Design and development of high-temperature superconducting magnet system with joint-winding for the helical fusion reactor

Innovative winding method by connecting high-temperature superconducting (HTS) conductors enables efficient construction of the helical fusion reactor FFHR-d1. A large-current capacity HTS conductor is being developed by incorporating a number of innovative ideas, such as simple stacking of the state-of-the-art YBCO tapes embedded in a copper jacket, surrounded by electrical insulation inside the conductor, and the outer stainless-steel jacket cooled by gas helium. A prototype conductor has reached a current of 100 kA at a bias magnetic field of 5.3 T and temperature of 20 K. A 100 kA current was successfully sustained for 1 hour at 4 K. A low-resistance bridge-type mechanical lap joint is being developed and the sample conductor confirmed a 2 nΩ resistance in the experiment. (author)