Prototype Superconducting Strand for ITER CS Coil Conductor Produced in Korea Using the Internal-Tin Route

The ITER tokamak being constructed in southern France will incorporate a central solenoid (CS) coil consisting of 6 modules stacked one on top of the other. Each module will be constructed from round-in-square Nb₃Sn based superconducting cable-in-conduit conductor (CICC). Production of CS conductor for the ITER tokamak had been delayed due to discoveries of faster than expected performance degradation. Investigations into mitigating this shortfall have included using internal-tin (IT) route Nb₃Sn strand in place of the bronze (BR) route strand that was originally proposed. Prototype ITER CS conductor samples have been produced using IT route Nb₃Sn strand in conjunction with cabling optimization, and conductor performance tests show that they satisfy ITER performance requirements. One of the suppliers of IT route ITER Nb₃Sn strand, which will be supplying superconducting strand for ITER CS conductor, is Kiswire Advanced Technology Ltd. (KAT) of Daejeon, Korea. The characteristics of their prototype Nb₃Sn strand for ITER CS conductor are presented. Furthermore, performance degradation of the CS strand due to possible strand deformations during the cabling process was also investigated. The results show similarities as well as differences with recent results obtained with BR route Nb₃Sn strand. However, direct interpretation of the strand deformation versus performance results may not lead to correct predictions of cable performance because of the strand contact interaction mechanism investigated.