MIRAI Program and the New Super-high Field NMR Initiative in Japan

Low-temperature superconductors (LTS) require liquid helium, yet can only generate a magnetic field lower than 24 T. For full-fledged commercialization of superconducting equipment, high temperature superconducting (HTS) conductors are preferred as they can be cooled by the more cost-efficient liquid nitrogen and they can generate a much higher magnetic field, such as 30 T at 4.2 K. However, one of the major drawbacks of the HTS conductor is its short maximum length of a single conductor wire, typically <500 m. As a result, many joints need to be installed in the superconducting equipment, resulting in a difficult manufacturing process and a complicated operating procedure. Thus, we commenced a 10-year JST-MIRAI Program in 2017, focusing on developing the joint technology for linking HTS conductors. The program has two important research and development directions:

1. Development of improved superconducting joints for a persistent-mode 1.3 GHz NMR magnet, i.e. the Super-High Field NMR Initiative. As the first stage, superconducting joints (10^(-13) Ω) between HTS conductors, such as REBCO[1] and Bi-2223, and HTS and NbTi [2] are being developed, which will be installed in the world’s highest magnetic field (30.5 T) NMR magnet [3], operated at a ¹H NMR frequency of 1.3 GHz in the persistent-mode. Based on NMR spectra achieved with the 1.3 GHz NMR for protein samples such as amyloid-beta, the feasibility and validity of the superconducting joints and the NMR magnet will be evaluated.
2. Development of ultra-low resistance joints between superconducting DC feeder cables for railway systems [4]. As the first step , ultra-low resistive joints (10^(-9) Ω) between superconducting DC feeder cables, > 100 mm in diameter, for railway systems will be developed; the DC cable is comprised of many HTS tapes and cooled by liquid nitrogen flow. It enables the on-site joining process between superconducting DC feeder cables. It will be evaluated by the operational test of a train fed by the joined superconducting DC cables in the Railway Technical Research Institute.