Development of a Nb3Sn superconducting strand with tie-processed Nb surface coating to limit inter-strand eddy currents in cables

摘要

ITER/TPX-type bronze-route Nb-coated Nb3Sn strands were successfully fabricated using a co-processing technique as an alternative to the existing hard chrome plating method. Results show that a continuous Nb layer as thin as 2-3 μm can be formed on the surface of TPX/ITER strands during strand processing. This Nb coating prevents the superconducting strands in a Cable-in-Conduit (CIC) conductor from sintering during Nb3Sn reaction heat treatment. It was demonstrated that the Nb surface coating does not degrade the residual resistance ratio (RRR) of the Cu stabilizer in the strand as well as the critical current density in superconducting filaments. The additional magnetization hysteresis loss due to the Nb surface coating is negligible when compared to the loss from Nb3Sn filaments in the strand.