Progress on Internal-Tin Route Nb_3Sn Superconducting Strand for ITER in China

摘要

Multi-filamentary Nb_3Sn strand for ITER has been successfully fabricated by a conventional internal-tin (IT) route at Western Superconducting Technologies, Co. Ltd. All the performances of the IT Nb_3Sn strand is able tomeet the ITER specifications. In 2010, one hundred kilograms of IT Nb_3Sn strand has been cabled, jacketed and integrated into conductor sample titled with TFCN2 by ASIPP in China and tested in CRPP, Switzerland. After 1200 cycles warm-up and cooling down, T_(cs) of the TFCN2 Sultan sample at 10.78 T, 4.5 K are 6.35 K for the left leg and 6.37 K for the right leg, respectively, which is larger than the ITER lower limit of 5.7 K. This is the first successful Sultan sample made of Chinese Nb_3Sn strand. In 2011, the influence of applied axial strain on critical current (I_c) was investigated using TFCN2 strand in the University of Twente, the Netherland. The irreversible degradation of I_c starts around +0.23% tensile intrinsic strain. The heat treatment influence of the duration at 650 ℃ on microstructure and performance was also studied. It was found that the fraction of un-reacted Nb after heat treatment is dependent on the position in the cross section. The hysteresis loss increases much faster than I_c when the duration at 650 ℃ increased.