Low thermal conductive Bi-2223 tapes sheathed with Ag-Au alloys

With the view of applying to power current leads for superconducting magnet systems and for other cryogenic power handling systems, low thermal conductive Bi-2223 superconducting tapes sheathed with Ag-Au alloy were fabricated and their thermal conductivities were measured from 12 to 260 K. The critical current density (overall-J_c ) was about 1700 A/cm² at 77 K, 0 T and remained nearly constant irrespective of Au concentration up to 11 at.%. The tape sheathed with Ag+11 at.%Au alloy, of which the superconductor cross-section ratio f_sc was 0.65, had a thermal conductivity value about 0.2 W/cmK at 77 K this value is as low as that of Cu-Zn. It was found that the thermal conductivity of the tape was close to the calculated one based on f_sc and the independently measured thermal conductivities of the Ag-Au alloy acid the Bi-2223 superconductor. The superconducting tapes sheathed with the alloy were confirmed to be suitable for the application as power current leads