Development of a Nb3Sn composite conductor with very fine filaments and basic studies on its power frequency applications

A Nb3Sn composite conductor with about 10 thousands filaments has been manufactured by the external diffusion process. Fine filament size of 0.36 μm (design value), a tight twist pitch of 0.61 mm for the wire diameter of 0.103 mm and bronze matrix resulted in a strongly reduced a.c. losses: the hysteresis loss and the coupling current loss were observed to be 500 kW/m³and 30 kW/m³respectively in the a.c. field of 50 Hz with an amplitude of 2.0 T. A triplex conductor was constructed by cabling three strands and a small Coil was wound from this cable. In the d.c. mode operation, the coil generated a field of 1.8 T at the critical current Ic= 28 A. In 50 Hz operation the coil was able to be operated up to the static critical current Ic. At this critical condition, the observed a.c. loss averaged over the windings was 450 kW/m³.