Sub-Micron Filament Nb-Ti Superconducting Wires with Cu-Ni-Mn Alloy for AC Use-Critical Current Density and RRR of Stabilizer Cu.

Critical current density and stability of sub-micron filament Nb-Ti superconducting wires with Cu-Ni-Mn alloy matrix are described. Characteristics of critical current density Jc depend on filament diameter df, kinds of matrix and ratio of filament spacing dn to df. In the case of large dn/df(=0.65-1) wires, increasing Jc with decreasing df is slight due to low pinning force. Residual Resistance Ratio (RRR) of the wires which were heat treated (100-250°C×1hour) at final size increased to 70-80. These values are three times those of the as drawn wires. The final heat treatment at more than 300°C degraded RRR and Jc, because of Ni diffusion. AC (50Hz) quench current at high field (>2T) of the secondary twisted cable with 36 strands (copper ratio 1.9) is higher than DC critical current of the secondary twisted cable.