Mechanical and Electrical Properties of a CFETR CSMC Conductor under Transverse Mechanical Loadings

The central solenoid model coil (CSMC) project of the China Fusion Engineering Test Reactor was launched in 2014 to verify the technological feasibility of a large-scale superconducting magnet at the Institute of Plasma and Physics Chinese Academy of Sciences. The short twist pitch design recommended by CEA is chosen for the CSMC Nb₃Sn cable-in-conduit conductors. In order to better understand the evolution of transport properties and coupling losses related to the effect of electromagnetic load cycles, the mechanical and electrical properties were measured and investigated employing a special cryogenic press facility for the transverse mechanical loadings. The results show that the transverse compression (d_y) versus applied load force (F_y ) is different from first to subsequent loading cycles. This mechanical behavior can be interpreted by the combination of strands bending between the crossovers and strands deformation at the crossovers. The fitting relations of d_y versus F_y are also presented. The evolution of interstrand contact resistance (R_c) in the cabling stages with cyclic history and pressure effects are discussed. In addition, a fitting relation of R_c versus F_y is presented based on a combination of strand's microsliding and copper matrix resistivity. A clear correlation between intrapetal resistance R_c and coupling loss is also found.