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 toroidal field (TF) coil has been designed to create a magnetic field of over 14.3 T. The TF conductors need to operate stably at 14.3 T, requiring the exclusion of conductor performance degradation from thermal and electromagnetic loading as much as possible. The maximum Lorentz force will reach about 1200 kN m^-1, which is much higher than that of ITER conductors. In previous research, performance degradation was found during electromagnetic cycles and warm-up-cool-down cycles. A correlation was found between a conductor's degradation and its mechanical properties. According to the analysis, a conductor with a short twist pitch (STP) scheme or a copper wound superconducting strand (CWS) design has large stiffness, which enables significant performance improvement in terms 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 conductors 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 with ITER TF and central solenoid conductors.