Superconducting joints for the 1.3 GHz persistent NMR magnet under JST-Mirai Program

Abstract

Superconducting joint technologies connecting high-T c superconducting (HTS) tapes, such as REBCO-coated conductors and Bi2223 silver-sheathed tapes, have been developed for the fabrication of superconducting magnets generating 30.5 T with persistent current operation at 4.2 K under the JST-Mirai Program since 2017. These are indirect joints using a superconducting intermediate layer to join highly crystallized HTS layers of tapes. Thus far, high I c values of above 100 A at 77 K in the self-field have been achieved by both joints. These performances are sufficient for installation to the 30.5 T magnet, while efforts to further improve the reproducibility of high I c for joints connecting long-length HTS tapes have been continuously made. The current status of HTS joint technologies is summarized in this paper partly from the view point of material science.