Ramp Rate Limitation of NbTi Cable-in-Conduit Conductor With Artificially Introduced Non-Uniform Current Distribution

NbTi cable-in-conduit-conductors (CICCs) are employed to fabricate plasma fusion experimental apparatuses. NbTi is a preferable material with low cost and good fabrication. In contrast, it shows lower stability compared to materials for high magnetic field applications, e. g. Nb₃Sn, due to its small critical temperature. For this reason, past achievements of nominal current densities of NbTi CICCs were rather small compared to the critical current density of NbTi. Furthermore, the stability is reported to be influenced by the current distribution among strands. In this study, we conducted ramp-rate-limitation (RRL) tests utilizing the SST-1 conductor. SST-1 is the plasma experimental apparatus at the Institute for Plasma Research in India. Artificial non-uniform current distribution (NUCD) was introduced by individual superconducting/normal conducting switches installed on separated fifteen 2nd-stage sub-cables in the end of the CICC. Owing to these sophisticated switches, we evaluated stabilities and RRL behaviors of the sample with different current distributions. Finally, remarkable degradation of quench current due to NUCD was observed in the RRL test.