High-temperature superconductors (HTS) are promising candidates for use in the high-field magnets needed in particle accelerators and thermal nuclear fusion reactors. Advanced Conductor Technologies is developing HTS Conductor on Round Core (CORC^®) cables and wires wound from ReBa₂Cu₃O_7-x (ReBCO) coated tapes, for use in high-field magnet applications. CORC^® cables are also developed for fusion magnets operating at currents in excess of 80 kA, requiring them to be bundled into cable-in-conduit conductor (CICC) configurations. The use of HTS cables enable demountable fusion magnets that would allow easier access to the fusion experiment for maintenance and parts replacement. Such demountable magnets require practical, low-resistance cable and CICC joints, capable of injecting current uniformly into the many tape layers that make up the CORC^® cables. Optimization steps on CORC® cables have resulted in high-current terminations with significantly reduced contact resistance, allowing even current injection at high ramp rates. Demountable joints between CICCs consisting of six CORC^® cables arranged in flat and round configurations were tested along with an LTS CICC consisting of NbTi Rutherford cables for comparison. Samples were paired up in various configurations (LTS-to-LTS, HTS-to-HTS, or LTS-to-HTS) and tested in series with currents up to 10,000 A, while the demountable joints experienced a background magnetic field of up to 8 T. A novel Hall-probe array was incorporated into each sample to study current distribution between cables during current ramping. The total resistance between samples, including their terminations and joint, was less than 10 nΩ at 4 K, with the contact resistance between the copper pressure joint being less than 1 nΩ. These initial tests prove the feasibility of producing remountable (dry) contacts with low resistance between superconducting magnet windings in future compact fusion machines.

Keywords: CORC, CICC, Fusion, Magnet