In a significant step forward for the development of high-temperature superconductors (HTS) for fusion applications, researchers from the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), and their international collaborators have successfully tested a prototype REBCO (rare-earth barium copper oxide) cable-in-conduit conductor (CICC) capable of withstanding a cyclic Lorentz load of at least 830 kN/m, corresponding to a transport current of 80 kA at 10.85 T and 4.5 K. This achievement marks a milestone in the development of HTS for large-scale and high-field magnet applications, as reported in Engineering.

The development of superconducting magnets operating at peak magnetic fields higher than 15 T is a critical technological challenge for the next generation of fusion devices, such as the European Demonstration Fusion Power Plant (EU-DEMO), the Chinese Fusion Engineering Test Reactor (CFETR), and the American Affordable, Robust, Compact (ARC) reactor. These devices require superconducting magnets capable of providing the poloidal and toroidal magnetic field components necessary for plasma confinement. The strength of the magnetic field is a key parameter in preventing the plasma from contacting the first wall and achieving the required conditions for fusion reactions.

The newly developed REBCO-based CICC design incorporates several optimizations and innovations to enhance mechanical integrity and operational stability. The CICC is composed of six twisted sub-cables, each made from 48 REBCO tapes helically wound around a copper core. The sub-cables are inserted into copper tubes and reinforced with copper “keystone” segments to prevent deleterious displacements and deformations. The jacket is made of a newly developed high-nitrogen material with combined high strength and ductility under cryogenic temperatures. These measures are expected to ensure good operational stability and the ability to withstand a Lorentz load exceeding 1000 kN/m.

The prototype CICC was tested at the SULTAN facility in Switzerland, where it demonstrated stable operation at 80 kA under a background magnetic field of 10.85 T. No performance degradation was observed after repeated warm-up/cool-down (WUCD) cycles and quench campaigns. The current sharing temperature (T_cs) at 40 kA and 10.85 T was measured to be around 39 K, providing a temperature margin of over 10 K with respect to an operating temperature of 4.5 K. When scaled to a 20-T peak field and 46.5-kA transport current, the CICC is expected to have a temperature margin higher than 15 K.

The successful testing of this REBCO-based CICC demonstrates its potential for use in next-generation fusion devices. The results show that REBCO tapes can meet the rigorous stability requirements needed for high-field fusion magnet applications. However, several key issues remain to be addressed, including scaling of manufacturing technology, alternating current (AC) loss evaluation and control, high-precision coil winding, reliable low-resistance splices, and sensitive quench detection and protection for large-scale magnets.

This achievement represents a significant step towards the practical application of REBCO-based CICCs in high-field fusion magnets. The research team plans to continue addressing the remaining challenges in a systematic and rigorous manner, with the goal of enabling the construction of the next generation of fusion reactors.

The paper “Performance of the First 80-kA HTS CICC for High-Field Application in Future Fusion Reactors,” is authored by Huan Jin, Guanyu Xiao, Chao Zhou, Chuanyi Zhao, Shijie Shi, Haihong Liu, Fang Liu, Huajun Liu, Yu Wu, Zuojiafeng Wu, Hugues Bajas, Jack Greenwood, Mattia Ortino, Kamil Sedlak, Valentina Corato, Richard Kamendje, Alexandre Torre, Arend Nijhuis, Giulio Anniballi, Arnaud Devred, Jinggang Qin, Yuntao Song, and Jiangang Li. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.05.015. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.