Development of a Compact HTS-FAIR Conductor for Magnet Application

Research and development of large-current capacity high temperature superconducting (HTS) conductors for magnet applications in nuclear fusion experimental devices is underway in the world. As a candidate conductor, the FAIR conductor has been developed, in which REBCO tapes and pure aluminum sheets are alternately stacked in an aluminum jacket, and the lid is covered by friction stir welding (FSW) method. Producing several prototypes of FAIR conductors, current transport tests have been repeatedly conducted in liquid nitrogen without an external magnetic field to optimize the manufacturing process of the conductor. In addition, we have also investigated the properties of the conductors in low temperature under high magnetic fields. As the next step, we have been planning to conduct coil shape tests in high magnetic fields. For installation in a test facility, we have developed a reduced diameter FAIR conductor from 12 mm to 6 mm. 1.5 rotations/m reduced version of FAIR was fabricated and current transport tested in 77 K, self-magnetic field. Compared with the results of critical current analysis considering the self-magnetic field, the retention of I-c was 67%. After cutting the fabricated the compact FAIR conductor and observing the inside, it was found that the REBCO tapes were folded by FSW. Therefore, it was found that further optimization of the FSW process was necessary.