Research and development of segmented high-temperature superconducting magnets intended for realizing innovative fusion reactors. Progress in development of remountable joints of high-temperature superconducting conductors

Segmented high-temperature superconducting magnet is considered to be a technology to bring about a big revolution to nuclear fusion reactor. As a mechanical jointing method for remountable high-temperature superconductor, bridge-type mechanical lap joint was studied, a joint resistivity of about 2 nω low enough to apply to the helical-type fusion reactor was achieved, and in addition continuous energizing at 100 kA for one hour was successfully conducted. However, since the mechanical strength of the joint may not be sufficient for large conductor, there is a need for improvement. As the non-destructive inspection method for the joint, X-ray CT method, and DC potential difference method / AC potential difference method have been studied. To prevent an increase in joint resistivity, indium foil is inserted at the joint surface, but this is insufficient to apply to large-sized conductor. Therefore, an attempt to improve the joint state by applying heat treatment during joint fabrication was made, and good effect has been obtained through the combination of baking treatment and heat treatment. In the future, the following items will be required: (1) fabrication of mock-up coil for segmented high-temperature superconducting magnets, (2) development of conductor insulation and cooling technology, and (3) development of industrial robot to automatically perform joint fabrication / inspection / dismantlement. (A.O.)