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

The performance of two mass-produced Nb
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.