Performance of first insert coil with REBCO CICC sub-size cable exceeding 6 kA at 21 T magnetic field

Abstract The Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP, CAS) is developing the REBCO cable in conduit conductor (CICC) technology for applications in the next generation nuclear fusion device. The aim is a CICC comprising six REBCO sub-cables to satisfy requirements of operation with a current of around 40 kA and a peak field up to 20 T. To qualify the performance of the sub-size REBCO cable to be used in the CICC, two 25-turn insert solenoids have been designed, manufactured and tested at a current exceeding 6 kA subjected in a background field supplied by a water-cooled resistive magnet. The insert solenoid, wound from a 11.5-meter long REBCO CORC cable, was designed to investigate its current carrying capacity under high field and electromagnetic (EM) load at 4.2 K. The background magnetic field amounts up to 18.5 T, resulting in a peak magnetic field on the inner most layer turns of around 21.1 T at an operating current of 6.3 kA. Effects of operation with cyclic EM loads were tested by repeated current ramps to around 95 % of the critical current. Moreover, the V-I characteristics were measured at 77 K and self-field, to check effects from warm-up and cool-down (WUCD) cycles between room temperature and 77 K with liquid nitrogen. The results show no obvious degradation after dozens of high-current test cycles in background fields ranging from 10 T to 18.5 T. The insert solenoid demonstrates stable operation of the REBCO sub-size cable for CICC with EM loads of about 90 kN/m and WUCD cycles between room temperature and 77 K. These promising results indicate the potentials of this technology for further applications, in particular for full-size CICC for high performance Fusion magnets.