Research on Mechanical Properties of High-Performance Cable-in-conduit Conductors with Different Design

The China Fusion Engineering Test Reactor (CFETR) is a new tokamak fusion reactor under preliminary design, where the toroid field coil was designed to create over 14.3 T magnetic field. The TF conductors need to operate stably at 14.3 T, requiring to exclude conductor performance degradation from thermal and electromagnetic loading as much as possible. The maximum Lorentz force will reach to about 1200 kN/m, which is much higher than that of ITER conductors. In previous research, performance degradation was found during electromagnetic cycles and warm-up cool-down (WUCD) cycles. A relationship was found between conductor degradation and its mechanical properties. According to the analysis, a conductor with a Short-Twist-Pitch (STP) scheme or Copper Wound Superconducting strand (CWS) design has large stiffness, which enables a significant performance improvement in view of the electromagnetic and thermal load cycling. The cable stiffness is closely related to the number of inter-strand contact points inside the conductor. Based on this concept, four types of prototype cable-in-conduit-conductor samples with STP and CWS design were manufactured. The number of inter-strand contact points was analyzed, and mechanical transverse load testing was performed at 77 K. The results show that the conductor with more contact points per unit length exhibit a higher stiffness. However, the cable designed with high cable stiffness caused strand indentation, which was also investigated. In this paper, the conductor design and experimental results are discussed and compared to ITER TF and CS conductors. Keyword: CFETR TF, CICC, conductor design, mechanical properties, strand contact points