Investigation of trade-off solution in mechanical edge joint of STARS conductors

Abstract

Mechanical edge joints of stacked tapes assembled in rigid structure (STARS) conductors have been proposed to be applied to remountable high-temperature superconducting fusion magnets. Our previous study showed the joint resistance decreases with an increase in stabilizer thickness and joint pressure. However, this induces a trade-off between joint resistance and critical current due to increasing strain in the REBCO tape during bending (winding) for the conductors. Furthermore, an appropriate joint surface structure has not been discussed about taking into account a remountable joint. Based on the above background, this study first numerically evaluated the joint resistance depending on the structure of REBCO conductors with copper jackets. The results showed the copper jacket does not efficiently decrease the joint resistance compared to a copper stabilizer. Furthermore, to make strains lower than irreversible strain limit, the joint length should be longer than 500 mm. In addition, the joint surface structure was investigated based on joint testing and observing the surface, from which it was proposed that protective layer on the joint surface is needed to remove the remaining indium and keep the flatness of the joint surface. Therefore, a new structure for the issue was proposed for a remountable joint and the reattaching performance was evaluated experimentally.