Experimental Research on the Critical Current Characteristics of HTS Cable-in-Conduit Conductor Under the Cyclic Transverse Load

Cables in large-scale fusion magnets are subjected to high transverse electromagnetic forces caused by high currents and magnetic fields. Consequently, they require sufficient mechanical strength to ensure safe and stable operation. To meet this requirement, a high-temperature superconducting (HTS) cable-in-conduit conductor (CICC) suitable for fusion reactors has been manufactured. Each conductor contains 10 round strands, and each strand is composed of a stack of 20 tapes (2mm wide) surrounded by filling material (Sn ₆₃ Pb ₃₇ ) and a copper former. The conductor is further encased in a round stainless steel jacket to accommodate the large Lorentz forces. To investigate the degradation of the critical current ( I_c ) under cyclic transverse loads, two prototype conductors, each approximately 1.4 m long, were fabricated using REBCO coated conductor tapes. Both conductors have the I_c around 8.8 kA in self-field at 77 K. Additionally, cyclic transverse loading tests were performed at 77 K, self-field. The results revealed that the conductors were able to withstand large transverse loads (>200 MPa) with less than 5% degradation of the I_c . However, a significant reduction in the I_c (∼25%) was observed after 100 cycles, with the load amplitudes ranging from 20 MPa to 200 MPa. When the conductor was subjected to 500 to 10,000 cycles, no significant change in the I_c was observed at ∼65% of its original value. Finally, to further understand and enhance the I_c characteristics of the conductor, we investigated the defects caused by fabrication imperfections and mechanical loading microscopically. Our results will have significant implications for further improving the mechanical strength of the conductor and its application in fusion magnets.