Performance Analysis of Mass-Produced Nb sub(3)Sn Conductor for Central Solenoid in ITER

The performance of two mass-produced Nb sub(3)Sn conductors for the ITER central solenoids was tested for the first time. 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 $T_{cs}$ were measured over 20 000 electromagnetic cycles, including four thermal cycles between 4.2 K and room temperature. The $T_{cs}$ of the former conductor increased and became almost constant through the cycling. In contrast, $T_{cs}$ of the latter conductor not only increased but also decreased slightly against cycling. The $T_{cs}$ decline rate after 10 002 cycles was $-4.50\times 10-6}\ \text{K/cycle}$. If this rate is assumed to continue after 20 000 cycles, $T_{cs}$ would decrease by -0.27 K over 60 000 cycles. Even so, $T_{cs}$ 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.