Chao Zhou

Growing demands for superconducting cables with high current density and excellent stability in nuclear fusion, high energy physics, and smart grids have rendered high temperature superconducting (HTS) cables based on REBCO coated conductors a critical technical route for next generation high field magnets. The Vacuum Impregnated Pressurized Roebel (VIPER) cable inherits the advantages of Twisted Stacked-Tape Cable (TSTC) and Cable-in-Conduit Conductor (CICC), constituting a novel HTS conductor architecture with high current carrying capacity and structural stability. To systematically investigate the influence of tape stacking number on the self-field current carrying performance of VIPER cables, three three dimensional electromagnetic models corresponding to 5 slot 8 layer, 5 slot 9 layer, and 5 slot 10 layer configurations were developed and simulated at temperature 77 K using Ansys Maxwel.The results demonstrate that the relative errors between simulated and experimental critical currents for all three configurations are within an acceptable range of 5%. As the number of stacked layers increases, the total current-carrying capacity rises from 3810.8 A (8 layers) to 4156.0 A (9 layers) and 4515.2 A (10 layers), while the inter-slot current distribution deviation decreases from 7.35% to 1.55%. Nevertheless, the self-field superposition effect intensifies, with a maximum value of approximately 0.433 T. The average current carried by a single tape decreases from 95.3 A to 90.3 A, and its ratio to the self-field critical current of an individual tape (195 A) declines from 48.9% to 46.3%. The local critical current of the tapes gradually reduces from approximately 183.6 A at the innermost layer to 94.96 A at the outermost layer, yielding a current-sharing efficiency of only 62.2%–63.2%, substantially lower than the theoretical upper limit under ideal full current sharing (6130–7149 A). The measured total current of the 10-layer cable reaches 95.1% of the conservative weakest-link limit (4748 A). The marginal gain drops from 9.1% for the transition from 8 to 9 layers to 8.6% for the transition from 9 to 10 layers, indicating diminishing returns when further increasing the layer count under self-field limitation, proposes optimal parameters based on theoretical and data analysis This study provides fundamental data and quantitative references for optimizing the stacking layer number of VIPER cables.

The performance of REBCO multi-stack cables is crucial for next-generation high-field fusion magnets, it is often limited by uneven current distribution. This study employs a 3D finite-element model based on the weak form of the H-formulation to analyze current non-uniformity within a novel BRAided Stacks of Tapes (BRAST) assembly. The model rigorously accounts for the nonlinear E–J power law of the REBCO material, as well as the effects of inter-tape and terminal resistances. The model’s accuracy is verified experimentally. Simulation results establish a clear hierarchy of stability drivers. First, non-uniform terminal resistance determines the inter- tape current imbalance. Low inter-tape contact resistance has a dual role: it amplifies short-range current imbalances at the cable entry point, leading to increased local current loading, while simultaneously promoting a more uniform longitudinal current distribution within the cable, thereby mitigating current inhomogeneity. Furthermore, the analysis reveals that tape regions with reduced critical current can be the onset of overall stack transition, and that the overall stability of the cable is determined by the minimum current-carrying capacity within the tape stack. This study provides quantitative guidance for controlling terminal resistance uniformity and optimizing contact resistance, thereby improving the stability and robustness of BRAST and similar multi- tape superconducting cable systems.

The helical-channel magnetohydrodynamic (MHD) thruster is a silent underwater propulsion device free of rotating mechanical components, which fundamentally eliminates the inherent mechanical noise induced by blades and shaft systems in conventional propeller-driven thrusters. Taking a 10 T-class superconducting helical-channel MHD thruster as the research object, this work establishes a three-dimensional numerical simulation model with bidirectional electromagnetic-fluid coupling via Maxwell–Fluent, filling the research gap of systematic optimization of helical pitch angles in existing low-magnetic-field numerical investigations. A composite magnetic circuit configuration consisting of main coils and compensation coils is adopted, achieving a magnetic field uniformity of 90.13% within the effective working section and markedly alleviating magnetic field attenuation at both ends of the flow channel. Three schemes with helical pitch angles of 23.00°, 17.66°, and 14.29° are quantitatively compared to analyze the effects of helical pitch angle on current density, static pressure, total pressure, radial/axial flow velocities and three-dimensional helical streamlines. Under the rated design mass flow rate of 15.5 kg/s, the scheme with the small pitch angle of 14.29° delivers a thrust of 262.56 N and an electromagnetic efficiency of 7.23%; compared with the large pitch angle scheme of 23.00°, its thrust is improved by 28% and electromagnetic efficiency rises by 53%. Reducing the helical pitch angle extends the effective coupling distance between seawater and the electromagnetic field, optimizes the uniformity of radial current distribution, suppresses eddy currents and Joule heat loss, converts more electromagnetic energy into fluid pressure energy, and thus greatly improves the energy utilization efficiency of the propulsion system. This study provides quantitative design references for the structural optimization and engineering prototype development of low-noise superconducting underwater propulsion equipment, and supports the engineering application of helical-channel magnetohydrodynamic thrusters.

A heat treatment system, which is used in combination with a stepwise heat treatment method, has been constructed at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) for the primary Bi-2212 (Bi2Sr2CaCu2Ox) CICC (cable-in-conduit conductors)-type high-field insert coil. The design and manufacturing of the first Bi-2212 CICC-type insert coil has been completed. Prior to the final heat treatment for the CICC-type coil, a validation experiment is required to demonstrate the effectiveness and feasibility of the system and method. The validation experiment was concluded with the implementation of a heat treatment process on the model coil and the witness samples. In the course of the validation experiment, the various parameters of the heat treatment process – including temperature, pressure and oxygen content – were subjected to meticulous monitoring by a range of measuring instruments. The temperature evolution and uniformity of the process meet the technical requirements of the heat treatment process for the Bi-2212 CICC-type coil. It is evident that the critical performance of the witness samples meets the requisite value. The results of the study demonstrate the efficacy and feasibility of the system and method of heat treatment employed in the final heat-treatment process of the first Bi-2212 CICC-type coil. Consequently, the concluding phase of the heat treatment process was initiated on the inaugural Bi-2212 CICC-type insert coil. It is evident from the findings of the experiment that the coil displays a critical current of 5.4 kA at 4.2 K and 20 T background field, thus indicating its superior capacity. The success of the heat treatment for the first Bi-2212 CICC-type coil establishes a solid foundation for the heat treatment of the future large-scale and full-size Bi-2212 cable-in-conduit conductor.

The use of High-Temperature Superconducting (HTS) technology in a fusion Central Solenoid (CS) magnet enables a significant enhancement in the inductive flux driving the plasma, achieved by increasing the magnetic field strength. This approach has garnered significant attention, leading Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) to join the research effort in designing and manufacturing a hybrid CS magnet that combines HTS and Low-Temperature Superconducting (LTS) coils. There is considerable mutual inductance between HTS and LTS coils, and their coupling can substantially affect the electromagnetic, mechanical, and thermal properties of hybrid CS magnet. Particularly, the quench of one or several coils can cause fluctuations in the performance parameters of the remaining coils, which is a critical issue in hybrid magnets that warrants further investigation. This paper analyzes and discusses the variations in electrical, magnetic, mechanical, and thermal parameters of the hybrid magnet following a quenching event, and offers reference insights for the design of such magnets from a stability-oriented perspective.

The next generation tokamak aiming to carry out D–T experiments and to demonstrate power generation, is under development at the Institution of Plasma Physics, Chinese Academy of China (ASIPP). A hybrid magnet configuration is proposed for the central solenoid (CS) coil of this tokamak, a high-temperature superconducting coil is inserted into an outer Nb ₃ Sn coil for increasing the flux. Minimization of the coupling losses is investigated in the Nb ₃ Sn cable-in-conduit conductor (CICC) with rectangular cross-section for the outer CS coils using numerical modeling and experimental verification. The AC loss was measured on several candidate conductors with a superconducting AC Dipole at ASIPP and the numerical modeling was performed with the JackPot-AC/DC ^© model, which was developed by University of Twente (UT). The data from the experiments tested in UT were used for calibrating and validating the model computations. With the model, further optimization on cable parameters was then carried out. The results show that the twist pitch (TP) of the first stage and the TPs ratio have an important impact on the rectangular CICC coupling loss, and the influences of these two factors are related. In addition, the use of a rectangular cross-section CICC can have significant advantages when used in CS magnets.

High field magnetic resonance imaging (HF-MRI) systems can achieve higher image resolution and sensitivity, resulting in better image quality and more biological information, which has significant value in life science and clinical medicine applications. The development of HF-MRI system depends on the development of high field superconducting magnet. HF-MRI superconducting magnet needs to solve problems such as high magnetic field uniformity requirements, large stray field range, high coil electromagnetic stress, and shrinkage stress in low-temperature systems. This article introduces the design and optimization process of 14 T at 175 mm warm bore size animal MRI superconducting magnet. We used a nonlinear multiobjective programming algorithm to simultaneously optimize warm bore space (diameter 175 mm), magnetic field homogeneity and the stray magnetic field (5 Gauss line) for a 14 T MRI magnet. The spatial position, electromagnetic density, and electromagnetic stress of different coils are obtained, and the design stability of magnet coil is evaluated using coil loading ratio and current safety margin. In addition, the magnet coil former is designed, and the finite element method is used to perform mechanical simulation analysis on the coil former. The optimization results show that the warm bore of the magnet is 175 mm, and the homogeneity of the magnet design is 1.1 ppm at 60 mm DSV, magnet stray field (5 Gauss line) is 2.9 m in the axial direction, and 2.4 m in the radial direction from the center of the magnetic field. The minimum safety margin of the magnet coil is 10.6%, and the maximum hoop stress of the magnet coil is 225 MPa. The magnet meets the design requirements and provides necessary reference for the engineering prototype of the 14 T animal MRI superconducting magnet.

To meet the scanning requirements for ultra-high magnetic field strength (≥7 T) and high uniformity within Magnetic Resonance Imaging (MRI) equipment, this paper presents the design and implementation of a fully automated five-axis micro-positioning platform with a positioning accuracy of 50 μm. The platform enables full-area magnetic field measurement inside MRI devices via high-precision automatic scanning, providing data assurance for the precise current loading of the homogeneous field system. A systematic design of the motion actuator, probe fine-tuning mechanism, and probe rod of the micro-motion platform is described, utilizing 3D modeling software. A three-dimensional model of the micro-motion platform driven by a ball screw is established, and its static, dynamic, and vibration characteristics are analyzed via finite element analysis. The results show that the design scheme exhibits excellent mechanical properties, dynamic characteristics, and stability. The micro-motion platform has been successfully applied and tested on a 7 T MRI system, enabling precise scanning of magnetic field data. This study offers design insights for magnetic field scanning devices in magnetic resonance equipment.

Quench protection is a major subject for superconducting magnets, which operate at high current densities with high stored energy. Large amounts of energy should be removed to protect magnets. Due to its nonlinear properties, the zinc oxide (ZnO) varistor shows strong advantages compared to the constant resistance. In this work, the characteristics and its superiority over the constant resistance are demonstrated. First, the changes of current and voltage are analyzed during the discharge process. We find that the discharge time are shortened and the efficiency are increased in case of ZnO. Second, we report the experimental setup, including the rare earth (RE) Ba₂Cu₃O₇-x (REBCO) magnet, energy transfer elements, and the corresponding test platform. The experimental results show that the constant voltage demagnetization can be realized. This is consistent with the presented theoretical analysis.