetization curves using vibrating sample magnetometer (VSM) in the Quantum Design PPMS (in the 0-9 T range, at 4.2-77 K) and a Cryogenics magnet (in the 0-16 T range, at 20 and 77 K). In-field performance was accessed by calculating lift-factors (LF) as the ratio of a sample’s magnetic moment at a certain temperature and magnetic field to that of the same sample at 77 K, 0 T. We will discuss the application of Zhang’s [2] fit model, to extrapolate the magnetic field dependences of lift-factors to 20 T. We also measured resistivity curves of the samples using PPMS in the field range from 0 to 9 T, and the samples were rotated from orientation H||c (θ = 0°) to H||ab (θ = 90°) at 30° increments. The curves were obtained by the 4-probe technique with a 100 mA measuring current. The microstructural characterization was performed by TEM, and it confirmed the presence of semi-coherent Y2O3 nanoparticles in the YBCO film matrix. In the talk, we will discuss the correlation between the HTS layer microstructure in the samples and the magnetic field, temperature and angular dependences of their superconducting properties.
[1] Molodyk, A., Samoilenkov, S., Markelov, A. et al. Development and large volume production of extremely high current density YBa2Cu3O7 superconducting wires for fusion. Sci Rep 11, 2084 (2021). https://doi.org/10.1038/s41598-021-81559-z
[2] Zhang, X., Zhong, Z., Ruiz, H. S., Geng, J. & Coombs, T. A. General approach for the determination of the magneto-angular dependence of the critical current of YBCO coated conductors. Supercond. Sci. Technol. 30, 025010 (2017).
In recent years, there has been a renewed interest in the suitability and use of the Bi-2212 wires in various fields of application. Many studies highlight the possibility to use Bi-2212 for high magnetic field magnets above 18-20 T.
The purpose of this work is to study the electrical properties of Bi-2212 wires at temperatures above liquid Helium. The samples were obtained via a novel process developed at CNR-SPIN based on an alternation of drawing and groove rolling (GDG). Two samples made by employing Nexans and the new Engi-Mat Bi-2212 precursor powders were investigated. A first characterization was performed with the aim to evaluate the irreversibility field as a function of the temperature (Birr(T)). The Birr(T) dependence was extracted from the bulk pinning force density obtained from the magnetic hysteresis loop M-H measurements performed at different temperatures with the magnetic field directed perpendicular to the sample longitudinal axis. These studies show the suitability of Bi-2212 wires for high magnetic field applications, with good stability of critical current, a non-abrupt decrease in the magnetic field in the range 8 - 12 K, and, most interestingly, an irreversibility field higher than 70 T at 10 K.
Second, by comparing the critical current densities obtained by electric transport and magnetic M-H measurements, by applying the Bean critical state model, we were able to describe the behavior of the filaments-connection bridges, typical in Bi-2212 wires. Moreover, we were able to determine the temperature and magnetic field conditions in which filaments within a bundle are electrically coupled, as well as the opposite limit in which single filaments behave as individuals carrying current elements. We believe that the reported results can be considered of general validity and useful in magnet design.
In this paper, a new configuration of self-shielding DC HTS cable with a “sandwich” structure by interleaving winding is proposed. The distributions of the magnetic field and the critical currents in traditional DC HTS cable and self-shielding DC HTS cable are analyzed and compared in detail. The simulation results show that the self-shielding DC HTS cable can minimize the outer magnetic field and raise the critical current to improve the current capacity, reduce the size of the cable and save superconducting materials. This new structure of cable has enormous prospects in industrial and marine applications where low voltage and high current are required.
High field magnet technologies are supported by the development of advanced superconducting (SC) cable constructed from the composite SC tape. The SC tapes in the helically wound composite cable experience flatwise as well as edgewise bending load together with tensile one. We analyzed precisely the influence of uniaxial tensile load to critical current (Ic) of BSCCO tapes, where the reversible stress / strain limits (R95 / A95) for critical current degradation up to 95% of Ic were defined.
In the helically wound cable, a complicated bending load including flatwise and edgewise components generates in the SC tape. For clarifing quantitatively the degradation of Ic due to bending load, it is efficient to investigate separately the degradation behavior from each flatwise and edgewise bending. In the present study, we designed two types of sample holder applying flatwise or edgewise load to the tape for Ic measurement at 77 K.
The critical currents measured by changing flatwise sample holders with different diameter (D). When bending the tape wire up to Dc = 60 ~ 80 mm, the critical current decreased up to 95%. On the other hand, when the Ic was measured by using the edgewise sample holders, Ic decreased up to 95% for Dc = 1000 ~ 1600 mm. This difference of critical diameters is caused relating to the maximum strain experienced by SC filaments locating at the most outside position. When calculating those strains equivalent to the critical diameters, they were in the same strain range between 0.25 ~ 0.28 %. So we concluded that the degradation of Ic due to both flatwise and edgewise bending originates from the same reason.
China Fusion Engineering Experimental Reactor (CFETR) is a major scientific project independently designed and developed by China and jointly with international cooperation. Engineering design and project infrastructure construction are currently underway. The design goal of CFETR is 1.5-2.0 GW fusion power, and the central magnetic field is up to 17 Tesla, which is much larger than the design parameters of ITER under construction in Europe. In order to achieve the desired high magnetic field, the pre-research of Bi2212 high temperature superconducting CICC magnet was carried out in the Institute of Plasma, Chinese Academy of Sciences. The Bi-2212 superconducting wire undergoes twisting and untwisting operations during the stranding of the cable. In order to study the performance changes of Bi-2212 during torsion and untwisting, twisting experiments with various angles were designed and tested and analyzed. It can be seen from the test results that there is no significant change in the heat treatment performance of the Bi-2212 superconducting wire after torsion. The Bi-2212 superconducting wire before heat treatment is not sensitive to torsion deformation.
Bi-2212/Ag round wires are promising conductor candidates for the development of high-field magnets up to 25 T. With very high upper critical magnetic field and critical current density, Cable-In-Conduit Conductor (CICC) comprised of Bi-2212/Ag superconducting wires is under designing for the central solenoid coils of the China Fusion Engineering Test Reactor (CFETER). The current degradation due to the inter-wire contact force is a key issue that required to be reduced. However, the relevant publications for Bi-2212/Ag superconducting round wires are very limited to our knowledge. In this paper, the critical current degradation of Bi-2212 round wires due to inter-wire contact force are studied at 4.2 K in a background magnetic field up to 14 T. The crossover straight wires are pressed, and reacted together with other un-pressed wires, the wire samples are reacted with and with no pre-pressure for comparison. The inter-wire contact force dependence of critical current of these wires are then investigated under various crossover angles.
High-temperature superconductors (HTS) are being considered for considered for use in high field dipole and quadrupole magnets for future particle accelerators. In comparison with low-temperature superconductors (LTS), the persistent current magnetizations of HTS are much larger. Because of this, the magnet error fields are much larger (since they depending on the size and shape of the superconductor). In this study, we measured the magnetization of a 9*12 Bi-2212 Rutherford cable. A 3 T dipole magnetometer system was used for the measurement. In this system, the sample is placed on a probe and inserted into a dipole magnet. There are six coils wired in series and arranged as three pairs of saddle shape coils on the outer part of the probe as compensations coils. In addition, a pick up coil is present around the sample. As a maximum ramp rate of 0.6 T/min, the magnet reached 3 T at maximum current of 150 A. The tests were performed in liquid helium environment and M-μ0H was measured. M-H loops and magnetization are compared to magnetization measurements on individual strands measured in a PPMS, and in a hall probe magnetization system.
High-temperature superconducting (HTS) tapes in a superconducting cable are twisted and stacked as multi-layer. The superconducting tapes are exposed to a combined magnetic field of the circumferential magnetic field created by the inner layers and the longitudinal magnetic field created by the twisted outer layers. The AC loss in superconducting tapes under HTS cable electromagnetic conditions is determined by the amplitude of the transport current, the amplitude and direction of the magnetic field, and the twist pitch of the HTS tapes.
Previously, the AC loss characteristics under these conditions were investigated. In this experiment, we reproduced the electromagnetic condition of one layer of the HTS cable in which the circumferential magnetic field was applied to the inside of a cylindrically twisted HTS tape by the transport of current through it, and the longitudinal magnetic field was provided by a solenoid coil. Under these conditions, AC losses were measured by a calorimetric method at HTS tapes twist angles of 5 to 20°. In this study, we modeled the AC loss under electromagnetic field conditions in the superconducting cable based on these data. In general, the HTS tape has the lowest loss when the magnetic field is parallel to the tape axis and the highest loss when it is perpendicular to the tape axis. Based on these characteristics, we modeled the AC loss by focusing on the maximum and minimum values of the loss. This model allows easy determination of the losses in each layer of the superconducting cable for minimizing the AC loss load of the superconducting cable.
Bi-2212 conductor is now a serious candidate for HEP, NMR, and other ultra-high field magnet applications since our demonstration that 50 bar over-pressure heat treatment (OPHT) is reliable and predictable for many coil reactions. As more magnet designs are generated, predictable and consistent critical current density ($J_{\text{c}}$) values are important too. In fact there are still $J_{\text{c}}$ uncertainties of order 30-40\% that we ascribe to a still poorly understood convolution of powder quality, filament uniformity and the OPHT itself. We here report an extensive study of the critical current distributions in $\sim$ 1 m long wires made by B-OST derived from $d^2V/dI^2$ analyses of the $V-I$ curves measured on ITER-like barrels. These transitions can be well fitted by Gaussian distributions and characterized by their relative standard deviations $\sigma/\mu$. We find that recent Engi-Mat powder wires made by B-OST have significantly higher $J_{\text{c}}$ and lower $\sigma/\mu$ than found in earlier B-OST wires made with Nexans or SCI powders. We also find that the highest $J_{\text{c}}$ values provided by minimum $T_{\text{max}}$ and minimum time in the melt ($t_{\text{melt}}$) during OPHT also correspond to significantly lower $\sigma/\mu$ values. We attribute this property degradation with higher $T_{\text{max}}$ to a loss of filament connectivity associated with worsening texture associated with filament merging during the melt step of the OPHT. We will report $d^2V/dI^2$ evaluations of many multifilament Bi-2212 wires made over the last decade and seek to deconvolute powder and filament quality effects from OPHT variations. A huge advantage of B-OST wires is that they can be made in continuous lengths of $>$ 1 km at 1 mm diameter. We believe that such $I_{\text{c}}$ distribution measurements may also be an important quality control tool to apply to lead-in and lead-out ends of coil windings.
R&D on joints between superconducting wires or tapes is one of the most important issues for the development of large-scale superconducting applications such as magnet, rotation machine and so on. Although the electro-magnetic properties between superconducting joints have been evaluated in several ways, the interfacial structure of the joint should also be investigated in order to sufficient understand the state of the joints. In this study, we have investigated the air-gap between the joints of REBCO tapes by using a non-destructive method, X-ray Computed Tomography (CT). The superconducting joint was prepared by a method using additionally deposited precursor layer and the R-T transition could be obtained. However, air-gap between two REBCO tapes was also confirmed by X-ray CT. Therefore, we have binarized the CT images for three-dimensional air-gap analysis. For the binarization, we have adopted an advanced binarizing method, “locally adaptive binarization processing” because the CT images were affected by artifacts such as metal artifact and beam hardening. After the process, three-dimensional model of the air-gap was successfully constructed. As the results, wide air-gap across the tape width was confirmed from the edge of the joint to the depth of 610 micrometer. In addition, one-side edge had longitudinal air-gap of the thickness of 44 micrometer. These results are significant for the estimation of the joint including the electrical and mechanical properties.
This study is partly supported by the JSPS KAKENHI Grant Numbers JP18H01928, JP19H05617.
Low resistivity joint technique for high-Tc superconducting (HTSC) tapes is one of the most indispensable techniques for practical applications. At the present time the solder joint technique is widely used for joining HTS tapes for the non-superconducting joint. However, in the case of a joint using a solder, the resistance across the joint cannot be very low because of relatively high resistivity of soldering material. Thus in the present study, we propose solid phase joining technique to make direct joint of REBCO tapes, as an alternative to solder joining technique. In this solid phase joining technique, we directly join the copper stabilizing layer and get rid of the soldering material, so that we can expect reduction of joint resistivity. We have succeeded in joining REBCO tape with this technique. The measured resistivity was about 23.2 nOhm for 20mm joint at LN2 temperature. The details of joining procedure and its properties will be shown in the presentation.
The author would thank Messrs. Y. Iwata, T. Yokoyama, Y. Ryoki, K. Iwai, K. Iwase, D. Okura, K. Ito, S. Kato for experiments, Dr. Sergey Lee for REBCO tapes.
The NUCLOTRON type cable has been chosen for developing a fast cycled superconducting dipole for the booster ring of the HIAF project at IMP. The splices of the cable are key components for the magnet. A design which has a resistance about 10-9 Ohm and is easy to be fabricated is developed. The structure of the joint is optimized with Opera software. And reliable fabrication process is developed. In this paper, the simulation of the structure, the key fabrication art and the cold test of the joint is discussed.
GdBa2Cu3O7-δ (GdBCO) has high critical current density (Jc) of the order of 106 A/cm2 at 77 K in self-field and higher critical temperature (Tc) than that of YBa2Cu3O7-δ. Therefore, GdBCO coated conductor (CC) has been expected as a promising wire material. For the wire application, superconducting joint of CC has been required to lengthen them. In our previous work, superconducting joint of GdBCO CC has succeeded via crystallizing two samples of CC with precursor film of GdBCO at face-to-face manner. To obtain high current with low resistance in jointed sample, high crystallinity of GdBCO at joint area and wide joint area play important roles. In this work, we investigated the joint conditions by focusing on heat-treatment temperature and precursor film thickness because these conditions affect crystallinity of GdBCO and joint area. Two GdBCO samples were prepared, one with a precursor film and another without it. The precursor film was prepared with thickness of approximately 50 nm to 200 nm by a pulsed laser deposition method. Then the samples were set face-to-face and crystallized at 720C to 820C under mechanical pressure of 40 Pa in an electric furnace to join them. In terms of heat-treatment temperature, X-ray analysis revealed that peak intensity ratio of GdBCO crystallized at 800C was 1.5 times than that at 720C. Optical microscope observation showed approximately 1.6 times increase of joint rate at 800C in comparison to the one at 720C. When we increase precursor film thickness from 50 nm to 200 nm, joint rate increased from 15.7 % to 25.4 %. These experimental results showed that heat-treatment around 800 C with thicker precursor film are effective conditions for this process.
In this work we performed a series of measurements investigating both electrical and thermal contact resistance of YBCO stacks and cables for various surface preparation conditions. We explored the transverse resistance for sets of REBCO tape stacks, measured in a “through-the-stack” configuration. We also explored the ICR of YBCO cables under selected conditions. We analyzed these direct measurements to examine the contributions of the tape surfaces vs the internal tape contributions, and quantified ICR in terms of a contact area independent parameter a contact efficiency, η, defined as η = Rc*Ac (the contact resistance * contact area). Measurements were made from 4.2 K to 77 K using a standard 4-point technique. We explored two different ICR modification approaches. In the first, various ten-layer tape stacks were heat treated at 200˚C in an Ar-O2 environment for 30 min. Before the start of the HT, applied pressures ranging from 0 to 15 MPa were applied by a mechanical constraint. During the HT the constraint remained fixed, which allowed some relaxation and pressure reduction. Constraint was retained until after ICR measurement. These measurements were also applied to round conductor on core YBCO cables with uniaxial applied pressure. In a second approach to surface modification, the individual tapes were electroplated with Ni and, alternatively, Cr before being assembled into a ten stack. ICR was measured for P up to 70 MPa. Mechanical modulus was also measured for both tape stacks and cables, and are reported. A final method was to apply epoxy with nickel filling in between the YBCO tapes, after which the tape stack was compressed under different pressures for curing, and subsequently measured for ICR. Results showed that the surface contact efficiency were modified significantly by these processes.
In REBCO tape having multi-layered structure, resistance of Cu/Ag and Ag/REBCO interfaces (interface resistance) is one of the major factors of joint resistance of tape-to-tape joints. Since the interface resistance depends on the manufacturer and/or lot number of REBCO tapes, it is necessary to evaluate the interface resistance beforehand at temperatures and magnetic fields of the operating environments of applications. In a previous research, the contact-probing current transfer length (CTL) method was proposed as a nondestructive method to evaluate interface resistivity (interface resistance for unit area). The temperature dependence of the interface resistivity has been evaluated with this method. In the present research, the authors evaluated the magnetic field dependence of the interface resistivity for several kinds of REBCO tapes.
The temperature of the test section was controlled by a conduction cooling system and heaters. The CTL was obtained by measuring electric potentials at seven points on the REBCO tape with contact probes at 10–70 K and 0–15 T. A numerical simulation was also conducted to evaluate the relationship between the CTL and the interface resistivity. Comparing the relationship and the experimentally evaluated CTL, the interface resistivity was derived for each REBCO tape.
As a result, interface resistivity tended to decrease with increasing magnetic field. The result indicated that resistance dependence of the Cu/Ag and/or Ag/REBCO interfaces on the magnetic field is different from that of ordinary metals.
The Nb3sn was prepared successfully by two methods of mechanical alloying followed by their respective heat treatment process. The microscope morphology, crystal structure, and superconducting properties were investigated. From the results, mechanical alloying was an effective method to produce the precursor, which changed the reaction formation energy of Nb3sn and can produce Nb3sn more easily and quickly. The phase transition processes were measured by XRD in different temperatures.
Keywords Nb3sn· Mechanically Alloying· Heat Treatment
The superconducting joint is one of key technologies to evolve high temperature superconducting (HTS) conductors and their applications. Various joint techniques have been proposed in these years [1]. To evaluate developed joint efficiently, we developed a resistance evaluation system for superconducting joints [2]. The system consists of a superconductor sample with a joint, a copper coil to inject (induce) current to the sample, and a superconducting magnet for external fields applied to the joint. Using this system, joint resistance (R$_j$) ranging 10$^{-15}$-10$^{-7}$ Ω can be quantitatively evaluated as a function of injected current (I$_i$$_n$) magnitude, temperature, and external magnetic field. In addition, I$_c$ and T$_c$ of the joint can be evaluated. In this paper, we report the evaluation results of the REBCO superconducting joint [3]. At 4.2 K without external field, R$_j$ stayed ~10$^{-14}$ Ω at I$_i$$_n$ up to ~300 A. This indicates that the I$_c$ of the joint is sufficiently larger than 300 A. At 77 K, I$_i$$_n$ of ~150 A rapidly decreased to ~116 A and evaluated R$_j$ was ~10$^{-12}$ Ω. This higher R$_j$ is considered to be due to a high load factor of ~100% at the joint. R$_j$ at 4.2 K showed almost no dependence on external field ranging 0 ≤ B ≤ 3 T. Even at 77 K and 3 T, the junction carried I$_c$ of ~17 A and R$_j$ was ~10$^{-12}$ Ω. This work is based on results obtained from a project commissioned by JST-Mirai Program Grant Number JPMJMI17A2, Japan.
[1] G. D. Brittles et al., Supercond. Sci. Technol. 28, 093001 (2015).
[2] K. Kobayashi et al., IEEE Trans. Appl. Supercond. 30, 9000204 (2020).
[3] K. Ohki et al., Supercond. Sci. Technol. 30, 115017 (2017).
Simply- and quickly-fabricated low-resistive joints between various high-temperature superconducting (HTS) tapes are needed for some cases in high-temperature superconducting (HTS) magnets such as nuclear magnetic resonance (NMR) magnets, nuclear fusion magnets, and so on. We have developed pressure welding with indium foil inserted between the joint surfaces at room temperature or with a low-temperature heat treatment at ~370 K. The joint achieved a joint resistivity (product of joint resistance and joint area) of 11–25 nano-Ohm cm2 for silver sheathed BSCCO tapes and 25–35 nano-Ohm cm2 for copper-stabilized REBCO tapes at 77 K, self-field with shorter joint length less than 10 mm, which were comparable or less than those for conventional pressure-controlled solder joints. The Joint resistivity was also reduced at 4.2–10 K to be from one-third to a half of that at 77 K. The joint performance has been improved sufficiently with short joint, however, longer joint with lower joint resistance is required for a practical usage.
In this study, we fabricated various joint samples using the pressure welding with indium insertion changing joint length and combination of HTS tapes, REBCO-REBCO, BSCCO-BSCCO and REBCO-BSCCO. The joint resistance and critical current were evaluated at 77 K (cooling with liquid nitrogen) at first, then evaluated at 4.2 K (cooling with liquid helium). The preliminary fabrication of BSCCO tape with 50–250 mm joint length showed that the joint resistivity became twice larger than that for short samples with critical current degradation. The joint performance of various longer joint samples with improved fabrication process and detail of the results are presented at the conference.
Though low resistance joint is important technology for persistent current operation of HTS magnet system, superconducting joints of REBCO wires require direct epitaxial growth between REBCO surfaces that can only occur in high temperature procedure. On the other hand, at 4.2 K operation, even conventional solder spliced joints of coated conductors should have quite low joint resistance if low enough interfacial resistance was obtained, because resistances for both solder and Ag metal themselves should be negligible. But usually the interfacial resistances between REBCO and sputter deposited Ag protection layer are 10-11～-12 $\Omega$$\cdot$m2 at wide temperatures for typical coated conductors.
We deposited deeply Ag-doped REBCO films of 0.5~2.0 $\mu$m thick by hot-wall pulsed laser deposition (PLD) method on 12 mm wide and 50 $\mu$m thick Ni-Cr alloy tapes with IBAD templates. Ag protection metal films of 2.0 $\mu$m thick were deposited on them by sputtering. Lap or bridge Joints of those tapes were made just by soldering. Joint resistances were measured by DC 4 probe method at 77 K and by loop current attenuation at 4.2 K. Microscopic structure was evaluated by XRD and SEM. Metal Ag particles were clearly dispersed in c- and a-axes oriented REBCO films. Jc of those REBCO films ranged from 0.2~1.8 MA/cm2 at 77 K, 0 T. Joint resistance was measured as 0.9~1.1x10-12 $\Omega$$\cdot$m2 at 77 K, and 1.6~2.8x10-13 $\Omega$$\cdot$m2 at 4.2 K. Double layer structure of a thin Ag-doped REBCO film on a high-Jc 2.5 $\mu$m thick REBCO film had also low joint resistance without spoiling high-Jc properties. The results indicate a possibility to make low resistance joint of 10-12 $\Omega$ just by soldering of commercial REBCO coated conductors.
We are studding the superconducting joint between multi-filamentary Bi2223 tapes with incongruent melting (JIM) method, to develop a high-field 1.3 GHz-NMR in Japan. We obtained critical currents of 12 A at 77 K and 177A at 4 K for the reinforced HT-NX type wire in early stage of the study [1], and a high critical current above 50 A at 77 K was obtained in non-reinforced H type wire [2]. For application in NMR magnet, improvement of the critical current in the HT-NX type wire is necessary. In this study, we developed a multi-spot heating device having two heating stages that two junctions can be heat treated simultaneously. In experiment, a joint sample with 5 junctions was prepared at 850 °C for a short time of 30 s. The critical current was measured at 77 K. The result shows that total critical current of the 5 junctions was about 23 A, and this value is about 2 times than that of previous result in HT-N type wire. To investigate the effect on total critical current in each junction, we also measured the critical current for the 4, 3, 2, and single junctions, by cutting off the junctions one by one from then end junction. The results will be presented in upcoming MT27.
Acknowledgements:
This work was supported by JST-Mirai Program Grant Number JPMJMI17A2, MEXT project of Leading Initiative for Excellent Young Researchers (LEADER) Project ID 16810210, and JSPS KAKENHI Grant Number JP18K04719, Japan.
[1] X. Jin, Y. Suetomi, R. Piao, Y. Matsutake, T. Yagai, H. Mochida, Y. Yanagisawa, H. Maeda, Supercond. Sci. Technol., vol. 32, 2019, Art. no. 035011.
[2] Shintetsu Kanazawa, IEEE Transactions on Applied Superconductivity, vol. 31, 2021, Art. no. 7000104.
In ITER magnet system, there are feeders for toroidal field (TF) coils, poloidal field (PF) coils, central solenoid (CS) modules, correction coils (CC), magnet structure cooling and monitoring instrumentation. Main busbar is used for TF, PF and CS feeders and corrector busbar for CC feeders. Main Busbar (MB) operated up to 68 kA with peak field of 3.6 T is used for TF, PF and CS feeders. Operating condition up to 10 kA with peak field of 2.9 T is led by CC feeder consisting of Corrector Busbar (CB). Nearly 250 feeder joints and coil to feeder terminal joints shall be realized during on-site assembly. The segments of superconducting busbars in each coil feeder are required to be connected in series and to the current lead and to coil terminals with busbar joints. Connections to each segment of MB and CB and coil rely on the twin-box shaking hands concept. The two half-joint boxes are assembled with shims as a means of misalignment mitigation of the assembly tolerance. In turn, ground insulation is made with compound tapes of glass-fiber and polyimide film to withstand the test voltage of 30 kV. Paschen test is considered in terms of technical benefits, risk and project schedules. Structure parts mainly consist of cooling pipes, instrumentation ducts, thermal shield and vacuum duct to complete the assembly of joint regions. The paper describes the assembly status of feeder-type busbar joints and its structures. This first-of-a-kind assembly on the segmented superconducting busbars is carried out using an approach where risks are identified, assessed and prioritized. Development on the busbar joint assembly processes via qualification and successful implementation of the technique to realization at assembly phase are addressed.
In recent years, magnesium diboride (MgB2) wire has become a promising candidate for the development of superconducting magnetic resonance imaging (MRI) magnets because of its critical temperature (39 K), which allows magnets to be operated without using liquid helium. Extensive research using unreacted MgB2 wire has enabled MgB2 MRI magnets to be operated in persistent current mode (PCM). We previously demonstrated the strong possibility of using the superconducting joint technique for developing MgB2 MRI magnets. However, MgB2 joints that have already reacted and are subsequently damaged by quenching are impossible to reproduce with the unreacted joint technique. In this study, we developed a superconducting joint technique for “reacted” MgB2 multifilament wires fabricated by a powder processing method using Mg and B powder (in situ) and reacted MgB2 powder (ex situ). A customized laboratory-built induction furnace was used to locally heat the jointed area to prevent the non-jointed region from becoming overheated. The superconducting properties of the joint such as the critical current and close loop test were evaluated. Moreover, the SEM images and EDS results were analyzed to determine the temperature and duration of heat treatment.
< Acknowledgment>
This work was supported by the Korea Basic Science Institute under Grant D110200
The next generation NMR spectrometer operated at 1.3 GHz (30.5 T) is currently being developed [1]. The superconducting magnet in this NMR consists of low temperature superconducting (LTS) coils using Nb-Ti and Nb3Sn, and high temperature superconducting (HTS) coils using Bi2223 and RE123, which are connected in series. Superconducting joints between Nb-Ti and Bi2223 are preferable to realize the persistent-current mode operation of this NMR magnet. However, we are facing difficulties to realize the superconducting joints between Nb-Ti and Bi2223 wires. Instead, we are developing ultra-low resistance joint between Bi2223 and Nb-Ti wires using superconducting Bi-Pb solder. The resistance of this joint is required to be sufficiently low, i.e., below 0.1 nΩ to operate the 1.3GHz NMR magnet in the persistent-current mode. The superconducting joint between Nb-Ti wire and Bi-Pb solder was achieved using the conventional method. On the other hand, Bi2223 wire was jointed to the Bi-Pb solder through Ag sheath. The resistance of the joint was measured by four-probe method at 4.2 K. We have successfully fabricated the joint between Bi2223 and Bi-Pb with sufficiently low resistance of 0.097 nΩ. This work was supported by JST-Mirai Program Grant Number JPMJMI17A2, Japan.
References
[1] H. Maeda, J. Shimoyama, Y. Yanagisawa, Y. Ishii, M. Tomita, IEEE Trans. Appl. Supercond. 29 (2019) 4602409.
This study analyzes the current bypass mechanism of a metal stitching smart insulation (SI) coil rolled by coating vanadium oxide (V2O3) on a metal stitching wire prepared by generating micro-holes into a second generation (2G) high-temperature superconducting (HTS) wire using a laser and by filling the micro-holes with metal solder material. Results showed that the metal stitching wire with laser-generated holes had a noticeably lower Ic loss due to damage and low turn-to-turn resistance. This facilitated the current bypass at the transient state of the SI 2G HTS coil. For effective analysis, the metal stitching SI coil was compared with a non-metal stitching SI coil, and the positive effect of the metal stitching apart from current bypass was discussed and analyzed.
V2O3 has been studied as a smart insulation material for 2G high-temperature superconducting (HTS) coils owing to its remarkable metal-to-insulator transition (MIT) upon heating or cooling via a critical temperature (Tc) of ~160 K. The smart insulated (SI) coil regulates its function according to the MIT properties of V2O3. At temperatures below Tc, V2O3 acts as an insulator, whereas it becomes a conductor above Tc. Under steady-state conditions, the SI coil operates normally as an insulation coil and when quenching causes the coil temperature to rise, the turn-to-turn resistance is lowered, and the current bypasses between the turns as in a no-insulation coil. However, V2O3 has a high critical temperature and low conductivity compared to GdBCO tape, resulting in a small amount of current bypassing the layers of the coil; consequently, this affects the stability and protection of the coil against quenching. Dopants can be incorporated in V2O3 to reduce the critical temperature and improve the electrical conductivity. In this study, we investigated the electrical characteristics of the GdBCO coil, insulated with V2O3 doped with Mo ((V1-x Mox)2O3), by carrying out charging/discharging and overcurrent tests. Additionally, we analyzed the elemental composition and surface morphology of the (V1-x Mox)2O3 paste using EDS and SEM, respectively.
< Acknowledgment>
This work was supported by the Korea Basic Science Institute under Grant D110200
The High Temperature Superconducting (HTS) magnet system is immersed in a sub-cooled liquid nitrogen (LN2) and continuously refrigerated by a cryogenic cooling system. Especially, in case of the side-wall cooling type, the HTS magnet system is located well below the level of LN2 for thermal and electrical safety and the cryogenic gaseous nitrogen (CGN2) is filled above LN2. However, the method of determining selection criteria for the optimum level of LN2 in HTS Magnet System has not been yet deeply investigated. . Therefore, in this work, the process of determining the selection criteria for the level of LN2 in HTS Magnet System is proposed. A sphere-to-plane electrode system made with stainless steel is used under DC and DC superimposed overvoltage. A sphere electrode is surrounded by CGN2 and a plane electrode is immersed into LN2 and, the dielectric experiments are performed according to the level of LN2. The electric filed intensity according to the level of LN2 is calculated by the finite element method (FEM) and is analysed using the weibull distribution. Moreover, the electric field utilization factor is adopted to analyze the uniformity of the electric field of the electrode system. As a result, it is found that the selection criteria for the level of LN2 influenced the cryogenic design of the HTS magnet system.
Abstract: The YBCO racetrack pancake coils were wound by dry wing followed by impregnation. Various materials such as epoxy resin, paraffin, grease and so on with and without fillers were measured to impregnate coils. The superconducting characteristics of the coils after above different materials of impregnation were tested. Due to the anisotropic of the racetrack shaped coils, the impregnation material need to improve the stiffness of the coil. Among the materials, paraffin-impregnated coil exhibited the stiffness to some extent, strong operability and repeatability but had the disadvantage of poor heat resistance.
Keywords：YBCO; Racetrack Pancake Coils; Vacuum Impregnation; Superconducting Characteristics
The weight loss of the organic composite materials and their matrix resins have been measured in vacuum. These are intended for use as insulating materials of fusion superconducting magnets or as structural materials used in aerospace application. Since in these applications they are used under the radiation environments, the degradation of mechanical strength will be measured together with the weight loss in the radiation environments.
In this experiment the before irradiation test was conducted to obtain a resin selection guideline. The resin used was basically epoxy and the resins with different numbers of functional groups and curing agents were prepared. The weight loss of these resins after curing was measured and the effect of post-curing was also investigated. Furthermore, Glass Fiber Reinforced Plastics (GFRP) and Carbon Fiber Reinforced Plastics (CFRP) were prepared using the identical resin matrices as the resin samples and the weight loss of each composite material was also measured.
Even in the epoxy with a low crosslink density, the weight loss was suppressed by the post curing. The weight loss was not also observed in FRP having a same epoxy matrix with identical heat treatment. No weight loss was observed for the polyfunctional epoxy and the FRP having the polyfunctional epoxy. Based these data, a guideline was obtained for selecting the epoxy materials used in vacuum.
This study analyzes the output characteristics of a 100-turn non-rotational-type metal insulation (MI) coil and a no-insulation (NI) coil installed inside a 1-MW armature with external fluctuating magnetic fields. Experiments were conducted to investigate the change of state and output performance of the superconducting coils based on the fluctuating magnetic field prior to the development of a superconducting rotating machine. Results showed the output magnetic field of the two coils decreased and the reduction of the NI coil was more significant than that of the MI coil. It was verified that the reduction rate was proportional to the intensity of the fluctuating magnetic field and the operating current value of the superconducting coil. The results were analyzed and the correlations were investigated by performing an eddy-effect analysis using the finite element method.
The performance of accelerator magnets is strongly relying on the dielectric strength given by the electrical and mechanical robustness of the insulation system. This is in particular relevant for the current development of high field superconducting Nb3Sn magnets with their insulation system made from fibre reinforced resin. During the assembly and operation, this insulation system is exposed to high mechanical compressive and shear stresses. The focus of the study was aiming to investigate this mechanical shear strength of the composite. The experimental tests have been performed at room and cryogenic temperature, determining the mechanical strength and the failure mechanisms of the cable insulation system. Within this test the inter-laminar shear strength (ILSS) and non-standardized combined shear compressive strength were determined. The test sample preparation was based on the manufacturing procedures and materials used in the series fabrication for the CERN HL-LHC Nb3Sn coils. The individual insulation systems are varying in the S2-glass yarn density, the sizing, and the fibre volume fraction. Furthermore, the presence of mica insulation on the mechanical strength has also been studied. This paper describes the applied measurement procedures used during the test campaign, and presents the relevant measurement results, identifying the mechanical limitations of the insulation system.
The strain sensitivity of Nb3Sn is considered one of the main challenges that has to be solved to use the full potential of this conductor in particle accelerator magnets application. In these applications, significant forces are applied to the superconducting coils both during the assembly and cooldown to cryogenic temperatures, and then during powering. The composite coil reacts to these forces, that are distributed between the insulation and the cables. In most common designs, the cable insulation is made of impregnated glass fiber, which can be significantly damaged during the coil reaction. This paper presents novel stiffer heat resistant insulation designs, that might allow to reduce the stresses applied on the conductor. The performances of the novel designs were tested on impregnated 10-stacks. The turn-to-turn resistance was measured at cryogenic temperatures, and the mechanical properties at room temperature. Finally, the potential impact on magnet performances was numerically demonstrated on a reference dipole magnet.
The Superconducting Conductor Testing Facility, which developed to evaluate the reliability of engineering technology and safe operation in fusion reactor operation environment., is under engineering design by ASIPP. In case of an emergency shut-down like in succession of a quench, the voltage across the coil may rise to about 2 kV. Therefore, the facility has to be provided with a reliable insulation. The preliminary design of the insulation system is introduced in this paper. The insulation system of Superconducting Conductor Testing Facility includes turn and ground insulation. And the insulation system is composed of S-glass fiber reinforced tape and vacuum-pressure impregnated in a DGEBF epoxy system. The mechanical and electrical properties are being subjected to investigations with respect to the design requirements and operating conditions. The test results are analyzed to verify the feasibility of insulation system design.
Since superconducting technology has advantages of high efficiency, large capacity, and eco-friendliness, HVDC superconducting power devices such as superconducting cable, transformers, fault current limiters, and magnetic energy storage are being extensively studied. The creepage distance of solid insulator is very important for the reliable and economical insulation design of the HVDC superconducting power device. The switching impulse superimposed on DC voltage, can cause critical stress to the insulation of HVDC superconducting power device and can potentially result in breakdown. Therefore, the solid insulator of HVDC superconducting power device must have sufficient creepage distance to avoid breakdown under switching impulse superimposed on DC. In this paper, the surface flashover experiments were performed by applying switching impulse superimposed on dc to glass fiber reinforced polymer (GFRP) and polytetrafluoroethylene (PTFE) specimen in cryogenic environment. The surface dielectric characteristics were analyzed according to the creepage distance and polarity of the applied voltage. From the experimental results, we concluded that increasing the creepage distance resulted in an increase in surface flashover voltage. The surface dielectric strength of GFRP was found to be higher than PTFE. In addition, surface flashover voltage was lower in case of superposition of same polarity voltage compared to the opposite polarity voltage. Therefore, the optimal creepage distance design of solid insulator in HVDC superconducting power device is possible by taking into account the same polarity superposition.
High-temperature superconducting (HTS) cables are rapidly developed for their increased transmission capacity and reduced power transmission losses, and PPLP with excellent low-temperature dielectric and mechanical characteristics is used as insulation materials for HTS AC cables. However, unlike AC, since the direction of the electric field does not change in the DC environment, the space charges are accumulated in the insulation materials, which distorts the electric field distribution and can cause partial discharge and electrical breakdown even at a low applied voltage. Especially, the space charges accumulate well at the interface between different materials, for the use of PPLP with several kinds of the interface in HTS DC cable, the research on space charge is essential. Although the study of space charges for PPLP at room temperature has been actively conducted, the study of space charges at cryogenic temperatures should be still needed. In this paper, the trap energy distribution of PPLP according to PP ratio at cryogenic temperature was analyzed. The space charge of PPLP for superconducting DC cables was studied by measuring isothermal relaxation current (IRC). The IRC theory is a way to know about the trap energy density of space charges by measuring the current generated during the trap and de-trap process. The measurement was conducted using an electrometer by applying a constant electric field in the liquid nitrogen (LN2). The measured current consists of polarization current and leakage current, the trap energy distribution was calculated from the polarization current, and the conductivity was calculated from the leakage current. And the optimum ratio of PP with the lowest trap energy density was derived by varying the thickness of PP and Kraft paper while keeping the total PPLP thickness constant. Also the trap energy distribution and conductivity according to the applied electric field were compared for each thickness ratio.
A variable resistance thin dielectric insulation coating for REBCO tape HTS coils has been developed. This new type of insulation system switches between fully insulating and conducting, after an increase in inter turn voltage. Non-Insulated (NI), fully soldered, HTS coils have proven to be very reliable; NI coils are achieving high magnetic fields above 25 Tesla and are almost impossible to quench. Over-current operation simply redirects the excess current out of the superconducting tape, to flow radially through the coil then back to the power supply. The internal coil resistance can then run the current down when the power supply is switched off. The disadvantage with NI coils is, as the coil volume and inductance increases, the charging / discharging time can take many hours, even days. This is not compatible with magnet systems that need accurate and fast current to magnetic field control, such as accelerators or other systems. With the Varistor Insulation (VI) we aim to achieve both robust performances as seen in NI coils and fast ramping with controlled current to field transfer functions.
In this paper we present the electrical characterization of the insulation at room temperature and cryogenic temperatures, along with simulated magnet operation during ramping, normal operation and failure modes. We discuss other features of the VI insulation such as, application methods to provide thin layers, and alternative formulations to tune its properties. Its ability to act as a distributed quench heater when the voltage threshold is exceeded is also discussed. Finally, the application of the insulation material is documented during the construction of small test pancake coils.
A quench detection system was developed for protecting and monitoring the superconducting solenoids for the Muon-to-Electron Conversion Experiment (Mu2e) at Fermilab. The quench system was designed for a high level of dependability and long-term continuous operation and is based on three tiers: Tier-I, FPGA-based Digital Quench Detection (DQD); Tier-II, Analog Quench Detection (AQD); and Tier-III, quench controls and data management system. The Tier-I and Tier-II are completely independent and fully redundant systems. The Tier-III system is based on National Instruments (NI) C-RIO and provides the user interface for quench controls and data management. It is independent from Tiers I & II. The DQD provides both quench detection and quench characterization (monitoring) capability. Both DQD and AQD have built-in high voltage isolation and user programmable gains and attenuations. The DQD and AQD also includes user configured current dependent thresholding and validation times.
A 1st article of the three-tier system was fully implemented on the new Fermilab magnet test stand for the HL-LHC Accelerator Upgrade Project (AUP). It successfully provided quench protection and monitoring for a cold superconducting bus test in November 2020 and later for the AUP magnets. A detailed description of the system along with results from the AUP superconducting bus test and the pre-series magnet tests will be presented.
The Universal Quench Detection System (UQDS) has been primarily developed to detect quenches in various superconducting magnets of LHC’s High Luminosity upgrade (HL-LHC). The functionality of the system, which comprises insulated high-resolution digitizing front-end channels and a central processing element, is mainly defined by the configuration of the central FPGA (Field Programmable Gate Array). Additional elements such as redundant power supplies, configurable interlocking capabilities and a communications controller are completing the functionality of the system. The system’s architecture is designed to be flexible enough to detect quenches in all superconducting elements of HL-LHC. The application-specific digital signal processing and quench detection algorithms are implemented in the firmware of the FPGA and thus can be changed according to the required functionalities. To facilitate this process, the firmware has been structured accordingly and automated code generation techniques are used.
The strategy of testing prototypes of the quench detection system with prototypes of the magnets allows an early evaluation of the system, minimizing operational issues in the final installation. This strategy has been already applied at CERN to the 11 T dipole magnets in previous years and extended as well to other magnet families of the HL-LHC Project.
We give a system description and focus on the specific configurations for three different magnet families. Prototypes of these magnets have been recently tested at CERN. For each of these, specific features and detection methods have been developed, implemented and evaluated during the magnet tests.
The super high field magnets using superconducting wires have been promisingly applied for thermonuclear fusion power generation such as Korea Superconducting Tokamak Advanced Research (KSTAR) and International Thermonuclear experimental reactor (ITER) systems. The quench detection system (QDS) is essential for high reliability in the super high field magnet facilities. Generally, the quench voltage detection system, which uses resistive voltages, has been adopted. Such an ITER magnet, the maximum operation current and voltage of superconducting keeps over 60kA and 50 kV DC. Generally, in the case of medium power, the power transformer has been adopted for QDS as an isolated power due to stable insulating and durable characteristics. However, unfortunately, the magnetic saturation of electric steel for power transformer remained fragile as well as the volume is increased under super high field magnet. From this reason, authors apply the wireless power system for QDS module as a reasonable option instead of power transformer since the wireless power system can supply power with highly insulating stability through air gap. Additionally, since the number of QDS module is required at least over 100-module in a super high field magnet, the multi receivers under single antenna for power supply of the QDS module is one of economic options due to minimize the amount of input power with antenna. In this study, authors suggest conceptual design of multi resonance receivers for various single-antennas combined with inserted strong resonance coils under 100, 370, and 750kHz, based on resonance coupling method of wireless power transfer in order to minimize of input power and improve the power efficiency.
A long-term scientific project such as the Large Hadron Collider (LHC) at CERN must undergo periodic, preventive and corrective maintenance of electronic components along their lifetime. Components that typically require replacement are the aluminium electrolytic capacitors. More than 36’000 units, rated 500 V and 4.7 mF are installed in the protection systems of the high field LHC superconducting magnets, and are in operation in the LHC tunnel since the start up phases of the collider in 2007.
Capacitor banks are integrated in the quench-heater discharge power supplies (HDS) that upon a quench detection, discharge their energy into the stainless-steel strip heaters installed inside each magnet. The quench protection electronics are in place to quickly detect a quench onset and then dissipate the magnet energy homogeneously inside the coils, such that the local peak temperature remains below damaging level. The quench heater strips heat up a large fraction of the magnet coils surface in order to quench them and spread up the coils internal resistive volume. A distributed internal resistance is causing an evenly energy dissipation over a large volume preventing local overheating and magnet damage. The HDS are thus safety-critical protection elements and so do the capacitors they integrate.
This paper describes the studies carried out with representative samples of the global population of capacitors. To this end, test beds have been assembled and ovens put in operation. Their main features are explained. Conclusive results obtained through the analysis carried out with several groups of capacitors effectively aged during more than one year at 85 °C and 70 °C are presented and discussed. Parameter values, such as capacitance, equivalent series resistance, leakage current and weight, have been measured regularly to evaluate the aging process.
The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Quench detection by voltage measurements is likely to be the fastest available technical solution to avoid coil’s damage caused by quench, but the voltage detection is a real challenge due to large noise induced by the power supply in alternating current operation. The pick-up sensors, comprise the co-wound wire (CWW) and the co-wound tape (CWT), are used in the CSMC quench detection system for noise compensation and suppression. To accurately compensate all related induced voltage in the multi-pulse coil system, the foremost task is to estimate the static inductance matrix between the CSMC and its pick-up sensors. In this paper, a numerical model is developed for inductance calculation and analysis. Moreover, several numerical simulations with this design model to evaluate the maximum inductive noises and quench detection signals by CWW and CWT have been conducted in case of the worst test scenarios.
L. Morici, C. Fiamozzi Zignani and G. Messina
The CS and PF coils of the DTT tokamak are operated in dynamic mode and, even in normal operation, the induced and self voltages across each coil are of the order of several 100 V. In DTT (Divertor Tokamak Test facility currently being built in the site of ENEA C.R.E. Frascati – Italy), these coils will be realized with superconducting materials and, as a consequence, a reliable and fast quench detection system is required in order to protect the magnets. Being the quench signals 4 orders of magnitude smaller than the operating voltages, the cowound (CW) technology must be adopted for the quench sensors, the only degree of freedom being among a wirnig configuration merely aligned with the coil winding (CWA) or aligned and twisted to the winding (CWA&TW). In this study, a model of the DTT poloidal magnetic system has been developed, up to the details of the single windings of the various coils for each magnet, together with the corresponding model for a CWA sensor. The signals coming from the magnetic system during the various plasma events (Single Null, breakdown, major disruption,
…) have been simulated and compared to the analogous signals coming from the CWA. Of course, the analysis has been developed up the level of the elementary structures of each coil of the system (single pancake in double pancakes magnet configurations; Low, Medium and High field portion of a layered magnet configuration). Finally, a simple theory has been developed aimed at the estimations of the improvements coming from the CWA&TW architecture. The outcome of the study will be used for the detailed design of the superconducting cable to be adopted in each portion of each magnet of the DTT magnetic system.
The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Although adequate operational margins have been taken into in the design to avoid the quenches, such events cannot be completely excluded in the life of the CSMC. In order to prevent quench from damaging the CSMC, the quench detection by voltage measurements plays an important role in the protection of the CSMC during commissioning and operation scenarios. To improve the accuracy and reliability of CSMC quench detection, an all-digital quench detection system based on FPGA has been designed for the processing of quench detection signals. This paper describes the design of the quench detection signal processing system, including the composition of quench detection units, the auxiliary compensation for further denoising, the discriminant of quench, and the safety interlock system.
Nested combined orbit correctors are needed for the upgrade of LHC. They are developed at CIEMAT, in collaboration with CERN in the framework of HL-LHC project. There are two types of magnets, so-called MCBXFA and MCBXFB, with different lengths (2.5 and 1.5 m, respectively), but sharing the same cross section. Coils of both magnets are wound with the same Rutherford-type NbTi cable, composed of 18 strands of 0.48 mm diameter, insulated with braided glass fibre sleeve.
Quench propagation has been computed with Roxie and Squid (CIEMAT in-house developed code). Results have been compared with the power tests performed on the prototypes. Different strategies of magnet protection have been analysed. Finally, damp resistors will be used for both magnets.
Institute of Modern Physics is developing the Fourth-generation of Electron Cyclotron Resonance source, also known as FECR. In order to fulfill the requirements of higher beam intensity and quality, the FECR needs a Nb3Sn superconducting magnet with high performance and complex structure. Therefore, a half-scale prototype is produced for the technical research, it was wound by a 1.3mm diameter Nb3Sn wire and consists of six racetrack dipoles and two solenoids. For the Nb3Sn magnet, it has obvious thermo-magnetic instabilities, so-called “flux jumps”, which means large voltage transients will occur frequently during the magnet training. The voltage spikes can lead to misjudgment of the Quench Detection System (QDS), that’s very harmful to the normal operation of the magnet. Especially, for this FECR prototype with a composite structure, the situation of flux jump is more complicated. In an effort to better characterize and understand these voltage spikes, as well as to make the quench detection faster and more accurate, we have done several experiments on the half-scale prototype and obtained a large amount of data. Through the analysis of these data, we have optimized the quench detection algorithm. In this paper, the analysis results of voltage spikes and strategy of quench detection are presented.
One of the technical issues in the application of High Temperature Superconducting (HTS) tapes is the need to wind long tape sections with uniform electric properties along their length. In recent years, the No-Insulation (NI) winding technique for HTS coils is emerging as a valid alternative to conventional insulated coils, as it allows a more effective current redistribution from the most stressed regions toward the rest of the winding, thus reducing the possibility of hot spots formation. Moreover, it has been reported that a NI coil can work properly even in the presence of defective superconductive regions, with a minimal drop of performance as compared to its “defect-free” counterpart. This could open up the possibility of manufacturing coils by jointing together several tape segments of limited length. This procedure could be applied without affecting significantly the coil electromagnetic properties, while lowering the conductor cost.
In this work, the Defect-Irrelevant (DI) behavior of a single pancake NI coil is studied in the presence of multiple joints, intentionally inserted along the tape before winding the coil. The electrical resistance of each joint was set independently, realizing either high or low resistance joints; the presence of the latter in insulated coils would require to substitute a section or the entire winding. The coil was tested both in a liquid nitrogen bath and in a conduction-cooling operation, at different temperatures and varying the charging rate. The voltage signals over different winding sections were acquired during the experiments, as well as the magnetic field generated in the bore. The results obtained on the defective coil were compared with those expected for its non – defective counterpart, which were computed with a numerical model. Finally, an equivalent lumped parameter circuit of the defective coil was applied to derive its effective parameters and analyze its electromagnetic behavior.
No-insulation (NI) technique has been proved to be an available approach for improving the thermal stability as well as the highest operating current of the high-temperature superconducting (HTS) coil. Nevertheless, the NI HTS coil suffers from a non-negligible charging delay inevitably. To address this issue, the parallel co-wound technique is a possible way. For investigating the performance of parallel co-wound NI HTS coil, in this study, we have built an equivalent circuit model coupled with a finite element model. The models’ predictions are in well agreement with experimental tests for a small size prototype, in which, the termination resistance is taken into consideration. Based on this model, the charging and discharging, as well as over-current behavior have been studied. The results show that with the increase of the turns of coil, the number of co-wound tapes needs to be increased for shortening the charging delay. Furthermore, the underlying mechanism of the uneven distribution of currents within each tape has been revealed as well. Overall, this work has provides a useful tool for the behavior prediction of parallel co-wound NI HTS coil, and the designation for specific application accordingly.
The use of high temperature superconducting (HTS) materials is promising for both DC and AC power applications and for high field magnets. However, HTS coils must be carefully protected against quench, since the formation of hot spots can damage the materials even more severely than in the case of low temperature superconducting coils. A possible solution to this issue is offered by the use of No-Insulation (NI) coils, wound without electrical insulation between turns. As compared to insulated configurations, NI coils allow a current redistribution, as well as an improved heat exchange, from the regions which turn normal due to a thermal disturbance to the neighboring turns in radial direction, which greatly improves the coils thermal stability.
In this work, the electro-thermal behavior of two layer-wound coils, realized with and without electrical insulation, is compared. Both coils are wound from the same BSCCO tape, and have a very similar geometry, with the same number of turns and layers. A heat input is applied to both coils, by tuning the current supplied to resistive heaters realized through stainless steel tapes wound on the mandrel at the inner surface of both coils. The heaters are in contact with one full inner turn of the winding. The coils are cooled in a liquid nitrogen bath, and the heaters are supplied with a constant current. Then, the windings are charged until the tape critical current is exceeded, and the tests are repeated for different heat loads. The signals acquired through voltage taps, suitably soldered at the same locations in both windings, are compared at the same working conditions. Finally, the current and temperature distributions in the windings are analyzed by comparing the experimental results with those obtained via a lumped-parameter equivalent electrical circuit, solved numerically in a time-varying regime, and a 1-D thermal model.
High-temperature superconducting (HTS) magnets have been widely studied for practical applications of NMR, MRI, and medical accelerators. 2nd-generation HTS, REBCO (Rare-Earth Barium Copper Oxide), coated conductors (CC) have a high critical field and excellent electrical properties, compared to other superconducting conductors. REBCO pancake coils using the no-insulation winding technique can carry a large current with small cross-sectional area and have shown a high thermal stability against local normal state transitions. NI REBCO pancake coils are expected to be used for practical ultra-high (>30 T) magnetic field applications.
One of critical issues on NI REBCO coils is a charging delay. To solve this issue, pancake coils wound with multi-bundled REBCO CCs was reported in journal papers. As an experimental result, a charging delay was improved, because the inductance of the NI pancake coil wound with multi-bundled REBCO CCs (MB NI REBCO pancake coil) is smaller than that of a conventional NI pancake coil wound with a single REBCO CC. The higher thermal stability of MB NI REBCO pancake coil is also expected than the conventional one. However, the current behavior of an MB NI REBCO pancake coil is complicated and has not yet been clarified. It is pointed out that an operating current may not be evenly distributed in each tape. In this study, the current and thermal distributions of MB NI REBCO pancake coils are investigated numerically, and the stability of the MB NI REBCO pancake coils during charging and against normal state transition is discussed by comparing three cases of MB NI coils with different resistances between turn-to-turn.
As the so-called no-insulation (NI) HTS winding technique or its variations have expanded their applications beyond laboratory magnets, technical concerns on lifecycle such as lifetime, fatigue, long-term performance variation have become an important and timely imperative issue for the actual application of an HTS magnet to real-world systems. This paper reports long-term time-varying operation results of a metal-insulation (MI) HTS magnet with a focus on temporal variation of key coil parameters. Specifically, to ensure temporal stability of the magnet, it is necessary to track changes in key parameters such as critical current or surface contact resistivity. The NI HTS magnet consists of a stack of double-pancake coils wound with REBCO tapes, and operates in a bath of liquid nitrogen at 77 K and/or under a conduction-cooling environment at temperatures ranging 20 – 77 K. The experimental results are analyzed using our in-house simulation tools including lumped circuit analysis, partial element equivalent circuit (PEEC) analysis and/or finite element analysis.
Acknowledgment
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249). This work was also supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-09.
We have been studying the No-insulation coil (NI coil) for applications to medical cyclotrons for cancer therapy and high-magnetic-field whole-body MRIs. Since the layers in NI coil winding are not electrically insulated from each other, the current can be bypassing the adjacent layers when a local defect or normal transition occurs in the coil. Therefore, NI coil is expected to realize both high current density and high thermal stability. In this study, we numerically investigated the electromagnetic behavior of large diameter (m-class) multi-stacked coil system, which consists of NI-REBCO double pancake coils, when local defect or normal transition occurs in one pancake coil. It is known that the behavior of NI coil systems is different from that of normal insulated coils because the generated magnetic field changes due to the varying current distribution in the coil even in the condition of the constant current carrying. In the previous study, the electromagnetic behavior analysis based on the PEEC (Partial Element Equivalent circuit) model has been conducted. This model is an equivalent circuit model that divides the NI coil winding into small elements and takes into account electrical resistance due to local defect or normal transition, turn-to-turn contact electrical resistance between layers, and the self and mutual inductance between elements. In order to analyze the behavior of the target multi-stacked NI-REBCO coil system, the computer program based on the PEEC model was modified to reduce the calculation time while maintaining the calculation accuracy. In this presentation, we will report the results of analysis and evaluation of the magnetic field of 10 T and operating temperature of 30 K (conduction cooling), assuming the application to high field MRI and medical cyclotron.
This work was supported by JSPS Grant-in-Aid for Scientific Research (S) from the Ministry of Education, Science, Sports, and Culture (No. 18H05244).
We are developing large diameter (m-class) no-insulation (NI) REBCO coil systems for applications such as cyclotrons for cancer treatment and high-magnetic-field whole-body MRI. NI coil technology is expected achieving both high thermal stability and high current density, which are essentially tradeoff relationships. Conventionally, superconducting coils have been required to quickly dissipate stored energy in externally connected protection resistance in order to avoid hot spot formation when a normal transition occurs. In contrast, our previous studies suggested that the application of NI coil winding technology may allow the coil to continuously operate even if some parts in the coil windings are degraded. Accordingly, by applying the NI coil winding technology, it can be expected that the use of REBCO coated conductor with defects or degradation, i.e., coil production that allows for variations in conductor characteristics, will lead to lower costs. Therefore, in this study, we analyzed the transient thermal stability of NI pancake coils wound with REBCO coated conductor has some defects using a numerical analysis program that combines the current distribution analysis based on the PEEC (Partial Element Equivalent Circuit) model and the temperature distribution analysis based on the finite element method. In this presentation, we will report the results of analysis assuming the magnetic field of 10 T and operating temperature of 30 K (conduction cooling) for the application to high field MRI and medical cyclotron. And the conditions for stable operation in a coil with defects are clarified using the number of defects, turn-to-turn contact electrical resistance and IOP/IC ratios as parameters.
This work was supported by JSPS Grant-in-Aid for Scientific Research (S) from the Ministry of Education, Science, Sports, and Culture (No. 18H05244).
We have been developing the No-insulation (NI) REBCO coil for applications to medical cyclotrons for cancer therapy and high-magnetic-field whole-body MRIs. NI-REBCO pancake coil is expected that can realize both high current density and high thermal stability, which are essentially trade-off relationship. Since in an NI coil, electrical insulation is eliminated, the operating current can bypass toward adjacent layers when a local defect occurs, and a local rise in temperature (hot spot occurrence) can be avoided, which allows high thermal stability of coils. Previous studies have shown that it is thermally stable when heat generation due to current bypassing toward adjacent turns through turn-to-turn contact electrical resistance is dominant. Compared to the small diameter coils for ultra-high field NMR (4.2 K operation), the density of heat generated by the current bypass to the adjacent turns is smaller in the large diameter coils (30 K operation), which are used in MRI and medical accelerators, and the local temperature rise can be suppressed resulting in higher thermal stability can be expected. However, in actual coil windings, the contact condition between turns is not uniform, and there is a possibility that an area that is not completely in contact exists. In this study, we assumed that turn-to-turn non-contact areas occur random or around the local normal transition of NI-REBCO coil. Numerical analysis was performed based on PEEC (Partial Element Equivalent circuit) model to investigate the transient stability of the NI-REBCO pancake coil using the length, the number of non-contact areas and load factor as parameters, and we examined the possibility of continuous operation.
This work was supported by JSPS Grant-in-Aid for Scientific Research (S) from the Ministry of Education, Science, Sports, and Culture (No. 18H05244).
We fabricated a conduction-cooled 3 T REBCO MRI magnet equipped with electrically conductive epoxy resin. The magnet is composed of 100 single pancakes and the total inductance is 91 H. When the operating current is 145 A, the central magnetic field is 3 T and the stored energy is 1 MJ. A quench protection test was carried out by raising the coil temperature using the heater. After the coil voltage exceeded 1 V, the supply current was interrupted. The stored energy of 1 MJ was dissipated by electrically conductive epoxy resin and the external protective resistor. Although the coil temperature increased from 45 K to 77 K, the thermal runaway was avoided successfully.
The no-insulation HTS coils can be excited above their critical current without burning out. The saturation of the magnetic field can be observed in the overcurrent excitation test, however, as the power supply further increases, there is still a risk of burning out of the NI HTS coil. This report uses a distributed circuit model validated by overcurrent experiments to study the overcurrent excitation process of a NI HTS coil and reveals the current distribution and the shunt between turns of the coil during the magnetic saturation stage, which will not only help the protection of NI HTS magnets but optimize the working status of NI HTS magnets. The model is further extended to the closed-loop coil. The current distribution and the shunt between turns of the closed-loop coil during the overcurrent excitation process, as well as the change of the magnetic field decay rate of the closed-loop coil under persistent current mode operation, are studied. Thus, the change of the magnetic field decay rate of the closed-loop coil under different current-carrying conditions can be predicted by this model.
Due to excellent thermal stability and high-power density in steady state, no-insulation (NI) winding technology is widely used in the application of superconducting magnets. However, current ripple and background magnetic field fluctuations caused by relative devices result repetitive turn-to-turn current of the NI interpolated coil, which will impose a great impact on the thermal stability of NI magnet. This paper analyzes the power characteristics and other electromagnetic parameters of NI magnet under dynamic operating conditions by 2D finite-element method. The results provide references of thermal conductive structure design and assessment of operational reliability of NI magnets in changing working conditions.
A tri-axial high temperature superconducting cable has the advantages of small size, large transmission capacity, low AC loss and high economic efficiency in power transmission of urban city. The essential difference between superconducting cable and traditional cable lies in their unhindered current-carrying characteristics. But when carrying alternating current or changing electromagnetic field in the environment, the tri-axial superconducting cable could produce the alternating current (AC) transmission loss. The generation of AC loss would lead to the local temperature rise in the superconductors, accompanied by the reduction of the pinning performance and critical current, which brings huge safety risks to the tri-axial superconducting cable. Therefore, AC loss is an important factor affecting the reasonable design and stable operation of the tri-axial superconducting cable. A digital compensation method for AC loss measurement has been proposed, and a AC loss test platform consisted of a three-phase power supplier, a signal acquisition unit, a control system, a signal processing and compensation software system has been built as well. The AC loss of a 10 kV tri-axial superconducting sample cable is tested. These results show that the AC loss of each phase increases linearly with the increase of transmission current, the outer phase superconducting cable is affected by the magnetic field generated by the inner phase superconducting cable, so its critical current degenerates and the AC loss becomes larger.
AC loss reduction is essential to apply high temperature superconducting (HTS) conductors to power devices. We have studied the effect of AC loss decrease of CORC that is a low-loss and high-current conductor. The currents through CORC are equally distributed to the CORC strands (HTS tapes) because the strands are helically arranged around a cylindrical former. We have confirmed that the AC loss of CORC was reduced when we replaced a wide HTS tape with narrow tapes in parallel. In this paper, we made HTS solenoidal coils with CORC. The HTS tapes for CORC had different widths. We prepared 3 kinds of HTS stands with the same net width. The first HTS strand was 12 mm wide single tape. The second one was composed of two 6 mm HTS tapes in parallel. The third one was composed of three 4 mm HTS tapes in parallel. The net width of the second and third strands was 12 mm. In addition, we also varied the pitches of the helical winding for CORC. The AC losses were measure by electrical method. The results were compared with the calculated ones.
Acknowledgement
“This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(2019R1I1A3A01063158)“
“This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science and ICT (2019R1F1A1063397)“
High current cables for large fusion magnets can be composed of hundreds of tapes. A convenient way to deal with such large number of tapes is multi-stage cabling. The stack of tapes is a basic element for the first stage of various high current cables designs. AC losses have been evaluated analytically in the limits of very low and very high sweep rates, providing a global overview of losses over the entire sweep rate range of interest for fusion magnets. It can be easily shown that a twisted stack has almost the same AC loss than a non-twisted stack. However, when several stacks are assembled in large cables, transposition and/or twisting provides a moderate reduction of losses. Both round and flat cables were studied, the number of stacks varying from four up to twenty. Eddy current losses in copper components are also evaluated and it was found that eddy current losses could represent a significative fraction of the total loss, when the copper is present as a single, large component. Moderate loss reduction (about one order of magnitude) can be obtained by the combination of: twisting and/or transposition of the stacks, stack cross section reduction and introduction of resistive barriers in the copper elements. Some of these techniques are less effective than in fine multifilamentary cables (NbTi and Nb3Sn), simply because a wide tape has intrinsically much higher losses than a fine filament. Therefore, all cables made with tapes (twisted or not) have higher losses than cables made with fine multifilamentary wires.
Striation (multifilament) is an effective way to reduce AC losses in the coated conductors for the applications of magnets or electrical power devices. Considering the robustness of the striated coated conductors, it is preferred to have some transverse conductance like copper between superconductor filaments. In such a conductor, however, the striation works for AC loss reduction only after the decay of the coupling current, which flows between transverse conductance and superconductor filaments and is characterized with the coupling time constant. Since the coupling time constant is proportional to the square of the conductor length for straight coated conductors, we proposed the spiral copper-plated striated coated conductor cable (SCSC cable), where the copper-plated multifilament coated conductors were spirally wound on a core to reduce the loop length of the coupling current. We prepared various models of the SCSC cable, in which copper-plated multifilament coated conductors with different conductor widths, filament numbers or copper thicknesses were wound on GFRP cores with different diameters. As references, we also prepared short straight pieces with different lengths. At 77 K, the frequency dependence of AC loss was measured in transverse magnetic fields with a small amplitude, where the coupling loss dominants the AC loss. The coupling time constants were determined from the frequency dependences of measured AC losses. The determined coupling time constants were smaller than the characteristic times of the magnetic field and/or the transport current changes in practical applications. Furthermore, in order to clarify the electromagnetic behaviors of the coupling current in SCSC cables, we conducted the numerical electromagnetic field analyses of SCSC cables. We compared the theoretical coupling time constants with the measured ones.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
The reduction of large AC losses in ReBCO coated conductors caused by their wide tape shape is a critical issue for their power applications. In principle, striating the wide superconductor layer of a coated conductor into narrow filaments (multifilament) is effective for the AC loss reduction. However, this approach is effective only when the filaments are decoupled electromagnetically, i.e. the coupling current between filaments decays, and, therefore, the experimental determination of their coupling time constants, which is the decay time constant of coupling current, are important. Our previous study suggested that the plated copper governs the transverse resistances between filaments in copper-plated multifilament coated conductors. If so, their coupling time constants could depend on temperature.
We are constructing an experimental setup to measure the frequency-dependent magnetization loss at 4.2 K and 77 K. In this setup, a cryostat, in which a sample is cooled in liquid helium or in liquid nitrogen, is installed in a pick-up coil, with which the magnetization of the sample is measured. The magnetic field whose frequency is from 10 Hz to 20 kHz is applied to the sample by a copper dipole magnet placed outside the pick-up coil. In order to apply wide range of frequency, the cryostat is made of GFRP to eliminate eddy currents affecting magnetic field.
We will measure the frequency dependence of magnetization loss ($Q_{m}-f$ plot) at 77 K and 4.2 K then fit the measured $Q_{m}-f$ plot plot to a Debye curve so that we can determine the coupling time constant. Finally, we compare the measured coupling time constant with numerical calculated one to determine the transverse resistance.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
Reducing AC losses in coated conductors is one of the important issues for HTS applications to electric power devices and magnets. Multifilament structure is a method to reduce AC losses. From the view point of improving the robustness of a multifilament coated conductor for local normal transitions, it is preferable to have a finite transverse conductance. When copper is plated over the superconductor filaments to allow current sharing, the effect of multifilament structure to reduce AC losses can be obtained only after the decay of coupling currents. To make coupling time constant shorter, we proposed the spiral copper-plated striated coated-conductor (SCSC) cables.
We need to evaluate ac losses in the SCSC cables accurately by numerical electromagnetic field analyses for actual applications. For accurate analyses, we have to consider following two essential factors. First, we need to model the copper-plated multifilament conductors’ structure appropriately to consider the coupling currents. Second, we need to develop large-scale three-dimensional numerical electromagnetic field analysis model not but analysis model of cross-section of the cable to consider the structure of the spirally-wound conductors.
We are developing a large-scale electromagnetic field analysis model for SCSC cables. We combine T-formulation and thin-strip approximation in the model, while there is a normal conductor between filaments whose thickness is same with superconductor layer. Additionally, in order to consider second factor, we use finite long model not but infinite long model with translational symmetry boundary condition. Because analyses with this model could require huge degree of freedoms (DOFs), we use hierarchical matrices to make faster the computation and reduce memory consumption. For example, an 80-mm long SCSC cable consists of 16 tapes, which we analyze as a test case, has 2.7 million DOFs.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
Dynamic loss is an essential parameter to consider for the design of high temperature superconducting (HTS) synchronous machine windings. For HTS coated conductors (CC), the existing definition of dynamic loss only considers the HTS layer, the validity of which compound with magnetic substrate is questionable. In response to the above concern, by use of the H-formulation based numerical multilayer modelling method, the influence of magnetic property of substrates on dynamic loss and magnetization loss of HTS CCs has been investigated. It is widely believed that the type-II high-Tc superconductor with magnetic substrate will generate larger dynamic loss compared to that with non-magnetic substrate. However, the result was rather surprising that the dynamic loss of the superconductor with non-magnetic substrate is slightly larger than the one with magnetic substrate when the background AC magnetic field is low. When the external AC magnetic field is high, the superconductor with magnetic substrate generates larger dynamic resistance than the one with non-magnetic substrate. The critical value of the AC magnetic field is dependent on the transport current in the superconductor. We explain this result in detail in this paper. This work is used to obtain insights into the characteristics of the substrate layer in the type-II high-Tc superconductor, including its relationship with the dynamic loss, magnetization loss and hysteresis loss.
In order to develop high temperature superconducting (HTS) tapes with excellent low-loss characteristics, a measurement system that enables us to measure AC loss characteristics of HTS tapes with high sensitivity is indispensable. We have successfully reduced background losses, which are apparent losses obtained by a pickup coil method in case where no specimen is located inside pickup coils. As a result, we have developed a measurement system by the pickup coil method that can measure AC loss characteristics of short and straight HTS tapes under transverse magnetic fields with high sensitivity. In the pickup coil method, pickup coils consist of a main pickup coil to measure signals of a specimen and a compensation coil to compensate signals from the main pickup coil when there is no specimen. In order to reduce background losses, first, a magnet for applying external transverse magnetic fields was designed and manufactured so that a pickup coil and a compensation coil could be arranged symmetrically. Next, the parameters of pickup coils were optimized to reduce the phase difference between the pickup coil voltage and the compensation coil voltage, which is one of the main cause of background losses. Furthermore, from the measurement results of background losses using various pickup coils, the relationship between the phase differences and the background loss was experimentally and theoretically examined.
Improvement in the production technology of a Conductor on a rounded core (CORC) cable allows it to reach high engineering current densities and therefore becomes suitable for high fields magnets like MRI or acceleration magnets. Due to high packed tapes within the cable being magnetically coupled, this results in an increase in the magnetization loss, the load on the cryogenic system and screening current creates instability of the magnetic field in the magnets. We modelled 3D CORC cable of monolayer and multilayers with up to 6 tapes and three material laws by H-formulation FEM model. Studying the material laws using constant J$_c$, a Kim-like magnetic field dependence J$_c$(B) model, and an adaptive angular magnetic field dependence J$_c$(B,Theta) model, shows significant difference and improvement in the estimation of magnetization losses by each law. The models reveal the 3D current in the applied field and the magnetization losses were compared with measured values at 77 K and up to 100 mT applied magnetic field. A further understanding of the magnetization losses will aid in the development of magnetic performance within a cable.
Acknowledgement
M.U.F. and M. C. thank for the funding support received by the College of Science and Engineering of the University of Leicester. M. C thanks also the EPSRC DTP Studentship program. This work was supported by the UK Research and Innovation, Engineering and Physical Sciences Research Council (EPSRC), through the grant Ref. EP/S025707/1 led by H.S.R. All authors acknowledge the use of the High Performance Computing facility ALICE at the University of Leicester.
The high temperature superconducting (HTS) quasi-isotropic conductor with high current capacity and quasi-isotropic performance is expected to have a wide application. AC loss is one of the major obstacles. This paper aims to study the AC loss of the quasi-isotropic conductor stacked by the second generation (2G) HTS tapes and copper tapes at 4.2 K. In order to fully understand AC loss characteristics of the stacked-tape conductor, an efficient 3D finite element method (FEM) model based on T–A formulation is adopted. This model can be adopted to handle the simulation challenges of HTS tapes with high aspect ratio and overall understand AC loss in the twisted quasi-isotropic conductor.
MQXFAP1b was the second test of a long prototype quadrupole magnet for AUP which ended with training clearly limited by a single coil (QXFP03). Post testing, an investigation was launched to try and determine what drove the difference in the performance of the limiting coil in comparison to one of the best performing coils (QXFP04). Visual observations were made, followed by electrical testing, glass transition temperature measurements and mechanical measurements. The mechanical measurements showed a substantial difference in coil mechanical properties, with QXFP03 being much more robust than QXFP04, both in terms of coil pack adhesion and coil modulus. Additional coils have also been sectioned and measured to see if there is a correlation between coil performance and coil adhesion.
Complex stress/strain can arise from the winding, cooling down and intense field in YBCO superconducting coils, which can induce maximum internal strain to several thousand micro-strain in coils. Thus, efficient production and operation of YBCO superconducting magnets will benefit from smart sensors that may be embedded within structure without damaging its structural integrity. Currently，most strain sensors are still not used in the YBCO coil for some reasons, such as intrusion, size and interference. In this work, using homemade soft polymer FBGs, internal strain distributed responses between two YBCO superconducting taps are investigated experimentally during tensile, compression and bending loading at room temperature and 77K. The internal and distributed strain responses during the complex loadings are recorded to show that measurement techniques have good precision and repeatability comparing with the theoretical ones. Compared to the common FBG，it is the most important that the distributed polymer-FBGs can be embedded softly in taps with good survival to measure the internal strain in the coils. The present results are expected to be able to provide basis methods on the internal strain of YBCO superconducting magnet/cable, which cannot be obtained using traditional strain sensors during fabrication and excitation of superconducting coils.
The new Nb3Sn superconducting magnet system for a 45 GHz electron cyclotron resonance (ECR) ion source is under developing in the Institute of Modern Physics (IMP). The sextupole coil, which is wound by a single Nb3Sn wire, is indeed a great technical challenge. Because of the complicated technology process and the stress sensitivity of the full-length Nb3Sn sextupole coil, a sextupole magnetic mirror structure based on the Bladder and Key technology during the magnet assembly was used for the coil’s performance evaluation. This paper presents the mechanical design of the Mirror structure along with fabrication details, describes the room temperature assembly, and reports the cryogenic test results.
The Fourth-generation ECR (FECR) ion source Nb3Sn Superconducting Magnet is being developed by Institute of modern physics, Chinese Academy of Sciences. In order to reduce the risk of development, a representative prototype is designed. The FECR prototype consists of two Nb3Sn solenoid coils and six Nb3Sn sextupole coils, This paper reports on the assembly process and cool-down to cryogenic temperature of the combined support structure of the FECR prototype. The structure of the FECR prototype magnet is designed to provide the adequate pre-stress, through the use of load keys, water-pressurized bladders, and an Al alloy shrinking cylinder. To validation the assembly and loading procedures, the structure was assembled with Al blocks (dummy sextupole coils) and extend stainless-steel formers (dummy solenoid coils) that replaced the brittle Nb3Sn coils, and then cooled-down to 77 K with liquid nitrogen. The evolution of the mechanical behavior was monitored via strain gauges located on different components of the structure (shell, rods, and dummy coils). We focus on the expected stresses within the structure after assembly, loading and cool-down. The expected stresses were determined from the 3-D finite element model of the structure. A comparison of the 3-D model stress predictions with the strain gauge data measurements is made. The coherence between the predicted contact pressure with high pressure Fuji Paper and strain/stresses with the experimental gauge measurements will validate the FEM model of the structure.
High field superconducting magnets sustain large Lorenz force during operation. The superconductors for high field applications like Nb3Sn is strain sensitive, therefore it is essential to measure the strain level in superconducting coils during operation. Compared with traditional approach with resistance stain gauges, Fiber Bragg Grating Sensors (FBG) has significant advantages in high field applications. FBGs are anti-electromagnetic interferential, possible to measure the local strain inside the superconducting coils, and only sensitive to strain at a low temperature range from 4.2K to 20K[1]. In this study, resistance strain gauges and FBG were impregnated in the racetrack Nb3Sn and iron-based superconducting coils in a high field dipole magnet, and also attached to the outer surfaces of longitudinal rods and Aluminum shell of the magnet. The measurement was performed from room temperature assembly to the excitation at 4.2K. The experimental results show that the strain measurement with FBGs is accurate, stable and repeatable in the entire process of the experiment. Compared with resistance strain gauges, FBGs have a lower noise and a better performance at high magnetic field, high stress level and high excitation speed, and could reflect the process of internal strain variation of the superconducting coils during the whole process, indicating the advantages of FBGs applied for strain measurement in high field magnets.
[1] S. James et al., “Strain response of fibre Bragg grating sensors at cryogenic temperatures,” Meas. Sci. Technol., vol. 13, no. 10, pp. 1535–1539, 2002
EU DEMOnstration reactor (DEMO) aims towards demonstrating the feasibility of commercial fusion power plant. Various activities are in progress as part of EUROfusion’s framework for the design of DEMO. As part of the mechanical assessment activities, various Finite Element (FE) analysis on these complex systems are performed. Due to the large dimensions of the magnets, a multiscale approach is often used. As a result of this, various strategies are followed by the fusion community in analyzing these systems like using 2D generalized plane strain assumption or sub-modelling techniques. This work focuses on these strategies and their capacity to predict the mechanical behavior on a Toroidal Field (TF) coil design by CEA (WP#3) for EU DEMO.
Superconducting magnets used in particle accelerators produce magnetic fields of high precision and uniformity to bend or focus the particle beam. For such magnets, the development of accurate and efficient numerical methods for the evaluation of the magnetic fields is of high importance. This work presents a hybrid Finite/Boundary Element Method (FEM/BEM) scalar potential formulation, implemented in PITHIA-EM software, capable of solving three – dimensional nonlinear magnetic problems in accelerator magnets. The present FEM/BEM formulation combines the advantage of FEM in treating problems with material nonlinearities and the efficiency of BEM in solving problems with high volume to surface ratio. Additionally, it avoids the use of the node – based vector potential formulation, which is characterized by high computational cost in 3D. The proposed formulation overcomes the interfacial jump condition difficulty and cancellation errors appearing in the total and reduced scalar potential formulations. The source magnetic field produced by superconducting coils is calculated with high accuracy via a Biot – Savart integral, allowing for a coarse discretization. The proposed FEM/BEM formulation is employed for the solution of representative 3D nonlinear magnetostatic problems, while the provided accuracy is assessed through comparisons made with corresponding results obtained by well-known commercial FEM packages.
The No-insulation (NI) REBCO as an insert magnet has been applied to overcome the field limitation of LTS NMRs. So far, NI REBCO pancake coils have shown a “self-protecting” characteristic in experiments and, consequently, basic mechanism of self-protecting from thermal runaway has been widely studied by analyses under a low magnetic field or cooled by liquid nitrogen. However, several HTS insert magnets are designed with <20 K operating temperature or >10 T background field assumption. The transient variations of magnetic field and temperature affects the local critical current in the magnet, and they determine different electrical behaviors in equivalent No-insulation REBCO circuit. Thus, the thermal stability during charging process or after quench should be considered in the preliminary ultra-high field magnet design. In this study, an electromagnetic-thermal model is introduced consisting of electric and thermal contact resistances between turns and inductance matrix for the numerical simulation, and then the transient influences are further discussed by different operating temperatures, coil sizes, and background fields during charging/discharging and after quench to propose appropriate electrical and thermal contact resistances of the magnet.
Due to the extensive application of soft magnetic materials in transformers, motors, reactors and other electrical equipment, the research of accurate iron loss prediction method becomes an indispensable part to ensure the safe operation of power system and to realize the optimal design of electrical equipment. However, the development of appropriate methods for predicting iron loss is hampered by various complex physical mechanisms in different magnetic materials. Because of the inhomogeneous distribution of magnetic variables caused by eddy current and hysteresis in magnetic materials, the parametric magneto-dynamic (PMD) model is improved in this paper by using a non-linear segmentation method when the thin sheet model is divided into several slices. By combining the fact that the magnetic field changes rapidly in the inner slice and slowly in the outer slice, this method appropriately reduces the thickness of the outer slice and increases the thickness of the inner slice when applying the parametric magnetic dynamic model. The improved parametric magneto-dynamic model can accurately predict the loss while considering the complex physical phenomena in ferromagnetic materials by using the nonuniform piecewise constant function to approximate the distribution of magnetic variables in the thin sheet. Simultaneously, the hysteresis properties of materials need to be stimulated by an appropriate hysteresis model when applying the improved parametric magneto-dynamic model. The parameter identification of the hysteresis model depends on the static hysteresis loop. To solve the problem that static hysteresis loops are not easy to measure, this paper extracts static hysteresis loops from dynamic hysteresis loops by using the inverse loss separation model. In this paper, the feasibility of the static hysteresis loop calculation method is also verified by velocity-controlled particle swarm optimization (VCPSO) to identify the hysteresis model parameters.
The magnetic system comprising all the superconducting poloidal coils is an important part of the Divertor Tokamak Test facility (DTT). It is composed of several parts mutually coupled among them: six Central Solenoid (CS) modules, six Poloidal Field (PF) coils, the passive structures and the plasma. This implies that a current variation in any poloidal coil can cause a significant current or voltage variation in the others, as well as a change of the plasma current. In particular, during a fast plasma disruption the magnetic flux in the tokamak changes rapidly, which in most cases will cause high-voltage and/or over-current across each CS and PF coil and may bring severe damage to the components. Therefore, to investigate the transient voltage and current waveforms excitations occurring on the terminals of the superconducting coils, an electrical model including poloidal coils (CS and PF), vacuum vessel (VV) structure, stabilizing plates and the plasma, has been described and presented.
In order to calculate the mutual inductance matrix of the poloidal coils and passive structures, a Finite Element Method (FEM) was used. Then, the matrix was implemented in the lumped model including the power converters, the crowbar, the Switching Network Units (SNU), bus bars and feeders. Different initial conditions were considered for electromagnetic analysis and a wide survey of possible scenarious was simulated: breakdown, fast plasma disruption and so on
To get an understanding of the magnetic field distribution in a superconducting magnet, computer simulations are needed which take into account the actual geometry of the magnet and the magnetic saturation in different materials. It is a further advantage that the software efficiently tackles the large number of unknowns needed for accurate 3D simulations and also allows the coupling of additional physics of interest (e.g. thermo-electricity for quench propagation, mechanics).
In this work we demonstrate the capabilities of a free, open source multiphysics FEM software to predict the magnetic field created in CERN’s Feather-M2 particle accelerator dipole magnet model as well as the magnetically induced mechanical stresses. Tools adapted for efficient 3D magnetic field simulations are used: a vector potential formulation is solved with edge shape functions and a spanning-tree gauging technique. A high performance domain decomposition algorithm is used to dramatically speed-up the heavy computation. The simulation performed in this paper is provided in an online example to the magnet designer community. Additional physics for thermo-electric simulations of quench propagation or mechanical simulations can be coupled to this example in a straightforward way within the same software.
Compared with conventional power cables, high-temperature superconducting cables (HTS) have the advantages of large current capacity, low loss, compact structure, and no electromagnetic radiation. With the continuous improvement of electricity consumption in all of the world, HTS cables are of great significance to improving the transmission capacity of power systems. Because the HTS cable has a multi-layer structure, when AC current is applied, if its structural parameters are not well designed, uneven current distribution in each conductor layer may occur, which will cause partial quenching of the cable and increase the AC loss with affecting the safe and stable operation of the cable. This article aims to realize the uniform current distribution of the conductor layer of HTS cable, while using particle swarm optimization algorithm (PSO) to optimize the design of three commonly types of HTS cables (three-phase independent, three-in-one and three-phase coaxial) and write it into software that is convenient for designers to use to meet engineering needs. At the same time, the finite element simulation software ‘Comsol’ is used to establish 2-D electromagnetic thermal models of different configurations of HTS cables to verify the conductor layer current distribution and AC loss of the cable, and to realize the thermal analysis of the cable. And use this software to evaluate and verify the design case of AC high temperature superconducting cable with rated parameters of 10kV/2.5kA, and select the appropriate cable configuration and structural parameters.
An advanced hybrid numerical method for the solution of nonlinear magnetostatic problems in superconducting accelerator magnets is proposed. The methodology is implemented in PITHIA-EM software and couples the Fragile Points Method (FPM) with the Boundary Element Method (BEM). The FPM is a Galerkin-type meshless method, based on a Discontinuous Galerkin weak form where simple, local, and discontinuous point – based interpolation functions are employed for field approximation. The local discontinuity inconsistencies, due to the discontinuity of these functions, are treated via numerical flux corrections. The FPM combines the advantages of mesh-free methods and the Finite Element Method (FEM) utilizing, however, fewer nodal points than the FEM for the solution of the same problem. On the contrary, the BEM is an efficient methodology in solving linear problems with high volume to surface ratio. In the present study, the nonlinear behavior of the ferromagnetic yoke in an accelerator magnet is treated by the FPM, while the BEM is employed for the infinitely extended, surrounding air space. The source magnetic field produced by the superconducting coils is calculated with high accuracy via a Biot – Savart integral. The FPM/BEM methodology is described and implemented for scalar and vector potential formulations. The efficiency of the method is demonstrated through representative nonlinear magnetostatic problems appearing in accelerator magnets.
The enhancement of the acceleration performance of a superconducting linear acceleration (SLA) system to inject the pellet container to supply fuel to the fusion reactor has been investigated numerically. To this end, a numerical code used in the finite element method has been developed for analyzing the shielding current density in a high-temperature superconducting film. In addition, the on/off method and the normalized Gaussian network (NGnet) method have been implemented in the code for the shape optimization of an acceleration coil, and the non-dominated sorting genetic algorithms-II have been used as the optimization method.
The results of the computations show that, for the NGnet method, even if the on-state of the filament is reduced by approximately 12% from the homogeneous current profile, the pellet speed of the SLA system increases by approximately 2.8 times. In addition, This is mainly because of the strength of the applied flux density generated by the optimized current profile using the NGnet method.
On the other hand, for the on/off method, the current profile is scattered, whereas the coil shape becomes hollow for the NGnet method. Consequently, the NGnet method is an effective tool for improving the acceleration performance of the SLA system and for obtaining a coil shape that is easy to design.
Several ultra-high magnetic field (>20 T) REBCO magnets are under development for fundamental research or practical applications. A few quench protection techniques, such as a no-insulation winding technique and a temperature rise technique by heaters, were proposed to protect REBCO magnets from thermal runaway and burning-out. Meanwhile, it was reported that REBCO tapes were plastically deformed after ultra-high magnetic field generations. A main research topic on magnet protection have shifted from thermal to mechanical damages. Hahn, et al. pointed out a locally concentrated stress due to screening currents. Last year, it was also reported that the screening current was reduced because of coil deformation. On the development of ultra-high magnetic field REBCO magnets, the importance of screening current and stress simulation increases.
We have developed an electromagnetic and deformation simulation tool; combining an extended partial element equivalent circuit (PEEC) model as a screening current and a finite element method (FEM) as a deformation simulation. Using the developed simulation tool, we will investigation the screening current and stress behaviors of LBC3 magnets, which generated 14.4 T inside an external resistive magnet generating 31.1 T. When considering the coil-deformation effect on the screening current, the screening current distribution differs from that without consideration of coil-deformation effect. We will also try to simulate the MIT 1.3-GHz HTS/LTS magnet. Finally, we will investigate a cause of plastic deformation of REBCO tapes.
Bearingless switched reluctance motor (BSRM) has the advantages of simple structure, no winding and permanent magnet on rotor, low cost, good robustness, strong fault tolerance and strong environmental adaptability. Therefore, the BSRM has broad application prospects in the field of high-speed direct drive system, such as aerospace, high-speed flywheel and turbo molecular pump.
The levitation force windings which produce radial levitation force are wound together with the torque windings in the traditional BSRM. The current of the two sets of winding is controlled coordinately to generate torque and radial levitation force simultaneously. Therefore, there is a strong coupling between the torque and levitation force, which makes the control system complex and difficult to achieve high-precision operation of BSRM. Furthermore, to realize the three degrees of freedom (3-DOF) suspension of the rotor, an axial hybrid magnetic bearing (HMB) and a radial 2-DOF BSRM are often used together to support the rotor suspension and rotation, which results in low torque density.
To solve the above problems, a novel 3-DOF BSRM with independent levitation force and torque magnetic circuit is proposed in this paper. It has combined characteristics of SRM and 3-DOF hybrid magnetic bearing. 3-DOF suspension is realized in one unit. We firstly introduce the structure and suspension operation mechanism. Then, the mathematical models of suspension force are deduced based on the equivalent magnetic circuit. Based on MagNet 3D, the finite element model is established and the transient and static suspension performances are analyzed. The simulation results indicate that the structure of the proposed BSRM is reasonable and it can be suspended and rotated stably.
The magnetic measurement of solenoids is based on different methods to characterize the field quality and the magnetic axis. Usually, Hall mappers and stretched-wire systems are used for this task. This paper presents an alternative: a fluxmetric method to measure the radial field dependence and the magnetic axis with a single instrument. The solenoidal-field transducer is based on a disc-shaped induction-coil array with concentric coils and 90 deg. arcs segments mounted on a precision translation stage. This allows to sample the magnet along its axis and to extract both the longitudinal and transverse field components from the nested coils of different diameters. Over the last years the innovations have resulted in a change of paradigm for the design of induction-coil magnetometers and their calibration, up to the point that the printed circuit board technology has become a new standard.
The paper presents the design, development, production challenges, and metrological characterization of the new instruments. Results of recent measurements of a normal and a superconducting solenoid magnet will be given.
In the framework of the High-Luminosity Large Hadron Collider (HL-LHC) project, 11 T dipole and MQXF quadrupole magnets employing Nb3Sn technology have been tested in short and long test configurations. Nb3Sn magnets are more sensitive than NbTi magnets to a potential degradation of their conductors during production, testing and cycling operation. In the SM18 magnet test facility at CERN, new diagnostics tools and measurement procedures have been developed to investigate in detail performance limitations of Nb3Sn accelerator type magnets, most importantly through advanced V-I measurements extracted from voltage taps on conductor sections as well as entire coils. For the analysis of performance limitations, a combination of data is studied, including temperature and ramp rate dependency of quench currents, and V-I measurements. A leading hypothesis for the cause of erratic quench behaviour and decaying voltages on current plateaus is the presence of an inhomogeneous defect in the Rutherford cable. Current redistribution for bypassing the defect takes place through a diffusion process, which leads to a decaying voltage over the affected cable sections. Using the simulation software THEA, the general behaviour of this phenomenon has been studied. Good qualitative agreement is found between model and magnet test results. The research is essential for better understanding performance degradation and for achieving a more robust magnet production considered essential for large-scale application of high field Nb3Sn accelerator magnets.
High-temperature superconductors such as REBa2Cu3O7-x (REBCO) can generate strong magnetic fields that are promising for applications in particle accelerators and compact fusion reactors. Lawrence Berkeley National Laboratory is developing magnet technology-based multi-tape REBCO cable conductors. Traditionally, voltage taps are installed in superconducting magnets. The voltage signals due to resistive transitions are important to develop magnet technology as they can help pinpoint the factors that limit the magnet performance. The architecture of the multi-tape REBCO cable such as CORC® wires, however, makes it difficult to apply the traditional method to identify the locations of resistive transitions. This difficulty precludes us from understanding and addressing the issues that limit the performance of REBCO conductors and magnets. Taking advantage of the thin and long optical fiber, the magnet community has been investigating the distributed fiber optic sensing (DFOS) to detect quenches in HTS conductors and magnets. In this paper, we demonstrate the feasibility of DFOS by applying Optical Frequency Domain Reflectometry to measure the thermal strain along CORC® wires and magnets with 0.65mm spatial resolution and 10Hz temporal resolution. The optical fiber is co-wound with the CORC® wire which is epoxy-impregnated. During the test, current was increased until resistive transitions occurred in the conductor. The results suggested that with proper heat isolation from the cryogen, DFOS can be used to identify the locations of resistive transitions in CORC® wires and magnets. The results allowed us to understand the causes of resistive transitions in REBCO conductors and magnets and to improve the development technology of REBCO magnets.
This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences and Office of High Energy Physics of the US Department of Energy under Contract No. DEAC02-05CH11231 and an LDRD program at LBNL.
Fermilab has been developing flexible printed circuit board (flex-PCB) based quench antenna (QA) probes since 2017, and these have seen a variety of improvements and customization for different applications over the years. The flex-QA have proven to be low-noise, low-cost, non-invasive, and highly sensitive sensors for quench characterization in superconducting magnets, with potential to extend to being used for quench detection as well. Recently we have been exploring applications in several directions: 1) small area sensors and feasibility for operations at high pressure; 2) sensor geometry and relative orientations to increase sensitivity and spatial resolution while rejecting noise; 3) multi-channel quench antenna arrays covering the complete area of the conductor (of the innermost magnet layer). Moving beyond refinements in warm and cold bore QA, we have also progressed to antennas which can be attached to conductor surfaces within accelerator magnets. Multiple programs and projects at FNAL and collaborating institutions have benefited from this work already, and our plans target further extensions of capabilities and applicability of these devices. In this paper, we present the reasoning behind the development steps taken so far, results from testing at various stages, and direction of near-term research on flex-QA at Fermilab.
ReBCO-based CORC® superconducting cables [1] can enable compact fusion reactors and high-field accelerator magnets. However, additional research is required to develop sensitive and robust quench detection methods. One potential technique utilizes Hall probe arrays in CORC® cable terminations to monitor inter-tape current redistribution [2] as a proxy for quench detection. In short-sample quench experiments done at 77 K, this method yielded detection sensitivities equivalent to or better than voltage-based detection [3-4]. Present work addresses a scale-up of the technique to longer 4-10-meter CORC® samples, and to 4.2 K. We are using large-scale Hall probe arrays to monitor variations of the axial and radial field caused by quench-driven current redistribution. We will discuss static and dynamic phenomena occurring during fast ramps and normal zone development, as well as new methods to improve understanding of current sharing. Finally, recent progress on a rotary cryogenic Hall probe scanner for CORC® cables is presented along with algorithms for current reconstruction based on an inverse Biot-Savart algorithm.
[1] D C van der Laan et al., 2019 Supercond. Sci. Technol. 32 033001
[2] M. Marchevsky et al., 2010 Supercond. Sci. Technol. 23 034016
[3] R. Teyber et al., 2020 Supercond. Sci. Technol. 33 095009
[4] J D Weiss et al. 2020 Supercond. Sci. Technol. 33 105011
To prevent an unintended shutdown of the high-temperature superconducting devices (HTS), the monitoring and diagnosing system to quantitatively estimate the degradation of superconducting properties before the normal transitions occur has been proposed. Only the active power component of the Poynting vector measured around the coil conducting AC transporting current is observed in the system. From these measurements, the distribution of local critical currents in the sample coil is obtained indirectly. It is necessary to quantitatively clarify the relationship between the critical current distributions in the coil and measured values via our system to realize this system. In our previous study, the experimental and analytical results are good agreement on a sample, whose shape is a single pancake coil wound with Bi-2223 multifilamentary tape, under uniform magnetic fields applied to the sample in direction to the parallel to the tapes face. The presentation reports the results of experiments and calculations on a solenoidal coil of 40 turns wound with YBCO tape, conducting ac transport current. Therefore, non-uniform magnetic fields were applied to each turn in the coil. The frequency and the amplitude of the currents were 20-50 Hz and 10–50 A. The tape has a critical current of 104 A in liquid nitrogen under a self-magnetic field. The I-V characteristics of the sample coils were in close agreement with the predictions. The validity of this method is verified by comparing the experimental and calculated results.
A dipole magnet generating 20 T and beyond will require high-temperature superconductors such as Bi$_2$Sr$_2$CaCu$_2$O$_{8−x}$ (Bi-2212) and REBa$_2$Cu$_3$O$_{7-x}$ (RE = rare earth, REBCO). Symmetric tape round (STAR™) wires based on REBCO tapes are emerging for such an application especially because of their unique tolerance to bending to a radius as small as 15 mm. Although STAR™ wires demonstrate excellent transport performance at 77 and 4.2 K, there is limited report on the magnet development based on STAR™ wires. Here we report a subscale canted cosθ dipole magnet using STAR™ wires to evaluate their performance in a magnet configuration. The magnet was wound with two STAR™ wires, electrically in parallel and no transposition between the two wires. The transport performance of the magnet was measured at 77 and 4.2 K, in addition to the dipole field at the magnet center. The magnet fabrication and test results allowed us to identify further development needs for both STAR™ conductors and associated magnet technology to enable future high-field REBCO dipole magnets.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program under Contract No. DEAC02-05CH11231. The work at AMPeers LLC and University of Houston was supported by US Department of Energy Office of High Energy Physics SBIR award DE-SC0015983.
Generally, electromagnet equipment such as an electric transformer is designed with the air-gap as narrow as possible for assuming that the magnetic flux in the air-gap does not spread. Therefore, it is possible to design the electromagnet equipment using the magnetic circuit theorem. However, the other electromagnet, such as a high-frequency electromagnet for magnetic hyperthermia, some equipment requires a wide air-gap to use the spatial magnetic field. In this case, the electromagnet cannot be designed by the magnetic circuit theorem because of the spread of magnetic flux in the air-gap. Then, it becomes difficult to estimate the magnetic reluctance of the wide air-gap. Therefore, it is difficult to formulate the center magnetic flux density in the wide air- gap. This work aims to discuss a simple calculation method for the center magnetic flux density of the electromagnet with the wide air-gap using the principle of superposition concerning simple solenoids. In this work, the authors assume that the wide air-gap of the electromagnet can be assembled by an infinite length solenoid with the opposite magnetomotive force finite length solenoid. In this model, the center magnetic flux density in the wide air-gap can be formulated using the magnetic circuit and the Biot–Savart law. The proposed model was tested in comparison with the experimental results of test electromagnets. The result shows that the proposed model can be used in the engineering design of the electromagnets with the wide air-gap.
Stress management techniques have shown great potential to mitigate the high level of stress appearing in high field accelerator magnets, which is especially critical for stress-strain sensitive superconductors, such as Nb3Sn or HTS. The Canted-Cosine-Theta (CCT) concept provides an effective method to intercept the Lorentz forces of each turn, leading to a lower stress accumulation in the magnet’s coils. In this context, the CCT subscale program, part of the U.S. Magnet Development Program (US-MDP), provides a rapid-turn-around and versatile platform for the development and proofing of technologies, and for further understanding the fundamental nature of training in stress managed magnets, which can be later applied to high field magnets.
This paper describes the general assembly process of the subscale magnets, including the layer-to-layer assembly technology, and strain gauge instrumentation. The baseline design of the magnet is shown along with all the variations in terms of structure, and impregnation materials of the coils. The training of all magnets is presented, analyzing their performance based on their mechanical response during powering, and comparing the results with finite element simulations.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program.
Fermi National Accelerator Laboratory (Fermilab) is building a new High Field Vertical Magnet Test Facility (HFVMTF) with a capability similar to the European facilities EDIPO and FRESCA2. This facility will be located at Fermilab. The background magnetic field of 15 T in the HFVMTF will be produced by a magnet provided by LBNL. This facility will serve two US national programs within the DOE Office of Science, the Magnet Development Program (MDP), and the US Fusion Energy Science (FES) program for testing HTS samples in a high magnetic field and wide range of temperatures. For the MDP, the facility will make it possible to test hybrid magnets built on LTS and HTS superconductors – an important step toward the 20 T dipoles to be used in future hadron-hadron colliders. This paper describes the current status of the facility including the civil construction, designs of the cryostat, heat exchanger, and lambda plate, and systems for powering, quench protection and monitoring.
Whole body ultra-magnetic field 14 T magnetic resonance imag-ing (MRI) magnet is now under design at Institute of Plasma Physics, Chinese Academy of Sciences, the main coil based on the preliminary designed of Nb3Sn Rutherford cable in Channel Conductor (RICC). Rutherford cable is a core components of the conductor. During cabling the strands are inevitably experience plastic deformation that strongly change the geometrical dimen-sions of the sub-elements. These deformations are especially se-vere on the cable edges and can result in significant reduction of the cable or strands critical current as well as of the Residual Re-sistivity Ratio (RRR) of the stabilizing copper. To check the sta-bility of the current-carrying properties of the Nb3Sn Rutherford cable under combined thermal and EM loads, a 4-turn solenoid insert magnet was wound using Nb3Sn Rutherford cable and tested at 4.2 K in a background magnetic field of up to 14T, the measured results are present in this paper.
Iron-based superconductors (IBSs) with their ultrahigh upper critical fields and low anisotropies have been expected for the high-field application in the future. In previous studies, the 7-filamentary Ba1-xKxFe2As2 (Ba122) tape which was produced by the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE-CAS) was proven to be applicable to fabricate the high filed insert coils. In this study, the research works are related with the development of an iron-based magnet. Firstly, the mechanical properties of the Ba122 tape will be tested to provide data references for the design of the IBS coils and magnet. The thermal stress characteristics of different Ba122 tapes with different winding technologies will be measured. The characteristics of the hard-way bending radius of Ba122 tape will be determined. Secondly, the design of 64 mm diameter double pancake (DPC) IBS high field insert coils were presented. The DPC IBS insert coils will be fabricated and tested under a 12 T background field at 4.2 K. In the fabrication process, the insert coils will be divided in groups according to the different technologies. The insulated and metal- insulated (MI) IBS coils will be developed and some of the DPC IBS insert coils will be fabricated via hot isostatic pressing. Finally, the design of an IBS solenoid operating under a conduction cooling system was presented in this study.
An aluminium stabilized superconducting cable is developed for the Circular Electron Positron Collider(CEPC) detector magnet. In order to measure the critical current of the prototype cable, an inductive method is developed: the cable is closed in a low resistance loop forming the secondary coil of a transformer, while the 6 Tesla background magnet serves as the primary.
The critical current is measured for the prototype cables before and after co-extrusion to ensure that the degradation from this progress meet the design requirements.
China Fusion Engineering Test Reactor (CFETR), a new tokamak device, is under concept design based on the experience of Experimental Advanced Superconducting Tokamak (EAST) and ITER. Research and development of TF coil for CFETR is carried out by ASIPP. TF coil is winding by Cable in-Conduit Conductor (CICC). Main manufacturing process of CICC includes welding of jacket, draw lead, winding and global helium gas tightness test. After winding, the diameter of TF conductor is about 4 m and the weight is close to 30 t. This paper describes structural design of dewar which is used for the global helium gas tightness test for the TF conductor after winding. A global finite element model is created based on the design geometry data to investigate the mechanical property of the dewar under static load and seismic load.
A joint-less winding method uses second-generation (2G) high-temperature superconductors (HTS) to make an HTS magnet for persistent current mode operation without superconducting joint. Starting with simple double pancake HTS coil wound, we have tried to make and test various types of the joint-less HTS coils. Most recently, a prototype of a concentrically arranged joint-less magnet was made and confirmed that the persistent current mode operation is possible for more than 18 hours at 77 K. In this paper, we proposed a 1 T class concentrically arranged joint-less HTS magnet. They have oxygen free copper bobbin for the conduction cooling with GM cryocooler. It was magnetized with a persistent current switch and operated in persistent current mode at the temperature of below 20 K. We also performed field mapping of the joint-less HTS magnet and verified the possibility of a high field HTS magnet. We also tried passive shimming installed in the room temperature bore in the center of the magnet to improve the quality of the magnetic field.
Acknowledgement
"This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science and ICT (2019R1F1A1063397)"
“This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(2019R1I1A3A01063158)“
EDIPO 2 (the upgraded EDIPO test facility) will provide a unique testbed for superconducting cables for fusion magnets, accelerators, and other applications. Compared to the previous magnet assembly, the magnetic field is enhanced from 12.35 T to 15 T, the aperture is enlarged from 90×141 mm2 to 144×144 mm2 and the uniform field length is increased from 680 mm to 1000 mm (assuming a 1% drop of the field along the sample axis). A number of magnet designs have been proposed for EDIPO 2 since the conceptual design activities started in 2017. The designs have converged into a flared-end block-coil dipole design with a purely rectangular cross-section (coil windings aligned in the high and the low field side). The use of a two-stage cable design is considered in order to increase the operating current, reduce the coil inductance, and consequently limit the discharge voltage. The magnet structural design keeps the pre-compression applied to the coil winding pack to a minimum and allows a gap to open between the coils and the test well during operation. Progress on the magnet design activities will be reported including the results of magnetic and mechanical analyses, as well as quench protection studies. The design of the helium vessel required to contain the liquid helium bath for magnet cooling will be presented.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
We have previously demonstrated proof-of-concept no-insulation style coils wound with a heavily filled conductive epoxy resin system. This epoxy resin system appears to eliminate REBCO delamination, and also allows for tuneable contact resistance between turns. The coils we have reported to date are small coils with an ID of approximately 25 mm and an OD of approximately 50 mm with an inductance of 0.1 mH.
As part of an ongoing National Institutes of Health funded program, we are developing a compact brain imaging MRI magnet using REBCO conductor. We intend to use the conductive epoxy resin system previously reported to provide quench tolerance in this REBCO magnet. The coils for this magnet range greatly in size, however; on average coils are approximately 400 mm ID and 450 mm OD, with inductances ranging from 1 mH to 500 mH.
Part of the optimisation process for the coils is achieving a particular contact resistivity $7.0 *10^{-6}~ \Omega*m^2$. This resistivity value has been chosen to allow the magnet to be rapidly ramped down in case of an emergency. During coil testing, in addition to verifying critical current performance, we need to measure the sudden discharge time of the coils to verify the contact resistance we have achieved at 40 K. The combination of large inductance, relatively high contact resistance and low temperatures means there are particular difficulties associated with designing a suitable sudden discharge switch and measurement system.
Here, we will discuss the limitations of a contactor based switching system and describe the design of an alternative IGBT based system for performing sudden discharge measurements reliably in the presence of high voltage.
Following presentation of the design, we will detail coil testing progress for the coils we have wound to date for the REBCO MRI magnet.
Starting with Gamma sources before moving to Xrays, Radiation therapy also proposes protons or heavier ions like carbon to treat cancer tumours with unrivalled accuracy. Today, radiation Therapy is a proven cancer treatment modality from which several tens of thousands patients benefit each year. But being a proven treatment modality does not mean it is not evolving.
In this plenary, we will start with an overview of radiation therapy systems using Xrays and heavier particles (protons, carbon ions), With a focus on the latter; we will depict their main characteristics and equipment needs for an efficient treatment. Then, we will describe and discuss a few of the current challenges in the field, with a focus on how various magnets technologies play a key role in addressing these.
Fusion power plants offer the prospect of a new sustainable source of energy for future generations. The design and R&D of future reactors is expected to largely benefit from the experience gained in the design, construction and operation of ITER. However, deploying reliable fusion power plants, requires to overcome the design challenges and to address the remaining readiness gaps. Europe is starting the Conceptual Design Phase for building a superconducting DEMOnstration Fusion Power Plant (DEMO) and starting operations around the middle of the century. The aim is demonstrating the production of 500 MWs of net electricity, with a closed tritium fuel cycle and adequate plant availability.
For the design of the Superconducting magnet system several variants of coils have been investigated in the pre-conceptual design phase, which has concluded in 2020. Some of them are very close to ITER design, therefore have a relatively high technology readiness level. The “alternative” proposed solutions, that are very promising in terms of costs and performances, need a validation to industrial scale in order to be eligible for the down-selection expected in 2024. In particular, the validation regards the design of the layer-wound graded TF winding pack based on React&Wind Nb3Sn conductors, and the hybrid, layer-wound graded CS coil. The challenging aspect is that the CS magnet is made of REBCO conductors in high-field, React&Wind Nb3Sn conductors in medium field and NbTi conductors in low field. Also innovative techniques need be studied for insulating critical parts of the coils, as penetrations, discontinuities and joints.
The main issues of the technological development are illustrated. A conspicuous R&D work plan is presented for the Conceptual Design phase to validate the technology within 2024 and demonstrate the operational capabilities by testing superconducting insert coils, that is about 50-m long wound conductors, by 2027.
The Chinese Fusion Engineering Testing Reactor (CFETR) is a DEMO design to bridging the gap between ITER and the first commercial fusion power plant. Toroidal field (TF) magnet system is one of the most challenge for CFETR project. The operating current of the TF magnet is 95.6 kA. The major radius and minor radius of CFETR is designed as 7.2 m and 2.2 m, respectively. To reduce the manufacture cost, a hybrid magnet is creatively adopted in winding pack (WP). For validating the rationality of a TF structure, electromagnetic and structural analysis were conducted. The result indicates that the peak field of the toroidal field superconducting magnet reach to 14.5 T, which can provide the 6.5T at the 7.2 m major radius of the plasma. The max intensity stress of TFCC is about 872 MPa.
The prototype TF coil will be manufactured before 2025 and be tested in ASIPP to verify the safety of engineering design. In the past 3 years, we already finished the detailed engineering design work of the prototype TF coil and also start to do related R&D research work such as internal SC joints, high performance insulation material, TF case sample and so on. We would like to share the status and progress of the prototype TF coil’s engineering design results and its key components’ R&D work.
In this study, we focused on the layered winding concept, in which the conductor can be optimized for each layer by grading, and succeeded in the significant improvement of the conventional rectangular conductor winding concept. The radial plate (RP) system is the main proposal for the toroidal field (TF) coil of Japan's DEMO (JA DEMO), because of its performance in ITER. However, the RP system has a problem of cost increase due to its difficulty in fabrication. In recent years, the double pancake winding concept using rectangular conductors has been investigated as an alternative to the RP method, which has advantages over the RP method in terms of manufacturability and cost, but one of the problems of the conventional rectangular conductor concept remains the reliability of the insulation, i.e., the reduction of stress on the turn insulation.
In this study, taking advantage of the grading in the layered winding concept, the conductor arrangement and the conductor cross-sectional shape for each layer were investigated and optimized to reduce the stress on the insulation. As a result, lower shear stress on the insulation was achieved than the RP method. In addition, the current sharing temperature Tcs was calculated from the maximum magnetic field of each layer, and the amount of Nb3Sn strand was optimized to achieve a temperature margin of 1.5 K in each layer. As a result, we have developed a concept in which the amount of Nb3Sn wire can be reduced by up to 62% from the conventional RP method or the double pancake winding concept with rectangular conductors while maintaining the temperature margin by grading.
Tokamak Energy Ltd is a UK company developing spherical tokamaks incorporating HTS magnets in the pursuit of fusion energy production.
A series of demonstration projects has been conducted on a rapid development cycle to generate stable and robust magnet structures, experimental test capabilities, and simulation tools sufficient for the design and construction of a major HTS magnet system demonstrator – “Demo4”.
The system will comprise 14 toroidal field (TF) limbs and a pair of poloidal field (PF) coils, and will be operated at a fusion-relevant temperature of 20 K. Each TF limb is 1m in linear dimension, containing an HTS double pancake coil wound with non-twisted stacked tape cable and a novel partially insulated construction – a tuned turn-to-turn resistivity. The PF coil pair is 1.5m in diameter and has a fully insulated construction, enabling operation in a fusion-relevant DC + AC modulated condition. The magnet makes use of 56 km of full-width REBCO coated conductor (CC) procured from four key manufacturers.
The system’s objectives are to achieve a peak field on conductor of 20 T and stored energy of ~18 MJ; to reach transverse compressive stresses on-tape in excess of 250 MPa; to simulate pulsed neutronic heating of HTS coils; to measure AC loss in large-scale HTS coil structures; to further explore the dynamic behaviour of complex mutually coupled coil arrays and compare with simulation; and to develop scalable coil manufacturing methodologies. The system will raise the technology readiness level of HTS magnets for fusion and other applications considerably.
This talk will present a technical overview of the magnet system, key simulation results, the status of the system and test facility (under construction now and due to be completed in 2021), and preliminary test results where available.
At the ENEA’s research center of Frascati, the DTT (Divertor Tokamak Test) facility is currently under construction. The activity of this experimental nuclear fusion reactor, will be focused on the optimization of the power exhaust management in view of DEMO. The project has been started during year 2014, when also the superconducting magnet system has been initially designed, basing on the available inputs coming from physics and on the desired goals for the machine. At present, the coils engineering design has almost been completed and the production of crucial components, such as the superconducting strands, conductors, toroidal and poloidal field coils, have already been started. For the remaining superconducting elements, the engineering design is being finalized. The result is a compact and flexible tokamak, with highly demanding requirements in terms of superconducting and structural performances, sometime close to the intrinsic mechanical limits of the adopted materials. Tight constraints on time, budget and resources forced the design team to walk through a complex path in these years for reaching a sound and satisfactory design of the complete magnet system. In fact, it was not possible to rely entirely on state-of-the-art and already assessed superconducting technologies, as was initially assumed. In particular, the trade-off between limiting the R&D phase and extending the performance demonstrated in other projects to the specific DTT requirements, pushed the team to take some risks, while providing a robust and fully performing magnet system design.
The Divertor Tokamak Test facility (DTT) currently under construction at the ENEA Research Center of Frascati, Italy, shall be an experimental fusion reactor that will contribute to the advancement of the EUROfusion roadmap to fusion energy. This work summarizes the design choices and the Finite Element Modelling (FEM) results in support of the Toroidal Field Coil (TFC) system design which is the current reference for the coil case manufacturing and winding pack integration industrial activities. Effort has been put into optimizing the various components in order to meet the requirements of the projected assembly procedure as well as the resource constraints that have been set for this project. Compared to other tokamak machines of similar performances, the relatively small size of the DTT required the adoption of some innovative solutions to comply with the structural capabilities of the materials employed. Nonetheless, given the tight schedule this project must follow, compatibility with the technological state of the art of today was mandatory.
The no-insulation (NI) high temperature superconductor (HTS) toroidal field (TF) coil or its variations have been regarded as a potential option for a compact, high magnetic field tokamak due to compactness in size and robustness in operational reliability. However, its real application still faces multiple challenges, e.g., we have limited experience in design, construction, and operation of "toroidal” NI HTS coils. Here we report a reduced size NI HTS TF module coil that is fabricated, tested, and analyzed to explore the feasibility of NI HTS technology to D-shaped TF coil. The TF module coil is designed to be 1/20 of the Korea Superconducting Tokamak Advanced Research (KSTAR) TF coil in height which is ~ 200 mm. The coil is wound with non-twisted stacked HTS tapes of 5 which could represent an HTS cable. The coil is tested under 20 K of conduction-cooled environment to evaluate the performance and characteristic parameters by examining the magnetic field and characteristic resistance. Various current charging/discharging tests are conducted to compare the results with lumped circuit model and/or turn-distributed circuit model simulation considering the effect of the straight section of the D-shaped coil on the contact resistance. By applying the verified circuit model to an actual size TF coil, a range of feasible contact resistance is deduced to search for the possible candidates such as metal insulation that can improve the charging delay of the NI HTS TF coil.
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249). This work was also partly supported by R&D program of “code No. CN2101” through the Korea institute of Fusion Energy(KFE) funded by the Government funds
We present the integration and initial test of the world’s first superconducting magnet system for Magnetic Density Separation, from coil winding to cryostat assembly as well as first cool-down and energizing. Magnetic Density Separation is a relatively new separation technology that allows the simultaneous sorting of multiple non-magnetic materials based on their mass density by combining a ferrofluid with a strong vertical magnetic field gradient. To maximize the field gradient in the ferrofluid, the distance between the NbTi coils operating at 4.5 K and the room-temperature ferrofluid is minimized. This is made possible by two design choices: conduction-cooling allowing for a single-wall cryostat; and vertical ‘stay rods’ that support the flat top plate of the D-shaped cryostat from the stiff bottom, allowing for a relatively thin wall.
The magnet system is designed, engineered and assembled at the University of Twente and comprises 3 side-by-side 0.3 m $\times$ 1.4 m racetrack coils that are shrink-fitted in an aluminum alloy cassette, which provides thermal pre-stress to balance the Lorentz forces. The vertical magnetic field gradient at the bottom of the ferrofluid reaches 20 T/m. The coils are cooled to 4.5 K with a 1.5 W @4.2 K GM cryocooler. A particular design challenge is to minimize the cryogenic load to enable conduction cooling by meeting competing requirements imposed by the support structure, the heat load from the cold mass with a large surface area, and a significant attraction force between coils and ferrofluid.
This work is part of the research program “Innovative Magnetic Density Separation for the optimal use of resources and energy”, project number P14-07, partly financed by the Dutch Organization for Scientific Research (NWO).
We have started to develop a magnetic refrigeration system for hydrogen liquefaction. This system has a superconducting magnet, in which an active magnetic regenerative (AMR) bed moves inside. During steady-state operation, there is a possibility that the superconducting magnet is conduction cooled by the cold of liquefied hydrogen. However, since it is in the development stage, the magnet is cooled using a cryocooler. Considering the applicability to the 20 K operation and the required magnetic field of 4-5 T into account, we have developed a high-Tc superconducting (HTS) magnet using Bi-2223. This Bi-2223 magnet is composed of 24 epoxy-impregnated double pancake (DP) coils. To minimize the magnetic field at both ends, two bucking coils consisting of four DP coils are placed at both ends. It is designed to generate 4.7 T in a 120 mm bore at 300 A operation current. Each DP was was tested in liquid nitrogen (LN2) bath to verify its performance before being stacked. So far, the fabrication and the LN2 test of the magnet have been completed. At present, the magnet test under the cryocooled condition is being prepared. The design, fabrication, and test results of the Bi-2223 magnet will be reported.
Acknowledgement: This work was supported by JST-Mirai Program Grant Number JPMJMI18A3, Japan.
High-temperature superconducting (HTS) coils and magnet systems are used in various applications today. Despite the great advantages they offer over conventional systems, their commercial success is yet pending. A major obstacle is a high price due to the cost of the HTS tape and the development effort needed to meet very specific requirements.
In various projects, we have developed techniques that open up possibilities for manufacturing magnet systems more cost-effectively. Central to this is accurate electromagnetic modelling and simulation to minimise the HTS tape requirement and allow cheaper lower-grade tape to be used in less demanding areas. We demonstrate how the cold bus can be integrated into large potted double pancake coils to optimise cooling conditions and avoid local hot spots. We have also developed processes for manufacturing non-insulated coils specifically for applications that require high resilience to multiple quenching events and high robustness against mechanical forces and shock.
By combining these techniques, we have developed solutions that significantly enhance the potential of THEVA HTS tapes for a wide range of applications from traditional industries such as aluminium forming, to exotic applications such as levitating magnets, to highly innovative technologies such as magnetic re-entry shields or ion engines for spacecraft.
Superconducting magnets are capable of producing exceptionally stable magnetic fields when operating in “persistent current” mode. In this approach, a superconducting switch disconnects the power source from the magnet circuit, allowing the magnet current to flow in a closed superconducting loop free of power supply noise. We present the design, fabrication, and test of a 1.9 T iron-dominated, round lens seeking to probe the limits of this persistent mode superconducting magnet technology for use in an electron microscope. First, we give an overview of the design and fabrication of a prototype magnet, superconducting switches, and superconducting joints. We then present the results of testing this lens system in liquid helium, with a focus on temporal field stability. Sources of remaining field perturbations, such as external noise and drift due to small residual circuit resistances, are characterized using cryogenic hall probes and SQUID magnetometry. Active methods for further stabilization of the lens, such as inductive flux transfer and other techniques, are compared and evaluated experimentally. Finally, strategies for shielding external noise are explored, including the use of a superconducting shield.
Magnetic spectrometers detect the rigidity of charged particles by measuring the bending of their trajectories as they pass through a magnetic field. A novel magnetic spectrometer for an astroparticle physics experiment in space should have a maximum detectable rigidity of about 100 TV. This motivates the design of a toroidal spectrometer magnet with a bending strength of 3 T m at an operating temperature of 20 K. The toroid consists of twelve HTS coils, where each coil contains two winding layers. The toroidal magnet requires about 60 km of 12 mm wide ReBCO tape with a current density of 1200 A/mm2, and has a peak magnetic field of about 12 T. Within the HTS Demonstrator Magnet for Space (HDMS) project, we have built and tested a small-scale demonstrator coil for the toroidal magnet system. The demonstrator coil consists of two individually built racetrack-shaped soldered metal insulation HTS ReBCO winding layers. The finite electrical resistance between winding turns enables self-protection against quenches. The winding layers are surrounded by copper bands functioning as current leads and layer jumps. The coil is supported by a lightweight mechanical structure made from aluminium alloy. We present an electrical characterization and magnetic measurement results for the demonstrator coil.
The self-field critical current Ic of 2G high temperature superconducting (HTS) tape can be reduced by applied dc magnetic field. This property can be used in the development of HTS switching elements through so-called Jc(B) switching. The design of a dc magnetic field switch is reported with both single and bifilar configurations. Dc magnetic field is applied by an iron-core field coil with copper windings, providing an applied field of up to 1.4 T. This allows for effective suppression of Ic. Here, it is also reported that the self-field Ic of the single tape is suppressed from 377 A to 195A in the presence of the iron-core. This is due to the presence of the iron core amplifying and distorting the self-field of the tape and is confirmed by experiment and finite-element modelling. This effect can be eliminated using a bifilar tape configuration, which recovered close to the no-core self-field Ic. Active dc switching by applied field was still achieved in the bifilar configuration, albeit at reduced efficacy due to screening. Such distortion and suppression may prove useful for the development of novel HTS circuit components.
Superconducting magnets have been attracting research interest due to their numerous applications, which include accelerator magnets, fusion magnets and superconducting trains. However, as the coils driving the magnets require large currents, the losses in the current leads supplying the coils can be problematic. Power semiconductor devices have shown improved performance at cryogenic temperature as their conduction and switching losses generally decrease at lower temperatures. In this paper, a cryogenic DC/DC converter is proposed to be placed between the current leads and the magnet to reduce the current passing through the leads by stepping down the voltage locally and acting as a transformer, thus reducing the transmission losses and the overall losses of the system. The paper will address the design, simulation and experimental testing of a converter for driving a superconducting magnetic coil. Finally, the overall efficiency will be measured with and without the converter, and a comparison and analysis will be carried out.
High-temperature superconducting REBCO tapes are expected to be applied to next-generation magnets for their high critical current density. One of their problems in the magnet application is the magnetic field instability caused by the decay of magnetization due to the shielding current caused by the tape shape. Therefore, it is important to evaluate the magnetization relaxation of REBCO tapes for the magnet design. We have studied on the magnetization relaxation in REBCO tapes with artificial pinning centers (APCs). In this study, we evaluated the magnetization relaxation of commercial REBCO tapes in a wide temperature and field ranges.
Commercial REBCO tapes with and without APCs from Fujikura, SuperPower, and SuperOx were cut into 2 mm squares and magnetization relaxation was measured using MPMS at temperatures of 4-85 K and fields of 0.1-5 T perpendicular to the tapes. As a result, the relaxation was smaller in the doped samples at higher fields and at temperatures above 40 K. It indicates that the APC suppressed plastic flux creep [1]. In the medium temperature range of 20-40 K, a maximum value was observed in the temperature dependence possibly due to the double kink excitation [2]. At low temperatures below 20 K, the magnetization relaxation was proportional to the temperature and showed similar values for all the tapes, which is explained by the collective flux creep due to thermal excitation [3]. We will report in detail on the characteristics of various companies' REBCO tapes, which are important for superconducting magnet design by suppressing magnetization relaxation.
Acknowledgments
This work was partly supported by JSPS-KAKENHI (20K15217), JST-A-STEP, NEDO.
References
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[3] P. W. Anderson and Y. B. Kim, Rev. Mod. Phys. 36, 39 (1964).
Non-insulated (NI) coils in superconducting REBCO high-field magnets provide electro-thermal stability. However, current transfer between turns through the metal causes transient currents and magnetic fields, increasing the AC loss and requiring longer times to charge the magnet. Therefore, magnet design and optimization requires numerical modeling. Although 3D modeling provides the full description, it is highly time consuming. In this contribution, we propose an effective cross-sectional 2D modeling method to model the screening currents and turn-to-turn currents in non-insulated coils within high-field magnets. This technique is based on the Minimum Electro-Magnetic Entropy Production method [1,2], which is programmed in C++ and enables parallel computing [2,3]. With this method, we analyze the screening currents, instantaneous AC loss and generated magnetic field in tentative designs of high-field superconducting magnets generating more than 32 T. The fast numerical method enables to evaluate the magnet performance considering either a homogenized approach or by taking the details of each turn into account. This method can also be applied to power devices, such as rotor windings in motors and generators. In the future, we expect to extend this method in order to take multi-physics modeling into account.
[1] E Pardo, J Souc, L Frolek, Electromagnetic modelling of superconductors with a smooth current–voltage relation: variational principle and coils from a few turns to large magnets, Supercond. Sci. Technol. 28, 044003 (2015)
[2] E Pardo, M Kapolka, 3D computation of non-linear eddy currents: Variational method and superconducting cubic bulk, J. Comp. Phys. 344, 339-363 (2017)
[3] E Pardo, Modeling of screening currents in coated conductor magnets containing up to 40000 turns, Supercond. Sci. Technol. 29, 085004 (2016)
High-temperature superconducting (HTS) composites are being considered for use in high-field magnets for future particle accelerators, as they allow the development of very high field dipoles and quadrupoles. As part of the US Magnet Development Program, LBNL is developing Bi2212- and REBCO-based insert magnets towards 20 T hybrid dipole magnets. The field quality of the magnets is important to assess and limited reports on HTS accelerator magnet field quality measurements are available. Furthermore, drift in the field quality resulting from flux creep in HTS is an important consideration. Here we report on field quality measurements of insert magnets measured at 77 and 4.2 K. The coils were based on canted cosθ designs and were wound with Bi2212 Rutherford cables and CORC® wires. Hall sensors and rotating coil fluxmeters were used to measure the generated magnetic field harmonics and their temporal evolution. The Bi2212-based coils included a 2-layer, 16 turn magnet made from Rutherford cables. The magnet is 40 cm long and has a 3 cm diameter bore. Another coil reached a peak current of 4.1 kA with a field of 0.7 T in the bore. The REBCO-based magnet had 4 layers and 40 turns and reached a peak field of 2.9 T. The magnetization and decay data from M-µ0H measurements performed at 4 K on samples of cables of the HTS composites were used as inputs to finite element and analytical models to predict the field error of a magnet made from the cables. We compare the results of the field quality measurements to calculated results from models based on the short cable magnetization data results. The study allowed us to better understand the field quality issues in HTS magnets and provided important feedback on the conductor development and strategies to improve the field quality of emerging HTS accelerator magnets.
In agreement with CERN the LASA laboratory of INFN (National Institute for Nuclear Physics) of Milan has carried out the industrial development of a novel type of magnet, for the High Order (HO) correctors of the High Luminosity - LHC (HL-LHC) project. These corrector magnets are based on a superferric design and will be installed in the new HL-LHC insertion regions for the ATLAS and CMS Experiments at CERN. These fifty-four correctors cover different harmonic order: from skew quadrupole up to dodecapole, and all assembled in one cold mass named Corrector Package, an absolute novelty for superferric in a collider. The first magnet batches have been already manufactured by industry and tested at LASA. Magnetic measurements have been performed at low current (at room temperature) as well as at operating current (4.2 K during cold tests at LASA). The measurements have been used as production monitoring and magnet acceptance. The measurement setup, based on a rotating coil system, is described including also the commissioning of the new PCB probe, supplied by CERN. To assess the suitability for collider operation the field multipoles and the transfer function for the various magnet types are reported in the paper. The results have been also compared to the 3-D model calculations highlighting the iron saturation effects.
Most of the existing AC loss experiments and simulations of High Temperature Superconductors Coils deal with low currents of less than 100 A, which does not provide sufficient data or analysis for the HTS coils with higher current at 500 A to 800 A. If the AC loss is considerably larger, it will result in high heat dissipation into the HTS coils, and so as to elevate the coil temperature and fail the magnet operation. A 50 turns of solenoids magnets with a diameter of about 30 cm, are being studied. It turns out that the AC loss in a 0.5 T coil is about 1000 – 10000 more than that in a single conductor, and may result in ~5000 W heat dissipation. A few new Methods have been experimented in this study to reduce the coil AC loss at frequency of 1 Hz – 10 Hz. (1) Divide the 50 turns into 5 identical coils, each has 10 turns, align them vertically on the same axis, with 2 mm gap between them. May try with or without steel core, and maybe flux diverter. (2) Divide the 50 turns into 5 different ID/OD coils, concentrically aligned with 3 mm gap. (3) Still the same 50 turns coil, but increase turn-to-turn insulation thickness, from 0.1 mm to 1 mm and 2 mm. AC loss calculation will be performed and compared to optimally reduce the AC loss in the fast-ramping HTS coil and the thermal load.
The Super Separator Spectrometer (S3) aims to study the limits of the nuclear existence [1][2].
In order to achieve large momentum as well as charge-state acceptance for S3 layout, a high-gradient field magnet technology that generates a pure normal multipole field has been designed. This magnet is designed according to the current sheet approach. For a better overall quality field produced by the magnet, it is also crucial to optimize the shape of the coil ends. Therefore, we have used the technique proposed by Walstrom [3][4] for designing the Superconducting Multipole Triplet (SMT). To our knowledge, this technique has never been used yet in a nuclear physics spectrometer application. Cryomagnetics Inc. and Advanced Magnet Lab Inc. have built seven SMTs that were recently delivered to GANIL. Each SMT assembles three singlets of 11 NbTi coils made up of 3 quadrupole, 3 sextupole, 3 octupole and 2 dipole coils.
To determine the efficiency of the Walstrom’ coil method for the magnets, we have developed two new field mapping setups. These latter use the same high spatial resolution three-axis SENIS Hall probe [5]. One setup was developed in Argonne National Laboratory, it relies on mapping along the azimuthal and axial direction of the cylinder, at a fixed radius. Then, using a numerical method described in [6], we can extract a full 3D field map. The second precise measuring field system was designed and built at GANIL to help ensuring the alignment of the cold mass in the SMTs. An extensive series of measurements is planned in GANIL laboratory at helium temperature, in June 2021.
Detailed information of the two experimental setups will be presented along with magnetic field analysis on the SMTs multipoles for multiple current values, coil combinations and different cooling cycles, thus providing sufficient data for the commissioning process.
Magnetic field and current variations are responsible for AC losses in superconductive magnets. These losses may induce an increase of temperature within the material and negatively affect the performance of the magnet.
Developed at CEA, the new fully analytical model named COLISEUM (COupling Losses analytIcal Stages cablEs Unified Model) aims at predicting the coupling losses at various scales only from geometrical and electrical parameters. In this model, a multiplet is composed of several elements. Those elements can represents either a strand, a multiplet of strands or multiplet of multiplets. COLISEUM simulates those elements through tubes of current that are characterised by several geometrical parameters such as their twist pitch, their cabling radius or their compaction. The most recent model version addresses the coupling losses for a full Cable in Conduit Conductor (CICC), accounting contributions from the strand to the nth-stage of the cable.
In the present work, we conduct an extensive parametric study on those geometrical parameters and investigate the output of the COLISEUM model, with associated interpretations on the link between inputs relevance and resulting outputs. We compare simple COLISEUM configurations with a full numerical approach. In addition, tomographic studies, conducted at INFLPR, on real cable designs (of JT-60SA TF type) allow us to investigate and validate our theoretical results on the cabling radius.
We conducted a crosscheck between experimental AC loss measurements and the COLISEUM model on various geometries of CICCs. Samples were tested at CEA Cadarache in the JOSEFA facility using the magnetization method and in SULTAN facility using calorimetric method. We compared the measured AC losses with the losses predicted by COLISEUM using the experimental geometrical and electrical parameters as inputs for the model. It allows us to evaluate the predictive capabilities of the model for various geometries.
During its nominal operation, strong current variation, more than 10 kA per second, can be imposed on the KSTAR PF (Poloidal Field) magnet system. Due to AC loss, transient massive backward flow can occur, especially at the cryogen inlets of each magnet. To protect cryogen circulator, several valves are activated to adjust or lower pressure below the circulator’s operation limit. In this work, we discuss whether currently available thermo-hydraulic code, such as SUPERMAGNET, can describe this overall dynamic flow characteristics of KSTAR PF magnet cryogenic network. First, three major functions of the KSTAR PF magnet cryogenic system during plasma operation are classified and discussed. Cryogenic components mostly related with other functions such as, cool-down process, are removed from the simulation circuit to minimize computation time as much as possible. SUPERMAGNET code was used with a slight modification in its cryogenic network simulation module, FLOWER. The codes for cryogenic valves are modified so that not only steady state but also general compressible flows can be described. A case study for an actual KSTAR plasma operation has been intensively carried out. It was shown that most relevant data, pressure, temperature and mass-flow, both at the inlets and outlets of the magnet, are in agreement with simulation results.
Over 30 years ITER has been through many design iterations and multiple novel solutions for the magnets have been tried, in some cases being carried through to successful manufacturing and in other cases being abandoned. Now that ITER operation is approaching, the fusion community is considering possible next steps, to a power producing fusion plant. If we consider the long road ITER has followed, what lessons can be learned for these next steps?
Looking back at the design iteration history of the ITER magnets, there are several key factors driving magnet design, such as superconductors, structural Support, voltage and thermal protection, power supply arrangement and feeders. We can see the new availability of advanced materials and design techniques including high Tc superconductor at low temperature, cable-in-conduit (CICC) development and analytical magnet design. The presentation will look at what ITER did in the early stages in this direction and how a future reactor design could utilise these concepts in the magnets.
Perhaps the most basic lesson is that if a tokamak reactor tries to satisfy the research priorities of many, it can end up as a machine being designed by a committee. This is really the political environment but it can be decisive (as in the case of ITER) in determining the nature of the project. Beyond this, we can look at the many novel technical solutions (those that made it into the final ITER magnets and those that did not) and consider whether we could have been more efficient….and whether we can see any signs of the same mistakes being repeated.
Superconducting accelerator magnets, due to their high aspect ratio and field configurations, have some unique design and fabrication issues, particularly for higher magnetic field configurations. After more than a half century, the accelerator magnet community is, for the first time, now on the verge of installing magnets based on Nb3Sn in the Large Hadron Collider at CERN. Much experience has been gained over the past several decades, but there is more to be done. High Temperature Superconductors (HTS) are relatively new in terms of their application in accelerator magnet configurations. Though very promising in terms of field performance, there are many issues to be resolved before seeing practical use. This talk will highlight some of the lessons learned in the development of accelerator magnets based on both Nb3Sn and HTS as well as some of the remaining challenges.
The upgrade of the LHC to increase luminosity (High Luminosity LHC) requires the construction of six different types of accelerator magnets based on LTS technology. Besides the quadrupoles in Nb3Sn, with peak field of 11.5 T, we have two different dipoles in the 4.5-5.6 T range based on Nb-Ti, and three types of correctors. All magnets are characterized by wide apertures (150 mm), posing significant challenges for the large accumulated stress in the midplane.
In this contribution, after recalling the specific features of the project, we will outline a classification of the typologies of the issues found during the design/prototype phase and we will discuss in more detail two cases. The first one is an unexpected contribution to field quality in the separation dipole, due to a cross talk between saturation and 3D effect that propagates well inside the magnet straight part. The origin of the problem, its simulation with finite element methods and the iteration in field quality to cure this effect will be presented.
The second one is a limitation in the magnet performance due to the torque induced by horizontal and vertical field in the coil heads of the nested corrector dipole. The first prototypes showed ability to reach the field requirements, but required retraining when changing the torque sign. A fine tuning of the coil design allowed to considerably reduce this issue, proving also how sensitive the magnet performance can be on details of the design, even in the case of Nb-Ti magnets.
The National High Magnetic Field Laboratory headquartered at Florida State University in Tallahassee, Florida, USA designs, builds, and operates a variety of ultra-high field magnets including superconducting magnets providing up to 32 T, dc resistive magnets providing up to 41.5 T, resistive/superconducting hybrid magnets up to 45.1 T, and pulsed magnets up to 100 T. Some of the "lessons learned" in the development of a variety of ultra-high field magnets since 1994 will be presented.
Firstly reported by MIT in 2010, the no-insulation (NI) high temperature superconductor (HTS) winding technique introduced a new philosophy of HTS magnet protection: “current sharing” with adjacent turns upon a quench. The protection mechanism of the NI HTS technique was later explained by RIKEN: the multi-turn-to-single-turn transition. To mitigate the charging delay, a major drawback of NI HTS magnets, variations of the NI HTS technique such as partial and metal insulations have been proposed. Most of “NI-class” HTS magnets were essentially immune to local burn-out from overheating upon a quench. Consequently, some NI HTS magnets were operated at substantially higher engineering current densities than those of insulated ones, e.g., the well-known “Little Big Coil (LBC)” by NHMFL, a 14.4 T NI-REBCO insert operating at 1260 A/mm2 in a 31.1 T resistive background magnet to reach a record high DC magnetic field of 45.5 T. Although the NI-class HTS magnets have been widely studied in various applications nowadays, multiple groups have reported failures of NI HTS magnets, mostly due to mechanical issues. Moreover, as some NI HTS magnets experienced long-term operation over years, operational issues such as characteristic resistance change and joint degradation have been also raised. Recently, the so-called “one-side-edge plastic deformation” of REBCO tapes of LBC due to the screening current induced stress (SCS) was reported by NHMFL. Yet, to date our community has been unsuccessful to quantitatively explain SCS with the conventional numerical approaches. This paper intends to summarize those lessons learned over the last decade on NI HTS magnets, identify key technical challenges, and introduce potential solutions for ultimate success of HTS magnet technology, if not limited to NI or its variations.
Quality Assurance (and the derived quality controls) define the Nuclear Quality Approach in ITER. The higher the impact of manufacturing and assembly errors, then the more rigorous the QA regime, leading eventually to Safety Specific controls such as the appointment of an Authorised Notified Body ANB, by the Safety Regulator. Requirements come from regulatory and safety surveillance, quality supervision, purchase arrangements and codes & standards.
The integrated Quality Approach to Superconducting Magnets covers a very wide range of manufacturing, assembly and operational items, weighted by impact. Typical impacted operational items are Reliability, Field Quality and Error Fields, Magnetic Forces and Stresses, Degradation and Training, Cryogenic Stability, Quench and Protection, Instrumentation and Measurement Techniques.
Methods and techniques for implementing quality assurance in ITER Superconducting Magnets started with Design Control, such as reviews of requirements and design verification. Then they extended to manufacturing quality control in procurement including control verification and methods of acceptance tests. As a staged project, currently ITER is now facing the Installation Process Control including component identification and tracing, tool proofing, qualification of installation, inspection and test personnel, qualification of installation procedures. Next will be the control of commissioning activities and verification functions until the hand over of Superconducting Magnets for operation.
In order to be compliant with the defined requirements and/or technical requirements, ITER developed a manufacturing database to monitor the progress of activities and control the quality during procurement control. ITER standardises an approach to non-conformances based on an on-line database which is used now by almost all suppliers.
HIAF (High Intensity Heavy Ion Accelerator Facility) is the new generation heavy ion accelerator under construction in China. The HFRS (FRagment Separator of HIAF) is a fragment separator and also a transfer-line between the Booster Ring and the Spectrometer ring, which has the magnet rigidity up to 25 Tm . It includes 11 superconducting dipoles and 13 sets of triplets. Several multipole magnets (an octupole, a quadrupole and a sextupole) are nested together to compact the length of HFRS-line. All of them have high gradients (11.43T/m, 20T/m2, 105T/m3) and large bores (320mm). To reduce the cold mass and ensure the field quality, the whole multipoles are all designed with coil dominated magnet of CCT (Canted Cosine Theta) and DCT (Discreted Cosine Theta). This paper will introduce the generally design process of a HFRS multipole module. The development process and testing results of the prototype will be also presented. manufacture processes and testing results to show the novel magnetic technology research.
A novel Canted-Cosine-Theta (CCT) coil technology is first proposed and applied to the HIAF (High Intensity heavy-ion Accelerator Facility) fragment separator, which can offer the absence of multipole components and meet the requirements of high magnetic stiffness (25 Tm). In this paper, a half-aperture CCT multipole prototype was built and successfully tested by the Superconducting Magnet Group at Institute of Modern Physics (IMP). This magnet consists of four CCT formers that produces the gradients of 20T/m@500A and 120T/m2@385A, with a clear bore diameter of 200 mm. Two types of superconducting cables are chosen and wound into the grooves of formers. The goal of the R&D of prototype is to verify the fabrication process, including coil winding, joints, assembly and impregnation. The detailed design and analysis for the half-aperture prototype magnet will be presented, along with results for the first set of tests.
The Superconducting FRagment Separator (Super-FRS) is a key experimental facility for FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. It consists of 24 super conducting dipole magnets and 30 multiplets. Three branches (a low energy, a high energy and a ring branch) allow to carry out a wide variety of nuclear physics experiments. Quadrupole magnets and corrector magnets are assembled as one cold mass column and they will be cooled in a common He bath with design pressure of 20 bars. There are 23 types of cryogenic modules depending on how a cold mass column is configured upon requirements of beam optics. This paper focuses on various aspects of the most complicated multiplet (FHF1YMQ11). The cold mass is fully configured with nine magnets and its weight and length are 45 tons and 6.5 m respectively. Two types of quadrupole magnets sharing the same 2D design but having a different yoke length and sextupole magnets are superferric magnets. Their warm bore radius is 192 mm and coils are vacuum impregnated racetrack coils made of Nb-Ti conductor. Two octupole and one steering dipole magnet are cos-theta magnet. Extensive design studies were performed for homogeneous cooling down of such a large cold mass in a reasonable time as well as for achieving required magnetic field quality. The construction was completed in Q4, 2020. The cold test of the long multiplet is now underway at a CERN cryogenic magnet test facility in the frame of a GSI/CERN collaboration work.
We will summarize the initial magnetic designs of the Interaction Region (IR) magnets for the Electron Ion Collider (EIC) that has been proposed to be built at the Brookhaven National Laboratory. This paper will be limited to the magnet designs based on the Rutherford cable (magnets based on the Direct Wind technology will be discussed elsewhere). The magnets to be discussed are: (a) 1.46 meter long quadrupole Q1ApF with a coil aperture of 141 mm, and a design field gradient 72.6 T/m, (b) 1.61 meter long quadrupole Q1BpF with a coil aperture of 186 mm, and a design field gradient of 66.2 T/m, (c) 3.8 meter long quadrupole Q2pF with a coil aperture of 280 mm, and a design field gradient of 36 T/m, (d) 3 meter long dipole B1pF with a coil aperture of 300 mm, and a design field of 3.4 T, and (e) 1.5 meter long dipole B1apF with a coil aperture of 270 mm, and a design field of 2.7 T. The goal was to develop magnetic designs that can be made using NbTi technology and can operate at ~4.5 K with a sufficient margin. A combination of large aperture and high field create high stresses and will require stainless steel collar with sufficient width. Another major challenge was to develop magnetic designs with a low leakage field from the high field superconducting quadrupole for the proton/ion beam on the superconducting quadrupole (or a hole in the iron for beam passage) for the electron beam. The crosstalk from the superconducting electron quadrupole on the proton quadrupole should also be low. This is particularly challenging since the two beams are in close proximity to each other with the separation between the two changing along the length. This paper will present a novel strategy to overcome this challenge.
Superconducting electron cyclotron resonance ion sources (ECRISs) using NbTi coils and optimized for 28 GHz resonant heating have been successfully operated for almost two decades. Moving to higher heating frequencies requires increased magnetic fields, but traditional racetrack-and-solenoid ECRIS structures are at their limit using NbTi. Rather than moving to a superconductor untested in this field, the Mixed Axial and Radial field System (MARS) being developed at Lawrence Berkeley National Laboratory employs a novel closed-loop-coil design that more efficiently utilizes conductor fields and will allow the use of NbTi in a next-generation, 45 GHz ECRIS. This article presents the design of the shell-based support structure central to the MARS-D magnet design, as well as structural analysis of its components and optimization of pre-load parameters that will guarantee its successful operation.
In the main linac of the International Linear Collider (ILC), superconducting magnets for beam focusing and steering will be located periodically in superconducting RF (SRF) cavity string for beam acceleration in common cryomodules. A concept of conduction cooling of the combined-functioned, split-able superconducting magnets has been proposed and investigated to adapt much different features and to meet different requirements for the superconducting magnet and SRF cavity in fabrication, assembly, and operation. It is required to integrate the superconducting magnet after the SRF cavity string assembly completed under ultra-clean environment, and to isolate and the magnet operation by using conduction cooling through thermal link to LHe cooling pipe. In addition, an important issue has been recently identified. High gradient SRF cavities naturally emit field emission electron flux from the inner surface, so called dark current. It may pass through the subsequent SRF cavity string and penetrate into the superconducting magnets placed downstream. It may heat up the superconducting coils may cause the quench. Therefore, further study on reliable conduction cooling and to secure the superconducting magnet operation with keeping sufficient safety margin. It is also important to integrae lessons learned from a model magnet development carried out in cooperation with Fermilab and KEK. In this report, we report the R&D progress in study on the conduction cooling of the superconducting magnet for the ILC main linac.
In high field applications, the HTS coils are commonly impregnated with epoxy resins for insulation and mechanical reinforcement to against the huge Lorentz forces. Till now, many of the epoxy impregnated ReBCO based HTS coils show some degree of performance degradation (Jc) due to thermal stress during cool down, electromagnetic stress during operation or any other reasons. It remains a challenging task to find an appropriate impregnation method for this type of HTS coils. In this study, for the first time, the effects of a new epoxy resin system IR-3 which was developed by the Institute of Physics and Chemistry, Chinese Academy of Sciences (IPC-CAS) were investigated in the Institute of High Energy Physics (IHEP-CAS) for the high-field application. At liquid nitrogen temperature, the cool down, local heat pulse and over-current results showed that the coils impregnated with the IR-3 exhibited almost the same superior thermal and electrical stabilities as compared to those potted with CTD-101K and Araldite MY750 that widely used in superconducting magnets. After 20 times of thermal cycles, all the IR3 impregnated HTS coils showed no decay in critical current. Study at 4 K under the high background magnetic field and the corresponding experimental results will also be presented and discussed. Considering the acceptable radiation resistances, higher strength than CTD-101K at low temperature and longer pot life than MY750, IR-3 resin system is a suitable candidate for impregnating high-field HTS coils.
Quench and protection in magnets wound with coated conductors is of great interest for many applications, including those of high energy physics accelerators. The relatively large slow normal zone propagation and large MQE of coated conductors and the potential of burn out in well insulated coils has led to an interest in non-insulation coils. A stability of block type dipole magnets wound using non-insulated YBCO Roebel and CORC cables has been modeled by FEM method. Critical currents of the magnets have been calculated using a self-consistent method based on anisotropic Ic(B) curves of the cables. Advantages and disadvantages of using the Roebel and CORC cables in dipole magnet windings have been discussed. Heat disturbances of different size, intensity and duration have been analyzed from the viewpoint of the magnet quench and stability.
BOnding eXperiments (BOX) are a novel, affordable and fast benchmarking solution aiming to reproduce specific mechanisms of training and performance limitations in Nb3Sn and Nb-Ti superconducting magnets. The BOX samples are tested at the University of Twente at 4.2 K within a solenoidal background field with sufficiently high magnetic forces. Following conventional manufacturing processes, the fully instrumented BOX samples have been shown to exhibit training and memory behavior similar to their respective full-scale magnets. Improvements to the fabrication of the BOX samples have successfully reduced training and more unconventional impregnation systems such as paraffin wax have reached the estimated ISSL with no training quenches at all. In this contribution we will discuss in detail the experimental results of the first test series of BOX samples.
The performance of accelerator magnets strongly relies on electrical and mechanical robustness of their components. With an increase of the energy, future accelerators will have to withstand integral doses around 35 MGy or higher during their lifecycle. Initially developed for the components of the D1 separation dipole magnet, designed and manufactured by KEK and part of the HL-LHC Project, this study was enlarged to characterise a spectrum of Glass Fiber Reinforced Polymers and resins that can be chosen to manufacture main components in superconducting magnets. As a collaboration between CERN, KEK (JP) and QST Takasaki (JP), an irradiation campaign was performed with gamma rays doses going from 10 MGy to 100 MGy. This paper describes the different methodologies applied for mechanical and chemical tests, both at room and cryogenic temperatures. The relevant results and the analysis are presented with the goal to provide a guidance on the choice of specific material or resins in HEP applications.
The U.S. High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) team is fabricating the 4.5 m long MQXFA magnets, a 150 mm aperture high-field Nb3Sn low-β quadrupole magnet, in the context of the CERN Hi-Luminosity LHC (HL-LHC) upgrade. To date, two prototype magnets and five Pre-Series magnets have been assembled and tested. The first two prototypes did not achieve full performance requirements, but the lessons learned from them were fed back into the assembly and testing of the subsequent pre-series magnets, MQXFA03 thru MQXFA07. As the project is now transitioning to Series magnet production the data obtained from the as-built Pre-Series structures is instrumental to understanding the various build parameters and how they might explain or predict the mechanical performance of the structure. This paper summarizes the available strain gauge data from these structures as it relates to the FEA models and actual CMM measurements from the structural components. We also report on the fiducialization measurements performed with the warm magnetic measurements.
This work was supported in part by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US HL-LHC Accelerator Upgrade Project, and in part by the High Luminosity LHC project at CERN.
As part of the U.S. contribution to the HL-LHC Accelerator Upgrade Project (AUP), Fermilab is designing and building cold masses suitable for use in the LHC interaction regions. The cold mass provides a vacuum-tight helium enclosure for the magnets. Two magnets are aligned both axially and in cross section at Fermilab based on survey and warm magnetic measurements. Bus work and instrumentation is added. A welded stainless steel vacuum-tight shell surrounds the two magnets, and the structure is prepared for insertion into the cryostat. This paper summarizes the design of the cold mass including alignment, bus work, weld details, and instrumentation.
Abstract— Fermilab is fabricating ten full length cold masses for the high-luminosity Large Hadron Collider Accelerator Upgrade Project (HL-LHC AUP). One practice assembly and one pre-series assembly have been completed. This paper summarizes the construction details. Topics include incoming inspection, bus assembly, component machining, shell forming, beam tube insertion, bus expansion loop installation, instrumentation installation, electrical testing, heat exchanger installation and final assembly welding. In-process surveys, alignment measurements and testing are presented and explained. Problems encountered during construction and their solutions are discussed.
*This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US HL-LHC Accelerator Upgrade Project
Cryo-assemblies with the low-beta Nb3Sn quadrupoles for the high luminosity LHC (HL-LHC) upgrade will be tested at Fermilab’s magnet test facility. Total of 10 cryo-assemblies will be delivered to CERN within the US HL-LHC Accelerator Upgrade Project (AUP). The horizontal test stand at Fermilab already has been used for testing the existing LHC inner-triplet quadrupoles, but the stand and related electrical and cryogenic sub-systems were not operational more than a decade.
In order to restore the test stand functions and meet the design and test requirements for the high luminosity LHC magnets, the existing horizontal test facility at Fermilab underwent a significant refurbishment of the cryogenic and mechanical components. Most of the upgrades were completed and then commissioned during so called zero-magnet test by late 2020. These tests with the shorted superconducting power leads verified the major cryo-mechanical installations, as well as the basic test stand operations, including controlled cooldown, current ramps, process controls and magnet protection.
Overview of the Fermilab’s horizontal test facility upgrade and commissioning of these upgrades during the zero-magnet test are presented in this paper.
The High Luminosity LHC (HL-LHC) Project is planning to install 16 cold-masses, made with the Nb3Sn quarupole magnets, in the LHC Interaction Regions to significantly increase its luminosity. Half of these cold masses are fabricated at BNL, FNAL, and LBNL under the US Accelerator Research Program (AUP). Each cold mass includes two identical Nb3Sn quadrupole magnets, called MQXFA, each with a magnetic length of 4.2 m. Currently, the AUP project has completed the fabrication of the first 4 pre-series magnet, and is working on the following 12 magnets for the series production. The brittleness and strain sensitivity of the Nb3Sn superconducting material require a careful definition of the allowable maximum stress in the windings during magnet assembly and pre-load, and a tight control of their variation within the whole coil length. Therefore, a series of stress specifications have been defined with the goals of minimizing the risk of conductor degradation and providing the mechanical support required to reach the nominal current during powering. In this paper we present the pre-load specifications set for MQXFA magnets, and we provide an overview of the previous experiences, coming from R&D magnets developed by the LHC Accelerator Research Program (LARP) and the MQXF short model program, which contributed to the definition of coil stress limits.
For the Hi-Lumi LHC Upgrade (HL-LHC) new high field and large-aperture quadrupole magnets for the low-beta inner triplets (Q1, Q2, Q3) are being built. These new quadrupole magnets are based on Nb3Sn superconducting technology. As part of the US-HiLumi Accelerator Upgrade Project (AUP) ten Cryostat Assemblies (LQXFA) for Q1 and Q3 replacement will be built, tested and delivered to CERN. The first of the LQXFA was assembled and prepared for cold testing at Fermi National Accelerator Laboratory (FNAL) during the summer of 2021. We will present the integration work of the Cold Mass assembly into the Cryostat Kit provided by CERN. Each Cold Mass contains two trained MQXFA magnets of ~ 5 m length installed in a stainless-steel helium pressure vessel. The Cold Mass will be surrounded by cryostat shields, piping, and vacuum vessel. We will discuss the metrology survey results and present the LQXFA measurements prior testing at the Fermilab Magnet Test facility.
Acknowledgement: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US HL-LHC Accelerator Upgrade Project.
Low emittance machines require lattices with many magnets of short length. Furthermore, successful lattices require strong gradients with strong dipole fields. These lattices are popular today, as MAX IV has demonstrated that a diffraction limited synchrotron light source can be based on such a lattice.
This paper gives an overview of the various magnets used by the different diffraction limited light sources – available, in built or designed. It compares the different magnet design and technology used and presents the magnet parameters in a consistent fashion.
RF system is one of the key components of a 2 GeV, 6 MW high power FFAG accelerator being designed at China Institute of Atomic Energy. In order to verify the design principle and the engineering feasibility, a small scaled RF cavity is under construction, which can also be used as the main accelerating cavity for a 100 kW electron irradiation accelerator. By the deflections of several 180 deg bending magnets, the electrons emitted from the electron gun can pass the cavity for multiple times. Due to the limited length of the cavity, the deflection radius should be as small as possible to ensure more acceleration times and consequently higher beam power, which will make the fringe field effect of the bending magnet be a problem. In addition, the bending magnet should provide beam focusing in both the radial and axial directions to compensate the space charge force of the beam and keep the beam envelope stable during the whole acceleration process. Based on the above reasons, the parameters of the combined function bending magnet, such as the edge angle, magnetic field gradient and shielding distance, have a great influence on the beam dynamics behavior in the accelerator, which bring great difficulty to the design of the combined function bending magnet. In this paper, the coupling design of the bending magnet with focusing function and the high intensity electron beam for this 100 kW irradiation accelerator will be illustated in detail.
Abstract: The High Energy Photo Source (HEPS) is been built in China and the magnets are in batch production. The octupole magnets with skew quadrupole component used in the storage ring have been designed and manufactured. This magnet has an aperture of 30mm, a field gradient of 735000 T/m3 and a length of 0.26m. Different design schemes are compared. The magnet consists of 2 yokes and 4 movable poles, with 4 water cooled loops. Two prototype magnets were measured with a hall probe and a rotating coil measurement system. The influence of the combined power-on mode on the magnetic field is studied. The temperature rise curve and the temperature effect on magnetic center and the integral field are also given.
The results of the development of a magnetic system for bending an electron beam in the industrial accelerator ILU-10 will be presented.
The ILU-10 accelerator has an operating energy range of 2.5–5 MeV. The available design allows to eject electrons only vertically. However, there is a demand for the ability to eject a beam bended at 90 °.
The paper presents two ways to solve this problem. The first system consists of 2 dipole magnets. First dipole magnet already developed and used at the facility was taken. Due to the change in the current in the coils of the 1st dipole, the beam deflection angle changes. In the second dipole, the current is constant. The system can provide scan of 1500 mm.
Another system is based on the use of a magnetic mirror. The beam from the accelerating structure enters the magnetic lens, and then the focused beam enters the magnetic mirror. This one will operate on one current and rotate the particles at the same angle, regardless of their energies. The dipole magnet used on actual accelerator system can be applied to scan the beam.
In this paper the results of modeling two magnetic systems in the OPERA software environment will be presented. Tracks of particles in the required energy range are calculated.
In order to design a pulsed electromagnet, it is necessary to consider eddy currents that depend on the pattern shape of the pulse excitation, and to design the structure and set the operating parameters considering the fluctuation of the magnetic field distribution and its effect on heat generation. Evaluation tests of a new bump magnet for the J-PARC RCS showed that the magnetic field distributions at the rising edge of the trapezoidal pattern and at the flat top are different from each other. This was also confirmed by the 3D dynamic magnetic field analysis of OPERA-3d. Since the skin-depth due to eddy currents depends on the time variation of the waveform, the effect is the same as changing the shape of the coil. From the relationship between the trapezoidal excitation pattern and the change in the magnetic field distribution confirmed in this study, it became possible to optimize the coil shape and a flat top time to match the pulse width of the injection beam and with less heat generation due to the excitation time. The measurement of the magnetic field distribution fluctuation was verified and evaluated using a flux meter, search coil, and Hall probe with different measurement principles. The heat generation of the electromagnets was also evaluated by trapezoidal patterns with different rise and flat top times. Furthermore, the effect of the residual magnetic field on the field distribution and the cancellation test were also evaluated. The results of the evaluation and verification necessary for the design of the electromagnets are presented here.
The electron cooling technology is applied in the spectrometer ring (SRing) for HIAF to boost the luminosity of high-density beam. There are 4 kinds of main coils are used to offer longitudinal field along electron path. In this paper, the three-dimensional magnets of the electron cooler are analyzed. The model consists of a gun section, two 90° angle toroids with a radius of 1 m, a cooling section with a length of 8 m and a collector section. The electron is transporting from the gun through the cooling section to the collector. For the model, the magnetic field along electron path and ion path is simulated and ion trajectory is displayed to offer data for correcting the orbit.
The Helmholtz Zentrum Berlin (HZB) developing a new synchrotron light source, BESSYIII, as successor to the excellent 3rd generation light source BESSYII. The BESSYIII storage ring will be designed for a beam energy of 2.5GeV and Multi bend achromat (MBA) optics for low emittances of 100pm-rad. In parallel to optimizing the optics of the MBA cells, we are starting to develop various magnet concepts to test beam optics against mechanical requirements. The focus here is initially on the transverse gradient bend (TGB), quadrupole magnets (QP) and combined quadrupole-dipole magnets (QD).
In this paper we will give an overview of the BESSYIII requirements and the current status of the magnet designs for the BESSYIII storage ring.
The Neutron Spallation Source (SNS) at ORNL upgrade from 1.0 GeV to 1.3 GeV is in progress now. There are number of water-cooled magnets which should be upgraded to transport 30% of higher beam energy. There were designed new Chicane Magnets, Injection/Extraction Septum Magnets, and Lambertson Magnet. The magnetic designs were a challenging task because new magnets must have a good combined integrated field quality and should occupy the old magnets space but with an integrated magnetic field increase of about 20 %. Additional strong requirements applied to the magnets fringe field do not disturb the circulating beam. The special field profiles should be provided in foil areas between magnets. The analysis was based on the OPERA3D simulations. The special technique was used for the integrated field harmonics analysis. Initially was simulated the particle track and along this track calculated for the reference radius integrated field components which were used for the harmonic analysis. 3D field maps were provided for the beam optics simulations. The final beamline analysis confirmed the good beam transmission and low losses.
Bulky metallic structures are needed in the toroidal field (TF) superconducting magnets for fusion applications to withstand the large Lorentz forces acting on the winding. The pulsed coil operation during the plasma scenario and the fast current discharge or a plasma disruption in off-normal operating conditions cause magnetic field variations, inducing eddy currents in the TF structures. The eddy currents generate heat in the structures close to the winding pack, eroding the temperature margin of the superconducting cables: such power generation is a key input for reliable thermal-hydraulic (TH) analyses. However, the computation of eddy currents in fusion magnets is a challenging topic since a transient, fully 3D electromagnetic (EM) model is required.
The EM problem is faced here by means of the finite element (FE) open source code FreeFEM++, the same adopted for the thermal analysis of the structures in the 4C TH code. First, the correct implementation of the EM problem is verified by means of suitable benchmarks against both simple analytical cases and the results obtained with state of the art FE commercial codes. Then, the following strategy is pursued: the EM code is applied to the evaluation of magnetic fields and induced eddy currents during the normal and off-normal transient operation; the output of the EM analysis is used as input to the TH analysis carried out with the 4C code, aimed at computing the temperature margin evolution. The effect of the thermal feedback on the steel electrical resistivity (and thus on the induced eddy currents) will also be assessed.
The application of this strategy to the analysis of a fast current discharge in the TF coil of a tokamak is presented here, with particular focus on the new 3D EM model. The results of the complete (EM + TH) analysis are also presented and discussed.
The demonstration fusion power plant DEMO by EUROfusion Consortium has now entered its conceptual design phase. DEMO is intended to demonstrate the necessary technologies for controlling a very powerful plasma, generating electricity consistently, and a reliable maintenance of the plant itself. Consequently, the plant design is a challenge not only for its physics conditions, but also for its engineering and technological requirements. Over the years, different baselines have been produced which - despite sharing a set of common characteristics - have nevertheless required revisions and updates of the studies of the magnetic system and its supporting structures. This work presents a 3-level modeling approach which is very fast and suitable to evaluate different requirements. At the macro-level, a global 3D model of the entire tokamak was developed, made of beam finite elements with an enriched formulation. This model is computationally very efficient (around 1 sec CPU time on a common laptop) allowing the development of parametric analyzes and sensitivity studies. Further, it can be used for an inverse design, i.e. to establish what are the minimum structural characteristics required to obtain the desired performances or safety margin. It is noted that, since the entire magnetic system is considered, no a priori hypothesis on the boundary conditions are needed. Going down one step, at meso-level a model of one sector of the system was developed, to analyze in detail the stress/strain fields and identify possible peaks. This model is very detailed, and the consistency is guaranteed by the imposition of the boundary conditions obtained by the global model. Finally, at the micro-level, ultra-refined local models were considered, incorporating the consistency conditions inherited from the intermediate level. All the models are developed in the thermomechanical field, considering temperature dependent material characteristics.
Several designs of Nb3Sn Cable-In-Conduit Conductors (CICCs) have been proposed so far for high-performance tokamak magnets. The Nb3Sn strands composing the conductors are submitted to mechanical stresses of electromagnetic (EM) and thermal origin, inducing local deformations and affecting the strands critical current carrying capability. Even though it is possible to test the conductors to evaluate their electrical performance, it is still not possible to predict them during the conceptual design phase. In the last ten years a numerical tool based on a finite element (FE) code simulations has been developed to simulate the mechanical behavior of the CICCs subjected to various types of loading. The main goal is to predict the electro-mechanical performance of the conductor in operation as a function of the design parameters such as the void fraction, the twist pitches and the conductor shape.
In this work, the numerical modelling of different conductors from the ITER, DTT, JT60 and DEMO projects is presented, describing the strands belonging to one sub-cable of the last cabling stage (the so-called petal, consisting of a few hundreds of wires). A study is carried out to highlight how the different design choices affect the cable electro-mechanical performance. A more detailed model of the ITER TF CICC is also presented, which describes all strands of the cable. The purpose of this study is to validate the 237-strands model describing the petal (which accounts for the action of the other petals on the analysed one) by comparison with the 1422-strands model of the whole cable. The detailed model including all strands proves useful for a deeper understanding of the mechanical phenomena occurring among the sub-cables during the conductor operation.
The Comprehensive Research Facility for Fusion Technology（CRAFT）project is a key pre-research project of the China Fusion Engineering Test Reactor (CFTER) device in China. The manufacture of a full-size CFETR toroidal field（TF）coil is one of the key sub-topics of the CRAFT project, which is completed by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). A hybrid superconducting magnet structure will be used for the TF coil design, in which the high-field and medium-field windings are made of Nb3Sn circle-in-square CICCs, and the low-field winding is made of NbTi circle-in-square CICCs. With a conductor operating current of 95.6 kA, a toroidal field of 6.5 T is generated and the peak field is 14.5 T. The CRAFT TF coil has a "D"-shaped profile. The shape of the Nb3Sn coil is about 19.5m in length, and about 11.01m in width and the maximum height is 1.1m. The Nb3Sn strands before heat treatment has excellent strength and toughness, which is good for coil winding, but the Nb3Sn strands after heat treatment will cause performance degradation under the action of trace stress and strain. Therefore, the process of “wind and react” will be applied to the manufacture of TF Nb3Sn coil. We plan to design a large-scale controlled atmosphere oven heat treatment system to complete the Nb3Sn coil heat treatment. The effective temperature uniform zone size of the heating furnace is 20.1m in length, 11.5m in width and 1.5m in height. This article will define the process requirements for the heat treatment of the TF coil, introduce the structure and composition of the heat treatment system and the heat treatment process. The process must meet TF requirements for control of the reaction environment, the temperature and time constraints, and coil deformation constraint.
This paper describes the design activities on the Toroidal Field (TF) conductor and coil of the DEMO Nuclear fusion power plant. As prototypes of future commercial tokamaks, DEMOs are expected to be able to produce cost-effective electrical power. In this view, an optimized design becomes a crucial aspect in the whole engineering design procedure. The 2018 baseline of DEMO reactor includes 16 TF coils. The TF Winding Pack (WP), designed by ENEA, is made-up of 6 𝑁𝑏3𝑆𝑛 double-layers with steel jacket thickness progressively increased from the highest field plasma facing side to the low field but most mechanically loaded side, and a Wind & React manufacturing approach. Although this solution has been recently excluded from the down-selection of the TF coil options for the Conceptual design phase, the design activity has evidenced some interesting methodological aspects, that will be discussed here. According to the results achieved in the present work, the optimized operating conditions will include 81 kA operating current and 13.1 T peak field.
In order to optimize the design, a parametric 2D FEA model of the inner leg cross-section was implemented in an optimization procedure to achieve the maximal peak magnetic field while guaranteeing structural integrity of the components, also considering the radial allocation requirements. A 2D parametric magneto-structural FEA model for the inner leg at equatorial plane, was used in order to map the magnetic field and evaluate the stress field in the WP at the conductor detail level, implementing a generalized plane strain formulation. Finally, hotspot temperature computations and conductor design for the optimized configuration were performed.
Conceptual design of the K-DEMO magnet system has been under way. From the up-to-date design activities, the TF magnets use two different types of cable-in-conduit conductors (CICCs) where high field region uses quite an amount of superconducting wires, but in relatively low field region, substantial amount of superconducting wires should be replaced by copper wires. The stored magnetic energy is estimated to be over 49 GJ. Eighteen TF magnets are series-connected and charged by a power supply, where the design current is 65.52 kA. Protection circuits for the K-DEMO TF magnets should be designed with a fail-free concept after interlock signals are received. The design activities to minimize the system failures are carried out to guarantee the reliable and stable operation
The Roadmap to Fusion Electricity draws on innovative experiments pivotal for the accomplishment of the European DEMO, i.e. the demonstration fusion power plant by the EUROfusion Consortium. At the end of the pre-conceptual design phase, the machine comprises three main magnetic systems: 6 poloidal field (PF) coils, 16 toroidal field (TF) coils and the central solenoid (CS), primary member of the ideal transformer in which the induced plasma is the secondary. Tokamak reactor operates under extremely heterogeneous and demanding loading conditions, leading structures and components near to the materials mechanical limits. All the structures must be assessed under the static and fatigue structural viewpoint. This work presents the advanced global model for the DEMO machine. This model consists of the main magnetic system, structures, auxiliary components, and joint connections. All the updated timepoints of the actual Single Null scenario have been analyzed via a dedicated electromagnetic FEM model. The routine adopted allows to analyse each magnet and each component with a fully detailed submodel and/or with a homogenised model and equivalent thermoelastic material properties.
The electrical and physical properties of $\mathrm{Nb_3 Sn}$ strands are strongly dependent on the heat treatment during which tin diffuses into niobium by solid-state diffusion. During diffusion, $\mathrm{Nb_3 Sn}$ grains grow at the Nb/bronze interface. The shape and size of the grain depend on the temperature of the last step of the heat treatment, its duration and the size of the Nb filaments. The volume of reacted $\mathrm{Nb_3 Sn}$ together with the grains’ structure influence the non-copper critical current density $j_c$ and the magnetization. Therefore, an optimization of the heat treatment with respect to $j_c$ and hysteresis loss is important when working on the design of superconducting cables. This contribution presents the results of a heat treatment optimization performed on a 1mm diameter, internal Sn $\mathrm{Nb_3 Sn}$ strands produced by KAT (Korea) for a $66\,$kA / $12\,$T prototype React&Wind conductor for the Toroidal Field Coil of EUROfusion DEMO. The heat treatments and the $j_c$ measurements on ITER barrels were performed at SPC (Villigen, Switzerland) at $4.2\,$K, in the range of $9\,$T to $15\,$T, the SEM micrographic studies on grain size and shape were conducted at CERN and the hysteresis loss was measured on a vibrating sample magnetometer (VSM) at ENEA (Frascati, Italy). Eventually, a heat treatment schedule is proposed for the prototype DEMO conductor and the scaling law for $j_c$ is updated.
One of the most actual problems of modern physics is the development of powerful radiation sources in the THz band. At the moment, the highest pulse and average power in the THz band are realized by the fast-wave devices – free-electron lasers and gyrotrons. The gyrotrons are vacuum electronics devices based on the stimulated cyclotron radiation of electrons moving along helical trajectories in an external magnetic field. To increase operation frequency, which is essential for such applications as controlled fusion, spectroscopy, and medicine, we need magnetic systems (solenoids) with high magnetic fields. For example, gyrotrons for fusion devices like ITER recently achieved an impressive output power of 1 MW in continuous wave (1000 s) regimes at the frequency of 170 GHz. Such gyrotron system used cryomagnet with 7T field intensity and 160 mm hot bore produced by JASTEC Ltd (Japan). For the next generation (DEMO, TRT, SPARC tokamaks), frequencies about 230-260 GHz is proposed. Gyrotrons with 30-40T pulsed magnets cooled by liquid nitrogen demonstrate frequency up to 1.3 THz with pulse duration several tens microseconds, and some applications need higher frequencies. Thus, it makes it a challenge to create much more intensive magnets. All magnetic systems for gyrotrons have specific requirements for field profile, hot bore, homogeneity, stability, etc. This report aims to formulate the demands and R&D goals for the magnetic technology community to develop novel magnetic systems for gyrotrons. The most interesting for nuclear fusion looks cryomagnets based on high-temperature superconductors. On the other hand, pulsed magnets with reasonable repetition frequency and field closed to 80-90 T for high power, ultra-high frequency (up to 2 THz) pulsed radiation sources for spectroscopy applications and diagnostic of various media.
Gyrotrons development is supported by IAP RAS project 0035-2019-0001
Paschen failures in ITER and W7-X superconducting coils at the acceptance tests have shown that it is highly desirable to lower the coil discharge voltage of the DEMO TF coils. Another benefit of lowering the discharge voltage might be the reduction of the number of coil feeders, i.e. connect in series the TF coils inside the cryostat, which is attractive for machine integration. For a given Ampere Turn (AT), one way to reduce the discharge voltage is decreasing the coil inductance. Since the inductance of a coil is proportional to $N^2$, where N is the number of turns, for a given total TF current $\mathrm{N_{turn}}\cdot\mathrm{I_{op}}$, decreasing the number of turns corresponds to a higher current flowing through each turn, which results in the inductance being proportional to $I_{turn}^{-2}$. This means that increasing the current will have a quadratic impact on the inductance and thus a linear impact on the discharge voltage making the design of a high-current ($\approx 105\,$kA) CICC attractive for the EUROfusion DEMO project. In the case of DEMO, increasing the operating current from $66\,$kA to $105\,$kA leads to a reduction of the TF discharge voltage of a factor 3. Designing a high current TF coil conductor layout include performing mechanical and thermo-hydraulic studies to investigate the conductor stability during operation. This contribution will thus present the first design for a react-and-wind TF conductor made of $\mathrm{Nb_3 Sn}$ and Cu as stabilizer designed for an operating current of $105\,$kA alongside the results of dedicated mechanical and thermo-hydraulic analyses.
Superconducting magnets in fusion reactors are subjected to a huge electromagnetic force of >100 MN/m. The magnets have to be sustained with a structure with a strong body to avoid high stress and deformation. Extrapolating existing fusion experimental device constructed ever, the total weight of the magnet system, i.e., the magnet and support structure, of a commercial fusion reactor is estimated to exceed 20,000 tons. Weight reduction is desired from the viewpoint of material procurement, cold mass, and the reduction of radioactive materials after decommissioning. Recently, novel structural shapes with significant weight reduction have been achieved using topology optimization techniques. Here, we employed the topology optimization technique to the magnet-support structure in the helical fusion reactor. Compared with conventional design, we achieved a weight reduction of >25%, which is worth thousands of tons. Furthermore, we confirmed that the maximum von Mises stress in the topology-optimized design was within the allowable stress limit of the structural material. However, the topology-optimized shape seemed sensitive to unusual loads, such as an earthquake, a fast down of the magnet excitation, a loss of coolant, etc. Thus, we performed seismic analysis using the mode superposition method referencing the virtual envelope of acceleration response spectra for recent significant earthquakes. Although robustness against an earthquake depends on the conditions of the ground and floor/building, the calculated results show that the safety of the magnet system could be provided with seismic isolation systems. The results of the seismic analysis under various conditions are presented.
Abstract-China Fusion Engineering Test Reactor (CFETR) is the next device in the roadmap for the realization of fusion energy in China, which aims to bridge the gaps between the fusion experimental reactor ITER and the demonstration reactor (DEMO).
The toroidal field (TF) coils play a major part in the tokamak, which provide the main magnetic field to confine the plasma, and one TF coil has been design in ASIPP since October, 2019, and planned to be completed in 2025.
CFETR consists of 16 TF coils and the length of major and minor radii are R=7.2 m and a=2.2 m. The TF magnet system will provide a 6.5 T magnetic field at the plasma center (at 7.2 m position) to confine the plasma. The plasma scenarios are characterized by a pulse length of 5000 s or more, with a plasma current 14 MA. In order to evaluate the feasibility of superconducting magnets used in CFETR, the thermal-hydraulic state of the coils is analyzed (e.g., normal operation, plasma disruption, quench, fast current discharge). The inlet and outlet pressure of helium cooling loops and operational temperature of the magnet is designed. The temperature margin of the superconducting magnets under different operation conditions are estimated.
Index Term- CFETR, totoidal field, thermal-hydraulic, temperature margin
This work was supported in part by the National Natural Science Foundation of China under Grant No. 51777207, by Comprehensive Research Facility for Fusion Technology Program of China under Contract (No. 2018-000052-73-01-001228).
The poloidal field coils (PF1 to PF6) of the proposed EUROfusion DEMO machine are to be operated in the pulsed mode. The heat is deposited in these coils due to field changes during a normal plasma cycle, due to field changes corresponding to a range of plasma control actions, due to nuclear heat load, etc. The PF2-PF5 coils winding packs (WP) are made up of the NbTi cable-in-conduit conductors (CICC) without a low-impedance cooling channel. The PF1 and PF6 coils are wound with the Nb3Sn CICC with a separate low-impedance cooling channel. In the proposed work, we first estimate the contribution to the total heat deposition by various factors. Then a thermal-hydraulic performance of all the WPs are evaluated during the normal operation. Thereafter, a quench analysis is performed to determine the maximum hotspot temperatures.
In the framework of EU design activities for dimensioning the future fusion DEMOnstration reactor (DEMO), extensive analyses were conducted in EUROfusion context, aiming at ultimately defining the design of the DEMO magnets system. In this objective CEA proposes design for all cryomagnetic systems especially on the Toroidal Field (TF) coils.
In the last DEMO reactor baseline, CEA designs for TF system was including two options: one without radial plates (called WP#3) whose concept shows a square conductor and an ITER-like concept with radial plates (called WP#4) which has a round conductor embedded in steel plates.
In order to consolidate both designs CEA developed specific tools that assess thermal-hydraulic and mechanical aspects in a detailed way to allow ensuring a refined criteria compliance. The use of those tools avoid relying on conservative approaches at pre-design stage, which often end in material over-dimensioning and therefore penalizing cost and space occupation merits. The tools will be applied on both TF concepts and the refined designs will be exposed.
On the other hand CEA designed and manufactured in collaboration with ASIPP a full-size conductor sample based on WP#3 concept, which is supposed to operate at 95 kA and 12T.
This sample was tested in SULTAN facility (Villigen, CH) and in JOSEFA (CEA, France) to assess its behaviour in both DC and AC regimes. The first analyses of the experimental results are presented and the first conclusions on conductor critical performances discussed.
During the integrated commissioning of JT-60SA tokamak, the superconducting magnets have experienced several tests such as current ramps or fast discharges. The time variations of the associated magnetic field have induced AC losses in the winding pack (WP) of the magnets, i.e. hysteresis and coupling losses, and in the casing, i.e. eddy currents losses, of the toroidal field (TF) coils.
From the thermo-hydraulic sensors installed in the tokamak in the inlet and outlet of the coils and of the TF casings, we have carried out enthalpy balances to estimate the total transient heat loads generated by AC losses. For the TF magnet, we have focused our analysis on fast discharges tests as they were producing more AC losses than the slow ramp ones.
In parallel, we have computed the AC losses generated in the magnets from the knowledge of the magnetic field map and the current profiles measured during the fast discharges. The hysteresis losses modeling is achieved using magnetization measurements at strand level, the coupling losses one using magnetization measurements at CICC level, and the eddy currents losses one in the TF casings using the inductance model presented in JT-60SA Plant Integrated Document (PID).
We then assess and discuss the consistency between these experimental and first theoretical analyses from the energy balance point of view. In a second step, we present and compare the results of several quasi-3D coupled thermal/thermo-hydraulic simulations performed using TACTICS code with the temperature sensors measurements during the experiment. These simulations aim at representing the TF magnet thermal and thermo-hydraulical response to transient heat loads at a more detailed scale to better anticipate the magnet stability in future operations.
The power exhaust represents a major challenge for the EUropean fusion reactor DEMOnstrator, asking for a new, robust design of the divertor, beyond the solution currently pursued for ITER. For this reason, the construction of a satellite fusion experiment, the Divertor Tokamak Test (DTT) facility, is being pursued in Italy. This compact tokamak, which must be very flexible in terms of plasma configurations, will test several DEMO-relevant divertor solutions.
The DTT superconducting magnet system includes 18 Toroidal Field (TF) magnets, 6 modules constituting the Central Solenoid (CS) and 6 Poloidal Field (PF) coils. All of them are cooled by forced-flow supercritical helium at 4.5 K. In the case of a plasma disruption, the fast reduction of the plasma current causes a magnetic field variation, inducing on one hand a sudden variation of the current in the PF and CS coils, and on the other hand AC losses in the conductors and eddy currents in the bulky steel structures of the TF coils. The former effect may increase the current in the coils above its nominal value, while the latter causes a heat deposition that could erode the available temperature margin. Both the effects can initiate a quench, requiring then a fast discharge of the coils.
The detailed thermal-hydraulic model of the DTT magnet system, developed using the 4C code, is applied here to simulate the effects of the plasma disruption. The heat load to the coil casing and to the winding pack, as well as the current evolutions, are used as input to compute the temperature margin during the transient and to assess if a quench could be initiated.
The results will give important feedbacks to the design of the protection system, such as the option of triggering a fast current discharge right after the disruption.
The “Divertor Tokamak Test” (DTT) is an experimental fusion reactor being built in Frascati (IT) in the framework of the European Fusion Roadmap. The DTT Central Solenoid, used to drive the current in the magnetically coupled plasma, comprises six Nb3Sn layer-wound independently energized modules. Each module is made of three sub-modules: High Field (HF), Medium Field (MF) and Low Field (LF) grades. Each sub-module includes a different CICC, optimized for the specific operative values of magnetic field and current density. Each of the three CICCs relies on a design with rectangular geometry, constant steel jacket thickness. Owing to the limited hydraulic lengths, no pressure relief channel is used, which contributes to the improvement of the coil engineering current density. In order to meet all goals of the DTT scientific program, a variety of plasma scenarios have been designed. These cause intense and heterogeneous loading conditions for the CS stack; from the mechanical point of view, each module is subjected to a vertical expansion or compression and to a huge radial action, whereas the current variations cause relevant heat loads due to AC losses, with impact on the coil temperature margin. To ensure the structural integrity of the magnet, an external system is defined for the application of the required vertical preload to the CS modules. The precompression structure prevents axial repulsion and follows the shrinking of the stack preventing any detachment between modules during all scenarios. This system consists of nine sets of inner and outer Tie Rods, one upper block and one lower anchor block for the rod, as well as nine sets of six superbolt pretensioners for the preload application.
This work presents the details of the updated design of the CS stack and the precompression system, and the static and fatigue structural analyses of the main components.
The JT-60 Super Advanced (JT-60SA) magnet system consists of toroidal field (TF) coils, central solenoid (CS), and equilibrium field (EF) coils, and all coils are thermally protected by a thermal shield. The CS consists of four stacked modules with 52 layers, and the conductor is designed with a cable-in-conduit conductor (CICC). The CS is cooled to an operating temperature of 4.5 K by supercritical helium (SHe). The CS is cooled over a month-long process, one of the temperature control conditions during the cool-down is to keep the maximum temperature difference in the coil below 40 K to limit the mechanical stress of the coil. The second condition is that the maximum temperature difference between the thermal shield and the coils is within 50 K. The 26 inlets and outlets are installed on the outer radius of the CS module, respectively, and the highest temperature in the conductor is likely to be near the center in the longitudinal direction due to heat exchange between supply and return. However, since the temperature measurements are only possible at the inlet and outlet, the maximum temperature difference in the coil cannot be measured. Hence, the estimating the temperature distribution in the coil is important for ensuring the safe cooling operation of the JT-60SA. In the previous work, a temperature distribution analysis model of the two layers in the CS module was created based on the measurement results of the CS module cool-down test, and the temperature difference between the inlet and outlet was calculated to keep the maximum temperature difference at 40 K during cool-down. In this works, based on the results of the previous work, the effect of the temperature conditions on the cool-down speed of the CS module was investigated.
The Divertor Tokamak Test (DTT) facility [1], under construction in Frascati, Italy, will rely on a fully-superconductive magnetic system. Thanks to the limited dimension of the machine, three cryo-lines will house all the Feeders for the Central Solenoid (CS), for the Toroidal Field (TF) and for the Poloidal Field (PF) coils, respectively. The in-cryostat route of the different Feeders (two for any of the 6 CS and PF coils, and 6 in total for the 18 TF coils, interconnected through 3 SC jumpers) will be up to ~ 10m each. The Feeders, designed with twisted NbTi and Copper strands in a Cable-In-Conduit Conductor (CICC) layout (with or w/out the central cooling channel for the different types of coils) with a square jacket, will be cooled by a dedicated line of Supercritical Helium at 0.6 MPa and 4.5 K at the inlet. In view of the different plasma scenarios foreseen for the DTT operation, it is important to verify that the thermal-hydraulic performance of the Feeders, subject in operation to AC losses, joule heating from the resistive joints located at the terminations, and parasitic load by radiation from the thermal shield at 80 K and by conduction from the clamping, does not pose any issues to the machine operation. The minimum temperature margin, computed for the different conductors in the most demanding plasma scenarios, is presented and discussed in this paper, showing the conservativeness of the design for such components.
[1] R. Martone, R. Albanese, F. Crisanti, A. Pizzuto, P. Martin. “ “DTT Divertor Tokamak Test facility Interim Design Report, ENEA (ISBN 978-88-8286-378-4), April 2019 ("Green Book")” https://www.dtt-dms.enea.it/share/s/avvglhVQT2aSkSgV9vuEtw
The JT-60SA large research tokamak is being constructed by the National Institutes for Quantum and Radiological Science and Technology (QST) in Japan, as a satellite tokamak project designed to complement the International Thermonuclear Experimental Reactor (ITER) and to produce demonstration data for use in the proposed DEMOnstration Power Plants (DEMO). JT-60SA started cool-down phase in April, 2021 as a part of integrated commissioning. The magnet system is composed of three kinds of coils, central solenoid (CS), equilibrium field (EF) coils and toroidal field (TF) coils. The CS consists of four electrically independent stacked modules covered by structures supporting the TFCs. The maximum voltage between the CS module terminals is designed to be 10 kV. This means that if the voltage is distributed homogeneously, the voltage between layers is 0.38 kV because the number of layers is 52. However, the power supply contains multiple frequency components, which means that the actual voltage between the conductors can become lager than the voltage under ideal condition due to the resonance phenomenon and transient response to supply voltage. It might even produce voltages high enough to damage the insulation between the conductors, and thus affect the operation of the JT-60SA CS. In a previous study, we created a circuit simulation model for the CS (which has four modules), including the structures (ground resistance, CS structure, TFC cases, and EFC covers), and used it to estimate the voltage distribution produced by the resonance phenomenon. In this works, we used the previous circuit simulation model to estimate the influences of the structures capacitance and conductance, the butt joint resistance in the CS and the current leads lengths on the voltage distribution, and the transient response to the power supply voltage in the CS. These results become fundamental data to operate JT-60SA safely.
In the framework of the commissioning of JT-60SA Tokamak (Japan), all the 20 Toroidal Field Coils (TFC) have been tested at Cold Test Facility (CTF, CEA-Saclay) during acceptance quench (with a quench temperature equal to 7.5 K at nominal current). Some complementary tests have been performed (September 2018), on spare coil TFC02 with different quench conditions, especially reduced current (at 75% and 50% of nominal current) and increased detection parameters (detection and action time Tda). The acceptance quench test of TFC02 shows a hot spot temperature (maximal conductor temperature supposed to be equal to measured maximal helium temperature) at nearly 23 K. Some models have been performed, with SuperMagnet (fortran, CryoSoft) including THEA (Thermohydraulic 1-D of Cable In Conduit Conductor, CICC) and Flower (external cryogenic cooling circuit model).
During complementary quench tests, an increased Tda causes, as expected, a higher hot spot temperature: 32 K and 35 K for detection and action time respectively equal to 0.5 s and 1 s. A reduced current, at 75 % of nominal current, implies a smaller hot spot temperature at nearly 14 K (maximal helium temperature due to less Joule Energy deposited). At 50 % of nominal current, a so called “smooth” quench occurs and the slower propagation and detection difficulty are the cause of a slightly greater hot spot temperature at nearly 16 K (maximal helium temperature). Each quench is characterised by a large increase of helium pressure and helium expulsion mass flow. The measurements are presented and compared to the calculated results with SuperMagnet (observed time delay governed by the modelled exhaust quench valve friction factor). These analyses shows, despite the respected hot spot criteria (temperature non-adiabatically smaller than 150 K), the potential criticality of the so called “smooth” quench and some further analyses would be performed in Tokamak environment.
NbTi superconductors with large cross-sectional area of high purity aluminum are used in accelerators, SMES, and fusion devices to improve their stability. The Large Helical Device (LHD) is a Heliotron-type fusion experimental device, which consists of a pair of superconducting helical coils and three pairs of superconducting poloidal coils. The LHD conductor used for the helical coils is a composite superconductor, which consists of a NbTi/Cu Rutherford cable, a thick pure aluminum stabilizer and a copper sheath around the composite. The peculiar quench phenomena, such as traveling normal zone and asymmetrical normal zone propagation are observed in the original LHD helical coil and also in small test coils wound with the LHD conductor. In this paper, the normal zone propagation in the LHD conductor against a thermal disturbance is numerically simulated. The transient stability of the composite superconductor with aluminum is discussed.
Divertor Tokamak Test facility (DTT) is the device devoted to tackle the power exhaust issue in the view of future fusion power plant [1]. The DTT construction is nowadays started in the ENEA site of Frascati, Italy. The DTT superconducting magnet system is comprised of 18 Toroidal Field (TF) coils, able to generate a magnetic field of 6 T at the plasma major radius (i.e., at 2.19 m from the z-axis), 6 independent Poloidal Field (PF) coils and a Central Solenoid (CS) made of 6 stacked, independently fed, graded modules. The DTT current feeding system consists of superconducting feeders, whose latest design foresees the use of NbTi Cable in Conduit Conductors (CICC), of Current Lead boxes (CLBs) and resistive busbars, operating at room temperature. The TF are fed in series with an operative current of 42.5 kA, whilst the PF and CS with a maximum current of 30kA, both at operative temperature of 4.5K. A feeders’ pair layout comprises both the positive and negative poles clamped together to counteract the electromagnetic (EM) force. Clamps, which are made of plates and a certain number of bolts, serve as constraints for feeder cables relative displacements during operations.
The aim of this work is to provide a preliminary structural assessment of the CICC jacket, together with the feeders clamps and bolts (both in terms of dimensions and number), resorting to a coupled EM and structural analysis. Exploiting a parametric model, developed within ANSYS APDL environment, it is possible to scan a wide solution range and to extrapolate a configuration that is compliant with the feeders design requirements.
References
[1] R. Martone, R. Albanese, F. Crisanti, A. Pizzuto, P. Martin. “DTT Divertor Tokamak Test facility Interim Design Report,” ENEA (ISBN 978-88-8286-378-4), April 2019 ("Green Book") https://www.dtt-dms.enea.it/share/s/avvglhVQT2aSkSgV9vuEtw.
JT-60SA is a tokamak magnetic confinement device for plasma experiments. This is one of a joint international research and development projects involving Japan and Europe. JT-60SA adopts superconducting magnets consist of cable-in-conduit conductors. The magnet system consists of 18 Toroidal Field (TF) coils and 4 Central Solenoid (CS) modules, and 6 Equilibrium Field (EF) coils. Poloidal field (PF) coils (including the EF coils and CS modules) are cooled in the same circuit. The number of flow paths of PF coils is 190, and all of them are cooled in parallel.
The construction of JT-60SA was completed in March 2020. The cool-down operation was started on 10 October, and the temperature of the superconducting magnet reached 4.5K on 27 November.
Supercritical helium at 4.4K was provided to PF coils with a cold circulator. The design flow of PF windings is 926 g/s without the flow for the feeders. In this work, the mass flow of PF windings was controlled within a range of 572 g/s to 1,162 g/s. We measured mass flow rate, pressure, and temperature at inlet and outlet of PF coils while changing the speed of the cold circulator. Based on the measurement, the formulas of PF coils friction factors at around nominal operating temperature were derived.
Abstract-Experimental Advanced Superconducting Tokamak (EAST) is the first fully superconducting tokamak in the world. The superconducting magnets are made of NbTi Cable-In-Conduit Conductor (CICC). The heat load due to plasma discharge rises the temperature of magnet. If the cooling of magnet is not sufficient and the temperature margin of the superconductive cables is not enough, it maybe induce the magnet quenches. In order to safe operation of EAST with higher plasma performance discharge in future, it is important to estimate the operation state of TF magnet. It is found that the outlet temperature rise of TF windings and cases is nearly proportional to plasma current, and the outlet temperature rise of TF windings is not related to the plasma duration, whereas the outlet temperature rise of TF cases seems to increase with plasma duration according to the experimental results.
In order to further study the relationship between the parameters of plasma discharge and the temperature rise of TF windings and cases, the SAITOKPF code is used to analyze the experimental phenomenon.
Index Term- EAST, toroidal field, plasma discharge, temperature margin
Acknowledgments: This work was supported in part by the National Natural Science Foundation of China under Grant No. 51777207.
In the context of tokamak reactors, the Poloidal Field Coils (PFCs) are magnets that surround the Toroidal Field Coil (TFC) assembly and generate a magnetic field which equilibrates the plasma and shapes it into specific forms. To enforce plasma requirements, the six PFCs of the Divertor Tokamak Test (DTT), a facility that will be built at the ENEA research centre in Frascati with the main mission of optimising the power exhaust management in view of DEMO (1), have been designed to reach as high a self – field as 9T, and in operation will withstand electromagnetic loads of several tens of MN. From a mechanical point of view the PFCs are highly interconnected components, whose structural response is influenced by their own loading conditions as well as by the TFC system they are installed onto. As the PFCs experience high time-varying vertical forces that would tend to separate the coils from the TFCs, a challenging task is attaining a robust design of their support structures. These latter must maintain the PFCs in place by exerting an intense counterbalancing precompression, without however compromising the integrity of the PF coil itself. This work discusses these and other design choices that have been made for the PF coil system of DTT, illustrating the in – operation behaviour and interaction among the TF coils, the PF supports and the PF magnets. Finite Element Analysis has been the principal, but not exclusive, means of investigation.
(1) R. Martone, R. Albanese, F. Crisanti, A. Pizzuto, P. Martin. “DTT Divertor Tokamak Test facility Interim Design Report, ENEA (ISBN 978-88-8286-378-4), April 2019 ("Green Book")” https://www.dtt-dms.enea.it/share/s/avvglhVQT2aSkSgV9vuEtw.
The persistent current switch (PCS) is essential for magnetic resonance imaging magnet (MRI) magnet which works in closed-loop mode. In this paper, the design of NbTi/CuNi thermally triggered PCS is presented. Furthermore, quench test and switching time test have been given at 4.2-K temperature and 0-3 T magnetic field.
The imaging quality of the Low-field magnetic resonance imaging (MRI) equipment is usually inferior to that of the high-field MRI equipment, however, the low-field MRI equipment has the advantages of lightweight, low cost, flexibility, etc., and is enough to meet most of the medical standards. With the progress of image reconstruction technology, the competitive disadvantage of the low-field MRI could be compensated owing to its improving image quality, which is bound to trigger a new boom for studying the low-field MRI. Passive shimming has been widely applied to correct the bare magnetic field of a fresh MRI magnet to the desired value. In the low-field MRI magnets, ferromagnetic materials used by passive shimming are usually in an unsaturated magnetization state, which is susceptible to the background magnetic field. Therefore, the passive shimming for the low-field MRI magnets becomes more complex and extremely challenging when it comes to the unsaturated magnetization problems. In this paper, an improved strategy for passive shimming in the low-field MRI magnets was proposed to improve the calculation accuracy of the magnetic field generated by the ferromagnetic materials, and some practical shimming measures were taken to improve the magnetic field homogeneity. The related passive shimming tests had been carried on a 0.5 T superconducting MRI magnet, which showed that the shimming efficiency was significantly improved, and the magnetic field homogeneity over some target volumes reached expectations.
Keywords: Low-field MRI, Passive shimming, Unsaturated magnetization, Superconducting magnet.
To study and explore the key technology of Ultra-high field MRI system, the 14 T body-size MRI magnet technology study activities has be launched by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). The Nb3Sn Rutherford-type cables is designed for the conductor structure due to the 14 T magnet. The preload must be applied for the coil at room temperature, to counteract the Lorentz forces during operation condition. However, the Nb3Sn superconductor is sensitive to the strain and maybe leads to an irreversible degradation. Therefore, it is necessary to design the reasonable preload structure and evaluate the performance of the structure. Firstly, a 2-angle model of main magnet is established. By simulating the preload, it is obtained that the stress and strain on the conductor will decrease with the increase of preload. Then the 1/4 model of the whole main magnet, with the pre-tightening plate arranged on the axial direction, is established. By optimizing the pre-tightening force in the bolt, the stress and strain of the conductor will be kept in a reasonable range. Finally, the requirements and feasibility of the preloading structure are discussed.
There is a very real need for compact MRI’s which are small and light enough to be essentially portable. This is especially true when you consider strokes. Not only does rapid diagnosis enable fast treatment but it is also essential before commencing treatment to determine the type of stroke. We have designed a compact MRI using HTS specifically to enable cephalic imaging. Using HTS enables us to minimise the footprint of the magnet and to operate cryogen free at 20K. The magnet is designed to run at 500 Amps which will provide a 1T imaging field. The magnet has an inductance of 85 mH and uses 3km of tape. The internal diameter of the magnet is 55cm which is sufficient to fit the shoulders of an adult male. To further minimise the footprint of the magnet it is powered using a flux pump which provides a compact means of supply. The magnet has been designed in Cambridge and is built in China by Professor Liu’s team
In September 2020, a 4-year national project was embarked on to develop a conduction-cooled 6 T 320 mm all-HTS magnet for MRI with support from the Korea Medical Device Development Fund. It is a collaborative R&D effort led by SuperGenics, Co. Ltd., in participation with Changwon National University, Korea Electrotechnology Research Institute, Korea Maritime and Ocean University, Korea University, Kunsan National University, Seoul National University, and Sungkyunkwan University. As the first step of the project, this paper reports a design of the magnet that consists of a stack of double-pancake coils wound with REBCO tapes. The target operating temperature is 20 K under a conduction-cooling environment. The winding diameter is set to be 320 mm, while a patient bore is expected to be 200 mm or greater with an estimated field of view (FOV) to be around 120 mm. The well-known metallic insulation technique is considered together with other advanced winding techniques such as multi-width and/or multi-thickness HTS windings. This paper reports key design parameters and performance analysis results on: (1) magnetic field homogeneity in consideration of screening current-induced field; (2) mechanical stresses in consideration of screening current-induced stress with our latest new E-J model; (3) charging simulations; and (4) post-quench analysis in consideration of the induced overcurrent stress during an NI-type magnet quench.
Acknowledgement
This work was supported by the Korea Medical Device Development Fund grant funded by the Korea government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety) (Project Number: 202011C21)
Abstract: Superconducting joints are essential for persistent-mode operation in a superconducting magnet system, the resistance has to be around 10-14-10-12 Ω thus to produce an ultra-stable magnetic field. Based on the national collaboration program of the MRI for small animals, the development of superconducting joints between bronze-route Nb3Sn multifilamentary wires manufactured by Furukawa is launched. In this paper, we report the rational design of the Nb3Sn superconducting joints in detail. To qualify the properties of the Nb3Sn superconducting joints, their critical current and resistance are examined through four-lead and current decay methods, respectively, at 4.2 K in a background magnetic field. The investigation aim to provide a feasible approach of Nb3Sn superconducting joints for the small animal MRI magnet systems.
Dry magnets using MgB2 wires are one of effective options to eliminate dependence on liquid helium in MRI scanners. In the dry magnets, however, lack of thermal mass of cryogen makes a controlled quench difficult and extends time for restarting the magnets after the quench. In this study, a novel rapid ramp-down procedure, which can be substituted for the controlled quench in emergency rundown, is proposed, and its feasibility is proven for a 1.5 T whole-body MgB2 MRI magnet. In this procedure, a power supply receives current from a persistent current switch (PCS), the PCS is turned off by heating, the power supply is interrupted by a breaker, and the stored energy in the magnet is mostly consumed at an external resistor. Owing to the large energy margin of MgB2 wires, the AC loss during the ramp-down does not bring a quench of the MgB2 coils. A niobium-titanium sheathed MgB2 wire 0.60 mm in diameter is made, and a PCS with high off-resistivity is designed using this wire. The shunt current during the ramp-down does not bring the burnout of the PCS when the wire length is sufficiently long, typically hundreds of meters. Because heat generation inside the cryostat during the ramp-down is a few percent of the stored energy in the magnet, the magnet is not heated excessively. As a result, the proposed ramp-down procedure should shorten the downtime of MRI scanners.
Nb3Sn strand was used to enable the development of short (1.4 m) segmented coil designs, as opposed to the nearly 2 m long compensated solenoid designs needed for NbTi machines. Using Nb3Sn strand will allow a conduction cooled design, if quench is properly managed. We modeled two designs with magnetic field homogeneity better than 10 ppm (part-per-million) within DSV (Diameter of Spherical Volume) of 45 cm. Several classes of Nb3Sn strand especially designed for MRI applications were considered as a possible candidate for winding such magnets. The magnets were assumed to achieve maximum on-axis magnetic field of 7 T. For this on-axis field a peak field inside the magnet windings was determined and parameters of the required Nb3Sn strands (such as critical current, engineering current density etc.) calculated. The coil load lines were compared to the critical currents of the Nb3Sn conductors and we find that such a segment coil design can be achieved with several classes of existing Nb3Sn conductor. Coil geometry, length of conductor, and overall magnetic performance, and current and thermal margins are discussed. This demonstrates that a viable compact 7 T whole body MRI is achievable using Nb3Sn conductor.
Acknowledgements: This work was funded by an NIH SBIR
A no-insulation (NI), cryogen free HTS MRI magnet is currently being developed at the Robinson Research Institute. Consisting of 23 double pancake coils of varying size, width and REBCO material, the magnet is designed to image the human brain (1.5T of moderate uniformity, +/- 150 ppm over a 200 x 150 ellipsoidal imaging volume).
Risk of a quench arises from several sources, such as defects in the HTS tape; placement of HTS tape in a location with an unfavorable magnetic field and/or field angle; or variability of the critical current along a length of HTS tape. It is important to understand how the magnet would behave if a quench does occur, to ensure that the magnet is sufficiently protected from the thermal and mechanical forces that could destroy the device.
This study used transport current measurements of the critical current at 77.5 K self-field to determine the localised Ic at every position in the magnet geometry, for both YgdBCO and EuBCO conductor. Then, a lumped circuit model was used to predict the behavior of the magnet over a variety of different failure modes, such as simulating a localised quench event iteratively over a large number of different positions in the magnet geometry.
This study revealed that the magnet is broadly resilient to damage during a quench event. The ability to tune the turn-to-turn resistivity, in addition to the relatively small inductive coupling between coils, resulted in a negligible amount of the simulations exceeding damage thresholds.
Abstract gradients minimized in order to retain thermal and operating margin. We have used 3D finite element method (FEM) simulation in COMSOL Multiphysics software to calculate the temperature distribution both along the winding direction and across the cross-section of an MRI segment coil at its equilibrium operating temperature. We have also modelled the evolution of the thermal properties during cool-down from ambient temperature. The heat capacity and thermal conductivity along the wire as a functi Superconducting magnets used for MRI scanners need to keep temperature on of temperature for the composite wire was calculated using a rule of mixtures. However, the thermal conductivity within the wire cross section (x- and y-directions) was computed using a 2D FEM model (translationally invariant in z) for the composite wire. Based on this, a time-dependent model was built to calculate the coil temperature throughout the winding during cool-down in our test cryostat system. The model included a heat leak component to the coil current contacts via conduction through the current leads as well as a radiation component from the surfaces of the cryostat. A key result was that a coil temperature difference of 5 K was seen along the coil winding direction even at the steady state. A temperature difference of 4.2 K across the coil cross-sectional area was also seen, indicating an Ic difference of 10.5 A based on experimental measurements. Benefits and complications on the new designs including using thermal straps with higher thermal conductance as well employing thinner current leads were analyzed.
High-quality magnetic resonance imaging (MRI) techniques can provide precise anatomical details of small extremities such as hands and feet. Conventional MRI systems use cryogenic superconducting magnets cooled by liquid helium, and these occupy a large amount of space. Therefore, we have been developing a compact and high-performance desktop finger MRI system using REBCO wires. The proposed HTS magnet was cooled by cryocooler with cryogen free and will be operated at 40 K. The target value of strength of magnetic field is 3 T and the magnetic field homogeneity is 10 ppm/cm2 in a cylindrical measurement space with a diameter of 20 mm and a height of 10 mm. In order to develop the desktop finger MRI system, it is necessary to downsize the entire system including the HTS coils. In the previous study, the structure of HTS coils used in the finger MRI as a previous study was designed using the Distributed Genetic Algorithm (DGA) method. The optimized structure of HTS coil designed by the DGA method is very complicated, so it is not suitable for the actual coil structure in which double pancake HTS coils are stacked. Although the effect of the incorrect magnetic field due to the screening current increases with decreasing the inner diameter of the HTS coils, the screening current was not considered in the previous coil design. In this study, we designed the HTS magnet for finger MRI using HTS coils while minimizing the influence of screening currents. We performed an analysis that combines the electromagnetic field analysis based on the 2-D FEM and the DGA method to improve the design accuracy of the HTS coils. The optimize structure of the HTS coils for finger MRI and the effects of calculated screening currents will be presented.
In this study, we report on the optimized design results of REBCO high-temperature superconducting magnets for 3T whole body MRI. That is, for the REBCO magnet consisting of the main coil, the compensation coil, and the shield coil, an optimized design using an immunogenetic algorithm is carried out with two objective functions of maximizing the magnetic field uniformity in the uniform sphere inside the coil and minimizing the 5-gauss region outside the coil, for different transport current values. The local magnetic field vector distribution of the designed coil is calculated in detail, and the local voltage was obtained using the magnetic field / temperature dependence of the electric field-current density characteristics evaluated with the short REBCO sample. Then, the voltage-current characteristic of the magnet is evaluated by adding it over the entire coil. By defining the current load factor (operating current / critical current) of the designed magnet using the above analysis results, it is possible to clarify the relationship among the operating current, the optimized magnet shape, and the required wire length with respect to the operating temperature. In particular, it is found that the required wire length and the transport current have a simple linear relationship in the range of the operating temperature of about 40 K or less.
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO).
A 1.15 GHz nuclear magnetic resonance (NMR) spectrometer magnet has been under study at the Institute of Electrical Engineering of the Chinese Academy of Sciences. This NMR magnet requires spatial field homogeneity to reach 4 per million (ppm) in a sphere with a diameter of 40 millimeters. To achieve such a high magnetic field quality, each double pancake was wound with Bi-2223 tapes to reduce screening current. However, the actual parameters of the magnet are different from the designed parameters due to manufacturing errors, which still affect central magnetic field qualities. In this paper, the effects of different kinds of errors on the homogeneity of the central magnetic field and the feasibility of fabrication of joints between double pancakes with different outer diameters are analyzed. And then a scheme was proposed to optimize the position of the double cakes with different sizes in the magnet. The simulation and experimental results show that the quality of the central magnetic field is obviously improved and the influence of the manufacturing error on the magnetic field uniformity is reduced, which will create favorable conditions for the subsequent active shim coils and multi-layer ferromagnetic shims.
We present the updated REBCO insert coil technologies applied to the 835-MHz REBCO insert (H835) for the MIT 1.3-GHz NMR magnet (1.3G). As a replacement for the previous 800-MHz REBCO insert that was damaged when it quenched during operation in 2018, we are constructing the 19.6-T H835 based on our new single-coil formation design with a stacked of 40 stainless-steel-co-wound no-insulation (NI) double pancake (DP) coils, each of which has an electrically and mechanically reinforced cross-over turn. We have renewed the H835 design which uses high-performance 4-mm-wide REBCO tapes for the end DP coils, replacing wider 6-mm-wide regular-performance tapes used in our previous design. We can expect to reduce the length of conductors and the screening-current-induced stresses in the end DP coils. We have built and validated a full-scale over-banded DP coil test module with a protection heater and a copper cooling disk attached on the coil surfaces. In this paper, we present: 1) a new H835 DP coil fabrication process including an over-banding; 2) analytical results of effectiveness of the cross-over reinforcement; 3) charging characteristic and Ic of the DP test coil cooled via the attached copper disk in the conduction-cooling system; and 4) a quench-protection heater design and its performance validation.
Acknowledgement: Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R01GM137138.
No-insulation HTS magnets with high thermal stability and high current density have great advantages in the fabrication of ultra-high field NMR magnets. However, the turns of the double pancake coil of NMR magnet made by no-insulation technology are usually inconsistent with the theoretical value to keep the outer diameter of the coil consistent in engineering application, which affects the homogeneity of the space magnetic field of the superconducting magnet. Moreover, no-insulation NMR magnets have the disadvantage of charging delay, and parallel winding of stainless steel tape is an effective method in engineering applications, but reducing the magnetic field. In this paper, a novel structure coil with stainless steel tape wrapped around the outer layer of the coil is proposed, and the electromagnetic coupling model is used for analysis. It can adjust the current density, ensure the homogeneity of space magnetic field and the consistency of coil outer diameter, greatly reduce the charging delay time, and reduce the magnetic field loss.
Keywords: no-insulation，NMR magnet，charging delay, current density
A desktop 300MHz nuclear magnetic resonance (NMR) superconducting magnet with conduction-cooled cryostat system was developed in Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). The magnet has a standard 54mm-diameter warm bore with length 600mm, and the 5 Gauss line is actively shielded within the region 650mm (z) ×400mm (r). The operating current is 111.46A with a safety coefficient 78.9%, which corresponds to a critical temperature about 5.5 K. A pulse-tube (PT) refrigerator was used for the magnet cooling and the minimum temperature can be amounted to less than 4K, which had adequate temperature margin to guarantee the magnet running in the superconducting state. A set of superconducting shim coils up to third order was equipped accompanying with the magnet coils. The magnet has been fabricated and energized to the target magnetic field strength and the magnetic field attenuation according to the measure data was less than 0.01 ppm/h. With a dedicated sample probe and room-temperature shimming device installed on the magnet system, the built NMR spectrometer was tested. A final proton spectrum with half-width 25.5Hz was achieved, namely 0.087 ppm in terms of the magnetic field homogeneity. The superconducting magnet will be used on solid NMR detection in the future.
Aiming at the very small-scale NMR magnets, the authors have studied to detect NMR signals for NMR relaxometry using the single-sided magnetic pole which contained the high temperature superconducting (HTS) bulk magnet. The NMR signal relaxation rate depends on the mobility of molecules, including fluctuations and diffusion, in the microscopic environment. This measurement method can acquire less information compared to ordinary NMR spectroscopy, but instead less magnetic field homogeneity is needed. The higher magnetic field strength achieved by HTS bulk magnet can give us a benefit of higher sensitivity for shorter measurement time and stronger magnetic field gradient for higher spatial resolution, compared to commonly used permanent magnet. Pulsed field magnetizing method was employed to activate the bulk magnet as the most compact and the easiest way to handle, which gave us the magnetic pole emitting intense field of 1.32 T at the surface. We measured the spin-echo signals of hydrogen emitted from a silicon rubber sample with a diameter of 4 mm and a length of 9.5 mm in the probe which was placed on the surface centre of the magnetic pole, and have succeeded in detecting the NMR signals at 47.8 MHz, installing the sample 3.7 mm away from the surface. This is the first single-sided NMR signal detection with use of the single-sided magnetic pole containing bulk magnet in the world.
A ferromagnetic shimming has been applied to improve the field homogeneity of NMR magnets. The study deals with the results of evaluating the magnetic field distribution for a 400 MHz all-REBCO NMR magnet at the 20 mm DSV(diameter sphere volume) with mapping experiments. The mapping path consists of 128 positions that moving along the surface of the cylinder 24 mm in diameter and 30 mm in height. The initial field homogeneity before shimming was very uneven at about 240 ppm. To improve it below 5 ppm, a multi-layer ferromagnetic shim was installed using a double cylinder. The outer cylinder was equipped with two shim sets composed of thick ferromagnetic shims. From the third round, the inner cylinder was installed with a shim set consisting of a thin shim stock of less than 3 mil(0.0762 mm). After successfully improving the field homogeneity to within 5 ppm at 20 mm DSV, long term operations will be conducted to check performance and stability to measure the magnetic field distribution of all-REBCO NMR magnets.
A nuclear magnetic resonance (NMR) magnet system equipped with a persistent current switch (PCS) operates efficiently without Joule loss in persistent current mode (PCM). The superconducting joint technique and a persistent current switch (PCS) are essential to develop the PCM. In this study, we fabricated NbTi superconducting joints and measured the resistance of these joints. Based on the superconducting joint technique, we designed an NMR system in which the PCS is connected to a 5 T NMR magnet with a superconducting joint, which enabled the system to be operated in PCM at 5 T. Furthermore, we used diodes to develop active protection for the NbTi high-field magnet to protect the magnet from permanent damage resulting from quenching caused by a fast charging rate or insufficient cooling. The effectiveness of the diode protection during quench testing was investigated using the value of the Z-function obtained from the results of the quench test.
< Acknowledgment>
This work was supported by the Korea Basic Science Institute under Grant D110200
This paper proposes a dual-stator high-temperature-superconducting modular linear vernier motor (DS-HTS-MLVM), suitable for long stroke applications. The dual stators are two pure slotted-cores and staggered by half the stator pole-pitch. The mover adopts a modular structure, installed with HTS excitation windings and copper armature windings. The cryostats for HTS windings also adopt a modular structure. In space, the HTS windings and the copper windings are perpendicular to each other and installed in different slots. The main merits of the proposed motor are that:1) the staggered stators with simple structure help to significantly suppress force ripple; 2) the distribution of the two sets of windings can eliminate the conflict of slot space; 3) the modular mover, and the modular cryostats for HTS windings reduce the installation difficulty; 4) the motor without permanent magnets can reduce the overall cost, especially when it is applied to long stroke applications. In this paper, the structure and the working principle of the proposed motor are elaborated. With the help of the finite element method, the electromagnetic performance of the proposed motor is analyzed, and compared with its counterpart. The results show that the proposed motor can significantly improve the thrust force and suppress force ripple. Specifically, compared with its counterpart, the proposed motor increases the average force from 42.97 N to 144.41 N, while the force ripple reduces by 85%.
The electrically excited high temperature superconducting (HTS) coils can replace the mover of the linear synchronous motor (LSM) for electromagnetic launching with an expectation of improving the motor’s efficiency. In this paper, three stators with different core and winding structures are designed for the LSMs with the movers made by HTS coils. The electromagnetic parameters of these three types of stators are evaluated and optimized respectively with finite element method to obtain the same electromagnetic thrust. Then both the AC loss of the HTS coils and the economy of designing stators are analyzed. Based on the research above, the most suitable stator design of HTS-LSMs for electromagnetic launching is proposed. The research of this paper can provide some reference for developing HTS-LSMs in future studies.
Marine energy power generation fits the concept of Sustainable Development Goals: SDGs because it is renewable, safe and widely available energy source. It is expected to be developed as a predictable energy resource in island nations and countries facing the sea since the force generated by seawater is persistent. Conventional generators are good for high-speed and low-torque fluid, so we need a new concept generator that captures the slow-speed and high-torque mechanical changes produced by seawater. Many kinetic generators are made up of rotating machines, but linear generators also have often been used to capture repetitive and sustained ocean energy. In this presentation, we show the conceptual design of a new linear power generation module we are developing to obtain the power by capturing fluctuations of seawater tidal currents or ocean waves. In general, a marine energy power generator is preferably small projected area so as not to obstruct the seawater flow. In order to realize a small power generation module with low flow velocity and high torque corresponding to seawater, we are studying an electrical novel structure that consists of multi-layered field poles with several strong bulk magnets. We expect that this linear power generation module will obtain high performance by using high-temperature superconducting bulk magnets for the field pole, so we will show the result of conceptual design by finite element analysis simulation compared with the case of using the permanent magnets. The properties of field pole which influences the size, weight, power density and torque of the linear generator are important for practical application of the marine energy power generation because they improve the commercial viability.
As the efficiency of ordinary linear motors for electromagnetic launching is not high enough, the high temperature superconducting linear synchronous motor (HTS-LSM) is proposed with an expectation to improve the efficiency. This research focuses on a unilateral type HTS-LSM which mover is made up of closing coils pre-excited. In the research, the motor’s electromagnetic thrust characteristics and mover coil’s critical current characteristics, which are influenced by the parameters of the stator, such as slot type, slot full rate and winding structure, are studied respectively. Based on the research above, Both the electromagnetic design process and the method of parameter optimization for this type of HTS-LSMs are proposed. Then, a prototype of the HTS-LSM is developed. The test of the prototype verifies the validation of the researches in this paper.
No-insulation (NI) high temperature superconducting (HTS) machine is a kind of synchronous semi-superconducting machine with high power density and enhanced thermal stability. This technique has a great potential for electric aircraft propulsion systems, in which the NI HTS coils are used as rotor windings. However, NI HTS coils suffer from eddy currents flowing through turn-to-turn contacts in synchronous machine environment due to the absence of insulation between turns, which is induced by ripple background magnetic fields from stator windings. The induced eddy currents and losses can significantly reduce the efficiency and safety of the HTS machine. In this paper, an electromagnetic shielding technique is developed to minimize this induced eddy current and loss in NI HTS rotor windings. An equivalent circuit network model is developed to analyze the eddy current and losses of NI HTS coils exposed to ripple magnetic fields. Experiments are performed to validate the model. Then the practicability of the loss reduction using electromagnetic shielding technique is studied using both modeling and measurements. The effect of copper shielding on the induced eddy current and loss is analyzed on single NI coil and multiple NI coil system respectively. Analysis results show that copper discs can effectively reduce the eddy current loss under 30K since the resistivity of the copper is relativity lower than the equivalent turn-to-turn resistivity of NI coils. The lower the operating temperature, the more obvious the shielding effect. Since the operating temperature of the HTS machine ranges from 20 K to 30 K, the electromagnetic shielding technique based on copper plats is promising to solve the problem of eddy loss in NI HTS machine design.
Electrodynamic suspension (EDS) system is promised to be the ideal option for high speed magnetic levitation transportation. The electromagnetic forces for levitation and guidance of the EDS system are based on the relative motion of onboard superconducting magnets and the null-flux coils fixed on the ground. This unique working principle requires an auxiliary device to suspend the vehicle at low speed range as well as start process. Moreover, the operation safety of the train is difficult to guarantee with passive levitation coils on the ground under extreme conditions. Through an active control of the levitation coil currents, a quasi-static suspension state can be achieved independently of the running speed, and the stability is controllable at high speed. A numerical model of an active electrodynamic suspension system is carried out in this work to study the suspension characteristic of the system and the current in the levitation coils is controlled under different operation states of the vehicle. Square wave current and sinusoidal current are respectively input to the null-flux coils to investigate the electromagnetic forces of the system. The peak value and oscillation properties of the levitation and guidance forces are calculated and compared under different control currents corresponding to various speed range.
Generally, the double sided linear HTS induction motor has higher propulsive force and higher efficiency because the HTS windings can carry higher current with lower loss. In this paper, the primary side of the proposed linear motor is made from silicon steel sheet, and ReBCO HTS tapes are used to wind the armature windings which are settled into the iron core. The secondary sides are made from copper plate and iron plate. Because the primary side is made from ferromagnetic material, it effects on the critical current and ac loss of the HTS coil, and then effect on the performance of the motor. To study the influence of the geometrical parameters of the primary iron core on the ac loss, a 2D model for the double sided linear HTS induction motor by T-A formulation is proposed in COMSOL. With the help of the model, the influence of the geometrical parameters, such as the width of the teeth and the height of the yoke, on the critical current and ac loss of the coils is studied systematically. Meanwhile, the typical operation conditions are taking into consideration, such as no-load operation condition, rate-load operation condition, and over-load operation condition. This work is very helpful for fully understanding the influence of the geometrical parameters on the ac loss of the coils and then estimating the performance of the motor.
This paper presents calculation results of time-varying behavior of no-insulation (NI) high temperature superconductor (HTS) field coil for synchronous motor considering armature reaction and slotting effect. Despite the direct current (DC) operation in synchronous motor with HTS field winding, NI field coils are under time-varying conditions caused by rotor field harmonics depending on armature winding configuration and structural features of stator. Under the time-varying condition, current flows not only in the azimuthal path but also in the radial path of the field coil due to the so-called “NI characteristics”, and such behaviors change the magnetic field generated by the field coil and have a significant influence on the performance of the motor. To investigate field harmonics effects on NI coil characteristics during steady state operation of synchronous motor, the circuit parameters varying with position of rotor are stored as look-up tables and the dq equivalent circuit simulations are implemented. For case studies, we select four NI HTS motor models having different stator topologies divided into air-cored and iron-cored teeth, and armature winding layouts classified with concentrated winding and distributed winding. Then, the following key characteristics are calculated: (1) turn-to-turn radial leakage current; (2) flux linkage; and (3) Joule heating loss due to contact resistance. Considering these characteristics, we found the most advantageous stator topology and armature winding layout in terms of performance parameters such as torque and efficiency of NI HTS motors.
Acknowledgement
This work was supported by the R&D Collaboration Programs of Hyundai Motor Company. This work was also partly supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249)
Development of High Temperature Superconductors (HTS) electrical machines results in applications of various fields, (linear machine, axial field machine), as they have higher efficiency and power density. Numerical modeling of superconducting electrical machines is usually performed by finite element method based on their electrical behavior. H-formulation of the Maxwell’s equations, is one of the models that are used tremendously due to its high flexibility and simplicity for its modeling of electromagnetic properties of superconducting materials. However, simulation of electrical machines includes more complexity, where a full vector field in a non-superconducting region adds degrees of freedom which will cause longer computation times. This paper uses a model that divides an electrical machine into two parts: the superconducting parts which are simulated with H-formulation, and non-superconducting parts (e.g. conventional conductors, machine structure) that are simulated by A-formulation. This model requires appropriate boundary conditions and continuity between these two regions, along with correct modeling of fixed and moving parts of the electrical machine, where the geometry of this model is based on a linear synchronous machine, which means the rotor is moving linearly instead of rotation.
Full superconducting generator uses superconducting magnets wound with HTS tapes to replace copper wires to form a strong magnetic field. As far as superconducting magnets are concerned, stabilization is the guarantee of reliable operation of superconducting magnets, because in the operation of superconducting magnets, small changes in temperature, magnetic field or current will cause magnetic flux jump, even lead to quenching phenomenon. In order to maintain a good working performance of armature windings, it is necessary to analyze the stability of superconducting magnets. Therefore, the armature winding structure of 1MW synchronous generator is designed in this paper, and YBCO superconducting magnet is used to form concentrated windings.Then, the electromagnetic-thermal-mechanical coupled problem in superconducting magnets is aimed to be solved by using a commercial software which is based on the finite element method. Firstly, for electromagnetic stability of superconducting magnets, flux density and AC loss of the armature winding with different stator groove shapes are calculated based on the given critical current. Secondly, for mechanical stability of superconducting magnets, the dynamic balance of superconducting magnets in the mechanical properties is analyzed. Thirdly, for heat transfer stability of superconducting magnets, heat dissipation capacity of armature windings is improved by analyzing two different kinds of heat pipes attached to the surface of superconducting magnets.Results show that semi-open slot is the most beneficial to improve electromagnetic stability of superconducting magnets.And a appropriate balance center of magnets can enhance mechanical stability of superconducting magnets. Meanwhile, the optimized cooling structure of armature windings greatly improves heat transfer stability of magnets. The model provides an effective tool for the optimization of working stability in superconducting magnets of the full superconducting generator.
A Linear synchronous motor (LSM) is more electrically and mechanically efficient as compared to a linear induction motor (LIM) when it is running at high speed. Therefore, LSM is especially suitable for maglev which is usually operated over 400 km/h. To acquire stronger thrust force, high-temperature superconducting (HTS) magnets are proposed to replace traditional permanent magnets or electromagnets as the secondary excitation part in a LSM since HTS magnets can generate a much stronger field intensity. In this paper, research and development process of a HTS magnet is presented for a small-scale bilateral HTS LSM. The HTS magnet is designed with no-insulation winding technique for the enhanced thermal stability during unexpected quench. The optimization process is achieved by MATLAB circulative iterations combined with FEM software simulations, and its target is to find a magnet structure with minimum HTS tape consumed while generating a qualified magnetic field and running in a safe margin. The analysis of basic characteristics including turn-turn resistance, changing and discharging time constant are deduced and tested by experiments. Then performances like filed intensity, total harmonic distortion (THD) analysis and safety margin in operation, are investigated by comparison of simulations and experiments. Besides, accessory structures such as current leads and cooling system are also designed to further ensure the successful and safe operation of the HTS magnet.
One of the biggest weaknesses of superconducting coils is that the coil burns out when quick action is not taken at the moment of quench. It is known that the no insulation (NI) technology of the high temperature superconducting (HTS) coil almost solved the problem of burning the coil by this quench. In HTS coil applications, the larger coil sizes and higher generated magnetic field strengths require the coil to be mechanically stronger. In addition, metal insulation (MI) technology, one of the NI technologies, is proposed to improve the slow current ramp rate of the NI HTS coil. The MI technology of HTS coils has been applied to quadrupole magnets for heavy ion accelerators and HTS induction heating devices. However, the MI coil technology has not yet been applied to propulsion motors in aircraft and ships. The MI HTS field winding is expected to exhibit the same response as the isolated HTS field winding in normal operation. However, in real operation the MI HTS field winding will inevitably experience sudden forces such as acceleration, load fluctuations, etc. This will definitely affect the MI HTS coil. Therefore, it is necessary to check whether the MI HTS coil quench occurs due to the fluctuating external magnetic field and how the generated magnetic field changes.
In this study, an armature coil of a three-phase linear motor was fabricated and a MI HTS model coil was installed on it. By applying alternating current of several frequencies to the armature using a commercial inverter, we will investigate the stability of MI HTS coil during start, maintenance, and stop. The result will be reported.
This research was supported by KERI Primary Research Program through the National Research Council of Science & Technology funded by the Ministry of Science, ICT and Future Planning (No. 21A01019)
The bearings of the flywheel energy storage system play an important role in supporting the flywheel, reducing frictional resistance, and ensuring the stability of the whole system. It is a key component that determines the energy storage capability, charging and discharging efficiency, and lifetime of the flywheel. The electromagnetic bearing is a multi-variable time-varying coupling nonlinear system. In order to realize fast and accurate control of the electromagnetic bearing, an adaptive control method is proposed in this paper. The displacement stiffness and current stiffness of the electromagnetic bearing are online identified. The parameter identification results are used to optimize the control parameters of the electromagnetic bearing in real-time. In order to verify the efficacy of the proposed approaches, simulations and experiments were carried out. The experimental results show that the parameter identification method can effectively identify the current stiffness and displacement stiffness of the electromagnetic bearing. The adaptive control strategy has strong anti-interference performance and can operate stably under various operational conditions.
As we all know, the motor equipped with hybrid magnetic bearings (HMB) is easier to get higher speed and higher power because HMB not only has the advantages of no friction and wear, but also has the advantages of high suspension force density and low power consumption. Therefore, HMB has important application value, especially in the field of high-speed direct drive. Until now, domestic and foreign scholars have researched three kinds of mainstream HMBs, namely three-pole HMB and six-pole HMB driven by one AC converter, four-pole DC HMB electrified by two bipolar DC switching amplifiers. Of course, the above three HMBs can achieve stable suspension of the rotor. Therefore, from the perspective of industrial application, it is necessary to comprehensively evaluate the detailed electromagnetic performances of the three HMBs. Therefore, in this paper, starting from the analysis of structure, magnetic circuit and suspension mechanism, we compared the mathematical model of suspension force and the maximum bearing capacity. In the case of the same volume, air gap length, axial length, sum of pole areas, and air gap bias flux density, the three kinds of analysis models are established, respectively. Then, the suspension force characteristics, coupling characteristics, power consumption and maximum bearing capacity of the three HMBs are compared in detail. Furthermore, the other advantages and disadvantages of the three kinds of HMBs are further investigated, which provides an important reference for the correct selection and design of HMB.
The named fully superconducting magnetic bearing (SMB) consists of a rotor of high temperature superconducting (HTS) bulk of YBaCuO and a stator wind of HTS coated conductor tapes. The fully SMB has been developed a prototype and under operation in Japan. The dynamics of fully SMB under long term operation is vital to engineering applications, however, the experimental and theoretical studies on dynamic behaviors of fully SMB has not be reported. In previous work, the levitation properties of HTS bulk exposed to the high magnetic field, larger than 2 T, generated by HTS coils winded by HTS coated conductor tapes, were numerically investigated and discussed with the fishtail effect in levitation force prediction in high magnetic field. In this paper, a 2-dimensional(2-D) model of the fully SMB is introduced and coupled with the 2-D motion 2nd-order equations with respect to time, to simulate the dynamic behaviors in the vertical and lateral directions. The dynamic responses of a fully HTS SMB under harmonic excitation will be investigated, such as the displacements in time and frequency domains, phase trajectories, and motion trajectories. This work will provide an initial promotion of quantitative discussion in dynamic characteristics and principles for applications of fully SMB.
We are presenting a detailed study of the magnetization of CC-tapes stacks by the flux pump method. Magnetization of a CC-tapes stack was carried out using repeated cyclical impact of a local magnetic field source. The size of the localized area of the external magnetic field was five times smaller than the size of the HTSC sample.
A commercially available 12 mm wide CC-tape from SuperOx was used for the measurements. The tape was cut into 12 × 12 mm pieces and assembled in stacks of various thicknesses. Also, more complex stack configurations were considered, in which part of the tapes has one or two cuts. A permanent magnet (2x2x2 mm) and a solenoid (inner diameter 2 mm) were used as the source of the local magnetic field.
The influence of the thickness and configuration of the stacks on the dynamics of magnetic flux penetration and the maximum trapped flux was investigated. To study the dynamics of magnetic flux penetration, the magnetic field distribution on the sample upper surface was measured using a Hall sensor after each magnetization cycle. The analysis of the results was carried out on the basis of numerical simulation of the distribution of the trapped magnetic flux by the finite element method. The calculation results are in good agreement with the experimental data. It is shown that repeated cyclic action of a local external field leads to the accumulation of the total magnetic moment in the sample. The results obtained make it possible to optimize the magnetization regime of a CC-tapes stack, as well as to achieve the maximum magnetization of the sample and the maximum levitation force.
This work was supported by a grant from Russian Science Foundation (Project 17-19-01527).
Due to the use of high-performance permanent magnet, hybrid magnetic bearing (HMB) has the advantages of compact structure, high levitation force density and low power consumption. In particular, the six-pole AC HMB can be driven by a three-phase inverter to generate radial two degrees of freedom (2-DOF) suspension force with low cost, symmetrical structure, good linear force current relationship. In addition, compared with the three-pole HMB, the difference of the 2-DOF maximum bearing capacity of the six-pole HMB is small and easy to control. Therefore, the six-pole AC HMB has a broad application prospects. However, there are two main structures of the six-pole AC HMB, one is to install the permanent magnets and the suspension windings together in the radial space, the other is to install the permanent magnets in the axial control, while the suspension windings is installed in the radial space, which leads to the big difference of their electromagnetic characteristics.
Therefore, under the premise of the same main parameters, this paper makes a detailed comparative study on the electromagnetic performance of the heteropolar and homopolar AC six-pole HMBs. Firstly, the structure, magnetic circuit and suspension mechanism of heteropolar and homopolar AC six-pole HMBs are analyzed. Two kinds of equivalent magnetic circuit are given, and the mathematical model of suspension force and the maximum bearing capacity are derived respectively by using equivalent magnetic circuit method. Under the condition that the parameters of the stator, rotor, winding, axial length and area ratio are identical, a three-dimensional analysis model is established to calculate the magnetic circuit, force-current relationships, maximum bearing capacity and electromagnetic loss. Finally, the electromagnetic performances of two kinds of six-pole AC HMBs are evaluated.
The ground semi-physical simulation experiment is essential for the reliability verification of micro satellites equipped with micro thrusters. The HTS translational system based on the complete diamagnetism of superconductors is a feasible scheme. In order to explore the levitation force, translational characteristics and the factors affecting the performance of superconducting translational system, this article designs an experimental system model composed of superconducting plane spliced by YBCO superconducting blocks and permanent magnet structure under zero-field cooling condition. The bearing capacity and effective working range of superconducting plane are explored by measuring the distribution of superconducting levitation force in the surface. Also, the damping characteristics of the superconducting translational system are analyzed by processing the motion trajectory. In addition, the effects of different superconducting plane areas and the number of permanent magnets in the permanent magnet structure on the translational performance are also studied. The results show that the bearing capacity of the superconducting plane in the experimental system is over 10kg. However, the superconducting plane has a large edge effect, that is, the permanent magnet structure tends to move out of the surface when it is close to the edge. This paper analyzes that this may be caused by the attenuation of the shielding magnetic field at the edge of the superconducting plane. Meanwhile, the damping of the permanent magnet structure will increase when it moves above the splicing gap of the superconducting block. In addition, it is also found that the permanent magnet structure with a single permanent magnet is in an unstable equilibrium state above the plane, and rollover occurs when it is slightly disturbed.
Keywords: translational characteristics, HTS translational system, semi-physical simulation, zero-field cooling
Superconducting magnetic bearing (SMB) is a promising candidate for flywheel energy storage systems due to its great advantages of low friction loss, long-life operation, and maintenance-free. Since the amount of the SMB stored energy is strongly related to its levitation force, in this work, we have proposed a novel structure of hybrid superconducting stator which combines the HTS bulks and HTS coils, taking the advantages of strong trapped magnetic field and large size respectively, to increase the magnetic field and improve the levitation force accordingly. The structure of the hybrid superconducting stator is firstly presented, in which several HTS bulks are fixedly arranged inside an HTS coil. Then, a verified 2-D axisymmetric finite element model is adopted to estimate the magnetic field distribution as well as the levitation force of the proposed SMB. The results indicate that the levitation force could be greatly improved with the hybrid superconducting stator comparing to the traditional way. Its feasibility is furtherly examined by using the proposed hybrid structure to replace the original superconducting stator of a flywheel energy storage system with a capacity of 100 kWh developed in Japan.
Superconducting flywheel energy storage system (SFESS) has the advantages of fast response, high power density, long life, unlimited charge and discharge and pollution-free. With the improvement of the mechanical properties of superconducting magnetic bearings（SMBs）, it will be a better choice for SFESS to adopt fully-superconducting bearing composed of HTS coil stator and HTS bulk rotor. Due to the high current density of the HTS tape, the magnetic field strength generated by the HTS coil could achieve several tesla, the HTS bulk rotor is subjected in strong magnetic field, which differs from the ordinary SFESS composed of electromagnetic magnet stator and HTS bulk rotor. As a result, the emphasis of this paper lies in the optimization of the levitation performance of the fully-superconducting magnetic bearing in strong magnetic field. A two-dimensional axisymmetric model of fully-superconducting magnetic bearing was established using H-formulation in the finite element software COMSOL. Both the magnetic field dependence and temperature dependence of the critical current density were adopted to better reproduce the the nonlinear electromagnetic behavior of the HTS bulk. In addition, the “fishtail effect” of the HTS bulk critical current density was also taken into consideration to study the levitation performance of the bulk rotor in strong magnetic field. Based on the aforementioned modle, the effects of the bulk rotor shape, size and working temperature were studied aiming to optimize its levitation performance. The results of this paper could serve as the design guideline of the fully-superconducting magnetic bearing.
The stability of a levitation transport system using a bulk superconductor levitated above a permanent magnet rail has been studied. We investigated the inclination of the superconducting shuttle to improve the stability of the superconducting levitation transport system. The roll angle of the superconductor shuttle was estimated by measuring the magnetic force acting on each part of the levitating superconductor. The condition in which the roll angle of the superconductor shuttle for the lateral displacement becomes the stable inclination was searched. The transport stability of the levitation superconductor was improved by optimized the magnetization direction and the width of the magnet rail.
The homopolar hybrid magnetic bearing (HHMB) has the characteristics of the same air gap magnetic field direction, simple manufacture and assembly, low hysteresis and eddy current loss because the axial magnetized permanent magnet is often used to provide bias flux. Therefore, the HHMB has often adopted to suspend the rotor of the high-speed motorized spindle to obtain good performances of long life, free maintenance, higher speed and power. Recently, the scholars throughout the world have researched several kinds of HHMBs, such as three-pole AC HHMB, six-pole AC HHMB, nine-pole AC HHMB, four-pole DC HHMB and eight-pole DC HHMB.
The research methods and ideas are similar. However, there is no unified mathematical model and general design method for these HHMBs. Therefore, this paper studies a unified mathematical model and a general design method for HHMBs. Firstly, the general structure and magnetic circuit of the HHMB are analyzed. Meanwhile, the levitation mechanism of the bearing is analyzed. Then, based on the magnetic suction decomposition by the equivalent magnetic circuit method, the mathematical model of the suspension force is obtained. The unified mathematical model of the levitation force is deduced. Take HHMBs with five different types of poles as examples, the finite element analysis software MagNet is employed to establish the levitation force of the HHMB prototypes. According to the given control current and number of poles, the maximum bearing capacity of different structures is obtained. Finally, the finite element analysis results are compared with the theoretical calculation results of mathematical model. The correctness of the unified mathematical model and design method is verified by the research results.
The magnetic bearing using the pinning effect of the high-temperature superconductor (HTS) has been developed. The rotor composed of the permanent magnet levitates without control with levitation gap g = 10 mm due to the pinning effect of HTS. In order to give the function of the secondary side of the induction motor (IM) to the magnetic bearing, a force other than the rotation direction due to torque is applied to the magnetic bearing rotor. Thereby, it makes the levitation unstable. In order to study the instability, the inclining angle during the rotation of the HTS magnetic bearing rotor is measured. The HTS is YBaCuO. The rotor is rotated by the rotating field generated by the stator. The rotor is composed of the ring type permanent magnet, the yoke, aluminum, and magnetic shield, and the diameter is 100 mm, the weight is 710 g.
In this experiment, the inclining angle of the rotor at n = 400, 600rpm is measured with the IM running. A three-phase current is applied to the IM, and after the rotor reaches an arbitrary rotational speed, the inclination of the rotor is measured with a transmission laser to evaluate the stability. From the experimental results, average angle due to the vibration of the rotor are 1.23°at n = 400, and 2.52°at n = 600. The average angle at n = 600 rpm is 2.05 times the average angle at n = 400 rpm. This is because resonance occurs due to the natural frequency of the rotor around n = 600 rpm. The weight and the equivalent spring coefficient of the rotor is 2830 N / m, so that resonance occurs at n = 603 rpm (calculated value). Therefore, the inclining angle at n = 600 rpm increased more than at n = 400 rpm.
Recently, radial hybrid magnetic bearings (RHMBs)，which can suspend the rotor stably by electromagnetic forces in radial two degrees of freedom (2-DOF), have received more and more attentions. Besides, RHMBs have the advantages, such as no wear, no lubrication, long life and free maintenance. Therefore, RHMBs have broad application prospects in industrial rotating machineries, especially in high-speed and ultra-high-speed motorized spindle, flywheel energy storage, vacuum molecular pump, high speed centrifuge and artificial heart pump.
According to the stator structure, RHMBs can be divided into four types, namely 3-pole, 4-pole, 6-pole and 8-pole. Permanent magnets are used to generate the bias flux instead of the excitation windings to reduce loss, volume and weight, and increase the suspension force density. However, due to the flux coupling in the X and Y directions, the error of the suspension force models derived from equivalent magnetic circuit method is large. Consequently, it is difficult to design the control system and achieve high-precision control.
To solve above problems, a novel 4-pole RHMB is proposed, in which X and Y stator cores with curved poles are adopted. One axially magnetized permanent magnet ring is located between the X and Y stator cores to generate the bias flux and separate the control magnetic circuits in the X and Y directions. The structure and suspension mechanism are first analyzed. Then, the mathematical models of the radial suspension force are deduced by EMCM. The electromagnetic performances analysis is carried out to verify the magnetic circuits, suspension mechanism and uncoupled characteristic of the proposed RHMB by finite element analysis software MagNet 3D. The research results have shown that the proposed RHMB has the rational structure and good electromagnetic performances.
As a novel type of rail transit system, high temperature superconducting (HTS) maglev has entered the research and development stage of engineering application. During the future practical engineering, the dynamics performance of HTS maglev system is very important. Because its vibration characteristics will affect the safety and comfort of vehicle operation. Although, lots of previous experimental studies have shown that the HTS maglev system is laterally-vertically coupled, the related researches are not sufficient. This lack of lateral-vertical coupling model will make it very difficult to analyze the vibration characteristics of HTS maglev system in a practical operation condition. Therefore, a lateral-vertical coupling dynamic model is established in this paper, and the response of the maglev system under forced vibration is analyzed. Firstly, we use a scaled-down maglev frame to carry out the free vibration experiment of the maglev system. Secondly, based on this mathematical model of two-dimensional force, a damping term is added to reflect the hysteresis, so as to establish a lateral-vertical coupling dynamic model. After comparing the simulation results of the dynamic model with the experimental results, the accuracy of the dynamic model is verified. Finally, this dynamic model is used to simulate the forced vibration of the maglev system, and the lateral-vertical coupling vibration characteristics of the maglev system under different working conditions are studied. Results show that the lateral-vertical coupling effect of the maglev system is significant, and the coupling vibration has strong nonlinear characteristics. This study is expected to provide relevant reference basis for the engineering application of HTS maglev.
The DC fault current does not naturally generate zero-point, so it generates a large arc when cut-off operation. If it is failure to quickly extinguish the arc generated at the moment, lead to fire and equipment damage. Therefore, we proposed a fast and reliable transformer-type superconducting DC circuit breaker. The transformer-type superconducting current limiting elements are highly and likely to be put into practical use due to their high fault current limiting rate and high technology. Transformer-type superconducting DC circuit breaker consists of a current limiting part and a cut-off part. In the current limiting part is a transformer structure, and the primary line is composed of a copper coil, and the secondary line is composed of a copper coil and a superconducting coil. In the cut-off part, a mechanical DC circuit breaker, an LC divergence vibration circuit, and a lightning arrester are connected in parallel. When an accident occurs, the superconducting current-limiting element changes to a normal conduction state due to the secondary current of the transformer and generates impedance. Therefore, the secondary current is limited, and amount of magnetic flux change occurring is related to primary coil(main line), thus the fault current of the main line is limited. Also, the mechanical DC circuit breaker cuts off the direct current by occurring an artificial zero point on the fault current.
In this paper, a DC simulation circuit was designed using the PSCAD/EMTDC, and the cut-off characteristics were analyzed by applying a transformer-type superconducting DC circuit breaker. As a result, the fault current and cut-off time decreased to about 60.89 % and 45.79 ms due to the influence superconducting element of the transformer-type DC circuit breaker in the transients. Additionally, there are the limiting of the maximum fault current was effectively appeared as the ratio of the transformer's turns decreases.
Abstract—The superconducting current limiter has the advantages of small on-state loss, fast fault response speed, and strong current flow capacity. It can quickly limit the short-circuit fault current in the power system and protect the safety of power equipment. Superconducting current limiters can be divided into resistive current limiters, inductive current limiters and hybrid current limiters based on current limiting impedance. They all have their own application occasions, and the continuous advancement of high-temperature superconducting technology has made their application prospects broader. The medium-voltage DC power distribution system is the development trend of the ship's power system in the future. At present, with the rapid increase of the access power of the ship's power supply system, limiting the short-circuit fault current to the limit on-off capability of the protection equipment has become an urgent problem to be solved. DC superconducting current limiter is worthy of consideration, but there is a lack of application comparisons of various current-limiting topologies in medium-voltage DC systems. This article introduces three types of superconducting current limiters, including resistance type, hybrid type and magnetic flux confinement type, and will verify their respective advantages and disadvantages in current limiting effects through experiments, and evaluate the best one.
Index Terms—DC superconducting fault current limiter, MVDC system, short current fault
Three-phase transformer type superconducting fault current limiter (SFCL) using two superconducting module (SM)s between secondary windings, which consisted of three-phase transformer windings wound on three legs of E-I iron core and two SMs connected between secondary windings, were suggested and its fault current limiting fault current limiting and recovery characteristics using double quench of two SMs were analyzed. To verify the effective fault current limiting operation of three-phase transformer type SFCL using two SMs between secondary windings, the unsymmetrical ground and the symmetrical ground faults were applied into three-phase power simulated system with the suggested SFCL. Additionally, to analyze its recovery characteristics due to the ground fault types, the faults after the several cycles removed.
Through analysis on the test results, three-phase transformer type SFCL using two SMs between secondary windings was confirmed to have effective fault current limiting and recovery operations through double quench of two SMs.
DC Interruption technology is essentially required as DC system and microgrid have increased. The Interruption technology also includes current-limiting technology, and it is suppressed the fault current that rises when the fault current occured. Until now, many hybrid Interruption technologies have been proposed in which a semiconductor element or a superconducting element is combined with a mechanical DC circuit breaker. In this paper, a superconducting element was used combined the DC circuit breaker. The advantage of a circuit breaker using a superconducting element is that no loss occurs and the faster more than the semiconductor device. When the fault current in the main line, a quench phenomenon of the superconducting element causes due to critical current and temperature of superconductor. The fault current is limited by the resistance generated during quenching and the fault current vibrates due to the LC divergence ocillation circuit. When the zero-point is generated by vibration, it is cut-off the fault current with a mechanical switching. Superconducting element are simple structure. And it exhibits different characteristics depending on its shape, material, and length. The purpose of this study is to maximize the efficiency of the superconducting element by changing the winding shape, material and length. Solenoid and toroidal windings set up that the same number of turns, pitch interval, thickness and width were modeled using the Maxwell 3D simulation program. As a result of the simulation, the toroidal winding generated more inductance than the solenoid winding. Also, we combined the superconducting element and the mechanical DC circuit breaker and analyze the characteristics of cutoff operating in transient state. As a result, the toroidal winding had a slower generated than the solenoid winding. In addition, the toroidal type had the higher the limiting rate of the fault current due to the relatively large impedance.
Among the current limiters whose performances were proved, there are many current limiters wherein their unique electrical characteristics are combined. Of these, the SFCL that uses coil and core are combined with a superconducting current limiting element and has a unique current limiting performance. Its applicability as a SFCL was proved. Especially, the initial current limiting operating condition of the SFCL that uses the core and coil depends on the inductance according to the coil wiring direction and the turn ratio. In this study, REBCO superconducting wire, which is frequently used these days, was combined as a current limiting element of the SFCL with electromagnetic core and a coil, to analyze the quenching behavior of the current limiting element and the current limiting characteristic of the SFCL according to inductance value. Two REBCO superconducting wires were used as SFCL elements. One was a wire with stainless stabilization layer and the other was a wire with no stabilization layer. The two REBCO superconducting wires had an identical specification in terms of width, critical current and critical temperature, the values of which were 4mm, 80Arms and 90K, respectively.
Among the short-circuit fault current limiting devices in shipboard medium voltage dc-based integrated power system (MVDC IPS), hybrid-type superconducting fault current limiter (H-SFCL) has unique advantages. However, the H-SFCL prototype has to work under normal condition of 10kV/5kA and limit the short-circuit current of nearly 100kA in shipboard IPS, so it must have large current-carrying capacity. The current-carrying capacity of a single strip is poor, hence it is necessary to parallel the strip or coil. Due to the different magnetic field configuration, the unbalanced current distribution caused by parallel connection is prominent. In this paper, to solve the problem of unbalanced parallel current distribution, two typical structures of parallel inductors, solenoid-type and annular-type, are discussed. The current distribution characteristic analysis and electromagnetic optimization design of parallel inductors with two structures are carried out respectively. The magnetic field characteristics, coupling degree and strip consumption of two schemes are compared. Through comparison, it can be seen that these two schemes have their own advantages. Considering the operational stability and technical feasibility of the magnet, the annular type parallel inductors scheme is selected to be applied in H-SFCL. The results show that the H-SFCL prototype with annular type parallel inductors scheme meets the design requirements and has superior performance in current reduction and loss.
Index Terms—Electromagnetic design, shipboard MVDC IPS, hybrid-type SFCL, fault current limiting.
The level of fault current increases as urban power grid expands rapidly in recent years. The traditional relay protection has difficulty in preventing increasing fault current damaging electrical devices in power grid. Magneto-biased superconducting fault current limiter (SFCL) is a novel technology with the ability of reducing the level of fault current in the first half of the cycle, which consists of a double-split reactor, a non-inductive YBCO component and a fast circuit breaker. Achieving its coordination with relay protection can reduce the reconstruction cost of power system and contribute to its promotion. This paper analyzes the SFCL’s operating mechanism and establishes the SFCL model at first. Then, a power system simulation model consisted of the magneto-biased SFCL is built to theoretically investigate the coordination protection strategy based on a typical 10 kV urban power grid in China. Finally, the response time, the action sequences and relay protection strategy of SFCL in 10 kV urban power grid are given.
In this paper, DC fault current limiting characteristics of the flux-lock type superconducting fault current limiter (SFCL) with parallel and series connection between two coils were analyzed.
The flux-lock type SFCL with parallel connection between two coils was composed of two windings connected in parallel and one superconducting module (SM), which was connected in series with the secondary winding. The flux-lock type SFCL with series connection between two coils was composed of two windings connected in series and one superconducting module (SM), which was connected in parallel with the secondary winding.
These flux-lock type SFCLs with parallel and series connection between two coils in the DC system are thought to perform the similar fault current limiting operation to AC system. However, since the transient period after the resistance in SM approaches into the constant value, its fault current limiting characteristics in the DC system are expected to be different from one in the AC system as well as its recovery characteristics after the fault removes.
To analyze its DC fault current limiting and recovery characteristics, DC short circuit tests were performed and the different operations of the flux-lock type SFCL in DC system were investigated from the test results.
As medium voltage dc-based (MVDC) technology is widely considered in the shipboard integrated power system (IPS), the short fault protection of shipboard IPS is urgent. Superconducting fault current limiter (SFCL) is an efficient way to solve the short fault problems in shipboard MVDC IPS. A hybrid type SFCL (H-SFCL) based on a non-quenching inductor and two resistors have been developed in this study. The H-SFCL can limit the first peak value and the steady-state short-circuit, with no quenching and little heating. In this study, the short fault mechanism and mathematical model of the MVDC IPS DC pole-to-pole short circuit is analyzed. The current limiting indexes are proposed according to the existing situation of circuit breakers and short fault, and the current limiting performance of H-SFCL is verified. The scheme of annular structure parallel inductors is proposed to balance the current distribution and eliminate circulating current. The electromagnetic design of a 10 kV/6 kA H-SFCL prototype is completed based on a genetic algorithm, along with the performances of current-limiting capacity, response time, and loss of the prototype. The current distribution characteristics and electromagnetic optimization design are analyzed. The simulation results show that the H-SFCL prototype with electromagnetic parameters meets the design requirements and has superior performance in current reduction and loss.
Index Terms—Hybrid-type SFCL, electromagnetic design, fault current limiting, shipboard MVDC IPS.
Three-phase transformer type superconducting fault current limiter (SFCL) using secondary windings with closed loop, which consisted of three-phase transformer windings wound on three legs of E-I iron core and two/three superconducting modules (SCMs), were suggested and its fault current limiting operations according to ground-fault types were analyzed. To verify the effective operation of the three-phase transformer type SFCL using secondary windings with closed loop, the unsymmetrical ground and the symmetrical ground faults were applied into three-phase power simulated system with the suggested SFCL. For the comparison, the ground faults were generated into three-phase transformer type SFCL with two/three SCMs. Through analysis on the test results, the SFCL with two SCMs was confirmed to have no different fault current limiting operation from the SFCL with three SCMs. The structure of E-I iron core with three magnetically coupled legs and the constitution of three secondary windings with the closed loop were analyzed to be contributed to the same fault current limiting operation.
The application scenario of Hybrid type superconducting fault current limiter (H-SFCL) is the ship DC system. Therefore, the superconducting coil works in low frequency environment. The use of iron core can effectively reduce the tapes consumption, help to reduce the end leakage magnetic field, and reduce the AC loss of the superconducting coil in operation. When designing a superconducting coil with an iron core, the design idea is divided into three parts:
1. The system parameter matching optimization algorithm is adopted to obtain the basic operating parameters of the H-SFCL.
2. Use the magnetic-circuit method to determine the basic size of the superconducting coil, use the finite element software to verify the electromagnetic design parameters and determine the final design parameters.
3. Use finite element software to simulate and analyze the operating characteristics of the superconducting coil, and verify the dynamic stability.
The main conclusions are as follows:
1. Through the optimization simulation calculation of the system, the target inductance value Lset of the superconducting coil, the maximum operating current Imax, the maximum uniform magnetic flux density upper limit Bmax are obtained.
2. Based on the magnetic-circuit method, the edge leakage flux coefficient is corrected, and the inductance calculation formula is obtained. The basic structural parameters of superconductivity are optimized by the combination of magnetic-circuit method and genetic algorithm. The finite element model verifies that the magnetic-circuit method has high accuracy and fast calculation speed in the optimization process.
3. Multi physics field simulation calculations are carried out through COMSOL, and the results show that the superconducting coil meets the design requirements in terms of electromagnetic, temperature and stress.
7-filamentary Ba1-xKxFe2As2 (Ba122) iron-based superconductor (IBS) tapes were proven to be applicable to fabricate the high filed insert coils in recent years. The iron-based superconductors with ultrahigh upper critical fields have expected to be used in future high-field applications. However, the current 7-filamentary Ba122 tape is also sensitive to strain. In order to promote the development of iron-based magnet technology, the mechanical properties of the Ba122 tape under high field were required to be tested and analyzed. This study focuses on the test and analysis of the critical soft-way and hard-way bending radius of 7-filamentary Ba122 tape. In this study, the mechanical structure designs for the critical bending radius test were presented. The Ba122 tapes within the structure of the bending radius test were simulated under the high background field. The bent Ba122 tape samples were assembled with the test mechanical structures before the reaction. The fabrication and testing process of the bent Ba122 tape samples were presented. The testing results of the critical bending radius of Ba122 tapes under 12 T background filed were analyzed and summarized.
The iron-based superconductor is a promising candidate for applications in polycrystalline forms owing to its high current transport performance under high magnetic fields. Especially, doped-BaFe$_2$As$_2$ (Ba122) is particularly interesting in terms of both small anisotropy and small weak-link issues [1]. Epitaxial thin films (ETF) of Ba122-type superconductors have been realized only with Co and P doping by both pulsed laser deposition and molecular beam epitaxy (MBE). Hence, extensive research on enhancing critical current density ($J_c$) has been carried out via introducing artificial pinning centers [2, 3]. However, the fabrication of K-doped Ba122 ETFs has not been realized due to its high volatility and high vapor pressure. Recently, we have succeeded in growing K-doped Ba122 ETFs on CaF$_2$ substrate with high crystallinity by MBE [4]. In the present study, we will report $J_c$ characteristics and nanostructure of the K-doped Ba122 ETFs. Surprisingly high $J_c$ over 10 MA/cm$^2$ was observed at 4 K by magnetic measurement. Note that our thin films showed superior superconducting properties to the pinning enhanced K-doped single crystals by ion irradiation [5]. TEM analyses revealed that low-angle grain boundaries developed in the K-doped Ba122 ETFs grown on CaF$_2$ substrates which could act as flux pinning centers and correspond to the record-high $J_c$.
This work was partly supported by JST CREST (Grant No. JPMJCR18J4) and Advanced Characterization Platform of the Nanotechnology Platform Japan (Grants No. JPMXP09-A-19-KU-1003 and 1004) sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
[1] H. Hosono et al., Materials Today 21, 278 (2018).
[2] L. Fang et al., Nat. Commun. 4, 2655 (2013).
[3] M. Miura et al., Supercond. Sci. Technol. 32, 064005 (2019).
[4] D. Qin et al., Phys. Rev. Materials 5, 014801 (2021).
[5] A. Takahashi et al., J. Phys.: Conf. Ser. 1590, 012015 (2020).
Along with development of hydrogen-use, sustainable society in which it is used as clean energy source as well as energy storage material, MgB2 superconducting power applications have been attracted scientific interest due to its huge potential of superconducting characteristics, made from affordable elements and applicability to liquid hydrogen cooling. As MgB2 wires have been commercially available in the last decade, our group had designed, fabricated and demonstrated Rutherford cables and magnets with kA current capacity to make large-scale magnets for superconducting magnetic energy storage (SMES) device, which is suitable for compensation of rapid-change, short-period power fluctuations originated from renewable power source unlike chemical batteries. Although the MgB2 seems to be one of the most promising superconducting materials because it does not include rare constituents, its strain sensitivity especially after heat treatment and Ic deterioration caused by strand deformation during twisting and compaction process in cable manufacturing are still big problems to apply it to magnets for energy storage device. In this study, we will report the design and fabrication results of the cable with nominal current of kilo-amperes and demonstrate transport properties under the wide-range of background magnetic field, boiled He gas cooled condition. Our research will accelerate making large-scale energy storage magnets suitable for developing hydrogen society and stabilize electric power from renewable power source.
Acknowledgement
This work is supported in part by JKA research grant, 2021M-183.
MgB2 has been regarded as the most attractive candidate for the next-generation superconducting material due to its high critical temperature and low material cost. Sam Dong Co., Ltd., Korea, is a supplier that produces a variety of the MgB2 superconducting conductors to meet customers’ requirements over the past 6 years. Recently, we have increased the area fraction of multifilamentary MgB2 wire up to 20% by controlling the particle size distribution and powder densification, resulting in high critical current. In addition, carbon doping further improved the critical current density in a high magnetic field. The critical current densities were estimated to be 120,000 A/cm2 at 6 T at 4.2 K and 16,000 A/cm2 at 3 T and 20 K, respectively. In this conference, we will introduce and discuss a newly developed MgB2 wire of Sam Dong Co., Ltd.
The iron-based superconductor (IBS) is a good candidate for high field magnet applications. The bending effect and properties of IBS tapes were systematically investigated in this work. The bent Ba1-xKxFe2As2 (Ba122/Ag/AgSn) 7-filamentary tapes with different bending diameters (D=10, 15, 20, 25, 30 mm) were prepared by wind-and-react method. A special mechanical structure was used to prevent the heat-treated IBS tapes from being damaged during joint soldering. The critical current (Ic) performances of all the bent samples have been tested at 4.2 K and 10 T. When the bending diameter is smaller than 30 mm, the transport Ic of bent IBS tapes decreases with smaller bending diameters. The average ratio of Ic (bent tape) and Ic (straight tape) was also calculated. Compared with the ratio value of 92.6% for D30 tapes, the ratio value for D10 tapes is 63%, which should be related to the cracks observed in the Ba122 superconducting cores. The Optical Microscope Images (OMI) show a lot of cracks that appear regularly in part of the superconducting cores under tensile stress, especially in D10 bent IBS tapes. In contrast, almost no cracks are seen in the superconducting cores subjected to compressive stress. The stress distributions in the bent tapes during the bending and annealing processes were simulated using the software. The most possible formation mechanism of cracks will also be discussed in detail.
Keywords: Iron-based superconductor, bent tape, critical current, stress, cracks
MgB2 has the highest Tc of 39 K among metallic superconductors [1] and is expected for applications at 10-20 K. MgB2 bulk permanent magnet [2] is interesting for compact, high field magnet applications. Recently, we developed the Magnesium Vapor Transportation (MVT) method [3] that transports magnesium vapor to precursor boron pellets. By using the MVT method, we have succeeded in obtaining MgB2 bulks with higher purity and higher density compared to those of the conventional in-situ bulks. On the other hand, the formation of secondary phases and cracks is sometimes observed in bulks prepared by the MVT method. Such structural defects would limit the current flow and the trapped magnetic field. In this study, the premix method [4] in which prereacted MgB2 is premixed in the precursor boron powder was introduced to suppress the formation of cracks during the MVT process. The effects of premix ratio x (xMgB2+B) on the superconducting properties of the MgB2 bulks after the MVT process were evaluated. Cracks were found on the surface of the bulk with the smallest premix ratio x=0.1, whereas macroscopic cracks were not observed in the bulks with x=0.3 and 0.5. Jc of all samples was improved compared to the in-situ bulks, especially Jc of the bulk with x=0.3 reached 770,000 A/cm2 at 20 K. Trapped field measurement was performed on the disk shaped bulk (20 mm in diameter, 2 mm in thickness). The bulk fabricated by the premix MVT method with x=0.3 trapped 2.3 Tesla at 10 K at the center of the bulk surface.
[1] J. Nagamatsu et al., Nature 410, 63 (2001).
[2] A. Yamamoto et al., Appl. Phys. Lett. 105, 032601 (2014).
[3] Y. Sanogawa et al., J. Japan Inst. Met. Mater. 83, 341-345 (2019).
[4] I. Iwayama et al., Physica C 460-462, 581-582 (2007).
In previous studies, Jc-strain relation in the reversible range and the irreversible external-tensile strain (ε_irr_t) of MgB2 filament were reported. In general, it is said that ε_irr_t is almost equal to the pre-compressive strain caused by cooling after heat treatment. In this study, the irreversible external-compressive strain (ε_irr_c) of MgB2 multifilament wire was measured. In measurements, a copper plate was soldered to a sample wire, then the sample wire was bent while the copper plate was applied outward. ε_irr_c can be measured by evaluating Ic vs bending-radius relation, because the external tensile strain by bending is negligible in this situation. In the damaged sample wire, some buckling were observed in inner filaments on bending. It suggests that the irreversible damage was made by compressive strain. In addition, ε_irr_c of additional sample wires, which have larger pre-compressive strain and were heat treated by higher temperature were measured. The difference values between ε_irr_t and ε_irr_c of samples were roughly same value. From this results, we can minimize the reversible bending radius by controling pre-compressive strain and thickness of copper plate.
Generally, the wind and react process is used to manufacture MgB2 coil. The react temperature is relatively high, around 650 °C, and this may increase the magnetic field inhomogeneity as a result of the distortion of the winding former. To solve this problem, Kiswire Advanced Technology has developed a twisted cable with fine MgB2 strands that can be wound after heat treatment. In this study, we developed optimized processes that can prevent damage to the MgB2 cable during winding and termination. The charging characteristics of the manufactured coil were evaluated at the temperature of liquid helium.
< Acknowledgment>
This work was supported by the Korea Basic Science Institute under Grant D110200
BaFe2As2 (Ba122) is one of the parent materials of iron-based superconductors, and superconductivity can be induced by elemental substitution. Ba122 is expected to be used for high field applications since it has a high critical temperature Tc and upper critical field Hc2. In addition, Ba122 is suitable for the fabrication of polycrystalline materials owing to a relatively large critical grain boundary angle (θc = 5-9°[1]). On the other hand, microstructural control is required for improving critical current density Jc of Ba122. In this study, Co-doped Ba122 polycrystalline bulks were synthesized under various sintering conditions by SPS (Spark Plasma Sintering), which is a field-assisted, high-pressure sintering method. The bulk density, phase purity, microstructure, and superconducting properties were evaluated. The Ba122 phase was obtained as the main phase and the relative density of the samples was over 90%. Tc measured by electrical resistivity was above 27 K, exceeding that of single crystal (Tc = 26 K[2]), and Jc calculated from magnetic hysteresis loop exceeded 2.0×10^4 A/cm2 at 5 K under self-field.
References
[1] T. Katase et al.: Nature Communications, 2 (2011) 409
[2] Y. Nakajima et al.: J. Phys. Soc. Jpn., 78 (2009) 023702
To minimise the (alternate current) AC loss, multi-filament high-temperature superconducting (HTS) costed conductors (CCs) have been investigated for years. Many methods for striating the HTS CCs are developed and proven effective, such as laser cut and mechanical cut. This paper presents a novel approach to create the filamentary structure. Instead of cutting the HTS tape after manufacture, patterning process is introduced to the buffer layer before the deposition of the superconducting layer. Filamentary tapes with different patterns on the buffer layer are manufactured and measured. Experimental results show the AC loss is decreased by a factor of filament numbers, which indicates the patterning process is successful. This technology can not only produce filamentary HTS tapes conveniently and economically, but also provide the possibility of creating HTS tapes with multi striated superconducting layers with low AC loss.
When the HTS tapes in the quasi-isotropic cable are insulated in middle but soldered together at terminals, it is call partially coupled quasi-isotropic cable. There are resistances at soldered parts which would form closed current loops. When the cable is carrying DC current and subjected into AC magnetic field at the same time, it would induce coupling current and change the current density distribution in tapes. So that, it effects on the dynamic resistance and dynamic loss of the cable. To study the characteristic of the dynamic resistance and dynamic loss of the quasi-isotropic cable with consideration of the resistance at terminals, the minimum electromagnetic entropy production (MEMEP) 2D model is proposed. The MEMEP 2D model is much faster than other commonly used methods, so that it is possible to use much better mesh strategy to get more accurate result. In this paper, the magnetic field dependence of the HTS tape will be considered well, and each tape in cable will be mesh into at least 40 and 32 elements in width and thickness directions, so that the dynamic resistance in low field can be calculated well. The dynamic resistance and dynamic loss of the cable are calculated under DC current and AC field with a series of amplitude and frequency, respectively. The dependence of resistance at terminals on the dynamic resistance and dynamic loss is obtained, which is very helpful for fully understanding the loss characteristic of quasi-isotropic cable, and it helps to design high field magnet.
Recently, a Wireless Power Transmission (WPT) system has been attracting attention for automobiles and electric railways. However, the power transmission efficiency in the conventional WPT system composed of copper coils is not high enough due to large resistance. Therefore, we have investigated the effectiveness of applying REBCO coils to WPT system. Since the increase AC loss of the REBCO coil leads to not only the temperature rise of the REBCO coil but also the reduction in the power transmission efficiency and the transmission power of the WPT system, it is important to reduce the AC loss of the REBCO coil. Therefore, in order to reduce the AC loss of the REBCO coil, it is necessary to investigate the magnetic properties of REBCO tape at low temperatures. In addition, it is necessary to evaluate the magnetic properties and losses of copper stabilizer, hastelloy substrate and so on. We have been developing equipment to evaluate the magnetic properties of magnetic materials such as non-oriented /grain-oriented electrical sheet, and our single sheet tester (SST) is one of them. In this study, we wanted to try to evaluate the magnetic properties of the component of REBCO wire under low temperature conditions using the SST. Since the SST is generally used at room temperature, it needed to modify the SST for cryogenics in order to measure the magnetic properties of REBCO wire and its component. Therefore, the existing SST was designed and fabricated in a small size that can be mounted on a conduction cooling system using 4K cryocooler. After confirming the sufficient measurement accuracy of the SST at room temperature, the magnetic properties of component of the REBCO wire were measured at low temperatures from 4.5 K to 40 K by the conduction cooling system and measured the results will be reported.
AC applications of REBa2Cu3Oy (REBCO) superconducting tapes require large current capacity and low AC loss properties. We have already proposed transposed parallel conductors in our previous study on the development of superconducting power transformers and rotating machines. The parallel conductor with the optimal transposition does not induce the additional AC loss. However, if the transposition points deviate from the optimal ones, shielding current is induced among the constituent tapes and AC loss increases. In the case of three-strand parallel conductors subject to uniform magnetic field, the tapes should be transposed twice at equal intervals. In our previous study, we evaluated additional AC loss properties of three-strand REBCO parallel conductors theoretically and experimentally, in the case that the two transposition points deviate by arbitrary length from optimal ones. Our theoretical equation of the additional AC loss was in agreement with the measured one. When winding the coil, it is difficult to transpose at the optimal points due to manufacturing errors and other factors. Therefore, in this paper, we evaluated the variation in current experimentally when slightly deviated from the optimal point. We measured the current distributions of the three-strand REBCO parallel conductor with three Rogowski coils. The details of the observed result and the discussion will be presented at this conference. This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO), the Japan Science and Technology Agency (JST): Advanced Low Carbon Technology Research and Development Program (JPMJAL1405), and the Japan Society for the Promotion of Science (JSPS): Grant-in-Aid-for Scientific Research (JP18H03783 and JP19K14964).
One of the properties in superconductor is perfect diamagnetism called as Meissner effect. Among superconductors, YBa2Cu3O7-δ (YBCO) polycrystals has high critical temperature (Tc) over 90 K and high critical current density (Jc) of the order of 104 A/cm2 at 77 K in self-magnetic field［1］, so it is expected as a material for shielding magnetic field under liquid nitrogen cooling. Concerning to use it in future electric aircraft, it is desirable to be large size with flexible shape and lightweight material. In this study, we tried to fabricate a magnetic shielding sheet consisted to YBCO powders and resin matrix because the resin is lightweight and flexible material. The diamagnetic performance of the sheet is affected strongly on current density of YBCO powders. Furthermore, no cracks and pores are desirable for the shielding sheet to suppress leaking magnetic field. So, we investigated particle size dependence of shielding rate and microstructure of the sheet. We prepared two types of YBCO powder with different particle size, 3.8 µm and 27 µm. The powders were mixed with resin, separately, and the mixture solutions were coated on substrates. Then, the coated substrate were dried at 135 C by electric hot plates. Magnetic field shielding rate was measured by a hall element device, and microstructure was observed by scanning electron microscope. Shielding rate of the sheet by YBCO powders of 3.8 µm and 27 µm were 16% and 14%, respectively, under external magnetic field of 20 mT. Microstructure observation showed cracks and pores in the sheet by the powder of 27 µm. So, it was considered that the difference of shielding rate was due to the difference of crack formation in the sheet. We succeeded in fabricating magnetic field shielding sheet with flexible shape and lightweight material.
［1］Nakamura Yuichi, Shiohara Yuh, OYOBUTURI, 61, (1992), 456-463 in Japanese
HTS cable conductor are promising with high current density and without Joule loss characterized by its intrinsic zero resistance. Therefore，HTS cable conductor with large current carrying capacity are expected to have widespread application in feeder lines large scale magnet. At present, the conventional design of HTS cable conductor, general several of 10 KA, are designed with goal of uniform current distribution by adjusting winding pitch same as AC HTS cable since the current in process of exciting and demagnetizing are alternative. Thus, AC magnetic field component generated on tapes of HTS cable conductor is non-negligible. If the AC magnetic field component is higher than its penetrated field of HTS tapes, there is inevitable dynamic resistance among them. Dynamic resistance is seldom considered in design of DC cable conductors before. The dynamic resistance significantly affects the current distribution among HTS tapes except for generating extra loss and instability. Different from conventional design method, this paper presents the design novel method of HTS cable conductor with large current capacity by considering dynamic resistance, so that the current uniformity among HTS tapes can be realized.
Keywords: Cable conductor, coated conductors, current distribution, dynamic resistance
One of the practical applications of the second generation HTS tapes (or CC – coated conductors) lays in the area of development of superconducting magnetic energy storages (SMES). In particular, HTS SMES will be applied for charging pulse mode magnets used in particle accelerators. The important particularity of such magnets is the rapidly changing operating current and magnetic field at low operating temperature. So, for successful development both SMES and future superconducting magnets for accelerators it needs to know the values of critical currents and hysteresis losses of HTS CC at various orientation of direction of magnetic field to the tape plane. These data may be obtained from magnetization measurements.
In our report we present new results of investigations of the HTS CC samples in a wide range of temperatures from 5 K up to 77 K and magnetic fields up to 8 T directed to the tape plane with the angles 0, 5, 10, 15, 30, 45 and 90 degrees. The measurements were done using vibration sample magnetometer PPMS-9 with using the specially made set of the sample holders. We found that the decrease in magnetic field angle results in not only reducing of the hysteresis losses but changing of the shape of magnetization curves as well as appearance of thermo-magnetic instabilities at low temperatures. We have done the analyses of the experimental data and proposed the approximation expression that fits well the dependence of hysteresis values on angle.
Recently, we proposed a REBCO split wire having multi-core structure. The split wire is fabricated by separating the REBCO layer using the commercial REBCO-coated conductor. The fabrication method is electrical separating by bending stress (ESBS) and electrical separating by pressure concentration method (ESPC) [1]. In the measurement of the screening current induced magnetic field, that was largely improved in split wire and coil [2, 3]. In this study, we measured and evaluated AC losses for the split wires and coils. For the wires, magnetic field dependence of magnetization was measured by using MPMS device, and then, AC loss was obtained by the calculation using the area surrounded by hysteresis carve. Two coils were fabricated by using original coated conductor and split wire with the same single pancake structure (wire length: 18 m, inner/outer diameter: 80 mm/111 mm). The measurements of the coils were carried out by nitrogen boil-off method without coil energization in AC magnetic field. This measurement method is considered to be better to improve the measurement precision of AC loss, that removed the unrelated loss due to current resistance at normal conducting wires. As a result, reduction of loss up to 95% was estimated for the split wires in 77 K and 4.2 K. Regarding the reduction of AC loss of a coil it was about 80% at 77K, which is the same as a split wire of the coil.
Acknowledgements:
This work was supported by the MEXT project of Leading Initiative for Excellent Young Researchers (LEADER) in Japan (Project ID: 16810210).
[1] Xinzhe Jin, Hidetoshi Oguro, Yugo Oshima, Tetsuro Matsuda and Hideaki Maeda, Superconductor Science and Technology 29 (2016) 045006 (8pp)
[2] Xinzhe Jin, et al, IEEE Transactions on Applied Superconductivity 29 (2019) 6601304
[3] Tetsuro Matsuda, Xinzhe Jin, Tetsuji Okamura, Cryogenics 86 (2017) 38–41
Commercial HTS coated conductors exhibit asymmetric Ic (B,θ) characteristics, where θ is defined as the angle between the applied magnetic field and normal component of the superconductor plane. Previous works reported influence of Ic (B, θ) characteristics on dynamic resistance in a coated conductor and AC loss of coil windings wound with coated conductors. However, the influence of asymmetric Ic (B, θ) characteristics on magnetization loss of HTS coated conductors has not been previously reported.
Here, we present experimental Ic (B, θ) and magnetization loss results in a 12mm-wide REBCO commercial coated conductor at 77 K, 70 K, and 65 K. In Ic (B, θ) measurement, θ was varied from 0° to 360° and B is up to 0.2 T. In the magnetization loss measurement, the applied magnetic field amplitude is up to 100 mT and field angle varies from 0° to 180° with 15° resolution. At each temperature, the magnetization loss values at various field angles vary and are dominated by the perpendicular magnetic field component as reported in previous works. Furthermore, we observed difference in magnetization loss values for θ and 180°-θ， which are in mirror symmetry relative to the superconductor plane. We attribute the difference to asymmetric Ic (B, θ) characteristics of the conductor. The difference in magnetization loss values becomes greater with decreasing operating temperatures. 2D FEM (finite element method) simulation using H-formulation was carried out by directly interpolating the measured Ic (B, θ) data and the simulation results reproduce the trend of the experimental results. Our results provide a valuable reference for the magnetization loss behaviors in REBCO coated conductors in various field orientations and temperatures.
Like quasi-isotropic conductor has the characteristics of high current-carrying, high engineering current density, and flexibility, which makes it uniquely advantageous when used in industrial scenarios such as nuclear fusion, SMEs, and MRI. In spite of that, the operating conditions of the conductor will be complicated by the screening effect caused by the alternating magnetic field. Therefore, the use of efficient methods to study its screening effect under alternating fields can provide an important theoretical basis for its high-field applications. Based on the T-A formulation, this paper proposes some corresponding optimized methods, so that it has high calculation speed and great accuracy when used to simulate the screening effect of complex superconductors. The influence of the amplitude, frequency and angle of the external magnetic field on the screening current distribution is studied using the proposed simulation model, which shows a high degree of consistency with the experimental results, and a higher calculation speed than the traditional T-A formulation. By comprehensively researching the experimental and simulation data, it can be concluded that the frequency of the magnetic field has little effect on the screening current distribution of the like quasi-isotropic conductor, besides, the magnetic field amplitude and penetration field are closely related to the distribution of the conductor screening current. The conductor shows high isotropy under external magnetic field with different angle.
Keywords: Optimized T-A formulation, alternating magnetic field, like quasi-isotropic conductor, screening current.
Cable-in-conduit conductors (CICCs) are applied in the superconducting magnets designed for fusion reactors, because of their high-engineering current transmission capacity and large heat removal capabilities. In previous research, CICCs exposed varying degrees of performance degradation during electro-magnetic (EM) loading cycles. To prevent this kind of degradation, CICCs must be designed considering proper choices for the cable layout and the conductor geometry, depending on the operating conditions. In all cases, limiting of strand and cable movements and avoiding filament fracture inside the cable are necessary to exclude or at least diminish the degradation. But no matter how effective the structural improvement is, the nature of its mechanical composite properties determines that there is a critical structural collapse limit. The EM performance of the cable will show a relatively fast degradation after the Lorentz load reaches the structural collapse limit. To inverstigate this, sections of CICCs are tested with EM loading cycles in SULTAN, and sections with similar layout are tested by method of hydraulic cryo-mechanical pressing cycles. The test plan and loads of the two groups are corresponding. By comparison of the EM and the cryo-mechanical press test results, the relatively fast degradation of cable’s EM performance can mostly be reproduced by the changes in its mechanical properties during the transverse mechanical loading test. This potential relationship has a high reference value for the design of future conductors and the preliminary evaluation of electromagnetic cycles.
A structural model has been developed for the VIPER cable, which is based on the Twisted Stacked-Tape Cable (TSTC) design and has four slots each containing 50 REBCO HTS tapes. Each slot contains a TSTC and the entire void space is filled with solder. The four slots are arranged around a central cooling channel. It is developed by Commonwealth Fusion Systems (CFS) in collaboration with the Plasma Science and Fusion Center (PSFC-MIT) [1]. The VIPER cable was designed for use in the Central Solenoid and Poloidal Field coils of the SPARC tokamak experiment. During the manufacturing and the operation of the magnets, the cable will experience including bending to the shape of the coil, cool down, and cyclic transverse compressive Lorentz loading. Understanding the stresses generated in the HTS tape-stacks during these conditions is crucial for characterizing the cable’s performance and optimizing its design.
In this work, structural finite element analysis is used to simulate the stresses incurred within the tape-stacks of the VIPER cable under the following conditions: as the cable is (1) bent to the 1 m diameter specified for the central solenoid, (2) cooled down to its operating temperature (10 K), and (3) subjected to a transverse Lorentz load during operation. The simulations are used to investigate the mechanical effects of the solder impregnation onto the tape stacks during bending and cool down. In addition, results obtained in this work shed light on the early-stage critical current degradation observed experimentally in the VIPER cable during the first 10 cycles of Lorentz loading (400 kN/m) [1]. The numerical modeling provides important information on the strain state of the tape-stacks and insights on the optimization of future configurations.
[1] Hartwig, Zachary S., et al. "VIPER: an industrially scalable high-current high-temperature superconductor cable." Superconductor Science and Technology 33.11 (2020): 11LT01.
A REBCO bulk magnet can make a higher magnetic field than the existing permanent magnets and electromagnets. Recently, various applications of the bulk magnet, such as a compact NMR/MRI system, a magnetic separation system, a generator for a large-scale wind turbine, an electric motor for a ship propulsion system, an aircraft electric population system, and so on, have been developed and considered. In the application to an aircraft electric motor, for instance, the power density, which is an electrical output per unit weight, is a significant parameter. That is, a minimization of the size and weight is required. When applying the bulk magnet to the motor and generator, its magnetization is an important problem. Then, the bulk as a field magnet is activated by the iron-cored field winding as an armature. Although an increase in the size of the soft-iron yoke leads to an increase in the magnetic field, the total weight of the system is also increased, and thus, the power density is decreased. Furthermore, a magnetization method is limited to pulsed field magnetization (PFM) due to a structural restriction in which a bulk must be cooled continuously and must be excited on-site. We study to improve a trapped field of REBCO bulk activated by PFM. The soft-iron yoke is used to expose the sample to a large amount of magnetic flux for a long time. We paid attention to the yoke and investigated the influence of its size and shape on the magnetizing characteristics. In our previous study, we estimated trapped-field performance when using disk-, ring-, and cross-shaped yokes experimentally. This paper investigates numerically the magnetizing characteristics when REBCO is magnetized by PFM with different shaped yokes.
A magnetic flux lens (MFL) exploits the induced screening current during an in-situ zero field cooling magnetization process to enhance the local flux density. It is a passive device being equivalent to an inner coil of a hybrid magnet. However, it requires no power supply and quench protection.
The magnetic flux lens has been first realized by using bulk HTS superconductors, and been recently extended to a novel hybrid magnet combining both trapped field magnets and magnetic flux lens. However, the flux instability and the limited mechanical strength of such a device restricted its high-field application. In this work, we demonstrate the design of a flux lens using stacked HTS tapes for high-field magnet. The numerical simulation shows that the stacked-tape MFL can perform effectively to enhance the central field by 50 % under magnetic field lower than 10 T, and by more than 10 % under field higher than 20 T which is still considerable. Further improvements can be realized by optimizing the design of the MFL. We will also show the results of our preliminary tests of a stacked MFL to verify the numerical simulation.
Iron-based superconductors (IBSs) are regarded as promiscing candidate for high magnetic field applications because of its relatively high superconducting transition temperature (Tc), and nearly isotropic upper critical field (Hc2) ~100 T. Amoung various IBSs, AEAFe4As4 (AE = Ca,Sr,Eu, A = K, Rb, Cs, 1144)[1] superconductors are one of the most recently developed IBSs with several unique features. The Tc, Hc2 and of 1144-type compounds are comparable to those of (Ba,K)Fe2As2, which is regarded as one of the best compound for high field applications. The CaK1144 have also unique features such as less compositional fluctuations due to large diffrence of ionic radii of AE and A, and existence of intrinsic defect structures found by STEM observations[2]. These features of the compound could be promising up to intermediate temperatures that are accessible with cryo-coolers. On the other hand, several trials of making CaK1144 as the wires and tapes were already attempted while the critical current density (Jc) performance is not so high due to reaction of CaK1144 with Ag sheath.
Recently, we have succeeded in synthesizing high density CaKFe4As4 bulks by the spark plasma sintering (SPS) method[3]. SPS synthesis allows complete dentification in a very short time, thus avoiding phase decomposition of CaK1144 phase. The relative density of the samples exceeds 95 % of theoretical CaK1144 density. The magnetic Jc of the SPS bulk sample reached 18 kA cm-2 at 4.2 K under 5 T. In this presentation, I will summarize the current situations and recent progress of bulk fabrication of CaK1144 superconductors.
REBa2Cu3Oy (RE123) melt-textured bulks are expected for high field applications using their excellent field trapping properties. RE123 melt-textured bulks are typically fabricated using the Top-Seeded Melt Growth (TSMG) or Top-Seeded Infiltration Growth (TSIG) method where bulks are melt grown from the seed crystals placed on top of the pellets, which results in bulks consisting of both a-growth and c-growth regions. Because of the different Jc-B properties between the two regions, it is usually difficult to design and fabricate bulks showing uniform trapping field properties. In addition, although enlargement of the bulk-size is a direct and effective way to improve trapped fields, it is not easy to increase bulk-sizes by TSMG or TSIG methods because the random nucleation is likely to be triggered by the supercooling especially at the outermost regions of the bulks.
In the present study, we will present trapping field properties of all c-grown RE123 melt-textured bulks prepared using the Single-Direction Melt Growth (SDMG) method which we have developed for the last few years. In the SDMG process, RE123 melt-textured bulks are only grown vertically, i.e. one direction, from the seed plates cut from the large melt-textured bulks utilizing the difference in peritectic temperatures of RE123 with different rare earth elements, resulting in bulks wholly consisting of c-growth regions. In addition, the SDMG method is suitable for fabrication of large bulks because the crystal growth time does not depend on the bulk diameter. In this study, Y123 and Dy123 melt-textured bulks were grown on Gd123 and Eu123 seed plates provided by Nippon Steel Co., respectively. The critical current properties and trapping field characteristics of these SDMG bulks will be presented.
The cost of high-field NMR systems has led to the development of low-cost ‘benchtop’ instruments for use by academic and commercial institutions. Whilst these devices have made NMR-spectroscopy more accessible, their use of permanent magnets limits the available resolution. Bulk high temperature superconducting (HTS) materials offer a route to bridge the performance gap to high-field devices.
Stacks of bulk HTS rings, magnetized in a NMR-grade field, have been demonstrated for use in NMR/MRI [1]. However, for practical applications, a low-cost, portable magnetization technique such as pulsed field magnetization (PFM) will be required. PFM has been shown to successfully magnetize disk-shaped HTS bulks, but is prone to inducing thermomagnetic instabilities (flux jumps) in rings, which can severely affect the trapped magnetic field [2]. Even if flux jumps can be avoided, the growth process of single-grain HTS bulks introduces local non-uniformity in the critical current density distribution. This impacts the flow of the supercurrent within the ring when magnetized and can introduce higher-order spherical harmonics to the field trapped in the bore of the ring.
Here we use finite-element models to investigate the impact of the size of circumferential inhomogeneity of the critical current density within the ring on the trapped field properties for both quasi-static magnetization and PFM. Following this, the models are extended to analyze techniques to mitigate the effects of the current inhomogeneity. Finally, we will compare the obtained results with the requirements for benchtop NMR, and discuss the implications of this for such benchtop devices.
[1] T. Nakamura et al., “Development of a superconducting bulk magnet for NMR and MRI,” J. Magn. Reson., vol. 259, pp. 68–75, 2015.
[2] D. Zhou et al., “Flux jumps in ring-shaped and assembled bulk superconductors during pulsed field magnetization,” Supercond. Sci. Technol., vol. 33, no. 3, p. 034001, 2020.
REBa2Cu3Oy(RE123, RE: rare earth element) melt-textured bulks are used as superconducting magnets using their high field trapping (BT) properties. Their BT performances are enhanced by both enhancement of critical current density (Jc) and an increase in size of the bulks. We prepared all c-grown Gd123 melt-textured bulks grown on a Eu123 melt-textured bulk as a seed plate using newly developed Single-Direction Melt Growth (SDMG) method. This method is particularly unique in that RE123 melt-textured bulks are grown only vertically from the seed plate cut from the large RE123 melt-textured bulks having higher peritectic temperatures. Therefore, melt growth proceeds in one direction on a large bulk plate, which enables both flexibility in shapes and short-time fabrication of large bulks. In this study, improvement of BT properties by control of starting metal composition and additions of pre-sintering or pre-melting process prior to the melt-growth was attempted. Jc-B properties of small pieces cut from bulks starting from Ba-rich compositions (Gd : Ba : Cu = 1.25 : 1.75+x : 2.5 (Gd123 : Gd211 = 7.5 : 2.5), x > 0) were improved compared with standard Gd123 bulks with x = 0, suggesting that RE/Ba substitution was suppressed by excess Ba compositions. In addition, introduction of the pre-melting process (1055°C in air) was more effective to achieve high Jc rather than introduction of pre-sintering process (960°C in air). Improved BT distributions of Gd123 bulks grown by SDMG method will be also shown.
Single-grain REBaCuO superconducting bulks have significant potential as a trapped field magnet (TFM) because they can trap a magnetic field, BT, over several tesla. To enhance the BT value, reliable seeding methods for the fabrication of REBaCuO bulks is essential to increase critical current density, Jc. The top-seeded melt growth (TSMG) technique is a well-known growth method to fabricate large single grains [1]. The top-seeded infiltration growth (TSIG) technique is also a reliable, alternative growth method, which has shown the potential to provide a more homogeneous microstructure and improved Jc properties compared with TSMG bulks. [1]. In a previous study, we performed the pulsed field magnetization of YBaCuO bulks prepared by TSMG and TSIG using a solenoid coil, for which the TSIG bulks achieved a BT over 2 T at Ts = 40 K by single-pulse PFM due to a reduced temperature rise [1]. In addition to this, a split coil with a soft iron yoke can potentially achieve higher trapped fields in TSIG bulks as required for a wide range of applications [2].
In the present work, we performed PFM experiments on GdBaCuO superconducting bulks prepared by TSMG and TSIG using a split coil. A maximum trapped field, BTmax, over 3.5 T was achieved at Ts = 40 K on the TSIG bulk surface by single-pulse PFM. The magnetization efficiency (= BTmax / Bapp) for the TSIG bulks was higher than that of the TSMG bulks, where Bapp is the applied field when the maximum trapped field was achieved. The differences in the magnetization properties are discussed including critical current density, Jc (H), and field cooled magnetization (FCM) measurements.
[1] D. K. Namburi et al., Supercond. Sci. Technol. 33 (2020) 115012
[2] M. D. Ainslie et al., Supercond. Sci. Technol. 29 (2016) 074003
REBCO melt-textured bulks are expected for strong magnet applications utilizing their high field trapping properties. Typical REBCO melt-textured bulks consist of a-growth and c-growth regions depending on the growth directions from the seed crystal placed on top of the pellets. We have developed a new method, Single-Direction Melt Growth (SDMG) method, for fabricating REBCO bulks wholly consisting of c-growth regions by using a large textured seed plate placed beneath the pellets [1]. Since the crystal growth proceeds only in the vertical direction, this method enables short-time growth of the large bulks regardless of the diameter of the bulks. In this presentation, we will report an attempt to fabricate large REBCO (RE = Y, Dy) melt-textured bulks with the size up to ~30 mm$\phi$ by SDMG method using single or multiple sintered pellets. It should be noted that superconducting joints among adjacent pellets are easily and reproducibly achieved applying the SDMG method. We will discuss the prospects for SDMG bulks based on their trapped field characteristics and microstructures.
[1] T. Motoki et al., Appl. Phys. Express 13 (2020) 093002.
Acknowledgment
This work was supported by the JSPS KAKENHI, grant number 19K05006, Japan.
We have been developed the compact NMR magnets consisted of the stacked high temperature superconducting (HTS) bulks trapped by a field cooling (FC) method. The HTS bulk annuli magnet for compact NMR relaxometry operating in liquid nitrogen was analytically designed and experimentally demonstrated. On the other hand, the high-quality magnetic resonance imaging (MRI) techniques can provide precise anatomical details of small extremities such as hands and feet. The low temperature superconducting (LTS) magnets cooled by liquid helium are used as conventional MRI systems and these MRI systems occupy a large amount of space. Therefore, we have been developing a compact and high-performance desktop finger MRI system using HTS bulks. The proposed HTS magnet is cooled by cryocooler and will be operated from 20 K to 40 K. The target values for magnetic field strength and field homogeneity in a cylindrical measurement space 20 mm in diameter and 10 mm in height without other magnetic field compensation methods are 3 T and 100ppm/cm2, respectively. Therefore, in this study, the structure and field properties of the HTS bulk magnets were designed and analytically calculated by the 3-D FEM. A face-to-face type HTS bulk magnet was proposed as the basic structure for the compact MRI magnet due to the limitation of the HTS bulk size. The minimum distance between the HTS bulks was set to 70 mm, and the shape of the HTS bulks and the characteristics of the critical current density were used as parameters. It was possible to improve the magnetic field homogeneity of the proposed HTS bulk magnet by assembling several bulks having different critical current densities. The designed structure of HTS bulk magnet for compact MRI and its calculated field performances will be presented.
REBaCuO, where RE denotes rare-earth elements, superconducting bulk materials are promising for high performance magnets that can trap large magnetic field in compact space. REBaCuO bulk materials are subjected to electromagnetic force and thermal stress in the devices. The electromagnetic force and thermal stress increase as the bulk size and critical current become larger. Thus improvements of the mechanical properties of REBaCuO bulk materials are useful for the development of high-performance devices. REBaCuO bulk materials are single-grain and they are fabricated by melt-processing using a seed crystal. REBaCuO bulk materials fabricated through conventional melt-processing contain pores that cause degradation of mechanical properties. On the other hand, low porosity bulk materials can be fabricated by infiltration growth technique. While conventional melt-processing uses single precursor, infiltration growth technique uses stacked precursor that consists of liquid phase source and solid phase preform. In this study, in order to investigate the mechanical properties of (Gd,Y,Er)BaCuO bulk materials fabricated by infiltration growth technique, tensile tests were carried out for the specimens cut from the bulk materials. After the tensile tests, porosity of the specimens were evaluated and the relationship between the tensile strength and porosity inside the bulk materials was investigated. Tensile strength increases with decreasing the porosity, which is due to the increase of net cross-sectional area and reduction of defects where the stress concentration occurs. Tensile strength of the (Gd,Y,Er)BaCuO bulk materials are comparable to those of other REBaCuO bulk material fabricated by infiltration growth technique and an REBaCuO low porosity bulk material obtained through melt-processing in oxygen atmosphere. Fracture mechanisms of the low porosity bulk materials will be discussed in association with the microstructures.
To magnetize superconducting bulks in a more cost-efficient way, pulsed-field magnetization (PFM) is a promising method using a conventional solenoid coil on a laboratory scale. The trapped field, BT, by PFM of a ring-shaped bulk reported to date is around 0.3 T at 60 K, which is quite low compared with that of field-cooled magnetization (FCM), as well as disc-shaped bulks by PFM. The reason for such a low BT is due to large local heat generation due to the rapid movement of flux inside the bulk [1]. Numerical modelling suggested that mechanical fracture is unlikely to occur during PFM because of a relatively small electromagnetic stress within the fracture strength limitation of the bulk material [2]. However, we have observed, experimentally, the fracture of a ring bulk with a large bore during PFM. Thus, it may be required that the thermal stress due to the local heat generation be incorporated in the modelling, which can simulate more realistic conditions in order to clarify the mechanism of the fracture and stress variation during PFM.
In this work, we performed PFM experiments on a GdBaCuO ring bulk (60 mm in O.D., 36 mm in I.D.) for various applied fields, Bapp, and initial temperatures, Ts. As a result, at Bapp = 3.88 T and Ts = 40 K, a flux jump and mechanical fracture occurred in the ring bulk. Numerical simulation of the mechanical stress due only to the local heat generation was performed, in which the width of the localized heated region and the maximum temperature were changed. The possibility of mechanical fracture of the ring bulk due to the local thermal stress during PFM is discussed.
[1] V. S. Korotokov et al., Supercond. Sci. Technol. 30 (2017) 095004
[2] T. Hirano et al., J. Phys. Conf. Series 1559 (2020) 012027
MgB2 in bulk form shows great promise as a trapped field magnet (TFM) as an alternative to bulk (RE)BaCuO materials to replace permanent magnets in applications such as desktop high-field magnet systems and rotating machines. In addition to being inexpensive and lightweight, they exhibit a number of additional advantages: a long coherence length, smaller anisotropy, strongly-linked supercurrent flow in untextured polycrystalline samples, and the relative ease of fabrication has enabled a number of different processing techniques to be developed.
In this presentation, we investigate the thickness dependence of the trapped magnetic field in bulk MgB2 superconductors. Two bulk MgB2 samples, 20 mm in diameter and 10 mm in thickness, were fabricated using the powder-in-closed-tube (PICT) technique. The trapped field was then measured after field-cooled magnetisation for thicknesses of 20 mm (both bulks stacked), 10 mm (single bulk), and then 7.5, 5, 4, 3, 2 and 1 mm, for which the sample was machined down to the designated thickness using an automated-wet-polishing technique.
A 2D axisymmetric finite-element model based on the H-formulation is used to simulate the experimental results and explain the observed thickness dependence of the trapped field. The numerical results, which assume a Jc(B) dependence based on the measured characteristics of small specimens taken from the bulk before and after machining, suggest that gradual degradation of Jc occurred with machining and hence reducing thickness. When accounting for this, the models and experiments showed excellent agreement. Consistent trapped field measurements on the top and bottom surfaces suggest this degradation occurred globally, rather than local to the machined surface.
ACKNOWLEDGEMENTS
1. EPSRC Early Career Fellowship, EP/P020313/1
2. JST CREST (JPMJCR18J4), JSPS KAKENHI (JP23246110, JP21H01615)
3. Prof. K. Kishio for advice and Mr S. Sugino for experimental assistance
In a big admount of superconductive applications it is necessary to introduce an high temperature superconductivity stage, in order to realize the current lead.
In particular, in the superconductivity industial applications, it is also necessary to find the best compromise between the cost and the technical performance.
This paper presents the result of a geometrical and soldering techniques optimisation in order to built an high current superconductive lead minimizing the admount of the expansive materials and avoiding the use of the helium gas.
As is known, heat losses through current leads largely determine the economic efficiency of the superconducting systems. Much attention is paid to the design of optimal current leads, but the benefits of standard approach are physically limited by the Wiedemann-Franz law. An innovative way to further reduce heat inflow is to use current leads equipped with Peltier thermoelectric elements. These elements are connected in series in the power circuit. Therefore, the thermoelectric effect counteracts the heat flow caused by the temperature gradient in the current lead when the transport current passes through the Peltier element. Another advantage of this design is that when the circuit is de-energized the heat loss is reduced due to the low thermal conductivity of the Peltier elements. In addition to theoretical works devoted to the Peltier current leads (PCLs), a number of experiments were carried out confirming a decrease in heat loss by about 30%. Moreover, PCLs were installed on 500- and 1000-meter HTS power transmission lines in Ishikari (Hokkaido, Japan). Further improvement of the characteristics of the PCLs can be achieved by cooling the current-carrying parts with evaporating nitrogen. In this work, experiment on testing gas-cooled PCLs was carried out for the first time. A 20% additional reduction in heat inflow was achieved. At the same time, the dependence of the specific heat loss on the current became flatter, which means an expansion of the operating current range. In the experiment, the vented gas passed through copper pipes used as conductors. To increase the efficiency of the gas-cooled PCLs, it is necessary to improve the heat transfer between the gas flow and the conductor by means of surface ribbing.
Superconducting (SC) current feeder system is an integral part of a large-scale superconducting magnets based machines like a tokamak or accelerator. One end of the SC feeder is connected to SC feeder of magnet and another end is connected to the power supply via current leads for powering the magnet. So far, low temperature superconductor (LTS) is the popular choice for such applications. Magnesium diboride (MgB2) considering its lower cost, superconducting transition temperature of 39 K, ductile nature and ease of availability, is now gaining wide attention for SC feeders system. To assess its suitability, we report 1-D thermo-hydraulic study of 10 kA rated MgB2 current feeders system cooled with 20 K helium for SST-1 tokamak as a case study. The temperature margin and corresponding pressure drop along this feeder are calculated for mass flow rates ranging from 0.3 g/s to 1.0 g/s helium at 20 K, 4 bar (a) with a cooling inlet from magnet side. It yields a temperature margin of 6 – 16 K across the entire length of feeder depending up on mass flow rate of helium. There is a possibility of cooling the binary current lead (HTS + MgB2) from cold helium coming out from the feeder. From our study, MgB2 current feeder system provides benefits of higher temperature margin, lower mass flow requirement and cryogenic savings by use of 20 K helium as coolant compared to existing NbTi based feeders. In future, it could provide a safe, reliable and cryogenic operational cost saving solution for SC current feeders for Tokamak applications.
A major focus of Nb3Sn high field accelerator magnets for HEP is on significantly reducing or eliminating their training by understanding the underlying physics mechanisms. We have been are investigating whether mixing organic olefin-based thermosetting dicyclopentadiene (DCP) resin, commercially available as TELENE○R by RIMTEC Corporation in Japan, with high heat capacity ceramic powders, increases heat capacity Cp of impregnated Nb3Sn. Using a high Cp DCP resin as impregnation material for Nb3Sn magnets is expected to considerably increase the specific heat of the superconducting coil package when compared with standard impregnation epoxies (CTD-101k). This novel technology will contribute to reduce Nb3Sn superconducting magnet training at a minimum cost.
The high heat capacity resins in this study were fabricated by a combination of a ceramics powder filler and the DCP resin. The DCP resin is typically cured by the use of an additive, which is the ruthenium complex. The curing time is controlled by the amount of retardant. The powder filler is selected among high heat capacity ceramics, such as Gd2O3, Gd2O2S, and other magnetic regenerating compounds. Al2O3 and SiO2 powders are used for standard fillers as a comparison. These powder fillers are mixed with the DCP resin by using a planetary mixer. The viscosity, heat capacity, thermal conductivity and other physical properties of the DCP resins with powder fillers were measured in this study.
High field resistive magnets use Cu matrix composites as conductors because composites conductors have high mechanical strength. The conductors are manufactured by cold deformation that introduces high densities of obstacles to resist dislocation motions. The increased density of these obstacles increases the mechanical strength of the conductors. Under cyclic loading, such as the loading condition in pulsed resistive magnets, the conductors may soften or harden depending on the interaction of the obstacles with the dislocations evolved during the loading. Understanding and predicting the performance of the conductors under cyclic loading helps researchers to predict the life of the coils made from these conductors and make efficient use of them in magnets and to manufacture conductors to meet the requirements of the magnets, particularly when the magnetic stress is above the yield strength of the conductors. The goal of this research is to understand the fatigue properties of selected composite conductors and to relate such properties to types of obstacles. The fatigue test loading is in displacement-controlled mode, which is like what occurs in a state-of-the-art pulsed magnet. This work sheds a light on the correlation between the tensile and fatigue properties in composite conductors by consideration of types of obstacle in composite conductors.
Acknowledgements
This was performed at the National High Magnetic Field Laboratory, USA, which is supported by National Science Foundation Cooperative Agreement [Grant No. NSF DMR-1644779] and the State of Florida, USA.
With commercialization of high temperature superconducting (HTS) RE (RE= rare earth) Ba-Cu-O tapes, it is extensively applied in the superconducting magnets with high magnetic field due to its high critical current density and excellent mechanical properties compared to low temperature superconducting (LTS) conductors. However, it is difficult to realize the persistent current mode (PCM) because of the immature superconducting soldering technique comparing with the conventional LTS magnet. Bitter-like HTS magnet stacked by annular REBCO plates and magnetized by flux pump or field-cooling is a promising to overcome such drawbacks without joint resistance. This paper firstly presents. This paper firstly takes the anisotropic characteristics into account to present the electromagnetic characteristics of a Bitter-like HTS magnet simulated by COMSOL software. After a mini-model Bitter-like HTS magnet is designed and fabricated by stacking annular HTS plates made from wide REBCO tapes, experiment on its electromagnetic characteristics is performed in 4.2 K with thermal switch excited by flux pump in order to validate the simulated results. Results show that Bitter-like magnet can be excited by flux pump with thermal switch, and HTS magnet stacked by many annular plates can operate in PCM without current leads and avoid soldering bottleneck without resistance comparing to conventional HTS magnet operation.
Index Terms: Bitter-like HTS magnet, electromagnetic characteristics, persistent current mode, REBCO annular plates, thermal switch.
Consumable pulsed magnets at the Pulsed Field Facility usually use a considerable amount of G10 fillers to create smooth and strong winding transitions from one layer to another. These fillers typically have complicated shapes to fill all the gaps at the transitions. They are expensive and time-consuming to fabricate. Even machining G10 is hazardous and unfavorable. G10 material was chosen because of its excellent mechanical and dielectric strengths in liquid nitrogen which is used to cool magnets down. In this paper, we investigate the possibility of replacing G10 material by a few glass fiber-filled thermos-plastic materials which can be used to fabricate fillers by the 3D printing technique. This replacement will significantly reduce the material cost for our consumable pulsed magnets. Nylon and Polyether Ether Ketone (PEEK) materials filled with chopped E-glass fibers will be used to 3D print the samples. The mechanical and thermal properties of the samples will be measured at temperatures between 77 K and 300K, and for directions parallel and perpendicular to the printing direction of the samples. The outcome of this study will also help to evaluate the possibility of using these 3D printing materials for other cryogenic applications such as experimental probes or parts for superconducting magnets.
One of the problems with a superconducting magnet is heat leak from the external environment to the inside of the cryogenic devices. In order to suppress the heat leak, the wireless charging has been proposed. Therefore, superconducting diode is expected as a novel rectifying element operating at cryogenic conditions [1]. In our previous study, we reported that YBa2Cu3Oy(YBCO) films grown on PrBa2Cu3Oy (PrBCO) buffer layers showed an asymmetric critical current Ic for current polarity which was enhanced by the small lattice strain [2]. In this study, we investigated the asymmetric Ic of superconducting diodes at various magnetic fields and temperatures, and investigated the optimal operating conditions toward the superconducting magnet applications.
The YBCO/PrBCO films were fabricated on IBAD substrates using the pulsed laser deposition method. Current-voltage characteristics including the reverse current were measured at 0-10 T and 10-88 K at High Field Laboratory for Superconducting Materials (HFLSM). The asymmetricity is defined by the ratio of the difference and average of the Ic for different current directions.
The asymmetricity had a peak of the magnetic field dependence at 0.1-0.2T, which is defined as a peak field. The peak field increased as the temperature became lower. It showed a peak of the temperature dependence at 70 K with the maximum value of 105.3 %. We will discuss the optimal operating conditions of the YBCO superconducting diode grown on PrBCO buffer layers toward the wireless power transfer superconducting magnet.
This work was partly supported by JSPS-KAKENHI (20K15217, 20H02682), JST-A-STEP, and NEDO. The metal substrates were provided from Dr. Iijima of Fujikura Ltd. This work was collaboration research with HFLSM in Tohoku University.
Reference
[1] S. A. Harrington et al.: Appl. Phys. Lett. 95, 022518 (2009).
[2] A. Mizuno et al.: Abstracts of ISS conference (2020).
Superconducting magnets for high-intensity accelerators and secondary particle sources are being required to operate in the high radiation environment by beam collisions and beam losses. Neutron fluence in the high-luminosity LHC and the COMET experiment is expected to exceed $10^{21}$ $n/m^2$. The stabilizer of superconductor is made of pure copper and aluminum and should degrade by such high radiation. Series of irradiation tests were accomplished to evaluate the degradation at cryogenic temperature. The effect of repetitive cycles of irradiation at cryogenic temperature and anneal at room temperature on stabilizer materials of copper and aluminum were measured using reactor neutrons at KUR. Also, pure metals are irradiated at cryogenic temperature by high-energy protons at J-PARC. This paper will review the results of repetitive irradiation tests on copper and aluminum with reactor neutrons and accelerator protons.
Based on finite element method (FEM) and difference method, a simulation method for the quench behavior of superconductors is introduced in this paper. With this method, the heat conduction equation of a superconductor under a thermal disturbance can be solved simply and visually. The stability of an REBCO high temperature superconducting tape under adiabaticapproximation is simulated, and results are in good agreement with experimental results. Based on this simulation method, two-dimensional even three-dimensional model of superconductors adiabatically or non-adiabatically can also be developed. It is very important to study the electromagnetic characteristics of superconductors under thermal disturbances and develop superconducting magnets with high stability.
Previously we reported our new circuit model, named as “B model”, for fast and effective simulation of a no-insulation (NI) high temperature superconductor (HTS) coil having a “single” defect. A primary benefit of the “B model” over the conventional distributed network model is to use only “five segments” of the defect-existing turn in an NI HTS coil, while a substantially larger number of turn segments is commonly required to the conventional network model. As a sequel to our previous study, here we report an upgraded version of our B model, named as “Adaptive B model”, for simulation of an NI HTS coil having “multiple” defects. To validate our new model, an NI HTS coil having 3 or more defects was constructed and its electromagnetic responses were measured for comparison with calculated results by use of our new model. For further verification, we also performed the comparison of simulation results between our new Adaptive B model and the conventional distributed model.
Acknowledgement
This work was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-09.
Abstract
This work presents an experimental study on electromagnetic and thermal behaviors caused by a quench propagation on a no-insulation (NI) high temperature superconductor (HTS) coil. To observe quench behaviors of NI HTS coil, 25-turn NI single pancake test coil was wound, and an overcurrent experiment was performed in conduction-cooled condition. Since the quench is a local and time-varying phenomenon, an integrated multi-physics distributed-circuit model, which consists of an electric circuit and thermal circuit, was adopted to analyze spatial and transient characteristics. The voltage difference between consecutive turns, the magnetic field at the center of the coil, and the temperature at every five turns were respectively measured by inserted voltage taps, a Hall sensor, and thermocouple taps in order to validate multi-physics distributed-circuit model. Considering not only conduction but also Joule heating computed by local voltage and current distribution, the quench propagation, which can be detected by local temperature variation, was analyzed.
Acknowledgment
This work was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-09.
High-temperature superconducting REBCO coated conductor is one of the main candidates for next-generation high field magnets in fusion reactors and particle accelerators owing to their high current-carrying capability. While these materials can operate at higher temperatures and generate higher magnetic fields than their counterparts with lower critical temperatures, protecting the REBCO magnet against quench is challenging. A variety of candidate technologies that may be able to enable self-protection, including no-insulation technology and insulative coatings with temperature-dependent resistance, are in development. In order to understand the current sharing and thermal processes during a quench, we model a REBCO pancake coil as an electrical circuit, and simulate current distribution using NGSPICE, considering the power generation and heat transfer between conductor turns. The magnetic field and coil terminal voltage predicted by the simulation was compared to published experimental results. Our results provide useful insights into how current sharing occurs and the impact of electrical contact contact resistances between conductor turns.
Conductor on round core (CORC) cables composed of YBCO coated conductors and a former show significance in high current capacity and mechanical flexibility. However, YBCO coated conductors are vulnerable to a local quench, and this disadvantage can affect the thermal stability of the CORC cables. Therefore, this paper first develops a 3D electromagnetic-thermal cable model with the termination resistance considered. Then, we implement a hotpot on one of the superconductors, and the shrinking, the stationary, and the expanding normal zones are respectively observed. The minimum quench energy (MQE) as a function of the transport current to its critical current is investigated. Meanwhile, we are monitoring the current redistribution among superconductors through cable terminals during the quenching process. The MQE with respect to the terminal resistance is to be shown. Finally, we will explore the effect of inhomogeneous terminal resistance on the CORC cable’s quench behaviour. The MQE is expected to improve with a decreased transport current and a lower termination resistance.
The No-insulation (NI) coil's turn-to-turn current paths prevent local heating by forcing the current to bypass into nearby turns when a hot spot appeared in a coil. However, the bypassing current will reduce the magnetic field that generates unwanted induced currents in the adjacent coils in a multiply-stacked HTS magnet. This induced current can temporarily exceed the designed maximum currents in the NI coils, which can damage the magnet. A partial-insulation (PI) coil, in which a single or multiple insulated, with a polyimide-like material, is inserted in the coil to hinder the current paths, can reduce the peak induced currents in the NI HTS coil's current paths. In this paper, we present the results of a simulation study on the peak-induced current upon a quench of the PI HTS magnet with multiple stacks. The study shows that the peak-induced current varies with insulation location, number of the insulated turns, and quench initiation location. We will also briefly discuss the differences in the hot spot behavior of PI and NI.
Acknowledgment: Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R01GM137138.
Chris Reis1,2, Laura Garcia Fajardo1, Tengming Shen1
1. Lawrence Berkeley National Laboratory, Berkeley, CA, 94720
2. University of California, Berkeley, CA, 94720
High temperature superconducting magnets have the potential to generate magnetic field of greater than 20 T for compact fusion reactors, particle physics colliders and nuclear magnetic resonance. A key remaining technology challenge is the quench detection and protection; the difficulty is mostly due to the low normal zone propagation velocity, on the order of cm/s. In this presentation, we report 4.2 K experimental data of a dozen of thermal runaway quenches of a prototype 1.64 T canted-cosine-theta dipole magnet constructed from a high temperature superconducting Bi-2212 Rutherford cable. We provided an analysis of the hot spot temperature reached, the size of normal zone, and how they vary with experimental parameters such as current ramping rate. An important question we try to answer is how large a safety margin we have with the quench protection scheme used (active energy extraction with a quench detection voltage of 100 mV and a dump resistor). We then discuss how a popular conventional quench protection analysis method widely applied for selection quench protection parameters for low temperature superconducting magnets, the MIITS method, should be modified for high-temperature superconducting magnets. We arrive at several recommendations of operation schemes, and a recommendation of a set of strategies for operating high-temperature superconducting magnets.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the U.S. Magnet Development Program, and a US-Japan HEP collaboration grant.
We designed and fabricated a prototype high temperature superconducting(HTS) sextupole magnet for the chromaticity correction of an asymmetric–energy collider, named SuperKEKB. The HTS sextupole magnet consists of six two-layer-rectangular REBa2Cu3Oy(REBCO) coils, which are wound with a 4-mm-wide coated conductor and impregnated with the epoxy resin. In this study, we measured quench characteristics of the two-layer-rectangular REBCO coil in order to confirm the applicability of a detection method using the balance voltage. The detection threshold was proposed by using the relation of the detecting condition and the maximum quench temperature. We also developed a numerical simulation code to clarify quench behaviors and to confirm the reliability of the detection method for the sextupole magnet. As the result, no coil degradation and burnout were observed in the quench test with the voltage detection method. The relation between the detecting condition and the maximum quench temperature was successfully determined from the experimental and simulation results. We confirmed the validity of the simulation code by comparing with the experiments. Finally, we proposed a detecting condition for the sextupole magnet to keep the maximum quench temperature below a design value of 200 K.
Implementing an efficient quench protection system in a classical insulated High Temperature Superconductor coil remains complicated and risky. Since about ten years, many groups have been working on novel windings consisting on removing the classical insulation between turns. This solution improves the thermal stability, and it avoids local degradations in case of a quench. One named them as “self-protected” coils as they do not need a dedicated safety system to ensure the quench protection. If such coils are much less sensitive to local burnings, the drawback is the loss of the control of the current path and all linked magnet aspects. It also induces new stresses distribution, which have to be mastered for designing a reliable magnet from a mechanical point of view. By setting appropriate value of the contact resistance, we can meet the different requirements.
This is why we have been developing since several years a multi-physics model dedicated to such coils. The model is built from a Partial Element Equivalent Circuit model coupled with a 2D finite difference thermal model and with a 3D magnetic model. This model makes possible to investigate the influence of the turn-to-turn resistance.
In this article, we present the thermo-electric behavior of a pancake with different values of the radial contact resistance. We consider different transient cases from the simple driven charge-discharge to the local quench inside a pancake. We then extend the model to a magnet made of several pancakes supplied in series; allowing to observe the temperature distributions, the radial and azimuthal current of each turn of the pancakes due to a source term generated on a sector of one of the pancakes. Finally, we present the results for the quench of a simple racetrack.
In this paper, we present results, analytical and experimental, of two dimensionally identical 1.5 T NbTi coils with a 2-T peak field, operated in the 4.2-6 K range, one impregnated with paraffin and the other solid nitrogen (SN2). In the paraffin coil, the paraffin prevents conductor motion and the coil operates stably in the temperature range. In the SN2 coil, although not as strong as paraffin, the SN2 provides a sufficient enthalpy, stored within the close-pack hexagonal formation, enabling the coil to operate stably. To further demonstrate beneficial effects of SN2 for magnet stability, one of the coils will also be operated without impregnation, paraffin or SN2, in liquid helium (LHe) at 4.2 K: without mechanical support or enthalpy enhancement, we expect the LHe coil to quench prematurely.
Acknowledgement: Research reported in this publication was supported by the National Institute of Biomedical Imaging and Bioengineering under award number R01EB022062.
Improvement of mechanical stability of superconducting cables under high mechanical loads is one of the most important challenges for their industrial application. Provided that impregnation is commonly adopted to protect coil wound by superconducting tapes from mechanical disturbance caused by Lorentz force generated from magnetic field and rotational vibration of machines such as motor, this paper focuses on the selection of impregnation materials towards conductor on round core (CORC) cables. Electromechanical behaviors of CORC cable samples impregnated by different materials, including solder, paraffin wax and epoxy resins such as Stycast, are investigated using experiment and related fractographic observations. Testing results shows a wide range of variation in degradation of measured critical current, which may be attributed to delamination and cracks observed on HTS tapes of cable samples. Therefore, proper impregnation materials should be chosen to maintain electrical performance while enhancing mechanical strength of CORC cable. We expect conclusions obtained from this paper can provide guidelines for future fabrication of coil wound by impregnated CORC cables.
In general, the field coils of a superconducting motor or generator need to be impregnated with epoxy resin to protect the coils from mechanical stress occurring during rotation. Recently, various studies that have been conducted to optimize the epoxy impregnation method revealed that coils impregnated by the vacuum pressure impregnation (VPI) method have superior thermal and electrical properties. However, epoxy impregnation can either introduce a difference in the thermal contraction between the superconducting tape and epoxy resin or degrade the thermal conductivity. Therefore, the selection of an appropriate filler material is important. In recent years, we suggested the use of various filler materials with high thermal conductivity and superior mechanical strength with the aim of supplementing and enhancing the low thermal conductivity of epoxy resin. In this study, we investigated the effects of the addition of various fillers such as carbon nanotubes, boron nitride, and silver on the thermal and electrical properties of GdBCO coils. Using these epoxy composites, GdBCO coils were impregnated by the VPI method. In addition, cool-down tests, repetitive-cooling tests, and over-current tests were performed to evaluate the thermal and electrical stabilities of the coils.
< Acknowledgment>
This work was supported by the Korea Basic Science Institute under Grant D110200
When a hotspot occurs in a conduction-cooled HTS superconducting winding, decrease of heating at the hotspot and decrease of local temperature rise are necessary. In order to do that, good thermal conduction around the heat-source materials such as an electric-insulation film on the HTS tape and a non-metallic structural material is important. The electric insulation materials are generally not only low electric conductivity but also low thermal conductivity. If the material having both high thermal conduction and low electric conduction properties is used in the HTS superconducting winding, the hot-spot temperature can be effectively decreased. We have been developing the Vectran fiber reinforced plastic (VFRP) which has the property of high thermal conductivity. Vectran is the trademark of Kuraray Co., Ltd., Japan. First, we fabricated some round bars made of VFRPs, and measured thermal conductivity of the bars at cryogenic temperature. According to the measured results, the thermal conductivity of the VFRP bars was more than twice of that of the glass fiber reinforced plastic (GFRP). Next, the thermal contraction of the VFRP bars was experimentally obtained at cryogenic temperature; the bars expanded along the Vectran fibers, and contracted conversely around the bars during the temperature decrease. Finally, we brought sheets made of the Vectran fibers into contact with a winding pack in which some short-YBCO tapes were stacked, and made heating the winding pack with a local heater. In spite that the heating was same, the temperature rise under the contacting of VFRP sheets were lower than that under the contacting of GFRP sheets. From those experimental data, we think thermal stability of the conduction-cooled HTS coils increases as the result of use of high thermal FRPs and sheets made of Vectran fibers.
Abstract—With higher critical current and temperature, 2G HTS tapes are hopefully applied in power system, such as HTS cables, transformers and generators. 2G HTS tapes usually transmit alternating current in power system. Although DC current transmission capacity of 2G HTS tapes is easily attained by critical current experiment, AC current transmission capacity of them has not been determined. In the paper, AC current transmission capacity of two types of 2G HTS tapes was investigated. In this study, the maximum AC current that 2G HTS tapes could transmit was determined, exceeding which HTS tapes cannot operate stably. AC loss would be generated in 2G HTS tapes under AC current, which could influence AC current transmission capacity. AC current transmission capacity and AC loss of 2G HTS tapes were measured under different frequency and refrigeration conditions. The obtained AC current capacity were compared with critical AC current based on the loss concept method. The experimental results were very significant for 2G HTS tapes used in power system.
Index Terms—2G HTS tapes, AC current transmission capacity, AC loss, AC critical current, different refrigeration conditions
A major problem of state-of-the-art Nb3Sn accelerator magnets is their long training due to thermo-mechanical perturbations. Increasing the specific heat, Cp, of the Rutherford cable would reduce and/or eliminate training by limiting its temperature rise. This paper studies feasibility of increasing the Cp of Nb3Sn Rutherford-type cables by using composite Cu/Gd2O3 and Cu/Gd2O2S tapes produced by Hyper Tech Research, Inc. Nb3Sn wire and cable samples outfitted with these high-Cp ribbons, or tapes, were prepared and tested at FNAL for the Minimum Quench Energy (MQE). The experiment was performed for both cases of localized and distributed disturbances.
A major focus of Nb3Sn high field accelerator magnets for HEP is on significantly reducing or eliminating their training. Samples of NbTi and Nb3Sn wires and Rutherford cables were impregnated with organic olefin-based thermosetting dicyclopentadiene (DCP) resin, commercially available as TELENE® by RIMTEC Corporation in Japan, mixed with high heat capacity ceramic powders. The high heat capacity resins in this study were fabricated at NIMS by a combination of a ceramics powder filler and the DCP resin. The DCP resin is typically cured by the use of an additive, which is the ruthenium complex. The curing time is controlled by the amount of retardant. The powder filler is selected among high heat capacity ceramics, such as Gd2O3, Gd2O2S, and other magnetic regenerating compounds. For impregnated wires samples, the Minimum Quench Energy was measured. In addition, a Transverse Pressure Insert (TPI) measurement system was used to characterize training-like behavior in each resin. For impregnated cables, a Rutherford cable test facility with superconducting transformer and spiral bifilar sample for cable tests up to 15 T and 30 kA was used to measure minimum quench energy of epoxy impregnated samples vs. TELENE® impregnated ones.
Recently, we proposed a novel winding technique, which entails employing grease materials as a turn-to-turn insulator to ameliorate the charging-discharging delay observed in no-insulation (NI) coils. As a result, we obtained coils that possess superior thermal and electrical stabilities without charging-discharging delays. However, because of the higher resistance of these grease materials as compared with HTS tape, the turn-to-turn resistance is high, which results in a small amount of current bypassing between the layers of the coil. Therefore, adding thermally and electrically conductive fillers to the grease could be an effective way to improve its properties. In this study, the quenching and recovery behavior of a GdBCO coil wound with grease that contains various fillers such as BN, CNTs, and Ag was examined with respect to the Joule heat energy induced by a local hotspot. Based on the experimental results, the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) of the coil were investigated. Furthermore, the feasibility of the proposed winding technique for the development of the GdBCO coil with extremely high thermal stability is discussed in detail.
<Acknowledgement>
This work was supported by the Korea Basic Science Institute under Grant D110200
MuSEUM experiment is in progress at J-PARC to measure the muonium hyperfine structure with a sensitivity as low as a few ppb. Muon g-2/EDM experiment is also planned in J-PARC to measure muon’s anomalous magnetic moment and electric dipole moment with an accuracy below 0.1 ppm. Both experiments require high homogeneous magnetic field below 0.2 ppm pp(peak-to-peak). Commercial MRI magnets successfully realize a homogeneity of several ppm in 40 cm DSV(Diameter Spherical Volume) by magnetic field shimming using iron pieces. An iron has a high saturation magnetization so that it is useful for magnetic field shimming from several hundreds ppm to several ppm. On the other hand, it is too high to perform fine shimming operation below 1 ppm. We have been developed a new shimming technique with materials having low saturation magnetization, that is, Nickle, magnetic fluid and magnetic putty. The latter two materials are commercially available. Those saturation magnetizations were measured at 1.7 T to use them for magnetic shimming, and about 19 and 22 % of iron for magnetic fluid and putty, respectively. The magnetic shimming test was performed using MRI magnet for MuSEUM experiment at 1.2 T with Ni thin plates and magnetic putty, and the homogeneities can be reached to 0.16 and 0.17 ppm pp, respectively.
This presentation reports the details of magnetic saturation measurement and shimming test with Ni, magnetic fluid and putty.
Experiments of g-2/EDM precise measurements are under preparation in J-PARC and they use a high field (3.0 T) muon beam storage magnet (MBSM) with a cylindrical fiducial volume with 3cm-radial width, 10cm-vertical (axial) height and 66.6 cm diameter with less than 0.2 ppm peak-to-peak magnetic field homogeneity. Muons will be injected through the spiral injection from the magnet top through iron-yoke, reducing axial momentum by the fringe field and will be stopped by a kicker radial field. However, there can be some error fields and some corrections of muon injection orbit are necessary. Then, the steering magnets (SMs) are under developments. They are planned to be placed inside and outside of the MBSM yoke. SMs should have active shield coils to avoid additional error fields from magnetic interactions with structural metals and inside one should be compatible with the high field. Then, they need active shields (ASs) and they are ASSMs. Under these specifications, the designs are undergoing. Such active shield coils can be seen in MRI scanner gradient field coils (GCs), in which precision magnetic field shieldings are necessary to obtain good MR Imagings. Expanded from the MRI GC design method, an ASSM design method has been developed and applied. The method defines a current carrying surface (CCS) on which shield coil pattern is designed. Since the CCS can be formed arbitral shape, the CCS can be tuned so that leak field is small. A trial design shield coil has small leak field and tuning of actual shield coil shape for ASSMs are undergoing.
MuSEUM experiment to measure the muonium hyperfine structure at 1.7 T, is planned at J-PARC. The objective is to measure hyperfine transitions in the ground state hyperfine structure interval of Muonium precisely. The essential parameter is the magnetic field homogeneity, which is required to be less than 0.2 ppm pp(peak-to-peak) within a spheroid region with an equational radius of 100 mm and a polar radius of 150 mm. A measurement system of magnetic field distribution using CW(Continuous Wave)-NMR probes with a resolution of less than 10 ppb are being developed to do the shimming operation of magnetic field and verify the magnetic field homogeneity. The 24 CW-NMR probes are aligned on a circumference of semi-ellipse to shorten measurement time in the present design. The probes are placed at a short distance each other, therefore, the effect of cross talk between probes has to be reduced. And also, the structural materials and electric circuit had better to be zero-susceptibility materials, otherwise the resolution would be reduced because of field distortion by those materials.
This presentation reports the development status of the measurement system.
In MuSEUM experiment at J-PARC, we are working on precise measurements of the muon hyperfine structure in the ground state. We are currently developing a device for experiments in a high magnetic field (1.7 T) in order to achieve higher precision than the previous experiments. For high-precision measurement of muon hyperfine structure, it is essential to improve the magnetic field accuracy in the muon capturing region (200 mm-300 mm area inside the rotating ellipse). In this experiment, it is required to keep the long-term stability of the magnetic field at 0.2 ppm peak-to-peak (hereinafter referred to as pp) during the experiment period while the spatial homogeneity is controlled below 0.2 ppm pp by adjusting the magnetic field using magnetic materials.
Long-term measurements of the magnetic field showed that the field changed with temperature. The factors that cause the magnetic field to change with temperature are considered to be the thermal expansion of the jig and the temperature dependence of the magnetization. Therefore, the magnetic field was measured while the jig was heated. From this result, we evaluate the temperature dependence of the magnetic field. In addition, we were able to separate the two factors of the temperature dependence of the magnetic field, which was concluded experimentally, from the simulation. From the above study, we discuss guidelines for improving the current system to achieve long-term stability of 0.2 ppm p-p for MUSEUM experiment.
The ITER outer vessel steady-state magnetic field sensors (OVSS) have been calibrated at Argonne National Laboratory’s 4 Tesla Magnet Facility, using a fixture and process developed by Fermilab. The OVSS consists of two bismuth Hall probe sensing layers and onboard thermocouple, designed to operate with a measurement error of 4 mT for the magnetic field up to 2.5 T at the OVSS location. To achieve this accuracy, the calibration requires metrology accuracy to 0.5 mrad, temperature measurement accuracy of 6 mK at controlled heating setpoints up to 104 degrees Celsius, and a calibrated magnetic field up to 3 T with a maximum error of 0.02 %. We will present how these requirements were achieved and the fixturing devised to allow the calibration process.
Acknowledgement:
This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. This material is based upon work supported by Strategic Partnership Projects Agreement No. FRA-2020-0005 (ITER Contract Number IO/20/CT/4300002162).
Disclaimer: This report was prepared by Fermi Research Alliance, LLC (FRA) on behalf of the U.S. Department of Energy (DOE), as an account of work sponsored by ITER Organization. Neither FRA, DOE, the U.S. Government, nor any person acting on their behalf: (1) makes any warranty or representation, express or implied, with respect to the information contained in this report; or (2) assumes any liabilities with respect to the use of, or damages resulting from the use of any information contained in the report. The views and opinions expressed herein do not necessarily reflect those of Fusion for Energy nor those of the ITER Organization.
In recent years, the REBCO tapes have a broad development prospect in the application of large high field magnets due to its high critical current density and superior mechanical property. Several conductors/cables with high carrying current capacity made of REBCO tapes, such as RACC, CORC, TSTC, RS, SSC, HTS-CroCo and Q-IS, are expected to fabricate cable-in-conduit conductor (CICC) or Rutherford. The critical bending radius of CICC is a significant parameter for the high field magnet design. This paper presents the bending characteristics of CICC based on Q-IS. Firstly, the CICC model is established in the finite element software to analyze the current distribution of CICC. A dummy CICC sample made from six Q-ISs arranged in the six helical slots is tested in the 77K to verify the feasibility of CICC simulation model. The bending diameter and current distribution of CICC at 4.2K under high magnetic field are simulated based on the verified model, which is useful for its application for the high field magnet.
Index Terms— Bending, critical current, cable-in-conduit conductor (CICC), Q-IS.
Manufacturing ReBCO tape into a cable structure is suitable for future magnet applications to carry large current and generate high magnetic fields. During cable manufacturing and operation, the ReBCO tape is subjected to combined axial tension, axial compression, bending, and torsion loads. Therefore, mastering the critical current of the ReBCO tape under axial strain is very necessary to design of the cable and the selection of the tape specification. The critical current (Ic) and n-value versus applied uniaxial strain were measured of ReBCO tapes produced by three superconducting manufacturers in China at 77K in self-field with the U-spring devices. The width of the ReBCO tape is from 3 mm to 5 mm, and the thickness of the substrate is from 25 μm to 60 μm. The critical current of most of the tapes is reversible under applied compressive strain. The width of the tape and the thickness of the substrate have an effect on the reversible tensile strain limit. The n-value of the ReBCO tape hardly depends on the strain condition.
The superior electromechanical properties (EMP) of REBCO coated conductor (CC) tapes made them enabled to be utilized in a wide range of practical superconducting applications such as coils, magnets, and generators. However, the extreme application environments degrade the current-carrying capabilities so it is important to develop a technique to evaluate the EMPs and their reversible limits for the design. Thus, the investigation of strain/stress dependence of critical current, Ic under different stress and strain modes, and a magnetic field is important. Moreover, understanding the Ic degradation behaviors of the CC tapes at the low magnetic field will provide an effective information in predicting the Ic behavior at operating conditions of a high magnetic field and low temperatures. The design data such as irreversible stress and strain limits (σirr/εirr.) for Ic degradation will further improve the design efficiency of superconducting devices. Therefore, in this study, the EMPs of the REBCO CC tape at 77 K were evaluated using our recently developed easy-to-use measurement system that can continuously measure variations in Ic while applying a load or deformation. Through the feedback control of voltages induced at the voltage taps on the sample under tensile load, it was possible to depict the Ic degradation behavior of the CC tapes due to the cracking of the REBCO film. Also, the strain sensitivity of Ic degradation under a magnetic field of differently stabilized HTS CC tapes can be evaluated.
Performances of ultra-high field superconducting magnets have been improving. On 2017, a world-record high magnetic field of 45.5 T was generated with insert no-insulation (NI) Rare-Earth Barium Copper Oxide (REBCO) pancake coils (14.4 T), called “LBC3”, and an outsert resistive magnet (31.1 T). After 45.5-T generation, the insert NI REBCO pancake coils were quenched, and plastic deformations of REBCO tapes were observed. Since the Hastelloy substrate of REBCO tapes are stiff, whose yield point is approximately 1 GPa, REBCO tapes have great mechanical properties as well as high critical current density and critical magnetic field. NI REBCO pancake coils showed their potential to generate an ultra-high magnetic field. However, after experiment, REBCO tapes were damaged in a several cases, e.g. the LBC3 and the MIT 1.3-GHz NMR insert magnet. The critical current properties of damaged REBCO tape were degraded. Therefore, to develop ultra-high magnetic field, it is necessary to clarify the mechanical phenomenon of both REBCO tapes and magnets.
So far, some journal papers on mechanical simulation on REBCO magnets have been published. In these papers, the finite element method (FEM) was employed as a mechanical simulation. However, the FEM cannot accurately simulate plastic deformations. Hence, in the presentation, we will model REBCO tapes with a particle method, which are able to represent plastic deformation of material, for mechanical simulation. We will show the simulated mechanical behaviors of REBCO tapes under large electromagnetic force.
Electromagnetic forming (EMF) is a high-speed forming process that has recently been explored in modern industrial applications to extend the forming limits of magnesium alloy or aluminum metal sheets. In this study, an experimental and statistical approach using analysis of variance (ANOVA) and response surface methodology (RSM) techniques is used to find the significant main and interaction effects to verify the relationship between controllable factors of the process and achieved displacement of the metal sheet. An experimental investigation is proposed using controllable factors involving the design of the actuator coil and the pulse unit parameters, such as capacitance, electrical potential, number of windings and pitch of the coil. The statistical software Design Expert is used to aid experimenters in selecting and constructing the experimental design, aiming randomization, replication, and blocking. Further, the design of the experiment is carried out using a factorial design method to study the joint effect of the controllable factors on the metal sheet displacement. The Matlab commercial software is also used to perform the ANOVA to verify the statistical significance of the main and interaction effects of controllable factors. The major aim of this paper is to conduct a factorial experimental design to find factor settings that maximize the free bulging displacement of metal sheets by the EMF process using a proposed and adequate regression equation. In addition, the combination of analyzed parameters for maximizing displacement of metal sheets is established according to desired criteria. Finally, design principles for the free bulging of metal sheets by EMF are outlined based on experimental and statistical methods. These results can contribute for spreading industrial applications of EMF process by introducing statistical approaches for the optimization of it.
High temperature superconductor (HTS) coils have been applied in high field magnet applications, such as nuclear magnetic resonance (NMR) and maglev trains. The accurate calculation on the critical current of HTS coils is key for the magnet design and optimization. In practical applications, HTS tapes are also often wound into different shaped coils, such as racetrack coil for motors and ‘D’ shape coils, which requires 3D model to calculate their critical current. This paper studies and compares critical current of special shaped HTS coils, including circular, racetrack and ‘D’ shape. The critical current of each coil is calculated by two methods: a critical state model based on T-A formulation with E-J power law, and a magnetic field model based on uniform current assumption. The key idea of T-A model is to separate the calculation of current from the magnetic fields, T-model gives the current distribution to A-model, in turn A-model gives the magnetic fields distribution to T-model. While in magnetic field method, current is distributed uniformly in each turn, so the calculation time is greatly shortened. The influence of coil shape and tape parameters are studied, the results of these two methods are also compared and discussed. This paper aims to provide a simple and fast modeling method for the critical current estimation with enough accuracy for HTS coils.
Within the framework of Open Science, set as a priority by the European Commission in Horizon Europe, the OPEN Super Conducting Cable (OPENSC2) code has been recently developed and released to grant the entire research community the possibility to analyse thermal-hydraulic (TH) transients in forced-flow superconducting (SC) cables for fusion and power applications. The code is flexibility in the reference cable topology, level of discretization, and capability of dealing with different fluids as coolants.
In this paper we present the current distribution model recently implemented in OPENSC2, based on the discretization of the different cable regions with flexible 1D elements with arbitrary orientation in 3D space. This choice allows studying superconductive cables with different levels of approximation, from superconductive tapes to wound twisted cables, from region level discretization to single strand representation. The integral formulation of the magneto quasi-static approximation of Maxwell’s equations is used, accounting for the inductive coupling among the elements, the local nonlinear behaviour of the SC material and possible element-to-element cross interaction due to electric contact. The flexibility of the formulation allows the user to introduce possible statistical effects on the strand distribution along the cable. While the electromagnetic (EM) and TH equations share the same discretization in space, the simulation of EM phenomena can occur on a faster time scale than the thermal response of the cable. Different coupling schemes, allowing simultaneous (implicit) or separate (explicit) time marching are then adopted according to kind of transient under investigation.
In the paper we show how the code, developed following an object-oriented approach, is currently capable to simulate EM-TH transients in both LTS and HTS cable-in-conduit conductors for fusion applications, as well as in HTS cables for power transmission.
Recently, permanent magnet synchronous motors(PMSM) are widely used in industrial fields due to various advantages such as high speed operation, high efficiency, and compact design. However, PMSM has the disadvantage of noise and vibration caused by high magnetic energy during the interaction between the stator and the rotor magnet. These drawbacks have a significant impact on machine performance. Moreover, vibration and noise cause eccentricity, bearing defects and PMSM misalignment. Therefore, it is important to identify the vibration sources of electromagnetic that cause vibration and noise. Therefore, torque pulsation must be taken into account at the design stage.
Therefore, in order to analyze the influence of each source, we propose a PMSM design with the same characteristic performance as the fractional pole/slot combination, and derive the dominant model of the pole/slot combination for each electromagnetic vibration source through finite element analysis, and the result of electromagnetic characteristic analysis. The pole slot combinations of the derived model are 8 poles/9 slots and 8poles/12slots. The main components of the 9-slot and 12-slot models are torque pulsation and electromagnetic force, respectively. Therefore, experiments with FEM and electromechanical coupling analysis were performed to analyze the effect of each vibration source, and then the results were compared with two different partial pole/slot combinations.
Therefore, in this study, we derived the dominant model for each electromagnetic vibration source, the pole/slot combination, to analyze the influence of each source. The derived pole-slot combinations are 8pole/9slot and 8pole/12slot. As torque ripple and cogging torque in the 9slot model, the torque pulsation is lower than that of the 12slot model. However, the electromagnetic force of the 12slot model is lower than that of the 9slot model. Detailed analysis and measurement results are discussed in the full paper.
One of the problems with the practical application of high-temperature superconducting coils is burnout due to the heat generated by a local low critical current density. At the current level of manufacturing technology for a high-temperature superconducting tape, it is not possible to manufacture long high-temperature superconducting tapes that do not completely include deterioration of local critical current density. To overcome this problem of high-temperature superconducting coils, a no-insulation coil, which is wound with uninsulated conductor, has been proposed as a coil structure. Previous studies have shown that this structure can prevent burnout even if there is a local critical current density degradation in the winding. However, a big problem is that the no-insulation coil has a long excitation delay time. Therefore, we propose a no-insulation coil wound with multiple high-temperature superconducting tapes without insulation between tapes in order to improve the excitation delay. In addition, multiple tapes are possible to reduce the critical current drop rate of the entire multiple tapes even if one tape in multiple tapes has a deteriorated part of the critical current density.
In this study, the transient electromagnetic phenomena in the no-insulation coil wound with multiple high-temperature superconducting tapes was calculated by the partial element equivalent circuit (PEEC) method. The calculated results showed that the excitation delay time could be shorted by multiple tapes. Furthermore, the current distribution in a no-insulation coil has local deterioration of the critical density in one tape of multiple tapes was examined. The calculated results showed that even if one of the multiple tapes has a local critical current density degradation, the current that greatly exceeded the critical current did not flow in each tape, and the current flew quickly to the adjacent tapes.
Switched reluctance motors (SRMs) have many excellent advantages of inherent simple structure, good fault tolerance, high rotating speed, high power and robustness. Magnetic bearing (MB) preserves the characteristics of no friction, no lubrication, free maintenance and long life. Bearingless switched reluctance motor (BSRM) integrates the functions of the SRM and MB. Therefore, the BSRM is especially suitable for special operating environments, such as high-speed and high-temperature applications. However, the suspension windings and the toque windings of the traditional BSRM are wound on the stator poles together to obtain suspension force and torque simultaneously. Consequently, there is a strong coupling between torque and radial suspension force, which makes the control system complex and difficult to achieve high-precision operation of BSRM.
To solve the coupling problem and obtain large suspension force and torque density, a novel BSRM with independent torque and suspension magnetic circuit and axial arranged torque cores is studied. The suspension wingdings and the toque windings are wound on the stator poles and toque poles, respectively. Consequently, the control flux and torque flux are independent of each other. The natural decoupling between torque and suspension force is realized. Moreover, a DC amplifier is adopted to drive the radial suspension of the proposed BSRM, which has simple control.
The basic structure and suspension principle of the propose BSRM are first introduced, and then, the mathematical models of radial suspension forces are derived. Based on the finite element analysis (FEA), electromagnetic properties of the BSRM are also analyzed and studied in detail, including flux field distributions, radial suspension forces and force-current relationships. The research results have shown that structure of BSRM is reasonable, and the magnetic circuit and mathematical model are correct.
For the traditional electrical machine, both the stator and rotor core are made of silicon steel sheets, and the main magnetic fluxes are worked in the 2D plane thus the 2D electromagnetic analysis is effective for such kind of electrical machines. However, for particular electrical machines such as claw pole machine (CPM), the accuracy rate of the 2D electromagnetic analysis is not effective due to the exists of 3D magnetic flux path. Besides the electromagnetic analysis, multiphysics coupling calculation is quite of essential for the analysis of electrical machine, as the final performance is determined by the temperature rise and etc.. Finite element method(FEM) has been widely used in the electromagnetic field analysis, however FEM is time consuming especially when related to 3D analysis and multiphysics analysis.
In this paper, a magnetothermal coupled model for CPM using 3D magnetic and thermal network is established. The model is proposed mainly for quick prediction of magnetic and thermal performance of CPM and it is suitable for speeding up the CPM optimization process. The accuracy of the proposed model is verified by using 3D FEM. The 3D magnetic network model(MNM) for CPM is first established. The MNM is composed of equivalent reluctance of air gap, PM, rotor and stator core. The winding and PM excitation are equivalent to the magnetic motive forces. The magnetic field distribution and electromagnetic performances are calculated by using established MNM. Then, a thermal network model(TNM) which possess a similar structure to MNM is built. The heat sources in TNM are calculated using magnetic density results calculated by MNM. To improve accuracy, the rotating magnetization core loss in stator is calculated instead of alternating magnetization loss. Finally, the MNM and TNM are coupled. The magnetic performance and thermal distribution in CPM are obtained by the coupling model.
Due to the wide application of non-linear loads and switching electronic devices, the current in the power grid is often mixed with many harmonic components. The non-sinusoidal currents will have certain effect that unstable voltage and increased heat dissipation on electrical equipment made of superconducting materials, such as superconducting motors, SMES and HTS magnets. In this paper, In this paper, high-order harmonics with different THD values are applied to the coated superconducting tape of magnetic substrates.The influence of power harmonics on the AC loss of the 2G HTS tape is discussed using the finite element method based on the H formulation.On this basis, we considered two different factors that magnetic substrate and harmonic frequency multiplication.The results show the higher harmonic content, the greater the AC loss value of the superconducting tape. Under the condition of applying AC harmonics and external magnetic field at the same time, the AC loss value of the tape with magnetic substrate is several times higher than that of the tape without substrate.
The Screening Current Induced Field (SCIF) is a crucial measurement to determine the gross contribution of screening currents in a superconducting coil, specifically coils wound with large aspect ratio, single filament high temperature superconductors (HTS) such as Rare Earth Barium Copper Oxide (REBCO). Our numerical model accurately predicted the behavior of the SCIF shape and magnitude during energizing to full field but diverged on de-energization. We suggest that axial clamping and its associated consequences at high field are responsible for the difference in the computed SCIF upon de-energization. Simple methods of approximating this effect and comparisons between numerical and measurement results are presented.
A number of programs aimed at modeling electrical, magnetic, thermal, and mechanical transients in superconducting magnets and circuits were developed at CERN as part of the STEAM (Simulation of Transient Effects in Accelerator Magnets) project. The framework includes software to accurately model quenches in a superconducting magnet, either self-protected or protected by energy-extraction, quench heaters, CLIQ, or a combination of these. It includes finite-difference programs to tackle these problems for multipole and solenoid magnets (LEDET, both 2D and 3D) and for canted cos-theta magnets (ProteCCT). These programs include physics-driven methods to account for filament magnetization, coupling losses or eddy currents in metallic magnet components. In addition, a powerful routine to automatically generate finite-element models of superconducting magnets was developed (SIGMA), which allows benchmarking of other models and definition of magnet details with enhanced flexibility. Since modeling of quench in busbars was routinely performed, it became convenient to develop a dedicated COMSOL-based simulation tool to model this problem (BBQ). The STEAM project features also an R&D program for the 3D time-domain simulation of magnetothermal phenomena in coils and magnets based on high-temperature superconductors, using the finite element method. Finally, different tools that are effective for modeling specific problems can be coupled together within a cooperative-simulation (COSIM). A library of models of most LHC and HL-LHC superconducting circuits was systematically developed, validated, and versioned. A few example transients modeled by STEAM tools are presented, covering a wide range of magnet sizes and geometries, conductor parameters, and quench protection systems.The STEAM framework is offered to the community as a flexible, effective, and computationally-efficient software package for simulating powering and quench transients in superconducting circuits and magnets.
Abstract: The high-frequency insulated core transformer (ICT) accelerator is expected to replace traditional ICT for its small size and high power density in the field of irradiation below 1MeV. As a key component of the accelerator, the ICT high-voltage power supply is used to feed the accelerator tube. Segmented core structure of the ICT will lead to uneven flux density distribution of each core section. The nonuniform power loss and structure results in uneven temperature distribution of the high-frequency ICT. In this regard, a thermal model with highly accurate temperature prediction on the high-frequency ICT parts is required. A thermal impedance network based on the high-frequency ICT is proposed, considering the thermal coupling of the ambient, cores and windings. The Multiphysics coupling analysis is carried out by COMSOL electromagnetic thermal module. Instead of linear materials, the measured B-P curve and B-H curve are applied for more realistic simulation model. Due to the complex ICT core structure, the parameters of the thermal model are determined by finite element simulation so that the precision of the network is improved. Finally, the thermal model demonstrates high accuracy within the simulation results, which verifies the effectiveness of the proposed model.
Key words: High-frequency insulated core transformer, Thermal network, Thermal model, Multiphysics simulation, Temperature distribution
By using a High-temperature superconducting (HTS) tape, it is possible to realize a coil that can generate much higher magnetic field. However, it is a problem to increase the inductance in an HTS coil since the number of windings increases due to restriction on the current capacity of an HTS tape. For coils with large inductance, large induced voltage and noise are induced between the coil voltage taps. Thus, it is very difficult to quickly detect the abnormal voltage when quench occurs. Magnetic energy cannot be removed immediately because the time constant of the coil with large inductance is long. Therefore, reducing the inductance of the HTS coil is very important in terms of coil protection. There is another problem that is burnout of a coil due to the heat generated by a local critical current deterioration. At the current level of manufacturing technology for an HTS tape, it is not possible to manufacture long HTS tapes that do not completely include deterioration of local critical current density. To solve these problems, we focused on an insulated HTS conductor with stacked multiple HTS tapes without insulation between tapes to reduce the rate of decrease in the critical current of the winding.
Current and temperature distributions in an HTS pancake coil wounded with the insulated conductor consist of three parallel HTS tapes during excitation and demagnetization were examined using the partial element equivalent circuit (PEEC) method and thermal conductivity analysis. Loop current was induced in multiple tapes during excitation and demagnetization. However, loop current did not flow enough to generate heat that destabilized the superconducting state. Furthermore, it was found that the HTS coil wound with insulated conductor consist of multiple no-insulated tapes could maintain stability by commutation to the adjacent tapes even if there is a local critical current degradation.
Cryogenic system plays a vital role in the development of magnet technology. Especially for superconducting magnet，it would be in more widespread use now if it were not for the problems associated with the cryocoolers or cryostats required to cool down those superconducting devices or facilities.
For a variety of high-Tc superconducting magnet applications such as energy storage, generators and superconducting maglev train, the technology itself is relatively mature. However, the problems associated with the used cryocoolers have hampered the advancement of their practical applications. An ideal cryocooler for the applications should have the following features: low maintenance, high reliability, stable operation, long life, high capacity and high thermodynamic efficiency.
In the authors’ laboratory, a cryogenic system based on the Stirling-type pulse tube cryocooler (SPTC) has been developed and built. The system was designed to be integrated into a new generation of high-temperature superconducting maglev prototype train. The developed SPTC is inherited from a series of ones developed for aerospace applications and thus keeps the merits of high reliability and long life which is evaluated to reach 5 years.
The high-capacity SPTC unit in the cryogenic system uses the configuration of multiple cold fingers, which can provide 100W of cooling capacity at the working temperature of 45K for a single superconducting magnet module. Another advantage of the cryogenic system is that it can vary freely from 35 K to above. The SPTC has also achieved high efficiency with a relative COP of 20% of Carnot at 77 K.
The overall design approach, coupling and integration of the cryogenic system for the high-temperature superconducting maglev train and the arrangement of related low-temperature circulation pipelines will be described. Meanwhile, the performance characteristics of the developed cryogenic system during the laboratory testing will be presented and discussed.
A 4.8-m-long cryostat has been developed to cool a pair of 1.9-m-long planar superconducting undulator magnets (SCUs). The final design and the thermal model of this cryocooler-cooled LHe-based cryostat has been completed. The cryostat is fabricated and a preliminary cool-down test has been performed. This paper presents a comparison between measured and calculated thermal performance of the 4.8-m-long cryostat for the SCU.
NIMS has started design of a magnetic refrigerator to cool quantum computers. As well known, quantum computer is bringing a revolution to the world of super computers. In general, 3He-4He dilution refrigerators are used to cool the quantum computers at operating temperature below 100mK. However, dilution refrigerator uses a lot of helium 3, that is very expensive these days. On the other hand, magnetic refrigerator is also able to reach temperatures below 100 mK. One of the biggest advantages of the magnetic refrigerator is to use much less helium 3, which might contribute whole refrigerator price. This study will report progress on specially designed NbTi solenoid magnet and conceptual design of the magnetic refrigerator for application of quantum computers.
A HTS conductors test facility can be inserted in a 19.5 T @200 mm bore resistive magnet and operating temperature ranges from 4.5 K to 50 K with current up to 100 KA is under design. A superconducting transformer with a 200 A primary winding composed of immersion cooled NbTI conductors and a 100 kA secondary winding composed of force-flow cooled CICC as the current supply for HTS sample. Helium can be warmed up to 50 K by heaters to cool the HTS sample to the test temperature. A HTS adapter connects the HTS sample under test and the secondary winding and limits the heat flux between them. Details of the cryostat and its performance are described.
In order to meet the normal operation of HECRAL (Hybrid superconducting Electron Cyclotron Resonance ion source with Advance in Lanzhou) superconducting magnet, a cryostat in the form of immersed in liquid helium was designed, which integrated two two-stage GM cryocoolers, helium tank, thermal shield, outer dewar, suspension structures, maintenance tower, binary current leads, corresponding monitoring and diagnosis system. The 1st cooling head of the two-stage cryocoolers was used to cool the thermal shield, copper leads and HTS (High Temperature Superconducting) current leads; Enough cooling capacity in the temperature region of 4.2K was supplied by the 2nd cooling head to condense the saturated helium vapor evaporated by thermal load (including static thermal load and dynamic thermal load), so as to realize the “0” liquid helium evaporation operation of the superconducting magnet. Corresponding structure and heat transfer of the designed cryostat were analyzed, and the WST(Western Superconducting Technologies Co.) was commissioned to install the cryostat and carried out cryogenic excitation test. The cryostat is now operated in IMP (Institute of Modern Physics, Chinese Academy of Sciences) and all parts of the magnet and cryostat are working normally, which ensures proper operation of the ion source.
Recently, energy production and cooling technology using hydrogen has been developed worldwide. In particular, the ortho-para conversion process, which was a problem in hydrogen liquefaction, was overcome through the development of catalysts. Hydrogen has been an attractive material as a refrigerant due to its low liquefaction point and high thermal conductivity. In superconducting applications, operating temperature is an important design condition for improved performance and stability. Compared to liquid nitrogen or liquid neon used for typical indirect cooling, liquid hydrogen can cool helium gas to a lower temperature, increasing the performance and stability of superconducting devices. Therefore, there is a need for the development of hydrogen-based cooling systems for superconducting equipment operating at cryogenic temperatures. This paper deals with the design of a helium-liquid hydrogen indirect cooling system for an HTS coil cooling. The helium-liquid hydrogen indirect cooling system consists of a hydrogen liquefaction system, a helium-liquid hydrogen heat exchanger and a 2G HTS coil. The hydrogen liquefaction system liquefies gaseous hydrogen precooled by liquid nitrogen using a cryo-cooler. The heat exchanger was located in the inner tank of a hydrogen cooling system filled with liquid hydrogen, and gaseous helium exchanges heat through the contact surface of a copper tube cooled with liquid hydrogen. The temperature distribution and heat load of the hydrogen liquefaction system and HTS coil were analyzed by a 3D finite element method program. The helium-liquid hydrogen heat exchanger was designed based on the outlet temperature of the hydrogen liquefaction system and the heat load of the HTS coil. As a result, the temperatures at the outlet and inlet of the hydrogen liquefaction system were 22 K and 31 K, respectively. The heat load of the HTS coil was 25 W, and the temperature during operation was maintained at 29 K.
The Fermilab horizontal test stand previously used for testing the LHC inner triplet quadrupoles has been upgraded to test cryo-assemblies for the HL-LHC upgrade. The test requirements of these new cryo-assemblies required additional capabilities of the test stand cryogenic system, including controlled cool-down and warm-up, helium recovery after a quench, and operation at higher pressures. Most of these upgrades were completed to support a zero-magnet test in late 2020, with the remainder of the upgrades completed to support the first pre-series cryo-assembly test in mid-2021. An overview of the design and initial operating experience of the upgraded test stand cryogenic system and associated process controls system are presented in this paper.
Acknowledgement: Work supported by the Fermi National Accelerator Laboratory, managed and operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes.
As the use of renewable energy increases in the future, hydrogen production is predicted to increase significantly. As the amount of hydrogen used increases, it is more cost-effective to transport in liquid hydrogen state than to transport in high pressure gas form. So, the more liquid hydrogen is used, the greater the opportunity for the high-temperature superconducting coil to cool the liquid hydrogen with a refrigerant. In the case of mobility, such as drones, automobiles, and ships, fuel cell systems that use liquid hydrogen can increase efficiency by reducing the size and weight. In addition, if a superconducting motor is used instead of a general motor, there is an advantage of reducing the weight. If a fuel cell is used as a power source for the superconducting coil, the mobility of the system can be improved.
In this study, first, a hydrogen liquefier was built, and an experiment was performed on the cooling of a high-temperature superconducting coil through helium gas using liquid hydrogen. In order to use the fuel cell as a power source for the high-temperature superconducting coil, the operating conditions for supplying current up to 40A to the high-temperature superconducting coil were investigated by controlling the flow rate of hydrogen and oxygen in the fuel cell.
A refrigerant circulation cooling system for a HTS (High Temperature Superconducting) coil shows better cooling performance than a heat conduction cooling system when the distance between a cryo-cooler and the HTS coil becomes large because the temperature gradient between the coil and the cryo-cooler becomes small. By combining this excellent cooling system with magnetic refrigeration technology that uses the magnetic field generated by the HTS coil, we aim to realize auxiliary cooling technology that can easily maintain around 20 K. Magnetic refrigeration requires a change in the magnetic field acting on the magnetocaloric material. The alternating magnetic field can be obtained by passing AC (Alternating Current) through the HTS coil, but this is not a good method considering the heat generated by AC losses. Therefore, we investigated a method of causing the magnetic field change by inserting or removing a magnetic shield made of a superconductor that blocks the magnetic field by the Meissner effect between the HTS coil and the magnetocaloric material. Numerical analysis confirmed that the shielding effect increases as the thickness of the shield increases. Experiments also confirmed the shielding performance of superconducting bulks in liquid nitrogen. In order to increase the cooling assistance effect of magnetic refrigeration, the waste heat generated with applying a magnetic field to the magnetocaloric material should be removed by convective heat transfer. Therefore, optimization of the waste heat by changing the circulation method of the refrigerant was investigated by numerical analysis. As mentioned above, this presentation reports on the magnetic shielding by superconducting bulks and the effect of magnetic refrigeration assistance on the cooling performance of the cooling system.
with the development of the preparation technology of high temperature superconducting (HTS) materials, the mechanical properties of HTS materials have been further improved and great progress has been made in practical applications. A 3.5 T HTS magnetic separation facility was designed and manufactured in China. A G-M cryocooler, as the cold source of the cryogenic system was used for providing the cooling capacity to maintain the magnet and its related components work temperature. To ensure the cooling effect, it was unavoidable to design and analyze for the conduction cooling system of the 3.5 T HTS magnetic separation. This paper focuses on the structural design and analysis of the conduction cooling system. Structural designed parameters of components were listed and the finite element (FE) analysis was completed based on theoretical heat losses and the cryocooler cooling capacity. The maximum von-mises stress of each component did not exceed the material allowable stress. Finally, a cooling experiment was carried out after the facility assembly, it indicated that the highest temperature of the magnet and the thermal shield were much lower than design requirements.
As an industrial application of the high-temperature superconducting coils (HTS coils), for example, an induction heating device that rotates a metal in a DC magnetic field by a superconducting coil have been studied. For that purpose, when operating the HTS coils, it is necessary to remove the heat from the coils and keep those at about 50K or less. In addition, assuming application to production equipment, it is desirable to be able to cool multiple coils away from a cryo-cooler at the same time. In this study, circulation cooling system have been studied that satisfies these conditions. By using the circulation cooling system, the coil installed away from the cryo-cooler to some extent can be cooled. We also investigated the effect of using the cryofan on the cooling performance of the circulation cooling system. By using the cryofan, it is not necessary to cool the refrigerant from room temperature of the steady state. Along with this, there may be merits such as being able to remove the precooled heat exchanger. Its total length is 60m, and it occupies more than 80% of the entire flow path in the cryostat of the current experimental equipment. On the other hand, the heat leakage from the cryofan and the energy input in the impeller part. It is conceivable that a part of the heat will be converted into heat. Based on these facts, it is necessary to verify the practicality of cryofans. In this study, we will discuss the results of experiments and numerical analysis on a circulating cooling system. In addition, the analysis results in case of using the cryofan will be discussed, including a comparison with the case where a conventional compressor is used.
Abstract : To cool the superconducting magnets of compact synchrotron, a forced flow cooling system based on GM/J-T concept with cooling capacity of 10 watts at 4.5K is researched. The cooling system consists of heat exchanger, precooling system, J-T valve and forced flow cooling tank. In refrigeration process, high pressure helium is cooled by the heat exchanger and precooling system, and then liquefied by the JT valve. To elucidate the performance of the heat exchanger based on enthalpy balance, the cycle point parameters are picked. Results of the experiment show the relations of temperature, mass flow rate and pressure of helium at the inlet of J-T valve on the cooling capacity of the system. Heat leakage analysis, design parameters optimization and cycle efficiency improvement in the system are also discussed in this paper.
Keywords:Helium refrigerator,Cryogenic system,Thermodynamic analysis,Heat leakage analysis,cooling capacity
In the superconducting magnet system, which is the core equipment of the fusion experimental device, a large number of measuring equipment are installed in the system for the operation and monitoring of the system. Although each measuring equipment is inspected and repaired during the maintenance period of the experimental device, there is a concern that trouble may occur in the measuring equipment that has been used for a long period of time. If a problem occurs in a measuring equipment that is important for system operation, it is necessary to stop the plasma experiment, raise the temperature of the superconducting magnet system to room temperature, and repair or replace the measuring equipment. Therefore, in this study, the development of a machine learning model was conducted to predict the state of the superconducting magnet system based on the measurement data accumulated during system operation. The object of model development in this study is the subcooling system for the Large Helical Device in the National Institute for Fusion Science. This system is suitable for the model development because it holds a huge amount of measurement data collected after about 10 years of operation.
The quench phenomenon of the accelerator superconducting magnet may occur in operation, which will cause the liquid helium in the cryostat to evaporate rapidly and release to the atmosphere. High-pressure helium will destroy significant components in the transmission line, and the helium released into the tunnel will lead to the ODH (Oxygen Deficiency Hazard), threatening the safety of operators. This paper mainly introduces the helium discharge process of fragmentation separator in HIAF (High-Intensity heavy-ion Accelerator Facility). Firstly, the flow state will be described by the energy equation and Navier-Stokes equation. Meanwhile, the velocity variation, distribution of temperature, and concentration of helium are simulated by 3D modeling when quench occurred in the tunnel. Based on the above analysis we will obtain a reasonable design scheme of the accelerator superconducting magnet relief system for HIAF Fragmentation Separator(HFRS).
Keywords: Emergency relief, The quench, Superconducting magnet, Cryogenic system, Thermodynamic analysis
Helium bubble retention phenomenon was observed in the development of high field magnets by the National High Magnetic Field Laboratory (NHMFL) of the United States in 2014. The retention of a large number of helium bubbles can inevitably lead to the blocking of high field magnet cooling. In the case of the high field, the magnetic field force generated by the diamagnetism of helium bubbles makes them trapped in a certain area and piled up in large numbers. The accumulated bubbles will attach to the surface of the magnet and degrade its heat transfer performance, breaking the thermal stability of the magnet and making it quench. This study focuses on the accumulation of helium bubbles in high field magnets. Firstly, the growth and gather process of liquid boiling bubble under different magnetic field gradient magnetic field was analyzed. Secondly, the trapping behavior of bubbles and the temperature gradient distribution in the bubble aggregation region are simulated under the high magnetic field. The thermodynamic behavior of bubbles concentrated areas was analyzed, emphatically. The design of the structure of high-performance heat transfer was presented for the large helium bubble position. Finally, the reliability of the structure was verified combining with the temperature distribution and heat transfer in the high magnet.
Keywords: Helium bubbles, Diamagnetism, Boiling heat transfer, Heat transfer analysis
Power electronic devices are typically utilized to provide quench protection for the superconducting magnets. Integrating quench protection devices in the Dewar can make the system more compact. The cryogenic characteristics of the power electronic device are therefore necessary to be studied in order to ensure that it can work properly under the low-temperature condition. The characteristics of power electronic devices, especially the threshold voltage, leakage current, and on-resistance, change significantly with temperature. Based on the typical structure, this paper analyzes the physical characteristics of several commercial SiC MOSFETs. The effect of temperature on SiO2/SiC interface is studied. Furthermore, a novel cryogenic model of MOSFET at low temperature is proposed, which is more suitable for a wide temperature range.
Persistent current switches (PCS) which switch between superconducting and resistive states enrich the operation scenarios of superconducting magnets and lead to simple but colorful charging procedures. The state of a PCS can be controlled through superconducting phase change such as in temperature controlled case, global failure of flux pinning such as in over current controlled case, or a series of local forced flux flow such as in the dynamic resistance controlled case. Thanks to the thermal stability of high temperature superconductors, over current becomes feasible for practical PCS control strategy, which is promising in real applications of superconducting magnets due to its simplicity. In this work, temperature and over current control of PCS are combined, leading to novel charging procedure of superconducting magnets. The PCS made by copper laminated ReBCO coated conductors is fabricated and tested under various of temperature and current conditions.
key words: Persistent current switch, over current controlled, superconducting magnets, HTS
Deperming of ship has been conducted since the World War Ⅱ by several Navies and faces hard work for the deperming of large-size ships. We have been investigating a ship deperming system using High Temperature Superconducting coil laid flat on seabed of shallow water. The investigation started from the calculation of magnetic field to be imposed on ship. Considering deperming procedure, the ship hull comprised of high-tensile steel is firstly depermed, and then under the effect of ship-hull on-board machinery comprised of steel is depermed. Magnetic field to deperm ship-hull is estimated from the magnetic property of steel, and for the on-board machinery consideration is needed of the shielding effect by ship-hull. Maximum magnetic field to deperm ship is several milli-Tesla and imposing this field over whole ship body at once requires the shape of the coil to cover the projected area of the ship which is stationed on sea surface. Our design of the coil is based on a set of race-track shaped multi-turn conductor in one coil, where the conductor is of HTS material assembled of CORC®s cooled by liquid hydrogen. Considering a large surface ship and a submarine ship of Japanese Maritime Self Defense Forces as targets, three sets of the basic coil component with different size are to be laid on seabed with common center. Magnetic field to deperm ship has to have a time sequence of alternative sign and decreasing intensity from the field to saturate magnetization of steel to zero intensity. Time dependent electric current through the coil conductor causes energy dissipation and large inductance of the coil needs large greater power. On the other hand, the deperming of ship will be required to complete in as short time as possible from the operational necessity. Optimization of power source design is discussed.
We have proposed a novel method to adjust the magnitude and direction of current in the second generation(2G) high temperature superconducting (HTS) coil by providing a strong constant magnetic field. This method can be contactless used in a variety of flux pump devices, such as linear-motor type flux pump, rotating flux pump and so on. We have redesigned the experimental device on the original basis and added a multi-turn (N=3000) DC coil with an iron core that provides a constant magnetic field. The focus is on the relationship between the background constant magnetic field, AC traveling wave characteristics and the open circuit voltage of the superconducting stator. It is found that when a constant magnetic field opposite to the magnetic field of flux pump is added in the continuous current mode, the magnitude and even direction of superconducting coil current in 77k liquid nitrogen will change, and this change can be controlled. This article introduces the application of the new device in controlling the magnitude and direction of HTS coil current. The non-contact and controllability of this method is very meaningful, and it can also provide some theoretical support for the practical application of flux pump.
The output power of high stability dc power supply system which drives the water-cooled magnet of Steady High Magnetic Field Facility (SHMFF) can reach up to tens of megawatt, so that the circuit usually adopts the realization scheme of Silicon-controlled rectifier plus LC filter. And in order to generate low-ripple magnetic field required by the High field nuclear magnetic resonance and other applications, the DC current ripple should be restricted to 10ppm or lower. The obstacle to improve current ripple is the uselessness of the suppression of low-frequency (50-150Hz) voltage ripple by the LC passive filter.
For the improvement of this parameter, the method commonly used is to add a series active filter device at the output end, which includes two ways: transformer coupled current injection and transistor linear adjustment.
In this paper, we propose a new scheme of using a high-frequency switching power supply which is series connection at output of the original power supply system as a series active power filter. Compared to the traditional way, the new scheme has advantages of lower control complexity and less power loss, and thus higher engineering feasibility. And due to its high response speed, it can realize good compensation for the low-frequency component of 300Hz, and further reduce the requirement for LC passive filter. In addition, when the output current is low, it is fully supplied by the active filter instead, which can improve the performance of the power up stage easily.
In this paper, firstly an overall scheme is determined, including specific topology structure, ripple component extraction of the output voltage and other key issues. Then the relevant control strategies are introduced and verified by simulation. Finally, a small prototype is made to verify the feasibility of the scheme.
A conventional rectifier based on a thyristor is widely used as a magnet power supply in the largest tokamak fusion device such as JT-60SA and ITER. The rectifier converts AC input power to DC output power supplied to the magnet bi-directionally. In order to energize and de-energize the magnet controlling power flow, the rectifier shifts phase angle of AC current with reference to input AC voltage. In the conventional rectifier, AC current always lags voltage due to the turn-on characteristics of the thyristor switch in forward bias state. The difference of phase angle causes the requirement of large reactive power and the unacceptable level of voltage drop in AC side. The Static Var Compensator and the motor-generator are utilized to compensate the lagging reactive power in ITER and JT-60SA respectively. However, the size and the capacity of these machines are quite large since the lagging reactive power is several times higher than the active power to energize the magnet.
In order to compensate the lagging reactive power, the rectifier with the series diodes and the commutating capacitors was proposed. In the configuration, the commutating capacitor provides forward bias voltage to the thyristor even at leading phase. Therefore, it can generate leading current in AC side. The capacitor is charged automatically during the commutation sequence.
This paper proposes the hybrid configuration composed of the conventional rectifier and the leading rectifier connected in series. The leading current cancels the lagging current generated by the conventional one. Consequently, the hybrid rectifier works with the unity power factor without any large compensation circuit. However, the hybrid rectifier generates voltage spikes in DC side at the current commutation and it may damage insulation inside the magnet. Feasibility study of the hybrid rectifier for superconducting magnets is carried out using resonance characteristics of them for JT-60SA.
For the electrodynamic suspension (EDS) system that uses superconducting magnets, the transmission efficiency of no-contact on-board power source will be affected by the eddy current loss generated on the outer wall of the cryostat. To address this issue, improving the structure of the generator coils is an effective approach. In this work, we have carried out the optimization of the structure of generator coils numerically. Firstly, we used an analytical model to estimate the harmonic components of the magnetic field generated by the ground coils .then, and applied the field on the boundary of a 3-D finite element model， in which, the cryostat and generator coils have been considered. Based on the model, the transmission efficiency for different strictures of the generator coils have been investigated. The results show that the optimized coil structure can reduce the eddy current loss of the vessel wall while maintaining a certain output power. This work can promote the development of no-contact on-board power source for EDS system.
For generating diversified magnetic field waveforms, a flexible control system of Pulsed High Magnetic Field Facility (PHMFF) has been developed at Wuhan national pulsed High Magnetic Field Centre (WHMFC). Firstly, in order to describe various magnetic field systems, a general physical model composed of energy storage modules, load unit, transport circuits, and other auxiliary units is established in the paper. And then by defining control data objects, all elements in the model can be abstracted and encapsulated. Combined with the control data objects, physical model is converted to a software data model, which can be directly embed into the control system to realize the reorganization and flexible control of magnetic systems. Meanwhile, the whole process of the construction of magnetic field system, the control strategy and the dynamic allocation of resources are introduced. Benefit from the control system design, PHMFF is able to easily and efficiently construct different magnetic systems and generate variable magnetic field waveforms such as half-sine, flat-top and repetitive pulses based on single pulsed magnet, which greatly improves the efficiency of scientific experiments and reduces the cost of PHMFF.
In order to meet the needs of scientific research, a Multi-stage Ultrahigh and Magnetic System (MUMS) has been developed at Wuhan national pulsed High Magnetic Field Centre (WHMFC) for generating 100 T magnetic field. Based on multi-stage technology, MUMS is composed of outer, middle and inner coils with three corresponding pulsed power supplies, and the field waveforms from three coils are superimposed at the right moment to obtain a higher magnetic field. Due to the complex structure of MUMS, the paper introduces a design method of control sequence to ensure the reliable and efficient operation. Firstly, the whole operation process of magnetic system is decomposed into a series of continuous actions to establish the operation process model. On the basis, for the complex coupling relationships between all sequence actions, a planning method based on directed graph is proposed to design the control sequence, which can be directly described and acted step by step in the control system. Finally, MUMS has been tested with the designed control sequence, and 94.7 T magnetic field has been achieved. The results verify the validity of the design method, and it also can be applied to the design of other complex magnetic systems.
We have succeeded in detecting local obstacles automatically in a 200-m-long RE-123 coated conductor (CC) by introducing deep learning based image recognition in reel-to-reel scanning Hall probe microscopy (RTR-SHPM). Longitudinal Ic homogeneity in CCs is one of the most important requirements for practical applications. Usually, such properties as Ic variation as a function of longitudinal coordinate is characterized by magnetization measurements adopting Hall probe array as a de facto standard characterization method for ensuring uniformity in long CCs. In this measurement, local Ic drop indicates the existence of current blocking obstacles. The group of authors also developed a magnetic microscopy applicable to reel-to-reel continuous measurements, RTR-SHPM, which makes it possible to visualize two dimensional magnetization current in the tape plane because of its high resolution imaging along the tape width. As a result, more elaborate defect detection is enabled. However, in the conventional technique, the observation depends on the human eye, therefore, there was a limit to analyse the magnetic image extending to thousands of images in the long tape of several 100 of meters. In this study, the image analysis based on the deep learning was introduced in our magnetic microscopy. The analytical model classifies the input image into the defect position and the normal position, respectively, together with a heat map and a score of confidence in the recognition. As a result, we have succeeded in detecting obstacles automatically from more than 4,000 of magnetic images. Furthermore, we revealed the existence of the obstacles which are not distinguishable by the local Ic criterion. This method allows us to clarify the origin of the instability of long CC wire and will have a strong impact as an evaluation technique for dramatically improving the reliability of the CCs.
Acknowledgements: This study is supported by the JSPS KAKENHI Grant Number JP19H05617.
For commercial large-scale magnet systems, the transient loss during the ramping process is an important evaluation metrics for refrigeration requirements, that is greatly influenced by contact resistance between winding turns. Due to intrinsic bypass current of no-insulation magnets, two part of the transient loss were considered: turn-to-turn loss generated by radial direction current, and magnetization loss produced by azimuthal direction current. In this study, the turn-distributed model is used to calculate the non-uniform current distribution, where the pancake coil is radially subdivided to each turn. The radial current was employed to calculate the turn-to-turn loss. The turn azimuthal current was applied to the boundary condition of the T-A formula to calculate magnetization loss in the cylindrical coordinate system. In the simulation, the superconductor index value model was used, in which the critical current density was conductor engineering current density estimated by a neural network fitting model. The contact resistivity dependent turn-to-turn loss and magnetization loss were presented. We conclude this study with reasonable advice for industrial applications
An electron cyclotron is to heat a plasma by driving current in a fusion system. This system requires strength and accurate magnetic field distribution for the interaction of the electron beam and radio frequency wave energy. The magnet of the system consists of a conduction-cooled superconducting magnet for 7 T and structures connected with a 2nd stage GM cryo-cooler of 1 W at 4 K for cooling of the magnet. This paper deals with the design of the magnet and conduction-cooling structures considering electrical and thermal stability. The magnet is wound with NbTi conductors. The inner bore of the superconducting coil is 240 mm to obtain the resonance region. Genetic algorithm incorporated with the linear programming is used for the optimal design. The objective function for optimization design of the superconducting coil is considered to minimize the amount of the superconducting wires. Then the design constraints including normal stresses generated by the electromagnetic force, magnet critical current margin, losses under the AC operation (charging/discharging) are also calculated to ensure safe operation of the superconducting magnet. After design, the quench analysis is carried out to verify the heat transfer and thermal stability of the gyrotron magnet. After the design, the 170-GHz gyrotron magnet will be fabricated with an auto-mated winding machine based on to the design results.
A system based on a novel scheme for generating the repetitive pulsed high magnetic field (RPHMF) is developed and applied to enhance the performance of NdFeB electrocatalyst in alkaline water electrolysis for the first time. In this system, the scheme for generating continuously high-frequency pulses depends on the cooperation of multiple power modules with new structure. Multiple power modules are connected in parallel to energize the pulsed magnet, and each module is composed of two capacitor banks and a pulse transformer, which is used to realize the conversion of the energy between the two capacitor banks. As the residual energy in one capacitor is transferred to another, the energy required to be replenished for the next pulse reduces substantially. Then the high repetition rate of the RPHMF can be achieved by discharging the capacitor banks of each module in sequence. The scheme has been validated by the experiment of a 2.4 T/12 Hz prototype with only one power module. Simulation shows that the frequency of the RPHMF can be improved to 12*N Hz with N power modules and a higher repetition rate of the RPHMF may bring new opportunities to the water electrolysis.
We experimentally studied the quench characteristics of coated conductors wound on metal cores spirally. The length of the metal core of each sample was 230 mm. A coated conductor was wound at the center 160 mm section of the core. Current terminals were attached over the coated conductor with 100 mm separation (effective section). Indium was filled in the gap between the current terminal and coated conductor in the sections under current terminals (terminal sections). We prepared the following four samples with four different insulation conditions.
Sample A: The entire core was completely insulated from both coated conductor and current terminals. Any current can flow in the core. The core is just a heat sink.
Sample B: The surface of the core was insulated from the coated conductor in the effective section. The current could be shared among the current terminals, the coated conductor and the core only in the terminal sections.
Sample C: The surface of the core was insulated from the coated conductor and the current terminals in the terminal sections. The current could be shared between the coated conductor and the core only in the effective section.
Sample D: No insulation was made on the core. The current could be shared anywhere.
Each sample was conduction-cooled at 55 K, and a normal zone was generated by a small heater. The normal voltages appeared in four samples were compared in order to examine the effect of the current sharing by the core as well as the effect of the heat capacity of the core on the normal voltages, which were related to the hot spot temperatures.
This work was supported in part by JST-Mirai Program Grant Number JPMJMI19E1 and in part by Japan-U.S. Science and Technology Cooperation Program in High Energy Physics.
Field pole magnet composed of stacks of high-temperature superconducting (HTS) tapes is a featured technology due to its simple manufacturing process, flexibility, and high current density thanks to intensified characteristic of HTS characteristics.
In this study, our group measured magnetic distribution of rounded stacks of HTS tapes in comparison with flat shaped ones. Normally, critical current in the bended tape is degraded by decreasing bending radius. However, results of the trapped field measurements on rounded and flat stacks showed an improvement for trapped magnetic field properties.
On the other hand, a modeling method based on the T-A formulation our group implemented to the commercial electromagnetic analysis was investigated to simulate trapped magnetic field of superconducting materials in previous research. We obtained tendency of the trapped magnetic field of HTS material even though the calculation method is affected by Jc-B curve used in the T formulation.
In this study, two models of stacked HTS magnets were created, one with a rounded stacks and the other with flat stacks. These models are created with electromagnetic analysis software and simulated with electromagnetic modeling based on the T-A formulation.
In the presentation, the results that the arrangement of tapes in fabricating stacked HTS magnet with rounded shape needs to consider together with stacking method and shape to optimize will be reported with latest calculation data.
The finite element analysis of electromagnetic coupling between a stainless steel shell and the 100 T pulsed magnet has been developed at the Wuhan National High Magnetic Field Center (WHMFC). The 100 T pulsed magnet consists of inner, middle and outer coil coaxially nested. The stainless steel shell is fitted tightly around the middle coil to resist the strong Lorentz force. The thickness of the stainless steel shell is 10 mm and the height is the same as the middle coil. The simulation results show that eddy current in stainless steel generated by rapidly changing magnetic field causes the peak magnetic field to drop from 102.3 T to 100.2 T, which is 2 % lower. The three coils magnet system has generated 81.4 T magnetic field, and the experimental results show that the eddy current suppression effect on the magnetic field peak is consistent with the simulation results.
Pb–Bi alloy and Wood's metal have been used for more than 30 years as representative superconducting solder intermedia to establish superconducting joints between NbTi and Nb3Sn wires. However, the use of Pb and Cd has been severely restricted by environmental regulations. The author has developed a novel alternative superconducting joint method between NbTi and Nb3Sn wires without Pb and Cd. The key point is to use a high-temperature-tolerable (HTT) Nb-alloy as an intermedia, whose critical current does not deteriorate even after exposure to temperatures higher than 650 °C. That enables us to establish a superconducting joint between Nb3Sn filaments and one end of the HTT Nb-alloy core via a chemical reaction, where a perfectly superconducting Nb3Sn layer is formed at the interface. Then, the other end of the HTT Nb-alloy core was cold-pressed with NbTi filaments to connect their active new surfaces to each other to create a superconducting joint. Ultimately, a superconducting joint between NbTi and Nb3Sn wires was realized. Hf-added Nb-alloys are promising candidates for the HTT Nb-alloy. The ultra-low resistance of the joint was confirmed by a current decay measurement.This method of forming a superconducting joint is promising for application in environmentally friendly nuclear magnetic resonance magnet systems.
In order to accurately evaluate the reliability of Pulsed High Magnetic Field Facility (PHMFF) at Wuhan national pulsed High Magnetic Field Centre (WHMFC), a reliability analysis method based on Markov chain and reliability block diagram is introduced in the paper. PHMFF is composed of lots of pulsed power modules, magnet coils and its corresponding control system. Based on the hardware of PHMFF, different magnetic systems are dynamically constructed for generating diversified waveforms. Therefore, the reliability of PHMFF is in fact determined by the actual operating magnetic system. In terms of the reliability of a specific magnetic system, firstly Failure Mode and Effect Analysis (FMEA) method is used to find out main failure modes of each subsystem in PHMFF, and then Markov chain model is established to analyze and calculate the reliability of subsystems. Finally, according to the reliability block diagram, the reliability of different magnetic systems can be concluded. The calculation results show that the reliability of all subsystems is above 95%. Although for some complex magnetic field system, the reliability index has declined, it still meets the experiments requirements.
Superconducting Magnetic Energy Storage (SMES) has the characteristic of fast response and high power density, which can be used to enhance the stability of power system and improve the power quality. With the increasing capacity of the power system, the application of a single SMES has certain limitations. By integrating individual superconducting magnet unit or SMES unit, modular SMES (M-SMES) with high reliability and strong scalability will become an important structural form of SMES. However, in the process of dynamic power compensation of the M-SMES, the AC loss and eddy current loss caused by the current change will increase the temperature of the superconducting magnet, thus affecting its thermal stability. Therefore, the analysis of the thermoelectric dynamic characteristics of SMES magnets is a complex nonlinear problem involving multi-parameter and multi-time-scale interactions. With the vigorous development of artificial intelligence technology, deep reinforcement learning (DRL) algorithms have emerged. DRL is a kind of data-driven algorithm with strong perceptual ability and decision-making ability, and is applicable for sequence control problems. In this paper, a DRL based M-SMES magnet state predictive control is proposed to solve the problem of the thermal stability of the magnet during the dynamic operation of SMES. Firstly, the interaction between temperature, current, state of charge and other parameters is comprehensively analyzed, and a state database of SMES magnet is established. Then, based on the real-time state and the compensation demand on the grid side, a DRL algorithm is adopted to predict the magnet state and coordinately control each SMES module, which aims at maximizing the compensation capability of the M-SMES within a safe range. Finally, through a case study of M-SMES in the micro grid under different operation modes, the effectiveness of the proposed method is verified.
The high energy physics community around the world is evaluating future collider options to enable exploration of the high energy frontier. As part of that effort, a new international collaboration has formed to evaluate the physics potential and design of a multi-TeV muon collider. Muons, with their short lifetime, require dedicated technology R&D that goes beyond requirements of current collider capabilities. This presentation will provide an overview of the status of muon collider concepts and the program that is being planned to fully develop these concepts in the coming years. This will be followed by a more focused discussion of the magnet technology requirements for such a machine and the R&D synergies that exist with other magnet efforts currently underway.
JT-60SA (JT-60 Super Advanced) is a full-superconducting tokamak, constructed in Ibaraki Japan. The operation of JT-60SA is being carried out under Japan and European Union broader approach project. The superconducting magnet system of JT-60SA has 18 toroidal field (TF) coils, 4 modules of a central solenoid (CS), and 6 coils of equilibrium field (EF) coils.
The TF coils are D-shaped coils lined up on the circumference, and CS and EF coils are circular coils put inside and outside of TF coils, respectively. Height and diameter of the superconducting magnet system of JT-60SA are more than 8 m and 10 m, and the total weight is about 700 tons. Maximum operating current and magnetic field are 25.7 kA and 5.65 T for TF coils, 20 kA and 8.9 T for CS, 20 kA and 6.2 T for EF coils, respectively. The stored energy of the 18 TF coils reaches 1.06 GJ. TF coils were procured by European Union, and CS and EF coils were procured by Japan.
NbTi Cable-In-Conduit Conductor (CICC) is used for TF coils and EF coils, and Nb3Sn CICC is used for CS. High-temperature superconductor current leads (HTSCLs), which are used for the current feeding system to reduce the heat load of cryogenic system, were manufactured by KIT (Germany), and HTSCLs were installed to the current feeding equipment called coil terminal box. Superconducting magnets are cooled with 4.5K supercritical helium. The helium refrigerator and supercritical helium supply system were manufactured by EU. A helium distribution system, including cryogenic piping system, volve boxes were procured in Japan. .
Previous tokamak system called JT-60U had been operated until 2008, then JT-60U magnet system was removed from tokamak building. In 2012, disassembling of the previous system was completed and the construction of JT-60SA started. The first installation of the superconducting magnet was conducted in 2013, and the last superconducting magnet was assembled in 2019. The cool-down of the magnet system started in October 2020, and energization tests were performed from January to March 2021.
It was achieved that the TF coils were operated stably at the rated current of 25.7 kA during 35min. For the CS and the EF coils, an individual energization test was performed. The operating current of CS and EF coils reached 5 kA, one-fourth of the rated current of 20 kA.
During rapid ramp-up and ramp-down test operated in maximum voltage of 5 kV, a current short circuit was generated and stainless-steel cylinder of SHe boundary melt by arcing. Then vacuum condition of the cryostat was lost, and the refrigerator stopped. As a result, commissioning was halted and is now under repair. Repairing will be finished at the end of this year. In 2022, the cool-down will restart, and the energization test will be resumed.
This presentation will report the overview of construction, the result of first commissioning, current works, and future commissioning plan.
The SPARC Toroidal Field Model Coil (TFMC) Project seeks to design, build, and test in a two-year time period a first-in-class, high-field, large-scale fusion magnet using Rare Earth Yttrium Barium Copper Oxide (REBCO) superconductor. The principal objective of the project is to retire the operational and manufacturing risks of REBCO toroidal field magnet technology at-scale for the SPARC tokamak, a net-energy fusion device now beginning construction outside of Boston Massachusetts. Weighing 9,270 kg (20,430 lb) and utilizing over 270 km (168 mi) of REBCO superconductor, the TFMC is designed to obtain 20 T peak field-on-coil and demonstrate quench handling with stored magnetic energy up to 110 MJ. The TFMC will operate at a nominal temperature of 20 K and current of 41 kA with the winding pack containing a total of 256 turns distributed across 16 radial plate-style pancakes. The magnet is now completing construction in a dedicated 370 m$^{2}$ (4,000 ft$^{2}$) facility at the MIT Plasma Science and Fusion Center (PSFC) with REBCO qualification and winding performed at Commonwealth Fusion Systems (CFS). The MIT PSFC has also established a specialized 836 m$^{2}$ (9,000 ft$^{2}$) magnet test facility, which includes several novel capabilities such as binary 50 kA REBCO current leads. The magnet is on schedule to be completed in June 2021 with the initial test campaign planned for July 2021. This talk will provide a high-level overview of the TFMC Project, including the magnet, initial experimental results, and the manufacturing and test facilities. The SPARC TFMC project is a joint effort between the MIT PSFC and the research sponsor CFS.
The plasma confinement of the International Tokamak Experimental Rector (ITER) is provided by the magnetic field generated by 18 toroidal field (TF) coils while 6 poloidal field (PF) and 6 central solenoid coils have the function to drive, shape and pre-heat the plasma. Fusion for Energy (F4E), the European Domestic Agency for ITER, is responsible for the supply of 10 TFC and 5 PFC to the ITER project. The ITER Organization (IO) team is instead responsible for the design of such coils as well for the coordination of the activities of the different Domestic Agencies (DA) producing the different components, and their assembly into the Tokamak. The PF coils utilize NbTi Cable-in-Conduit-Conductor and have different diameters between 7 and 25 meters and a weight up to 400 tons. So far two EU PF coils have been delivered to IO. PF6 has been manufactured by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) under a collaboration agreement with F4E. PF5, has been manufactured at the ITER site by a cluster of suppliers managed and supervised by F4E. The remaining 3 PF coils, also being produced in Cadarache: PF2 will be completed by 2021 while the last coil (PF3) will be ready 2023. The TF coils utilize a Nb3Sn conductor and are manufactured with the “Wind, React & Transfer” method. At the time of the abstract, the first 3 TF coil have been completed and delivered to ITER, and 2 more coils will be delivered within 2021. The remaining TF coils will follow at a rate of about one every 3-4 months. We will report on the main aspects of the 6 coils completed so far, on the main results obtained together with some statistical analysis as well as on the status of the remaining coils.
QST, as Japan Domestic Agency (JADA) in ITER, has responsibility to procure 9 ITER Toroidal Field (TF) coils and all 19 TF Coil Cases (CC). The 9 TF coils are procured by two suppliers to accelerate their production. In the first supplier, four TF coils have been fabricated and three of them has been delivered to the ITER site. On the other hand, the second supplier fabricates the forth TF coil in JADA as their first TF coil and this TF coil was completed. More detailed measurement of dimension and more optimized quality control during fabrication was performed from the experience in manufacturing TF coils in the first supplier. As a result of these efforts, we succeeded in more precise controlling of the required tight tolerances. For example, current center line (CCL) of the final coil is estimated within deviation of 0.3 mm in radius at the inboard straight section of TF coil, where most tight tolerance of 1.3 mm in radius is required. These outcomes of the first TF coil manufacturing, especially assembly of winding pack and CC, in the second supplier will be reported in this paper. In addition, progress of ITER TF coil fabrication in Japan is briefly reported.
The Central Solenoid (CS) is a key element of the ITER Magnet system, including six identical coils, called modules, assembled together to form a 4 m outer diameter, 13 m high solenoid. It is a superconducting magnet, using a 45 kA Nb3Sn conductor internally cooled by circulation of supercritical helium at 4.5 K with a peak field up to 13 T. It is enclosed inside a structure providing vertical pre-compression and mechanical support. Procurement of the components and the special assembly tooling of the ITER CS is the responsibility of US ITER, the ITER Domestic Agency of the USA, while the ITER Organization (IO) will carry out the assembly of these components.
US ITER has awarded several contracts since 2011 to supply seven modules, including a spare, structure components, and the special tooling required for the CS pre-assembly. All deliveries are organized with the objective to start the CS assembly at IO site by the end 2021. IO is now starting first phases of the assembly mostly focused on on-site assembly contractor.
The paper describes the general CS assembly status and outcomes from first module factory acceptance tests results overview, preliminary training for special activities up to the start of the first module stacking. The special assembly processes and related tooling qualifications will be detailed. A focus is given on the module factory acceptance tests, lifting tool and the busbar joint assembly qualification.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
The poloidal magnetic field of ITER is provided by 6 Niobium–Titanium (NbTi) coils mainly for plasma shaping and position control. The fabrication of the two lower coils PF6 from China ASIPP and PF5 from European F4E has been completed and the coils installed in the bottom of the Tokamak pit in 2021. This paper presents the challenge of the manufacturing process, which involves manufacturing of several dozens of superconducting double pancakes, requiring bending, insulating and welding steps to keep accuracy of a few mm on dimensions up to 25m. The reproducibility and reliability of the manufacturing processes to manage magnet winding/insulation and cryogenic skills are essential for final quality and schedule robustness.
After having successfully completed final thermal cycles for site acceptance in Cadarache, the PF6 and PF5 have been delivered simultaneously and handed over to IO. This paper demonstrates the assembly scenario of the two coils, including assembly tools for transportation, preparation for lifting, lifting tooling design, temporary supports design in cryostat and alignment of positioning on supports from assembly hall to the tokamak pit. The coils are sensitive components and preservation steps are needed to protect them in the pit during other assembly operations.
In future, the two coils will sit in pit for several years until mounted onto the TF coils through the support then connected to feeders at the coil terminals. PF6, PF5 will firstly rest on temporary supports, and later shift up by jacks and conical guides to align onto TFC. The alignment & shimming processes and tightening will be presented to show the practical functionality and avoidance of interferences with the other components of the ITER tokamak which achieving high accuracy to avoid error fields.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
The ITER Poloidal Field (PF) coils consists of six coils, PF1 through PF6 that serve to stabilize the position and control the shape of the plasma in the tokamak. PF1 coil, which is one of six PF coils, is procured by the Russian domestic agencies (RFDA) under procurement arrangement between ITER and RFDA. After signing the PAs, for the supplier of PF1 Coil, RFDA has selected Efremov institute as a main supplier of the fabrication of PF1 coils. For the preparation work for PF1 coil manufacturing, RFDA and Efremov institute have completed the activities on the building and tooling preparation in 2014.
As a first step of manufacturing, several qualification samples such as helium inlet sample, a mock-up with 3x3 dummy conductors and the turn insulation samples with resin were fabricated. Mechanical and electrical testing of the samples have been carried out at room temperature and 77 K. As PF1 coil is fabricated by stacking 8 double-pancakes wound by two-in-hand winding scheme, a dummy double pancake and a winding pack mock-up have been fabricated to check the quality before starting real manufacturing of PF1 coil.
Based on the experiences of various qualification, eight double pancakes have been successfully fabricated and these eight double pancakes have been successfully stacked and impregnated to make a winding pack.
This paper focuses on the latest activities for ITER PF1 coil, which include the requirements, the various tests, the acceptance criteria and the manufacturing process. Finally, the paper concludes with a summary of the result of PF1 coil manufacturing and future work to be carried out.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
The Wendelstein 7-X (W7-X) stellarator equipped with a large cryogenic magnet system (MS) [1] has been extended for the long pulse operation at the Max-Planck-Institute for Plasma Physics in Greifswald, Germany. If the main focus of mechanical engineers during first two experimental campaigns was on the static structural strength of the MS, the issue of component cyclic behavior is addressed now. Therefore in parallel to the W7-X completion process, the MS global finite element model (FEM) and its postprocessing have been developed further to consider the effect of winding pack (WP) embedding (EB) process on coil stiffness and deformations as well as on planar coil case pins and bolts plastification. The updated post-processing routine predicts now how many electromagnetic cycles with particular loading patents could be safely withstood with required margins by the system components after cool down-warm up cycles.
The procedure of implementing the EB effect in the ANSYS® global FEM is based on the death/birth feature of particular elements, special fixation algorithm and careful check of the unavoidable artificial stress level.
The paper focus is on the structural cyclic behavior modelling of the W7-X magnet system components. Several related issues are addressed, such as:
1). Specific features of winding pack embedding modelling;
2). Reasonably simplified modeling of multiple pins and bolts in the FE global model;
3). Accurate prediction of plastic strain and stress levels using detailed local pin/bolt FEMs;
4). Influence of WP embedding on mutual coil displacements, stress levels, number of cycles and sensor signals to be monitored in the nearest future.
In addition, lessons learned so far are also briefly summarized.
[1] V. Bykov, J.Zhu, et al, Cyclic behavior of Wendelstein 7-X magnet system during first two phases of operation, IEEE Trans. Applied Superconductivity, Volume: 30, Issue: 4, page(s): 1-5, June 2020
Neurospin is a neuroscience research center located in France at CEA Saclay. The facility is already hosting several MRI magnets and Iseult, an innovative Whole Body 11.7 T MRI system, will be available very soon.
The core part of Iseult is an actively shielded NbTi magnet cooled with a superfluid helium bath at 1.8K, that will provide a homogeneous field of 11.7 T within a 90 cm warm bore. After 15 years of work and efforts, the magnet successfully reached its nominal field for the first time in July 2019. Since March 2019, the magnet is being kept continuously at 1.8K. The field homogeneity has been adjusted and the control system tested against internal and external faults that could affect the future MRI operation. The MRI equipment has been integrated and commissioned individually. The interaction between the gradient coils and the magnet, plus its impact on cryogenics and on the magnet safety system has also been studied up to 11.7T. The paper will summarize the status of the Iseult MRI commissioning, the cryoplant status after two years of operation at nominal temperature, and it will present the first images obtained in October 2021 after 20 years of efforts.
We are developing a helium-free 3T-MRI high-temperature superconducting magnet for whole-body imaging using REBCO wire. The development of a meter-class REBCO magnet has few practical examples, and the problem in the manufacture has not been clarified. Therefore, we grasped the characteristics of REBCO coils by manufacturing meter-class coils and evaluating the current-voltage characteristics of each coil.
The prototype MRI magnet consists of more than 200 single pancake coils. The maximum inner diameter of the coil is φ1.2 m. The REBCO wire is 4 mm wide and insulated with a fluorine-coated polyimide tape. Vacuum impregnation with epoxy was performed to facilitate the handling of the coil. After that, the current-voltage characteristics were acquired for each coil in liquid nitrogen, and it was judged as a good coil or a degraded coil. The yield rate was 82%. To improve the yield rate, we have been investigating the degradation factors of REBCO coils. Based on the insights of the failure mechanisms in the coil winding, possible measures in the coiling has been discussed. Details will be reported in the presentation.
Part of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO).
Curved superconducting bending magnets have clear potential for compact hadron therapy gantries and medical synchrotrons. A combined function superconducting bending magnet design based on collared cos-theta coils is proposed for a novel compact hadron therapy gantry initiative, SIGRUM. These 3 T magnets, based on the technologies extensively developed for the LHC project, include several gantry-specific features that shall be developed and validated by a demonstrator magnet. The main development areas include fabrication of epoxy-impregnated cos-theta Nb-Ti coils with 2.2 m radius of curvature along with the assembly of the surrounding curved cold mass. The demonstrator magnet test will also serve to validate and fine-tune the advanced numerical models for the electromagnetic and thermal optimization of the final conduction cooled gantry magnet. This paper presents the magnetic and mechanical design optimization of the demonstrator magnet, the results of the numerical modelling of the transient losses during operation as well as the magnet quench protection analysis.
The innovative concept of using a combination of two identical superconducting bend magnets working at a fixed field in a proton therapy gantry, allows for a light and compact design, while being able to deliver protons over a range of 70-230 MeV. In this concept, the gantry is conceived as achromatic, allowing the magnets to operate at a constant field, and therefore avoiding the technical challenges and risks of the fast-field ramping required in other designs to accommodate various beam energies.
The proposed design of the superconducting magnets consists of a series of straight, double-pancake coils embedded in an iron yoke. These coils are made of Bi-2223/Ag (DI-BSCCO) tape, and produce a maximum magnetic field of about 3 T at 12 K, with a multi-stage conduction cooling system. This paper presents the mechanical and thermal analysis of the magnet, based on finite element simulations. The main components of the mechanical structure, winding of the coils, assembly, and values of stress in the conductor due to the electromagnetic forces are discussed. Furthermore, the cooling design, along with the expected temperature gradients within the superconducting coils are also addressed.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program under contract No. DE-AC02-05CH11231.
A collaboration between CERN, CNAO, INFN and MedAustron has been formed with the aim at designing a light rotating gantry suitable for hadron therapy based on 430 MeV carbon ion beams. After a preliminary design based on 3 T dipole field, now the collaboration is engaging to improve the design to 4 T or more. The magnets are designed according to cosθ layout to be wound with Nb-Ti superconductor Rutherford cable. One of the main challenges of these magnet is the very small curvature radius of 1.65 m with a relatively large aperture, 90-100 mm. Another challenge is the use of cryogen-free magnets despite the cycling operation with 0.3-0.35 T/s. The design of these 4 T dipoles, to which will be superimposed a further 0.3 T of quadrupole field, is therefore very challenging. The paper will report the preliminary design at 4 T (aiming at least 20% margin in operative conditions) as well as the parameters of a 1 m long demonstrator to be manufactured at INFN-LASA in one and half year. The conductor measured characteristics, with 3 micron Nb-Ti filaments embedded in a Cu-Mn alloy matrix. The resulting gantry is very compact, and we are working on integration between gantry structure and magnets to allow reducing the rotating weight to less than 50 tons, which is a factor five gain on the present state-of-the art.
The use of carbon ions in particle therapy can enhance the treatment quality, introducing higher biological effectiveness compared to photons and protons.
Rotating gantries are nowadays used to deliver particle beams from different directions to obtain precise conformal dose mapping at the tumour location. The mechanical stability requirements during the rotation usually require heavy structures.
Superconducting magnets can be used to reduce size and weight of the machine, but complex cryogenics systems are needed to maintain superconductivity during the gantry rotation.
The seek of novel gantry configurations for carbon ions is one of the greatest challenges that need to be tackled to widen the accessibility of hadron therapy to a larger number of patients.
The concept of GaToroid, a steady-state toroidal gantry implemented with superconducting magnets, can be used to deliver the beam from different directions without the rotation of neither the structure nor the patient.
In this work, we present the magnetic design of two GaToroid solutions for Carbon ions, conceived to operate with Nb-Ti cables in the range of 6-7 Tesla. The first solution was designed with 20 pairs of coils, to maximize the flexibility of the treatment, and with an internal diameter of 3.5 meters, to allow a complete couch rotation on the plane.
The second option, based on a more conservative design with an internal diameter of 2.3 meters and 8 couples of coils, aims to be a compromise between the complexity and cost of the machine, and the flexibility of the treatments.
For both configurations, the coil geometry and current distribution were optimized to maximize the carbon ion momentum acceptance for complete coverage of the treatment range without variation of the toroidal magnetic field.
The studies here presented can be considered as the first milestone toward the design of toroidal gantries for heavy ions.
We aim to develop a high-resolution 1.3 GHz (30.5 T) nuclear magnetic resonance (NMR) LTS/HTS magnet operated in the persistent-mode. For this magnet, superconducting joints between HTS tapes are indispensable. We have already developed a persistent-mode 400 MHz (9.39 T) LTS/REBa2Cu3Oy (REBCO, RE = Rare Earth) NMR magnet with superconducting joints between REBCO tapes. The operational data revealed that the REBCO superconducting joints perfectly functioned in the persistent-mode NMR magnet.
On the other hand, the 1.3 GHz NMR magnet also needs superconducting joints connecting (Bi,Pb)2Sr2Ca2Cu3Oy (Bi2223) tapes. In our recent study, novel superconducting joint technology for commercial Bi2223 tapes was developed using intermediate Bi2223 joint layers. Small joint samples showed high critical current properties and low joint resistances typically less than 10−12 Ω [1–3]. However, the performance of the joint has not been evaluated in a persistent-mode NMR magnet thus far. In the present study, we have been developing a world-first persistent-mode 400 MHz LTS/Bi2223 NMR magnet with the Bi2223 superconducting joint. The Bi2223 inner coil wound with one Ni-alloy reinforced Bi2223 tape was terminated with our joint technology. The coil was successfully operated in self-field at 4.2 K in the persistent-mode prior to the construction of the whole magnet. Evaluation of the performance of the Bi2223 joint will be performed through the 400 MHz NMR magnet operation.
[1] Y. Takeda et al., Appl. Phys. Express 12 (2019) 023003.
[2] Y. Takeda et al., presented at ASC2020, Wk1LPo3F-02.
[3] K. Kobayashi et al., presented at ASC2020, Wk2LOr1A-05.
This work was supported by JST-Mirai Program Grant Number JPMJMI17A2 and Special Postdoctoral Researcher Program at RIKEN, Japan.
One of important application for HTS bulk magnets is compact NMR/MRI. We have developed a single-sided (unilateral) HTS bulk magnet and a home-built NMR spectrometer to get NMR relaxometry signals from the sample on the outside of the magnet. The NMR signal relaxation rate, the only parameter that is observed in NMR relaxometry, still gives us the information about the mobility of molecules, including fluctuations and diffusion, in the microscopic environment. This measurement method needs less magnetic field homogeneity compared to ordinary NMR spectroscopy. NMR relaxometers using permanent magnets are applied for food science to determine moisture content, solid fat content (SFC). HTS bulk magnets can supply higher magnetic field, which means higher sensitivity for shorter measurement time and stronger magnetic field gradient for higher spatial resolution. The bulk magnet was activated by pulsed field magnetizing method. Trapped magnetic field strength at the center surface of the cryostat was 1.32 T.
Our home-built NMR spectrometer is a key part of our achievement. A modified USRP-2920 (National Instruments) is applied as an NMR spectrometer. This device is called software-defined radio (SDR) and functions traditionally implemented in hardware are implemented by software. We have developed an NMR spectrometer software using LabVIEW and NI-USRP (National Instruments). Our spectrometer suits for compact HTS NMR/MRI magnets, because it is not only very compact and cheap, but also very flexible with higher sensitivity. The 1H NMR signals at 47.8 MHz were observed using spin-echo excitation pulse, even the silicone rubber sample with 4 mm in diameter and 9.5 mm in length was settled in inhomogeneous magnetic field at 3.7 mm away from the center surface of the cryostat. We have succeeded to get 1H NMR signals from a single-sided HTS bulk magnet by pulse field magnetization for the first time in the world.
We have been developing conduction-cooled HTS magnets wound with REBCO-coated conductors for MRI systems, with the aim of developing 9.4 T MRI magnets for whole-body and brain imaging. One of a key technology to implement the REBCO coil is quench protection and we proposed a quench protection method using electrically conductive epoxy resin [1]. The electrically conductive epoxy resin is attached to the edge of the winding. When the coil voltage rises unintentionally, the excessive current can be automatically bypassed from turn to turn through the electrically conductive epoxy resin. In order to verify the effectiveness of this method with a large-scale coil which has higher stored energy, an HTS MRI model magnet equipped with conductive epoxy resin was designed and fabricated. The magnet has a REBCO multi coil composed of 100 single pancakes whose inner diameter are 500 mm. The total conductor length is 31 km, and the total inductance is 91 H. The central magnetic field is 3 T at 145 A, and the size of the homogeneous magnetic field region is 200 mm diameter spherical volume (DSV). This paper presents the design, fabrication of the REBCO multi coil and test results of the HTS MRI model magnet in a conduction-cooled configuration.
[1] H. Miyazaki, S. Iwai, et al: “Study on a Stacked REBCO Coil Composed of Six Single Pancakes with Electrically Conductive Epoxy Resin,” IEEE Trans Appl. Supercond., vol. 30, no. 4, Jun. 2020, Art. no. 4704105.
In the last few years High Temperature Superconducting (HTS) non- and partially insulated coils have shown exceptional resilience towards quench and other disrupting effects in many practical experiments. These coils are therefore widely investigated as an approach towards larger high field HTS magnets for both Fusion and Particle Accelerator applications. One of the main concerns for these applications is the quench detection and protection. However, due to the complexity of the physics involved, only few models are capable of simulating the emergent behavior of these coils. To scale to much larger systems, it is necessary to gain a detailed understanding of the electro-magnetic and thermal behavior. To this aim a network model named Raccoon was developed. The model can simulate full-scale, non-, and partially insulated coils down to tape level detail. In this paper these numerical simulations are compared to experimental data that was acquired during quench tests on multiple solenoidal coils, further complemented by data from literature. The comparison is intended as validation, but it additionally provides a unique view of the normal zone propagation and corresponding current redistribution in HTS coils. Using the numerical results, a more theoretical approach will be devised that allows to explain many of the effects observed.
The MADMAX project is a dark matter Axion research project where the mass of which is expected to be in the range of 100 µeV. To study this particle, a large superconducting dipole magnet composed of 18 coils and generating a field of 9 T in a 1.35 m bore has been designed. For this application, a new conductor have been developed in a Cable-In-Conduit-Conductor (CICC) configuration with a copper stabilizer and cooled with stagnant superfluid helium in the CICC channel. As several hundreds of meters separate the center of each coil from the helium bath surrounding the whole magnet, and given the small helium cross-section in the CICC, quench dynamics is clearly an issue for the MADMAX project.
In order to study experimentally the quench propagation in such a magnet, we designed a MADMAX-like solenoidal prototype called MACQU based on numerical modeling performed with THEA®. The goal of this study is to measure a MADMAX-like quench propagation velocity to demonstrate that the magnet protection design is safe. Another target of the study is to compare the experimental results with numerical computations that predict two different dynamic phases: a first quench propagation with a constant speed and a second one with acceleration. The MACQU coil prototype has been instrumented to capture the quench propagation phenomenon with heaters, temperature sensors, voltage taps and SQD (Superconducting Quench Detection wires).
This paper will give the main features of the MACQU coil design and the rationale behind it to be representative of the Madmax quench behavior. The whole experiment will be presented including instrumentation and quench test protocols. The experimental data will be analyzed in detail in order to identify the main physical phenomenon driving the quench dynamics. Finally, the experimental velocities will be compared to the numerical ones and the results discussed.
REBCO coated conductors (CCs) are expected to be applied to high field magnets due to their high longitudinal tensile strength and excellent critical current characteristics in high fields. For large scale magnets with large stored energy, the coil design is determined by the feasibility of quench protection. Although various quench protection methods have been proposed for REBCO magnets, the most traditional and straight forward approach is to increase the copper stabilizer and reduce the current density. This approach leads to a significant increase in conductor length to generate a required magnetic field in case a small bore diameter magnet, while the conductor increase would not be serious in case a large bore diameter one. Based on this approach, we have successfully fabricated a practical cryogen-free magnet with a large bore of 200 mm-diameter and a central field of 5 T using REBCO CCs laminated with 0.3 mm-thick copper tapes [1]. For further study, we investigated the feasibility of quench protection through quench tests and analysis in this study. We conducted quench tests on samples of copper-plated REBCO CCs with additional copper tape to assume an energy recovery method with external resistance. In the quench tests, the decay time constant after shutdown was varied to find the conditions that can protect the magnet with high stored energy. In the analysis, we estimated the normal voltage and hot-spot temperature in the quench tests by coupled thermal-electrical analysis. We confirmed that the experiment and analysis were in good agreement and that quench protection was feasible under practical conditions.
[1] M. Daibo et. al., IEEE Trans. Appl. Supercond., 23 (2013) 4602004.
Growing interest for high-temperature superconducting (HTS) tapes, in particular the 2nd generation with functional layer of REBCO (RE = Y, Gd, Er,…), is motivated by an impressive progress in capability of such conductors to transport large currents. Nevertheless, this essential property, characterized by the value of critical current, Ic, quite often fluctuates along 100-1000 m lengths by more than 5%. Particularly dangerous are the „weak spots”, with sudden reduction of critical current on the scale of few milimeters. At transporting the currents comparable to the Ic, determined on the “healthy” portion of conductor, this location will experience disproportionate heating. In some extent, the excess heat could be removed to its surroundings. Recently we developed an analytical prediction for the maximum of current that could be transported before turning the weak spot into a “hot spot”, with rapidly increasing local temperature. One of the outcomes of this model is the prediction that, on parity of the locally reduced critical current, shorter weak spots will sustain higher currents than larger weak spots. On the other hand, testing of the critical current is usually performed on conductor lengths substantially exceeding the milimeter size of a weak spot. Then, smaller weak pots could easier escape attention during such inspection. A quantitative analysis including both these phenomena allowed to find the relation between the critical current, obtained in testing of the sample containing a weak spot, and the current causing its thermal runaway. It is then possible to draw recommendation for a minimum distance of voltage taps during the critical current check in a conductor intended for manufacturing of a HTS coil.
High-temperature superconductors (HTS) are expected to have a major impact on the development of future particle accelerators and fusion energy systems. One of key challenges associated with HTS is a slow propagation of the normal zone that complicates early detection of thermal runaway (quench) in an HTS magnet using voltage-based techniques. Furthermore, fusion systems require field ramping rates up to several T/s under strong time-varying ac magnetic fields imposed on the conductor which makes voltage-based quench detection difficult or impractical. We propose an alternative non-voltage quench detection solution based upon monitoring mechanical stress wave propagation in a solid fiber-like flexible waveguide. The latter can be co-wound with the superconducting cable and carry acoustic wave over long distances. Acoustic waveguide technology allows for measuring local variation of strain or temperature in a way similar to optical fibers. However, unlike fiber-optic sensors, mechanical waveguides are constructed of robust materials and eliminate the need for expensive and complex signal receivers and data processing equipment. We will present our early developments in cryogenic acoustic waveguide technology, and discuss preliminary experiments conducted towards validating it for future use in practical HTS magnets.
A Mach-Zehnder Interferometer (MZI) based optical fiber sensing technique developed and patented by EPFL is an efficient and economical way to detect hotspots in HTS applications. Due to the MZI sensitivity being a composite of strain sensitive and temperature sensitive contributions, the MZI gives an instantaneous response to a quench (within 10 ms) resulting from the quick strain transfer to the optical fiber. However, the MZI output signal also manifests the environmental noise caused by mechanical vibrations, bubbling in the cryostat and temperature variations along with the response to the quench. This presents the problems of false alarms and indiscernible response to a quench. Discrete wavelet transform (DWT) has been proven to be a useful tool for feature extraction in different fields requiring signal categorization, and hence holds the potential to enable quench recognition in the MZI output. This paper proposes an effective approach of performing DWT based feature extraction on experimental data and subsequently using the extracted features for the MZI response classification. Feature extraction is implemented using discrete wavelet coefficients extracted at different decomposition levels to calculate statistical features useful for clustering and identifying quench in the MZI signal. This method could be a valuable supplement to the MZI technique by enabling the development of a real time application that can process the MZI output data as well as eliminate the occurrences of false alarms, thereby facilitating reliable quench detection. With this development, the MZI technique would become an even more attractive solution for the health monitoring of HTS applications.
The critical heat flux in liquid hydrogen is ten times higher than that in liquid helium, and is approximately half of that in liquid nitrogen. Since the resistivity of pure metal such as copper or silver at 20 K is less than one-hundredth of that at 300 K, HTS magnets immersed in liquid hydrogen are expected to satisfy the cyostable condition at a practical current density for electric power equipment. In order to examine cryostability of HTS magnets in liquid hydrogen, a pool-cooled Bi2223 magnet with a 5 T magnetic field at 20 K has been designed and fabricated. The magnet consists of six outer double pancake coils with the inner diameter of 0.20 m and four inner double pancake coils with the outer diameter of 0.16 m. The turn numbers are 77 turns per layer for the outer coils and 73 turns per layer for the inner coils, and the 5 T magnetic field is induced between the outer coils and inner coils at the current of 400 A. Each double pancake coil has been tested in liquid nitrogen to check the soundness before assembling. Prior to excitation tests in liquid hydrogen, the whole assembly is planned to be tested in liquid nitrogen to evaluate the allowable heat generation, over which the resistive voltage continues to rise. The excitation tests in liquid hydrogen are planned in summer this year.
The Grenoble Hybrid magnet is a modular platform using resistive and superconducting technologies to produce various DC high magnetic field and flux configurations for the scientific community. They range from 43 T in 34 mm diameter with 24 MW of electrical power to 9 T in 800 mm diameter, when the superconducting coil is used alone. Thanks to the ongoing upgrade of the electrical power installation at LNCMI-Grenoble to 30 MW, and possibly to 36 MW, the possibility to increase the total field up to 45-46 T in the near future is anticipated and studied in detail. The key design parameters will be recalled including the specifically developed Nb-Ti/Cu conductor, the large-bore outsert superconducting coil, the magnet cryostat with its structure including the eddy-current shield, the cryogenic line for the interconnection with the cryogenic satellite and the fully dedicated 150 l/h He liquefaction plant. All components of the hybrid magnet platform have been built, tested and delivered to LNCMI-Grenoble, where integration and final assembly are continuing. The status of the project will be presented together with the main problems encountered and solved. It includes the recent commissioning tests of the cryogenic satellite producing the pressurized superfluid He at 1.8 K as well as the successful powering tests of the specially developed current leads at ultimate current and under fully degraded cooling conditions simulating the worst-case accidental scenario.
This project is supported by Université Grenoble-Alpes (UGA), CNRS, French Ministry of Higher Education and Research in the framework of “Investissements pour l’avenir” Equipex LaSUP (Large Superconducting User Platform), European Funds for Regional Development (FEDER) and Rhône-Alpes Region.
To extend its user’s facilities the High Field Magnet Laboratory (HFML) of the Radboud University is in the process of building a 45 T hybrid magnet. The magnet system will consist of a 22 MW, 32.7 T Florida-Bitter type of resistive insert and a 600 mm bore, 12.3 T Nb3Sn based CICC type of superconducting outsert magnet. The Nijmegen hybrid magnet will be operated with separate current sources for the superconducting and resistive coils (20 kA at 10 V, and 40 kA at 550 V, respectively). The superconducting outsert coil was wound, heat-treated and impregnated at the National High Magnetic Field Laboratory (FL, USA) and arrived in 2018 in Nijmegen. At present, system assembly and integration near completion, all auxiliary systems are in place and are going through their final commissioning phase. In this paper, we present the status of the cryostat, the binary (Cu/BSCCO) current leads jointly developed by HFML and NHMFL, the cryogenic and electro-technical installations, system control, quench and coil protection and the manufacturing process of the resistive insert. We particularly highlight implemented new concepts for the mechanical support systems of both the insert and the outsert coils.
In the quest for all-superconducting very high field magnets, the first successes where obtained with High Temperature Superconducting inserts wound using BiSrCaCuO conductors. It is the case for the 25T CSM (Cryogen-free Superconducting Magnet) installed in 2015 at the HFLSM (High Field Lab. for Superconducting Materials). It remains to date the only magnet above 24T that is fully open to users, with a convenient 52 mm room-temperature bore. Even though BSCCO conductors are still improving, REBaCuO Coated Conductors are more attractive for magnets exceeding 30T, due to their higher mechanical-strength/critical-current ratio. One of the difficulties for the practical implementation of REBCO inserts is the protection in case of thermal runaway due to local defects. This problem is rendered particularly difficult by the extreme energy densities that these inserts can reach.
Different approaches are being studied to solve this problem. We recently proposed to use a conductor made of two REBCO tapes co-wound, reducing significantly the likeliness and potential impact of local defects. In addition, we propose to use a sensitive voltage-based detection system to obtain advance warning of thermal runaways, allowing a safe protection discharge at moderate speed. This solution was chosen for the ongoing project to upgrade the 25T CSM to 30T by replacing the existing BSCCO insert, while keeping the outsert and the cryogen-free cooling system. The R&D effort conducted in the course of this project aims beyond 30T. We will present practical design solutions for a 33T conduction-cooled magnet, in terms of electromagnetic and mechanical margins, cooling, and protection. These solutions are validated by recent R&D coil results. We then discuss the options to improve the present conduction-cooled technology for 40T+ designs, in particular in terms of HTS/LTS combination and HTS winding mechanical reinforcement.
A largescale of R&D project for China Fusion Engineering Test Reactor (CFETR) named the comprehensive research facility for fusion technology (CRAFT) has been launched in Sep. 2019. A superconducting experiment testing platform (Super-X for short) will be constructed for evaluating the future superconducting part performance. The maximum testing magnetic field is 15 T, the dimensions of testing space are 100 × 160 × 550 mm, the field homogeneity of testing space is better than 95%, and the maximum testing current 100 KA. For now, the engineering design for Super-X has been accomplished. The DC magnet is a kind of split coil includes two symmetrical coils assembly. Each coil assembly is composed of three concentric Nb3Sn coils. The peak field is 15.7 T and the field homogeneity reach to 99.3%. The innermost diameter is about 600 mm and the outermost diameter is 2874 mm. The high-Jc Nb3Sn cable-in-conduit conductor (CICC) is used for the high field coil (HFC) and medium field coil (MFC) and the ITER grade Nb3Sn CICC for the low field coil (LFC). This paper present the engineering design of the DC magnet system.
A large-bore Nb3Sn “cable test facility magnet” designed to test advanced cables and inserts in a high transverse background field, is here proposed. The project is funded by the U.S. Department of Energy (DOE) Office of Science (SC). The test facility dipole magnet (TFD) creating the background field is developed at the Lawrence Berkeley National Laboratory (LBNL). In line with the design considerations of LBNL HD2, and CERN-CEA FRESCA2, the TFD magnet is conceived as a block-type dipole, with coils tilted in the ends (flared), and that uses a support structure based on the bladder and key concept using an external aluminum shell. In the axial direction, steel rods and endplates provide the axial support to the coil ends during the powering of the magnet. The TFD magnet creates a maximum field of 15 T at 1.9 K, in a bore of 100 x 150 mm. This paper presents the main engineering design of the magnet, defining the cable, coil layout, winding parameters, and main structural elements. Furthermore, the central aspects of coil fabrication and magnet assembly are also addressed.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program under contract No. DE-AC02-05CH11231.
A 35 T/17 mm cold-bore full superconducting magnet has been designed. It consists of a 15 T LTS background magnet with the inner radius of 150 mm, and a 20 T HTS insert magnet with the inner radius of 17 mm. We hybrid used no-insulated and steel-insulated REBCO tapes to wind the HTS insert, with the aim of protecting part of HTS coils in a relatively safe state. Two mechanical models were built to estimate the stress distribution inside the HTS coils during operation. The influence of the screening current field on stress was discussed. A quench circuit model was built to simulate the influence of mutual inductance between the two HTS coils during quench. The 20 T insert magnet is being fabricated by ASIPP and Tsinghua University and planned to be tested in 2021. No-insulated HTS coils have been completely wound and current-capacity test results at 77 K were presented and discussed.
A 25 T All YBCO superconducting magnet with a warm bore of 52mm is designed for high-frequency gyrotrons in Wuhan National High Magnetic Field Center (WHMFC). The designed peak-peak field inhomogeneity is 50 ppm within 10mm Diameter of Spherical Volume (DSV). The magnet includes Inner, middle and Outer Coils which consists of 34, 56 and 68 double pancakes (DP) wound by bare YBCO tape, respectively. The first part of this paper presents an in-house superconducting magnet optimization code to obtain optimal electromagnetic design with integer numbers of layer and turn. The constraints such as central magnetic field, inhomogeneity, stray field, dimension and critical current characteristics are considered. The second part of this paper presents the stress analysis. The contact status within the magnet and effects of winding tension and over-banding are studied. The third part of this paper presents AC loss calculation model which includes magnetization loss, turn-turn loss and eddy current loss, which results in helium boil-off.
In 2015, we achieved 24.6 T by the 25T cryogen-free superconducting magnet (CSM) with a Bi2223 insert. Then it has been used as a user magnet at High Field Laboratory for Superconducting Materials, IMR, Tohoku University. The Bi2223 insert consists of 38 double pancake coils with high strength Ni-alloy/ Bi2223 tapes (Sumitomo type HT-Nx) [1]. In this case, we used turn separation in the middle section (52-185 turn in 257 turns) of the Bi2223 pancakes to reduce the maximum hoop stress. However, the problem of short circuit in a part of Bi2223 pancake was found related to the weak stiffness of turn separated pancakes. Then we modified the Bi2223 pancakes to mechanically separated 5 section pancakes, in order to improve those stiffness. Finally, the 25.1 T can be generated with an 1 hour ramping time. In the new 25T-CSM, the maximum stress in the Bi2223 insert could be decreased and the number of spike noises under ramping are much reduced. Previous problems, modified design, operation results and magnetic field stability will be presented in the presentation.
References
[1] S. Awaji et al., Supercond. Sci. Technol. 30 (2017) 065001.
We report experimental and theoretical results of power generation characteristics of a 1 kW class fully High Temperature Superconducting Induction/Synchronous Generator (HTS-ISG) that consist of a stator winding using REBCO coated conductor and a rotor winding using BSCCO tape.
Recent advances of the HTS material technology make it possible to realize electric machines that show high efficiency and power density. In particular, REBCO coated conductor has excellent critical current characteristics even in a relatively high temperature region near atmospheric pressure boiling point of liquid nitrogen, and also has excellent mechanical resistance to bending diameter.
In this study, we designed and manufactured a prototype of 1 kW class fully-superconducting generator (4-pole), with reference to the results of fully superconducting 50 kW model motor [1]. The three-phase stator winding is made of REBCO coated conductors and the squirrel-cage rotor winding is made of BSCCO tapes. In particular, attention should be paid to the challenge of a structure in which the bending diameter of the stator REBCO coil is about 20 mm or less. For the first time, we succeeded in a superconducting power generation test in liquid nitrogen (77K) and observed a lot of unconventional generation characteristics. We will also make theoretical discussions to explain the experimental results. Furthermore, using the above test results as a benchmark, we will report on the status of studies on increasing the current capacity of the HTS-ISG by applying the Face-to-Face Double Stacked (FFDS) conductor, of which two REBCO tapes are joined each other with low resistance [2]. This study would provide a strong reference for the practical application of fully-superconducting generators.
This work was supported by JSPS KAKENHI Grant Numbers 19H05617 and 17H03218.
[1] T. Nakamura et al., IEEE Trans. Appl. Supercond., 29(5) (2019) 5203005
[2] T. Kiss et al., 30th ISS, WB6-6-INV, 2017
The cryogenic and electrical tests of a hundred-kW HTS dynamic synchronous condenser (DSC) prototype were conducted in recent months. The performance of this prototype, which was developed to verify some key technical aspects for the future 10-Mvar HTS DSC, was evaluated based on the test results. The active power test results were nearly the same with design values, which indicated that the air-core stator has small synchronous reactance as the electromagnetic simulation predicting. The temperature data of HTS rotor during the running period, which were acquired from a rotating data acquisition devic (rDAQ)，showed that forced helium-gas circulating method + conduction cooling is sufficient for the cryogenic requirement. Also, in the fast-excitation process of the HTS rotor, the temperature of the HTS magnet almost unchanged. But in the long-time 1500-PRM running test, the temperature increment of the rotor bearings influenced the stability of the HTS rotor through the epoxy torque tubes. In both static cooling procedure and rotating tests, the helium cryogenic rotating coupling (CRC) performed well, which can be applied in the future 10-Mvar HTS DSC.
A no-insulation (NI) high-temperature superconductor (HTS) winding technique has been mainly applied to direct-current (DC) high field magnets, while its application to alternative-current (AC) machines is limited. One of the potential applications of the NI HTS winding technique is a synchronous rotating machine, typically employed in aircraft and ship electric propulsion. Under an ideal steady-state operation of a synchronous machine, the NI HTS field winding experiences essentially DC magnetic fields, therefore the steady-state responses of an NI HTS field winding are likely to be identical to those of the conventional insulated windings. However, in an actual operation, the NI HTS field winding inevitably experiences transient operational dynamics such as an acceleration, load fluctuations and more, which obviously affects the torque and speed characteristics of an NI HTS synchronous machine mainly due to the well-known “NI” characteristics of the NI HTS field winding. Here we report a numerical and experimental study on the dynamic responses of a synchronous machine with NI HTS field windings. A 300-W 4-pole machine was designed, constructed and operated in a bath of liquid nitrogen at 77 K as coupled to a customized dynamo test bench. Its dynamic characteristics were evaluated in selected transient operation scenarios, and the effect from NI characteristics was thoroughly analyzed based on the proposed equivalent circuit model as well as the finite element model.
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B3009249).
Recent developments in low ac loss MgB2 conductors are of significant interest, given revived interest in fully superconducting (SC) generators. Evaluating AC losses in SC armature windings is critical to develop a feasible fully SC machine. In fully SC machines, SC armature windings experience rotating magnetic fields with spatial and time harmonics which has an undisputed impact on ac losses. Existing ac losses models in the literature are validated for stationary sinusoidal external fields. But there is not enough research on validating the ac loss models for multifilament MgB2 cables with rotating magnetic fields. Further, available models do not capture the time and spatial harmonics impacts on the ac losses. This paper evaluates ac losses in SC with simulated current and field waveforms experienced by an armature conductor in a machine. Various analytical models available in the literature to estimate ac loss in multi-filament MgB2 conductors are compared. Spatial and time harmonics obtained from a transient fully SC machine analysis are fed into the analytical model to estimate the losses. These results are then compared against the finite element analysis (FEA) results to evaluate model fidelity. The analytical models are then refined to capture different parameters influencing ac losses in machine application. Using the analytical and FEA results, new ac loss estimation methods are proposed for multifilamentary cables with spatial and time harmonics with rotating magnetic field. Typically, to evaluate the total loss in a machine, losses are evaluated across a strand and then integrated over total armature conductor length. However, when the strands are packed in to winding the losses may differ from the losses generated from an individual strand. Therefore, the packaging effect in SC winding ac loss is analyzed using FEA. These results are then compared against the individual multi-filament wires modeled in an FEA.
The properties of high-temperature superconductors (HTS) have inspired several applications in electric power systems. In particular, their zero resistance and high current capacity can lead to more compact and efficient generator designs.
Despite its zero resistance, HTS experiences losses under time-changing current or magnetic fields. These losses are fundamental during the design of superconducting devices since they can strongly influence the cooling power requirements and operating temperature. Several analytical solutions have been developed to estimate losses in HTS tapes and wires. However, these expressions can not be directly used to study complex operating conditions such as AC transport current and externally applied magnetic fields in superconducting electrical machines.
Maxwell's equations in the T-A formulation form can be used to model and estimate losses in HTS tapes and coils by employing the finite elements method (FEM). This formulation requires the current as a function of time in each superconducting tape as an input. We show in this work a methodology to calculate this current distribution in superconducting generators. The approach is applied to a 10 MW machine with permanent magnets in the rotor and superconducting coils in the stator. Particular attention is given to the position of the coils inside a slot and several coil configurations are presented. It is shown that certain coil arrangements lead to a significantly lower loss in the coils, a more uniform loss distribution, which ultimately leads to the possibility of increasing the operating temperature.
Acknowledgment
The underlying work of this article was funded by the German Federal Ministry for Economic Affairs and Energy (project name “SupraGenSys”, funding reference number 03EE3010A and 03EE3010D). The responsibility for the content of this article lies with the authors and does not necessarily reflect the opinion of the SupraGenSys project consortium.
Our group has successfully developed SCML-03, which was used to study the dynamic behavior of high temperature superconducting (HTS) maglev. As the experimental speed of SCML-03 can only reach 300 km/h, it is no longer competent for research tasks in a higher speed range. At present, HTS maglev has entered the key stage of engineering application. In order to study its dynamic characteristics and stability under higher speed conditions, a high-speed maglev test rig is developed to undertake this research task. The test rig is mainly composed of a frequency conversion timing AC motor, the transmission mechanism, a brake, a guideway rotor, the control system, the HTS maglev measurement system and the permanent magnet electrodynamics levitation (EDL) measurement system. In the test rig, the circular guideways are rotated vertically, and the Halbach-array PMG and aluminum guideway are fixed inside the stainless-steel rotor to solve the centrifugal effect of high-speed rotation. In order to ensure that the test rig can run stably at the speed of 600 km/h, the design is strictly in accordance with the standard of 700 km/h during the development process. This paper further verified the reliability of this important component through modeling and simulation of the guideway rotor. The ultra-high speed maglev test rig has abundant functions, which can be used to study the high-speed dynamic characteristics and stability of HTS maglev and permanent magnet EDL, which has great practical significance to promote the research and development of maglev.
Abstract: The High temperature superconducting flywheel system for energy storage is attractive due to its self-stable levitation of the rotor without control and a great reduction in the rotational loss of the bearings. It can improves the energy storage capacity and density of single machine, and will have broad application prospect in the future. This paper presents the recent progress on HTS flywheel energy storage system in China.
Keywords: Superconducting magnetic levitation; High-temperature superconducting bearing; flywheel energy storage system
Internal oxidation technique could generate nano oxide particles in Nb3Sn strands, which could significantly refine the Nb3Sn grain size and boost the high-field critical current density. . In this paper, we will report the recent progress of the APC (Artificial Pinning Center) Nb3Sn wire in Hyper Tech. Our APC Nb3Sn wires with Ta and either Zr or Hf doping demonstrated substantial grain refinement and significantly increased Jc,nonCu, while retaining the high Bc2 values of the best ternary Nb3Sn conductors. The non-Cu Jcs of these APC conductors has surpassed the best state-of-the-art Nb3Sn and the Jc,non-Cu specification of the Future Circular Collider (FCC). Their Bc2 was about 28 T, about 1-2 T higher than present state-of-the-art conductors. This strand has been made to 217-filament restack strands getting filament size of 35 micros at the 0.7 mm strand.
In order to improve the current performance of the Large Hadron Collider (HL-LHC project) or to construct the particle accelerators for the Future Circular Collider (FCC), the development of high field Nb3Sn magnets is of high importance. A Heat Treatment (HT) is required for the formation of the Nb3Sn superconducting phase that leads to various physic-chemical phenomena inside the superconducting wires with significant dimensional changes of the coils.
The current study is focused on Rod Restacked Process (RRP) conductors. The heat treatment is composed of several dwells, activating different diffusion mechanisms and phase transformations. During the HT formation of different intermetallics between Sn, Cu and Nb take place. The growth of intermetallics is mainly controlled by diffusion mechanisms at large times. These mechanisms, located into each strand's sub-element area, naturally lead to variations of the crystalline structure and compactness. To predict the mechanical state and therefore the stress conditions of Nb3Sn conductors at a higher scale – cables and coils – it is primordial to first study the phase transformations occurring at the level of sub-elements inside the strands.
Thus, a simplified one-dimensional model is proposed to evaluate the temporal evolution of different phases in the system during HT. Special attention is paid to the consideration of residual stresses inside the system and their influence on the diffusion process. The set of observations was performed on cross-sections of Nb3Sn strands at the different times of HT. The amount of each component is here determined experimentally using Scanning Electron Microscopy. Experimental observations are compared with the model predictions.
Recently, we have reported successful fabrications of the Jelly-Rolled Nb/Al composite monofilament wires having 50 microns in outer diameter. Those Nb3Al super-fine wires show a ductile mechanical performance and may be promising to apply for the React and Wind high field superconducting magnets. However, those Cu/non-Cu ratio was 0.5. So far in our study, it has not been succeeded to draw down them to 50 microns in diameter, when all of copper stabilizer has been located at the outer-most of the Nb/Al composite monofilament wires. In this paper, we have investigated a cross-sectional design of Nb/Al composite monofilament wires with Cu/non-Cu ratio of 1.0. Especially, the optimal location of copper stabilizers and their drawability were studied. We eventually obtained over 1,000 m in the piece length for Nb/Al composite monofilament wire having 50 microns in diameter and Cu/non-Cu ratio of 1.0. Some of 50 microns wire have been drawn down surprisingly to 17 microns, which is the smallest diameter to break the world record (30 microns) of Nb3Al wires. Those superconducting properties and microstructures will be reported in this paper.
Nb3Sn superconducting wires made by the restacked-rod process (RRP®) exhibit a precipitous change of their intrinsic irreversible strain limit εirr,0 with heat-treatment temperature , called the strain irreversibility cliff (SIC). The occurrence of SIC over a very narrow range of , within the domain of temperatures typically used for heat-treating magnets made of RRP® wires, can be a challenge for choosing suitable heat-treatment conditions that optimize the wire’s transport, strain, and thermal properties all at once. To understand the root cause of SIC, we studied the microstructure of strained samples taken from three RRP® Nb3Sn wires, doped with either Ta or Ti, and having either a standard or reduced Sn content. We used light and scanning-electron microscopy to locate cracks and CuSn phases in strand cross-sections and energy-dispersive spectroscopy (EDS) to measure Sn content in the remnant CuSn phases. We also conducted neutron-diffraction experiments at the Japan Proton Accelerator Research Complex (J-PARC) to identify the various phases in the samples. Samples were reacted at ranging from 600 to 700 °C. In this paper, we show a strong causality between the SIC behavior and the existence of a brittle CuSn phase in the microstructure. We present the evolution of lattice parameters of the main wire constituents as a function of and that of Sn content in both Nb3Sn and in the CuSn adjacent phases. Correlations between the nanostructure and microstructure of the samples and their electromechanical behavior will be discussed to unambiguously identify the root cause of the SIC.
In the continuity of the Large Hadron Collider (LHC) large-scale projects are under development, such as the HiLumi - LHC and the Future Circular Collider (FCC), in order to produce particle collisions at higher luminosities and energies. The achievement of these projects strongly relies on the development of high field Nb3Sn magnets. The Nb3Sn intermetallic superconducting phase is produced through diffusion and phase transformations during a heat treatment at about 650 °C. Due to the brittleness of the conductor, Coils are usually wound and then heat treated in a dedicated tooling.
During the heat treatment, phase transformations and internal stresses relaxation lead to significant dimensional changes. If these changes are not taken into account by the fabrication tooling, resulting stress may lead to mechanical damage and degradation of the superconducting properties. In order to limit these degradations it is of crucial importance to characterize and quantify the dynamics of the deformations occurring during the heat treatment.
An innovative experimental device, using high temperature in situ Digital Image Correlation (DIC), has been designed. This experiment allows the measurement of a 2D displacement field at the surface of Nb3Sn Rutherford cables as a function of temperature. A significant longitudinal contraction (of Rutherford cable) is first observed, that is consistent with results reported in the literature. The experiment provided on the other hand a measurement of a transversal swelling as a function of temperature. Associated dilatation reaches values higher than 1% at the end of the process. Observations at the microscopic scale allow a fine analysis of the strand motions within the cable and help for a global interpretation of dimensions changes.
The DEMO ENEA Low Field W&R (Wind and React) conductor, developed in the frame of the conceptual design studies for the Toroidal Field (TF) coils of DEMO, has been designed to be constituted of a small number of superconducting Nb3Sn strands and a high number of stabilization copper wires. It has been extensively characterized at the SULTAN facility in February 2021. The conductor has been operated up to its target current, 70.8 kA, and characterized up to a background magnetic field of 10.78 T. The test program included AC loss measurements with sinusoidal pulsing and measurements of current sharing temperature (Tcs) and critical current (Ic) before and after cyclic loading. At the end, the AC loss measurements were repeated with the sinusoidal pulsing and also with unipolar trapezoidal ramps. Critical temperature (Tc) measurements were also performed on the virgin conductor at the beginning of the test campaign and at the end of the test campaign. In the present work, the main DC and AC characterization’s results and analysis are reported. Concerning DC tests, premature quench phenomena prevented from operating the conductor at the target current – field conditions, probably owing to the sample layout in the transition region to the joint box. Nevertheless, Tcs stability was observed, with no performance degradation due to cycling. A comparative analysis of sinusoidal and trapezoidal measurements is presented, aimed at evaluating the characteristic cable coupling time constant as function of the field variation rate, and at comparing the results to other previous low and high field conductors, as well designed and characterized for the DEMO TF coils.
AC loss in the Nb3Sn cable-in-conduit conductors (CICC) usually decreases after the conductor undergoes electromagnetic cycling. This can be attributed to the increase of inter-strand resistance due to strand-bonding detachment during cyclic loading. In the years 2018 to 2020, ITER launched a series of test campaigns in SULTAN test facility, whose aim was to study the Tcs degradation of TF conductors of all manufactures. Along the main scope of the project, an accompanying study of the AC loss evolution has been measured on two samples. The AC loss was measured prior any electromagnetic loading, after 1, 5, 50 and 1000 cycles, and at the very end also after a thermal cycle to room temperature. Sinusoidal AC loss was measured in the frequency range of 0.1 to 1.0 Hz. The measured AC evolution will help to predict heat load generated in the TF coils during the initial phase of ITER operation. It may also serve as an input to analysts for deducing the evolution of inter-strand resistance during electromagnetic cycling.
In the framework of the US Magnet Development Program (MDP), Fermilab has developed and tested a high-field Nb3Sn dipole demonstrator MDPCT1 for a post-LHC Hadron Collider with the goal to achieve the field of 15 T in the aperture. The magnet design is based on 60-mm aperture 4-layer shell-type coils, graded between the inner and outer layers to maximize the magnet performance. An innovative mechanical structure with aluminum clamps and a thick stainless-steel skin was developed to pre-load brittle Nb3Sn coils and support large Lorentz forces at high fields. The coil axial motion under Lorentz forces is controlled by thick stainless-steel end plates connected by eight stainless steel rods. MDPCT1 was tested in three test runs. The magnet reached record fields for accelerator magnets of 14.1 T at 4.5 K in the first test and 14.5 T at 1.9 K in the second test and then showed large degradation of its quench performance. After tests the magnet was disassembled to the level of individual coils, and all the key structural components and the coils were inspected, and results were analyzed. The most important results and lessons learned from the MDPCT1 R&D program are presented and discussed in the paper.
MDPCT1 is a four-layer cos-theta Nb3Sn dipole demonstrator developed and tested at Fermilab in the framework of the U.S. Magnet Development Program. The magnet reached record fields for accelerator magnets of 14.1 T at 4.5 K in the first test and 14.5 T at 1.9 K in the second test and then showed large degradation. While its inner coils performed exceptionally well with only two quenches up to 14.5 T and no evidence of degradation, the outer coils underperformed and degraded over the course of testing. By adopting new measurement and analysis techniques at FNAL we are discussing in detail what happened. Both success and failure in our diagnostics are discussed. The evolution of techniques over the course of two tests (and three thermal cycles) shows the path we were taking to address challenges brought by the first four-layer magnet tested at FNAL. This paper presents the analysis of quench data along with diagnostic features and complimentary measurements taken in support of the magnet performance analysis.
The most effective way to achieve very high collision energies in a circular particle accelerator is to maximize the field strength of the main bending dipoles. In dipole magnets using Nb-Ti superconductor the practical field limit is considered to be 9-10 T. When Nb3Sn superconducting material is utilized, a field level of 15-16 T can be achieved. To further push the magnetic field beyond the Nb3Sn limits, High Temperature Superconductors (HTS) need to be included in the magnet design. The most promising HTS materials for particle accelerator magnets are Bi2212 and REBCO. However, their outstanding performance comes with a significantly higher cost. Therefore, an economically viable option towards 20 T dipole magnets could consist in an “hybrid” solution, were both HTS and Nb3Sn materials are used. We present in this paper a preliminary conceptual design of different 20 T hybrid magnet concepts. After the definition of the overall criteria and specifications, the general coil dimensions and parameters are investigated with analytical models based on simple sector coils. Preliminary 2D cross-section computation results are then presented and three main lay-outs compared: cos-theta, block and common-coil. Both traditional designs and more advanced stress-management options are considered. Finally, quench protections and mechanical issues will be addressed.
In 2012, after the discovery of the Higgs particle by the Large Hadron Collider in Geneva, scientists in China proposed Circular Electron Positron Collider (CEPC) and Super Proton Proton Collider (SPPC), to study the physics beyond the Standard Model. SPPC needs thousands of 12~24 T accelerator magnets to bend and focus the particle beams. Novel high field magnet technology is highly expected to help reduce the cost of the project.
The iron-based superconductors (IBS), which was discovered in 2008, having a critical field over 100 T, strong current carrying capacity and much lower fabrication cost comparing with other traditional high field superconducting materials. In 2016, the world’s 1st 100-m long IBS tape was successfully fabricated. In 2018, the first IBS solenoid coil was fabricated and tested at 24 T. In 2018-2019, the first IBS racetrack coils wound with 100-m long IBS tapes was fabricated and tested at up to 10 T. The works verified that IBS could be a promising candidate for the application in high field magnets.
In parallel, we are developing high field model dipoles with Nb3Sn and ReBCO technology: the 1st model dipole reached 10.7 T in two apertures at 4.2 K in 2018-2019. A novel transposed cable with ReBCO conductor is under development, and a 16 T dipole magnet is in the fabrication process. An overview of the high field magnet program for SPPC pre-study, latest progress and the future plans will be introduced.
The accelerator Nuclotron is one of the most important installations of the NICA accelerator complex in Dubna, which also includes a booster synchrotron and a collider. The superconducting booster synchrotron was put into operation at the end of 2020, the superconducting collider is in the final stage of assembly. Its launch is scheduled for late 2022. The magnetic system of the superconducting synchrotron Nuclotron has been in operation since 1993 and will require upgrade in the coming years. One of the possible options for upgrading the Nuclotron is to replace its magnets with magnets made of HTS material. A model superconducting quadrupole magnet with a winding of HTS material has been developed and manufactured at Veksler and Baldin Laboratory of High Energy Physics of Joint Institute for Nuclear Research. The design features and the first results of cryogenic tests of the magnet are discussed.
The High Intensity Heavy-ion Accelerator Facility (HIAF) is a new project under construction in China, which will provide beams of stable and unstable heavy ions with high energies, high intensities and high quality. This paper discusses the superconducting magnet system for this accelerator complexes. It will consist of a Nb3Sn magnet with the peak field of 12 Tesla for the ECR ion source operated at 45 GHz, 96 solenoids typically 676 mm long with an operating field of 7.5 Tesla for the superconducting Linac called iLinac, 11 superferric dipoles with 320 mm wide good field region, 13 coil-dominated multiplets with an aperture of 320 mm, gradient 11 T/m for the fragment separator HFRS, and 20 dipoles integrated with quadrupoles and sextrupoles with the central field of 3 Tesla for the spectrometer ring called SRing. This papers reports the design and prototype development status of the main components.
The COMET experiment, which is being prepared at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai-mura, Ibaraki Prefecture, aims to explore the rare decay phenomenon of muons.
This phenomenon is not allowed in the Standard Model of elementary particles but is expected to occur due to new physics beyond the Standard Model.
In the COMET experiment, superconducting magnets are used throughout the muon beamline.
One is the pion capture solenoid to focus the pions generated by the injection of proton beams into the target.
Since this magnet surrounds the target, it is designed to operate in a high radiation environment.
The second is the muon transport solenoid to guide the muons generated by the decay of pions.
This magnet maximizes the muon yield and reduces the other background particles.
The third is the detector solenoid to track the electrons generated by the decay of muons.
These superconducting magnets are now being developed and manufactured.
And the current lead box is also manufactured to supply high currents to the magnets, with a thermal gradient from the room-temperature part of the power supply to the low-temperature part of the coil.
It is designed to provide a large thermal gradient over a short distance using high-temperature superconductors.
Thanks to the current lead box, all magnets, including the high-temperature superconducting leads, are cooled by conduction cooling.
In this talk, the construction status of the COMET superconducting magnet system will be reported.
Cuprate high-temperature superconductors (HTS), such as RE-Ba2Cu3O7-d (REBCO, RE=rare earth) coated conductors, (Bi,Pb)2Sr2Ca2Cu3O10-x tapes and Bi2Sr2CaCu2O8-x wires, have enabled the development of high-field superconducting magnets. The brittle nature of HTS requires elaborate means to protect them against the high stresses associated with high-field magnet operation, which so far have prevented reliable high-field HTS magnets to becoming a reality. Here we report the results of an extensive optimization campaign to increase the mechanical strength and resilience to axial strain of CORC® conductors. Minimizing the tape winding pitch of the helical wind of the REBCO tapes allowed us to mechanically decouple the brittle REBCO film from the overall CORC® conductor. As a results, we were able to reach a tenfold increase in the irreversible strain limit under axial tension to over 7 % in optimized CORC® wires, compared to only 0.6 % in single REBCO tapes. In addition, high-strength alloy and composite cores allowed the critical tensile stress of CORC® conductors to exceed 600 MPa, making them some of the strongest superconductors available. We will show how the effect of axial tensile stress and strain on the critical current of short CORC® wires measured in liquid nitrogen is supported by analytical and finite element modeling. The breakthrough, in which the irreversible strain limit of high-strength CORC® conductors exceeds that of all other HTS and most low-temperature superconductors by a factor of 10 to 20, presents a monumental shift for HTS magnet technology. It allows a significant simplification of the magnet design and construction, while bringing reliable high-field superconducting magnets for compact fusion machines, the next generation of particle accelerators, and 40 – 60 T research solenoids within reach.
Superconducting magnets designed for high energy physics and nuclear fusion require mechanical stabilization and electrical insulation to perform at high currents and magnetic fields. Vacuum pressure impregnation (VPI), a process of curing epoxy in and around the superconducting wires, is most commonly used to support and consolidate a magnet. However, the heat and mechanical stresses associated with the process can degrade the wires, significantly lowering the critical current. This study explores different methods of potting and curing CORC® wire with the aim of reducing wire performance degradation to less than 3% measured at 77 K, self-field. The wires were 2.9 mm in diameter consisting of six REBCO tapes each (three layers of two tapes). Two bending diameters (40 mm and 100 mm) were tested to mimic the winding shape of a magnet. Mix 61 epoxy was used in preliminary tests for potting due to its relatively lower temperature cure of 16 hours at 60 ℃ followed by 24 hours at 100 ℃. For each test, two wires were used and their critical currents were measured simultaneously in liquid nitrogen at 77 K - in their straight form, then bent, followed by the heat treatment used for Mix 61 but without epoxy and finishing with the full epoxy impregnation test. Here we report the experimental results with multiple CORC® wires and different curing schedules. The VPI process with minimum degradation in critical current, as demonstrated by this work, will provide a proven VPI procedure to develop high-field dipole magnets using CORC® wires.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program under Contract No. DEAC02-05CH11231.
High current Rare-Earth Barium-Copper Oxides High Temperature Superconductor (HTS) Cable-In-Conduit (CIC) Conductor conceived for large fusion magnet applications based on aluminum slotted-core incorporating HTS tape stacks has been successfully proposed in the last years [1]. In this work, the activity carried out for designing and manufacturing CIC samples aimed at the investigations of thermal stability and quench behavior under fusion relevant conditions to be performed at the SULTAN facility (Swiss Plasma Center) is presented. The sample, based on the 6-slot core with straight slot configuration, will consist of two 3.6 m long conductors electrically connected by a joint at the bottom and connected to the facility current lead at the top. The sample layout and the HTS tape arrangement have been defined with the support of the simulation codes implemented for the electromagnetic performances and a thermal-hydraulic conductor model of the CIC sample for the analysis of the quench phenomena [2, 3]. Based on the single tape performances, this choice will assure a conductor critical current slightly in excess of 15 kA at 5 K, 11 T in agreement with the experimental facility requirements. The HTS conductor quench behavior will be monitored by voltage taps and temperature sensors arranged along the conductor length either on the external jacket along the conductor length or embedded within the conductor cross-section to monitor the occurrence of the temperature gradients across the conductor cross-section as predicted by thermal-hydraulic simulation.
The sample designing and manufacturing details as well as the expected performances based on simulation analyses will be presented and discussed in view of the applications of this CIC conductor concept in actual fusion reactor magnetic systems.
[1] G. Celentano, et al.,IEEE TAS 24 2014, 4601805
[2] G. De Marzi, et al.,SuST 34 2021, 035016
[3] A. Zappatore, et al.,IEEE TAS 30 2020, 4603307
As the high critical current at high field, the representative second-generation high-temperature superconductor (2G HTS) ReBCO serves as a good candidate for future fusion devices, i.e. the Chinese fusion engineering test reactor (CFETR), the Demonstration Power Station (DEMO) with magnet field higher than 15T. The main goal of CFETR is to build a fusion engineering tokamak reactor with a fusion power of 50–200 MW, and test the breeding tritium during the fusion reaction. This requires the central solenoid and toroidal field coils with a maximum magnetic field exceeding 15 T.
A 80 kA class Cable-in-Conduit-Conductor (CICC) under 15 T is targeted in the CFTER project. ReBCO is considered as a potential and promising superconductor. R&D activities are ongoing at the Institute of Plasma Physics, Chinese Academy of Sciences for demonstrating of a CICC based on ReBCO tape manufactured by Shanghai Superconductor. One sub-size conductor cabled with more than 45 tapes and then a coil wound with this conductor reaching peak field of 20T under background field were designed, manufactured and tested. In this paper, the transport properties, dependence on the strain of the ReBCO tape, as well as the performance of the sub-size conductor and the insert coil are investigated and reported. The results exhibit the feasibility of ReBCO CICC for Fusion magnet delivering high field.
After more than 20 years of development, the manufacturing of high-temperature superconducting (2G-HTS) wire has been quite well established: a thin (1-2 microns) layer of YBCO superconductor epitaxially deposited on a biaxially aligned metal substrate. Such a conductor is very susceptible to current blocking defects. These defects are typically caused by mishandling of the tape between the processing steps, failures of epitaxy, deposition system malfunctions, etc. Currently, in the manufacturing of 2G tape, a series of quality control procedures are carried out to reveal the YBCO layer imperfections. It was discovered, however, that some defects remain undetected by off-line quality control methods. Such defects are most often hidden until they reveal themselves during low-temperature high-current tests when they result in a magnet failure.
Here we report the performance of a coil wound from a defect-tolerant superconducting cable. The defect tolerance is achieved by continuous current sharing between the filaments. The cable is comprised of a stack of four 2 mm wide filaments. The current sharing is achieved by fusing the filament during the winding process with a directed hot air stream. To demonstrate the concept, each of the four filaments in the cable was cut on purpose, resulting in the superconducting layer breakage every 2 meters. The coil was tested in field up to 1 T at 77 K and 4.2 K. We show that despite discontinuities in each of the filament the winding demonstrated no dissipation below the critical current down to the level of 10 nV over 5 meters of winding. We propose the design of a multi-filamentary cable that would be tolerant of current blocking defects several meters apart.
The work at Brookhaven Technology Group was supported by U.S. DOE through an award DE-SC0020832.
Recent progress in superconducting joint technologies connecting coated conductors (RE123) [1] had triggered reconsideration of development of superconducting joints connecting Bi2223 tapes.
Through the systematic studies on polycrystalline Bi2223 thick films [2,3] and establishment of polishing technology with very low angle to expose most of the filaments in Bi2223 tapes, we succeeded in the development of high Ic superconducting joints connecting Bi2223 tapes via Bi2223 polycrystalline intermediate layer[4]. Introduction of intermediate pressing and optimization of heat-treatment conditions increased Ic of Bi2223 joints above 100 A at 77 K under self-field and 300 K at 4.2 K in 1 T. Since the predominant factor limiting joint Ic is considered to be critical current properties of Bi2223 polycrystalline intermediate layer and interface between this layer and Bi2223 filaments, further enhancement of joint Ic can be expected by improvements of microstructure and chemical composition. If the joint Ic is increased up to the Ic of Bi2223 tapes, applications as for superconducting magnets with persistent current circuit operating at various temperatures will be realized. In this paper, potential and future prospects of Bi2223 joint technology will be discussed from various viewpoints, such as critical current properties of Bi2223 thick films, effective joint area ratio at the joint interface and possibility of further improvement of Jc-B characteristics of Bi2223 tapes and joints.
Acknowledgement: This work is partly supported by JST-MIRAI Program, JPMJMI17A2, Japan.
We have succeeded in measuring critical current, Ic, in multi-filamentally Bi-2223 tapes at extremely low electric-field criterion down to at around 10^-13 V/m, at 5 K and external magnetic fields up to 4.5 T perpendicular to the tape surface which is comparable to the operation condition of Bi-2223 based insert magnet for 30 T-class NMR magnet in persistent mode operation. While the Ic of the Bi-2223 tape is usually evaluated by the transport measurements at electric-field criterion of 10^-4 V/m, the Ic at actual operation condition need to be clarified at around 10^-12 to 10^-13 V/m which is significantly lower than that of the transport measurements. One possible approach is to measure magnetization relaxation of the tape sample, however, the influence of the filament coupling and in-plane anisotropy in the tape are not understood. In this study, we developed a novel method based on in-field scanning Hall probe microscopy. From spatially resolved time dependent magnetic-field profile, we obtained local current density and electric-field from inverted Biot-Savart law and Faraday’s law, respectively. From the comparison between our measurement and transport measurements [1], it has been shown that the magnetic field dependences are similar but the value of Ic at 10^-13 V/m is about 1/2 of that obtained by the transport measurements. For example, the Ic at 5 K and 4.5 T of perpendicular field is 226 A at 10-13 V/m, whereas 458 A at 10-4 V/m. Electric-field vs. current-density relationship can be also described reasonably well by the percolation transition model taking into account flux creep [2].
This work was supported by the Japan Science and Technology Agency (JST)-MIRAI Program, JPMJMI17A2 and JSPS KAKENHI Grant Numbers JP19H05617.
[1] M. Bonura et al., IEEE TAS, vol. 29, pp. 6400205 (2019)
[2] T. Kiss et al., Physica C, vol. 392-396, pp. 1053-1062, (2003)
MgB$_2$ superconducting wires hold the advantage over traditional NbTi wires of higher temperature operation, at lower cost than REBCO tapes, and allowing the use of existing winding techniques. The adoption of MgB$_2$ wires into large-scale applications such as MRI solenoid magnets, long-length power cables, wind turbine generators or industrial magnets requires a robust production process yielding long length wires with consistent performance. Bekaert and Epoch wires have developed a scalable powder-in-tube technique capable of producing MgB$_2$ wires in km lengths.
Achieving performance close to short sample in a solenoid coil is an essential step towards larger demonstration assemblies and coils, in wind-and-react or react-and-wind configurations. Here, we report on the performance of a compact wind-and-react solenoid coil wound from Bekaert/Epoch wires 1+6 MgB$_2$ cable. The filament diameter is 0.4 mm, the cable has a twist pitch of 26 mm and a Cu:SC ratio of 0.9. The coil is wound from 148 m of S-glass insulated cable in 6 layers, on a former with diameter 52 mm, and was reacted in a vacuum furnace. The coil was tested without epoxy impregnation.
The coil was tested in a He-vapor cooled VTI inside a 10 T Cryofree magnet, at 10 K and 20 K and at up to 4 T background field. The maximum current in the coil was 300 A at 10 K, generating a self-field of 1.47 T. Voltage taps monitored the inner 4 layers and outer 2 layers of the coil, both whilst ramping up and when shutting off the current from 300 Amps to zero. The coil was tested at 10 K at close to 100% of the short sample performance without any voltage generated, which is a clear confidence check for the consistency of the 1+6 MgB$_2$ cable over long lengths.
Superconducting magnets are employed in accelerators to achieve higher magnetic fields to attain a higher particle-beam deflection. However, superconductivity, i.e. the complete absence of electrical resistivity, is lost upon exceeding a critical temperature leading to the quench phenomenon. Then, the affected magnet regions shift to normal-conducting state and begin to heat up. In the worst case, this can lead to a thermal runaway and extensive damage to the magnet.
Numerical simulations play a crucial role for understanding and predicting quench phenomena. However, the simulation of superconducting accelerator magnets imposes both a geometrical and physical multi-scale problem leading to unreasonably high computational times if tackled with conventional three-dimensional (3D) finite-element (FE) methods.
This work presents an alternative approach, in which a two-dimensional FE method on the transversal magnet cross-section is combined with one-dimensional orthogonal polynomials in the longitudinal direction. The result is a quasi-3D (Q3D) method with hybrid shape functions, which proves to have superior efficiency compared to the conventional 3D FE method while delivering accurate results with much less computational effort. The method is employed to carry out a magneto-thermal coupled simulation on a superconducting magnet component.
This work has been supported by the German BMBF project “Quenchsimulation für Supraleitende Magnete: Steigerung der Auflösung in Zeit und Raum” (BMBF-05P18RDRB1) and by the Graduate School Computational Engineering at TU Darmstadt.
The R&D project of compact high-temperature superconducting (HTS) cyclotron system for radioisotope production is ongoing, supported by Japan Science and Technology Agency (JST) and Japan Society of the Promotion of Science (JSPS). This HTS cyclotron has two major features: (1) the magnet has no iron core (air-core), and (2) the output energy is variable. The developing HTS cyclotron system is named ‘Skeleton Cyclotron,’ and consists of main coils for isochronous field generation and triangle coils for azimuthally varying field (AVF). With progress of this project, we need to design a magnet system with iron shield, because leakage field and radiation must be suppressed. Note, in conventional AVF cyclotron magnets, iron is also used for the purpose of generating AVF; however, in the proposed system, iron shield is not for that purpose.
When designing Skeleton Cyclotron magnet with iron shield, the finite element method (FEM) or the magnetic moment method is commonly used for magnetic field simulation, and a large-scale system of equations must be solved. In addition, field computations with many iterations are required in an optimization design process. To accelerate an optimization computation, the model order reduction (MOR) method, which reduce the dimensions of system of equations, is employed. In our case, the magnetic moment method is employed as a field computation method, and 52,080 dimensions could be decreased into 4 using the MOR. The simulated annealing is used as an optimization method. Finally, it was successful to greatly shorten the optimization computation time.
In the full paper, we will present the detail of MOR and the optimized configuration of Skeleton Cyclotron magnet with iron shield.
High-field REBCO magnets contain several pancake coils with many turns, which are vulnerable to high stress and strain due to the large background magnetic fields. In addition, screening currents substantially increase the stress. Electro-thermal quench is another issue which is required to be taken into account while designing a high field magnet. Thus, there is a need for fast and accurate software to numerically model the overall performance of full-scale magnets. High temperature superconducting coils can be modeled using different Finite Element Method (FEM) techniques for the electro-magnetic (such as H-formulation or A-V formulation), thermal, and mechanical analysis. However, it takes a lot of time to model the electro-magnetic, electro-thermal, and mechanical behavior of superconductors simultaneously in a commercial software. We have developed a novel and fast model programmed in C++, which performs coupled electro-magnetic, electro-thermal, and mechanical analysis, using variational methods based on Minimum Entropy Production [Minimum Electro-Magnetic Entropy Production (MEMEP), Minimum Electro-Thermal Entropy Production (METEP), and Minimum Mechanical Entropy Production (MMEP), respectively]. The models are applied to the case of an axi-symmetric coil for transient design (thermal quench reliability and mechanical strength), taking screening currents into account. The electro-magnetic formulation has been benchmarked with H-Formulation in our previous works. The electro-thermal model in our software, using METEP, is benchmarked with a Finite-Difference method. The mechanical model assumes the material as isotropic for initial simplicity, with the ability to extend the scope to consider the orthotropic nature of superconductors. The model developed can be used for a quick and complete electro-magnetic, electro-thermal, and mechanical analysis of practical superconducting applications such as coils for high field magnets or fault current limiters.
A high-temperature superconducting magnet is one of the core technologies of a superconducting maglev train. The multiphysics fields including electromagnetic, mechanical, and thermal effects should be taken into consideration in design. Traditional design methods rely on the initial configuration and the engineer's experience, and only consider the optimization design for the heat conduction performance of the heat conduction structure, without considering the strength of the thermal structure, which often significantly increases the weight while increasing the cold conductivity. To solve the above problems, aiming at the heat conduction structure of superconducting magnets, based on COMSOL Multiphysics software, the mathematical model of topology optimization of the heat conduction structure is established with Lorentz force as the input load. The objective function was assigned to dissipation of heat potential capacity, combined with volume fraction constraint conditions. The solid isotropic material with penalization (SIMP) theory is used to construct the material interpolation model and carry out the topological analysis of multiphysics and the innovative structure of heat conduction structure is obtained. Through finite element numerical simulation of multiphysics fields, the maximum temperature, stress safety factor, and weight were taken as evaluation indexes to compare the heat conduction performance, structural strength, and lightweight degree of the topology optimization structures with the traditional structures. The results show that this method can effectively enhance the cooling efficiency and alleviate the stress concentration without increasing the weight of the heat conduction structure. The work of this paper provides a theoretical foundation for the engineering design of the heat conduction structure of a high-temperature superconducting magnet.
A 46 T all-superconducting magnet is being designed at the Institute of Plasma Physics Chinese Academy of Sciences. This magnet consists of, from the outside to the inside, the CFETR CS model coil capable of producing a 10 T central field, a REBCO-CORC insert coil providing an additional 10 T central field, and three REBCO insert coils which are dry wound with 4 mm wide REBa2Cu3O7-x tape conductors. First, the electromagnetic design is optimized by considering the central field, perpendicular field, hoop stress and strain, and conductor lengths. Then, special attention is paid to the screening current effect of the three REBCO insert coils. When the magnet is energised, persistent screening current will be induced in the winding. Subsequently, the non-uniform current distribution in the REBCO tape, including a varying-field induced screening current, will lead to critical magnetization effects that not only deteriorates the field strength, but also may overstress the conductor and result in irreversible degradation of the magnet performance. A code based on the T-A formulation is written to calculate the screening current effect. Meanwhile a finite-element software is also employed for comparison. We will focus on predicting and mitigating the screening current and its associated stress/strain in the 46 T magnet.
The quench process in a superconducting magnet is inherently transient and three-dimensional (3D). In many cases, such as magnets protected by active protection systems, it is possible to accurately simulate this transient with a two-dimensional model. However, a more complex 3D model is required in case of a self-protecting magnet. Simulations are particularly challenging due to physical and geometrical features, such as highly non-linear material properties, sudden appearance of localized heat generation, non-isotropic conductor composed of superconducting, resistive, and insulation materials, and relatively thin insulation layers. It is crucial to reduce simulation time in model development and validation in order to perform within an allocated project timeframe all necessary tasks such as evaluating the suitability of model assumptions, generating models of new magnets, and performing parametric analyses. Thus, a simulation time under one hour, and ideally of a few minutes, is beneficial. Finite-element method (FEM) enables simulations of electro thermal coupled problems of complex geometry. Various FEM programs are commercially available, which provide very good flexibility and are bench-marked for a number of cases. However, a very long solution time makes 3D FEM simulation of a quench in a full-scale magnet system often impractical. In this work, it is shown how the quench and heat diffusion in 3D geometry can be accurately yet rapidly simulated using the finite-difference method. The presented numerical implementation has simplifying assumptions that benefit computational efficiency while achieving required accuracy. The coupled electro-thermal problem is solved with a semi-implicit Euler method. This 3D approach is included as a new feature in the STEAM-LEDET quench simulation program. As a study case, a simulation of the transient following a quench occurring in one of the self-protecting LHC magnets is presented and compared to experimental results.
Commercial REBCO tapes are a promising technology for power and magnet engineering. Due to their complex manufacturing, they present inhomogeneities of the critical current distribution and silver stabilizer thickness along their length. It is therefore paramount to investigate the impact of inhomogeneities when designing superconducting devices based on such tapes.
This kind of study requires extensive use of Finite Element Analysis (FEA) since such inhomogeneities are not known a priori, and various scenarios (degree of inhomogeneity, statistical distributions, etc...) need to be investigated. However, due to the very large number of degrees of freedom present in modeling large 2-D or 3-D systems, the computational cost can be very high.
In this work, we present a 1-D electro-thermal model implemented in COMSOL with MatLab, aiming to reduce the computational efforts while simulating many inhomogeneous case scenarios. The electric part is homogenized (0-D) and assumes that the thickness of the REBCO tape is negligible; the thermal part is one-dimensional (1-D) and accounts for heat propagation along the conductor length. The model accounts for both the nonlinear electrical and thermal dependence of the materials and the heat exchange with the liquid nitrogen. The resistivity models considered are the widely used power-law model and the more recently developed overcritical current (eta-beta) model. Finally, it is possible to select a statistical distribution (uniform, normal or Weibull) and its parameters to simulate the degree of inhomogeneities of the superconducting properties and/or that one of the stabilizer along the length of the tape. The FEM model is verified by comparing the simulations with DC fault measurements performed on a commercial REBCO tape.
With only 1 µm thickness of high temperature superconducting (HTS) material, HTS tapes are very fragile and can easily undergo an irreversible damage when operated near to its rated values. When wound into coils, this phenomena intensifies, limiting the operating values to only 50-80 % of its rated values. This is mainly due to the restricted HTS current path and poor thermal conduction between the turns. By adding a low resistive turn to turn conduction path, this risk can be mitigated. This was proven as an effective solution for the HTS coils, enabling the magnet engineers to operate them up to 100 % of its rated values. However, under dynamic operating conditions this parallel turn-to-turn conduction path will alter the current path, resulting in varied inductance. Also, due to the high aspect ratio of the HTS tapes and varied Jc(B,θ) characteristics, the current distribution along the width of the HTS tape is not uniform and will also contribute towards the varied inductance. To date the entire literature on NI coils considers the inductance of the coil to remain constant. With the recent advancements in the NI coil modelling, it is now possible to model the NI coil using the stand-alone finite element (FE) model. Using this FE model, we have evaluated the inductance of the coil while varying the applied current magnitude and the ramp rates. For slow ramp rates (< 1 A/s), the inductance of the coil is observed to vary up to 10 % with varying applied current. This change is more evident for higher ramp rates (> 1 A/s). Finally, the effect of this varied inductance is visualised using the magnetic field decay characteristics. These results are key for understanding the NI coil behaviour and will determine the operating conditions of the high field magnets.
It is required to improve yield of coiling for REBCO-based magnet developments, however, the conventional test method represented by the end-to-end current transport measurement of the coil could not derive detailed information such as the positions of the defects and the mechanisms for the failures. In this study, we have developed a novel method adopting hybrid microscopy integrating magnetic microscopy, scanning electron microscopy, and optical microscopy in order to track down the positions of the defects in the coil winding and followed by microstructural analyses to clarify the mechanisms of the failure in the coiling. We have succeeded in identifying defects in a part of a large-bore shielding coil (over 1 m in the inner-diameter), which is for the 1/2-size whole body REBCO MRI magnet system, and have clarified their mechanisms caused by the pancake-coil winding process. One type of the failure was caused by an insufficient mold release treatment during the impregnation in which a part of the resin was fixed on the tape surface and caused damage in the superconducting layer just under the fixed resin mark with thermal stress in the cooling. As far as the author know, this is the first direct observation that indicates the internal thermal stress due to the anisotropic thermal shrinkage in the coil becomes a cause of coil damage. The other type of the failure was originated from partial interference between the winding frame and the tape edge during winding. These findings allow us to establish appropriate measures for coiling. Namely, this novel approach can be a powerful tool as a fundamental evaluation method for improving the reliability and reproducibility of the coil.
This work was supported by JSPS KAKENHI Grant Numbers JP19H05617 and the New Energy and Industrial Technology Development Organization (NEDO).
High temperature superconducting (HTS) magnets working as inserts inside low temperature superconducting (LTS) magnets are foreseen to enable >16 T class accelerator dipoles for future particle colliders. Under the U.S. Magnet Development Program (US-MDP), LBNL has been making steady progress towards designing and fabricating practical Bi-2212 and Nb3Sn canted-cosine-theta (CCT) dipoles that have stress management capability to enable high fields. The next step is the integration of the HTS and LTS magnets to work in hybrid configuration. At LBNL, two hybrid magnet tests are planned in the short and mid-terms. The first test consists of a 0.4 m long two-layer Bi-2212 CCT magnet inside a 1 m long two-layer Nb3Sn CCT magnet. The Bi-2212 insert, called BIN5c, has a 30 mm bore and was designed to generate 2.5 T in the bore. It was fabricated at LBNL in collaboration with NHMFL and recently tested. The Nb3Sn magnet, called CCT5, has a 90 mm bore and was also fabricated and tested at LBNL. It produces a bore field of 8 T. The second test consists of a 0.8 m long two-layer Bi-2212 CCT magnet inside a 1.5 m long four-layer Nb3Sn CCT magnet. The Bi-2212 magnet, called BiCCT1, is a 5 T magnet with 40 mm bore. It fits inside the 120 mm bore Nb3Sn magnet, called CCT6, which is designed to produce a background field of 12 T. Both magnets are under fabrication. In this work, we present the detailed magnetic and mechanical analysis of the magnets in hybrid configuration, and an analysis of the challenges and practical considerations including mechanical assembly, stress management and quench detection and protection associated with the hybrid tests.
The U.S. Magnet Development Program (US-MDP) aims at developing high-field accelerator magnets with magnetic fields beyond the limits of Nb3Sn technology. Recent progress with composite wires and Rutherford cables based on high temperature superconductor Bi2Sr2CaCu2O8-x (Bi2212) allows considering them for this purpose. However, Bi2212 wires and cables are sensitive to transverse stresses and strains, which are substantial in high-field accelerator magnets. To prevent large degradation of the Bi2212 coils and achieve the required field quality, an innovative design which provides turn positioning during coil fabrication and operation and manage azimuthal and radial strains/stresses in the coil has been proposed at Fermilab. This paper describes the development and fabrication of a small-aperture two-layer Bi2212 dipole inserts with stress management. The design and main parameters of the superconducting wire and Rutherford cable, the coil stress management structure design and the coil FEA in the dipole mirror and dipole test configurations are presented and discussed. The key Bi2212 coil fabrication steps, its instrumentation and assembly in a dipole mirror configuration inside an Nb3Sn outsert coil are also reported in the paper.
Recent development of Bi-2212 insert coil technology at National High Magnetic Field Laboratory (NHMFL) has shown promising in-field performance, ~ 440 A/mm2 at 16.3 T peak field in 2019, thanks to the matured conductor technology and reliable heat treatment process. Now Bi-2212 coil technology is entering to a new stage to be considered as a competitive candidate for high field (above 20 T) inserts against other suitable superconductors such as Nb3Sn or ReBCO. Unlike the other HTS conductors, the commercial Bi-2212 conductor still has no reinforcement at the conductor level and the developers must design their own reinforcement method for the 2212 coils to manage high magnetic stress during their operation. To achieve this task, we have developed a suitable material and reinforcement method for Bi-2212 high field insert. However, those reinforced Bi-2212 coils become a complex composite of 2212, braided insulation, epoxy, and reinforcement materials and it is complicated to confirm the effectiveness of the proposed reinforcement method quantitatively. To find out the effectiveness of our reinforcement design precisely, a set of similar coils (in terms of size, number of turns, and conductor length) with different reinforcement layout will be made and tested in 14 T LTS test bed located at Applied Superconductivity Center (ASC) of NHMFL. The test results will be analyzed with FEM stress analysis.
Acknowledgement : This work is funded by the DOE (HEP Award No. 227011-520-032288), the NSF (Award No. DMR-1157490), and by the State of Florida. This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program.
The article presents the results of the preliminary development of the HTS conductor based on the VS-type design for the central solenoid of the compact thermonuclear reactor TRT, which is under development in Russia. The operating current of the conductor have to be at least 60.0 kA in the field of 15 T at temperatures of 5-20 K. The compactness of the magnetic system requires the creation of a conductor with a high engineering current density, reaching of 90 A / mm2. In the central solenoid, the wire is subjected to significant mechanical loads caused by the Lorentz forces. In addition, the significant stored energy in the magnet requires the presence of elements in the conductor that provide an emergency energy output at an acceptable voltage and heating of the winding, which does not lead to damage to its elements. Two constructive versions of the VS type conductor based on radially arranged HTS tapes are considered. At the same time, the required amounts of stabilizing and reinforcing materials are included in the conductor design. The analysis of the proposed conductors calculated characteristics under various operating modes of the electromagnetic system of the TRT tokamak is carried out. The results of calculations by the finite element method of the distribution of the magnetic field in the conductor, its current carrying capacity and the assessment of energy losses in a changing magnetic field are also presented.
An asymmetric dependence of the critical current on the direction of an applied magnetic field in HTS coated conductors has a non-trivial influence on the AC loss of coil windings. We report the modelled influence of real conductor critical current asymmetry on the AC loss characteristics of a 1 MVA HTS transformer design previously demonstrated by the Robinson Research Institute as well as a stand-alone coil having the same geometrical and electrical parameters as the low voltage (high current) winding of the transformer. We compare two commercial HTS conductors with distinctive differences in their critical current asymmetry and show a maximum variation of 15% and 29% in the calculated AC loss of the transformer and the stand-alone coil winding, respectively, when the conductor orientation is varied in the top and bottom halves of the windings. AC loss simulation giving consideration to asymmetric conductor critical current before winding the transformer could lead to substantial AC loss reduction even using the same amount of conductor and the same transformer design.
Renewable energy and electric power liberalization have become important watchwords for present electric power system. However, the stability of electric power systems is also a serious concern because of the lack of inertial energy of conventional synchronous generators. Since a low system stability may cause an unexpected power oscillation with the natural frequency of an electric power system, power system operation requires an excessive margin to maintain a high system stability. To enhance the resilience of the electric power system, the authors discussed the feasibility of using a superconducting magnetic energy storage (SMES) system for the direct measurement of eigenvalues that express the oscillation modes of a power system. The authors carried out a design study on a 1MJ-class mobile SMES system using MgB2 Rutherford cables whose components such as SMES coils, cooling systems, and power converters are installed in a 40 feet dry container. From the design flexibility depending on the power system conditions, the output power of the SMES system can be adjusted from 1 MW to 4 MW by selecting a cooling temperature. The operating current variations of the SMES coil were estimated as 1800 A at 2.0 T for 20 K, and 2700 A at 3.0 T for 10 K. The SMES coil can be cooled using 3 or 4 sets of conventional cryocoolers, including the cooling system for the 80 K thermal shield even when the cooling temperature is 10 K. In this work, the authors investigate the effective installation sites for eigenvalue measurement and evaluate the re-cooling time interval and optimization of the cooling scenario to achieve full mobility of the SMES system using cryocoolers.
We have been developing DC superconducting cable with magnetic energy storage function. This novel application offers high-speed and high-power charge/discharge operation indispensable for compensating output power fluctuation from renewable energy sources such as photovoltaic, wind turbine, etc. In this paper, we will report its development status under a Japanese national program: (1) conceptual design of the superconducting cable for a 10-MW-class micro-grid, (2) the structure and the control method of the micro-grid, (3) fabrication of a prototype of the superconducting cable, and (4) its operation for compensating output power fluctuation from renewable energy sources. For example, a superconducting cable with a stored energy of 1 GJ was designed by considering the performance of a RE-123 coated conductor, and its small prototype was fabricated and tested by a hardware-in-the-loop (HIL) simulation with Real-Time Digital Simulator (RTDS). As a result, it was successfully demonstrated that very large output power fluctuation with a similar scale as the power capacity of the micro-grid could be compensated completely by the superconducting cable although such an operation is difficult by conventional batteries. We believe that this novel application based on superconducting magnet technology will become a promising solution for large-scale utilization of renewable energies for carbon-neutral society.
This presentation is based on results obtained from a NEDO Feasibility Study Program (Uncharted Territory Challenge 2050).
A power supply system with transformer type superconducting magnetic energy storage (SMES) is being created to power the superconducting magnets of the particle accelerators Booster and Nuclotron of the NICA complex at JINR. The system includes a solenoid made of HTS cable, with an operating temperature of 28 K, with flow cooling by liquid neon, and an operating current of up to 8 kA with 4 s pulse period. The solenoid will consist of 3 inductively coupled windings with dielectric frames, to which semiconductor converters are connected to charge Booster magnets, Nuclotron magnets, and to feed the SMES from the distribution grid. The power supply system with the SMES will improve a power supply quality of the accelerator magnets, eliminate the influence of the accelerators operations on the distribution grid, and provide galvanic isolation of the power supply circuits of Booster and Nuclotron from the distribution grid and from each other. The work is being carried out in cooperation with ASIPP. Both JINR and ASIPP develop their own similar 2G HTS cabling technologies and different solenoid winding technologies – layer winding with screw-on frames (JINR) and double pancakes (ASIPP). A comparative description of the technologies, test facilities and research methods developed in Dubna and Hefei, R&D results obtained, and samples prepared is presented. Based on the results of R&D the technical design of the power supply system and the SMES will be developed by the end of 2021.
Magnetised bulk superconductors can be used as super-strength, stable permanent magnet analogues capable of providing magnetic fields of several tesla in a compact and portable magnet system. In addition to a large magnetic field, B, the magnetic field gradients (dB/dz, dB/dr) are naturally large. This makes them attractive for a number of engineering applications that rely on high magnetic fields and/or field gradients, including desktop nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), magnetic separation and magnetic drug delivery systems.
In this presentation, we report our recent developments in the Bulk Superconductivity Group, University of Cambridge, in portable, desktop high-field magnet systems using bulk high-temperature superconductors, including:
We report a detailed summary of our recent experimental results, including comparisons of solenoid- and split-coil PFM and single- and multi-pulse (including multi-temperature) PFM, for a range of (RE)BCO bulk superconductor samples (Y, Gd and Eu) fabricated in-house and by commercial suppliers. In particular, we describe the reliable trapping of magnetic fields greater than 3 T in disc-shaped bulks and record-high trapped fields in ring-shaped bulks greater than 1 T using optimised multi-pulse, multi-temperature PFM with pulse waveform control.
ACKNOWLEDGEMENTS
Only a handful of high-temperature superconducting (HTS) electric machines using HTS bulks as magnetic poles have been developed. This is mostly due to the need for the bulks to be magnetized before use, which is a challenge for practical application. It is important to develop a magnetization method for the bulk arrays because recently we have used them as an armature for high power superconducting rotating machines. To magnetize easily the bulks, a pulsed-field magnetization (PFM) method is preferable over a slower field cooling method. However, the time and practicality gained are often at the expense of the intensity of the trapped magnetic field. Several methods have been developed to improve the PFM of a single or two bulks, but the magnetization of multiple bulks arranged in an array has not as often been addressed in the past. In this presentation, a rectangular array of HTS bulks has been modeled to reproduce the magnetic pole of a superconducting motor. An H-formulation has been used to model the bulks, surrounded by A-formulation to solve the regions without superconductors using the potential vector A. The thermals of the bulks during the magnetization will be taken into account. The magnetization process of the bulks using different types of coils has been considered as well as the impact of the modification of the shape and size of the coil on the trapped magnetic field. The order in which the bulks are magnetized is also important as magnetizing bulks close to already magnetized bulk could reduce the overall trapped magnetic flux density. The thermal behavior and trapped magnetic field quality depending on various parameters are discussed.
BaFe2As2 (Ba122) shows high upper critical field (Hc2 > 50 T) with small electromagnetic anisotropy (γ ~ 1-2) [1] and large critical grain boundary angle (θc ~9˚) [2], and therefore is a promising material for applications in polycrystalline form. Foreseeing high field magnet applications, Weiss et al. have reported demonstration of trapped field of 1 T for K-doped Ba122 polycrystalline bulks synthesized by hot isostatic pressing [3]. In this study, we synthesized K-doped Ba122 bulks by combination of high-energy-milling of precursor powder [4, 5] and Spark Plasma Sintering (SPS) [6] and evaluated trapped field characteristics of them. In order to accelerate the optimization of synthesis conditions to obtain high Jc, machine learning technique has been employed [7].
References
[1] A. Yamamoto et al., Appl. Phys. Lett. 94, 062511 (2009).
[2] T. Katase et al., Nat. Commun. 2, 409 (2011).
[3] J. D. Weiss et al., Supercond. Sci. Technol., 28, 112001 (2015).
[4] S. Tokuta and A. Yamamoto, APL Materials 7, 111107 (2019).
[5] S. Tokuta, Y. Shimada, and A. Yamamoto, Supercond. Sci. Technol. 33, 094010 (2020).
[6] S. Tokuta et al., ASC2020, Wk2MPo3B-05 (2020).
[7] A. Yamamoto et al., ASC2020, Wk1MOr3B-02 (2020).
Acknowledgement
This work was supported by JST CREST (JPMJCR18J4), JSPS KAKENHI (JP21H01615), MEXT Elements Strategy Initiative to Form Core Research Center (JPMXP0112101001), and Nanotechnology Platform (A-18-TU-0037) of the MEXT, Japan.
JT-60SA is a superconducting tokamak constructed in a project being undertaken jointly by Japan and Europe. The thermal shield provides screening of the superconducting coils from the plasma vacuum vessel at elevated temperature and the tokamak cryostat at ambient temperatures. The thermal shield is made of stainless steel plates and is cooled by helium gas which flows in embedded pipes along the plates. The total surface area facing the warm components is 1150 square meters. Multi-layer insulator covers 40 percent out of total surface area. The coolant helium gas is typically supplied by 400 g/s at 80 K, and 1.4 MPa. The design heat loads for the whole thermal shield are 33 kW in nominal operation and 135 kW in baking operation, respectively. The first cool-down operation for the entire coil system including the thermal shield was conducted in 2020. The measured heat loads for the thermal shield are 30 kW in nominal operation and 100 kW in baking operation. In this work, a detailed operation method and measured data for JT-60SA thermal shield are revealed. The heat loads are analyzed in terms of difference between assumptions in design phase and measurements derived from the manufactured components.
We present a systematic design approach to the cryogenic system of ReBCO coated conductor based high-temperature superconducting actuators used in highly dynamic applications. While ReBCO coils operating around 20 K can in principle increase the force-density of linear actuators by nearly a decade, the thermal design of such a system poses two important challenges. First, the foreseen AC loss levels are considerable in such a high-dynamic application with an array of ReBCO racetrack stator coils typically exposed to the magnetic AC fields of copper mover coils, which can reach up to 1 T peak-to-peak and contain many higher harmonics above the main actuator frequency of 10 Hz. Second, these substantial losses created heat that needs to be drained from the moving system, since the ‘stator’ in many actuator applications acts as a balance mass and thus needs to be mobile, albeit typically with a lesser stroke than the mover experiences.
A range of design options is available for the various components in the cryogenic system of such a machine. In the presented initial feasibility study systematically several types of cooling schemes have been investigated including bath-, conduction- and gas-cooling. In order to assess and rank their applicability, a set of criteria is presented against which each potential cooling solution can be assessed. Following this systematic approach, the most promising cooling methods are identified and subjected to more detailed thermal modelling to assess whether or not they can maintain the intended operating temperature under the foreseen heat load. For the linear actuator under consideration, conduction cooling is the most promising candidate, since it avoids sloshing-induced vibrations associated with a bath; is relatively compact and robust; and enables a thin-walled cryostat, which reduces the air gap between the cold stator and the warm mover.
A project to develop a 10-Mvar high temperature-superconducting (HTS) dynamic synchronous condenser is carried out by China Southern Power Grid Corporation. In order to cool the magnets to 20-30 K, a set of cryogenic system using circulating helium as the working fluid was developed, and it has been coupled and tested with the 10-Mvar class dynamic synchronous condenser. Six cryogenic coolers are used as the cold source to provide more than 240 W@20K cooling power. And they will be transferred to the circulating helium gas through the specific designed heat exchangers with an efficiency higher than 95%. Two cryogenic helium pumps are employed to overcome a pressure drop of about 5 kpa induced by the helium gas circulating in the transfer tubes about 10 meters. In addition, a set of pressure adjuster is also put forward to achieve pressure fluctuations below 0.2 bar, including the processes of start-up, operation and shut down. In the static tests coupled with the 10-Mvar class dynamic synchronous condenser, 5 days are needed to cool the entire magnets to approximately 26 K. Once the motor speeds up and reaches the design value of operation, this temperature rises slightly to about 27 K, which can also satisfy the demand of keeping the magnet in superconducting state. This paper will describe the design and optimization of the cooling system in detail as well.
Railway Technical Research Institute is researching the magnet technology on the application of the railway system.
In magnet technology, we are fabricating and evaluating magnetic materials. As applications of magnet, we are developing research on the high-temperature superconducting magnets, the superconducting magnetic energy storage, the superconducting traction transformer, the non-contact power supply system, the linear induction motor-type eddy-current rail brake system, and so on.
And we are also conducting research technologies such as the ground and levitation propulsion coils for maglev.
These magnet technology for railway will be introduced in detail on this presentation.