Recent progress in superconductors in Japan

Abstract

The bronze-processed (Nb,Ti)/sub 3/Sn conductors achieved an improvement in high-field performance by increasing Sn concentration in the matrix. A new process using Ta-Sn core produces thick (Nb,Ta)/sub 3/Sn layers and a non-Cu J/sub c/ of 1.2/spl times/10/sup 4/ A/cm/sup 2/ at 23 T and 4.2 K in resulting (Nb,Ta)/sub 3/Sn conductors. The production technologies of jelly roll-processed Nb/sub 3/Al conductors with large J/sub c/ at 12 T have been established. The continuous quenching and subsequent phase transformation provides Nb/sub 3/Al conductors with excellent high-field properties. Ultra-thin filamentary Nb-Ti and Nb/sub 3/Sn conductors for AC use made substantial progress in their performance. A Bi-2212 insert coil stably generated an incremental 3 T in a back up field of 18 T. The PAIR process produces an appreciable increase in the J/sub c/ of the Bi-2212 tape. The ROSAT Bi-2212 round wire with tape-shaped filaments and triple rotation symmetry shows almost no anisotropy in J/sub c/. The J/sub c/ of long-length Bi-2223 tape remains 23/spl times/10/sup 4//cm/sup 2/ at 77 K. The mechanical strength of the Bi-2223 tape has been improved by a factor of /spl sim/3 without degrading its J/sub c/. Test power transmission cables and 20 K-operated large-bore magnet are being developed by Bi-2223 tapes. Biaxially aligned Y-123 tapes are being fabricated through different routes. A few meter-long IBAD-processed Y-123 tape keeps a promising J/sub c/ at 77 K. Meanwhile, a Sm-123 disc with Ag/sub 2/O addition traps a field exceeding 2 T at 77 K.