The MIRAI Program and the New Super-High Field NMR Initiative and Its Relevance to the Development of Superconducting Joints in Japan

Magnets using low temperature superconducting conductors require liquid helium cooling, yet can only generate a magnetic field <24 T. For full-fledged commercialization, high temperature superconducting (HTS) conductors are preferred as they can be cooled by liquid nitrogen, enabling electric power transmission lines. Furthermore, they can generate a much higher magnetic field, in excess of 30 T, in liquid helium, which makes them applicable to super-high field nuclear magnetic resonance (NMR). Unfortunately, the short maximum length of a single HTS conductor requires many joints, resulting in a difficult manufacturing process and a complicated operating procedure. Thus, we have commenced the MIRAI Project in 2017, focusing on developing joining technologies for linking HTS. The program has two important research and development directions: 1) Development of superconducting joints for a persistent mode 1.3 GHz (30.5 T) NMR magnet, i.e., The Super-High Field NMR Initiative in Japan. 2) Development of ultra-low resistance joints between superconducting dc feeder cables, enabling to connect adjacent railway substations that are 2-5 km apart. This paper first overviews the MIRAI Project. Second, it will describe initial results from investigations on superconducting joints for a persistent mode NMR magnet. Preliminary designs of the 1.3 GHz NMR magnet will also be discussed.