Performance Analysis of Mass-Produced Nb3Sn Conductor for Central Solenoid in ITER

The performance of two mass-produced Nb3Sn conductors for the ITER central solenoids was tested for the first timmass-produced Nb3Sn conductorse. One was cut from the forward end of an 80-m-long conductor, and the other was cut from the forward end of a 918-m-long conductor. The fifth-stage twist pitches of these conductors were lengthened by approximately 16% during cable insertion and compaction with conduit. The current sharing temperatures Tcs were measured over 20 000 electromagnetic cycles, including four thermal cycles between 4.2 K and room temperature. The Tcs of the former conductor increased and became almost constant through the cycling. In contrast, Tcs of the latter conductor not only increased but also decreased slightly against cycling. The Tcs decline rate after 10002 cycles was -4.50 × 10-6 K/cycle. If this rate is assumed to continue after 20000 cycles, Tcs would decrease by -0.27 K over 60000 cycles. Even so, Tcs is higher than an acceptance criterion of 6.5 K at 60 000 cycles. The ac losses Q of both conductors at a current of 0 kA were almost the same as or slightly lower than Q of a short sample conductor whose fifth-stage twist pitch was not lengthen. On each conductor, Q at 40 kA was approximately 10% higher than that at 0 kA; thus, the effect of the transport current on Q was not large.