High magnetic fields play a critical role in the development of modern science and technology, breeding many significant scientific discoveries and boosting the generation of new technologies. In the last few years, China has undertaken a great deal of work on the application of ultra-high-field (UHF) superconducting magnet technology, such as for the Synergetic Extreme Condition User Facility in Beijing, the UHF nuclear magnetic resonance/magnetic resonance imaging, nuclear fusion energy, particle accelerator, and so on. This paper reports the research status of UHF superconducting magnets in China from different perspectives, including design options, technical features, experimental progress, opportunities, and challenges.

The world’s first database on the effect of stabilizers on the resistivity and thermal conductivity of 20 different commercial REBa₂Cu₃O_7−δ (REBCO) tapes was established. The resistivity and thermal conductivity in the radial and circumferential directions were listed. The charging loss and self-protection ability of 20 different commercial REBCO tapes in the no-insulation coils were evaluated via simulation. By comparing and analyzing the data, the Cu/Ag interface was found to be the most probable primary factor determining the resistivity and thermal conductivity of REBCO tapes. Such a database can support abundant data for the design of the REBCO magnet or even the choice of REBCO switch or current lead. Another goal was to help the REBCO manufacturers find a feasible way to adjust the resistivity and thermal conductivity, thereby meeting different requirements of the REBCO magnet.

Metal-insulation (MI) REBCO high-temperature superconducting (HTS) magnet has the advantages of short charging delay, low contact losses, and self-protection abilities, which shows important application prospects in many fields. Recently, Institute of Electrical Engineering, Chinese Academy of Sciences developed a prototype on-board MI HTS coil used for electrodynamic suspension (EDS) system working with an acceleration of beyond 8 g. To design a reliable engineering on-board magnet, specific I_c angle dependence data of short sample under different fields were fully considered to estimate the operating margin and losses accurately of the on-board magnet. A semi-analytical method, combination of the dynamic circuit method and finite element method, was used to analyze the dynamic electromagnetic force distribution inside the on-board magnet under motion state, in which the effect of the propulsion coils and the figure-eight-shaped coils were taken into considerations. Finally, a full-size MI double pancake racetrack coil was fabricated and tested in a liquid nitrogen bath. The test results meet the design requirements and verify the feasibility of the design, which provides an important reference for the experiment of on-board EDS with high acceleration in the future.

Detailed simulation can play a fundamental role in the design, manufacture, and operation of high-field magnets. This study introduces a new equivalent circuit simulation method for the no-insulation (NI) superconducting magnet. The refined circuit model (RCM) can describe the current distribution inside the REBa ₂ Cu ₃ O _{7- δ} (RE, rare earth elements) tapes in the equivalent circuit model. A single turn of REBCO tape was divided in both the width and length directions to achieve better results. A simulation model for a NI REBCO insert magnet was established through the RCM. Simulation results show that the screen current starts to saturate within 500 s during the excitation of the HTS magnet. The refined circuit model can help to make a more detailed mechanical analysis of the REBCO magnets. It can also guide the excitation of the HTS magnet and screen current reduction through real-time simulation.

Active shielding technology has been widely applied to the superconducting magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) magnets design, revealing excellent performance on the stray field control. For such a highly homogeneous field superconducting magnet design, an appropriate optimization strategy is essential to guarantee the magnetic field homogeneity in the central region and the expected 5 Gauss line range, especially for the ultrahigh field superconducting magnet. Based on the compensating field optimization method, an actively-shielded whole-body 14 T MRI magnet and an actively-shielded 1.3 GHz NMR magnet were presented, and detailed analyses were conducted to evaluate the feasibility of the designs. The developed magnet design method, coil pattern, wire arrangement, and stress/strain adjustment will be used to guide the corresponding project implementation.