Development of cable-in-conduit conductor for ITER CS in Japan

Abstract

The National Institutes for Quantum and Radiological Science and Technology has the responsibility to develop a cablein-conduit conductor (CICC) for the ITER central solenoid (CS). Qualification tests of CICCs fabricated in the initial development stage were carried out at the SULTAN test facility; the superconducting performance (T cs = current-sharing temperature) was found to be degraded by the repeated cyclic loading that simulates realistic ITER operating conditions. From destructive examination and neutron diffraction tests, this degradation appears to result from bending strain on the strands generated by electromagnetic forces. In response, the cabling of the CICC was optimized by shortening the twist pitch to make it stiffer against electromagnetic forces. No T cs degradation of the optimized CICC was seen in the subsequent SULTAN test; further, a CS insert (CSI) test was performed at the CS model coil test facility, which included hoop strain for a more realistic simulation of ITER conditions. Good performance was also achieved in the CSI test.

Performance tests of ITER CS conductor samples from series production

“…Following the serious issue that was encountered at the time of the testing of the first ITER CS conductor qualification samples-which exhibited degradation with EM cyclic loading [40]-these remarkable results demonstrate the robustness of the selected design parameters, which, for the ITER CS operating conditions, ensure that there will not be performance degradation as a function of EMand thermal cycling. The design robustness was also confirmed by the subsequent test of an ITER CS Insert coil in the Naka test facility in Japan (see [41,42]), which exhibited test results in line with expectations from the SULTAN test results.…”

Examination of design parameters affecting Nb3Sn CICC current sharing temperature using necessary condition analysis

“…If the V f values of the reviewed CICCs represent the optimal values for the given cable design, the conclusion is that smaller V f is attained more frequently with larger L p1 /D s , or in other terms, that strands in cable with smaller L p1 /D s ratio can get damaged more easily during CICC manufacturing than if the ratio were larger, a postulate with some evidentiary observations [16,19,23,24,32,37,51,52]. Furthermore, the observed correlation of decreasing V f with increasing L p1 /D s would suggest that whatever phenomenon appears at large V f may be observed at small L p1 /D s and vice versa explaining the seeming mirror images between figures 5(c) and 6(c).…”