Welcome to the MT25 Conference !
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This site comprises the Conference Program and detailed Timetable. It also shows all Abstracts, and all Oral and Poster Presentations.
ITER, a first-of-a-kind nuclear tokamak, is being constructed by a partnership between China, European Union, India, Japan, Korea, Russian Federation and USA, in southern France. The buildings are well under construction and the tokamak components, largely supplied in kind by the partners, will start arriving at the end of this year. Component assembly activities start in 2018 and continue until 2025. Fabrication of the vacuum vessel is moving forward, manufacturing of the thermal shield is in progress, and cryostat elements delivered by India are being assembled into large-scale sections of the cryostat (~29m diameter ~29m height). The magnet system, with 50GJ of stored energy, will be the largest ever built. Over 600t of Nb3Sn and 300t of NbTi superconducting strand were produced for these magnets and 95% of the superconductors for the magnets are now complete. Winding packs, weighing 100t each, for the first 2 toroidal field coils were completed in Europe and the double pancakes for a further 2 were stacked in the EU and Japan. About 60% of the winding of the TF coils is completed. Winding of the first central solenoid coil is underway at a supplier in USA. The first double pancakes for the poloidal field coils are being wound in the European Union, Russia and China. The feeders, complex and vital parts of the system, are fabricated by Chinese suppliers and the first units will be delivered in August. At this point the project is successfully overcoming multiple challenges simultaneously. For example, as the first magnets are built and tested adjustments and corrections are made to maintain performance, without loss of schedule. The restructuring of the ITER organization in 2015 and 2016, and a positive spirit of mutual collaboration among the partners, is helping us to stay on track for first plasma in December 2025.
Abstract— The Large Hadron Collider (LHC) upgrade, called High Luminosity LHC (HL-LHC) is planned for the next decade. A wide range of magnets and new technologies are currently under development. One of these systems will be a set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS & CMS experiments. This twin aperture magnet system comprising 16 magnets, approximately 2 m long, with large 105 mm clear aperture coils. Each aperture will independently deliver 5 T.m integral field, between apertures the field vectors are rotated by 90° from each other, and individually powered.
This paper presents the sequence of component developments to produce a cost-performant, canted cosine theta (CCT) model magnet. We describe the challenges encountered during the manufacture of the coil formers with their helical canted coil winding process which places a number of insulated wires into the CNC 3.5 axis machined slots. We describe the: pressurized impregnation process, multiple jointing to connect inner and outer sets of wires within the confines of the coil assembly, magnet assembly into support structure and yoke. Finally we present the quench performance and, initial magnetic field measurements of this novel coil configuration.
Large aperture beam separation dipole magnets (D1) need to be developed for the high-luminosity LHC upgrade. The important specifications of this magnet are a coil aperture of 150 mm and field integral of 35 T·m at 12.0 kA and 1.9 K. The coils in the D1 magnet have a single layer structure and are wound with Nb-Ti/Cu Rutherford cables with the width of 15.4 mm. In such a thin and large aperture coil, precise prediction of coil size change during fabrication, cooling and excitation has importance to maintain the coils under appropriate pre-stress and that is a key to realize superior quench performance. KEK is in charge of development of the D1 magnet. The first 2 m model magnet (MBXFS01) was fabricated and tested at cold in 2015 – 2016. Quench current of this magnet reached 105% of the nominal current, however, the ultimate current of 13 kA as an acceptance criteria was not achieved. Measurements of azimuthal coil stress at the pole during excitation suggested that coil stress was completely released at the current much lower than the nominal one and the insufficient pre-stress was thought to be the main reason of unsatisfactory quench performance. After the cold test, MBXFS01 was once disassembled and reassembled after inserting shims to the coil mid-plane to enhance azimuthal coil pre-stress by 40 MPa. In this paper, we will report reassembly of the first 2 m model magnet (MBXFS01b) and the results of the cold test. Influence of coil pre-stress on training performance will be discussed and other test results such as magnetic field measurements and heater tests will be also introduced.
During 2016, one quarter of the LHC main dipoles have been powered above the 7.7 T operational field, to reach a field of the order of 8.1 T. These tests were done to confirm the extrapolation of the training behaviour based on a Gaussian tail of the quench distribution. In this paper we show that the training is compatible with the expectations, but on the lower side of the extrapolation. These tests also allowed to assess the quantity of magnets quenching twice during the training, which is shown to happen in a 10% fraction of the production. Moreover, one eight of the LHC was warmed up to replace a magnet, adding precious information on the magnet behaviour on successive trainings. We then propose an asymmetric distribution to better model the quench distributions. Based on these new elements, we show that around 500 quenches are expected to reach the operational field of 8.3 T for the whole LHC dipoles (corresponding to 7 TeV operational energy). We show that very little correlation is found between the training in the installed magnet and individual test in virgin condition (first cool-down). On the other hand, a better correlation is found with individual test after a thermal cycle (second cool-down); unfortunately, the uneven sampling of these test (done on 10% of the production) did not cover the production showing slower training in the LHC.
Nested orbit correctors magnets so-called MCBXF are needed for the upgrade of the LHC, in the framework of the HL-LHC project. There are two versions (A and B), with different physical lengths, respectively, 2.5 and 1.5 m, which share the same cross section to decrease the fabrication cost. These magnets have a large aperture of 150 mm. Due to the high radiation dose, a mechanical clamping is necessary to hold the large torque between both dipoles.
Magnetic and mechanical conceptual design is described elsewhere. This paper describes the final magnetic design, with special attention to 3-D electromagnetic calculations and the different operation scenarios. It also includes the results of a number of mechanical FEM models, which analyze the stress distribution and deformations at several load steps: assembly, cooling-down and energization. Finally, a mechanical model has been designed, fabricated and tested to show the feasibility of the proposed clamping structure. This paper also describes other tests performed to improve the accuracy of the FEM models, such as the measurement of the Young modulus of stacks of impregnated cables.
Acknowledgments: This work has been partially funded by CERN contract KE-2292 and the Spanish Ministry of Economy, Industry and Competitiveness under projects ref. FPA2013-47883-C2-2-P and Resolution on May 24th, 2016.
INFN is developing at LASA lab (Milano, Italy) the prototypes of five corrector magnets, from skew quadrupole to dodecapole, which will equip high-luminosity interaction regions of the High Luminosity-LHC (HL-LHC). These magnets are based on a superferric design, to allow a relatively simple, modular and easy to construct magnet. This program takes place within the framework of a collaboration agreement between CERN and INFN. In the paper we present an overview of the present activity, from the design, to the construction and test at the operation condition.
The luminosity upgrade of the Large Hadron Collider requires that the new separation/recombination dipoles D2 shall deliver a field integral of 35 Tm. A design has been developed of a twin dipole generating a magnetic field as high as 4.5 T in apertures of 105 mm and 7.78 m magnetic length. The magnetic field direction is identical in both apertures causing a not negligible magnetic cross talk, which could be highly detrimental for the field quality. In order to minimize the cross talk effects a design based on asymmetric coils has been developed in the past years. Recently the design has achieved a level of maturity allowing the starting of a second phase of development involving the construction of a short model and, later on, of a prototype. The short model (1.6 m long) has been designed in all aspects and it is presently under construction in industry. The contribution is focused on the design of the short model with emphasis on the mechanical aspects, which include a novel approach to the integration of coils in the mechanical structure through the use of Al-alloy sleeves. General aspects related to the integration of the D2 in the IR are discussed as well.
The Large Hadron Collider (LHC) at CERN has been operating and producing physics since September 2008, and has entered after a first long shut down its second, 4-year long physics run. The LHC is to date the largest superconducting installation, counting some 10000 magnets along its 27 km long circumference. A significant operational experience has been accumulated, including the occurrence and consequences of electrical faults at the level of the main magnets, as well as their protection and instrumentation circuits. The purpose of this paper is to provide a first overview of the typical electrical faults and their frequency of occurrence in the first years of operation, and to perform a statistical analysis that can provide typical values for similar future productions.
By combining resistive polyhelix and Bitter inserts with a large bore superconducting outsert, the new hybrid magnet in construction at LNCMI-Grenoble will produce in a first step, an overall continuous magnetic field of 43 T in a 34 mm warm bore aperture. After a brief reminder of the specificity of hybrid magnets, namely the strong electromagnetic and mechanical couplings between resistive and superconducting coils, the main specificities of the proposed design are presented. The superconducting coil will provide a nominal magnetic field of 8.5 T in a 1.1 m cold bore diameter relying on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled down to 1.8 K by a bath of superfluid helium at atmospheric pressure. The novelty of the RCOCC concerns the in-laboratory assembly and induction soft-soldering of the Rutherford cable on a Cu-Ag hollow stabilizer allowing a strict control of the interstrand contact resistance. A stainless steel reinforced copper shield inserted between the superconducting and resistive coils will allow reducing the coupling currents induced within the RCOCC as well as the extreme mechanical force exerted on the superconducting coil. After successful thorough reviews of the Grenoble hybrid magnet design anticipating possible upgrades of the maximum magnetic field produced, this project is now well engaged in its construction phase. The status of this project is presented together with the next milestones.
A superconducting magnet with large inner diameter of 920 mm was developed for an outsert of a hybrid magnet at the High Magnetic Field Laboratory of Chinese Academy of Sciences (CHMFL). The superconducting magnet was successful tested and produced 10 T on November 5, 2017, and the hybrid magnet combined with the superconducting magnet and also an insert resistive magnet was also successful tested and produced 40 T on November 13, 2017. The superconducting magnet consists of 3 nested coils and made of 4 kinds of Nb3Sn cable-in-conduit conductor. It is cooled by forced flow helium at 4.5 K. During the commissioning of the outert superconducting magnet, a series of performance tests have been carried out, including the AC losses test, the current dumping test and so on. This paper reviews the important specifications and design features for the outsert superconducting magnet, and also discusses the test results of the first commissioning.
The National High Magnetic Field Laboratory (NHMFL) has commissioned a 36.1 T magnet with homogeneity and stability of 1 ppm over a 10 mm diameter spherical volume to be used for solid state NMR. Most NMR magnets use single strands of superconducting wire carrying a few hundred amps and persistent joints and switches. This magnet uses a 20 kA superconducting cable in a steel conduit for the outer part of the magnet and copper-alloy sheet metal for the inner part of the magnet.
While >15 hybrid magnets have been built worldwide, they typically have a field uniformity of ~250 ppm/cm DSV and stability might be no better than 10 ppm. To attain 1 ppm uniformity, current density grading was employed in the resistive coils to cancel the z2 term. In addition coils were shifted after the first map to reduce the z1 term. Ferroshims and resistive shims were installed in the bore to attain 1 ppm over 10 mm. The large inductance of the superconducting coil reduced the ripple 5-fold compared with all-resistive magnets. A pick-up coil based stabilization system reduced the high frequency ripple and an NMR lock reduced the low-frequency drift to attain 1 ppm stability.
In 2007 the Nijmegen High Field Magnet Laboratory has embarked in a programme to design and construct a 45 T hybrid magnet to provide the highest magnetic field available to its user programme. We present the final design of the resistive insert coils for this hybrid, which will operate in the 12.3 T background field of the superconducting outsert magnet. The insert magnet has an outer diameter just shy of 600 mm and consists of five Florida Bitter coils, with the Nijmegen cooling hole optimisation. The coils will operate at 38 kA, with the innermost coils (A1 and A2) powered in parallel, and generate an on-axis field of 33.0 T. The power consumption is restricted to 21 MW to accommodate, if necessary, additional power to compensate for variations in Bitter disk thickness or deviations in cooling properties. Construction of the stamping tools for the disks has started and the first disks will be produced in the spring of 2018.
In this study, a 3D multi-filament FEM model is developed for some kinds of superconducting strands, such as LMI strand, SMI-PIT strand and Bi2212 round wire. Some important factors, such as the initial thermal residual stress, the breakages of superconducting filament and twist pitch (for LMI, SMI-PIT) are taken into account. In this FEM model We calculate this thermal residual stress system, and apply the results into the multi-filament model. For considering the influence damage of SC filament on the electromechanical behavior of SC strand, we choose the representative volume element (RVE) as a concentric cylinder with a single filament in the matrix. Since the damage of the filament and its evolution are almost random, hence, we consider the distribution of the break points to be of a Weibull form. According to the GLS model of Curtin and Zhou, the effective constitutive relation of this RVE can be obtained. So a 3D FEM model of SC strand is built. The tension, bending and cyclic behaviors of these strands have been investigated, respectively. From the comparisons with these two experiments in axial tension and bending respectively, it can see that our model has good accuracy in the prediction of the mechanical behavior of the SC strands. The critical current of the strand under axial and bending loads are calculated with the invariant temperature and field strain functions, the results indicate that the damage and current transfer length in the strand have significant effects on the critical current. The calculated critical currents under tensile and bending load with every factor taken into consideration agree well with the experiments.
The twisted, stacked-tape cabling method allows developments of high current REBCO cables for various high field applications, such as fusion magnets, magnetic resonance imaging (MRI) devices and accelerator magnets. The single tape performance under applied loads is crucial to understand cable limitations, and important for choosing an appropriate cable geometry. In this paper, we theoretically investigate the effect of twisting morphology on the mechanical properties of HTS tapes by using the Timoshenko beam model. Particular attention is paid to the transverse bending of a pre-twisted HTS tap. The analytical solution is first derived for the deflection of the HTS tap under a uniformly or periodically distributed transverse force. Then, the critical current of a twisted tape is calculated by the integration of the critical current densities corresponding to the strain distribution over the tape cross-section using axial strain data of the pre-twisted tape. The results show that the twisting morphology can significantly improve the resistance of HTS tap to transverse bending, thus reduce the superconducting performance degradation. This study helps understand the electro-mechanical properties of pre-twisted HTS taps and provides theoretical reference for the design of novel HTS cable structures.
Acknowledgments: The authors appreciate the financial supports from the National Natural Science Foundation of China (11572143 and 11421062).
The superconducting dipole magnets being developed at CERN for the HL-LHC project are equipped with coils manufactured from Nb3Sn Rutherford cables, following the Wind & React fabrication technique. The brittleness of the multifilamentary structure of the Nb3Sn within the cable strands exposes the coils to permanent performance degradation when subjected to excessive strain during assembly and operation. The coils have to be heavily pre-stressed to ensure the required mechanical stability of the cables under the Lorentz forces when the magnet is powered to maximum current under high field. Reaching the maximum acceptable stresses during assembly and operation without causing permanent damage requires refined knowledge of the mechanical behaviour of these epoxy impregnated Nb3Sn coils. This paper will show a detailed analysis of the characterisation of cable stacks (10-stack) under compression using representative coil material in order to predict the behaviour of the Nb3Sn coils. By means of standard mechanical measuring techniques and finite element analysis, the results from the 10-stack measurements are extrapolated to an actual and fully detailed coil cross section using 2D imaging techniques. The stress and strain distribution from the actual coil geometry are used to predict the stresses and strains at the strand level and the filaments within the strand. The model of the strand and filaments is based on a scanning electron microscope image of a strand of interest within the original coil in order to provide a realistic geometry and a better representation of the stresses and strains within the multi-filament structure. The results from this multi-scale approach has allowed for a better understanding of the stresses and strains that are observed at the strand and filament level by accounting for the global stresses and strains of the realistic coil geometry.
An analysis model was developed to evaluate the axial pre-compression for the central solenoid (CS) magnet of KSTAR. The model represents the preloading relatively well in assembly, cool-down and current charging conditions. However, the model for cool-down condition needs to be modified for the accurate estimation of preloading. The smeared material properties of the CS winding pack were reevaluated. The electromagnet forces of the coils are evaluated during plasma operation conditions like large plasma current and long pulse H-mode discharges. The structural analysis of the CS magnet is performed using the updated model and the analysis result is compared to the measured strains. The analysis methodology and the model have been consistently updated to increase the reliability of the analysis through these processes. Studies on the structural behavior of the CS magnet are expected to provide guidelines for future KSTAR operation in spite of insufficient preloading.
Fatigue failure had recently occurred on a 60T pulsed magnet at the Wuhan National High Magnetic Field Center (WHMFC). It was designed to produce a peak field of about 63T and had practically endured a total number of 2124 shots with 573 of them above 56T. In this paper, the cause of failure is numerically analyzed using the conductors and reinforcing fibers at the mid-plane of the magnet. The damage-coupled constitutive model of conductor is applied with two failure criteria so that the mechanical behavior and fatigue life of the magnet during multiple pulses can be predicted. The analysis is divided into three steps where special attention is paid to the effects of bending pre-strain and axial pressure on conductors. The first step is about the stress distribution during the first pulse. It is found that the maximum stress of reinforcing fibers can be increased by about 600 MPa at 63T considering the axial pressure and pre-strain. The second step is failure analysis at certain level of magnetic field. It is found that the fatigue life of the magnet between 56 ~ 63T drops rapidly from about 1000 pulses to less than 100 pulses as the field increases. In this region, the main cause of failure is the axial strain of conductor reaching its critical value. The third step is failure analysis according to the practical sequence of pulses. It is found that the 573 pulses above 56T decides the failure of magnet where the axial strain keeps increasing until the critical value is reached.
Functional diagnostics of superconducting magnets is essential for ensuring their safe and reliable operation and understanding performance limitations. Among various known diagnostic approaches, acoustic techniques being non-invasive and inexpensive carry a significant potential that is not yet fully explored. Firstly, acoustic emissions provide direct access to magnet mechanical disturbance spectra, allowing localization, and in some cases identification of the type of disturbances leading to premature quenching, training and memory phenomena. Next, they allow for real-time structural monitoring of mechanical integrity, contact stiffness and coupling between magnet structural parts. Finally, early detection of heat release in coil windings during current ramping and quench development can be accomplished using active acoustic sensing of local variation of the Young’s modulus. Acoustic detection of hot spots using this principle is complementary to the conventional voltage-based quench detection, and can be especially useful for high-temperature superconductor magnets exhibiting slow quench propagation. We demonstrate how the described range of diagnostic capabilities can be achieved with in-house developed package of passive and active acoustic analysis and sensor hardware. We present a novel “acoustic heartbeat” monitoring tool, allowing for in-depth real-time analysis of disturbance types, structural integrity and heat release in the magnet. Validation of our tool during testing of the canted-cosine-theta Nb3Sn dipole and ReBCO tape stacks will be discussed.
During the development of MQXF, the new Nb3Sn quadrupole to be used in the LHC inner triplets for the Hi-Luminosity upgrade, three short models were tested: MQXFS1, MQXFS3 and MQXFS5. These models differ in the use of thin or thick laminations for the iron components, and in the coil strands, RRP or PIT. In the MQXF design, the azimuthal prestress is provided at room temperature by means of the bladder-key technology, and it is further increased during the cooldown by the differential thermal contraction of the various components. Four aluminum rods provide the longitudinal prestress. Both systems allow for a flexible control of the amount of prestress applied. As a consequence, it was possible to test the models exploring different azimuthal and longitudinal prestress conditions, in an attempt to understand their impact on the magnet performances. This paper studies the mechanical behavior of these short models, also providing the strain and stresses measured by means of strain gauges installed on the aluminum shell, on the winding poles and on the rods. Finally, the paper compares the measures with the results from FE models.
For the quadruple magnets, the harmonic components at reference radius can be used to express the field quality using relative harmonics which is the high harmonics components (order > 2) by 2nd component. Generally speaking, the high harmonics components have negative effects on beam focusing. Therefore, the relative harmonics should be decreased to meet a target value. However, the specific influence of the relative harmonics on beam focusing in three dimensional is difficult to be expressed. In order to estimate the effects of each harmonic component on particle movement, this study presented beam trajectory analysis in three dimensional with respect to harmonic components by SCALA. Frist, magnetic field distribution was obtained from a given quadruple triplet using Fourier analysis. Then, the harmonic components which compose the field inhomogeneity were removed one by one from the total magnetic field of the given quadruple triplet. Several magnetic field distributions with different harmonic components were generated. Therefore, the beam trajectories can be simulated in SCALA with respect to magnetic field harmonic components. The field quality of quadruple magnets can be expressed by the effects of harmonics components on beam focusing.
The future high luminosity upgrade of the Large Hadron Collider (LHC) at CERN will include twenty 4.2 m long Nb3Sn high gradient quadrupole magnets which will be components of the triplets for two LHC insertion regions. In order to test these and four pre-production models, the vertical superconducting magnet test facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL) has been upgraded to perform testing in superfluid He at 1.9 K, which is the operational condition at the LHC. This has involved extensive modification of the 4.5 K cryogenics plant, including piping, compressors, and other upgraded components; a new vertical test dewar which can accept larger diameter magnets; a modernized power supply system upgraded with IGBT switches and fast shutoff capability, and that can supply 24 kA to test high field Nb3Sn magnets; and completely new data acquisition, signal analysis, and control software and hardware, allowing for high precision and large volume data collection. This paper reports on the design, assembly, and commissioning of this upgraded test facility and the first magnet test performed, on a mirror model, which consists of a single coil quadrant and an iron yoke filling the other three quadrants and is designed to have peak fields close to that of the production quadrupoles.
The detailed calculation of the current and losses distribution during the electrodynamic transients is of great importance for the design of superconducting accelerator magnets made of Rutherford cable. On the one hand, the current distribution affects the field harmonics generated by the superconducting magnet; on the other hand, the loss computation is necessary for the design of the cryogenic system. This paper presents the analysis of current distribution and losses in a prototype race-track coil configuration, the so-called Short Model Coil (SMC), developed at CERN in the frame of a test campaign of possible cable candidates for the HL-LHC project of CERN. The SMC 11 T was wound with a 40 Nb3Sn strand Rutherford cable in two layers, with 35 turns per layer. The loss measurements were performed at CERN by means of an electrical approach to analyse different transport current cycles. The THELMA model of the Rutherford cable, which represents the conductor at the strand level, was used for the analysis of the current distribution and losses in the coil during the transport current ramps. In this way, the inter-strand current diffusion and the corresponding time constants could be analysed in detail. In the paper, the comparison between the numerical and the experimental results is presented, together with the relevant information on contact conductances between strands, current distribution and losses.
The High Luminosity LHC Project target is to reach an integrated luminosity of the LHC of 3000 fb-1, corresponding to a factor 10 increase in number of collisions with respect to the current accelerator. One major improvement foreseen is the reduction of the beam size at the collision points. This requires the development of 150 mm single aperture quadrupoles for the interaction regions. These quadrupoles are under development in a joint collaboration between CERN and the US-LHC Accelerator Research Program (LARP). The chosen approach for achieving a nominal quadrupole field gradient of 132.6 T/m is based on the Nb3Sn technology. The coils with a length of 7281 mm will be the longest Nb3Sn coils fabricated so far for accelerator magnets. The production of the long coils was launched in 2016 based on practice coils made with copper cable. This paper provides a status of the production of the coils made with low grade and full performance Nb3Sn cable and will describe the production process and applied quality control. Furthermore an outlook for the prototype assembly will be provided.
Abstract - In recent years, the Superconducting Nb3Sn cable material became the privilege mature candidate for the High Field magnets in new projects like High Luminosity LHC (HL-LHC) accelerator at CERN. The technology needs in the years 2017-2021 to be deployed through unprecedented magnet series production with dedicated on-line quality control. The key fabrication stage of the Vacuum pressure impregnation after heat treatment reaction of Nb3Sn coils like on the new 11 T dispersion HL-LHC dipole enhances both the structural integrity and the dielectric strength of winding packs. The final epoxy CTD-101K resin impregnated insulation system composed of mica-fiber glass is commissioned under 5 kV high voltage test to ground. The global vacuum impregnation pressure method exhibits various merits in insulation performance and high dielectric strength reliability which strongly dependent on the success of the resin filling cycle. There is currently limited information and understanding on what could be a good dielectric frequency domain response of Nb3Sn coils. Due to importance of this issue, the monitoring of the resin content is introduced on using capacitance measurement and the quantitative dielectric response analysis both in the time and frequency domain. This proposed method enables during the VPI cycles to derive comparative master trend curves of various coils. These quantitative measurements enable to improve the quality of the composite insulation by possibly optimizing the heat and pressure cycle. Optimally, a combination of above methods can further help taking decision during manufacture on the wetting extent and bring insights on the impacts of resin type, the degree of curing, effects of void contents and coil geometry on the dielectric response. An independent insulation dielectric permittivity measurement provides a reference for the impregnation manufacture quality. The frequency impedance measurement of first short dipole model provides the distributed network lumped circuit fitting electrical parameters.
For the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC), the development of the 11-T Nb3Sn dipole is progressing. At present, one double-aperture and five single-aperture short-model magnets have been built and tested. Magnetic measurements have been performed both at ambient and cryogenic temperature. Besides, the first 5.5-m-long prototype is being produced and the first collared-coil assembly has been measured at ambient temperature. In this paper, the results collected up to the present moment are reported and discussed. The geometrical field multipoles, the iron saturation effects as well as the effects of persistent currents are presented. Experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE, and discussed in view of the construction of the final magnets.
The High-Luminosity upgrade of the Large Hadron Collider Luminosity (HL-LHC) requires new high-field and large-aperture quadrupole magnets for the low-beta inner triplets (MQXF). CERN and LARP collaboration are currently developing a 150-mm-aperture quadrupole based on Nb3Sn superconducting cables for the coils, and an aluminum shell with the bladder-key technology for the support structure. This paper presents the test setups for magnetic measurements, both at ambient and cryogenic temperatures, and the instrumentation being used for the first two short-models of MQXF built and tested at CERN. Finally, the measurements results, in terms of field quality, effects of persistent currents, and iron saturation, are reported and discussed.
The FRESCA2 dipole magnet has been developed within a collaboration between CEA Saclay and CERN. The main goal of the magnet is to provide a 13 T nominal bore field into a clear aperture of 100 mm diameter, for the second generation cable test facility FRESCA2 (Facility for the REception of Superconducting Cables) at CERN. The coils have been produced in a joint effort between CEA Saclay and CERN. The magnet has been assembled at CERN, pre-loaded at room temperature, cooled-down in liquid helium, and powered with several current cycles. The magnet is mechanically instrumented with strain gauges on the external shell, tie rods, and central post of the coils. This paper reports the results of the mechanical measurements collected during pre-load, cool-down, powering, and warm-up of the magnet. This data is also compared with a 3D mechanical model, in order to validate different assumptions such as friction coefficients, material properties, and pre-stress levels.
Lawrence Berkeley National Laboratory (LBNL) in collaboration with the Institute of Modern Physics (IMP) is developing a Nb3Sn superconducting magnet system for a fourth-generation ECR source operating at the microwave frequency of 45 GHz. This paper presents a mechanical design capable of supporting the magnet up to the required operational level, resulting in peak coil fields of the order of 12 T, without exceeding the stress limits of each component, in particular the brittle Nb3Sn conductor. The coil system, based on the sextupole-in-solenoid configuration, is supported by a shell-based structure that uses an aluminum cylinder pre-tensioned with water-pressurized bladders during the magnet assembly. High thermal contraction of the shell allows reaching the target preload level at a cryogenic temperature without over-stressing the coils during assembly. We present the optimization steps of the support structure, describe its main components and assembly procedure, and we analyze expected coil stress at each step of the magnet assembly and operation using three-dimensional finite-element mechanical model.
The high luminosity upgrade project US LARP/HiLumi has successfully tested the first 1.5 m prototype quadrupole MQXFS1 at Fermilab’ Magnet test facility. Several thermal cycles and test programs were performed, with different pre-load configurations. To localize the quenches a quench antenna and the information of the voltage taps is used. The Quench Antenna was placed in the warm bore of an anti-cryostat centered in the magnet. We varied the length between quench antenna segments from 1” to 6”, and shifted the location of the antenna to localize the quench origin along the various wedge and spacers transitions in the lead end of the magnet. We will present results on the identified quench locations for the second and third thermal cycle in this paper.
The planned upgrade of the LHC collimation system requires the installation of 11 T Nb3Sn dipole magnets. Due to the large stored energy density and the low copper stabilizer section, the quench protection of these magnets is particularly challenging. A total of ten coils assembled in five single aperture and two double aperture short model magnets have been tested at CERN with different heater to coil insulation lay outs. This paper reports on the test results of the model program, which are used to validate numerical models and to optimize the quench protection performance. A parametric analysis on the impact of different conductor and operation parameters on the peak temperature is presented. Coil voltage to ground and turn to turn voltages are also evaluated under nominal conditions and failure case scenarios.
The use of spin-polarized neutrons in neutron scattering experiments provides fundamental information on magnetic properties. One of the key issues is to maintain the polarization of a neutron beam on its way through the large magnetic fringe fields produced by a high field superconducting magnet. Up to now, most Low Temperature Superconducting (LTS) magnets for neutron scattering use active shielding coils to reduce the fringe fields around the neutron spin flippers and an asymmetric mode to guide polarized neutrons through the region of the zero-field node. By exploiting the use of iron in the magnetic circuits, High Temperature Superconducting (HTS) magnets offer an easier solution to maintain neutron polarization. Recently a passively shielded 3T HTS magnet for polarized neutron scattering experiments was designed, constructed and tested by HTS-110. This split-pair magnet provides a maximum horizontal magnetic field of 3 tesla while the fringe field is less than 1 mT at 0.5 m from the magnetic center in the magnet axial direction and the fringe field is less than 0.1 mT at 1 m from the magnetic center in the magnet radial direction. Furthermore the zero-field nodes are located outside the magnet cryostat easing the control of neutron polarization at entry to the magnet. The magnet has a vertical room temperature bore of 80 mm in diameter for sample access and 4 horizontal bores with an opening angel of 32° for neutron access, allowing high flexibility without any material in the beam to cause a scattering background. In this paper we report the test results of this magnet. Aspects of HTS magnet design specific to the combined requirements of neutron scattering including magnetic field, fringe field and sample and neutron access are discussed.
The 12 GeV Upgrade Project at Jefferson Lab is complete and all new systems have met their Key Performance Parameters(KPP). The Super High Momentum Spectrometer(SHMS) in JLAB’s Hall C is an 11 GeV/c particle spectrometer with a resolution of 0.5 x 10^-4 , 4.4 milli Steradian acceptance and a +20 %/-10% momentum bite. All five SC magnets have been delivered, installed, cooled down, tested and all have reached and exceeded the currents required for operation at the nominal settings for 11 GeV/c. Details of the magnet’s installation, testing, cryogenics, cool down, quench history and training will be presented. The equipment in Hall C consisting of the SHMS (2017) and the HMS (1994) have operated and demonstrated their Key Performance Parameters(KPP) and performed preliminary data taking experiments to qualify the new equipment. This is the conclusion of a long and very successful project.
Acknowledgement: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Three large superconducting magnets have been designed and built by Sigmaphi (France) for the Jefferson Lab’s 11 GeV/C Superconducting Spectrometer. These SHMS Dipole and Q2/Q3 quadrupoles use the same collaring system based on aluminum force rings designed to ensure coil integrity and avoid conductor motion. The coil properties have been determined thanks to mechanical tests at room temperature and at 4.2K. Conclusions of the FEA analysis performed by Sigmaphi have been verified thanks to strain measurements on a collaring prototype and during final collaring. Final acceptance tests done at JLAB are also presented.
In the frame of the ongoing design study of the Future Circular Collider (FCC), new options for detector magnets are being developed. In the current concept, the first phase of the FCC may be the FCC-ee, an electron-positron collider operating at energies up to 350 GeV in a 100 km long tunnel. As second phase it may be replaced by a 100 TeV hadron-hadron collider (FCC-hh). The particle detectors and their superconducting magnets are required to provide sufficient resolution. For FCC-hh, for example, this requires 4 T over 20 m in a 10 m diameter free bore. In current general-purpose detector systems, the magnetic field not only encloses the inner tracker where the magnetic field is actually needed, but also the electromagnetic and hadronic calorimeter. Essentially because current high field detector magnets are insufficiently radiation transparent. This implies a waste of magnetic field, stored energy and financial resources. A proposed solution is to build an ultra-thin,particle transparent solenoid, which only covers the inner tracker, similarly to the ATLAS Central Solenoid. The idea is to build a thin coil (<1 radiation length), which is able to provide thermodynamic stability and quench protection. This requires a conductor with a RRR of > 500. In addition, the conductor has to act as mechanical reinforcement to handle the magnetic pressure leading to hoop stress of about 300 MPa. Advanced doped Aluminium alloys are most promising given their density to strength ratio. The development of such a conductor is approached from different sides. One is to look for a multi-material reinforced sandwich like alloy with high RRR and sufficient tensile strength at 4.2 K. Second is to create a hybrid conductor from micro-alloyed Aluminium providing electro-thermal stability to the superconductor, reinforced by welding to an ultra-high yield strength Al-alloy of the 7000 series, or a mixed option.
The baseline design of the FCC-hh detector magnet system with 14 GJ stored energy and providing 4 T for particle tracking, comprises 3 large size superconducting solenoids. The main solenoid is 20 m long and has a 10 m free bore, while the so-called forward solenoids have a free bore of 2.6 m and a length of 4.2 m. The designs of the cryostats take into consideration not only vacuum and cold mass weights of 1.05 kt and 0.048 kt respectively, but also those specific for the detector such as the high weight of 4.6 kt of the calorimeters and trackers resting on the bore tube. A specific challenge in the design is to choose the type of cold mass supports since these entails an important mechanical local load on the cryostat. The choice of materials and their properties has significant impact on both heat load by conduction and strain in the tie rods. The design of both vacuum vessels and suspension systems of these very large magnets will be presented. Also an estimate of the various heat loads seen by the cold masses are provided.
The BabyMIND Experiment, supported by the CERN Neutrino Platform program, is a downstream muon spectrometer on the T2K beamline for the WAGASCI experiment at J-PARC in Japan. The BabyMIND detector aims to improve the measurements of the ratio of neutrino interaction cross-section on water and carbon, and to establish charge identification for muons with momenta below 1 GeV/c, where multiple scattering degrades muon momentum measurements. The detector’s magnet system comprises a horizontal stack of 30 mm thick individually magnetized iron plates of size 2.0 m by 3.5 m. The overall mass of the block shaped magnet system is about 65 t including 2.3 t of insulated aluminum strip-shaped conductor. An innovative method of plate magnetization was developed. The magnetization scheme developed is optimized flux return for minimum stray field and operating current, while maximizing the useful tracking area with one-directional homogeneous magnetic field of 1.5 T. The magnet is operated at 140 A for generating the nominal field in the iron plates requiring only 12 kW power consumption with no need of any active cooling system. The magnet system for BabyMIND was constructed in 2016 and tested at CERN early 2017. In this paper the development and optimization of a new type of magnetization layout and its advantages are discussed. The coil module and overall system design, coil winding method, construction of the magnet modules, system assembly on site, as well as the results of the module and system testing are presented.
In 2015, the first ever polarized Drell-Yan experiment was performed at the COMPASS spectrometer at CERN. A 190 GeV/c pion beam with an intensity of 108 pions/s interacted with a transversely polarized NH3 target. The hydrogen nuclei in the solid-state NH3 are polarized by dynamic nuclear polarization (DNP) in a 2.5 T longitudinal magnetic field, while the target material is cooled down to below 100 mK. Transverse polarization is obtained by rotating the magnetic field and thus making use of the superposition of the magnetic fields generated by a solenoid as well as a dipole magnet, which are both superconducting and integrated in a common cryostat. The main solenoid coil comprises three sections and is complemented with 16 superconducting shim coils. It provides a 2.5 T magnetic field along the particle beam axis. The magnet has a large aperture, which is essential for the COMPASS spectrometer acceptance. The Solenoid has inner and outer radii of 340 mm and 361 mm, respectively. Over the volume of the target cells, the homogeneity is better than 10-4. Besides this homogeneous solenoidal magnetic field necessary for the DNP, in addition a saddle type dipole coil enclosing the solenoid is required, providing 0.63 T transverse magnetic field used in the frozen-spin mode to keep the polarization during data taking. It has inner and outer radii of 420 mm and 452 mm, respectively. The system is slightly over 2 m in length. One of the operational difficulties is the interaction between the main coil sections and the large forces that are involved. The stored energy of the system at nominal current, i.e. 650 A for the main solenoid – and 590 A for the dipole circuit, are 2.58 MJ and 0.468 MJ, respectively. The operational experience with this unique system and its controls will be presented.
Nuclotron-based Ion Collider state-of-art design involves innovative solutions in superconductive applied technology. Thanks to its consolidated experience, ASG has been directly involved into the program by providing to Joint Institute for Nuclear Research (JINR) a large 0.5 T Nb-Ti superconductive magnet equipped with an active (resistive) modulation system. Typical solutions have been specifically optimized in order to guarantee the maximum flexibility in all operative conditions. ASG has been involved in the whole design of magnetic, structural, thermal and protection systems. Magnetic configurations meeting optimized field requirements have been identified also accounting in detail the expected significant technological deviations. The two resistive coils, forming the active modulation system, principally perform the identification of the optimized magnetic configurations. Lorentz forces and coil interactions produced by the system have been calculated in order to verify mechanical structure and stresses on the coils. The protection system of the magnet in case of quench has been designed in order to minimize thermal stresses on the cold mass components. The electromagnetic interactions between components, during dynamic events, have been evaluated in order to verify the cryogenic and structural stability of the system. Manufacturing phase is ready to start. Main results will be presented to illustrate the adopted process and technological solutions.
We present the current status of design, testing and manufacturing of the magnet system of the PENeLOPE neutron lifetime measurement experiment, carried out by Babcock Noell GmbH on behalf of and in close cooperation with Technical University of Munich. Ultra cold neutrons produced by the experimental reactor facility in Garching are stored in a large volume magnetic bottle and held confined for periods of several minutes, where the combination of electric and magnetic fields allows basically all protons emerging from neutron decay to be captured by a high efficiency detector. This allows the decay curve to be captured with unprecedented accuracy. The magnetic bottle is formed by an nested array of 24 pairwise oppositely poled superconducting coils with local fields up to 5.5 T providing magnetic confinement for neutron energies up to 110 neV while maintaining an essentially field free trap volume. The coil formers made of 316LN constitute the wall between experimental vacuum and the LHe bath providing the cooling and support the force of the repelling coils. This circumstance and the intricate geometry makes manufacture particularly challenging. The coils are wound and potted on individual formers, which are then assembled to the full magnet structure. This is achieved by means of laser welding. Due to spatial constraints, the welds are as close as 6 mm to the coil windings. With the help of specialized companies we were able to produce 6 mm deep vacuum tight and load bearing structural welds without raising the temperature at the coil’s windings above 180°C, which is considered the maximum acceptable temperature for the insulation and potting resin chosen.
In this paper, we present results, experimental and analytical, of a small-model study, from which we plan to develop and apply a full-scale field-shaking system to minimize or even eliminate the screening current-induced field (SCF) in the 800-MHz HTS Insert (H800) of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) currently under construction—the H800 is composed of 3 nested coils, each a stack of no-insulation (NI) REBCO double-pancakes. In 1.3G, H800 is the chief source of a large error field generated by its own SCF. To study the effectiveness of the field-shaking technique, we use a set of 3-nested and series-connected coils (3-Coil Sample) composed of 3 NI REBCO double-pancakes, one from each of the 3 H800 coils, and place it in the bore of a 5-T/300-mm room-temperature bore external magnet (5TM). 5TM is used not only to induce SCF in the 3-Coil Sample but also eliminate it by the field-shaking. For each run, we induce SCF in the 3-Coil Sample at an axial location where the external radial field Br > 0, then for the field-shaking, move to another location where the external axial field Bz >> Br. To examine if other SCF eliminating techniques, e.g., the current-sweep-reversal (CSR) method, is applicable to H800 even when L500 and H800 are series-connected, we perform similar sequences of test for other combinations of the 3-Coil Sample axial locations. Additionally, we energize the 3-Coil Sample to study SCF dependence on transport current. In this paper, we report 77-K experimental results, develop an analysis that satisfactorily explains the results, and apply the analysis to design a field-shaking system for 1.3G at full operation.
Acknowledgment: Work supported by the National Institute of General Medical Sciences of the National Institutes of Health.
Today, researches on the all 2G HTS magnets are actively underway in the field of high magnetic fields. No-insulation coils without insulation between turn-to-turns are very stable against quenching. The characteristic resistance of the no-insulation coil depends on the turn-to-turn contact resistance, which is an important factor determining the current ramping rate. In no-insulation coils, the turn-turn contact resistance is very small and the current ramping rate is very slow. The resistance between these turn-to-turns simply depends on the contact area of one turn and the resistivity and surface conditions of the metal where contact occurs. The metal insulation coil co-wound with stainless steel tape has a higher current ramping rate than the no-insulation coil. The metal insulation coil has two contact interfaces compared to the no-insulation coil, and the resistance of the stainless steel tape is larger than that of the surface material cooper of the 2G HTS wire. So if you can control the turn-to-turn resistance in the desired HTS magnet, it will be very useful for designing HTS magnets. In this study, we conducted a study to change the contact resistance of metal-insulation coils by coating some metal material on the surface of the co-winding metal tape. The result will discuss the controllability of the contact resistance between the turn-turns of the 2G HTS coils.
Comprehensive studies of the transport and the magnetic properties of MgB2 wires were carried out at temperatures 4.2-20 K and magnetic field up to 8 T. Cryomagnetic system with MgB2 coil was designed and constructed based on the received data. Cryomagnetic system is designed to create a permanent magnetic field of up to 5 T in the warm bore of 40 mm in diameter. The operating current of the system is 100 A. The magnetic field is created by a system of three concentric solenoids. The inner coil is composed of a 10 double pancakes wound with the 2nd generation HTS tape produced by SuperOx. Middle coil is made of multifilament MgB2 wire with a diameter of 1 mm produced by Columbus Superconductors. Middle coil has height of 120 mm, an inner diameter of 80 mm and an outer diameter of 88 mm. The inner and middle coils are connected in series, what allows both sections to operate at temperature range from 4.2 K to 20 K. The external coil of background field is wound of NbTi. It is powered by a separate pair of current leads. The solenoids are cooled by cryocooler though copper bar. The present report describes the design, the manufacture and the test results of the cryomagnetic system.
High temperature superconductors (HTS) have become a viable option for high field magnets, mainly due to its superior in-field current carrying capacity at greater than 20 T. However, the price of HTS conductors is still high and impedes widespread use. Provided that the need for a defect-free “long” piecelength of HTS conductor is a primary cost driver for most applications. Results previously reported from our defect irrelevant winding (DIW) technique of a no-insulation (NI) pancake coil wound with REBCO tapes containing multiple “defects” was subjected to a temperature of 77 K. A defect is defined as a section of the tape of which the average critical current is less than 80 percent of the lengthwise average over the entire length. The DIW coil performance, such as critical current, field constant, and coil voltage, was barely discernible from that of its “healthy” counterpart. Demonstrating a potential of the DIW technique for significant cost reduction of REBCO devices that may be operated at low current and high operating temperature. This study is to further investigate the validity of the DIW technique in 4.2 K. New pancake coils were wound with REBCO tapes containing multiple defects and tested in a bath of liquid helium at 4.2 K. Key parameters of each coil were measured and compared with simulations by the use of our lumped circuit model containing critical current data of a “healthy” portion of the tape used to build the DIW coils. The DIW coils underperformed at 4.2 K, i.e., the coil critical current was measured to be 60 – 70 percent of that of its healthy counterpart.
Acknowledgement: This work was supported by the National High Magnetic Field Laboratory (which is supported by the National Science Foundation under NSF/DMR-1157490), the State of Florida, and the KBSI grant (D37611) to S.-G.L.
It is well known that critical current (Ic) of an high temperature superconductor (HTS) magnet comprising a stack of pancake coils is limited by that of "one" pancake, while the rest of the pancakes still have substantial margin to their own Ic. This unfavorable design issue is often mitigated by the so-called multi-width (MW) technique, where pancake coils wound with the narrowest tapes were placed at and near the magnet center and those with progressively wider tapes toward the top and bottom of the magnet. To date, several MW HTS magnets were fabricated and successfully generated their target fields significantly larger than those of their single-width counterparts. Currently, the SuNAM provides MW tapes grading width of 4 – 12 mm in every 1 mm. So far, critical currents of the previous MW magnets were mostly limited by the Ic of the top or bottom most pancake wound with the narrowest tape, chiefly due to the angular dependency of the tape’s Ic. Further grading of the tapes, say in every 0.5 mm, may be beneficial in terms of mitigating the tape’s angular dependency in the magnet. This paper investigates an optimal design methodology for MW HTS magnets. For a given design target of field strength and winding bore, input parameters include tape width, number of grading tapes, and number of pancakes coils for each tape, while the main objective is to minimize the magnet volume, i.e., essentially the stored energy and thus the cost. A magnet with a single-width tape is also designed as a control sample for comparison. The results are expected to be beneficial to determine the practical level of HTS tape grading and estimate a volume of an MW magnet.
This work was supported by KBSI grant (D37611) to S.-G.L funded by the Korea Basic Science Institute (KBSI).
Advances in HTS technology have the potential to enable high field magnets with fields in excess of the maximum obtainable with purely LTS magnets. HTS insert coils may be operated in the bore of a high field LTS magnet, or ‘outsert’, in order to enhance the overall central field. The HTS inserts are usually operated at the same low temperatures as the LTS coils as this allows a common cooling system to be used and because the critical current density of the HTS is significantly higher at lower temperatures. A remaining barrier to widespread commercial application of HTS insert coils in this space is adequate protection of the HTS coil during quench, where the behaviour of such coils is substantially different from that of LTS coils. Oxford instruments is in collaboration with Bruker-OST and Dresden High Magnetic Field Laboratory to design, build and test a set of HTS insert coils to be tested in the bore of the 19T 150mm LTS magnet currently in operation at Dresden. The coils are wound from B-OST Bi-2212 round wire and are of lengths up to 300mm and diameters up to 125mm. Selected coils have been instrumented for quench initiation and propagation velocity measurements and the relationships between minimum quench energy, quench propagation velocity, operating current and background field have been explored experimentally. Here we discuss the challenges in design, manufacture and test of this set of coils and present experimental results at low and high background field.
A 3 T 100 mm all-REBCO multi-width (MW) no-insulation (NI) magnet was designed constructed, and currently being tested at the Korea Basic Science Institute. Key features of the magnet include use of “metallic cladding (MC)” REBCO tapes, i.e., a 1-um thick stainless steel cladding layer hermetically surrounds the tape in order to increase the turn-to-turn contact resistanc of the NI coils. The magnet successfully reached its full field of 3 T at a designated operating current of 200 A that corresponds to an engineering current density of 353 A/mm2 for double pancake coils wound with the narrowest width tape of 4 mm. Recently, the magnet experienced unexpected power supply trips twice during its long-term field mapping experiment at the full field, after which the magnet was fully discharged in 5 seconds. This paper reports the transient behaviors of the magnet in details during the sudden discharge events. Key parameters to have been measured include: (1) terminal voltages of individual 32 double pancake coils; (2) temperatures at the magnet top, middle, and bottom; (3) power supply currents; and (4) center magnetic field. A lumped parameter circuit model was used to analyze the electromagnetic responses during the sudden discharge. The magnet survived without any damage after each trip of the power supply and is currently being operated normally without any performance degradation. The results imply the self-protecting feature of the MC REBCO magnet, which has been experimentally demonstrated in a magnet level for the first time.
This paper presents electromagnetic design and 3D finite element analysis (FEA) results to develop prototype machine system for the high-temperature superconducting (HTS) rotating machine integrated with a contactless HTS excitation device (CHED). This is connected and integrated on the same shaft of the rotating machine and charge the HTS field coils by pumping magnetic flux with non-contact method. Therefore, this can be excellent alternative to replace a contact type conventional excitation device which has thermal and mechanical instability by physically connecting cryogenic temperature environment inside HTS rotor with room temperature environment outside HTS rotor. In this paper, 1-HP-class HTS rotating machine was basically designed by analytical method to build 3D FEA model and then, the initial design model was electromagnetically analyzed using commercial 3D FEA software. The basic magnetic field distribution information on HTS rotating machine with CHED was investigated and the various output performances of HTS rotating machine in steady state operation were analyzed. Especially, the real charging data achieved by preliminary experiment with HTS coil and CHED prototype was used in 3D FEA as a input boundary condition to simulate the electromagnetic characteristics in initial charging mode of 1-HP-class HTS rotating machine.
Acknowledgement: This work was supported in part by the Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), grant funded by the Ministry of Trade, Industry & Energy, and by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP), Republic of Korea. (Nos. 20164030201230 and 2016R1A2B4007324)
As a vertical transportation apparatus for moving people and goods between floors, the elevator or lift plays an increasingly important role in the high-rise buildings. The requirements for fast velocity, comfort ability, reliability and safety issues become higher and higher. Due to its inefficiency and complicated operating system, the conventional cable elevators, which usually utilize rotational drives and hoist cables with counterweights, are no longer acceptable. By using the linear motor for propelling the elevator car, it can travel smoothly from standstill to high speed while eliminating the cables and counterweights. Hence, the efficiency, stability and reliability can be significantly improved. Linear induction motor (LIM), linear synchronous motor (LSM), and linear switched reluctance motor (LSRM)are applied for cableless elevators in recent years. For the reliability and safety concerns, LIMs and LSRMs which possess rugged and passive moving parts are favorable. The purpose of this paper is to propose a doubly-fed doubly-salient HTS linear motor (DFDS-HTSLM) for linear drives in the cableless elevator. The proposed linear motor possesses the advantages of both LSRM and LSM. It adopts a doubly-salient structure which is very similar to the LSRM. By equipping the HTS field winding for providing the field excitation, a higher thrust density can be achieved. Moreover, by adopting 5-phase armature design, the high fault-tolerance capability can be realized. With these merits, the proposed DFDS-HTSLM not only provides a high thrust density with flexible thrust control, but also can achieves higher reliability with fault-tolerant operation. By coupling the finite element method model of the proposed linear motor with the circuit simulator, the transient characteristics of the proposed motor will be performed at both the accelerating and decelerating conditions. This work is supported by a grant (Grant No. 51607114) from the National Natural Science Foundation of China.
This paper proposes an optimal control algorithm through lateral displacement and yaw angle in curved road of shallow-depth subway systems. In the case of the surface transportation, which has recently been introduced, severe curved driving performance is required for the downtown. The existing researches are the main research theme of the lateral displacement restoration control, but there is a limit to smooth operation when the curve is run only by receiving the lateral information. However, when the yaw angle information is obtained, it is possible to consider the turning angle of the vehicle while the vehicle is driving in a curved road. However, it is difficult to control because the change of yaw angle is more sensitive than lateral drift. Therefore, this paper suggests an algorithm that uses both lateral displacement control and yaw control. The proposed method will be verified with the Matlab/Simulink model and the effectiveness of the proposed method will be verified through small-scale bogie system.
This paper proposes an algorithm to obtain better results in the integrated control by reflecting the characteristics of the individual control of the front wheel and the rear wheel of shallow-depth subway systems In the case of the surface transportation, which has recently been introduced, severly curved driving performance is required for the downtown. It is possible to decrease the curve radius and to improve the performance of the straight running with the individual torque control. Therefore, the individual torque control performance of the motor is the most important point of the surface transportation. The front and rear wheels have different torque characteristics, and the length of the bogie during curve travel also affects these results. This system is more controllable than the system with 1C4M(1Controller 4Motor) in the form of 2C4M with the front and rear wheels being individually controlled, allowing more precise control because of its higher degree of freedom. Because of this individually controlled characteristic, it is possible to control more precisely in the integrated control considering the characteristics of the front wheel and the characteristics of the rear wheel. The validity and usefulness of the proposed control algorithm is verified by experimental results using a small-scale bogie system
BLDC motors and controllers are used in many industrial fields due to the decline of permanent magnet price and the lower cost semiconductor devices. The BLDC motor is easy to maintain as compared to the DC motor and has the advantage of small size, high power, low noise, etc. The BLDC motor is generally used a lot of 120degree energizing method. Also, this motor is commonly controlled by a Hall sensor, which is a relatively low-resolution position sensor, or by a sensorless control method, which is controlled without a position sensor.The hall sensor detects the magnetic field generated by the magnet inserted in the rotor of the motor and uses it as a position signal.When the hall sensor is used for control, the energizing period of the BLDC motor is determined by the position signals of the three hall sensors. These hall sensors detect the position of the rotor by attaching three hall sensors to the rotor at intervals of 120 degrees. However, there may be an error in the mounting position of the hall sensor. The incorrect energizing interval is caused by the mounting position error of the hall sensor. In this paper, the phenomenon of incorrect energizing interval due to the mounting position error of the hall sensor is analyzed. The value of this error is derived as an equation and an algorithm that compensates for the error value is studied. In addition, the maintenance of accurate energization interval is verified even though Hall sensor has the positional error. Therefore this paper provides the quantitative analysis of the error by the mounting position error of the hall sensor and the effectiveness of the algorithm which can compensate for the error.
Frozen permeability method has been widely used in separating the PM torque and reluctance torque and calculating inductance. For conventional frozen permeability method (CFPM), only the core permeability is fixed. It is suitable for the machine applying rare-earth PM materials such as NdFeB, since the material B-H curve is linear and coincide with the recoil line. However, when dealing with machines applying nonlinear PM materials, CFPM will cause obvious errors. Unlike rare-earth magnet, AlNiCo has nonlinear demagnetization curve and the recoil lines of different operate point are a set of parallel lines with different coercive force, causing the output of AlNiCo different. So when accounting for the effectiveness of AlNiCo, the recoil line should be kept as same as full load condition. Therefore, this paper proposes a synthetic FPM (SFPM) to accurately calculate torque components of machines applying nonlinear PM materials. Hybrid permanent magnet variable flux machines (HPM-VFM) applying both linear and nonlinear PMs are proposed to validate the accuracy of SFPM. For the machine analysis, nonlinear FEA at a particular load condition is carried out firstly. In each simulation block, operation points of AlNiCo are recorded and a linear PM material which passes through point (Bi, Hi) with a slope of the recoil permeability is defined. Then a FEA with this linear material is carried out. Entire machine torque calculated by SFPM is 6.36Nm, which matches well with the result calculated by the nonlinear FEA 6.52Nm with only 1.07% error. Besides, AlNiCo PM torque, NdFeB PM torque and reluctance torque calculated by SFPM is 2.46Nm, 3.90Nm and 0.23Nm respectively. The CFPM results, whose PM torque is 5.88Nm and reluctance torque is 0.23Nm has 6.29% error comparing with nonlinear FEA. More elaborate results of analysis and comparison will be exhibited in the full paper.
A transverse flux single-phase tubular switched reluctance linear motor (TF-TSRLM) is proposed in the paper, and it is compared with the longitudinal flux single-phase tubular switched reluctance linear motor (LF-TSRLM) in electromagnetic thrust. The stator consists of five ferromagnetic rings that are divided by four spacer rings. On the cross section of the TF-TSRLM, a stator ferromagnetic ring has six poles with coils winding on. The mover threads through the tubular stator rings. Different from the LF-TSRLM, the interval sleeves which break the mover tooth rings are made by non-ferromagnetic material for isolating any longitudinal flux. When the windings are excited, magnetic lines of force form closed loops through stator poles, air gap, mover tooth ring, and stator yoke. The plane where the surround magnetic flux paths exist is perpendicular to the mover movement direction. four structures with respectively 2 poles, 4 poles, 6 poles, and 8 poles on the cross section are proposed. The poles of structures with 2 poles, 4 poles, 6 poles, and 8 poles are distributed uniformly at 180°, 90°, 60°, and 45° intervals respectively. The sensitivity analyses were made on some parameters to achieve new dimensions with better thrust performance, such as different stator yoke thickness, different mover cylinder’s thickness, different stator pole width, different pole width ratio. In the analysis process, the excitation current is fixed as 15A. After the sensitivity analysis on four important parameters, the final dimensions of proposed TF-TSRLM are determined. The electromagnetic thrust curves of LF-TSRLM and TF-TSRLM with final dimensions are calculated by 3D FEM in3A, 6A, 9A, 12A and 15A respectively. It shown that the electromagnetic thrust of transverse flux single-phase tubular switched reluctance linear motor with 6 poles is greater than that of longitudinal flux single-phase tubular switched reluctance linear motor at the same excited current values.
DR-SRM is a novel structure device which can be evolved from conventional SRMs with a single stator and single rotor by increasing a rotor and changing the structure of stator and rotor. The double mechanical ports and double electrical ports are formed by increasing the number of rotor. This paper presents a model for dual rotors switched reluctance motor consisting of two airgaps, an outer-stator, a middle-rotor and an inner-rotor. This model can optimize structure geometry size parameters and polarity distribution of DR-SRM. The average torque of middle rotor in the outer airgap contributing to the main parts of energy conversion with different geometry size of stator and rotors. The sensitivity of inner-rotor pole-arc coefficient, inner-rotor yoke thickness, outer-stator pole-arc coefficient, outer-stator yoke thickness, middle-rotor inner tooth pole-arc coefficient, middle-rotor outer tooth pole-arc coefficient, and middle-rotor yoke thickness is analyzed based on the present model. The final geometry size is designed for enhancing the average torque of middle-rotor in the outer airgap considering the limitation of outer-stator outer radius and laminated thickness of motor, the configuration intensity and manufacture techniques. Comparison of torque on the dual rotors switched reluctance motor and the conventional single inner rotor switched reluctance motor is made. Three kinds of magnetic polarity distribution of outer-stator with four kinds of magnetic polarity distribution of inner-rotor are studied. NSNSNSNSNSNS magnetic polarity distribution of outer-stator with NSNSNS magnetic polarity distribution of inner-rotor is selected for enhancing the average torque of middle-rotor in the outer airgap. The comparison results of torque on the dual rotors SRM and the conventional single inner rotor SRM show that the torque on dual rotors SRM is larger than that on the conventional single inner rotor SRM since the dual rotors SRM has two sets of excitation windings.
In this paper, the flux linkage curve of the second form is analyzed. The characteristic of the flux linkage is presented in the form of a high order polynomial, which makes it easier for data-fitting. The flux linkage curve of the form ψ-θ curves for different i values is analyzed. The flux linkage data of the SRM prototype is obtained on 4 specific rotor positions (0°, 7.5°, 15°, 22.5°). The imitative effect of the flux linkage is not good enough especially when rotor positions are ranging from 0° to 7.5°. It is resulted from the following three reasons: Only 4 specific rotor positions are chosen to get the entire characteristic of the flux linkage. The highest degree of the data-fitting polynomial is three. The derivative of rotor positions ranging from 0° to 22.5° should be greater than 0 when using the least square method. It is easy to find that the error trend of different currents is same with rotor positions ranging from 0° to 7.5°. An error percentage correction coefficient can be introduced into the flux linkage curve for better accuracy when rotor positions changing from 0° to 22.5°. The flux linkage model can also be constructed through ψ(in, 0°) rapidly. ψ(in, 0°) is linear to the currents ik, so the equation for the fast flux linkage model can be obtained by draw into an coefficient matrix when the current is ik. The torque of the origin model, modified model, and fast model can be calculated by this method. Then make comparison with FEM calculated result to verifies the correctness of the modified model and fast model. The experimental verification is carried out based on the prototype. The results show that the simulation waveforms are consistent with the experimental waveforms, which verifies the accuracy of the model.
Currently, the tubular linear permanent-magnet machine has been increasingly adopted for active vehicle suspension, since it has zero net radial force between the armature and stator, no end-windings, and volumetrically efficient. However, it suffers from relatively low thrust force and poor fault-tolerant capability. Thus, a novel modular-stator tubular vernier permanent-magnet machine will be proposed in this paper, which not only improve the force performance, but also significantly enhance the fault-tolerant capability. Both magnets and armature windings are on the stator, while the mover is only consisting of iron with salient teeth which work as modulation teeth. Meanwhile, the modular complementary stator structure is designed to decoupling the adjacent phase windings, hence offering the desired fault-tolerant capability. Moreover, The PMs with two magnetized directions are adopted, namely radially and axially. One is used to produce the main flux, while another can reduce fringing leakage flux, hence increasing the thrust force capability. The electromagnetic performances of the proposed machine is analyzed by using the finite-element method. Thus, it can be known that the back electromotive force of the proposed machine is symmetrical and sinusoidal due to its complementary permanent magnet magnetic circuits. Moreover, the ratio of the mutual inductance to self-inductance of the proposed machine is only 0.90%, revealing that the proposed machine possesses the desired fault-tolerant capability. The average thrust is 720 N when the electric load is 183A/cm, while the thrust ripple of the proposed machine is 8%. Detailed results and discussions will be given in full paper.
Electrical aircraft are an important area of modern engineering development to meet the increasing air travel demand while managing a reduction of dependence on fossil fuels. The challenge is exacerbated due to the high sensitivity of aircraft performance with respect to mass and therefore superconducting machines are seen as a possible solution. A key enabler is to reduce the overall size of the system including cooling to lower the mass. Key importance to adoption of superconducting motors is the A.C. loss phenomena which increases the cooling power required to operate HTS systems. In the past several demonstration machines have not measured the in-situ A.C. loss or tested new loss reduction technologies [1]. In order to progress the field motor performance as a function of the A.C. loss needs to be understood as well as being able to test A.C. loss reduction techniques resulting from simulation and manufacturing advancements. Therefore, in this paper a novel machine design is presented to enable the measurement of A.C. loss within a machine environment to be built and tested this year and an accurate estimation of the airborne cooling power required is detailed. The novelty of this machine is the enablement of quick and accurate A.C loss measurement of a wide range of superconducting technology including MgB2, Roebel cables and pancake coils Along with the new design preliminary simulation and experimental results are outlined which are used to calculated anticipated A.C. loss cooling power required aboard an aircraft using real load demand data supplied by Airbus.
[1] Ainslie, Mark, Mitsuru Izumi, and Motohiro Miki. "Recent advances in superconducting rotating machines: an introduction to the ‘Focus on Superconducting Rotating Machines’." Superconductor Science and Technology 29.6 (2016): 60303-60305.
In various industries, ultra-high speed motor is actively studied and developed for diverse industrial applications like generators/starters for micro gas turbines, turbo-compressor, vacuum pump and turbine generator. Electric Turbo Compounding System (E-TCS), which operates with motor/generator unit at a very-high speed, is the most realistic alternative technology that can respond to fuel efficiency regulation by applying an electrical system to the existing turbocharger. In the low-speed region where the exhaust gas energy in the turbocharger is insufficient, the motor assists the compressor to improve the dynamic characteristics and output of engine, whereas in the high-speed region where the energy of the exhaust gas remains, it operates as a generator and produces electrical energy with excess exhaust gas energy and improves system energy efficiency. This paper presents the design of an ultra-high speed PM motor driven by 10kW at the rated speed 70,000 rpm and the maximum speed 100,000 rpm for applying E-TCS. In this paper, Response Surface Method (RSM) and Finite Element Method (FEM) are used to perform the optimal design of PM motor. For operating at the ultra-high speed, the design of PM motor should be considered the mechanical and structural safety of rotor and losses for the high efficiency. Therefore, the objective function of RSM are the secureness of mechanical and structural safety of rotor and the minimum of losses, occur at the rotor and sleeve. Furthermore, this paper presents the design of the sleeve according to the materials. As the results, the optimal design method of PM motor, using carbon fiber is proposed to not only reduce the eddy-current loss, prominently occur at very-high speed, but also ensure the structural safety. Finally, experiment is performed to verify the validity of the proposed design method and effectiveness of the PM motor, fabricated as a prototype.
Switched reluctance machines are widely used in variety application in automotive, renewable energy, aerospace and domestic appliances sectors, due to its low cost, high torque capacity, simple and robust structure. In order to improve the reliability of SRM further, a dual-channel SRM (DCSRM) was proposed and their fault tolerant capacity was verified. However, the traditional topology of inverter is used, resulting in complicate construction. Meanwhile, the mutually coupled SRM (MCSRM) can be excited by sine-wave currents, and then the standard inverter can be adopted. Hence, this paper proposes a novel DCSRM using two 3-phase standard inverters. The key of proposed DCSRM is two operational models. In first operational model (Model I), it works like one 3-phase traditional SRM supplied by H-bridge inverter, which is drove by square-wave currents. In second operational model (Model II), it can be considered as two MCSRMs which are supplied by sine-wave currents. Model I is adopted for switching fault because the H-bridge inverter is adopt, which can keep the amplitude of the current under power switch fault and just change the direction of the current. Since the reluctance torque is not related with direction but amplitude of the current, the torque output will not reduce when power switch fault happens. Meanwhile, the Model II is employed for phase open-circuit fault. In sinusoids current supply model, when a phase is open, the currents of other two phases in fault channel are forced to be opposite. Then the neutral current is set to be zero. Since only two phases can work, the second and fourth order torque ripple cannot be neglected. In order to compensate the torque loss and torque ripple, the amplitudes of currents in healthy channel are set as a variable. Then, the proposed motor can be used to overcome different fault conditions.
As demand for motors that are capable of high-torque direct drive operation is increasing, Vernier motor is gaining its importance. Vernier motor is a type of permanent magnet (PM) motor, which is specialized for low speed and high torque operation applications. Unlike conventional PM synchronous motor (PMSM), which generates torque mainly from fundamental flux component, Vernier motor utilizes magnetic flux harmonics to develop additional torque component with harmonic flux component. Moreover, the Vernier motor is also a flux modulation machine, which has operation characteristic analogous to that of the magnetic gear. The magnetic gear ratio of Vernier motor is determined by ratio of the stator winding pole pair number and the rotor pole pair number, which has effect on torque produced by the Vernier motor. For these characteristics, the Vernier motor is regarded as one of possible candidates for future motor applications. However, it is necessary that PM used in the Vernier motor does not suffer from irreversible demagnetization, as it has negative effect on the output performance of the motor. Therefore, it is requisite that analysis on the Vernier motor considering irreversible demagnetization of the PM is carried out, to examine how the motor output performance is influenced. Furthermore, design optimization considering design parameters should be carried out to prevent irreversible demagnetization on the PM, to guarantee performance of the motor. In this paper, the Vernier motor is analyzed under several operation conditions to observe how the motor output performance is affected by irreversible demagnetization of PM. Then, the Vernier motor is redesigned regarding certain design parameters to enhance irreversible demagnetization of PM. Finally, the output performance characteristic of enhanced Vernier motor is compared to that of the base motor.
INTRODUCTION: Following to the recently emerging environmental regulations and energy depletion, HEV and EV draw attention as future cars. And there are many studies carried out for traction motor design. This study is about a design algorithm which can make wound field synchronous motor design easier and faster. Because main flux path is sensitive to magnetic saturation and heat problem is caused in a rotor by copper loss, basic design considering that problems is necessary especially in case of high torque density application. Non-linear magnetic equivalent circuit is constrcted to calculate non-linear design parameters of motor exactly and a thermal euivalent circuit is also made to select accurately current density. This paper proposes the basic design algorithm based on the non-linear magnetic and thermal equivalent circuits and accuracy of equivalent circuits is verified by a comparison with FE analysis. A basic design of 140kW-class wound field synchronous motor is done with the proposed basic design algorithm. And a test results of final model design will be added in the full paper.
Surface permanent-magnet (SPM) machines with a fractional-slot concentrated winding (FSCW) present several advantages, such as high copper packing factor, short end-winding length, low cogging torque, small volume and good fault-tolerant capability, because of which SPM machines have been increasingly applied in aerospace applications. However, the key challenge of utilizing FSCW is abundant magneto-motive force (MMF) harmonics. These MMF harmonics result in high rotor eddy-current loss, acoustic noise and vibrations. In this paper, an analytical equation is derived to present the relationship between MMF harmonics and phase numbers. Finally, a 24-slot and 22-poles SPM FCSW machine is designed, adopting three, six and twenty-phase for validation, respectively. The slot-pole combination of 24-slot and 22-pole is selected. And the FCSW is adopted to improve copper utilization rate and reduce copper loss. In order to maximize torque density, the SPM rotor topology is employed and entire stator structure has been optimally designed. Besides, the machine adopts three, six and twelve phase, which is able to cancel some MMF harmonics with increased phase number. At the same time, the shape, size and pole-arc coefficient have been optimally designed to obtain better electromagnetic performance. Analytical method is adopted to derive the relationship between MMF harmonics and phase number. And finite-element analysis is employed to verify the electromagnetic performance of the designed SPM machine. The 1th, 5th and 7th harmonics are sub-harmonic, while 13th, 35th and 37th are the main slot harmonics. By using the multi-phase winding, the sub-harmonics are completely almost eliminated compared with those of three-phase winding. Also, the greatly decrease of the MMF harmonics, contributes to significantly reduce the PMs eddy-current loss. Besides, the unbalance magnetic force of nine-phase winding is smaller than that of three-phase winding due to the absence of sub-harmonics.
The dual-stator switched reluctance motor (SRM) is based on the traditional SRM and increases one electrical port with two stators and a rotor. The outer-stator adopts salient pole structure of 12 poles, the inner-stator adopts 6 poles, the middle-rotor is doubly salient with 8 poles. The outer-stator and inner-stator have concentrated windings. That is to say, the outer motor is three-phase 12/8 structure machine, and the inner motor is three-phase 6/8 structure machine. Different inner-stator pole-arc, coefficient, different outer-stator pole-arc coefficient, different rotor teeth pole-arc coefficient, different rotor yoke thickness, different outer-stator yoke thickness, different inner-stator yoke thickness are analyzed for enhancing the average electromagnetic torque. The rotor teeth and the inner-stator pole-arc width are equal in order to avoid that the rotor inner teeth pole-arc width effects the inner stator pole-arc coefficient. The rotor of dual-stator SRM has no windings, the each teeth of the stator has a central coil, and diametrically opposed two coils are connected in series. According to the series in different ways, it can be divided into positive and negative distribution. When the stator windings are energized in one direction, the stator teeth have a pair of NS poles and two pairs of NN poles, and the layouts of windings are different too. According to its positive and negative distribution and different layouts, the motor windings have 12 kinds of layouts. First, when the outer-stator winding layout is NNNNNNNNNNNN, the stator windings can be SSSSSS, SSSNNN, SNSNSN and NNNNNN, four kinds. When the outer-stator winding layout is NNNNNNSSSSSS, the stator windings have SSSSSS, SSSNNN, SNSNSN and NNNNNN, four kinds of distributions. When the outer stator winding layout is NSNSNSNSNSNS, the stator windings have SSSSSS, SSSNNN, SNSNSN and NNNNNN, four kinds of layouts. The NSNSNSNSNSNS with SNSNSN is selected for enhancing the torque by FEM calculation.
In this research, we designed Interior Permanent Magnet Synchronous Motor (IPMSM) type traction motor for 130kW Electrical Vehicle (EV). In addition, we analyzed its electromagnetic characteristics related to Permanent Magnet (PM) such as eddy current loss of PM, demagnetization, electromagnetic force especially radial magnetic force, and performed the noise analysis using the noise map in accordance with input control method, both SVPWM and six-step control under high speed and flux-weakening region. IPMSM has broad applications in domestic, automotive and marine field, and motor vehicle electrical system due to its high efficiency, power density and environmental issues. In the case of IPMSM, a voltage saturation problem is a major drawback in the high-speed region (over base speed) due to a back-electromotive force and the limited inverter voltage. The EV traction motor system requires various operating points and wide driving speed region to substitute role of the planet gear system. To satisfy its performance specification, the flux-weakening control is inevitable for IPMSM, generally. In terms of the flux-weakening control, the magnetic flux cannot be directly controlled because it occurs from PMs. Therefore, the stator current of d-axis, which is the direction of magnetic flux, must flow to generate magnetic flux in the direction opposite to the one of the PM to reduce the effective magnetic flux magnitude of the air-gap. It allows IPMSM to operate wide operating region under the limited input voltage condition. In the flux-weakening region, however, high speed and the magnetic flux from d-axis current bring about more harmonic components in air-gap flux density, ideally regarded as sinusoidal wave. We analyzed these harmonic components effect on PM eddy current loss, demagnetization, and radial force which leads to noise and vibration depending on the input control method by the coupled analysis of finite element analysis, FFT, and Simulink.
Permanent magnet (PM), such as NdFeB, in the interior permanent magnet synchronous motor (IPMSM) used to be irreversibly demagnetized when the motor operate at high temperature. Therefore, the motor is designed considering irreversible demagnetization of PM. However, it is difficult to optimize motor design because we can’t forecast the exact temperature of PM when the motor operate. In addition, it is difficult to measure the temperature of PM using thermocouple because of rotating the rotor. So, this paper proposes the method which it estimates the temperature of PM using reduction of d-axis current to know irreversible demagnetization of the PM. The estimated the temperature of PM is first obtained using experiment and then it is compared with the simulation data, such as d-axis current and torque, to verify the correlation between simulation and experimental results design.
This paper analyzed the flux characteristics of a single-phase tubular switched reluctance linear motor (TSRLM) based on magnetic equivalent circuit (MEC) method. The stator is composed of a stator sleeve and a bread type winding. There are two teeth on the stator. The bread type winding is embedded in the slot of the stator, which can improve the coil factor and decrease the end effect. The mover is mainly composed of the mover teeth rings and the mover yoke sleeve. Three mover teeth rings are uniformly distributed on the mover yoke sleeve. The single-phase TSRLM is divided into five different parts, which are the teeth of the stator, the yoke of the stator, air gap, the teeth of the rotor, and the yoke of the rotor. The reluctance of every part is expressed in analytical formulas at five special mover positions. The flux linkages at five special mover positions are calculated by magnet tube method and Gauss-Seidel iteration method which takes the saturation into consideration. It gives the analytical expressions of reluctances of each part in the single-phase TSRLM. Therefore, the flux linkage at certain mover position and certain current can be calculated with MEC method. A high order Fourier series is used to map the nonlinear relationship between flux linkage, current and mover position with the flux linkage data calculated by MEC method. The calculated flux linkage is consistent with 3D finite element method (FEM) and experimental results. Three specific currents are chosen to compare the generated static thrust, which are 2A, 4A, and 6A. The dynamic and static performance of the simulation utilized with MEC method are consistent with those in experiments, which verifies the accuracy of the MEC method proposed in this paper. The proposed MEC method can obtain the flux linkage data quickly under acceptable accuracy.
Linear induction motors (LIMs) have been widely applied in urban transit systems, such as in metros and low-speed magnetically levitated train. Due to the inherent eddy-current loss on the secondary reaction plate, the LIM applied in urban rail transit suffers from poor power factor and efficiency. And the efficiency of the current linear synchronous motors in urban rail transit is also unsatisfactory. A high efficiency permanent magnet linear synchronous motor (PM-LSM) is proposed in this paper. This single side PM-LSM adopts coreless long stator with single turn single layer wave winding which is segmented, and the secondary is a PM array fixed under the train. As a result of the tiny stator inductance, the PM-LSM’s power factor is very high. In order to maximize the thrust in the direction of the motion of the train and get the maximum output power at some a speed, one pole of the secondary is consisted of four PMs and furthermore the magnetization direction of two adjacent PMs is 45 degrees to get an appropriate magnetic circuit. Through selecting the appropriate length of the stator segment to diminish the copper loss. Considering the facts and high efficiency, we selected the proper current amplitude of the coils, speed of the train, the length of the stator segment and number of the PM-LSMs installed on a train to build a finite element model and carry out simulation and optimization. The simulation results show that the power factor of the proposed machine can reach 0.98 and its efficiency runs up to 92%. More elaborate results of analysis and comparison will be exhibited in the full paper.
Variable Flux Memory Motor(VFMM) is able to vary its magnetic field intensity of the permanent magnet(PM). Thus, VFMM has advantage for high speed operation with higher efficiency, when field intensity of PM is reduced. However, shape of the motor and arrangement of PM are important factors within restricted geometry of VFMM, because large d-axis current pulse is requisite to achieve high demagnetization and remagnetization ratio of PM. Moreover, the variable magnetized PM(VMPM) with low coercive force(Hc) is selected in general, for smooth remagnetization and demagnetization. For this reason, undesired demagnetization occurs on PM in load condition, since the magnetic field generated by stator reduces the magnetic field at rear edge of PM, which leads to output performance reduction of VFMM. Thus, it is necessary to design motor considering easily demagnetized part of the PM. This paper proposes a novel design method of surface mounted PM(SPM) type hybrid VFMM(HVFMM). The rotor pole of proposed structure is composed of two different PM materials in each pole. The rotor PM placed in front of the rotational direction is ferrite VMPM, which is selected to vary main flux field by varying its magnetic field intensity. The PM placed at rear of the rotational direction is constant magnetized PM(CMPM), which uses NdFeB, to produce the main flux of the rotor. The arrangement of these PMs is determined to prevent demagnetization of the PM in load condition, and to take advantage of the combined PM pole, which are increase in thrust of the magnetic system and torque density of the motor. To verify the validity of the proposed structure, nonlinear 2-dimentional finite element method and magnetic equivalent circuit are adopted to analyze operation characteristics of VFMM. Finally, we propose novel design configuration and parameters of SPM type HVFMM for 30kW traction motor.
A coaxial magnetic gear (CMG) is a non-contact machine that is used to transfer torque and to accelerate or decelerate. This type of gear has several advantages, including no mechanical loss, no required maintenance, and outstanding protection against overload [1]. As a result, they are used in various applications, such as wind power generation and electric vehicles. However, CMGs have high transfer torque ripples due to the difference in the magnetic resistance between the two rotors and the pole piece, and the torque ripple of the inner rotor is higher than that of the outer rotor. These torque ripples must be minimized during the design process because they cause vibration and noise. Therefore, in this paper, a new pole piece form is proposed that reduces the transfer torque ripples in the CMG. The response surface method (RSM) was used to investigate the relationship between the design variables used for the proposed pole piece and the response variables, such as the transfer torque and the transfer torque ripples. The Box-Behnken design (BBD) was used to establish the experimental plans, and a 2-D numerical analysis based finite element method (FEM) was used to determine the response variables. In addition, an analysis of variance (ANOVA) and regression analysis of the design variables and response variables were used to estimate the response surface equation of the response variables to the design variables, and to determine the optimum design variables for the proposed pole piece. Detailed contents in the topology optimization procedure will be presented in full paper.
This study focused on efficiency improvement of BLDC motors via reduction of torque ripple, core loss, and permanent magnet loss. To achieve this objective, we proposed an improved 150° commutation method for three-phase permanent magnet brushless DC (BLDC) motors to improve the current waveform. Although the 120° commutation method is generally employed for a BLDC motor, the 150° commutation method is introduced in order to operate the BLDC with the same efficiency as a brushless AC (BLAC) motor. Moreover, an improved 150° commutation is proposed to reduce the phase current harmonics. The study investigates the attributes of different commutation methods analytically and experimentally in order to determine the optimal commutation method. The result of this study indicates that the improved 150° commutation method is optimum in terms of harmonic attributes, and reduced torque ripple, thereby improving the motor’s efficiency.
Recently, As environmental problems such as global warming have appeared, MPES (Minimum Energy Performance standard) that regulates the efficiency of industrial induction motor is being implemented centered on developed countries. MPES limits the use of induction motors less than a certain efficiency to improve the energy efficiency. There are cases where the use of induction motors below IE4 level is restricted. Unfortunately, the research to improve the efficiency of induction motors have reached saturation point. As an alternative, the research of SynRM was activated. the SynRM has a merit of economical advantage compared to an induction machine because it does not use a permanent magnet, and it also has a merit in durability with a simple structure. the opearating principle is that using reluctance torque generated by the difference between d-axis and q-axis inductance. Generally, the d-axis,q-axis inductance was directly connected in the output of the SynRM. Generally, output density of SynRM is proportional to the number of layers. However, if the number of layers is increased, the mechanical strength becomes weak, so high-speed rotation becomes impossible. In this paper, we propose a design method of 3D printing manufacturing method and SynRM designing method. First we have designed many layers for SynRM that has maximum output density but also has minimum mechanical strength. To compensate for the mechanical strength, 3D printing structure is placed inside the layer. In the case that made only using iron core, it is impossible to drive cause by mechanical stress. but the 3D printing structure is placed inside the core, it is confirmed that the 3D printing structure is dispersed in the stress concentrated on the iron core. To prove this design technique, the motor is manufactured and tested. As a result, the validity of the design method was verified.
Electrification of urban transportation systems has been considered as the most promising solution for reducing the air pollution, the oil dependence and improving the energy efficiency. Therefore, it becomes more and more popular around the world. The fundamental components in these systems are electric motors which provide the propulsion force. Practically, the electric propulsion by linear motors is characterized by rapid acceleration / deceleration, negotiate steep gradients, immune to be bad weather and reduced maintenance cost. Thus, this technology attracts more and more attention recently. The purpose of this paper is to propose a new linear variable reluctance motor (LVRM) for the electric propulsion in urban transportation systems. The new LVRM will be equipped with both armature and field windings for a doubly excitation. Thus, the so-called excitation penalty existing in traditional VRMs can be alleviated. Furthermore, by introducing an additional superconducting DC field winding used for excitation, the air-gap flux can then be flexibly controlled hence extending the constant-power range, and improving efficiency. The stator (rail) is simply composed of iron core without windings nor PMs. This contributes to a very low inertia and low cost system, robustness and suitable for high speed operation. Since each phase of the proposed machine is magnetically decoupled from each other, it is easy to design a 5-phase machine based on the proposed machine topology. Within the mover (car), each phase is separated with a certain electrical degree. While inside the stator (rail), successive toothed-pole structure is adopted which is similar to other doubly-salient linear machines. The detailed design, analysis and verification will be presented in the full paper.
This work was supported by a grant (Project No. MYRG2015-00218-FST) from Research Council of the University of Macau, and a grant (Grant No. 51607114) from the National Natural Science Foundation of China, China.
Based on the Meissner effect a superconducting hollow sphere rotor is levitated in the vacuum housing. During the high speed rotation, the dynamic deformations caused by the centrifugal force and the temperature variation will generate magnetic disturbing torque on the superconducting rotor. The deformations of the rotor are analyzed and simulated by finite element method, and the deformation laws are obtained. According to the results, an analytical model is presented to calculate the magnetic suspension disturbing torque due to the dynamic deformations. A case study is given to discuss the disturbing torque and the drift error. It has significant theoretical value for the design and optimization of the rotor structure.
Due to the significant penetration of wind generation, the fast capacity resources are needed to handle the fluctuations caused by the wind generation. Battery Energy Storage Systems (BESSs) could be the solution as resources to back up the unpredictable fluctuation caused by the wind generation. However, the life cycle of batteries deployed in balancing operations could be a lot shorter compared to other capacity resources, caused by frequent charging and discharging operations. The alternative could be a superconducting flywheel storage system (SFES) with virtually unlimited cycle life and a high ramping rate, being able to come up with the fluctuations caused by the wind generation. The capacity of the SFES is relatively limited whereas BESS does not have such problems. The SFES can be synergistically used in combination with BESS to deal with the fluctuations caused by the wind generation. In this paper, a mixed integer linear programming (MILP)-based SFES capacity allocation method for fluctuation compensation in wind farm is proposed. The fluctuation of wind generator is divided into high and low frequency component by lowpass filter to be allocated to SFES and BESS.
The hybrid magnetic bearing (HMB) is an electromagnetic device which supports the rotor without mechanical contact by using the attractive electromagnetic force and permanent magnet force. Compared with the conventional bearings, the HMB possesses several advantages such as no friction, no lubrication and sealing, high speed, high precision, long service life. Thus, the HMB has a broad prospect of application in the modern rotating machinery, including high-speed machine tool spindle, nuclear energy, flywheel energy storage system, and so on. As the most key part of the HMB system, the controller not only determines the rotor levitation performance, but also directly affects the key indexes of the HMB such as the turning precision of the rotor and bearing capacity. Thus, the design of the controller is particularly important in the design of the HMB system. Active disturbance rejection control (ADRC) is not dependent on the accurate mathematical model of the controlled object, and has characteristics such as high precision, low overshoot, fast convergence speed, and etc. To realize the high precision nonlinear decoupling control of the HMB, a linear/nonlinear active disturbance rejection switching control (SADRC) is proposed in this paper. Firstly, the basic structure of the HMB is introduced in detail, and the mathematical model of the suspension forces is developed by utilizing the equivalent magnetic circuit method. Secondly, a control strategy based on the SADRC is proposed. Then, the PID and SADRC model are designed and compared, and the simulation results show that the decoupling effect of the SADRC is better than that of the PID control. Finally, an experimental setup of HMB is built, and the feasibility and effectiveness of the proposed decoupling control strategy is validated with the results of the experiments.
Bearingless motors (BMs) with built-in magnetic bearings are receiving more and more attention. Compared with other types of BMs, the bearingless synchronous reluctance motor (BSRM) has been extensively investigated due to its advantages of simple structure, low cost, low temperature rising and high speed drive. The BSRM is a typical nonlinear multivariable system. There is a strong magnetic coupling among the electromagnetic torque and the radial suspension forces in the x- and y-direction. Therefore, the dynamic decoupling control is of particular importance to realize stable operation of the BSRM. The differential geometry method shows superiority in solving the problem of global linearization and decoupling control. In this paper, a new state feedback linearization method based on differential geometry theory is proposed to realize the decoupling control of the BSRM. Firstly, the mechanical structure and operation principle of the BSRM are analyzed, based on which the mathematical model is established. Secondly, the equation of state is established. The original nonlinear system is transformed to an equivalent affine nonlinear system. By using differential geometry theory and coordinate transformation, the state feedback control law is derived and this affine nonlinear system is transformed to three decoupled pseudo-linear subsystems, and then the closed-loop controllers are designed by using the single-input-single-output linear system theory. Thirdly, the simulation platform based on MATLAB/SIMULINK is developed. The simulation results show that the presented control algorithm based on the differential geometry theory can realize precise linearization of the original nonlinear system, and that the variables of motor speed, radial displacements in the x- and y-direction are decoupled effectively. Finally, the experimental platform of digital control system is established and experiments are performed. The corresponding experimental results show that the presented control algorithm realizes the stable suspension and rotation of rotor with satisfied dynamic and static performances.
For the superconducting magnetic bearings (SMB) employed with stacked high-temperature superconducting (HTS) tapes, rotational or linear, its static and dynamic performance are essential for engineering application. Up to now, most works reported on the HTS tapes of SMB were focused on experimentally or numerically studies on levitation and guidance forces under quasi-static conditions. However, the dynamics of SMB has not been investigated primarily. In this work, a linear magnetic bearing composed of a stacked HTS tapes and a permanent magnetic guideway was built up for maglev application and its response on pulsed excitation was investigated. Three identical stacked HTS tapes with each 120 layers were used to form an assembly-sample which was exposed to the magnetic field produced by permanent magnet guideway of Halbach array. A force imposed on the sample was excited by a hammer with replaceable head. The laser displacement sensor (LK-G80) and uniaxial piezoelectric acceleration sensor (4507-B-004) were used to measure the response of sample at different field-cooling heights and amplitudes of impulse, the decay curves of displacement and velocity were obtained. Additionally, the resonant frequency of the levitation system was determined by spectrum analysis. Definitely, this work is of great value for better understanding the dynamics of SMB and promote its application.
For the virtues of no friction and abrasion, high-speed and high-precision, long life, and etc., bearingless motors have wide application prospects in high-purity and high-speed areas. Meanwhile, multi-phase motors are superior over three-phase motors for their higher torque density and lower torque ripple. For a five-phase motor, the torque density can be further increased when the third-order harmonic current is injected. However, the rotor MMF produced by square-shape surface-mounted permanent magnets (SMPMs) contains abundant harmonic resulting in large torque ripple. Although the torque ripple can be decreased by optimizing the SMPMs into sine-shape, it has adverse effect on output torque. To balance the contradiction mentioned above, a five-phase 10-slot/8-pole bearingless PMSM (10/8 BPMSM) with PMs shaping is proposed in this paper. The mathematical model of stator MMF is established in detail based on the winding function method. By optimizing the SMPMs into the saddle-shape, the rotor MMF mainly contains the fundamental and third-order harmonic. The optimal ratio of the third-order harmonic of saddle-shape PMs is deduced and verified by finite element analysis (FEA) to obtain the maximum average torque. In addition, the variable edge thickness of PMs is analyzed to compensate the inter-pole flux leakage. Accordingly, the production principle of suspension forces is elaborated based on the harmonics interaction between stator and rotor MMFs. The SMPMs in sine-shape and square-shape are designed respectively for comparison. The simulation results show that the average torque and suspension force increase about 13% and 6% when PMs are saddle-shape compared with the one with sine-shape, while the torque and suspension force ripple decrease about 16.1% and 6.7% compared with the one with square-shape, respectively. Finally, the motor with saddle-shape SMPMs are prototyped and experimented to validate the analysis.
For the development of CC-tapes based bearings and transportation systems it is important to have not only information on the levitation force, but also the data on stability of the system in response to the lateral displacements. This work continues series of studies on the levitation properties of CC-tapes stacks and primarily focuses on the guidance force. In our report, we present new results on investigation of both levitation and guidance forces of CC-tapes stacks subjected to different lateral displacements above a permanent magnet. In the measurements we used 12 mm wide commercially available CC-tape manufactured by SuperOx. The tape were cut into pieces 12 mm x 12 mm. The number of layers in the stack ranged from 5 to 200. For stacks magnetization we used 8 T superconducting magnet. The experimental investigations on the influence of lateral displacement on the levitation performance of stack of various thicknesses with different various fluxes were processed in this work. In addition, effect of measurement height and maximum lateral displacement distance on the guidance force was studied. Results show that both trapped flux and stack height have much influence on the guidance force. The increase of trapped magnetic flux leads to a larger lateral restoring force. Hysteresis of the restoring force of the stack was observed. The hysteresis increases with decreasing of measurement height. Smaller lateral displacement may lead to the elastic lateral motion of the stack. The influence of lateral displacement distance on the relaxation of both levitation and guidance forces were studied. The rate of change of levitation force and guidance force was different for different maximum lateral displacements. The experimental results were compared with the results of calculations performed using COMSOL Multiphisics. The analyses and conclusions of this work are useful for the practical application in magnetic-force-based systems.
The high temperature superconducting (HTS) bulk in cryostats is an important part of HTS maglev systems. For the potential application to evacuated tube transportation, it is necessary to recognize the levitation and guidance performance of the bulk under a low-pressure condition. Based on a home-made pressure-reducing platform, we have studied the levitation performance of two kinds of bulks (YBCO and GdBCO) above a Halbach permanent magnet guideway (PMG) under different pressure conditions. Measurements of the levitation force versus vertical motion and the force relaxation were performed in the cases of field-cooling (FC) and zero-field-cooling (ZFC), and measurements of the guidance force versus horizontal motion at a levitation height of 12 mm were performed in the FC case. The experimental results show that the reduced air pressure can significantly improve the levitation force, the force relaxation and the guidance force due to the increasing critical current of HTS bulks in the low-pressure environment, and this phenomenon is universal in the two kinds of bulks. The levitation force of YBCO, GdBCO can increase up to 10.1% and 10.7% in FC, 20.9% and 19.1% in ZFC at 0.2 atm compared with the atmospheric pressure, respectively. The guidance force in FC can increase up to 13.8% and 9.7%, respectively. Moreover, we have found a phenomenon that the same sized YBCO can get the similar levitation performance as GdBCO at low pressure with the same applied guideway. The results further prove the superiority of our work with the combination of HTS Maglev and evacuated tube.
In the traditional magnetic bearings, displacement sensors are used to estimate position of rotors, which increase size and cost of magnetic bearings, and decrease its dynamic performance. The soft sensing technology can not only solve the problems above, but also eliminate the mutual coupling of motion equations, which makes the design of controller easier. As a result, soft sensing technology for high speed and high precision occasion arouses wide public attention. Currently, a variety of soft sensing methods have been proposed, however, there are still some problems need to be solved, such as complexity of structure, strict requirements for controllers, excessive reliance on precise mathematical model, and so on. Thus, a soft sensing modeling based on continuous hidden Markov model (CHMM) is proposed in this paper. It has no additional signal input and signal processing circuits. Furthermore, it has higher prediction accuracy and shorter computing time than other machine learning soft sensing methods. Firstly, the structure and operation principle of a 3-degree-of-freedom hybrid magnetic bearing (3-DOF-HMB) are described, and the nonlinear mathematical model of the 3-DOF-HMB in large air-gap is derived by using equivalent magnetic circuit method. Secondly, combining the well prediction ability of CHMM, a position prediction model is built by collecting representative current-displacement data, meanwhile, basic Baum-Welch parameters revaluation formula is improved to optimize parameters of the CHMM prediction model. Then, a soft sensing credibility evaluation index is proposed for real-time monitoring. Finally, mean squared error (MSE) is taken as model evaluation index to compare the predictive ability of proposed CHMM and other soft sensing methods. The simulation results show that the MSE value of the CHMM prediction model is obviously smaller than that of other soft sensing models. The effectiveness of the proposed soft sensing method based on CHMM is verified by experiments.
Superconducting magnetic energy storage (SMES) enables to offer many technical advantages, such as high energy efficiency, quick response and great controllability, and the SMES applications in distributed renewable energy sources are critical for power systems. This paper suggests a SMES to enhance the transient performance of a 100 kW grid-connected photovoltaic (PV) generation system, and conducts the conceptual design and performance evaluation. Considering the PV fluctuation and transient compensation during a fault, the stored energy of the SMES is designed as 80 kJ, and the Yttrium Barium Copper Oxide (YBCO) tapes made by the Superpower Company are adopted. The high-temperature superconducting (HTS) magnet uses the single-solenoid structure, and its detailed parameters including critical current, tape length, parallel/perpendicular magnetic field are optimized by the genetic algorithm. In order to achieve a comprehensive performance evaluation, not only the effects of the SMES on the PV generation system, but also the magnetic field, mechanical stress and operation loss of the SMES are assessed in the simulations. From the results, using the SMES can effectively improve the fault ride-through (FRT) capability and smooth the power fluctuation of the PV generation system. During the transient process of the power exchange, the maximum stress of the SMES magnet is within the tolerable allowance, and the mechanical strength of the YBCO tapes can be well ensured. Moreover, the operation loss of the SMES magnet is controlled to an acceptable level, and the joule heat caused by the charging and discharging of the SMES is limitable. The demonstrated design and evaluation will lay a good foundation for the prototype manufacture and experimental testing in the future.
High temperature superconducting magnetic energy storage (HTS SMES) is expected to be utilized in power grid for dynamic power compensation with low losses and high energy storage density during steady-state operation. Under transient operating conditions, especially in the case of fast power switching process, AC losses of the SMES will occur and lead to changes in equivalent resistance, total inductance, and critical current distribution throughout the magnet. In this paper, the dynamic performance of a 150kJ SMES has been analyzed based on a co-simulation model of MATLAB and COMSOL. The SMES element is a customized module by self-code S-Function in MATLAB. A magneto-thermal finite element model based on the PDE and Heat Transfer Modules of COMSOL is built in the module. Thus, the operating states of the SMES such as the distribution of the AC losses, magnetic flux density, critical current, maximum temperature increment, and the fluctuation of inductance and equivalent resistance have been comprehensively monitored in the power switching process.
Since MgB2 wires have been developed and commercially available, large scale cable assembled with MgB2 strands is required for fabricating Superconducting Magnetic Energy Storage (SMES) devices. To form the MgB2 superconducting material, heat treatment procedure is needed forming intermetallic compounds like Nb3Sn. In general, magnets using those types of materials are constructed in simple processes, where the magnets are wound before heat treatment, namely “Wind and React (W&R)” method, and the heat treatment process is performed before coil fabrication, called “React and Wind (R&W)” method. The W&R process simplified initial development. The R&W process has several important advantages, such as reasonable heat treatment reactor size, simple insulation, compatibility with existing coil winding and SMES manufacturing, and dimensional control of the coil. Therefore, we have chosen to explore the R&W approach. For instance, the difficulty of applying the R&W process is that we should design the cables and magnets in which the strain must satisfy the acceptable level, only 0.24 %after heat treatment. To verify the applicability of the fabrication process, we performed the feasibility study based on the bending strain analysis of cable and double-pancake coil for several tens of kJ class SMES system. Calculation of curvature distributions based on a three-dimensional space curve theorem for both round cable and rectangular cross section cable like Rutherford type are investigated. They strongly depend on cable dimension parameters such as twist pitches, coil radius, and conductor former. The investigated results can allow us to construct the robust energy storage system using MgB2 wires.
Acknowledgements: This work was supported by Advanced Low Carbon Technology Research and Development Program (ALCA) of Japan Science and Technology Agency (JST).
An magnet was manufactured and tested for a 1 MJ/0.5 MVA Superconducting Magnetic Energy Storage and Fault Current Limiter system (SMES-FCL) with HTS tapes recently. It consists of 46 double pancakes with an inductance of 13.3 H, and the rated operating current is 388 A, the maximum magnetic field is up to 3.5 T. In this paper, the fabrication and tests of the 46 double pancakes, the assemblage of the magnet are described in detail. And then, the fundamental performances testing of the magnet were carried out at liquid nitrogen and sub-cooled liquid nitrogen, respectively. And then, the magnet was soaked in liquid neon and cooled with four AL325 cryo-coolers to keep zero neon vaporization. After the whole 1 MJ/0.5 MVA SMES-FCL were field installed and tested, it had been put into operation since January 6 of 2017 at a 10.5 kV wind farm locating in Yumen, Gansu Province of China.
The high-frequency high-voltage (HFHV) transformer acts as a key part for galvanic isolation, energy transmission and voltage conversion in high-frequency resonant converter. And the performance is highly affected by the parasitic parameters, especially the parasitic capacitance. However, the existing techniques have a lot of shortcomings when determining the parasitic capacitance of multi-section multi-layer multi-turn HFHV transformers. A methodology has been proposed to predict the parasitic capacitance of multi-section, multi-layer and multi-turn secondary winding of HFHV transformer based on a 2D-axisymmetric model using finite-element analysis (FEA) software of COMSOL. The magnetic field produced by the coils and the corresponding voltage of each turn were evaluated. The electric field distribution along the windings was analyzed. A 20 kHz, 40 kW transformer with the input voltage of 380 V and the output voltage of 25 kV was designed. The capacitance of the windings with different number of sections, layers and turns was investigated. And an optimum structure of winding was derived, consisting of 9 sections, 9 layers and 4 turns. The winding was manufactured and the parasitic capacitance was measured by the LCR meter using frequency sweeping method. Compared to the classical analytical method with the maximum error of 21%, the method proposed in this paper drastically reduces the error to be less than 10%. The error resources of the classical analytical method are analyzed by the electric energy distribution.
It has previously observed that superconducting magnets have been conventionally excited by a unified current which limited by the largest perpendicular magnetic field usually on the top of magnet due to anisotropic properties . In this case, the current carrying capacity of these pancake windings except that on the ends of the magnet can’t get fully used .This paper provides a new method to improve the energy storage density by applying step-currents on pancake windings according to the different perpendicular magnetic field on the different position. A iteration method is proposed to obtain the critical step-currents. The paper establishes the finite element models of double solenoid magnet and toroidal magnet. The two kinds magnets with step-current are analyzed and the variation trend of the perpendicular magnetic field, central magnetic field, critical currents, storage and mechanical stress are given to verify its feasibility.
MgB2 wires with Tc ~ 39 K has been developed for the applications such as various coils. Considering hydrogen society in the future, MgB2 coils for the Superconducting Magnetic Energy Storage (SMES) devices under conduction cooling are worth serious consideration. First, the authors evaluated critical current density in commercially available MgB2 wires as a function of magnetic field and temperature (Ic-B-T) under conduction cooling. Ic of these MgB2 wires aligned in straight and curve lines under an external magnetic field up to 3.5 T by superconducting magnets was measured at 20-30 K. And then, the authors analyzed bending strain of MgB2 cable and coil, and designed double-pancake coils for several tens of kJ class SMES system. Finally, the authors produced a prototype pancake coil (200 mm inner diameter, 269 mm outer diameter, and thickness 7 mm) experimentally and evaluated coil properties under an external magnetic field. These results suggest can allow us to construct the robust energy storage system using MgB2 wires.
Acknowledgements: This work was supported by Advanced Low Carbon Technology Research and Development Program (ALCA) of Japan Science and Technology Agency (JST).
High-temperature superconducting (HTS) tapes are expected to improve small sized high field magnets such as superconducting magnetic energy storage (SMES). The authors proposed the force-balanced coils (FBC) concept as a feasibility option for SMES. Although the FBC can minimize the mechanical stresses induced by the electromagnetic forces, the FBC has three-dimensional complex shapes of helical winding. Therefore, when the tensile strain, the bending strain and the torsional strain simultaneously apply to the HTS tapes, the critical current of the HTS coils decrease. The objective of this work is to clarify the critical current property of HTS tapes for the applying complex mechanical strain due to the winding process, winding configuration and electromagnetic forces through the development of a 1-T class HTS model helical coils based on the FBC concept. As a first approach, the authors developed a prototype winding machine whose motion was optimized to prevent from decreasing the critical current of the HTS tapes during winding process. The authors fabricated the one-turn helical coils wound onto the pure torus surface without the winding slot using YBCO and BSCCO wire. From the excitation test results with liquid nitrogen cooling, the authors confirmed the feasibility of the helical winding techniques without a decrease in the critical current. As a next step of this work, the authors are planning to carry out the test winding onto the winding slot whose shape has helical coil trajectory. In this case, the complex mechanical strain will directly apply to the HTS tapes compared with the winding case using the pure torus surface. This work discusses the critical current property dependence on the winding technique of the HTS coils thorough the test winding results and a numerical analysis of the applying mechanical strain.
With the development of the technology, the wireless power transfer (WPT) which can realize power transmission without wires，has attracted much attention in recent years. This technology is promising in the applications of mobile devices charging and biomedical implant powering with the advantages of contactless and flexible. In the WPT system, the transmitting and receiving coils are the core components for the power transmission. It affects the system efficiency and the transmission power directly. In this paper, a comprehensive analysis of the transmitting and receiving coils is conducted based on the circuit and electromagnetic simulation. The effects of the structural parameters and the magnetic core of the coils on the power transfer performance are studied. Finally, aiming at the improvement of the transmission power and efficiency, an optimal design of the coils is carried out according to the characteristics of the WPT system.
Recently, electronic devices using a wireless charging method are increasing with development of technology. The wireless charging method is free from the space limitation and has an advantage in mobility. However, the wireless charging method has a disadvantage that the efficiency is much lower than the wired charging method. In order to improve the efficiency of the wireless charging method, the coupling factor indicating the degree of coupling between the two coils must be increased. The coupling factor varies depending on the design method of the transmitting and receiving coils.
In this paper, to improve the efficiency of the wireless charging method, the coupling factor according to the diameter of superconducting transmitting and receiving coils was analyzed. To analyze the coupling factor, the diameter of the transmitting coil was fixed and the diameter of the receiving coil was changed to a certain size. As a result, it was confirmed that the coupling factor is the highest when the receiving coil has a specific diameter. Whereas when the receiving coil grew above a certain diameter, the coupling factor could be confirmed to be smaller. Through these considerations, It is possible to get the high efficient wireless charging if the transmitting and receiving coils are designed with the optimal coupling factor.
This research was supported by Korea Electric Power corporation [grant number: R15XA03]. This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology (NRF-2015R1D1A1A01059489)
Wireless power transfer (WPT) is of increasing interests today. HTS (high temperature superconducting) WPT has been demonstrated to be more efficient than copper WPT. In our previous work, the efficiency of WPT from a copper coil (as the transmitting coil) to a HTS coil (as the receiving coil) is lower than the efficiency of WPT from the same HTS coil to the same copper coil. Namely, asymmetry exists and degrades WPT performance. In this paper, it is demonstrated theoretically and experimentally that, for WPT between a HTS coil and a Litz coil: asymmetry does exist and influence properties; the root of the asymmetry is the different resistances between the HTS coil and the Litz coil; the effects of the asymmetry can be eliminated by optimizing the load; the proposed theoretical calculation fit the experimental results well.
Recently, The use of electronic devices such as mobile phones and notebooks, tablet PCs, etc. is rapidly increasing. But, There is an inconvenience that electronic devices frequently need to be charged because battery life is short. To solve this problem, The wireless power transfer(WPT) system is drawing much attention. However, WPT system used in real life requires more research for increasing distance. In this research team, transmitter and receiver coils were fabricated using a superconductor for increasing distance and efficiency of WPT system. It was confirmed that the efficiency of wireless power transfer using superconducting coils(SWPT) was increased. In this paper, The characteristics of SWPT according to the number of transmitter and receiver coils was investigated. As the number of coils, the mutual inductance also changed. At this time, We analyzed resonance frequency of SWPT by mutual inductance. As a result, The optimum number and distance of transmitter and receiver coils were estimated with maximum efficiency.
This research was supported by Korea Electric Power corporation [grant number: R16XA01] This research was supported by Korea Electric Power corporation [grant number: R15XA03]
Electromagnetic forming (EMF) is acknowledged as a potential forming method because of its advantages relative to traditional forming technique. However, the multi-physics coupling process makes it a daunting task to analyze the forming mechanism. It is necessary to decouple the effects of velocity and thermal in EMF. Since the electromagnetic ring expansion is used as a one-dimensional simplification of EMF process, a dual-ring expansion experiment is designed and performed on AA5083 aluminum alloy, in which a copper ring (known as driving ring) is placed between the aluminum ring (also known as workpiece) and the driving coil side by side. Copper rings can shield part of the eddy current in the workpiece, so the thermal effect in the workpiece caused by the eddy current can be decoupled. According to the simulation, while the thickness of copper rings (0.5 mm, 0.8 mm and 1.2 mm) increases, the eddy current in the copper ring and electromagnetic force increases significantly. Then the different deformation strain rates can be achieved. The dual-ring expansion experiment with three different thicknesses driving rings were carried out, and the single aluminum ring expansion experiments were performed comparatively as well. The experiments results show that the average strains to failure at different strain rates appear positive related to the strain rate. The ductility of AA5083 aluminum alloy can be improved from 17% to 25% due to the high strain rate, and from 17% to 30% due to the high strain rate and thermal effect. This study suggests that the forming behavior is influenced by the high strain rate in addition to joule heat caused by the eddy current.
The most important point in electromagnetic design for the drive motor design of an electric TVC(Thrust vector control) system for space launch vehicle is the right choice of the maximum allowable current density considering the heat transfer condition of the vacuum environment and light weight design through high output density design. Thermal-electromagnetic interaction analysis considering the heat transfer conditions of the system’s environment is performed, where the heat flow between the system components is determined by the specific heat and the heat transfer coefficient. In the heat transfer method, the heat transfer coefficient is determined by the kind and area of the material and the temperature difference in case of conduction and radiation, but in the case of convection condition, the conduction coefficient changes according to the pressure. The thermal conductivity coefficient was calculated considering the operating environment of the system in the stratosphere, and the maximum allowable current density of the TVC system could be calculated through this calculation. The output density is usually expressed as a volume-to-volume output, which is a criterion for how efficiently a motor can produce large forces. In the situation where the allowable voltage and the limit drive speed are determined, the achievement of the maximum output density can be achieved through the electromagnetic improvement design. An analysis of how much TRV(Torque per unit rotor volume) has been increased compared to the existing design through the application of various latest high power density design techniques.
Abstract—With the power conversion device proposes greater efficiency and higher power, the new HTS induction heating equipment shows a wide application prospect in the future in the field of metal material through heating treatment. Efficiency analysis for the traditional induction heating and new structures for the HTS induction heating are studied in this paper. Calculation models for induction heating system electromagnetic field and billet region temperature field analysis are established. The MW class conduction-cooled YBCO magnet system is designed. The magnet consists of an iron core and HTS coils wound with the spliced YBCO-coated conductors. The magnet system is cooled by two AL325 GM refrigerators with the pluggable structure and the operating temperature is 20~30 K. Furthermore, the prototype YBCO coils with the same thickness are fabricated and tested to evaluate the performance of conduction-cooled YBCO magnet. In this paper, test results of the prototype magnet are presented.
We have developed a desktop-type superconducting bulk magnet using a Stirling cryocooler with the aim of miniaturizing the magnet system. As a result of cooling and magnetizing tests using a GdBCO bulk material 45 mm in diameter and 15 mm thick, the lowest achieved temperature was 51.3 K, and the maximum trapped field was approximately 2.8 T at the center of the bulk surface in the applied field of 7.0 T. For this paper, we remodeled the bulk magnet system in order to attach a large bulk 60 mm in diameter and 20 mm thick for the purpose of enhancing the total magnetic flux. This was based on the idea that a total magnetic flux was increased if the volume of the bulk was expanded, while we were anxious about the reduction of the trapped field due to the low cooling capacity of the refrigerator and a high ultimate temperature. When cooling and magnetizing tests were carried out using φ60-mm GdBCO bulk, the sample was cooled from room temperature to the ultimate temperature of 55.6 K for approximately 6.5 hours, and the total magnetic flux was 2.0 mWb, which was about twice that of φ45-mm bulk, indicating that the aim of this study was achieved. Moreover, the maximum trapped field was 3.0 T in the applied field of 6.2 T, which was the maximum value in the pulsed-field magnetization using a large bulk at temperatures beyond 50 K.
Permanent magnetic actuators (PMAs) have been widely used in driving mechanism of medium-voltage vacuum circuit breakers (VCBs) due to their high reliability and controllability. Different from the applications in medium-voltage situations, the PMA used in high-voltage power system has much longer stroke and requires a much higher velocity, which limit the application of traditional PMA in high-voltage field. In the available literature a bistable PMA with separated magnetic circuits has been proposed. The PMA consists of holding and driving components whose magnetic circuits are separated, which helps to improve the efficiency of coil currents to drive the movable contact. This PMA exerts a good closing performance, however, its breaking performance is not satisfactory due to the fact that coil inductor prevents the rapid growth of current during the initial phase of breaking operation. This paper focuses on the optimization of a monostable PMA with separated magnetic circuits, in which the breaking operation is completed by the spring. This paper divides the whole optimization into three sub-optimization modules, including the optimization of permanent magnetic holding mechanism, breaking spring mechanism and closing driving mechanism. These three sub modules are optimized sequentially and recurrently until the overall performance reaches the best. The average velocities of closing and breaking operations are set as the constraints to make them within the specified range, which is critical to successful operation of VCBs. Final velocities, time durations of both operations and the volume of the mechanism are selected as the optimization goals. As design variables, parameters of excitation circuits and spring, and dimension parameters will be optimized through transient analysis, which is realized by finite element method. The optimization model and algorithm will be studied and the performances in the initial model and the optimized model will be compared in the full paper.
For the improvement of the critical current density of a multifilamentary Nb3Sn strand, a high integrity of Nb filaments should be obtained by the optimal cold-drawing process for reducing the cross-section of the filaments. However, as the number of drawing cycles increases, the strain-hardening exponent of the Nb filaments also increases, which consequently hinders the area reduction, and even incurs the problem of breakage of the Nb3Sn wires. In this study, the hardness and microstructure of Nb filaments were analyzed to evaluate the strain-hardening exponent changes with respect to the number of the drawing cycles. In addition, the stress analysis using the finite element method was conducted to investigate the effect of the drawing stress on the drawability.
Acknowledgement: This work was supported by the Materials and Components Technology Development Program of KEIT [10053590, Development of MgB2 wire and coil with a high critical current and long length for superconducting medical•electric power equipment].
The degradation of transport current property by the mechanical strain on the practical Nb3Sn wire is serious problem to apply for the future fusion magnet operated under higher electromagnetic force. Recently, we developed various Zn solid solution ternary Cu-Sn alloy (Cu-Sn-Zn) matrices for the internal matrix strengthened Nb3Sn wires. Zn remained homogeneously into the matrices after the Nb3Sn layer synthesis, and then Zn substitution in the matrices promoted the synthesis of Nb3Sn layers. We thought that remained Zn might act as the solid solution strength factor of the matrix after the Nb3Sn synthesis. We fabricated easily the Nb3Sn multifilamentary wires using various Cu-Sn-Zn matrices through the conventional bronze process, and also carried out the tensile test under 4.2 K and magnetic field of 15 T on the Nb3Sn multifilamentary wires using various Cu-Sn-Zn matrices. In the stress-strain curves of Nb3Sn multifilamentary wires after heat treatment, Young’s modulus was increased with increasing nominal Zn content of Cu-Sn-Zn matrix. In addition, fracture stress of Nb3Sn wire using Cu-Sn-Zn matrix was relatively higher compared with the conventional bronze processed Nb3Sn wire. In the case of the sample using Cu-10Sn-10Zn-0.3Ti matrix, the peak tensile stress in the maximum critical current density was remarkably increased, and it obtained to be about 200 MPa. This tensile stress was similar to CuNb reinforced Nb3Sn wires. In this study, changes of the mechanical properties with different Cu-Sn-Zn matrices were reported. Especially, transport Ic and Hc2 behavior by the tensile deformation on the Nb3Sn multifilamtary wire using various Cu-Sn-Zn matrices was also investigated.
Acknowledgements: This work performed to the Fusion Engineering Research Project (UFFF036) in NIFS, and collaborated with the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University (Project No.15H0024). And this work financially supported by KAKENHI (Grant-in-Aid for Scientific Research (B), 16H04621).
In the past much of the emphasis in the development of Nb3Sn superconducting strands has been on improving the non-Cu critical current density (Jc). Different design Nb3Sn strands were manufactured by the bronze route artificially doped with titanium in bronze. The influences of bronze to Nb volume ratio, filament diameter and Ti content were studied.Bronze to Nb volume ratio affected Jc largely for the different Nb3Sn volume formed after heat treatment. The study of filament diameter on Jc indicates that Jc increases small with the filament diameter increases. Ti diffused into Nb filament when temperature is higher than 340℃ and no Ti element has been found in the Cu-Sn matrix after heat treatment.Results shows that Ti content had weak influence on Jc.Microstructure images show that residual Nb core can be seen in each filament. The Nb3Sn grains are almost equiaxed and uniform in size.
Practical Nb3Sn superconductive strands of composite material were utilized for a cable-in-conduit conductor (CICC) for ITER central solenoid (CS) which consist of 576 Nb3Sn strands, 288 Cu strands and a stainless-steel jacket. During the manufacture of CS, heat treatment up to 923 K is applied to the CICC for reaction of Sn and Nb in Nb3Sn strands. the CICC is cooled down to approximately 4 K to operate ITER magnets. Thermal strain on Nb3Sn filaments of the strand is induced by large temperature difference and different coefficients of thermal expansion among components of the strands and the jacket. Strain dependence of critical current, which is used for prediction of the conductor performance, is influenced by thermal strain. Therefore, it is important to understand mechanism of the inducing thermal strain on the Nb3Sn filament. To distinguish contributions of the Nb3Sn strand components and the jacket to thermal strain on Nb3Sn filaments, internal strain measurement of the Nb3Sn strand was carried out by using neutron diffraction during cool down from 300 K to 12 K. As the results of the measurement, it was found that compressive thermal strain on Nb3Sn filaments was -0.1% at 300 K and -0.2% at 12 K in axial direction. In this paper, stress-strain state of components of the Nb3Sn strand during cooldown is discussed.
Acknowledgement: We acknowledge the support of the Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, in providing the neutron research facilities used in this work.
For the high luminosity upgrade of the large hadron collider (LHC) the US accelerator research program (LARP) is developing a magnet designated MQXF and its associated 40 strand Nb3Sn Rutherford cable designated QXF. To suppress interstrand coupling currents generated during field ramp 25 μm thick stainless steel cores may be included in the QXF cables. For the present study cables with cores of various widths were wound and interstrand contact resistances (ICR) were extracted from the results of AC-loss measurements obtained by way of pickup-coil magnetometry. The ICR so obtained is generally the combined result of crossover- and adjacent- strand contact resistances, Rc¬ and Ra, respectively. In preparation for AC-loss measurement each cable stack was reaction heat treated (RHT) in a closed fixture just large enough to contain it when expansions of 1.5% in width and 4.5% in thickness are expected to take place, a protocol that follows magnet fabrication specifications. In previous studies when RHT was performed under considerable uniaxial pressure the ICR was very low in uncored cable and increased with increasing core width. In the present case, in which RHT took place under ambient pressure, the crossover contact was found to be nonexistent. With Ra left as its sole contributor, ICR turned out to be relatively large, independent of core width, and unpredictable in value.
In the ITER magnets consisting of Nb3Sn conductors, the magnets are fabricated through the so-called wind & react (W & R) technique. In the W & R process, the conductors are wound prior to the heat treatment to form the Nb3Sn superconducting strands from the non-superconducting ductile precursor ones. Then the heat-treated windings are encased into the radial plate keeping their winding shape as it is. The Nb3Sn strands have lower strain sensitivity, so that the applied bending strain to the Nb3Sn strands should be suppressed as small as possible. However in DEMO reactor magnets whose size becomes much larger than the ITER ones, the problems concerning dimension accuracy and fabrication cost should become much bigger. In this context, the react & wind (R & W) process would have to be considered as a solution to construct the magnets. The Nb3Al strands have small strain sensitivity for Jc characteristics. Hence, they could be one of the alternative conductors for realizing the R & W coil. In the R & W application, the irreversible strain characteristics of the strand should be also an important factor as well as the strain sensitivity. The irreversible strain limit should be an index indicating how much the strand is bendable. Hence in this study, we compared the irreversible strain characteristics of various technical rapid-heating, quenching and transformation-processed (RHQT) Nb3Al strands with a different matrix material and filament diameter.
The "Facility for Antiproton and Ion Research - FAIR" will be built near the premises of the renowned physical research institute GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt Germany. The company Luvata has been the sole supplier for low loss Superconducting wires for the SIS100 main magnets. SIS100 is a ring accelerator (heavy ion synchrotron) with a circumference of 1100 meters to be associated with a complex system of cooler and storage rings and experimental setups. The synchrotron will deliver ion beams of unprecedent intensities and energies. A total of 1030 km of 25 000 ultrafine filament wire having filament diameters around 3 μm, has been delivered for the project. The OK25000 wire has a CuMn interfilamentary matrix embedded in a high purity copper matrix, all manufactured in house at the premises of Luvata. To guarantee low loss performance Luvata incorporated several technologies to reduce the AC losses. In this paper we will present the results of the wires electromagnetic performances, including critical current density, twist pitch, hysteresis losses, RRR and resistivity compared to the customer specified values.
Nb-rod-method Cu-Nb reinforced bronze process Nb3Sn (Cu-Nb/Nb3Sn) wires are applicable to React-and-Wind processed Nb3Sn coils. The Cu-Nb composite material functions as a reinforcing stabilizer during the superconducting magnet operation. Moreover, it suppresses the damage of reacted Nb3Sn filaments due to the applied stress during manufacturing process such as the pre-bending treatment, the insulating and the winding. Plural new Cu-Nb/Nb3Sn wires with the high tin bronze (Cu-15.7wt%Sn-0.3wt%Ti) were investigated in the superconducting properties. The round wire of 0.8 mm diameter with pre-bending strain of ±0.5% demonstrated the non-Cu-Jc values (at 4.14 K, defined by 10 micro-V/m) of 1150 A/mm2 at 12 T and 410 A/mm2 at 17 T, which were 1.5 times and 1.4 times larger than those of the previous wires (with Cu-14wt%Sn-0.2wt%Ti). As for rectangular wires of 1.7 mm x 1.13 mm, the pre-bending strain was applied from the flatwise direction and/or the edgewise direction. In case of pre-bending strain of ±0.5% applying alternately from both directions, the non-Cu-Jc was 355 A/mm2 at 17 T of which was 1.6 times larger than that of the as-reacted wire without pre-bending treatments. These results suggest that the performance of large capacity conductors consist of the advanced Cu-Nb/Nb3Sn wires can be further improved by controlling both magnitude and direction of the pre-bending strain in React-and-Wind process.
After mass production for ITER, Western Superconducting Technologies, Co. Ltd. (WST) still takes great efforts at internal-tin (IT) Nb3Sn strand with higher Jc and lower Qh, for next generation of fusion reactors, such as DEMO in Europe and CFETR in China. Three routes, i.e. Cu split, Sn spacers and 37 subelements were carried out to obtain such strand, based on the structure and process of IT Nb3Sn strand for ITER. The route of Cu split was discovered to be most efficient to decrease Qh, which could be as low as 300 mJ/cm3, 30% lower than the average of ITER IT Nb3Sn strand. Nevertheless Jc was also reduced to about 900 A/mm2, 10% lower than the ITER average due to the loss of Nb area by inputting Cu split. Sn spacers between outermost subelements enhanced Jc to about 1100 A/mm2 without obvious increase of Qh, though Sn spacers could be quite harmful to the deformation of Ta barrier. Jc of strand with 37 subelements could reach 1100A/mm2, about 20% higher than the average Jc of ITER IT Nb3Sn strand, and Qh could be as low as 400 mJ/cm3. This strand was delivered to EPLF, Switzerland to fabricate experimental conductor sample for DEMO.
The Fermilab Mu2e experiment seeks to measure the rare process of direct muon to electron conversion in the field of a nucleus. The experiment makes use of three large superconducting solenoids: the Production Solenoid (PS), the Transport Solenoid (TS), and the Detector Solenoid (DS). The TS is an “S-shaped” solenoid with a warm-bore aperture of half a meter and field between 2.5 and 2.0 T. The three solenoids feature four different Al stabilized NbTi superconducting cables. All the conductors are manufactured conforming a NbTi Rutherford cable into an aluminum matrix. Cables are subsequently cold-worked to meet the mechanical and electrical cable requirements in terms of yield strength and RRR of the Al stabilizer. This paper describes the various steps that led to the successful procurement of over 700 km of superconducting wire and 44 km of Al-stabilized cable needed to build all the 52 coils for the Mu2e Transport Solenoid (TS). The main cable properties and results of electrical and mechanical test campaigns are presented and discussed for each stage of the cable development process. Critical current measurements of the full stabilized cables are presented and compared to expected critical current values as measured on strands extracted from the final cables after etching of the Aluminum stabilizer. Effect of cable bending on the transport current are also investigated and presented.
A rig was fabricated to test single-strand excitation and current sharing in Nb3Sn Rutherford Cables. Measurements were performed on a 40 centimeters length of 27-strand cored and non-cored cables which were mounted on a U-shaped holder. Samples were reacted and epoxy impregnated using magnet-like protocols. Current was injected into a single strand at varying I/Ic and a heat pulse was used to initiate current sharing. Current-distribution was measured using voltage taps. These measurements were performed as a screening for cable and cable preparation protocol for larger scale measurements.
High-performance Nb3Al superconducting wire has wide potential applications in high-field magnets, magnetic confinement fusion, high energy particle accelerator, etc. However, km-grade Nb3Al wires with high-performance are still not available to the large-scale engineering application due some fabrication problems and intrinsic physic-chemistry properties. In this paper, we reported the comparison study on the superconducting properties and microstructure of Nb3Al superconducting wires fabricated with two different techniques: The first is an in-situ powder-in-tube (PIT), which were made by using the mechanically alloyed Nb(Al)ss supersaturated solid solution, as well as the low temperature heat-treatment at 800 -950 C; and the second is a jelly-roll Nb3Al precursor long wire followed with different rapid heating and quenching (RHQ) heat-treatments. We found that both mechanical alloying and RHQ methods can produce the Nb(Al)ss supersaturated solid solution phase, however, the performance of the consequent Nb3Al wires are quite difference. The wires fabricated by RHQ method has a much better Tc and Jc than those prepared by mechanical alloying technique. Microstructure and compositional analyses reveal that these two methods results quite different microstructure and local chemical composition in nanometer scale, which may affect the superconductivity and flux pinning behavior in the Nb3Al wires.
An apparatus is constructed for Nb3Al short wires heat treatment with rapid heating and quenching (RHQ) method. Multifilamentary Nb/Al precursors are fabricated by rod-in-tube (RIT), powder-in-tube (PIT) and jelly-roll (JR) processes. These precursors are RHQ heat treated in the apparatus and then transformation heat treated at 800 °C for 10 h in a vacuum furnace. Transport and magnetization tests are performed to investigate the superconducting properties of the various short wires. The influences of RHQ time and maximum temperature on superconducting properties are also investigated. The highest onset TCs for RIT, PIT, JR wires are 17.2 K, 16.8 K, 17.5 K respectively. Microstructural observations show that wires prepared by JR method has homogeneous and stoichiometric A15 phase. The calculated JC based on Bean model for JR wire is 1100 A/mm2 @10 K, 2 T, which is the best of the three wires. All the results show that JR method is the most suitable method to prepare Nb3Al precursor for RHQT heat treatment.
We have designed a 500 A class high temperature superconductor (HTS) current lead using Bi2223/AgAu tapes for a conduction cooled superconducting magnet. The HTS current lead consists of two terminal blocks, a support tube, and seven Bi2223/AgAu tapes with support tapes. An operating condition is 500 A at 70 K, 0.6 T by conduction cooling, and heat leakage through the current lead is 0.32 W from 50 K to 4 K. Based on the design, we fabricated a prototype of the HTS current lead (PHCL). Critical current value was 738 A at 77 K in self-fields. The initial critical current at 77 K was maintained after five thermal cycles. The PHCL could carry 500 A at 70 K, 0.6 T by conduction cooling even after 21,000 cycles of electromagnetic force (Lorentz force). These results showed that the HTS current lead had sufficient current capacity and strength against thermal stress and Lorentz force. In addition, the critical current value was measured under various magnetic field and temperature conditions. These results will be reported in this paper.
The superconducting joint technology used for high-temperature superconductors (HTS) is key for realizing persistent operation of HTS magnets. Recently we have succeeded in developing a superconducting joint between REBCO conductors using a polycrystalline intermediate, which has a critical current (Ic) of >100 A at 77 K [1]; A REBCO micro-polycrystalline intermediate was prepared on the surface of the REBCO layer of a conductor and it was transformed into large poly-crystals or single-like crystals as a joint.
We measured the persistent field decay of a small double pancake coil, terminated with this type of joint, at 77 K in a self-field with an operating current of ~10 A (~14% of the calculated coil Ic) for three days. The field decay rate decreased exponentially for the first several hours and then logarithmically, corresponding to a characteristic resistance between ~3×10^-12 to ~5×10^-13 Ω. The logarithmic decay implies that the joint resistance was not constant and might depend on flux creep. The effect of screening current relaxation on field decay and the coil load factor dependence will be investigated.
We also measured Ic-B characteristics of the joint in the temperature range from 4 K to 77 K in a field of <10 T. In a self-field, Ic at 4 K was ~7 times higher than that at 77 K. At 4 K, Ic steeply reduced with the field of <1 T and gradually decreased in the range of 1-10 T. The result shows that the joint structure includes a superconducting current path which is weak against a magnetic field. The superconducting current mechanism through the joint device will be discussed based on SEM and TEM observations.
[1] T. Nagaishi et al., Presented at 1st Asian ICMC and CSSJ 50th Anniversary Conference, 3A-p02, Kanazawa, Nov.7-10(2016)
This work is supported in part by the MEXT.
This study presents the design and performance results of a pair of vapor-cooled MgB2 current leads for a 1.5 T MRI magnet developed by Kiswire Advanced Technology Ltd. in Korea. To reduce the liquid helium (LHe) consumption of the MRI system, the current leads were designed as a retractable type to be detached from the magnet operated under a persistent-current mode. From the cryogenic evaluation, the cold-end heat input of the vapor-cooled current leads was calculated using the LHe consumption measured by a LHe-level sensor and mass flow meter. Furthermore, thermal analysis of the current leads was carried out using the finite element method. During operation tests at various operating currents, the voltage and temperature of the current leads were measured to evaluate the effects of employing the MgB2 wire on the thermal performance of the leads. In addition, conventional vapor-cooled copper current leads were also examined and the results were compared with the test results of the proposed vapor-cooled MgB2 current leads.
Acknowledgement: This work was supported by the Materials and Components Technology Development Program of KEIT [10053590, Development of MgB2 wire and coil with a high critical current and long length for superconducting medical•electric power equipment].
Within the frame of the R&D activities carried out in Europe for the Toroidal Field (TF) Coils of the nuclear fusion device DEMO, different proposals have been given so far. All of them rely on superconducting (SC) Low Tc wires (Nb3Sn). The present paper deals with a Wind & React solution based on Cable-In-Conduit Conductors (CICCs). The TF coil is a graded layer one, with varying SC, Cu and SS quantities every 2 layers, thus permitting an optimized distribution of the materials and consequent cost savings. The whole Winding Pack (WP) is formed by 6 Double Layers (DLs), each wound over the previous one. This solution makes the internal joints connecting two different DLs a crucial topic for a sound performance of the coil. Basing on previous successful experiences, as for instance the EDIPO and the NAFASSY Nb3Sn coils, our team is designing a proposal for such intermediate joint so to possibly “embed” it in the WP. This is feasible only if the whole junction is kept within the same external dimension of the two joined conductors. A complete description of the joint design for each connected DL is given here, along with hints about the manufacturing of a SULTAN sample, foreseen to be tested in order to confirm the joint electrical performances, both in terms of ohmic resistance and AC losses under variable magnetic field and temperature.
The High Field Magnet Laboratory has designed, manufactured and tested a pair of 20 kA binary vapour cooled/superconducting current leads for the superconducting outsert magnet of its 45 T hybrid magnet system, in close collaboration with the National High Magnetic Field Laboratory (FL, USA). The resistive section of each lead consists of 22 parallel copper plates cooled by a flow of nitrogen vapor evaporating from a level controlled liquid nitrogen reservoir. As shown during the test at the HFML of similarly cooled 20 kA binary leads for NHMFL’s Series Connected Hybrid this cooling scheme ensures a very stable temperature of about 77 K at the transition from the resistive section to the warmest part of the HTS section. The HTS section is made up of 60 pre-soldered stacks of 4 Ag/Au sheathed Bi-2223 tapes. The ese stacks are soldered simultaneously into machined slots of a stainless steel cylinder and onto both the 77 K copper interface and the 5 K copper bus bar connector block. The dedicated test facility at HFML provides the required current, a level controlled liquid nitrogen supply, and a closed-loop supercritical helium supply at 5 K and 5 bar. A test assembly is made, including the pair of current leads, an actively cooled jumper made from an aluminum stabilized NbTi Rutherford type of cable, instrumentation and mounting hardware. In this paper we present details of the design and manufacture of the current leads and the test facility and report results from the powering tests including measurement of the temperature, current and field safety margins for the HTS section and the response to loss of coolant.
Superconducting high field magnets use the principle of superconductivity of the material, thus working with very high current density in thin cables. The cables are cooled down to cryogenic temperatures inside of a vacuum insulated cold box. In order to feed the high current into the cold box, it is important to cool down the conductors progressively. The less coolant is needed for current unit, the more efficient is the system. Hybrid current leads, using the properties of BSCCO 2223 (High Temperature Superconductor), have an almost-zero resistivity already at higher temperatures around 50 K and are a very efficient way to reduce the consumption of cooling energy. This philosophy has been applied to a pair of 25.7kA current leads, aimed for a magnet test facility of CEA Saclay for verifying the Toroidal Field Coils of the Tokamak JT-60SA. This contribution describes the design features and parameter and its confirmation through the first commissioning results.
Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) was contracted by General Atomics Company to develop a superconducting feeder system containing a pair of 52 kA high temperature superconducting (HTS) current leads for ITER Central Solenoid （CS） magnet test. These HTS current leads are majorly based on the previous ITER lead design experiences. However, the vertical assembly design which is different from ITER horizontal assembly causes the water leakage in the insulation flange during the initial phase. Some improvement was recognized and avoids the potential risk for further prototypes and series production of ITER leads. Some development experience will be shared in the paper. The HTS current leads contain BiSCCO AgAu tapes to minimize the heat load to 4.5 K end. Its resistive part is cooled by 50 K helium. The HTS part is cooled by conduction. The HTS current leads were integrated in the feeder system to perform 4.5 K full current test. The factory acceptance test was implemented to verify the high voltage and thermodynamic performances. The maximum current was achieved at 55 kA. The test indicates the helium mass flow consumption is 3.3 g/s per lead, and loss of flow accident (LOFA) time is close 10 minutes at the nominal current with the stoppage of 50 K helium. The insulation flange passed the high voltage test of 15 kV with less than 1 micro Ampere leakage current after the improvement. More detailed test results will be shown in the paper. The development of the whole feeder system for CS magnet test will be contributed on the different paper presented at this conference.
In the framework of the French-German project Iseult, we chose to design the 4.5 K vapor cooled current leads of the 11.75 T MRI magnet using a burn-proof approach, i.e. they are able to withstand a 3-hour current slow dump without any active cooling. This constraint led us to select brass instead of pure copper, resulting in higher mass and thus in higher thermal stability. The drawback is a slightly higher cryogenic consumption. We present here the design studies of those currents leads and compare their theoretical characteristics with the experimental results obtained during the test campaigns at CEA-Saclay.
The MRI industry is reliant on persistent-mode superconducting electromagnets for high magnetic fields and increased stability. Achieving persistent coils is entirely dependent on the formation of high quality superconducting joints, currently made using Pb-Bi solder. Whilst this is an effective solution, there is legislative pressure to remove the lead even from medical instruments. There is also a technical driver to explore new joints in that the critical field of Pb-Bi is much lower than that of the NbTi wires, so joints must be located in regions that experience fields of 1 T or lower, meaning they must be removed from the highest field regions of the magnets. Recent studies of alternative lead-free solders have found no drop-in replacement for Pb-Bi, with even the best of these new alloys having much lower Bc2 values [1]. Other lead-free approaches such as spot welding and cold pressing lack the reproducibility required for MRI production [2]. We are developing new approaches for joint fabrication, using NbTi as the current-carrying intermediary material between commercial NbTi wires. Several designs of joints have been analysed by SEM, SQUID magnetometry and high current measurements and compared against the performance of Pb-Bi soldered joints. This presentation will compare the properties of these different joint strategies, and suggest which are the most promising directions for the development of lead-free persistent mode joints.
TD is supported by an EPSRC CASE studentship with Siemens Magnet Technology.
1. Mousavi et al., Supercond. Sci. Technol., 29, 2016
2. Brittles et al., Supercond. Sci. Technol., 28, 2015
The paper describes the result of the ITER feeder main busbar joint sample qualification test as confirmation of the requirement of busbar joint resistance; 2 nΩ at 70 kA at zero background field, as well as those of joint performance in various magnetic fields to investigate stability and current distribution characteristics in feeder-type joint box. The results support the quality of the joint manufacturing process for ITER main busbar joint. The qualification sample design was prepared to be tested in SULTAN facility. The production of the full-scale sample was manufactured in ITER magnet workshop located at CEA with contribution from CEA collaborators. The SULTAN joint ample consists of joints to be qualified at the level of the peak field and upper terminations. In bottom joints, twin-box feeder-type paying hands configuration is applied. In upper terminations, one of them is made with solder-filled cable for optimum current distribution. The other takes the same length of the copper sole and contact with the busbar cable as those positioned in bottom of the sample. The performance of this leg is compared with the other leg consisting of both ends manufactured with two twin-box feeder-type joints, which could have a lowered Tcs if the current redistribution is an issue. The sample undergoes a test program including joint resistance measurement, AC losses and stability margin test. The outcome of the following test program are to be reported; DC joint resistance measurement by voltage taps and calorimetry at 0 - 70 kA and 0 - 3.8 T, AC loss measurement with AC field transverse to copper face, stability limit under
single trapezoidal field pulse transverse to copper face, and joint degradation study under repulsive and attractive load applied to the joints.
The views and opinions expressed herein do not necessarily reflect those of the ITER
Organization
The advent of new kind of superconductors can introduce a new application age. Modern magnet designs and applications push towards persistent mode system realized with multiple superconductive connected coils. The quality of field persistence is fundamental in order to characterize the goodness of the superconductive joint technical implementation. A theoretical methodology able to predict the field and the current evolution in the superconductive closed loops is necessary to introduce innovative material as MgB2 in fabrication technology and to develop robust joint techniques. ASG laboratory developed a new energetic model able to predict the ending currents of closing circuits and evaluate the persistent circuit total efficiency with short field acquisitions. This innovative model represents a powerful and flexible tool, as it is easily implementable in the study of arbitrary superconductive closed loops and applicable to complicated winding geometry. The mathematical method will be presented, and theoretical results will be compared with experimental measurements performed on specific MgB2 winding samples.
Current leads with use of high temperature superconductors (HTS) permit to reduce sufficiently heat transfer to liquid helium in many superconducting magnets applications. They are one of the widest HTS applications. For example, in Large Hadron Collider more than 3000 units of such current leads are used providing sufficient saving of heat transfer to liquid helium. HTS current leads made of 1G HTS tapes are considered for ITER magnet system as well. In most cases the HTS current leads are working in a self-field being removed from the area of a scattered magnetic field generated by a magnet. However, in certain cases with a tight cryostat space it could be necessary to place current leads close to the magnet into an external magnetic field of a magnet. Some specific optimization of current leads in such a case is necessary. We are participation in the project in which due to space restrictions the limited size of a cryostat demands placing horizontal HTS current leads in magnetic field ~2 T. In this paper, we performed the optimization study of HTS current leads used 2G HTS tapes and able to work in the magnetic field up to 2 T. The optimal parameters of the current leads have been determined using numerical simulation. In order to approach the maximum efficiency, it is necessary to have a very good heat exchange between the current leads and evaporating helium gas. The impact of the external magnetic field on the heat leak from current leads into liquid helium has been studied.
The Karlsruhe Institute of Technology (KIT) agreed to construct and test the High Temperature Superconductor Current Leads (HTS-CL) for the tokamak JT-60SA presently under construction in the frame of the Broader Approach agreement between Europe and Japan. In total 6 HTS-CLs for 25.7 kA for the TF coils and 20 HTS-CLs for 20 kA for the PF and CS coils are required and all of them have to be tested at operating temperatures in the test facility CuLTKa at KIT. The manufacturing started in 2014 and the last current leads will be tested in July 2017. The main parts of the acceptance test are the determination of the heat load at 4.5 K, the 50 K He mass flow rate through the heat exchanger, and the simulation of a loss of flow accident. One test of the PF current leads includes a pulse test at 20 kA to demonstrate their PF operation capability.
In the present paper an overview of the manufacture and the acceptance tests of the HTS current lead is given. The results for the different current leads are summarized and compared to the specifications showing a good and reproducible performance.
HTS superconducting magnets for MRI or NMR should be operated in persistent current mode to achieve high homogeneity and stability. A persistent current switch and a superconducting joint are the key technologies for persistent current operation. Recently, a superconducting joint has been fabricated successfully in Furukawa Electric Co., Ltd. We made a persistent current system including the superconducting joints, a persistent current switch and a REBCO double pancake coil. In this paper, we report detail results of persistent operation test of the system in self-field and applied magnetic filed of 1 T. The double-pancake coil of 160 turns with the inner radius of 44 mm and the persistent current system were fabricated with SuperPower REBCO tapes (6 mm width). The persistent current system was cooled by the second stage of the GM cryocooler in a cryostat installed in a room temperature bore of a cryocooler-cooled superconducting magnet. The current decay behaviors in the persistent current mode up to 170 A at 20 K were measured using a Hall probe located at the center of the coil. The magnetic field generated by persistent current was 0.59 T at 170 A and the decay rate of the field after five days operation was estimated to be 1.5 ppm/h in self-field. The detailed results will be discussed with considering operating current and applied field dependences.
The electrical interconnections between the LHC main magnets are made of soldered joints (splices) of two superconducting Rutherford cables stabilized by a copper busbar. In 2009, a number of splices were found not properly stabilized and could have burnt through in case of quench at high current. The LHC was therefore operated at reduced energy and all Rutherford-cable joints were continuously monitored by a newly installed layer of the Quench Protection System (QPS). During the first Long Shutdown (LS1) in 2013-14 the high-current busbar joints were consolidated to allow a safe operation of the LHC at its design energy, i.e. 14 TeV center-of-mass. The SMACC project (Superconducting Magnets And Circuits Consolidation) has coordinated the consolidation of the 10170 13 kA busbar splices. Since 2015 the LHC runs at the energy of 13 TeV center-of-mass. This paper will briefly describe the QPS data analysis method and will present the results and comparisons of the Rutherford-cable splice resistance measurements at 1.9 K before and after the LS1, based on an unprecedented amount of information gathering during long-term operation of superconducting high-current joints. A few outliers that were still found after the splice consolidation will also be shortly discussed.
Magnesium diboride (MgB2), which has a critical temperature (Tc) of 39 K, is a candidate for use in liquid-helium free magnetic resonance imaging (MRI). Since the discovery of MgB2, the performance of MgB2 wires and the manufacturing technology for long-length conductors have dramatically improved.Moreover, the superconducting properties of MgB2 wires have improved. Wires subjected to internal magnesium diffusion (IMD) processing show particularly high performance compared to Power-In-Tube processed MgB2 wires. Our group has been developing high-performance IMD wires with Jc and Je values greater than 100 kA /cm2 and 10 kA /cm2, respectively, at 4.2 K and 10 T. MRI magnets usually require persistent-mode operation to obtain high-quality images. Therefore, for wide applicability of MgB2 in MRI, more work is required on the joining process.
We prepared two unreacted IMD wires having a diameter of 0.8 mm. The edge of each wire was compressed by a press machine to flatten it into a tape shape . After one side of the tape was polished, two tapes were packed into a metal tube and pressed again to form a joint. The IMD wire with the joint was heat-treated at 670°C for 6 h. We performed Ic measurements using the probe method and observed the specimens by scanning electron microscopy (SEM) after the measurements. The maximum Ic values in the wire were depressed 10% compared to those of a normal IMD-processed wire for each investigated magnetic field. However, the Ic values of the joint part at 3 T were equal to the Ic values of normal IMD wire at 10 T, suggesting that this joint was effective for use at magnetic fields weaker than 3 T. SEM observations revealed several B-rich compounds. We will report further improvements of the IMD technique.
Recent studies on no-insulation (NI) winding techniques for high temperature superconducting (HTS) coils have demonstrated that an NI coil has a self-protecting feature: a localized quench heat inside the coil can be automatically diverted in the radial direction owing to the absence of turn-to-turn contacts. The obvious benefits of NI may resolve difficulties in the protection of the HTS coil, which is highly vulnerable to the quench. However, prior to applying the NI technique to the full-scale magnet including several double pancake (DP) coils, it is essential to examine the availability of the self-protecting features between the “axially connected DP coils” as well as between the turn-to-turn contacts in each DP coil. In this study, post-quench behaviors of an HTS magnet including four GdBCO DP coils were investigated through over-current tests. The purpose of the over-current tests was to intentionally quench the HTS magnet, thereby subjecting it to severe operating conditions, and then examine the thermal, electrical, and magnetic integrities of the magnet, validating the intactness of its axial self-protecting feature.
Acknowledgement: This work was supported by the Korea Basic Science Institute under Grant D37614.
Super High Momentum Spectrometer (SHMS) of Hall C, part of 12 GeV Upgrade at Jefferson Lab, is tested and complete. We will present the measured quench data and the simulated ones of the Q2/3, and Dipole superconducting magnets using the quench code of Vector Fields’ Opera-3D. A multi-channel Tektronix DPO is used to record the signals of the current, voltage of the dump resistor, and other voltages of interest for the Q2/3 and Dipole; the sampling rate used in the tests is 1.0E-4 s. The energy balance method is employed to figure out the energy deposited into the coil during the quench. The deposited energy is correlated with the measured temperatures of the coil. Opera-3D 18.0 is used to model and analyze the quench behaviors of the Q2/3 and Dipole. Material properties of the coils are updated with the real manufacturing data. The measured current decay and measured temperatures of the coil during real quenches will be compared with the simulated quenches from Oper-3D. The differences between the measured and simulated behaviors will be discussed to provide guidance for design of similar superconducting magnets in the future. The training curves of three magnets will be presented also.
Detailed localisation of the quench start in Nb3Sn accelerator magnets by voltage measurements requires a large number of voltage taps, which is less feasible in long prototype coils. Localisation with quench antennas is a proven concept for longitudinal quench localisation in full length accelerator magnets. Quench antennas are also excellent vibration detection tools, and give important information on the cause of the quench. Dedicated quench antennas were produced using state of the art flexible printed circuit boards. The quench antennas were tested at the CERN based SM18 superconducting magnet test facility in Nb3Sn model magnets; the results were validated with voltage measurements and compared with numerical model predictions.
For the high temperature superconducting (HTS) coils supplied by DC powers, a thermal disturbance may cause local temperature rise and irreversible damage because of constant current. In contrast, when a thermal disturbance occurs, the current flowing in a closed-loop HTS coil operated in persistent current mode (PCM) will decrease correspondingly. In this paper, a closed-loop single-pancake HTS coil energized by persistent-current switch (PCS) is tested to obtain the minimum quench energies (MQEs) and normal zone propagation velocity (NZPV), which we use to describe thermal stability, as well as an unclosed one. A FEM model coupling with PDEs and thermal module is built to reveal the mechanism. The experiment results coincide with the simulated ones and show that the closed-loop coil has larger MQEs and better thermal stability.
The simulation analysis of thermal and electromagnetic behaviors in ReBCO coils after a local normal conduction transition has been performed by many research groups. The numerical analysis, however, were about the behaviors after generating an initial normal spot and the occurrence factor of the initial normal conduction transition has not been sufficiently clarified yet. To clarify the occurrence factor of the initial normal conduction transition is very important to take coil protecting measures against the local normal conduction transitions. We focused on local critical current degradation and investigated the influence of the local critical current degradation on the thermal and electromagnetic behaviors around the local degradation region and the time change characteristics of the voltages across the degradation region. The local critical current degradation was produced by cutting a part of the width of a GdBCO tape. The current at the disconnection of the tape and the increasing speed of the voltages across the degradation region were measured in short samples and coils using the GdBCO tape. In the sample without stabilized copper layers covered by Styrofoam, the voltage rapidly increased in a short time and the sample was disconnected soon after the operating current exceeded the local critical current. On the other hand, the tape with the stabilized copper layers cooled by LN2 could stably maintain the voltage even when the operating current largely exceeded the local critical current. Moreover, the current at the disconnection of the tape with the stabilized copper layers cooled by LN2 was improved much more than that of the tape without the stabilized copper layers covered by Styrofoam. The differences of the current and thermal distributions between these samples and the relationship between the voltage increase and the current and thermal distributions were investigated by the finite element analysis.
It is generally agreed that the development of a self-protective MgB2 magnet may not be achieved because of the slow normal-zone propagation velocity of the MgB2 wires, compared to their low-temperature superconductor counterparts. However, the use of the no-insulation (NI) winding technique can allow the MgB2 magnet to be self-protecting, because the excessive heat and current generated by local quenching can be automatically bypassed through the uninsulated turns. Nevertheless, to utilize the NI winding technique for large-scale superconducting magnets such as whole-body MRI magnets, it is essential to ameliorate the charging/discharging delays observed in the NI windings. As an alternative solution, this study examines a partially insulated (PI) MgB2 magnet that employs layer-to-layer insulations only, in the absence of turn-to-turn insulations. A monofilament MgB2 wire manufactured by Kiswire Advanced Technology Co. Ltd., was used for the fabrication of the PI MgB2 magnet. The charge-discharge and over-current characteristics of the PI MgB2 magnet were investigated to demonstrate the feasibility of employing the PI winding technique to develop a self-protective MgB2 MRI magnet with fast charging/discharging rates.
Acknowledgement: This work was supported by the Materials and Components Technology Development Program of KEIT [10053590, Development of MgB2 wire and coil with a high critical current and long length for superconducting medical•electric power equipment].
Second generation (2G) high temperature superconducting (HTS) tapes are now capable of carrying very high transport current and promising for a wide range of applications. A large-capacity wind generator prototype has been developed using HTS tapes. The racetrack coils wound with 2G HTS tapes are used in the rotor, whereas the conventional technology is employed in the stator. The reliability of superconducting field winding is one of the most important factors for the developed wind generator. Racetrack coil can experience severe quench because of various disturbance, so it is necessary to investigate its stability and normal zone propagation characteristics. In this study, the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) of racetrack coil are investigated using the voltage and temperature profiles in a conduction cooling system. Meanwhile, a numerical model is built to verify the measured results. The major innovation of this paper is the developed numerical model which combines COMSOL and MATLAB and couples electric field, magnetic field and thermal field. Moreover, this model can be used to predict the quench process of large racetrack coils. The detailed results about the experiments and the numerical analysis are presented and discussed in this paper.
When a high temperature superconductor (HTS) magnet consisting of a stack of pancake coils is wound, precisely controlling both the outer diameter and number of turns in the coil is difficult, mainly due to manufacturing uncertainty of the HTS tapes. To “arbitrarily” adjust the number of turns in each pancake is often adopted to precisely control the outer diameters, which obviously jeopardizes the ideally designed field homogeneity of the magnet, an important issue particularly for nuclear magnetic resonance or magnetic resonance imaging applications. A common approach is to place intermediate metal strips in-between selected turns of the pancake coils in a way to control both the outer diameter and number of turns to the design values. Yet, if this approach is used for a no-insulation (NI) HTS pancake coil, there is concern whether or not the coil will maintain the self-protecting feature. This paper investigates this issue in experiments in a bath of liquid helium at 4.2 K. An NI pancake coil was wound with metallic cladding REBCO tapes having a 1 – 2 um stainless steel cladding layer. Multiple quench tests were performed with the coil placed in a bore of a 10 T low temperature superconductor background magnet. The post-quench behaviors of the coil were monitored in various operating currents. The tests were repeated as the coil was reconstructed with different configurations such as the number of copper strips, size of strips, and strip locations. The results are expected to provide some insight for the baseline design of our future NI-REBCO NMR or MRI magnets.
ACKNOWLEDGMENTS: This work was supported by the National High Magnetic Field Laboratory (which is supported by the National Science Foundation under NSF/DMR-1157490), the State of Florida, and the KBSI grant (D37611) to S.-G.L.
Cea Saclay, in collaboration with the French SMI Sigmaphi, have fabricated a 50 kg solenoid with 2 km of Columbus MgB2 rectangular wire (3*0.7 mm²). The magnet was powered with 100 A at about 10 K and reached 4.2 T on the wire, with an external magnetic field of 3 T. A comparison between the protection and stability theoretical study and experimental results is presented. The quench propagation measurements have been performed at various temperatures, coil currents, and external fields. More than 20 quenches have been triggered using quench heaters mainly around the nominal design condition (10 K; 4 T and 50 A/mm² of overall conductor current). These measurements values are compared to the results of the design calculations. The differences with the numerical model are analyzed and a possible explanation of these differences is given by not taking into account eddy currents and ground insulation thickness. The validation of the experimental parameters is necessary for designing the protection of high field MgB2 magnets magnet in the frame of our development program. The performances of recent MgB2 wires allows us to reach magnetic fields over 5 T.
Since 2010 to present, several sub-size magnet assemblies, designed as test beds for impregnated Nb3Sn-based coil technology validation, are tested at the CERN Superconducting Magnet Test Facility (SM18). These Short Model Coils (SMC) and Racetrack Model Coil (RMC) have been used to characterize two types of Rutherford cables foreseen for the coils of the Nb3Sn magnets for the HL-LHC and High Field Magnets program of CERN. During several SMC and RMC test campaigns, the Rod Restack Process (RRP) and the Powder In-tube (PIT) conductors have been characterized in terms of performance, transversal and longitudinal Quench Propagation Velocity (QPV). Hot Spot Temperature (HTS) increase during quenches were registered and signals analysed as function of current and energy. In this paper, the multi-physics problem of quench propagation is addressed by means of a set of analytical formulae and three Finite Element Models (FEM) using MATLAB, ANSYS Mechanical APDL and COMSOL packages aimed at describing the conductor behaviour in lumped 1D, 2D and 3D non-linear transient thermal framework coupled with electric constitutive laws for Nb3Sn and copper. The paper discusses in detail the relevance of the model assumptions taken at the composite cable boundaries (adiabatic condition, normal to superconducting state transition) needed for model reduction as computing time rapidly becomes an issue. The sensitivity of the models on the material properties distribution across the composite and on their temperature, as well the magnetic field dependence along the winding are presented. The comparisons of QPV and HST derived from the voltage and fibre optics sensors signals with the simulation results show a good stability of the models. The paper concludes with an attempt to normalise the QPV data sets from different tested coils.
A Ni-alloy reinforced Bi-2223 conductor (Bi-2223) enables the construction of a compact high field magnet due its high mechanical strength. However, its thermal runaway behavior has not been investigated. The purpose of this paper is to investigate (a) the thermal runaway behavior and (b) the subsequent degradation of a Bi-2223 coil. For this purpose, a five-turn pancake with an artificially degraded section was made and tested at 77 K. The different behavior between the Bi-2223 coil and a REBCO coil will be discussed.
The degraded section in the middle turn continuously generates heat, resulting in a premature thermal runaway. In a case of the Bi-2223 coil, the thermal runaway initiation current for the paraffin impregnated coil (adiabatic) was 117 A, 105 % of Ic, while that for a dry coil (cooled) was 158 A, 142 %. The corresponding heat generation was 4.4 W and 28 W, respectively. In the case of REBCO coil, the thermal runaway current for a paraffin impregnated coil was 53 A, 54 % of Ic, while that for a dry coil was 90A, 92 %. The respective heat generation was 1.7 W and 5.3 W. Thus, from a viewpoint of thermal runaway, the Bi-2223 coil is several times more tolerant than the REBCO coil. Based on numerical simulations, such a high tolerance is due to the lower n-index and higher Tc of Bi-2223.
For the Bi-2223 coil, fatal degradation did not appear until the temperature exceeded 483 K, i.e. the melting temperature of the solder bonding a Bi-2223/Ag and a Ni-alloy. This temperature is higher than that of a REBCO coil, 340 K [1]. Thus, the Ni-alloy reinforced Bi-2223 coil is superior to the REBCO coil from a view point of thermal runaway tolerance and permissible temperature rise.
[1] Yanagisawa, et al., SUST075014, 2012.
The 32T all-superconducting user magnet comprised of a REBCO tape pancake-wound dual-coil insert and an LTS multi-coil outsert has been tested at the NHMFL. The magnet protected-quench behavior was simulated using a custom-written Fortran computer code. The simulation results and their sensitivity to the input data are discussed. The effect of insert quench protection system parameters on the protection efficiency was also analyzed. The simulation results are compared with the measurements in the insert coils during deliberate quenches.
Acknowledgement: This work was supported in part by the U.S. National Science Foundation under Grants No. DMR-0654118, DMR-1157490, DMR-0923070 and the State of Florida.
A REBCO pancake coils using a no-insulation (NI) winding technique is received attention. An NI winding technique greatly enhances the thermal stability of REBCO pancake coils, and it is desired to be applied to high magnetic field NMR/MRI magnet, etc. The high thermal stability of NI REBCO magnets was confirmed in many experiments and numerical simulations, even though any accident due to mechanical or thermal factors caused a quench of NI REBCO magnets. However, a new problem arised after a quench when an NI REBCO magnet was operated under a high magnetic field. When NI REBCO pancake coils transitions into a resistive state, the operating current bypasses a turn to adjacent turns in the coil-radial direction. That is an inherent feature of NI REBCO pancake coils. The radially bypassing current flows under a high magnetic field, so that the Lorenz force is generated in the coil-circumferential direction. This circumferential force works to the quenched NI REBCO pancake coils as a torque. The coils or joints may be damaged by unbalanced torque. When NI REBCO pancake coils transition into a normal state, most of the operating currents carry in the radial direction. In cases of a large operating current, the large torque has to be considered to protect from damages. Moreover, the larger bore and/or the larger thickness NI REBCO magnets have, such as a high-field whole-body MRI application, the larger torque is generated. So far, an overcurrent test or a quench test of NI REBCO pancake coils under a magnetic field higher than 10 T has not been reported. Hence, there is no report about unbalanced torque generated in NI REBCO pancake coils. In this paper, we will discuss a risk of unbalanced torque generated in high magnetic field NI REBCO pancake coils after quench.
LTS magnets are typically used and kept at 4K, but when being build or retrofitted they will be at ambient temperature. Cool-down at the factory or installation site can be done using LN2 and LHe, but this is an inefficient process involving a number of operational steps. This paper described how cool-down can be achieved simpler and more efficiently using a closed loop helium gas flow. In this concept no nitrogen gas is introduced in the LHe cryostat, while a temperature of less than 20K will be reached, which will limit the amount of LHe required. The helium gas is cooled by a cryocooler and circulated through the magnet using a high efficiency cryogenic fan. The temperature of this loop will gradually drop from ambient to final temperature. This will give maximum cooling capacity and efficiency of the cryocooler as it is kept at relatively high temperatures as long as possible. The challenge in the design of such a closed loop is the allowed cryostat pressure and connection sizes of each individual magnet design. These tend to be low and small, resulting in high volume flows and large flow losses. In this paper we describe the flow and heat exchange models we have designed to determine the most effective cooling loop for a certain set of parameters for an individual magnet design.
Thermal siphon system is a cooling method for a large scale superconducting magnet system by circulating cryogen through cooling channel. In this paper, a small scale prototype thermal siphon system for single crystal ingot growth magnet is designed based on liquid and gas He circulation. The designed system is tested as a part of design method validation process. The cooling performance of the system is analyzed with experiment. The experiment is conducted in different heat input conditions to investigate different magnet heat input conditions such as AC losses. The system is also tested with two different helium levels to analyze the effect of the amount of cryogen. Finally, a revised topology of the prototype system, which is a candidate cooling system of the single crystal growth magnet product, is suggested based on the test results.
An electron beam ion source (EBIS) is required to fulfill the diverse requirements of proton-beam users facilitating enhanced application. Superconducting magnet is a critical part of EBIS, and cryogenic systems are essential for the design and the operation of the superconducting magnets. Thus, this study demonstrates the development of cryostat of 7 T superconducting solenoid for electron beam focusing in the EBIS system. The proposed cryostat will be used to cool the NbTi coil by using liquid helium. During the full operation of EBIS system, the strong emission of x-ray prevents the easy access to the apparatus. Therefore, through our study, we have realized the development of liquid helium recondensed system. Once the cryostat is filled with coolant, evaporated helium gas will be liquefied again at the recondensing device, which is directly connected to the cryocooler. The design of 7 T superconducting magnet comprises inner and outer diameters of 280 mm and 324 mm, respectively and the height is assigned as 2000 mm. Based on the unique shape of the superconducting magnet, the cryostat also has horizontally long configuration. Cooling margin of cryocooler is precisely calculated to obtain efficient performance of helium recondensation, including heat invasion from conductive and radiative components. Detailed specifications and design considerations of proposed cryostat will be explained through the extended paper.
The oscillating heat pipe (OHP) is a two-phase flow device used for transferring heat without external mechanical power. In this paper, a cryogenic OHP with neon as working fluid for conduction-cooled superconducting magnet is fabricated. The mock-up magnet is cooled down with the cryogenic OHP. The cooling down process of the mock-up magnet is investigated, andthe effect of the liquid filling ratio on the heat transfer characteristics of the OHP is discussed. The result shows that the cooling down process of the mock-up magnet can be significantly accelerated by the presence of neon in the cryogenic OHP. The cryogenic OHP possesses the optimal liquid ratio, which has the maximum the effective thermal conductivity at the same heat input.
Since 1992, the largest Russian cryogenic helium complex of the superconducting accelerator Nuclotron with the cooling capacity of 4000 W at 4.5 K has been operating at JINR in Dubna. The construction of this high efficient cryogenic system included a large number of technical ideas that had never been applied before in the world: the fast cycling superconducting magnets, cooling by the two-phase helium flow, parallel connection of cooling channels of the magnets, «wet» turbo expanders, screw compressors with the outlet pressure of more than 2.5 MPa and jet pumps for liquid helium. In the near future it is planned to construct a new accelerator complex, comprising besides the Nuclotron, a superconducting booster and collider to provide collisions of high-intensity beams of heavy ions up to gold Au+79. The helium cryogenics of the NICA complex will be based on the modernized liquid helium plant for the Nuclotron. The main goals of the modernization are: to increase the total refrigerating capacity from 4000 W to 8000 W at 4.5 K; to create a new system of liquid helium distribution; to ensure the shortest time of cooling down three accelerators rings with the total length of about 1 km and the “cold” mass of 290 tons. These goals will be achieved by means of commissioning of a new 1000 l/hour helium liquefier, “satellite” refrigerators of the booster and the collider. Besides, a new closed-cycle 2300 kg/h nitrogen cryogenic system for producing and distributing of liquid nitrogen and re-condensation of nitrogen vapors will be constructed. New technical solutions in the design of the NICA cryogenic systems will be discussed.
SuperKEKB accelerator consists of 7 GeV electron and 4 GeV positron main rings (HER and LER). The target luminosity of SuperKEKB is 8×10^35 which is 40 times higher than KEKB. After the Phase-1 commissioning operation of the accelerator, the construction of the superconducting final focus system Construction is progressing on schedule. The magnet-cryostats have being installed into the beam interaction region (IR). The QCSL magnet-cryostat, which is placed in the left side to the interaction point (IP), has 25 superconducting magnets including the superconducting corrector magnets, and the QCSR magnet-cryostat in the right side has 30 superconducting magnets. During the beam operation, the magnet-cryostats will have the electro-magnetic force over 40 kN from the particle detector solenoid field. In this paper, we would like to present the design of the magnet components and the required material in the cryostats from the beam operation and the physics experiment, and the construction conditions and the difficulties.
A cryostat for measurements in pulsed high magnetic fields has been designed by employing a small scale helium liquefaction system directly. The helium liquefaction using a 1.5 W @ 4.2 K GM cryocooler can supply more than 800 ml liquid helium per hour. Experimental result shows the sample chamber can be cooled lower to 1.5 K very conveniently and be stable for over 20 minutes. More importantly, the helium liquefaction system is equipped outside the cryostat and away from the magnet which means the vibration of the cryocooler could barely affect the measurements. This cryostat has performed excellently in the electric transport measurement under a 60 T pulsed high magnetic field.
The cryostat with cryocoolers for the Wiggler is capable of keeping helium consumption close to zero(less than 0.03 l/hr in average per year).The wiggler magnet is placed into a bath with liquid helium of 4.2K and all heat emission inside the magnet and heat in-leak outside lead to liquid helium evaporation process. The cryostat chiefly consists of external vacuum housing, 60 K shield screens, liquid helium vessel with a SC multipole magnet inside, vacuum chamber (beam duct) with copper liner inside, four 2-stage coolers with stage temperature 4.2K/60 K. Current leads heat in-leak interception in vacuum using cryocoolers. The helium vessel is suspended with four vertical and four horizontal CFRP(T300) tension rods connected to the external cryostat vessel. These tension rods pass throughout the 60K shield screens and attach to bolts on the external housing walls and are used for precise alignment of the vertical magnet position.
We present a recent successful program to develop a 1.5 Tesla MRI magnet with a maximum helium inventory of less than 50 litres. The Magnet Technology Demonstrator was fully evaluated in a Siemens MRI system and found to deliver comparable imaging performance to a conventional bath-cooled magnet. As well as the development of the novel magnet technology, other key enabling technologies were developed. These included an automatic ramp-down system for protection against power outages and methods for cooling the magnet both within a manufacturing facility and on site.
The program culminated in the successful demonstration of key technologies required to realise the next generation of whole-body MRI magnets with much reduced dependency on scarce and increasingly expensive helium.
For the safe operation of high-temperature superconducting (HTS) maglev vehicles, the liquid nitrogen level of the onboard cryostat should be monitored in real-time during the whole running process. The previous liquid nitrogen level detection method was proposed by using platinum resistance sensors as testing equipment and estimating the liquid level by threshold value judgment. However, the fluctuation of liquid nitrogen level causes great disturbance for the liquid level detection during the running vehicle, which leads to the false level by the previous detection method. To eliminate the interference caused by liquid nitrogen level fluctuation, the state estimation theory of using particle filter algorithm was employed in this paper to process the data. The real-time measurement results illustrate that this method is able to meet the requirements of the liquid nitrogen level detection with high precision, and a simple hardware is valuable for the practical applications of the HTS maglev vehicle.
With the introduction of new wide bore, high field magnets up to 19 Tesla at 150mm and 15 Tesla at 270mm cold bore, new large insert designs have lead to an interest in low vibration measurements with large sample sizes at low temperature. Oxford is developing a new generation of high persistence, high field, wide bore magnets moving on from the current generation of driven magnets requiring improvements with respect to helium consumption.
Large cryostats tend to have large helium consumption and traditional nitrogen shielding cannot be used due to the very high vibration from boiling nitrogen. Even with vapour shielding, there are challenges to reduce helium use and associated vibration. This paper describes the latest developments using high enthalpy shielding with liquid nitrogen pre-cooling. This can dramatically reduce helium consumption without the need for other cryogens and the associated vibration.
A hybrid magnet which is capable of producing more than 40 T steady field has been put into operation eraly this year at CHMFL. The superconducting outsert of the hybrid magnet is wound with Nb3Sn CICC and cooled with forced flow supercritical helium at 4.5 K. The helium cryogenic system mainly includes a helium refrigerator and a cryo-distribution box for cooling superconducting coils, structures, transfer line and current leads. This paper highlights the main features and operating situations of the helium cyrogenic system.
A prototype HTS (High Temperature Superconductor) quadrupole magnet of In-flight fragment separator was developed and successfully tested to generate field gradient of 9 T/m. This paper describes thermal characteristics of the quadrupole magnet. The magnet is composed of four race-track coils and each coil consists of two double pancake coils with ReBCO wires and stainless steel tape for turn-to-turn metallic insulation. The magnet is cooled by circulation of gaseous helium below 40 K instead of the conventional liquid helium cooling because the magnet will be used at an intensive neutron radiation region. The gaseous helium is generated by a separate cooling system composed of a cryogenic blower and three GM cryocoolers. To cool down and remove the heat penetration, helium channels are installed on the surface of coil bobbins and they are connected to the external cooling system. The test was conducted to find out the optimum operational parameters of the cooling system since the coil temperatures depend on the inlet temperature, the pressure and the mass flow rate of gaseous helium. By adjusting the helium pressure (5~8 bar) and the mass flow rate (5~10 g/s), it was possible to keep the magnet temperature below 40 K while the magnet generated the field gradient of 9 T/m by transporting the rated current of 330 A.
Acknowledgment: This work was supported by the Rare Isotope Science Project of Institute for Basic Science funded by Ministry of Science, ICT and Future Planning and NRF of Korea (2013M7A1A1075764)
Repetitive Flat-top Pulsed High Magnetic Field (RFPHMF) could widely be applied to biology, materialogy, iatrology, condensed matter physics, and many industrial applications. Nowadays, the development direction of the RFPHMF focuses on accelerating the magnetic field establishment, elevating the pulse amplitude, extending the pulse duration, enhancing the flat-top precision, boosting the charging frequency. The magnet being energized, the coil resistance skyrocket to 7~10 times bigger due to the temperature rising, hence consuming more energy, jeopardizing the flat-top current precision and the cooling-process/charging-frequency. A three-level charging system has been brought out to acquire the high flat-top precision, high charging frequency magnetic field mentioned above. The structure of the 1st level, a bridge circuit of SCR Diode and IGBT, is used to obtain short rise time by using capacitor to charge the magnet with the cascaded protecting inductor, and to return the current/energy back to the capacitor after the flat-top stage, resulting capacitor’s quick recharging and less heat-production/power-dissipation, thus less cooling process and higher charging frequency. The 2nd level structure, a capacitor with low initial voltage-setting and high capacitance, works as a current stabilizer in freewheeling stage to roughly compensate the decreasing flat-top current. Use the 2nd level capacitor to balance out the whole circuit energy-consumption, so that 1st level capacitor can be recharged to initial setting voltage. The 3rd level structure contains an H-bridge and a transformer parallel connecting to the protecting inductor through another big inductor, is designed to regulate the load current by controlling the applied voltage. A prototype of charging device and its matching magnet that can generate 10T magnetic field with precision of 0.1‰ and charging frequency of 10Hzhas been designed and assembled. The simulation and the entity experiments validated the demanding index.
Programmable logic and integrated technologies, as SoC, FPGA and DSP, have became mature enough to be employed in high performance magnet power supply applications. The use of a configurable mixed current and voltage digital control, combined with adaptable complex algorithms for protections (e.g. quench in superconducting magnets) and auxiliary integration (e.g. transverse flux density in a dipole gap) allows obtaining the perfect fit for each specific magnet application. An entire series of power supplies, coming from a background of particle accelerator applications, has been developed for both bipolar and monopolar operation with high bandwidth (fast fields as in corrector magnets and steerers) and high adaptability with a user-friendly interface and an embedded Linux OS that allows users to implement their own applications directly on the power supply. The use of 24-bit Analog-to-Digital converters and state-of-the-art PWM generation (with possible application of dithering techniques to reach 60-65 ps resolution) enables to obtain fields actuations in the ppm-level range. Some power converters, for specific applications (usually dipoles or superconducting), are equipped with closed-loop zero flux transducers that feeds their signals to temperature-stabilized electronics to reach current temperature coefficient values of 1 ppm/K.
PHiX (Plasma with Helical field initiative eXperiments) is a small tokamak to research MHD phenomena such as restraint of elongated plasma instability and protection of tokamak devices from disruption. The device has 16 toroidal field coils (TF coils) and 10 poloidal field coils (PF coils) magnets. We found that we must drive these coils for more than 5-ms and the response of PF coil current must be less than 1-ms to have clear experiment and control unstable elongated plasma. That is because MHD time scale or the time constant of plasma movement is nearly 1-ms in our device. It is desirable that the TF coil current keep constant during experiments to make it easy to control plasma current, position and shape. To achieve this requirement, we developed a 55kW inverter-driven flywheel motor-generator. Advantages of the MG are comparably-long duration, quick power response, and easy implementation of power control compared with conventional capacitor-type power supply. The duration of the current flat-top was extended to 1-s, which is much longer than those of conventional small devices. To control plasma position and shape, PF coil currents must follow the command value within 1-ms and the power supplies must be able to output enough voltage. We manufactured 900-kVA PF coil power supply system that can excite 10 individual coils. To realize enough voltage, we designed the circuits to reconstruct them to cascaded H-bridge multilevel inverters with floating capacitors. These output are connected in series and capacitors are connected to DC-links of some of H-Bridges. This idea enables to heighten output voltages without extra transformers. In our presentation, we report the details of power supplies such as construction, circuits and control and the tokamak experimental progress and result of PHiX.
High pulsed magnetic field is an important basic research tool, which has been used more and more widely in physics, biology and materials. Higher magnetic field can provide more opportunities for scientist to reveal new phenomena in scientific research. Aiming to achieve a higher magnetic field, Wuhan National High Magnetic Field Center (WHMFC) has designed a power supply system for 100 Tesla magnetic field under existing power supply conditions in April 2015. The magnet of 100 Tesla energized by multi power supply system consists of three coils. The outer coil is energized by a pulsed generator-rectifier connected to battery banks in series. The middle coil and the inner coil are energized by capacitor banks respectively. Coordinated control and stable operation of such complex systems is a great challenge. To ensure safety and reliable operation, control sequence as well as protection system for the power system is designed and developed. A test system with the prototype of three-coil magnet is established at WHMFC. And a series of tests are carried out for hybrid power supply systems, control sequence and protection system. 75 Tesla peak field is reached as the highest magnetic field in the test. Test results presented in this paper show the hybrid power supply system is feasible and operable. And it will be used to energize the magnet for generating 100 Tesla pulsed magnetic field at WHMFC in the summer of 2017.
Acknowledgements: The authors would like to acknowledge the supports of the National key research and development program of China (2016YFA0401702) and the Program for New Century Excellent Talents in University.
A 60T pulsed high magnetic field facility is designed for the study of magnetic material at Xi'an Jiaotong University. The pulsed high magnetic field facility is energized by two 1.2MJ/3.84mF capacitive power supplies. Each supply consists of 24 capacitor banks, a protection inductor, crowbar circuit, dump circuit. To simplify system configuration, two supplies are equipped with one charge unit, one thyristor switch and one switchgear. The magnet wound with CuNb wire reinforced internally with Zylon fiber composit and externally with stainless steel shell is designed to provide 60T/60ms magnetic field in a bore of 26mm. The control system provide integrated charge/discharge procedure and a remote control terminal. The whole system will be installed in May 2017, and the Preliminary test results will provided in the paper.
Acknowledgements: The authors would like to acknowledge the supports of the National key research and development program of China (2016YFA0401702) and the Program for New Century Excellent Talents in University.
With the increasing applications in physics, biology, chemistry and many other basic scientific fields, high-stability flat-top pulsed magnetic field is demanded for a higher field intensity and a lower ripple. To meet this demands, this paper proposes a hybrid power supply to generate a high-stability flat-top pulsed magnetic field at the Wuhan National High Magnetic Field Center. The hybrid power supply which is adopted to energize a dual-coil magnet, consists of an 11 MJ/25 kV capacitor power supply and a 100 MVA generator-rectifier power supply. A coupling transformer is adopted in the circuit to compensate the influence of the mutual coupling between the two coils. To protect the system from the damage of a short circuit fault occurring between the first turns of the inner coil and outer coil, which will produce oscillation voltage with a high peak value and high frequency (45 kV and 776.6 kHz) on the rectifiers, a protection circuit consists of an R-C branch, a diode array and a metal-oxide arrester is presented. The self-adaptive PI controller with the coefficients corrected by back propagation neural network is adopted to reduce the ripple of flat-top. The MATLAB/SIMULINK is used to model and simulate the proposed system, and a 65 T/100 ms high magnetic field with a ripple less than 160 ppm is generated. Acknowledgements: The National key research and development program of China (2016YFA0401702) and the Program for New Century Excellent Talents in University.
High magnetic field technology has played an important role in basic scientific researches. High-stability flat-top pulsed magnetic field can meet the demands of high field intensity and high stability in modern scientific experiments. The higher stability of flat-top magnetic field would be the more benefit to the observation of experimental phenomena (such as specific heat measurement and NMR experiment). In order to reduce the ripple of flat-top magnetic field, an active ripple compensator is presented in this paper for the 50 T dual-coil magnet system at the Wuhan National High Magnetic Field Center. The compensator is composed of a compensation coil and its power supply. The compensation coil, which is put inside the 50 T dual-coil magnet coaxially, is used to generate a magnetic field to compensate the ripple generated by the 50 T dual-coil magnet. The energy to operate the coil is provided by a 16 V/500 F super capacitor. To accommodate the needs of this coil, a PWM full-bridge circuit with variable output and bidirectional energy flow, is designed as the discharge circuit. The active ripple compensator has the advantages of modularization, flexibility and low energy consumption. The simulation model including the generator-rectifier power supply is established on the MATLAB/SIMULINK platform. The ripple of 50 T magnetic field is reduced from 1000 ppm to 100 ppm, which verifies the feasibility of the scheme. Acknowledgements: The National key research and development program of China (2016YFA0401702) and the Program for New Century Excellent Talents in University.
This paper studies the use of a novel high stability of power supply used in superconducting system, this power supply with high stability, low output current ripple characteristics. Also, the slope slew of raising and failing were be change through the firmware in order to satisfy the operation of the system. The superconducting coil wingding has a total length magnetic period of 56.56cm, total magnet length of 478.9cm and vertical (horizontal) magnetic field of 18.7T. The operation principle and steady-state analysis of the proposed converter were discussed. Finally, a hardware prototype system with output current of 320 ampere was constructed in a superconducting laboratory of Taiwan Photon Light Source.
A 100 MVA/100 MJ flywheel pulse generator system with the characteristics of high energy density and good control performance has been developed to energize the pulsed magnet at the Wuhan National High Magnetic Field Center (WHMFC). To realize the flexible, accurate, real-time and safe remote monitoring of the pulse generator system, a set of monitoring system using the total control plus sub-control mode was proposed so that the two sets of 12-pulse rectifier system can be used alone or together. Programmable Logic Controller (PLC) suitable for the industrial control was chosen as the central control system of the total control cabinet, which collected real-time operating parameters of rectifier transformer, direct current sensor, pure water cooler and other supporting facilities, and realized interlocking, protection and other function of electrical rules. High-speed and high-performance Digital Signal Processing (DSP) was chosen as the main controller of the sub-control cabinet to improve the accuracy of the firing angles. In addition, introducing the Complex Programmable Logic Device (CPLD) technology integrated the peripheral digital circuit of microprocessor into a piece of chip, which reduced the complexity of the system external wiring, improved the integration and reliability of the system. The host computer was realized by Monitor and Control Generated System (MCGS) based on OLE for Process Control (OPC) technology, which solved the problem that PLC protocol is not open. The proposed monitoring system has controlled the pulse generator system to energize the 50 Tesla magnet and the outer coil of the 100 Tesla magnet. The result shows that this monitoring system is stable, reliable, and easy to use, and can meet the security, flexibility and visualization requirements of the control system applied to pulsed magnetic high filed facility.
The 45 T hybrid magnet project is developed by High Magnetic Field Laboratory in Nijmegen, Netherlands from an existing 22 MW power supply for its resistive magnet and a new 20 kA current source for the outer superconducting magnet. With 10 V load voltage it requires half an hour to charge to full current. The current source is fed from the 400 V mains and consists of a 12-pulse topology (4x3 pulse) with passive filtering. This will be further detailed in the paper. The new current source will feed the magnet through safety devices that will mostly prevent the superconducting magnet from quenching. These devices will contain redundant DC circuit-breakers opening the current path from the current source and transferring the load current into the parallel connected dump resistor. Further parallel connected with the load is a series connection of dump resistor, DC circuit breakers and semiconductor make switch: the slow dump circuit. Various abnormal and fault scenarios can be dealt with. Coordination in the control of the switches at certain fault levels in one of the power supplies and its protective action will therefore be mandatory to avoid the risk of a possible quench to be minimized. At a positively detected quench or such cases the load current will be transferred within 8 ms into the fast dump resistor at 2.5 kV maximum avoiding any possible damage to the part of the superconductive cable that became normal conductive. A slow dump facility is connected parallel to the load to more slowly reduce the current to zero at 50 V reverse avoiding quenching. Closing the thyristor make switch while opening the fast dump breakers will initiate the load current transfer to the slow dump resistor. In the paper several above mentioned scenarios will be explained.
The requested beam precision of the Facility for Antiproton and Ion Research (FAIR) requires the regular calibration of the main components of the current control system such as the Zero-Flux Direct Current-Current Transducer (DCCT) and the analogue-to-digital converter (ADC) module at a level of 1ppm or better. To reach this goal, a dedicated calibration laboratory is designed and prepared for construction. Due to the requirement to use a power converter in the vicinity of calibration arrangement and the limitation of available space, the calibration laboratory is to be located in the building where the power converters of the beam transfer lines are installed. In order to determine the spurious electromagnetic emissions from these power converters and the associated power distribution system, EMC tests were conducted. On the basis of the results, requirements for the electromagnetic shielding and other EMC mitigation measures were defined. As expected, typical inductive components such as transformers were identified as relevant sources of low frequency magnetic field. Unexpectedly, significant levels of low frequency magnetic field were identified in the planned calibration laboratory when all power converters were turned-off (including their supply cables and filters). This launched a further investigation which led to the conclusion that the 400V supply system in a TN-C (Terre Neutre Combiné) or TN-C-S (Terre Neutre Combiné Séparé) configuration is an additional source of low frequency magnetic disturbances. The paper presents the approach of the EMC investigation, the EMC test results and the conclusions. Measures to reduce electro-magnetic interferences for sensitive instrumentation systems are presented. The authors would like to highlight to the accelerator community the significance of a structured EMC assessment of the EM environment including the design of the power supply configuration in order to minimise the effects of electromagnetic interference in sensitive and complex instrumentation systems.
A thin superconducting solenoid is used to provide magnetic field in the CMD-3 particle detector. For power supply of the solenoid a superconducting fullwave AC/DC rectifier is designed. The rectifier is a current step-up superconducting transformer with two thermally controlled superconducting switches connected to its secondary windings. The CMD-3 solenoid is indirectly cooled, so the indirect cooling method is used for the rectifier. The transformer and switches are mounted on the outer surface of the stainless cylindrical vessel. They face the protection vacuum of the CMD-3 cryogenic system. The vessel is filled with liquid helium, so the rectifier is cooled via thermal conductivity of the vessel’s wall. Placing the rectifier outside of the liquid helium bath allows avoiding the use of vacuum tight high current connectors for current leads from the rectifier to the solenoid. The rectifier is designed to provide charging the solenoid, long-term magnetic field stabilization and discharging the solenoid. At the bench tests with dummy coil the rectifier output current up to 1600 A had been achieved. The solenoid operational magnetic field is 1.3 T with 860 A current. The rectifier charges the solenoid to this field within 7 hours. Achieved long-term stability of the field is 2×10-5 Т. The rectifier has been demonstrating good reliability since 2010, when the magnet system of the CMD-3 had been commissioned. Design, test results and performance of the rectifier are reported here.
High pulsed magnetic field is becoming more and more widely used in physics, biology and materials. For serving scientific experiments better, a power supply system for 100 Tesla magnetic field is designed at Wuhan National High Magnetic Field Center (WHMFC). In the preliminary design, the 100 Tesla magnet consists of three coils in a coaxial structure. The outer coil is powered by pulse-rectifier generator in series to battery banks. The middle coil and the inner coil are energized by capacitor banks separately. Each coil is fired in designed sequence. Because of the magnet is a multi-coil system with a strong-coupling structure, the current of the outer coil will drop when the middle coil fired. And the current drop will cause adverse effects that the burden of the power supply and the stress of magnet increase. Based on analysis of the mathematical model for power supply circuit, a modified design for power supply system is proposed which is connecting a coupling transformer to the outer coil and the middle coil for the compensation of the current drop. Parameters of the coupling transformer and the requirements of power supply are also discussed. In order to verify the feasibility of the scheme, the simulation model based on the MATLAB/ Simulink platform is established and the tests are carried out on the prototype of three-coil magnet. Both simulation and experimental results verify the feasibility of the proposed design and the effectiveness of the compensation method.
Acknowledgements: The authors would like to acknowledge the supports of the National key research and development program of China (2016YFA0401702) and the Program for New Century Excellent Talents in University.
For the upgrade of the booster of the European Synchrotron Radiation Facility in France, an IGBT based ramping current injection system for the dipole electromagnets has been developed, delivered and commissioned. The main function of the dipole power supply is to drive the necessary voltage for an accurate 4 Hz triangular current wave injection in the electromagnets with peak value of current 1600 A. The inductance of the dipole magnets is 180 mH and their ohmic part 0.56 Ohms. The maximum peak to peak voltage ripple at the specified 6.4 kHz ripple frequency is required lower than 40 V peak to peak which leads to extremely low current ripple. Special requirement for the 4 Hz ramped current injection system was the design for reliability of 90 million load cycles before maintenance. The dipole power supply has been realized by 2 synchronized identical water-cooled units in series connected. Each unit is realized by a 5-level neutral point clamped topology with a passive output filter and it is fed by a 12-pulse rectifier system. FPGA digital control is implemented for the controlled voltage source which results to precise high current injection in the dipole magnets. The synchronized operation of the two units offers in total 9-level output voltage which, in combination with the oversampled digital feedback control, leads to high dynamic performance. The ramping injector power supply also offers IGBT switching frequency 4 times lower than the ripple frequency in the magnets and proper thermal behavior in its nominal operation for high power cycling capability. Test results are available.
In Wuhan National High Magnetic Field Center, a new explosive DC breaker switch based on the pulsed electromagnetic forming (EMF) technology is developed to shut down the Battery Bank power supply for protecting the long pulsed magnetic field system when terrible fault happens. The switch is reformed from the aluminum wire electrical explosive switch of the Laboratoire National des Champs Magnétiques Intenses in France. The new DC breaker switch consists of pulsed magnet (EMF coil), aluminum tube (the main contact of DC breaker) and its supporters. The switch uses pulsed magnetic field to apply repulsion produced by induced eddy current to expand the aluminum tube, which can be broken at the weaknesses of V-shaped slots in a very short time. The concept of repulsion is based upon inducing currents flowing in the contrary directions in the pulsed magnet (EMF coil) and in the aluminum tube, which, according to Ampere law, results in repulsion forces between the pulsed magnet and the tube. By combining the advantages of the aluminum wire electric explosive DC breaker and the electromagnetic forming (EMF) technology, the analytical model based upon the solution of Maxwell is built by the software COMSOL Multiphysics to simulate the distribution of magnetic flux, magnetic force, tube deformation and their interactions. Both simulation and primary experimental results show that the design of the new DC breaker with compact volume and easy maintenance is feasible. In addition to the pulsed high magnetic field facility, the breaker can also be applied to numerical potential industrial fields.
Pulse generator is one of the common power supply for flat-top pulsed magnetic field for its advantages of large energy storage and flexible control. However, some characteristics of pulse generator, such as nonlinearity and time-varying, limit the effect of measures by optimizing control strategy to improve the stability of flat-top. On the base of pulse generator power supply system for flat-top pulsed magnetic field at Wuhan National High Magnetic Field Center (WHMFC), a scheme of parallel active regulator composed by cascade H-bridge converter is proposed in this paper. PI feedback control with Carrier Phase Shifted Sinusoidal Pulse Width Modulation (CPS-SPWM) is adopted by the regulator to adjust the ripple during the flat-top. A 50 T/140 ms flat-top pulsed magnetic field with the ripple less than 100 ppm is achieved through system modeling and simulation. An optimal control strategy combining selective PI control and repetition control is proposed to restrain the circulating current between pulse generator and active regulator. Selective PI control is designed for the regulator that the ripple at flat-top is divided into two parts by 20 Hz low pass filter. One part with the frequency under 20 Hz is regulated by ripple tracking control and the other is regulated by PI control. Repetition control is used for the pulse generator to optimize the triggering angle of the rectifier. In order to verify the effectiveness of the optimal control strategy for high-stability flat-top pulsed high magnetic field with the active regulator, experimental data about the triggering angle of rectifier is employed into the simulation model, and the result shows that circulating current between pulse generator and active regulator has been suppressed effectively.
Acknowledgements: The National key research and development program of China (2016YFA0401702) and the Program for New Century Excellent Talents in University.
A magnet composed by three coaxially nested coils has been developed to generate 100 Tesla pulsed magnetic field at the Wuhan National High Magnetic Field Center (WHMFC). The flywheel generator system has great energy storage density and can control the waveform of the magnet current, therefore the outer coil is energized by a 100 MVA/100 MJ flywheel pulse generator. To reduce the magnet heat and solve the generator output voltage overshoot, the power supply system works in the inverter state after rectification. As the pulse generator power system has rich harmonics and unbalanced three-phase voltage, the speed of adjusting inverse angle and the value of the maximum inverse angle is critical to avoid the inverter failure. In this paper, an appropriate speed of adjusting inverse angle and the optimal inverse angle are derived in detail, which is based on the simplified schematic and some assumptions. Considering that the spike voltage caused by the change of inverse angle affects the safety and stability of the power system, a method of reducing peak voltage by changing excitation voltage is proposed, which restrained peak voltage effectively. When the inverter time exceeds the protection value, the switchgear trips and cuts off the power supply with the magnet into the freewheeling state. simulations and experiments show that this proposed operation mode including rectification, de-excitation, inverter and tripping can meet the power supply needs of the outer coil, improve the efficiency of the pulse power and ensure the safe and stable operation of the system.
A facility, which will generate 100 T pulsed high magnetic field, is under development recently at Wuhan National High Magnetic Field Center (WHMFC). The pulsed magnet is composed of three coils, and driven by four power supplies of three types. The outer coil is driven by the battery bank of 1620 lead-acid batteries connected in series with the 100 MVA / 100 MJ pulsed generator, The middle and inner coils are respectively energized by 1.6MJ and 18MJ capacitor banks. In order to control synchronous discharging of different types of power supply, an Integration Control and Data Acquisition System (ICDAS) has been developed. The ICDAS is developed based on the NI CompactRIO system, which adopts three-layer structure. The programmable FPGA is used as the lowest level with the characteristics of fast response. The control logic and strategy implemented on FPGA provides timing triggering signals, failure protection and data acquisition. The real-time layer serves to perform data collection, storage and conversion. Human machine interface (HMI), which accepts parameter inputting and displays the experimental results, is achieved on PC layer. A real-time communication system is established based on TCP/IP protocol between the HMI and the existing control subsystems of the power supplies, by which the HMI sends control command to the control subsystems and monitors the status of the subsystems to achieving the coordinated control sequences of the four power supplies. The ICDAS has been put into practice in the 100T facility, and implemented synchronic control and data acquisition of three-type power supplies. A magnetic field of 70 T has been achieved and the discharge experiment of 100 T is planned to be carried out this year according to the work plan of WHMFC.
The Grenoble steady magnetic field facility is one of the four high field facilities part of the European Magnetic Field Laboratory. The upgrade of the Grenoble facility has started in 2013 and aims in a first phase at increasing the electrical power from 24 to 30 MW and to develop the high field magnets accordingly. A new 18 MW power converter has been made available to users in 2017 and replaces two of the four 6 MW units. It will be used during the next three years at a reduced 12 MW power imposed by the current power transformer. 18 MW will be available after the commissioning of a new 60 MVA transformer. In 2017 the flowrate pumped from the nearby river will be increased from 1400 to 2000 m3.h-1. A new 36 MW heat exchanger will be installed at the interface between the primary circuit and the deionized water closed loop. The last step will consist of upgrading the 2 remaining 6 MW units. At the end of this operation, 36 MW should be available to feed the magnets. In parallel, the LNCMI is developing a new compact polyhelix insert capable of absorbing 18 MW instead of 12 MW. This insert needs to have the same outer diameter as the 14 helix insert currently in operation so as to fit in existing external bitter magnets. To optimize the energy costs incurred by this upgrade, studies are being conducted to take advantage of the heat generated by the magnets to heat neighboring buildings. The performance of the new power converters will be assessed from the detailed analysis of the stability of the magnetic field and the electrical currents.
The JT-60SA experiment will be the world’s largest superconducting tokamak when it is assembled in 2019 in Naka, Japan (R=3m, a=1.2m). It is being constructed jointly by institutions in the EU and Japan under the Broader Approach agreement. Manufacturing of the six NbTi equilibrium / poloidal field coils, which have a diameter of up to 12m, has been completed. So far 14 of the 18 NbTi toroidal field coils, each 7m high and 4.5m wide, have also been manufactured and tested at 4 K in a dedicated test facility in France. The first three of four Nb3Sn central solenoid modules have been completed, as have all of the copper in-vessel error field correction coils. Installation of the toroidal field magnet, around the previously welded 340° tokamak vacuum vessel and its thermal shield, started at the end of 2016. The TF magnet will in turn support the EF and CS coils.
This presentation will summarise some of the highlights of the JT-60SA magnet system design and manufacturing achievements as well as briefly describing the tests performed on the coils and the status of their assembly.
The construction of a full-superconducting tokamak referred as JT-60 Super Advanced (JT-60SA) is in progress under the JA-EU broader approach projects. The magnet system of JT-60SA consists of 18 toroidal field (TF) coils, 4 modules of central solenoid (CS) and 6 equilibrium field (EF) coils.
The diameter, the height, the number of layers and the number of turns of CS module are 2.0 m, 1.6 m, 52 layers and 549 turns, respectively. GKG (Glass-Kapton-Glass) tape was wound around conductor as a turn insulation of CS module. Vacuum pressure impregnation (VPI) process was selected to fix the insulation tapes for CS module of JT-60SA.
During VPI process, CS module needs to be pressed in order to increase the bonding strength between turn insulation and conductor. The total insulation thickness of CS module is very thick of about 70 mm because of large number of layers. It was considered that the insulation thickness was shrunk during VPI process under the pressurized condition and traditional rigid jigs could not deal with this large shrinkage.
We conducted the VPI test using stacked insulation tapes to measure the amount of shrinkage. Amount of shrinkage was evaluated as 15mm for JT-60SA CS module. Displacement of 15mm was too large for traditional rigid jigs to be used for VPI process. We developed jigs with moving system and modified procedure of VPI process. VPI process of CS module was successfully performed, even though there was large shrinkage, by using developed jigs and modified procedure.
In this paper, result of VPI test, developed jigs and modified procedure for VPI of CS module will be described.
In the framework of Broader Approach program for the early realization of fusion with the construction of JT-60SA tokamak, ENEA has to provide 9 of the 18 TF coils of JT-60SA magnet system. The supply has been subsequently increased to include the procurement of an additional TF coil for spare purposes. The production of the spare coil started in 2016, after the supply to ASG of the corresponding six unit lengths of cable in conduit conductors procured by ENEA through a contract with ICAS consortium in 2016.
The principal milestones of the six year contract with ASG Superconductors are here summarized: at the end of September 2013 the completion, of the engineering phase and of the qualification activities related to winding operations, started production phase. In the course of 2014, the first two winding packs (WP) constituted by 6 double pancakes have been manufactured, impregnated and successfully tested. In 2015, the rest of WP production has been completed and the final integration of the first WP in its casing components set started. In 2016, six WPs have been inserted in their casing components sets and in 2017 the rest of the manufacturing operation are going to be completed.
This paper provides an overview of the contract that ENEA signed with ASG Superconductors for this supply. Also main electrical, geometrical and fluidic results of the TFC completed so far are reported in order to give a general assessment of the performances and functionality of the coils.
JT-60SA is a fusion experiment which is jointly constructed by Japan and Europe and which shall contribute to the early realization of fusion energy, by providing support to the operation of ITER, and by addressing key physics issues for ITER and DEMO. In order to achieve these goals, the existing JT-60U experiment will be upgraded to JT-60SA by using superconducting coils. The 18 TF coils of the JT-60SA device are provided by European industry and tested in a Cold Test Facility (CTF) at CEA Saclay. At the summer 2017, 15 TF coils will have been successfully tested at the nominal current of 25.7 kA and at a temperature between 5 K and 7.5 K. The main objective of these tests is to check the TF coils performances and hence mitigate the fabrication risks. These tests allowed checking a certain number of performances of the TF coils: DC/AC insulation, cooling down characterization, RRR of the conductor, pressure drop in the winding pack and temperature margin against a quench. This paper will show the testing program progress and give an overview of the main experimental results obtained during these tests. The main performances of each coil will be summarized, analyzed and discussed in the light of the expected TF coils performances.
The determination of coupling losses induced in cable-in-conduit conductors (CICCs) when subject to time-varying magnetic field is a major issue commonly encountered in large fusion tokamaks (e.g. JT-60SA, ITER, DEMO). The knowledge of these losses is crucial to determine the stability of CICCs but is yet difficult to achieve analytically in a satisfying way given the specific and complex architecture of these conductors: superconducting and copper strands twisted together in several helical cabling stages. Numerical modeling however, by THELMA and JACKPOT, already provided solutions. In an attempt to ease the resolution of this problem, we have previously presented a theoretical generic study of a group of strands twisted helically together (representative of a single cabling stage of a CICC) and analytically derived the expressions of coupling losses using the electrical and geometrical properties of the conductor. We have now up scaled this analytical study to a two cabling stages conductor and derived the expressions of its time constants and partial shielding coefficients which, in the Multizone Partial Shielding (MPAS) model, are used to model coupling losses and determined experimentally (e.g. JT-60SA TF conductor). We derive these coefficients as functions of the effective electric and geometrical parameters of the conductor and present an iterative method to model coupling losses in a N cabling stages CICC. In a second part, the real strand trajectories of JT-60SA TF conductor obtained via X-ray tomography are used to find the effective geometrical parameters needed in our modeling, and the experimental coupling losses of this conductor determined from tests within Sultan facility enables us to apply our modeling on a real case to discuss its validity. Furthermore, we compare our results to these of THELMA and JACKPOT numerical modelings on specific geometries. This modeling opens new perspectives for the study of CICCs (e.g. stability and dimensioning).
Japanese researchers succeeded in developing a 1.02GHz NMR (24T) in 2014. The next field target is a 1.3GHz (30.5T) and we have commenced designing a high resolution 1.3GHz LTS/HTS NMR magnet, operated in persistent current (PC) mode. The basic concept and relevant technical problems are identified in this paper.
To reduce the magnet size, high current density HTS coils are used that generate as high as 23T, enabling a compact magnet as small as a 800-900MHz LTS NMR magnet. Two probable designs have been examined so far; one uses reinforced-Bi2223 coils and the other REBCO/reinforced-Bi2223 coils. From a viewpoint of screening current, the former is better; while from a viewpoint of PC mode operation, the latter is preferred. The stress criteria are 350MPa in hoop stress and 50MPa in axial compressive stress; they are below the tolerance limit of the conductor. Numerical simulations of the screening current induced field are being developed; the magnet design will be modified later based on the simulation results. The RT bore may be enlarged to install stronger RT shims and ferromagnetic shims. The magnet will be self-shielded by a shielding coil for being installed in the NMR facility of RIKEN. 4K pulse tube cryocoolers will be installed to reduce helium consumption. We recently succeeded in developing a new type of superconducting joint between REBCO conductors, which may be available for use on this magnet. However, more investigations must be made in this regard. More details will be presented at the conference.
This work is supported in part by the MEXT. The authors would like to thank members of the HTS Magnet Technology Working Group in a program of the MEXT for their technical comments on the designs. Part of experimental data to be presented was obtained in the S-innovation Program of the JST.
In 2005 the Committee on Opportunities in High Magnetic Fields (COHMAG) issued a challenge to develop a 30 T high-resolution NMR magnet. In response, the National High Magnetic Field Laboratory (NHMFL) is investigating all three commercially available high-temperature superconductors (HTS) including REBCO, Bi-2212 and most recently, a reinforced Bi-2223 conductor supplied by Sumitomo Electric, designated Type HT-NX. Recent investigations of Type HT-NX conductor at the NHMFL and by others suggest that operation at stress above 400 MPa, and strain above 0.7% may be feasible. The next steps in our program are reported here, and include fabrication of coils made with conductor piece lengths above 300 meters and testing of those coils at their stress limit at 4.2 K in a 16 Tesla background field. Findings from experience developed during fabrication and testing of these coils are reported. Some details of the coil technology development are presented, including continuous layer winding, splice joints and reduced current density ‘notch’ windings. For long-term operation, the conductor needs to tolerate repeated cyclic loading. Results from cyclic fatigue measurements of the conductor, and of a test coil are reported, along with estimations made of load and cycle limits.
We have developed RE-Ba-Cu-O (REBCO; RE=rare earth) superconducting magnet operated in subcooled liquid nitrogen (68 K). The superconducting magnet is a stack of six double pancake (DP) coils. Each DP coil was made of a REBCO coated conductor. The conductor was insulated by polyimide tape wrappings. The width and thickness of the insulated conductor were 4 mm and 0.2 mm, respectively. The outer diameter, inner diameter, and height of the coil stack are 107 mm, 57 mm, and 68 mm, respectively. The number of turns was 770. Ferromagnetic SS400 flanges were used on both ends of the magnet to improve performance, because they changed the field profile to reduce radial component of the magnetic field, which corresponds to perpendicular component for conductor. The magnet generated 1.6 T at 67 K for 1 hour stably. It generated 2.1 T at 66 K for 1 minute. Temperature dependence of the coil performance, the effect of ferromagnetic flanges, and applicability for NMR will be discussed.
Acknowledgement: This work was supported by JSPS KAKENHI Grant Number JP26288012.
Since 2014, the Korea Basic Science Institute (KBSI), the Korea Institute of Machinery and Materials, the National High Magnetic Field Laboratory, and the SuNAM Co., Ltd. have been on international collaboration to develop a 9.4 T (400 MHz $^1$H frequency) 100 mm winding-diameter metal-clad no-insulation all-REBa$_2$Cu$_3$O$_{7-x}$ (REBCO, RE = Rare Earth) high-resolution NMR magnet cooled by conduction. Once successfully completed in 2019, the magnet will be installed at the KBSI to serve as a new 400 MHz solid-state NMR user magnet. Prior to completion of the 400-MHz NMR magnet, a 3 T 100-mm metal-clad no-insulation all-REBCO “Demo” magnet was fabricated and tested, demonstrating that the approach of “metallic cladding” enables significant reduction in charging delay of a no-insulation magnet without losing its self-protecting feature and thus faster field shaking that is efficient for mitigation of screening current induced field. This paper presents the recent progress in development of the 9.4 T NMR magnet.
This work was supported by KBSI grant (D37611) to S.-G.L. funded by the Korea Basic Science Institute (KBSI).
Nowadays, remotely-controlled catheter ablation has emerged as a novel approach to reduce fluoroscopy exposure and provide stable and reproducible catheter movement during in cardiac surgeries for arrhythmias. A remote catheter magnetic navigation system (MNS) which provides real-time navigation of the catheter in the heart is under development in IEE. The catheter navigation system consists of eight magnets aligned spherically, which generate the dynamically shaped magnetic field around the heart of the subject, about 15 cm3 region with a maximal uniform field of 0.2 Tesla. An X-ray generator is mounted underneath the subject’s torso while the image detection system is above the subject’s torso. Eight four-phase power supplies, which excite the eight magnets to create the needed magnetic field in time, are controlled by a programmed navigation software via a joystick providing the console. Different from CGCI, the magnetic field in our MNS is homogeneous in the navigation region, which only exerts sufficient torque on the ablation catheter tip, while the push/pull of the ablation catheter is carried out by another special device, with a stepping motor to push or pull the catheter. The navigation algorithm, which determines the performance of the system, is the soul of the catheter magnetic navigation system. In this article, how the navigation algorithm works is firstly introduced, and then four navigation algorithms are proposed and compared, and finally a navigation algorithm with simplicity and no dead zone in spherical coordinate system is chosen. Preliminary test results show that this navigation algorithm has good practicability and robustness and thus can be applied to the remote catheter magnetic navigation system.
A project to develop fundamental technologies for accelerator magnets using REBCO coated conductors is currently underway funded by the Japan Science and Technology Agency (JST).
In this project, an FFAG (fixed field alternating gradient) accelerator for the carbon cancer therapy system is one of the primary applications. In the first step of this project, REBCO coils with complicated winding shapes were fabricated and a reduced-size test magnet was developed to verify the winding technology required for the HTS accelerator magnets. In the following stage, there are plans to develop an another experimental REBCO magnet for the performance evaluations in the beam line of the HIMAC (Heavy Ion Medical Accelerator in Chiba) at NIRS (National Institute of Radiological Sciences). This development has two main objectives; demonstration of beam guiding characteristics and stability verification of the magnet against beam loss. For these experiments, a cryocooler-cooled magnet with REBCO coils has been developed to generate dipole field in the room temperature bore. The magnet consisting of multiple REBCO pancake coils with racetrack shapes was designed. The coils were designed to generate a peak field of 2.3 T at the beam orbit and also designed to meet the target value of the field accuracy. A cryostat structure and a layout of the coils have been studied to verify the stability against beam loss as compared with the Monte Carlo simulation. In the experiments, magnetic field distribution in a beam duct will be also evaluated to reveal the effect of the magnetization behavior of coated conductors. This paper describes design and fabrication results of the REBCO coils, magnetic field calculation, and simulation of ion beam transport in the dipole field.
Acknowledgements
This work was supported by the Japan Science and Technology Agency under the Strategic Promotion of Innovative Research and Development (S-Innovation) Program.
A high field twin-aperture dipole magnet is under development as the key technologies R&D for high energy circular colliders like SPPC. The magnet is designed with combined Common-coil and block-type configurations. The main field is 12 T with 20% operating margin at 4.2 K. The aperture diameter is 30 mm. The fabrication and experimental test is divided into 3 steps: 1) 4 flat racetrack NbTi coils and 2 flat racetrack Nb3Sn coils are firstly fabricated and tested, to evaluate the fabrication process and stress management of Nb3Sn coils. 2) 2 more Nb3Sn coils are fabricated and tested together with the 1st 2 Nb3Sn coils, to provide 12 T main field in the top and bottom apertures with the diameter of 20 mm. 3) 2 racetrack ReBCO coils with flared ends are fabricated and inserted into the 4 Nb3Sn coils, to provide 12 T main field in the top and bottom apertures with the diameter of 30 mm. The main design parameters, structure, fabrication process and preliminary test results of the magnet will be presented.
In the framework of the EuroCirCol project the high field accelerator magnet design work package 5 focuses on double-aperture dipole magnets made of Nb3Sn conductors and providing a field of 16 T in a 50-mm aperture. Three options are considered: block-coils, common-coils and cosine-¬theta, the workload being shared between several research institutes. All options are explored and compared based on the same assumptions, in particular in what regards the conductor performance, operating temperature and margin. This work describes the status of the block-coil design. A 2D electromechanical analysis in a double aperture configuration is presented as well as a 3D investigation in a single aperture configuration towards the manufacturing of a prototype.
EuroCirCol is a conceptual design study for a post-LHC research infrastructure based on an energy-frontier 100 TeV circular hadron collider. In the frame of the high-field accelerator magnet design work package of this study, the feasibility of a 16-T dipole in common coil configuration is being studied. This paper shows the electromagnetic calculations performed to achieve the required field quality while minimizing the superconductor volume and taking into account the input parameters and assumptions of EuroCirCol study. FEM models have been used to analyze the stress distribution and deformations under the large Lorentz forces due to the very high magnetic field. Several iterations have been necessary to obtain a feasible magnet design. 3-D electromagnetic calculations are also included in this paper.
Acknowledgments: This work has been partially supported by the European Union's Horizon 2020 Research and Innovation Programme under grant No. 654305, EuroCirCol project.
After LHC will be turned off, a new accelerator machine will be needed in order to explore unknown high-energy Physics regions. For this reason, the project FCC (Future Circular Collider) has started at CERN, with the target of studying the feasibility of a very large hadron collider with 50 TeV proton beams in a 100 km circumference. The EuroCirCol project is part of the FCC study under European Community leadership. In particular, it has the outcome of producing a conceptual design of the FCC within 2019. One of the main activities is the development of a superconducting dipole able to produce a bore field of 16 T, in order to bend the beams within energy and size constraints. Here we present the conceptual design of a Nb3Sn cosθ dipole layout, in a double-aperture configuration (LHC style). We show that it is possible to produce a bore field of 16 T with a good field quality, with reasonable assumptions on the conductor features, and with a reasonable amount of cable. A bladders and keys mechanical structure is also presented, proving that the electromagnetic forces can be maintained, keeping the stress within the coils under a safe limit. Finally, we present a preliminary quench study, showing that the magnet can be protected using well-known technologies.
The US HEP Magnet Development Program is developing accelerator insert coils based on REBCO coated conductors. These insert coils will operate in high dipole or quadrupole background fields and enhance the field generated by the outsert coils made of Nb$_3$Sn or NbTi conductors. The inserts are of canted $\cos\theta$ (CCT) design configuration, which effectively intercepts the accumulation of azimuthal stress that can potentially damage the conductors. Through the collaboration with Advanced Conductor Technologies, we use the CORC® round wire due to its potential to offer high engineering current density in a mechanically and magnetically isotropic conductor form. The design and fabrication of the CORC® CCT dipole insert coils is presented. These coils were also tested at 77 K and 4.2 K in self-field, and we report on the coil performance including quench current and magnetic field measurements in the coil aperture.
The luminosity upgrade of the Large Hadron Collider at CERN requires the installation of additional collimators in the dispersion suppressor regions of the accelerator. Amongst other things, the upgrade foresees the installation of one additional collimator on either side of IP 7 at the location of existing main dipoles that will be replaced by shorter and more powerful dipoles, and of one additional collimator on either side of IP2 at the location of existing empty cryostats. This paper describes the design and the construction status of the first full-length prototype of the 11T dipole magnet, which is needed for IP7. This magnet features a two-in-one structure, like the LHC main dipole, impregnated coils made of Nb3Sn conductor, an inner bore of 60 mm and a magnetic length of about 5.3 m. Two 11 T magnets are needed to replace a 15-m long MB. A by-pass cryostat placed in between the two magnets allows creating a room temperature space for the additional collimators. The magnet is designed to provide the same integrated field as the MB at nominal field. However, due to the difference in transfer function at lower field, a correction by means of a trim current as been considered. A full length prototype is currently under construction at CERN with the goal of developing the manufacturing and inspection procedures prior to launch the series production. For this, new tooling has been developed and optimized during the fabrication of fully representative practice coils. This paper describes the main manufacturing steps and corresponding quality indicators which will be used to monitor the series production. Finally, the production and installation schedule will be presented.
For the upgrade of the LHC a few 15 meter Nb-Ti main dipole magnets are foreseen to be replaced by two 11 T Nb3Sn dipoles, 5.5 meter long each. A series of model magnets has been produced to verify the design choices that are important for the prototype and series production. A fourth and fifth 2 meter single aperture model and a second double aperture model coil were produced, assembled and tested. In this paper the cold powering tests of the newly tested single aperture models and double aperture model will be presented and the results will be compared with the previous models. Special attention is given to the upper limit of the magnet powering which was found to be in the mid plane for some of the models.
The U.S. Magnet Development Program is developing Canted-Cosine-Theta (CCT) magnet technology for future high field accelerator magnets. The CCT concept prevents Lorentz force accumulation by placing turns within precision-machined grooves that are separated by ribs and a spar that intercept forces, sustainably reducing the stress in the conductor. With other non-stress managed coils, now approaching the 200 MPa limit, some form of force interception like the CCT will eventually be required in future high field magnets. CCT4 is the fourth in a series of CCT dipole magnets that have been designed, built, and tested at the Lawrence Berkeley National Laboratory. The design of this two layer, 1 m long, 90 mm bore, Nb3Sn dipole is to demonstrate achieving a 10 T bore field plateau. The methods used in fabricating and assembling this magnet will be described and test results presented.
This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
US Magnet Development Program (MDP) is developing a 15 T Nb3Sn dipole demonstrator for a post-LHC pp Collider. The magnet design is based on 60-mm aperture 4-layer shell-type coils, graded between the inner and outer layers to maximize the magnet performance. An innovative mechanical structure based on aluminum IC-clamps and a thick stainless steel skin was developed to preload brittle Nb3Sn coils and support larger Lorentz forces at high fields. To study mechanical properties of this structure as well as to optimize the magnet assembly and coil pre-load procedures, the structure was assembled with aluminum cylinders serving as “dummy” coils. These cylinders were instrumented with strain gauges to monitor radial and azimuthal and axial stresses during structure pre-loading. This paper describes the design of the 15 T dipole demonstrator, magnet fabrication status, and mechanical model test results.
Fermilab, in collaboration with CERN, has developed a twin-aperture 11 T Nb3Sn dipole suitable for the high-luminosity LHC upgrade. During the 2012-2014, a 2-m long single-aperture dipole demonstrator and three 1-m long single-aperture dipole models were fabricated and tested at FNAL Vertical Magnet Test Facility. Collared coils from the two 1-m long models were then used to assemble the first twin-aperture dipole demonstrator. This magnet was extensively tested in 2015-2016 including quench performance, quench protection and field quality. The paper reports the results of measurements of persistent current effects in the single-aperture and twin-aperture 11 T Nb3Sn dipoles and compares them with similar measurements in previous FNAL magnets.
The CCT (Canted Cosine Theta) Technology has been studied for its suitability for an FCC main dipole in terms of magnetic and mechanical performance, electro-thermal protectability, as well as efficiency. In this paper we present lessons learnt from our search for efficient CCT solutions by means of 2-D magnetic and mechanical simulations, discuss the 3-D periodic mechanical model, as well as 3-D electromagnetic analysis of the end regions. Temperature and voltage distributions during a quench under simplifying assumptions are discussed. Eventually, we present quench propagation in CCT-type high-field magnets, and how it may impact quench detection when compared to classic cosine-theta coils. Several new insights into efficient CCT design could be gleaned from these types of analyses and are summarized.
A HTS linear synchronous motor prototype that could be used as the traction system of high speed railway was demonstrated in our laboratory. The stator was made of traditional ferromagnetic yoke and three-phase copper windings. To control the three-phase travelling magnetic field of the stator, a frequency-variable convertor was applied to the system. Different from the permanent magnet mover of traditional synchronous motor, the secondary was assembled by YBCO-coated conductor which has powerful ampacity to create high-intensity magnetic field. The YBCO coils were electrically connected in series and were injected dc currents to behave as magnets. To take a comprehensive study of the developed HTS linear synchronous motor, a finite-element model was established to simulate its thrust and normal force which are the key factors for traction. To validate the simulation model, we have developed a three-dimensional force-measuring system. A three-dimensional force sensor was used to observe the thrust and normal force of the HTS linear synchronous motor under different conditions. As the key parameters, the trust and the normal force of the linear synchronous motor play an important role in the traction system because the speed and the load-ability are the key factors for railways. In this paper, the combination of the finite element method (FEM) and experiments presents the mechanical properties of the HTS linear synchronous motor prototype and provides some references for optimizing.
A novel Permanent-magnet Machine with Counter-rotating Dual Rotors (PMCDR) is proposed in order to improve operation performance of underwater vehicle anti-rotation propulsion system. It can be substantially simplify system structure, decrease volume, reduce mass and cost, moreover, improve reliability without brush and slip-ring. The idea and principle of electromagnetic design are provided in order to meet power angle characteristic corresponding to uniform or similar between Inner Rotor Permanent-magnet Machine Unit (IRPMU) and Outer Rotor Permanent-magnet Machine Unit (ORPMU). Magnetic field, Stator yoke flux density , air gap flux density, inductance, no-load back-EMF and torque angle characteristic are obtained through the finite element method. A prototype has been designed, built, and tested. The method of detecting no-load back-EMF with search coils is proposed. The validity is verified by FEA results and experimental measurements.
The flux-reversal linear permanent magnet machines (FRLPMs) have the features of high thrust density, high efficiency and robust stator structure, which make it a suitable solution for linear traction motors, wave energy generators and linear servo motors. But the FRLPMs suffer from the doubly-salient structure and thus it is hard to further improve the flux-linkage and the thrust density of the machine. In this paper, in order to improve the thrust density of the machine, a novel flux-reversal linear permanent magnet machine with consequent-pole permanent magnets and high-temperature superconducting (HTS) bulks is proposed. The permanent magnets (PMs) are mounted on the teeth top of the mover and the HTS bulks are mounted on the stator slot, between every two adjacent stator teeth. Only half of the teeth top of the mover is inset by the PM and all the PMs have the same polarity, which is so-called consequent-pole PMs. The HTS bulks can shield the flux leakage and strengthen the modulation effect of the stator teeth. Moreover, the consequent-pole structure can reduce the usage of PMs and further improve the flux-linkage of the armature windings. In other words, the flux density of the machine can be improved with the combination of consequent-pole PMs and HTS bulks, which results in the improvement of the thrust density. The analytical expressions of magnetic motive force (MMF) excited by the PMs, the air-gap flux distribution and the back electric motive force (back-EMF) will by derived in the paper. Finite element method (FEM) will be employed to verify the superiority of the proposed machine. It can be seen from the FEM results that the thrust density of the proposed FRLPM can be improved by 31% compared to the regular FRLPM.
For the past few years, notable progress has been made in the no-insulation (NI) high temperature superconductor (HTS) magnet technology. Electromagnetic (thus fast) quench propagation, the key mechanism for the "self-protecting", has been demonstrated in experiments of >100 NI modules and test coils, as well as various numerical simulations. Major drawbacks of the NI technique, including the intrinsic charging delay and non-linear electromagnetic behaviors, have been actively studied; variations of the NI technique together with complementary techniques have been proposed for performance improvement of NI magnets. This paper presents a brief overview of the recent progress in the NI REBCO magnet technology, which include: (1) a 11 T NI-REBCO insert that generated 42.5 T at a coil current density of 1150 $A/mm^2$ in a bore of the 31 T resistive background magnet at the National High Magnetic Field Laboratory (NHMFL); (2) a 20 T all-superconducting magnet consisting of a 13 T NI-REBCO insert and a 7 T NbTi background magnet, which will be on service as the first user magnet in early 2017 at the Applied Superconductivity Center of the NHMFL; (3) partial and metal insulation approaches for faster charging and their "safe" operating conditions without losing the self-protecting feature; (4) active feedback control to mitigate the charging delay and non-linear behavior of an NI coil; (5) "defect-irrelevant" behavior of NI coils at 4.2 K and 77 K.
Acknowledgement: This work was supported by the National High Magnetic Field Laboratory (which is supported by the National Science Foundation under NSF/DMR-1157490), and by the State of Florida.
Due to low turn-to-turn contact resistances, non-insulated (NI) REBCO coils possess much higher thermal stability than their insulated counterparts. Experiments even showed that NI coils are in general self-protecting, recovering from a quench without external quench protection mechanisms. Recent studies showed that an uncontained local quench can amplify itself quickly, leading to an abrupt loss of the azimuthal current and thus a sudden drop in the magnetic field. Moreover, within a NI multi-coil magnet, a quench-resulted sudden drop in magnetic field in one coil can inductively induced another quench in another coil. These phenomena result in lower thermal stability and lengthened recovery time in self-protecting NI magnets. The ultimate consequences are lower operational reliability and availability, and even catastrophic disruption in operational functionality. Here a novel graded-resistance method is proposed to tackle the mentioned problems while maintaining the superior thermal stability and self-protecting capability of NI magnets. The method is studied and designed via a network-thermo-electromagnetic NI REBCO multi-coil model. The multi-coil model is composed of multiple serially connected, spirally-wound equivalent circuit network pancake coil models coupled with an equal number of three-dimensional thermal and electromagnetic pancake models. Patterned thermally and electrically resistive-conductive layers are inserted at strategically selected turn-to-turn contacts to contain hot-spot heat propagation while maintaining the turn-wise current sharing required for self-protection. The heat containment enables the retention of useful azimuthal current responsible for magnetic field generation, resulting in faster post-quench recovery and reduced magnetic field transient. Through the proposed method, REBCO magnets with higher thermal stability, lower likelihood of quenching, and rapid, passive recovery can be built to enhance operational reliability and availability. The effectiveness of the method is assessed by comparing the recovery times, magnetic field transient rates and thermal stabilities between the modified and original NI multi-coil magnets at 4.2 K and 77 K.
A straightforward analytical model is presented that describes the observed slow thermal drift of the conduction-cooled ReBCO coils developed for the EcoSwing project. In the vicinity of their critical surface, both the temperature and the voltage across these coils drift upwards in response to a current step, on a time-scale ranging from minutes to hours. Eventually, such drift results either in a quench or a new equilibrium temperature. EcoSwing aims to demonstrate the world’s first superconducting low-cost, light-weight wind turbine drivetrain. In order to validate the rotor pole design, THEVA produced a series of sub-scale test-poles which reflect the actual layout of the full-scale poles. Several of these sub-scale coils were tested at the University of Twente in terms of superconducting behavior and thermal housekeeping. The voltages across the coils were measured over time at various current levels and base temperatures ranging from 55K-77K. To explore the thermal drift effect described above, an analytical model was devised based on self-heating of the winding pack. The model, which essentially combines a simple heat-balance equation with a non-linear power term, shows how the detailed ratio between initial heating and cooling leads to two sharply separated types of eventual outcome, either stable or unstable. The heat capacity of the coil does not influence this outcome, although it does determine the time scale. Model predictions were compared to experimental data, showing excellent qualitative and relatively good quantitative agreement. As such, the model provides a better understanding in the thermal behavior of conduction-cooled HTS coils and may be used to guide their design. EcoSwing has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No656024. Herein we reflect only the author's view. The Commission is not responsible for any use that may be made of the information it contains.
A portable magnet system based on bulk (RE)BCO, high temperature bulk superconductors, which constitute high-field magnets, has been designed constructed. The use of a small-volume sterling cryocooler with a base temperature of 50 K has enabled a portable and compact magnet design. The magnetization of the bulk superconductors was realized by a pulsed field magnetization (PFM) technique. The PFM process was considered difficult previously because of the high external field required to fully magnetise high quality bulk samples, according to limitations of the Bean model and to the generation of heat during the magnetisation process. A flux jump phenomenon observed during the rise of the pulsed field, however, was used to drive magnetic flux into the superconductor during the magnetisation process. A peak trapped field of 3.2 T has been achieved at the surface of the bulk superconductor by applying a pulsed field of only 4.86 T as part of this research.
The Cable-In-Conduit Conductors (CICCs) for the ITER magnets are subjected to fast changing magnetic fields during the plasma-operating scenario. In order to anticipate to the limitations of the conductors under the foreseen operating conditions, it is essential to have a better understanding of the stability margin of the magnets. In the last decade ITER has launched a campaign for characterization of several types of NbTi and Nb3Sn CICCs comprising quench tests. The conductors are subjected to a singular sine-wave fast magnetic field pulse and relatively small amplitude with respect to the ITER plasma operating scenario. The Minimum Quench Energy (MQE) tests, performed in the SULTAN facility, were reproduced and analyzed using JackPot-ACDC, an electromagnetic-thermal model for CICCs, developed at the University of Twente and THEA (Thermal, Hydraulic and Electric Analysis of Superconducting Cables). The experimental results were used to calibrate the numerical models and to reproduce the energy deposited in the cable during the MQE stability tests. The agreement between experiments and models shows a good comprehension of the various CICCs thermal and electromagnetic phenomena. The results provide a good basis for further investigation of conductor stability and extrapolative scaling for different magnetic field pulses with lower ramp rate and higher amplitude.
Disclaimer: The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
Demand continues to be high for high-temperature superconducting (HTS) wires and tapes to wind coils of high field quality for NMR or MRI applications. A magnet bore field mapper of relatively simple design and operation is needed to confirm the low-order spherical harmonics during testing after construction of such coils, irrespective of compensation. Presented here is one probe design of a compact, cylindrically fixed array of inexpensive Hall elements normally used in consumer, industrial, and automotive electronics. At most, the probe is only 50.8 mm in diameter and 124 mm in height. The several (i.e., 20) gallium arsenide (GaAs) Hall elements required are incorporated into this probe only after careful and systematic calibration of each at room and low temperatures (i.e., at 298 K and 4.22 K), and moderate magnetic fields (i.e., from 0.0 T to 9.0 T by 0.25 T), in this case, using a Physical Property Measurement System (PPMS) manufactured by Quantum Design. Furthermore, because the array is fixed rather than rotating, the low-order spherical harmonics from the magnet bore may be probed in real time. Thus, the severe magnetic distortions generated by induced screening currents in anisotropic (RE)BCO coated conductors (e.g., in no-insulation pancake windings) may be followed with respect to time.
This work was funded by the National Institutes of Health (NIH) under Grant 5-R21GM111302-03, by the National Science Foundation (NSF) under Cooperative Agreement DMR-1157490, and by the State of Florida. The content of this work is solely the responsibility of the authors.
Babcock Noell GmbH (BNG) and the Institute for Beam Physics and Technology (IBPT) of the Karlsruhe Institute of Technology (KIT) are collaborating in an R&D program focused on the development of superconducting undulators (SCUs). After successfully completing SCU15, a full scale 15 mm period length device installed in ANKA in 2015, the team developed SCU20 a second device with 20 mm period length. The goal of SCU20 is to develop a commercial product. During the conceptual phase over 90% of the components have been redesigned with focus on reproducibly and reliability of the manufacturing process. Moreover the reduction in weight of the cold mass and the optimization of the cooling system, led to faster cooldown and reduced thermal gradients. This contribution describes the performance of SCU20 and the most significant design improvements in comparison to the previous generation device.
The Institute for Beam Physics and Technology (IBPT) of the Karlsruhe Institute of Technology (KIT) and Babcock Noell GmbH (BNG) are collaborating to develop superconducting undulators for ANKA and low emittance light sources. The collaboration is now focusing on a superconducting undulator with a period length of 20 mm (SCU20) planned to be installed at the accelerator test facility and synchrotron light source ANKA. The local magnetic field and the field integrals of the SCU20 1.5 m long coils have been characterized in a conduction cooled horizontal test facility developed at KIT IBPT. Here we present the main results, as well as their analysis including the expected photon spectrum.
To measure magnetic field with Hall probe, the accuracy needs to be considered synchronously. Therefore, the improvements of measurement system are presented, including the magnetic needles and a zero-field shielding were simulated by OPERA. The design of magnetic needles with N-N type is significant that the misalignment of magnet could be calibrated. The doping area of Hall probe was sensitive, whose position should be defined before measuring. Also, a zero-field shielding is used to reset the value of magnetic field to zero. However, the data of simulation is reported in this paper.
During the last decade nine multipole superconducting wigglers were manufactured in BINP on the base of NbTi superconductor. These wigglers are operating in various synchrotron radiation centers worldwide. High magnet design parameters were achieved by using the NbTi wire of high NbTi/Cu ratio, up to a factor of 2, and by grading current density in coils. So, further increase in the magnet parameter is limited by the properties of NbTi conductor. Also important peculiarity of the BINP wigglers is the design of the magnet where superconducting coils were separately manufactured and connected with splicing resistance well below of 0.1 nOhm at operating current about 1 kA. It benefits in significant decrease of heat load on cryocoolers because the total amount of splicing in one wiggler is more than 200. There are demands in superconducting wigglers and undulators for higher magnet parameters that can be realized by using the Nb3Sn wire. The ultimate aim of the current work is to make an Nb3Sn superconducting wiggler with separate coils which terminals will be connected with NbTi wires with low splicing resistance, below 0.1 nOhm. During assembling of such wiggler these coils will be connected via NbTi terminals by existing in BINP technology. This presentation reports on first results of testing of five samples of Nb3Sn-NbTi connection. Experimental setup will be described. The samples represent a two turn loops made of Nb3Sn and NbTi wires. The loops were charged by currents up to 500 A, and the resistance of these superconducting wire connection was evaluated by the current decay via a Hall sensor. All samples have demonstrated very low resistance, estimated as several fOhm, because during several days no current decay was detected by voltmeter in the range of several hundreds micro volts with sensitivity of 1 micro volt.
China Spallaion Neutron Source (CSNS) accelerators include a 80 MeV Linac, 1.6 GeV Rapid Cycling Synchrotron (RCS) and two beam transport lines. There are nearly 300 magnets for these accelerators, including 24 DC biased 25Hz AC dipole magnets, 48 DC biased 25Hz quadrupole magnets, 16 DC sextupole magnets, 34 AC correcting magnets and 23 injection & extraction magnets for the RCS and other DC magnets for the Linac and the beam transport lines. In this paper, the status of RCS magnets will be presented, which includes the key technologies for the magnet production, some interesting results of the magnetic field measurements and some vital faults in process of the magnet commissioning.
The 3-GeV Rapid-Cycling Synchrotron (RCS) at the Japan Proton Accelerator Research Complex (J-PARC) has achieved the designed high power beam operation at 1 MW output. The study of an upgrade plan is then started to realize the 1.5-MW beam power. Regarding the radiation protection at the upgrade plan, a new injection system has been proposed to secure enough space for radiation shielding and maintenance work. For this purpose, it is necessary to integrate the splitted iron cores of the injection shift bump magnet into one core, the length of which is shorter than the total length of the splitted cores. The number of coil turns for the new one core magnet is then increased from 2 to 4. The structural design of the new shift bump magnet excited at 25Hz repetition rate is in progress from view point of eddy current losses at the magnet edge and the coil temperature by using the OPERA-3D. This paper details these aspects and outlines the new power supply briefly.
Large-scaled induction furnaces for non-ferrous metal billets operated at commercial frequency have an energy efficiency of only 50~60% due to the considerable loss from the copper coils used to generate the magnetic fields. Efforts to improve their efficiency are hampered by physical limits. A DC induction heating using HTS magnets has been suggested for achieving higher energy efficiency. A 10kW-class prototype for an HTS DC induction heater was developed in 2013. Changwon National University and TECHSTEEL will have completed a project to develop a 300 kW-class superconducting induction heater(SIH) with HTS magnets in 2017. This project was supported by Korean government.
In the operation of an HTS magnet, ensuring thermal stability against uneven quench is the most important factor. The metal insulation winding method using stainless steel allows the HTS magnet to maintain a great thermal stability by distributing the quench energy evenly and minimize the charging and discharging time. In this paper, we are going to introduce a 300 kW-class SIH and its performance test results. The HTS magnets were fabricated and excited under the conduction cooling condition, successfully. Now, the SIH with the HTS magnets are being fabricated and tested to heat up the metal billets including both the ferrous and non-ferrous metal billets. The performance test results will be applied for the commercial product of SIH.
Small tube bulging by electromagnetic forming is a challenging issue because the coil must be placed inside of the pipe to generate repulsion electromagnetic force. To solve this problem, a novel method for forming pipe fittings by using electromagnetic attraction is proposed. To generate an electromagnetic attraction, a special current is used to drive the coil. This special current consists of a wide pulse current and a narrow pulse current. For the sake of verifying the feasibility of this method, a circuit-electromagnetic-structure coupling finite element model was built to analyze the deformation process, and an electromagnetic forming system with two sets of power supplies was designed and fabricated. Two capacitor bank power supplies (1MJ/25kV/3200μF & 75kJ/25kV/240μF) have been used to energize the coil which produces a pulsed magnetic field. A series of bulging experiments used of AA 1060 aluminum alloy tubes with a thickness of 1mm have been carried out on this system. The tubes were successfully deformed and the maximum deformation reached 5 mm.
A major problem of long duration manned missions in the deep space is the flow of high energy charged particles of solar (SPE) and galactic (GCR) origin. SPEs have short duration but can be extremely intense and can lead to acute, even lethal, effects. GCR flux is much less intense but is continuous, isotropic and more energetic; it increases the risk of carcinogenesis and can affect the nervous and cardiovascular systems, limiting missions duration to few months. It is commonly believed that the problem of space radiation can be solved by surrounding the spacecraft habitats with large superconducting magnets, even though a considerable technological effort would be required. However, magnetic shielding has several basic limitations which restrict the reduction of the radiation dose. As an example, particles in the high energy region of the GCR spectrum, that cannot be deflected out of the cabin by the magnetic shield, have a significant biological effect. Moreover, the interaction of cosmic rays with magnet and spacecraft materials generates secondary particles which have a major effect on the radiation dose. The physical and technological constraints of space radiation magnetic shields are discussed in the paper. Despite such limitations, a superconducting magnet could completely eliminate the risk due to SPE. Moreover, it could reduce the GCR adsorbed dose enough to make acceptable the risk of developing long term diseases after a return trip to Mars.
In the electromagnetic tube expansion process, both electromagnetic force and workpiece deformation are axisymmetric. Hence, the forming performance of tube is better than that of sheet and then electromagnetic tube expansion is widely used in industry processing. However, the cylindrical coil is always applied to generate the electromagnetic force in electromagnetic tube expansion process at present, the radial electromagnetic force in the tube end is less than that in the tube middle because of the end effect, with the result that the workpiece deformation could not meet the industrial requirements. In order to obtain more uniform radial electromagnetic force in the axial direction, electromagnetic tube expansion method with concave coils is proposed in this paper. Firstly, the effect of coil structure parameters on the radial electromagnetic force distribution is studied. Secondly, the concave coils for a given workpiece is designed to meet the workpiece deformation requirements. Finally, the advantages of using concave coils in electromagnetic tube expansion are verified by comparing the workpiece forming performance of cylindrical and concave coils.
An electromagnetic induction coilgun system accelerates a projectile in the axial direction which is a non-periodic moving. In addition, since the electromagnetic coilgun system converts the electrical energy to mechanical energy, the interactions between variables are very complex. Therefore, during a design process of the coilgun system, the design considerations are much more complicated and difficult to analyze compared to others electro-mechanic systems. Some of the design considerations have been published in previous researches, but some others are still deficient in study. A thorough study of the design considerations is necessary to design the coilgun system. This paper investigates the design considerations of an electromagnetic induction coilgun system and suggests reasonable parameters of the system to achieve high energy efficiency.
Some common design considerations such as capacitance, voltage level, length of the barrel, switching time, initial position and output velocity of the armature will be evaluated and then their influences on operation and energy efficiency will be assessed from the evaluated data. Some others which still are lacking in researches such as wire size, resistance, air gap, and distance between stator coils will be investigated and explained. A mathematical model of the coilgun is used to study the impact of the design considerations. Finally, the recent achievements, challenges, and trend of the coilgun system will be addressed briefly. We believe that the summary and study on the design considerations are useful and essential to design the coilgun system and largely contribute to its development.
The Normal Zone Propagation Velocity (NZPV) and quench are areas of intense research for High Temperature Superconductors (HTS). While normal zones travel with speeds in the order of magnitude of m/s in Low Temperature Superconductors (LTS), in HTS coated conductors this speed is in the order of cm/s. This makes ensuring a quick and uniform quench, and thereby the cryostability of tapes, challenging. Such slow NZPV can lead to excessive local heating and hotspots in applications such as cables and magnets, leading to the destruction of the equipment. To develop new HTS tape manufacturing techniques and architectures that help increase the NZPV a reliable measurement method is needed for evaluating the merits of these technologies.
In this work a new optical method is presented for thermal imaging and measurement of quench propagation and NZPV in HTS tapes. The novelty of the method is that it allows mapping the temperature distribution on a 2-D surface, in real time. The technique is based on the temperature dependent light emission of a rare-earth fluorophore in conjunction with a high-speed camera, capable of recording the fluorescence at 2500 frames per second. Together these allow for direct observation of dynamic events, such as the quench, in the time domain of milliseconds. Using the light intensity of each pixel in the recording and adequate post-processing steps allow for the extraction of thermal data. Hence the measurements serve with both qualitative and quantitative temperature information, which can be used to compare quench behaviour of various tapes and architectures. This work shows a proof of concept of the developed method together with preliminary results of quench propagation measurements in silver stabilized HTS tapes.
Quench propagation and degradation properties are critical in quench detection and protection of high temperature superconductor (HTS). It is essential to understand the strain influence on quench propagation velocity (QPV) and degradation limits in HTS in practical applications since there are unavoidable for pre-strain and deformation in its manufacture and operation. In the present work, the quench propagation and degradation behaviors of critical property for pre-strained high temperature superconducting composite tapes are investigated experimentally during a heater triggered quench process. The distributed voltage taps, low-temperature strain gauges and thermal couples are attached on the tape to measure the QPV, strains and the quench degradation limits. In addition, the numerical predictions are presented to discuss the inherent relationship between the pre-strains and quench behaviors of the pre-strained HTS tape. It shows a reasonable consistent with the experimental data. Preliminary results indicate that the QPV increases and the degradation limits decrease for large pre-strained tape with tension deformation. The correlation between detection strain and hot point temperature is analyzed and discussed in detail. The potential applications with pre-strained HTS tape on the quench detection and protection are also discussed.
The Future Circular Collider is at the conceptual design phase and one of the main components are the high-field Nb3Sn dipole magnets targeting 16 T of bore field. With very high current densities and high stored energy, the quench protection is an essential part of the magnet design. The quench protection design relies largely on simulations and naturally, the reliability of the software is crucial. The aim of this paper is to validate the simulation tools with measurements on existing high-field Nb3Sn magnets, namely the MQXFS, 11T-models and RMC racetrack models. We consider those experiments where the protection relies on quench protection heaters.
We consider the following simulation approaches (and their combinations): 1. adiabatic model with thermally independent coil turns and heater delays simulated before experimental validation 2. The model using experimental input for the heater delays, longitudinal quench propagation, fit parameters for turn-to-turn propagation, and quench delay caused by the ac-losses, and 3. scaling law deduced from a few measurement points and magnet's parameters for predicting quenches over the whole range of operation conditions.
The results of the study will be used to assess the suitability of different simulation approaches, and finally to what level of current density and stored energy the designed magnets for FCC can be protected with quench heaters.
As part of the High Luminosity LHC (HL-LHC) upgrade, a novel type of canted cosine theta (CCT) twin aperture beam orbit corrector, the so-called MCBRB, is being developed that will provide 5 Tm of bending power per aperture in the approach to the ATLAS & CMS experiments. This CCT coil is a novel type of dipole coil, featuring aluminum formers with specially prepared slots that maintain the superconducting Nb-Ti strands in the correct configuration. The quench behaviour of this type of coil is intrinsically three-dimensional in which both the axial quench propagation and the transverse thermal exchange between neighbouring strands, the strands and formers, neighbouring turns, adjacent formers, and towards the helium bath play a role. A three-dimensional quench propagation simulation tool is being developed to investigate how the peak hotspot temperature and internal voltages are affected by the design choices of the CCT coil. The implications of conductor composition, strand insulation, external energy extraction, former insulation, helium cooling, bypass diodes, and quench back are presented. The calculation results are compared to experimental observations of the quench behaviour of a CCT model and the results of this comparison are used to formulate quench-protection-related design choices for the final design.
The ITER TF Insert (TFI) coil is a 43 m long single-layer solenoid wound in the grooves of a stainless steel mandrel, using one of the Nb3Sn circular cable-in-conduit conductors adopted in the winding of the ITER TF coils and cooled with supercritical He in forced circulation at ~4.5 K. The TFI is the last in a series of ITER Insert Coils, all tested in the bore of the ITER Central Solenoid Model Coil at Naka, Japan, under conditions relevant for the actual ITER operation. Several tests were devoted to the study of quench propagation, aimed at the assessment of the hot spot in the conductor. The quench was initiated pulsing an inductive heater, located at mid length of the TFI, at increasing energies. Different delay times (3 s, 5 s, 7.5 s) after quench detection were imposed, before the 68 kA TFI current was dumped on an external resistor. In the first part of the paper, the main results of the TFI quench tests are presented and discussed. In the second part, we focus on the numerical analysis of the quench using the state-of-the-art 4C code: for the first time since the ITER Insert Coils program started, more than fifteen years ago, an attempt was made to predict the quench propagation in the strict sense, i.e., performing the simulations before the tests. Here we present the results of the comparison between predictions and measurements, showing that global as well as local voltages, i.e. the hot spot temperature and the propagation of the quench, were very well predicted by the 4C code. The success of this predictive exercise confirms that the 4C code can be reliably used to address quench-related issues in the design of future Nb3Sn magnets and/or in the planning of their operation.
No-insulation (NI) high temperature superconductor (HTS) winding approach has been progressing as a promising technique to produce compact, reliable and robust magnets, and has demonstrated electromagnetic quench propagation and self-protecting nature. Comprehensive distributed network simulation models have been used to understand the mechanism of the self-protecting behavior in a qualitative manner. However, the electromagnetic responses of actual NI magnets consisting of a stack of multiple coils have not been fully understood. Our approach uses previously described “lumped circuit model,” where each NI sub-coil in a magnet is modeled as an inductor and a resistor connected in parallel. Combined with an adiabatic lumped thermal analysis, the model reasonably well simulates the electromagnetic quench propagation among magnetically coupled sub-coils, much faster than the comprehensive distributed approach. Yet, some time-varying variables including transient responses of individual pancake voltages showed substantial discrepancy between measured and simulated results. The goal of this research is to investigate this discrepancy and improve our code for more precise simulation. An NI magnet comprising a stack of 3 double-pancake coils was constructed with REBCO tapes of which the lengthwise critical current over the entire length and the angular dependency of critical current of a short sample had been measured before construction of the coils. Fast ramping and over-current quench tests of the magnet were performed in a bath of liquid nitrogen and liquid helium, and the results were compared with simulated ones based on the inverse calculation approach. This allows us to investigate the validity of our code in a more controlled manner and better understand the electromagnetic behavior of an NI magnet more accurately.
Acknowledgement: This work was supported by the National High Magnetic Field Laboratory (which is supported by the National Science Foundation under NSF/DMR-1157490), the State of Florida, and the KBSI grant (D37611) to S.-G.L.
The ITER magnetic system includes 18 Toroidal Field (TF) Coils constructed using Nb3Sn cable-in-conduit superconductor. Each TF coil comprises a Winding Pack (WP) composed of 7 Double Pancake (DP) modules stacked together, impregnated and inserted into a stainless steel coil case. 10 TF coils are being produced in Europe, under the responsibility of Fusion for Energy (the European Domestic Agency (DA)) while the remaining 9 TF coils are being produced in Japan. F4E has implemented a procurement strategy aimed to minimize costs and risks, by subdividing the procurement into three main procurement packages, each foreseeing first an R&D and a qualification phase. One procurement package is related to the construction of 70 radial plates, another to the fabrication of 10 WP and a third to the cold test and coil-case insertion of 10 WP. After 7 years of R&D and qualification activities and of industrial production, the first ITER TF coil winding pack has been completed in Europe. The test,consisting in a combination of leak and pressure drop tests and electrical tests at room temperature and at 78 K, should be completed by middle of 2017. In parallel the series production of the 10 TF coils in Europe is underway. So far, 65 (over 70) radial plates have been completed and delivered, 65 DP have been wound and heat treated and 35 Double pancakes (over 70) have been impregnated and completed. In addition 3 new winding packs are in the final phase of their construction. In this paper we will report on the main phases and results of the qualification, production and test of the first TF winding pack. In addition we will report on the status of the production and on the following phases needed for the completion of the ITER first TF coil.
National Institutes for Quantum and Radiological Science and Technology, (QST), as Japan Domestic Agency in ITER, has responsibility to procure 9 ITER Toroidal Field (TF) coils. QST completed series production of the first seven double-pancakes (DP), all of which are for the first TF coil. The target tolerance of impregnated DP, 2 mm flatness, was achieved in all these DPs. These DPs were stacked and ground insulation was wound around the stuck DPs. The impregnation of these stuck DPs to form winding pack (WP) is being prepared. In addition, series production of DPs for later TF coils are being proceeded. Including the first TF coil DPs, Winding of 26 DPs, heat treatment of 21 DPs, fabrication of 16 radial plates (RP), transfer of 16 DPs and cover plate (CP) welding of 13 DPs were completed until end of Feb. 2017. Challenging tight tolerances in conductor length, +/-0.01%, was achieved to enable transfer of heat-treated conductor into RP groove. 1 mm flatness was achieved in RP, whose height and width are 13 m and 9 m. In addition, about 2.5 mm flatness was achieved after CP welding by optimizing welding sequence. The flatness of 2 mm could be achieved for all DPs completed and DPs for the first WP was successfully implemented. These results justify that series production of TF coil DP in Japan is going well.
Qualification tests of the ITER Toroidal Field (TF) conductor joints have been carried out by testing short joint samples with test facilities in National Institute for Fusion Science. The joint sample consists of two short TF conductors with the length of 1,535 mm, which is restricted by the conductor test facility with 9 T split coils and 100 kA current leads. Each conductor has two joint boxes at both ends. The lower joint is a testing part that is full size joint of the TF coil, where the cables is compacted from the void fraction of 33% to 25% on the length of 440 mm, the same as the final twisting pitch length. The total length of the joint box is 675 mm including the transition region of cable compaction. In order to attain the original conductor part of 300 mm length for setting voltage taps at three positions, the length of upper joint box is shortened to 560 mm, where the joint length of the cables and copper sleeve is shortened to 325 mm. The voltage drops between L-leg conductor and R-leg conductor are measured with six voltage taps per position per conductor while holding currents for three minutes at 1, 15, 30, 45, 60, 68 kA. The joint resistance of the lower joint is estimated from the increase of the average voltage drop among the six taps against the currents. Five joint samples were tested until 2016, and all the samples satisfied the requirement of the joint resistance less than 3 nano-ohms. The method of the measurement is explained and the voltage distribution among the voltage taps is discussed.
Performance of the ITER toroidal field (TF) coil conductor has been measured in the SULTAN facility with 3.6 m straight configuration and joints at the sample top and bottom. However, this test condition includes large gradients of magnetic field along the conductor length caused by its only 0.45 m high field length. This condition, which is not present inside the ITER TF coils, could lead to an increased drop of Tcs: current sharing temperature. In order to study the TF conductor performance without such large field gradient, a TF Insert Coil (TFIC) was tested in the CSMC facility in Naka Fusion Institute, Japan. The TFIC is a single layer 8.875-turn solenoid coil wound from ITER TF conductor. The coil diameter is 1.44 m and the conductor length is around 40 m. The TFIC has been tested from October 2016 to March 2017 and its Tcs was measured through 1,000 electromagnetic cycles and then several times of warm-up and cool-downs from room temperature to cryogenic temperature. In parallel with the TFIC test, Tcs measurement with similar procedure was also carried out in the SULTAN with a TF conductor sample, which was cut from the one for the TFIC during its fabrication, and both Tcs results were compared. The result showed that the Tcs of the TFIC was around 0.7 K higher than that in SULTAN mainly caused by hoop stress in the coil, and the change in Tcs through the electromagnetic cycles was almost identical in both cases. However, the Tcs results after the warm-up and cool-downs were different for each case and the TFIC showed smaller Tcs degradation than the SULTAN sample. The result of the Tcs measurements and following analysis are reported in this presentation.
The ITER Central Solenoid (CS) components are now being manufactured. This superconducting magnet will provide the magnetic flux swing required to induce up to 15 MA as plasma current. It includes six identical coils, called modules, stacked on top of each other to form a solenoid, enclosed inside a structure that has nine subsets, to provide vertical pre-compression and mechanical support. Using a 45 kA Nb3Sn superconducting conductor requires a long heat treatment at 650 °C to form the Nb3Sn alloy. The conductor lengths wound into multiple pancakes are connected with each other before heat treatment and electrically insulated afterwards. High mechanical stresses in materials and high voltages call for the use of high mechanical resistance structural materials and high dielectric strength insulating materials. The pulsed operation imposes materials with high fatigue resistance at cryogenic temperatures. The unique requirements derived from the operating conditions impose specific materials, manufacturing routes and dedicated working stations for the different steps in the manufacture of the components to achieve the required quality. Whereas for the structure, large existing manufacturing tools are required, the modules required construction of a dedicated manufacturing line. Qualification of the different manufacturing procedures is of prime importance to ensure that the magnet will meet the requirements during operation. A comprehensive qualification programme is being performed at the manufacturers before applying procedures for the production of the CS components. The paper describes the main characteristics of the CS components, their manufacturing routes and the different elements of the qualification programme. The overall plan for the manufacture is reported, including the identified risks and the mitigation items. The status of the first components manufactured is shown as well as the planned delivery schedule to the ITER site.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
Following a decision made at the ITER Council in November 2013, two types of In-Vessel Coils (IVCs), namely ELM Coils to mitigate Edge Localized Modes and VS Coils to provide Vertical Stabilization, have been incorporated in the ITER design. Strong coupling with the plasma is required so that the ELM and VS Coils can meet their performance requirements. Accordingly, the IVCs are in close proximity to the plasma, mounted just behind the Blanket Shield Modules. This location results in a radiation and temperature environment that is severe necessitating new solutions for material selection as well as challenging analysis and design solutions. Due to high radiation environment, mineral insulated copper conductors enclosed in a steel jacket have been selected. A key component of the MIC is the mineral insulation which will consist of compressed MgO powder. The insulation provides three main functions, namely structural support of the copper conductor, thermal conduction between the jacket and the copper conductor, and electrical insulation between the jacket and copper conductor. A major advantage of the coil design is the long conductor length which eliminates the need for any internal joints. In-situ winding of the VS coils is asking for a development of a creative solution for the unspooling, straightening, precise winding tools, bending, and metrology processes in a tight and congested environment. The contract for the procurement of the IVC Conductor has been signed with two suppliers for phase 1: Development, Qualification of all processes, final tests and one full conductor length. Phase 2 includes series manufacturing, storage and delivery of all required conductor lengths. The procurement strategy aimed to select multiple contractors for Phase 1 of the project to mitigate the risk on qualification, cost and schedule and to keep the cost within acceptable limits thus maintaining competition for Phase 2.
The EU-funded EcoSwing project aims at demonstrating the world's first superconducting low-cost and lightweight wind turbine generator. This generator will use field coils based on second generation (2G) HTS wire which are manufactured using Pro-Line HTS tapes. During the development subscale test coils with different number of turns were produced and tested in liquid nitrogen as well as cooled by conduction in vacuum and variable temperature. Design details and test results will be reported. After the successful test of these subscale coils the design for the generator coils could be finalized and a first full size coil was manufactured for the type testing. The generator coils have an overall length of 1.4 m and incorporate several hundred meters of tape for realizing about 200 turns. The type test proved that the performance of the coil at operating temperatures and magnetic fields reached the desired values so that the series production of coils for the generator was started. The current status of this production will be shown together with results of type and routine testing.
This work was supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 656024.
High Temperature Superconducting (HTS) generator for a large-scale wind power generation system draws much attention as a contemporary research item. Excitation systems in HTS generators, particularly brushless HTS exciters are a new challenge.This paper deals with the performance analysis of a 10 kW HTS wind power generator with brushless exciter and examines application possibility of the generator for wind turbines through hardware integration with the exciter. To supply DC current into the HTS coils, a brushless exciter was adopted in the generator. The field current of the generator supplied by the brushless exciter passed through the HTS coil without any mechanical connections. The HTS generator, which consisted of 6 pole racetrack type HTS coils for rotor and 36 slots copper windings for stator, was designed and fabricated. The HTS coils were mounted in a vacuum vessel integrated into the rotor, and cooled down by thermo-syphon cooling method with a cryogenic refrigerator. Through the physical fabrication of the machine, we confirmed several important results as follows. The rated output power of the generator reached to 10 kW at 300 rpm, and the operating temperature was maintained at 30 K by the cooling method. The operating field current was 95 A at operating temperature. When the performance results of the conventional power supply and the brushless exciter were compared, the magnetic flux densities of the generators were almost identical, and the total harmonic distortion of the output voltage of the generator using the brushless exciter was 3.2% which is under the IEEE standard limit of 5%. The results will be utilized to practical design of a generator with brushless exciter through which the heat loss reduction of the field winding and the simplicity of the structure of a large-scale HTS wind power generator will be achieved.
Outside of the application field of (scientific) particle accelerators, in the applications area of semiconductor manufacturing equipment, demanding modules similar to accelerator magnets are developed and used: high field accuracy, high power levels (for high productivity), ultra-high vacuum regimes (EUV lithography), very limited outgassing and particle contamination (contamination of substrates impairs yield) and excellent reliability (equipment up-time is important). We believe that these modules are worth being considered by the magnet community, potentially inspiring novel engineering practices. Typical topologies: An application area is the e-beam technology: critical magnetic design in vacuum environment with strict thermal requirements for stability. Another application area are electrodynamic actuators, for magnetic levitation and active position control with µm or sub-nm level accuracy. They generate highly accurate forces of several kN peak. A typical short stroke electrodynamic actuator consists of a yoke with permanent magnets, and a coil unit in between, enabling contactless actuation in a UHV environment. Force levels and linearity are constantly improved, leading to high-density designs of coils and permanent magnets topologies and the use of high grade materials. Water cooling is applied on both sides of the coil, achieving a high thermal efficiency (temperature gradient in the order of 10 K) at only a small expense in air gap. Both coil and permanent magnet structures are encapsulated for use in UHV. For this, high-reliability designs and manufacturing processes have been developed. Why consider these modules for accelerator magnets? By building magnets closer to particle beam, smaller (aperture) size can be realized, leading to smaller (chromatic) aberrations, higher achievable field strength and a lower volume claim for total magnet system. Challenges for (scientific) particle accelerators: Special materials are required for use in the 1E-10 to 1E-11 mbar regime and complex shape magnetic lenses will require special (e.g. 3D-printed) thermal cooling channels.
Compact, lightweight and large-scale generators are desired for offshore wind energy application due to transportation and installation requirements. In order to reduce the levelized cost of wind energy, larger and larger wind turbines are under researches and superconducting wind generators are proposed as they have high power density and light weight. Due to the expensive price of the superconductor, iron core is usually employed to reduce consumption of the superconductor as well as to divert the flux direction to the superconductor. However, in many designs and studies, losses and permeability of the silicon lamination sheets used in cryogenic temperature are from room temperature, which is not appropriate. Hence, the performance of the silicon lamination sheets at low temperature is essential and in urgent need to develop and commercialize the superconducting wind generators. We made magnetic properties tests of toroidal cores at both room temperature and 77 K with four different materials and the result shows that the permeability of silicon sheets and losses are higher at 77 K than room temperature.
A high precision superconducting levitation system for gravity measurement has been developed which used the levitation of a superconducting sphere by the magnetic field of two superconducting coils. The magnetic levitation is designed to provide independent adjustment of the levitating force and the force gradient. A GM cryocooler is employed to cooldown the system. This article reviews the construction and operating characteristics of the system. The test results show that the system is allowed at least 10-10g sensitivity.
The 32T Magnet system, under development at the NHMFL, is a large all superconducting user magnet that is comprised of a 15 T LTS outsert magnet, made by Oxford Instruments, and a 17 T REBCO inner magnet, made by the NHMFL. With the high critical temperature and low quench velocity of REBCO conductors, even at fields as high as 32 T, a large amount of thermal energy must be quickly deposited in the HTS insert magnet in order to properly protect it. In order to distribute enough energy to prevent strain or thermal damage, a series of protection heaters have been integrated to the coil and are powered by a large bank of lead acid batteries and a redundant array of switches. Fault detection is performed by two independent systems that are each capable of activating the protection heaters and triggering the outsert protection system. Details on the detection scheme, hardware, circuits, levels of redundancy, and the performance of the system are presented.
The application of high temperature superconductors for the generation of high magnetic field is still limited by technical issues like quench detection. A novel quench detection technique is developed using Rayleigh backscattering interrogated optical fibers (RIOF). In particular, the technique is based on the comparison of Rayleigh backscattering signals of a reference and perturbed state. A spectral shift quantifies the mismatch between the two conditions, which depends on temperature and strain changes between the two compared states. Several HTS coils have been fabricated, instrumented and tested. Results show that RIOF is a viable choice for quench detection. In addition to demonstrating that the system works as a detector of normal zones, strain, the experiments also show the different advantages of the fiber optic system over a conventional voltage based one. In particular, optical fibers are co-wound with HTS wire using different integration schemes. Experiments at temperatures as low as 4.2 K have been performed and show that RIOF is operable at 4.2 K with no fundamental differences relative to higher temperature operation. The combination of high spatial resolution and high speed allows for rapid detection and localization of hotspots. Additionally, RIOF allows for a fine calculation of the instantaneous normal zone propagation velocity as a function of time, along with the normal zone size as a function of time. These capabilities, along with a deeper understanding of the minimum propagating zone (MPZ), enable the use of a criterion based on the MPZ to identify unstable (propagating) normal zones, instead of the conventional threshold voltage.
The newly developed concept of Coupling-Loss Induced Quench (CLIQ) used in the domain of superconducting magnets quench protection has opened a new path towards efficient magnet protection. Subsequently to the first trials using ad hoc solutions in order to confirm functionality and performance of the method, two pre-series of three units each with different hardware configurations have been recently manufactured at CERN. Starting from the design phase, the hardware realization follows industrial standards and associated quality control. At the same time aspects related to the long term operation of the units have also been addressed. This paper discusses the design and manufacturing issues, the construction details and the decisions made on choices considering their operation in test stations and in a final accelerator environment. The results of the tests of these units before connecting them to a superconducting magnet will be presented and analyzed.
Sumitomo Electric has been developing conduction-cooled magnets using Bi2223 wire (DI-BSCCO). Due to high in-field critical current of the wire, the magnets can operate around 20 K. Consequently, iterative excitations and, central field of 10 T or R. T. bore of 300 mm in diameter have been achieved. With respect to reliability of the magnets, quench (thermal runaway) protection might be a problem generally for high temperature superconducting magnets such as BSCCO and REBCO magnets due to the small NZP velocity. Sumitomo Electric confirmed that a bridge circuit with a dump resistor, which detects a quench and dumps the stored energy into the dump resistor, can protect Bi2223 magnets. The experimental coil consists of epoxy-impregnated double-pancake coils between copper cooling plates. The coil was conduction-cooled and then heated around 30 K until it generated a certain voltage. Relationship among the decay time constants, the quench detecting voltages, and the heat loads was investigated. The comparison of different sized coils between inductance 0.4 H and 15 H indicates that the difficulty of the magnet protection depends on the heat production rate of the hotspot, but not on the size of the coil. The operating currents are 200 A, 250 A, and 300 A. The higher operating current, the lower the protectable detecting voltage is. If the decay time constant is long, the protectable heat production rates are almost the same. The results of the experiments have been reflected in the practical design of the magnets.
The dynamic strain/stress characteristics and responds of a low temperature superconducting (LTS) sextupole magnet during excitation, pre and post spontaneous quench are investigated in the present work. The strains are measured by using a half-bridge circuit composed of a cryogenic strain gauge and dummy resistances. The strain gauges are directly embedded within the magnet structure, which are located between the superconducting windings and the stainless steel. A fast data acquisition system with wireless and a resolution of 1ms is used for the strain measurements of the SC magnet during excitation and spontaneous quench. The results show that the strong turbulence and high value of measured internal strains are always detected in advance compared to the transport current, magnetic field and temperature signals recorded when a spontaneous quench occurs. It indicates that the transient internal strain measured in the SC magnet can capture the quench feature timely. To better understand the dynamic strain histories in the SC magnet during the excitation, initial and post quench processes, a spectrum analysis of the measured strain signals is conducted. It is indicated that several spectral peaks are always observed at the onset of a quench. When the current is increased, the amplitudes of these spectral peaks for the pre quench are weakened and the corresponding frequencies are enhanced. The observations indicate that the accumulated disturbance energy from the deformation or movement of SC wires inside the magnet may be dominant for occurrence of a quench. By means of quench training, the movement inside of coils is gradually constrained resulting in the structural frequency being increased.
For future particle colliders at the energy frontier such as the future circular collider for hadron-hadron collisions (FCC-hh), 16 T dipole magnets are needed to maintain the high-energy particle beams on their trajectories. This type of magnet features a very high stored energy density resulting in a challenge from a magnet quench protection perspective. A possible method for improving magnet quench protection involves using secondary normal conducting coils, so-called quench absorption coils, placed in close proximity to the primary superconducting coils. As the primary coil quenches, current is inductively transferred into the secondary coils and a substantial fraction of the stored energy is dissipated there. The secondary coils comprise insulated copper windings which are placed in series with a blocking diode, so that during regular ramping undesirable heating and field errors are avoided. In a previous numerical analysis of the R&D Nb3Sn dipole ‘HD2’, it was found that by adding the quench absorption coils to the heater-based magnet protection system (without an external dump resistor), the hotspot temperature was reduced by 100 K and the peak resistive voltage by 50%. We explore the feasibility of this concept for the FCC-hh block coil design, with an emphasis on magnet cost reduction. Firstly, a study is done to determine how much the size of the superconducting coil can be reduced while maintaining the specified hotspot and peak turn-to-turn voltage and voltage-to-ground. Secondly, the inductive interaction between the secondary coils and the coupling-loss-induced quench system (CLIQ) is studied. Thirdly, a mechanical analysis is performed to see if and how the presence of the secondary coils affects the overall mechanical behaviour. Based on the results of these investigations, the costs and benefits of this concept are weighed to see whether this magnet quench protection concept may prove useful for this type of magnet.
The Large Hadron Collider (LHC) upgrade, called High Luminosity LHC (HL-LHC) is planned for the next decade. A wide range of magnets and new technologies are currently under development. One of these systems will be a set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS & CMS experiments. This twin aperture magnet system, with large 105 mm clear aperture coils. Each aperture will independently deliver 5 Tm integral field, between apertures the field vectors are rotated by 90° from each other, and individually powered. the base-line magnet design length is forced to be longer than 2.2m due to the cross talk that limits the maximum field to about 2.6 tesla. Above this field errors that are generated in the adjacent aperture exceed the beam optics limit. Within the string of magnets there is limited space between the D2 dipole and the crab cavities. CERN is working on fine adjustment to give extra centimetres of space.
This paper presents a novel solution to reduce the length of this magnet design significantly from that 2.2 m baseline, to a 1.4 m long 4 Tesla design. Utilizing a selection of novel techniques we present a high field design which eliminates totally the adjacent field errors throughout the full bipolar current range. The design uses a set of Canted Cosine Theta ‘CCT” air coils with a system of correctors which run in series with each apertures main dipole coils and council totally the errors for both apertures. We present :field quality, quench calculations, assembly structure within the D2 cold mass. The design liberates ~ 1 m of axial space within the D2 cold mass. We also present a comparative cost estimate between the base line design and this CCT air coil design.
In the context of the HL-LHC project, a NbTi double aperture quadrupole magnet called MQYY is being developed. This 90 mm aperture quadrupole magnet has a magnetic length of 3.67 m and an operating gradient of 120 T/m at 1.9 K. Its development is done along two parallel paths: 1) the design, fabrication and test of a short model, 2) the design and fabrication of two full scale prototypes in industry within the H2020 EU Pre-Commercial Procurement project QUACO implemented by CERN, CEA, CIEMAT and NCBJ. We report here on the short-model design choices, the status of its fabrication and the preparation of the tests. In particular, we describe the magnetic and mechanical design relying on self-supporting collars, the protection aspects and the assembly process. In addition, we present the unusual scheme of the QUACO project leading to the prototypes fabrication.
The QUACO project has received funding from the European Union’s Horizon 2020 PCP programme under Grant Agreement no. 689359
Sections of the superconducting magnets of SIS100 particle accelerator (under construction at GSI, Darmstadt) are going to be connected with by-pass lines used to transfer electric current and liquid helium. Each by-pass line will contain four pairs of Nuclotron-type superconducting cables (bus-bars) used to supply the different types of magnets with electric current. Since the accelerator is going to be powered with fast-ramping currents, some interactions between the bus-bars are expected. In this work the electromagnetic behaviour of the line is considered. The distribution of the magnetic field around a superconducting cable is analysed and used to find some electrical properties of the line - its electric capacity, self-inductance and mutual inductances between the bus-bars. Inductances are then applied in the calculation of cross-talk currents. Knowledge of these currents is crucial for the operation of the accelerator. The disturbance in the amount of supplied current can lead to the deformation of the magnetic field generated by the superconducting and in turn the decrease of luminosity or even the loss of particle beam.
We have been developing the beam separation dipole magnet for the High Luminosity LHC (HL-LHC) upgrade. The magnet has a coil aperture of 150 mm using NbTi superconducting cable and dipole magnetic field of 5.6 T will be generated at 12 kA at 1.9 K to provide the field integral of 35 Tm. We have started development of the first 2-m-long model magnet (MBXFS01) to evaluate the design and the performance. In the first cold test in 2016, quench performance was not satisfactory because the coil stress at pole was completely released during excitation. It was decided that the model magnet was reassembled with increasing the coil stress to improve the quench performance. The excitation test of the modified model magnet (MBXFS01b) was performed at 1.9 K from February 2017 at KEK. The magnet showed much better quench performance and succeeded to reach the ultimate current of 13 kA as acceptance criteria. After the train campaign, magnetic field measurement was performed by a rotating coil method. The coil systems with an internal compensation of main dipole field were superior to simple coils in measuring the high-order multipole components and eliminating a variety of measurement errors. Due to the large coil aperture and limited outer diameter of the iron yoke, the control of iron saturation effects on the field quality has been a design issue. Regarding the magnetic performance, field saturation effects on the transfer function and the multipole field variation along the excitation, and coil end effects to the straight section need to be evaluated by the field measurement. In this work, field measurement results will be presented and the comparison with the 3D field calculation will be discussed.
The new D1 beam separation dipole is currently developed at KEK for the Large Hadron Collider Luminosity upgrade (HL-LHC). Four 150 mm aperture, 5.6 T magnetic field and 6.7 m long Nb-Ti magnets will replace resistive D1 magnets in the insertion regions of the LHC. The development includes fabrication and testing of 2.2 m model magnets. The magnet has single layer coil and thin spacers between coil and iron, giving a non negligible impact of saturation on field quality at nominal field. The magnetic design of the straight section coil cross section is based on 2D optimization by means of the ROXIE code, and a separate optimization of the coil ends. However, magnetic measurements of the short model showed a large difference (tens of units) between the sextupole harmonic in the straight part and the 2D calculation. This difference is correctly modelled only by a 3D analysis: 3D calculation performed with Opera-3D and ROXIE show that the magnetic field quality in the straight part is influenced by the coil ends, even for the 6.7 m long magnets. The effect is even more remarkable in the short model. In this paper we investigate similar 3D-effects for other magnets, namely the 11 T dipole for the HL-LHC for which the effect is clearly visible for the single aperture model. On the other hand in the double aperture configuration with field in opposite direction the effect is negligible. We also consider the case of the 4.5 T recombination magnets for HL-LHC (D2), where the lower field and the larger space between coil and iron makes this effect less important, but still visible. We conclude the paper by outlining the different classes of accelerator magnets where this coupling between 3D effects and iron saturation can be relevant.
High-luminosity Large Hadron Collider (HL-LHC) upgrade aims increase of peak luminosity by a factor of five and integrated luminosity by a factor of ten over the life of the upgraded machine in comparison with the current LHC. Large aperture final focusing quadruple magnets play a major role to obtain a smaller \beta*at an interaction point and they are being developed by CERN and US-LARP. Large beam separation dipole magnets (D1) are also needed for the new beam optics and KEK has been in charge of development of D1 in the framework of CERN-KEK collaboration. This magnet is based on Nb-Ti technology and generates field integral of 35 T·m at 12.0 kA and 1.9 K in a coil aperture of 150 mm. One of the difficulties in magnetic design of D1 is management of severe iron saturation due to a large coil aperture and limitation of an outer diameter of iron yoke. Main design parameters were once fixed after a series of design studies and the first 2 m model was fabricated and tested at cold in 2015 – 2016. However, it was recently decided by CERN that heat exchanger holes have to be in line with those of the inner triplets and modification of cross section of D1 magnet was requested. This was a very large impact on field quality and re-optimization of coil and iron yoke should be performed. In this paper, we will report magnetic design with new cross section of the coil and the iron yoke with four heat exchanger holes. Optimal conditions of the field tuning holes to reduce variation of multipole coefficients from the injection to the nominal current will be discussed. Optimization of coil end shape will be also mentioned considering minimization of cable strain and integrated multipoles over 7 m long magnet.
Magnetic measurements of the NICA booster superconducting magnets NICA is a new accelerator collider complex under construction at the Joint Institute for Nuclear Research in Dubna, Russia. The facility includes a new superconducting booster synchrotron consists of 40 dipole and 48 quadrupole superconducting magnets. Booster magnets are under series production, assembling and testing at new test facility in Joint Institute for Nuclear Research, Dubna. Dipole magnets for the NICA booster are 2.14 m-long, 128 /65 mm (h/v) aperture magnets with design similar to the Nuclotron dipole magnet but with curved (14.1 m radius) yoke. Measurement of magnetic field parameters is assumed for each booster magnets. We present “warm” and “cold” test results obtained by magnetic measurements almost all of dipole magnets and compare them with the predicted values and the requirements of specification.
CEA has the responsibility of the design studies for the superferric 1.6 T dipole magnets of the Superconducting FRagment Separator (SuperFRS) which is part of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. After completing the study for the 21 superferric SuperFRS standard dipole magnets, CEA is currently analysing conceptual solutions for the 3 superferric branched dipole magnets. Branched dipole magnets are necessary to allow the separated particles to be directed along each of the three branches of the separator. The branched dipoles will keep most of the features incorporated in the standard dipole magnet design but they will have increased complexity to make them compatible with the vacuum chamber layout at the branches locations (Y-shape). The magnetic design of the yoke will be slightly modified whereas a new cryogenic design is required. We present in this paper the design concepts envisioned for the FAIR SFRS branched dipole magnets along with preliminary design simulation results (magnetic, cryogenic and mechanical analyses).
Construction of the High Luminosity Large Hadron Collider (HL-LHC) is being planned for an increase of luminosity in order for the further exploration of the physics beyond the Standard Model. Under this program, a series of final focusing magnets, including a beam separation dipole (D1), has to be upgraded, and we, KEK, are responsible for development of the new D1 magnet. This magnet is designed to have an aperture size of 150 mm and to generate a field integral of 35 Tm. Fabrication of the first 2 m model magnet of D1, called MBXFS01, was completed in 2016, and the subsequent cold test was conducted to ensure its performance. After the test, we re-assembled MBXFS01 to enhance the coil pre-stress, and the second cold test was conducted with the re-assembled one (MBXFS01b) in 2017.
During the first and second cold tests, study on the quench protection was made using spot heaters (SHs) and quench protection heaters (QPHs). SHs are bonded to the inner surface of a single turn of the coil with the highest and the lowest fields, and the detection time of the balanced voltage are experimentally evaluated at given operating currents. The model magnet (MBXFS01 and MBXFS01b) also equips QPHs which cover the outer surface of the coils. These heaters are used to estimate the total heat input required to trigger a quench. In addition, we study how the maximum temperature of the coils varies with given operating currents when we rely only on these QPHs for an extraction of the coil energy. In this paper, we report a series of the quench protection studies and results from the measurements.
The Magnet Section of the Paul Scherrer Institute (PSI) upgraded in 2017 its Hall probe magnet measurement bench with an in-house developed 3D Hall sensor of a distinctive type and of a high accuracy, named Hallcube. The first major magnetic field measurements at the upgraded bench were performed on a split coil magnet with iron housing. This magnet is routinely used on the low energy muons (LEM) spectrometer on the muE4 beam-line at PSI. At the maximal current the main field component in the magnet aperture is 0.35 T and the side field components due to the split coil configuration rise above 0.1 T. Hence, and for the purpose of tuning the muon beam transport and optimising the operation of this worldwide unique facility, accurate 3D field maps of the spectrometer magnet are crucial. To ensure a high relative accuracy of 1E-4, extra measures were taken to cancel out the influence of the earth magnetic field and the lab environment on the measurements. In addition to the magnetic field measurements, the spectrometer magnet has also been modelled in 3D using the Vector Fields OPERA simulation software. A description of the measurement system, detailed analysis of the results and the comparison with the calculation are presented.