T-cs degradation of ITER TF samples due to fast current discharges

Direct current tests performed in the past on the conductor samples of the toroidal field (TF) ITER coils revealed degradation of current sharing temperature, T-cs. The degradation progresses with repetitive electromagnetic loading, and also with thermal cycles between 4.5 K and room temperature. This feature was observed on short samples in SULTAN test facility (EPFL-SPC, Switzerland) as well as in TF Insert Coil tests in CSMC test facility (Naka, Japan). We present three independent observations suggesting that initiation of sample quench followed by a fast current discharge, which normally complements every I-c and T-cs test in both SULTAN and CSMC, enhances the T-cs degradation rate. The exact mechanism of this contribution to the degradation remains unidentified.