Performance of low-loss demountable joints between CORC® cable-in-conduit-conductors at magnetic fields up to 8 T developed for fusion magnets

High-temperature superconductors (HTS) are promising candidates for use in the high-field magnets needed in particle accelerators and fusion reactors. HTS conductor on round core (CORC®) cables and wires wound from ReBa2Cu3O7-x (REBCO) coated tapes are being developed for use in high-field magnet applications including fusion magnets operating at currents beyond 80 kA, requiring them to be bundled into cable-in-conduit conductor (CICC) configurations. The use of HTS cables enable demountable superconducting fusion magnets that would allow easier access to the fusion machine for maintenance and parts replacement. Such demountable magnets require practical, low-resistance joints, capable of injecting current uniformly into the many REBCO tapes that make up different cable designs. Optimization steps on CORC® cables have resulted in high-current terminations and joints with a joint resistance measured between a pair of 30-tape CORC® cables of 51 nΩ at 76 K and 1.9 nΩ at 4 K. Demountable joints between CICCs consisting of six CORC® cables arranged in flat and round configurations were also tested and compared to joints between low-temperature superconducting (LTS) CICCs consisting of NbTi Rutherford cables. Samples were paired into two configurations (LTS-to-LTS and HTS-to-HTS) with a demountable joint between them that were each tested in series with currents up to 10 000 A in an applied background magnetic field of up to 8 T. The total loop resistance of the HTS-to-HTS sample, including their terminations and joint, was about 4 nΩ at 4 K in self-field with the resistance of the copper pressed joint being less than 1 nΩ. At 8 T, the total loop resistance increased to 6.9 nΩ with the pressed joint contributing 1.4 nΩ. These initial tests prove the feasibility of producing remountable (dry) joints with low resistance between superconducting magnet windings in future compact fusion machines.

高温超导体（HTS）是粒子加速器和核聚变反应堆所需的高场磁体的有希望的候选材料。正在研发由ReBa₂Cu₃O₇₋ₓ（REBCO）涂层带材绕制的圆形芯高温超导（CORC®）电缆和导线，用于高场磁体应用，包括在超过80 kA电流下运行的核聚变磁体，这要求它们被集束成导管内电缆导体（CICC）结构。高温超导电缆的使用使得可拆卸的超导核聚变磁体成为可能，这将使核聚变装置更易于维护和更换部件。这种可拆卸磁体需要实用的低电阻接头，能够将电流均匀地注入构成不同电缆设计的许多REBCO带材中。对CORC®电缆的优化步骤已经产生了大电流终端和接头，在一对30带CORC®电缆之间测量的接头电阻在76 K时为51纳欧，在4 K时为1.9纳欧。还对由六根呈扁平状和圆形排列的CORC®电缆组成的CICC之间的可拆卸接头进行了测试，并与由NbTi卢瑟福电缆组成的低温超导（LTS）CICC之间的接头进行了比较。样品被配成两种结构（LTS - LTS和HTS - HTS），它们之间有一个可拆卸接头，每个样品在高达8 T的外加背景磁场中进行高达10000 A的电流串联测试。HTS - HTS样品的总回路电阻，包括其终端和接头，在4 K自场下约为4纳欧，其中铜压接接头的电阻小于1纳欧。在8 T时，总回路电阻增加到6.9纳欧，其中压接接头贡献1.4纳欧。这些初步测试证明了在未来的紧凑型核聚变装置中，在超导磁体绕组之间制造低电阻可重新安装（干式）接头的可行性。