Development of (Nb,Ta)/sub 3/Sn multifilamentary superconductors using Osprey bronze with high tin content

In this work we present the properties of three multifilamentary (Nb,Ta)/sub 3/Sn wires, using a new Osprey processed bronze with 15.4 wt.% tin content and Nb7.5 wt.%Ta as core material. Wires were produced by hot hydrostatic extrusion and subsequent cold drawing with a few intermediate anneals. Two experimental wires with a wire length less than 100 m each were produced and the process parameters were successfully applied on an industrially manufactured wire with a total length of 8 km. Critical current density (J/sub c/) measurements were performed up to 25 T at 4.2 K on all three wires heat treated by two different reaction anneals. High values of J/sub c/ (non copper, 10 /spl mu/Vm/sup -1/) and n were obtained for the conductor with a matrix/filament ratio 3.0: J/sub c/=184 Amm/sup -2/ and n=36 at 18 T and 4.2 K, which are results comparable to nowadays commercially available wires. Microstructure analysis (i.e. the amount of reacted layer and the residual tin content of the bronze) tries to explain the differences in J/sub c/ values. Only small influences of the matrix/filament ratio and reaction parameters on the irreversibility field B/sub c2/ (estimated by the Kramer extrapolation) and critical temperature T/sub c/ (measured by SQUID) have been observed.