Experimental Results of Large-Current Capacity HTS Conductors

Large-current capacity high-temperature superconducting (HTS) conductors suitable for high-field large-scale DC magnets, such as of helical-type fusion reactor FFHR, are being designed by employing YBCO tapes. As the first step of R&D of such an HTS conductor, we have fabricated short conductor samples using Bi-2223/Ag tapes. The HTS conductor was made by simply stacking and soldering Bi-2223/Ag tapes inside a copper sheath. The HTS conductor sample was fabricated in a hair-pin configuration and was tested under a bias magnetic field of 8 T. The conductor was thermally insulated by epoxy and GFRP and was conduction-cooled by liquid helium from the ends. Resistive heaters attached to the surface of the GFRP-insulated conductor were used to increase the temperature of the conductor for testing at elevated temperatures up to 30 K. The critical currents of the HTS conductor at 4.2 K, 10 K, 20 K, and 30 K were measured in a bias magnetic field of 8 T. The stability margin of the HTS conductor was examined in conduction-cooled conditions at different temperatures. The conductor was found to be very stable even at high currents closer to the critical currents.