Search

Microstructure and magnetic properties were studied for the commercial Sm(CoFeCuZr)z magnets before and after post annealing treatment. The results show that the phases composition and orientation of the magnet do not change after post annealing treatment, but the substantial redistribution of Cu element within multiscale (the microscale crystal grain and the nanoscale cellular structure) had been observed simultaneously. In detail, as the Cu redistribution, the thickness of the Cu-rich Sm(Co,Cu)5 cell boundary becomes thinner, and the Cu concentration in the boundary increases sharply. The pinning field of domain walls and corresponding coercivity increases remarkably with slight remanence and maximum energy product loss, and the overall magnetic performance of (BH)max (MGOe)+Hcj (kOe) increases by 54.3% as a result. Moreover, the thermal stability of the magnet improves as well. On the other hand, Cu-lean phenomenon was observed along the grain boundary region, triggering to magnetic domain reversal process and slightly undermining the squareness of the demagnetization curve of the magnet.

This paper proposes a novel approach to the modelling of HTS transformer-rectifier flux pumps that can charge HTS magnet-ic loads without the need for bulky current leads or expensive cryogenic requirements. The model was built in MATLAB/Simulink for a flux pump with 2 HTS switches, an HTS transformer with a primary inductance of 15 mH, second-ary inductance of 50 H and an HTS magnetic load with an in-ductance of 2 mH. With a 5 A pk-pk triangular current wave-form at 2 Hz the system can load the HTS load to 34.63 A in 5 s. This incremental addition of flux to the load demonstrates the advantage of flux pumps as they can charge high-field magnets without the need for large power sources. The speed of flux pumping is improved by increasing the system frequency, the magnitude of the dynamic voltage developed in the HTS switches and by increasing the primary inductance of the trans-former. This has widespread industrial applicability in fields such as the charging of high-field magnets for MRI systems.

Macroscopic responses of magnets are often governed by magnetization and, thus, have been restricted to ferromagnets. However, such responses are strikingly large in the newly developed topological magnets, breaking the conventional scaling with magnetization. Taking the recently discovered antiferromagnetic (AF) Weyl semimetals as a prime example, we highlight the two central ingredients driving the significant macroscopic responses: the Berry curvature enhanced because of nontrivial band topology in momentum space, and the cluster magnetic multipoles in real space. The combination of large Berry curvature and multipoles enables large macroscopic responses such as the anomalous Hall and Nernst effects, the magneto-optical effect, and the novel magnetic spin Hall effect in antiferromagnets with negligible net magnetization, but also allows us to manipulate these effects by electrical means. Furthermore, nodal-point and nodal-line semimetallic states in ferromagnets may provide the strongly enhanced Berry curvature near the Fermi energy, leading to large responses beyond the conventional magnetization scaling. These significant properties and functions of the topological magnets lay the foundation for future technological development such as spintronics and thermoelectric technology.

In recent years, high-power microwave (HPM) generator with a low working magnetic field has caught more attention as this device has the merit of low energy consumption and the potential of using a permanent magnet package in the HPM system. However, the conversion efficiency of this device is generally low because the electron beam will fluctuate transversely and the modulation depth will decline when the guiding magnetic field is low. To obtain concurrently high-power, high-efficiency, and low operating magnetic field, a transit-time oscillator (TTO) with two bunchers is designed and fabricated. Two bunchers are adopted in the TTO to modulate the electron beam twice. By introducing the second buncher, the modulation depth of the electron beam increases by 23%, and the conversion efficiency increases from 25% to 40.5% in simulations. A microwave with a power of 3.65 GW and a frequency of 4.31 GHz is obtained with a 600-kV, 15-kA electron beam under the guidance of a 0.5-T magnetic field in simulations. Furthermore, the corresponding experiments are carried out to verify the two-buncher TTO, and a microwave with a power of 3.3 GW and a frequency of 4.31 GHz is obtained. The experimental efficiency is 32% with an external magnetic field of 0.48 T.

Over the past four years, the magnetism of 2D magnets has been extensively studied by the full arsenal of probing techniques. 2D magnets can be incorporated to form heterostructures with clean and sharp interfaces, which gives rise to exotic phenomena as a result of the interfacial proximity effect. Here we report a detailed study of the spin (ms) and orbital (ml) moments of an epitaxial (CrSb/Fe3GeTe2)6 superlattice. The synchrotron-radiation based x-ray magnetic circular dichroism (XMCD) technique was performed to probe the microscopic magnetic properties of the superlattices in an elemental resolved manner. We unambiguously obtained a bulk-like moment of Fe3GeTe2 i.e., ms = 1.58 ± 0.2 μB/Fe and ml = 0.22 ± 0.02 μB/Fe. Future works to explore the tuning of the spin polarized band structure of 2D ferromagnetic superlattices will be of great interest and can have strong implications for both fundamental physics and the emerging spintronics technology.

Although coercivity is one of the fundamental properties of permanent magnets, it has not been well understood. In this paper, micromagnetics and thermal activation magnetization reversal theories are briefly reviewed, and then our recent macroscopic and microscopic experimental approaches for thermally activated magnetization reversal in advanced Nd-Fe-B hot-deformed magnets are explained. Our experimental results are well supported by the recent atomistic spin model calculations. Moreover, the systematic micromagnetics simulation study makes much clearer the physical picture of the thermally activated magnetization reversal process in permanent magnets., Graphical abstract

High temperature superconducting (HTS) tapes could be introduced into large scale electrical machines in order to improve the power density. However, the alternating current (AC) loss of HTS tapes will cause the reduction of efficiency. On the basis of analytical and numerical model calculations, this paper presents an optimal design of the HTS armature winding aiming at lower AC loss. The main contribution of this work is that the relationship between the installation parameters and the AC loss of such HTS armature windings has been figured out based on the analysis of the shape feature of the HTS tape and the external magnetic field. When the tape is placed along a particular direction where the perpendicular component of external magnetic field has the lowest amplitude, the AC loss is the smallest. The modified installation location and angle are found based on the proposed generator. These results are verified using finite element method (FEM).

To solve the problem of complex operating device and permanent magnets (PMs) demagnetization at high temperature, a new type of permanent magnet fluxed-switching coupler (PMC) with synchronous rotating adjuster is proposed. Its torque can be adjusted by rotating a switched flux angle between the adjuster and PMs along the circumferential direction. The structural feature and working principle of the PMC are introduced. The analytical model of the novel PMC was established. The torque curves are calculated in transient field by using the three-dimensional finite element method (3-D FEM). The temperature distribution of the novel PMC under rated condition is calculated by 3-D FEM, and the temperature distribution of the PM is compared with that of the conventional PMC. The simulation and test results show that the maximum temperature of copper disc and PM of the novel PMC are 100 °C and 48 °C respectively. The novel PMC can work stably for a long time under the maximum load condition.

Various technologies have ever been developed to minimize the detent force of linear motors. Although the traditional modular structure can effectively reduce the detent force, the width of the flux barrier and the number of units severely limit its application. To solve these, this paper proposes a new modular type of tubular permanent magnet synchronous linear motor (TPMSLM), which consists of two identical unit motors. For simplification, a subdomain analytical method of the unit motor is firstly established, and its accuracy is verified by a comparison with that of the finite element method. Using the two approaches, the important parameters of the motor are analyzed. A modified two-unit modular TPMSLM is also proposed through the star vectograms of the electromotive force, which achieves thrust performance similar to the traditional three-unit modular TPMSLM with a smaller axial size. Moreover, to make full use of the volume of the flux barrier, end teeth are added at both ends of the unit motors. The simulation results indicate that a reasonable end tooth structure can not only reduce the magnetic leakage phenomenon of the end but also effectively improve the thrust of the motor.

The effects of temperature on the dynamic characteristics of a high-Tc superconductor (HTS) and permanent magnet (PM) system at different field cooled (FC) gaps and different masses are studied theoretically and experimentally. Results indicate that the resonant frequency of the HTS-PM system decreases with increasing FC gap or mass at different temperatures. Although decreasing temperature augments stiffness of the interaction force between the HTS and the PM. The effect of decreasing temperature on stiffness and resonance frequency is more significant at a smaller FC gap. It means that the enhancement of lowering temperature on stiffness and resonant frequency also depends on the magnetic field gradient.

Characterizing critical current IC of Nb3Sn strands as function of a strain is very important for large high field superconducting magnet applications such as the superconducting outsert coil of the series-connected hybrid at the NHMFL and the ITER magnets. Apparatuses for measuring IC versus longitudinal strain and transverse stress have been developed and used at the NHMFL. We have characterized the IC strain sensitivities of a few candidate strands for the series-connected-hybrid. In addition, IC irreversibility strains are measured for the recently developed ITER high JC strands. The different strain sensitivities for different strands are discussed., 4 pages, 6 figures

During the last decade, Budker Institute of Nuclear Physics (BINP) manufactured nine multipole superconducting wigglers on the basis of NbTi superconductor. These wigglers are operating at various synchrotron radiation centers worldwide. High magnet parameters were achieved due to using NbTi wire of high NbTi/Cu ratio, up to a factor of two, and by grading the current density in the coils. So, further increase in the magnet parameters is limited by the properties of NbTi conductor. Another important feature of the BINP wigglers is the magnet design, with superconducting coils manufactured separately and connected with a splicing resistance of well below 0.1 nΩ at an operating current of about 1 kA. That yields significant decrease in the heat load on cryocoolers because the total amount of splicings in one wiggler exceeds 200. The existing demand in superconducting wigglers and undulators for higher magnet parameters can be realized by using Nb3Sn wire. The ultimate aim of the on-going work at BINP is to make an Nb3Sn superconducting wiggler with separate coils, the terminals of which will be connected by NbTi wires with low splicing resistance, below 0.1 nΩ. During assembling of such a wiggler, these coils will be connected via NbTi terminals by the technology available at BINP. This article reports on first results of testing five samples of Nb3Sn-NbTi wire splicing. The experimental setup is described. The samples are two-turn loops made of Nb3Sn and NbTi wires. The samples were charged by currents of up to 500 A, and the resistance of these superconducting wire connections was evaluated from the current decay using a Hall sensor. All samples have demonstrated very low resistance, estimated as several Ohm.

Dysprosium compounds with high magnetic anisotropy are widely studied as single molecule magnets (SMMs). Here the anisotropic magnetocaloric effect in a Dy(III) SMM, {[Dy(OSiMe3)2(4-Mepy)5(BPh4)] 0.5Toluene}, was studied by single crystals. Angular dependent magnetization can be observed at 300 K because of its high magnetic anisotropy. SMM behavior measured along the easy axis direction is identical to that of the polycrystalline sample. Rotating magnetization from the easy axis to the hard plane gives a maximum magnetic entropy change (–ΔSR) of 3.05 J/(kg∙K) at 19 K at ΔB = 5 T, which enables the Dy(III) SMM to be used as a low-temperature rotating magnetic refrigerant.

To study the temperature dependence of magnetic properties of permanent magnets, methods of treating the thermal fluctuation causing the thermal activation phenomena must be established. To study finite-temperature properties quantitatively, we need atomistic energy information to calculate the canonical distribution. In the present review, we report our recent studies on the thermal properties of the Nd2Fe14B magnet and the methods of studying them. We first propose an atomistic Hamiltonian and show various thermodynamic properties, for example, the temperature dependences of the magnetization showing a spin reorientation transition, the magnetic anisotropy energy, the domain wall profiles, the anisotropy of the exchange stiffness constant, and the spectrum of ferromagnetic resonance. The effects of the dipole–dipole interaction (DDI) in large grains are also presented. In addition to these equilibrium properties, the temperature dependence of the coercivity of a single grain was studied using the stochastic Landau-Lifshitz-Gilbert equation and also by the analysis of the free energy landscape, which was obtained by Monte Carlo simulation. The upper limit of coercivity at room temperature was found to be about 3 T at room temperature. The coercivity of a polycrystalline magnet, that is, an ensemble of interactinve grains, is expected to be reduced further by the effects of the grain boundary phase, which is also studied. Surface nucleation is a key ingredient in the domain wall depinning process. Finally, we study the effect of DDI among grains and also discuss the distribution of properties of grains from the viewpoint of first-order reversal curve.

Based on our novel dc vacuum interruption technology under composite transverse magnetic fields (TMFs), the arc voltage of dc vacuum arc can be effectively improved to interrupt the dc current. The objective of this work is to experimentally investigate the vacuum arc characteristics and their evolution in dc current interruption under composite TMFs. The composite TMFs were generated by both multipole permanent magnets and cup-type TMF contacts. The vacuum arc photos were recorded by a high-speed camera. The experimental results indicate that under these composite TMFs, the dc current could be successfully interrupted, which was closely related to the dc vacuum arc characteristics and their evolution. The experimental dc current and voltage were less than 500 A and 500 V. First, the evolution of the dc vacuum arc could be divided into Stable and Unstable stages, according to the characteristics of the arc voltage waveform. In the Stable stage, the dc vacuum arc might be stagnated, constricted, and rotated with a stable arc voltage of 20 V. In the Unstable stage, the dc vacuum arc was transferred to the outer periphery of the contact in the form of a ``C''-shape, and the arc voltage significantly increased higher than the supply dc voltage. Second, there was an Extinction Area in the middle of Area 4 under the composite TMFs, which made the dc vacuum arc always extinguish at this position. Third, repeated fluctuations of the arc voltage are caused by the formation and extinction of the ``C''-shaped arc. Finally, when the distance between the igniting area and Extinction Area increased, the duration of the Stable stage increased, while the duration of the Unstable stage decreased.

It is still an open debate whether the 1:5H cell boundaries (CBs) or the intersections of 1:3R platelets and 1:5H CBs are the strong pining sites for the cellular nanostructured 2:17-type Sm-Co-Fe-Cu-Zr high temperature permanent magnets despite that they have been widely applied in advanced industries since 1970s. Herein, through tuning the volume fraction of Zr-enriched 1:3R platelets by varying the second-step aging time, the pinning behavior in a model magnet Sm25Co44.9Fe21.5Cu5.6Zr3.0 (wt%) was investigated. The results show that the volume fraction of 1:3R platelets can be effectively enlarged without changing the cell size (i.e. the volume fraction of CBs) by extending the aging time at 400 °C. Microscopic TEM characterizations combined with macroscopic magnetic measurements reveals that the locally thickened 1:3R platelets after long-term second-step aging reduce the effective pinning area by interrupting the magnetic domain walls at CBs, weakening the average pinning strength and the coercivity of the magnet. Consequently, our work supports that the 1:5H CBs act as the dominating pinning sites instead of the intersections of 1:3R platelets and 1:5H CBs, which may provide an important insight towards understanding the hard magnetism of pinning-controlled permanent magnets.

Efficient magnetic control of electronic conduction is at the heart of spintronic functionality for memory and logic applications1,2. Magnets with topological band crossings serve as a good material platform for such control, because their topological band degeneracy can be readily tuned by spin configurations, dramatically modulating electronic conduction3–10. Here we propose that the topological nodal-line degeneracy of spin-polarized bands in magnetic semiconductors induces an extremely large angular response of magnetotransport. Taking a layered ferrimagnet, Mn3Si2Te6, and its derived compounds as a model system, we show that the topological band degeneracy, driven by chiral molecular orbital states, is lifted depending on spin orientation, which leads to a metal–insulator transition in the same ferrimagnetic phase. The resulting variation of angular magnetoresistance with rotating magnetization exceeds a trillion per cent per radian, which we call colossal angular magnetoresistance. Our findings demonstrate that magnetic nodal-line semiconductors are a promising platform for realizing extremely sensitive spin- and orbital-dependent functionalities. A study reports a colossal angular magnetoresistance in the topological magnet Mn3Si2Te6, resulting from a metal-to-insulator transition caused by controlled lifting of a topological band degeneracy, and discusses the key parameters involved.

Grain boundary diffusion in Dy vapor was conducted during sintering to prepare large-sized bulk (Nd, Dy)FeB magnets. The morphologies, elemental compositions, and magnetic properties of the (Nd, Dy)FeB magnets were analyzed via scanning electron microscopy, energy spectrum analysis, X-ray diffraction, plasma emission spectrometry, and magnetic property testing. The effects of diffusion sequence, temperature, and time on the Dy distribution and magnetic properties were systematically investigated. The effective penetration depth of Dy exceeded 15 mm in the bulk (Nd, Dy)FeB magnets obtained via the grain boundary diffusion method. The optimized ΔHcj/ΔBr was up to 23.08 in the bulk (Nd, Dy)FeB magnets obtained under diffusion temperature of 980 °C and diffusion time of 8 h, which is much higher than that of the magnets obtained via Dy powder doping.

The torque ripple is affected by both the stator and the rotor magnetic field harmonics. In synchronous reluctance motors (SynRM), there are only rotor permeance harmonics existing on the rotor side for the absence of the rotor windings. Since the asymmetric rotor flux barriers are widely applied in the SynRM rotor, it is difficult to calculate the rotor permeance accurately by the analytical method. In this article, the effects of the rotor permeance harmonics on the air-gap magnetic field are studied by a virtual permanent magnet harmonic machine (VPMHM), which is a finite-element (FE) based magnetostatic analysis model. The air-gap flux density harmonics produced by the SynRM rotor are extracted from the VPMHM model and used as the intermediate variables for the torque ripple optimization. The proposed method does not need to solve the transient process of motor motion. Hence, the time of the optimization process can be significantly shortened. Finally, a full electric cycle is simulated by dynamic FE simulation, and the torque ripple is proved to be effectively reduced.

Poor stability of the permanent magnet electrodynamic levitation hinders its application in the maglev field. Therefore, building a control-oriented model to improve its stability is most challenging. However, intractable electromagnetic models leading to an implicit relationship between levitation force and gap, yields a barrier for model-based controller design. To solve the above-mentioned problem, this paper develops a control-oriented model by two stages. Specifically, the first stage is to show an explicit formula of the levitation force with regard to the levitation gap by neglecting end effect; meanwhile the “maximum–minimum rectification” method is put forward to evaluating an accurate levitation force. The second stage is to bring forth the control-oriented model on basis of the estimated levitation force. Although the paper focus mainly on the development of the control-oriented model, an example of PD controller is provided to verify its validation. Experiment results demonstrate the estimated levitation force is highly consistent with the real one. Simulation results show that the control-oriented model is sufficiently reliable. The research bridges the gap between the physical model and the model-based controller for the electrodynamic levitation with permanent magnet Halbach array.

The emergence of van der Waals (vdW) magnets has created unprecedented opportunities to manipulate magnetism for advanced spintronics based upon all-vdW heterostructures. Among various vdW magnets, Cr1+δTe2 possesses high temperature ferromagnetism along with possible topological spin textures. As this system can support self-intercalation in the vdW gap, it is crucial to precisely pinpoint the exact intercalation to understand the intrinsic magnetism of the system. Here, we developed an iterative method to determine the self-intercalated structures and show evidence of vdW "superstructures" in individual Cr1+δTe2 nanoplates exhibiting magnetic behaviors distinct from bulk chromium tellurides. Among 26,332 possible configurations, we unambiguously identified the Cr-intercalated structure as 3-fold symmetry broken Cr1.5Te2 segmented by vdW gaps. Moreover, a twisted Cr-intercalated layered structure is observed. The spontaneous formation of twisted vdW "superstructures" not only provides insight into the diverse magnetic properties of intercalated vdW magnets but may also add complementary building blocks to vdW-based spintronics.

Scorpius is a multipulse linear induction accelerator (LIA) under development for flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). Therefore, it is more susceptible to corkscrew motion of the beam, which also depends on beam energy spread and focusing magnet misalignments. For energy spread and alignment tolerances expected for Scorpius, a magnetic tune designed to suppress BBU is shown to produce corkscrew motion within the range that can be controlled through the use of steering dipoles on existing LIAs. A gap-voltage modulation scheme is shown to almost completely eliminate chromatic effects such as corkscrew.

Abstract In this study, dense bulk iron nitrides (FexN) were synthesized for the first time ever using spark plasma sintering (SPS) of FexN powders. The Fe4N phase of iron nitride in particular has significant potential to serve as a new soft magnetic material in both transformer and inductor cores and electrical machines. The density of SPSed FexN increased with SPS temperature and pressure. The microstructure of the consolidated bulk FexN was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. XRD revealed a primary phase of Fe4N with secondary phases of Fe3N and metallic iron. Finite element analysis (FEA) was also applied to investigate and explain localized heating and temperature distribution during SPS. The effects of processing on interface bonding formation and phase evolution were investigated and discussed in detail to provide insight into fundamental phenomena and microstructural evolution in SPSed FexN. Graphic abstract

The High Temperature Superconducting (HTS) Conductor on Round Core (CORC) cables have been widely utilized to fabricate various superconducting applications for power transmission, fusion, and magnets with high current density. Understanding the AC loss behavior of CORC cables during the cable design process is essential for analyzing its electromagnetic performance and evaluating its future industry potential. The aim of our research is to investigate the AC loss dependence caused by the magnitude and frequency of applied external variations to the magnetic field. This paper describes the simulation models of HTS CORC cables based on the finite-element method (FEM) by using an H-formulation in a commercial software named COMSOL Multiphysics. Three-dimensional (3-D) CORC models, with three HTS tapes wound around each layer, were built and analyzed. The 3-D CORC models, built using the FEM method, were then verified with published experimental results. AC losses dissipated in the CORC cables, resulting from applied external varying magnetic field, were calculated and examined.

HL-2M tokamak is one of largest magnetic confinement fusion devices designed and constructed by Southwestern Institute of Physics (SWIP), China National Nuclear Corporation (CNNC), the first plasma was obtained on December, 4th, 2020. The magnets system which plays an important role for the plasma confinement consists of 20 toroidal field (TF) coils and 18 poloidal field (PF) coils. The magnets system commissioning was carried out by two phases: self-commissioning and integrated commissioning. The first phase: self-commissioning including joint resistance commissioning, turn to turn insulation commissioning, ground insulation commissioning, deionized water sealing commissioning was accomplished during the installation and test of the magnets system. The second phase: the integrated commissioning with power supply system, ground system, measurement and data acquisition system, plasma control system, interlock and safety system was accomplished based on the results of the first stage. The total commissioning of magnets system in HL-2M tokamak for the first plasma have been accomplished successfully.

The traditional permanent magnet electrodynamic suspension (PMEDS) structure has a high cost and low lift to drag ratio caused by sizeable magnetic resistance, which limits its widespread use. Hence, an annular Halbach structure of permanent magnet electrodynamic wheel (EDW) is studied in this paper, which is able to convert the magnetic resistance into the thrust force and avoid extra energy consumption, thus have the potential to be applied into the maglev car system. This paper established an experimental platform to measure the levitation force and thrust force of the EDW, then the force characteristics and variation tendencies were analyzed. Next, to verify the effectiveness and accuracy of the experiment, the comparison between force results from the experiment and that from the 2D FEM simulation were studied. Eventually, this paper lays a foundation for further research on the dynamic levitation characteristics of the EDW. And it provides an individual experimental basis and theoretical guidance for the study of maglev cars based on the PMEDS principle.

In this study, firstly, an artificial intelligence algorithm based on particle swarm optimization was adopted to create the electromagnetic and structural mechanics coupling design program of the main magnet system and its active shield. Using this computer program, the main magnet was optimally designed to be a split structure composed of HTS multi-stacked pancake coils, and its operating temperature was under 20 K. Then, we confirmed that the magnet accuracy in 200 mm DSV, the magnetic error of spherical harmonic expansion, the magnetic field distribution in the room-temperature bore, the distance to 5-Guass line and the electromagnetic stress characteristic of an optimally designed magnet are all sufficed requirement of the design. Finally, we reported the system integration of the main HTS split magnet and active shield, verified the effectiveness of the structural stability during the operation of the compact 3-T MRI.

To develop the application potential of conductor on round core (CORC) cables in the next generation of fusion magnets and accelerator magnets, fully automatic mechanized winding technology is required for the long CORC cables manufacturing. Meanwhile, the manufacturing and usage of the CORC cable are both limited by the strain sensitivity of the wound ReBCO tape on the CORC cable, because the processes may cause the superconducting layer of the ReBCO tape damaged when the strain limit is exceeded. The strains can arise from the manufacturing, bending, cooling, and operation of the cable and magnet, especially for the needed cyclic bending-straightening procedure for a long and multilayer cable winding layer by layer. Thus in this manuscript, a 1-m-long 12-layer CORC cable was manufactured to study the influence of cyclic bending on the critical current carrying performance of the CORC cable. It is consisted of 28 ReBCO tapes from Fujikura with 4 mm width and 0.05mm substrate thickness. The central core has an outer diameter of 3.85 mm. The cyclic bending-straightening experiment was conducted with a bending diameter of 900 mm and 700 mm, the Ic was tested at 77 K and self-field. After the cyclic bending test, the sample was bended to a diameter of 95 mm, which is planned to be used for the following insert solenoid coil, and has been verified no influence on the critical current carrying performance if bended without cyclic bending-straightening treatment. The results show that the required diameter for the reel experiencing cyclic bending-straightening procedure for ReBCO cable winding is suggested to be larger than 700 mm, especially for the equipment used for multilayer cables winding.

In this paper, the power factor (PF) characteristic for a flux-modulated permanent magnet (FMPM) motor has been analyzed and investigated. To obtain high PF FMPM motor, the magnetic source topologies effect is analyzed based on flux-modulated principle. Firstly, the PF calculation method of the FMPM motor is derived, and some key parameters affecting the PF are analyzed theoretically. Secondly, compared and analyzed the PF from perspective of magnetic source topologies (MSTs) effect, the initial model is determined. And some key parameters are designed and the FMPM performances are evaluated. Finally, research results show that a FMPM motor with surface-embedded PM topology and 18-slot 28-pole has high PF and torque capacity. Moreover, this paper provides guidance for the same design to gain high PF from perspective of magnetic source topologies effect.

The HTSConductor on Round Core (CORC) Cables have been widely recognized as the proper candidate for superconducting applications such as the high-field magnets and power transmission cables. This article presents the modeling of HTS CORC cables using the FEM H -formulation model merged into the package COMSOL Multi-physics. The 2D and 3D H -formulation models of HTS CORC cables were compared and analyzed. There were two important parameters in our CORC design: (1) the gap angle between the HTS tapes in a single layer, and, (2) the degree of twist for HTS tapes (normally identified as the pitch). The 2D CORC model has much faster solving speed over the 3D model and sometimes is able to model the AC loss in a reasonable range, while, the 3D CORC model has the advantages over 2D CORC model with respect to more information in each sector with the different conditions of two parameters above, and more realistic loss calculation.

In this work, SEM images analysis and fractal dimension calculations are performed on the fracture surfaces for N50-type with low coercivity, 30 EH-type with high coercivity, and isotropic Nd-Fe-B permanent magnets. It is discovered for the first time that the difference between the fractal dimensions of fracture surface parallel and perpendicular to the c-axis D ∥ and D ⊥ for N50-type magnet with low coercivity is large, and the difference between the fractal dimensions of D ∥ and D ⊥ for 30 EH-type magnet with high coercivity is small. However, there is almost no difference in the fractal dimension of D ∥ and D ⊥ for isotropic magnet. The correlation between anisotropic fractal dimension of the fracture surface and coercivity is revealed. The difference between the fractal dimension of fracture surface D ∥ and D ⊥ not only reflects the difference in micro morphology, but also serves as an important performance parameter to characterize the coercivity of the magnet, which provides new insights for studying the relationship between the magnetic properties and the microstructure of permanent magnetic materials.

The engineering design of the China Fusion Engineering Test Reactor (CFETR) has been completed in 2020. A largescale R&D project for CFETR named the comprehensive research facility for fusion technology (CRAFT) was initiated in Sep. 2019. As a sub-task of the CRAFT, a superconducting experiment testing platform (Super-X for short) is planned to be constructed for evaluating the future superconducting parts performance. Its main technical parameter includes: the background field of 15 T, the dimensions of testing space of 100 × 160 × 550 mm, the field homogeneity of testing space ≥ 95%, and the maximum testing current of 100 kA. For now, the preliminary design for Super-X has been accomplished. The DC magnet provides the background magnetic field for Super-X. It is a kind of split coil that includes two symmetrical coils assemblies. The innermost diameter is about 644 mm, the outermost diameter is 2874 mm. Each coil assembly is composed of three concentric Nb3Sn coils. The peak field is 15.7 T and the field homogeneity reach to 98.2%. The high field coil (HFC) and medium field coil (MFC) is typically dominated by high- Jc Nb3Sn cable-in-conduit conductor (CICC), and the low field coil (LFC) by ITER grade Nb3Sn CICC. This paper presents the preliminary design of the background DC magnet system (BM).

The design of a 14 T MRI system was recently announced by the Institute of the Plasma Physics Chinese Academy of Sciences. Thissystem is operating at 4.5 K and 1848 A to produce a magnetic field of 14 T. Because of the high magnetic field and high working current of the system, the 14 T MRI magnet is subjected to huge electromagnetic load and mechanical load during the operational period. The preload structure of MRI is used to overcome the coil gravity and eliminate the relative gap between the coils. In this paper, the preliminary structure design of 14 T MRI system is introduced, and the mechanical properties of preload structure and support structure are evaluated. Through the finite element analysis, the preload structure meets the material strength, and the design is reasonable.

A prototype of the high temperature superconducting (HTS) Maglev system for the electromagnetic launch was built in our laboratory. To meet the higher carrying capacity requirement of this practical application, multi-pole permanent-magnet guideways (PMGs) with different flux concentration methods and various arrangement schemes of HTS bulks have been proposed. The magnetic field distribution of these multi-pole PMG with the iron and permanent magnet (PM) concentration schemes has been estimated by employing both analytical and finite element methods. Meanwhile, a two-dimensional simulation model was established to evaluate the levitation and lateral performance of the Maglev system with several arrangement cases of HTS bulks. It has been validated that the total levitation force of the system can be significantly improved by increasing the pole number of the PMG and applying the optimal arrangement scheme.

The High-temperature Superconducting (HTS) magnet is one of the most promising technologies to accommodate various high field applications. With the high magnetic field, the quench problem of HTS material should be considered with extra care, and the specific quench protection scheme should be projected. In this article, the modeling of the quench protection of an HTS magnet for the MRI system is presented. The modeling strategy was composed of two stages: Stage 1 the HTS magnet was in the normal operation circuit, and Stage 2 the HTS magnet was switched to the heat dissipation circuit. The 1st stage was based on the finite element method (FEM) using the H -formulation together with the thermal-coupled model, which simulated the current distribution of typical HTS tapes and showed the process of temperature increase when the hot source occurred. The 2nd stage was based on the analytical model to investigate the reasonable damping resistance and the hot spot temperature of the HTS magnet.

To deal with the coupling between the levitation force and torque, a new bearingless switched reluctance motor (BSRM) is presented in the paper, in which the torque flux is separated with the levitation flux. In addition, due to the low cost and power of the three-phase power converter, the radial levitation of the proposed BSRM is driven by a three-phase power converter. The structure of the proposed BSRM is first introduced. The mathematical models of radial levitation force are second established by employing equivalent magnetic circuit approach. Finally, the electromagnetic characteristics of the BSRM, such as flux field distribution, transient levitation force and force-current relationship are investigated through the MagNet 3D. The research results indicate that the novel structure has good performances.

In this paper, a hybrid permanent magnet (HPM) motor with unique external q -axis flux barriers design is investigated. The equivalent magnetic circuit models of dq -axes are established. Based on this, the relationship between the design parameters of dq -axes and saliency characteristics is analyzed. By rational design of dq -axes parameters, the contrary saliency characteristics of HPM motors can be achieved. Then, two HPM motors with contrary saliency characteristics, namely positive saliency HPM (PS-HPM) motor and inverse saliency HPM (IS-HPM) motor are obtained by a multi-objective optimization method. To explore the impact of saliency characteristics on motor performance, the inductance, torque, anti-demagnetization characteristics of PS-HPM and IS-HPM motor are compared and discussed in detail. The comparison results indicate that the HPM motor with IS characteristic is a more competitive candidate for over-load operation due to better anti-demagnetization and overload capability.

The flux-modulated machine based on air-gap magnetic flux modulation theory has become a focus in low speed and high torque density applications. In this paper, the optimal design of a large scale flux modulation (FM) permanent magnet (PM) generator with high temperature superconducting (HTS) bucks for wind energy conversion systems is presented. Firstly, the working performances of the generator with and without HTS bucks sandwiched between iron segments are analyzed and compared through finite element analyses (FEA). The FM effect enhancement by employing the HTS bucks is proved through the comparisons. Secondly, the sensitivities of the generator structural parameters on the back electromotive force (EMF) and the cogging torque amplitude are analyzed by Taguchi method to decide the optimization variables and their variation ranges. Thirdly, the structural parameters determined by the sensitivity analyses are optimized through the coupling of genetic algorithm (GA) and FEA to maximum the generator output power capacity. The calculation burden during optimization is reduced with a reduction on the optimization variable number through the Taguchi method based sensitivity analyses. Finally, the electromagnetic characteristics of the FMPM generator with optimized structural sizes are numerically investigated.

The permanent magnet linear synchronous motors have the advantages of high efficiency, high thrust density and high power factor, which is mostly attractive to the fields of electromagnetic launch. The electromagnetic field of long primary PMLSM with different structures are analyzed firstly by finite element method in this paper. Then, the thrust characteristics of the motors with different topologies are studied and compared, which fully demonstrates the advantages and feasibility of the proposed PMLSM.

For rope-less elevator applications, a novel high temperature superconducting (HTS) flux modulation linear motor (LM) using Halbach permanent magnet (PM) arrays is investigated in this paper. The flux modulation structure with iron segments can serve simultaneously and regulate the magnetic field. The HTS bulks are filled between the iron segments to further improve the flux modulation effect based on the Meissner effect. Compared with conventional counterparts, the force density of the proposed LM with HTS fillers is apparently higher. Furthermore, the mover with Halbach PM arrays is used to reduce the force ripple and increase the output force. The electromagnetic performances of the flux-modulated LM are researched by transient finite element analyses (FEA) to prove the effectiveness of the proposed structure. Finally, the parameters of the motor structural are optimized and analyzed by the combination of FEA and genetic algorithm (GA).