First Results of AC Loss Test on ITER TF Conductors With Transverse Load Cycling

The influence of the expected Lorentz loading and time dependent operating conditions of a magnet on the conductor AC loss is experimentally simulated by a cryogenic cable press that applies cyclic mechanical loading. A series of ITER conductor tests with the press have commenced and we report on the results from the first set of two TF conductors, which have the option-II cabling scheme but consist of NB₃Sn strands from different manufacturers. With the press, we apply a transverse load of 578 kN/m and the load cycle is repeated up to 30,000 times. As a function of load cycles, we measure the cable mechanical stiffness, interstrand contact resistances, and the coupling loss. When compared with a previously measured option-II type conductor, the present conductors have higher initial losses. However, they showed greater cable displacement and larger increase in contact resistance with load cycles. This is due to the lower cable stiffness thought to be related to the lower axial strand stiffness, resulting in greater cable displacement than the previous cable. Consequently, the two conductors tested here have lower losses already within the first few cycles.