Western Superconducting Technologies Co. Ltd. (WST) has been keeping in the research and development of internal-Tin NbSn strand for higher performance level, for the future fusion reactor after ITER. Deformation optimization, Cu splits, and Sn spacers were applied to prepare NbSn strand with higher J{{\rm{cn}}} and lower hysteresis loss, and the effect of these three factors on performance was investigated and discussed. Compared with the NbSn strand for ITER, strand distortion was obviously reduced by deformation optimization and J{{\rm{cn}}} was improved, but at the same time hysteresis level was increased. To reduce the level of hysteresis loss, Cu splits were used to replace a few Nb filaments in each subelement. Cu splits could break the bridging NbSn filament rings and as a sequence hysteresis loss was dramatically reduced along with the reduction of J{{\rm{cn}}}, which is attributed to low reaction degree of Nb filaments in the outermost subelements. Therefore, Sn spacers between the outermost subelements and the Ta barrier were added, and a 37-subelement structure was used to shorten the diffusion path of Sn. The reaction degree of the filaments was enhanced as well as J{{\rm{cn}}}. Finally, it could be concluded that a 37-subelement structure with Cu splits is effective to reduce the level of hysteresis loss and raise the level of J.
Liu 施一公 Wu Bo Zhang Li Liu Xianghong Feng Yong Zhang Pingxiang
IEEE Transactions on Applied Superconductivity
2018