Effect of sub-cooling channel in an ITER 13 T-40 kA Nb3Sn coil (CS insert) on stability

This paper analyzes the stability of a center solenoid (CS) insert and describes the effects a sub-cooling channel (central channel) at the center cross section of a cable-in-conduit (CIC) conductor has on stability. First, the calculation results are compared with test results in a center solenoid (CS) insert, and the effectiveness of the calculation is verified. Next, the effects of central channel on stability are examined by comparing the energy margin between a case in which perforations exist between the bundle region and the central channel, such as a CS insert, to allow the fluid to migrate and a case in which perforations are blocked to prevent the coolant from migrating. The following points are clarified: (1) if most of the thermal disturbance is applied to the jacket, the case with perforations is more stable than the case without perforations, thus the central channel contributes to the improvement of stability; (2) if thermal disturbance is applied only to the cable and is produced for about 20 ms, the central channel hardly has any effect on the stability. If the thermal disturbance is produced for about 400 ms, the central channel contributes to the stability; (3) the effect of cooling the bundle region by means of heat conduction through the central channel wall is very small, and it hardly affects the stability at all.