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.