CHARACTERISTICS OF NB3SN MULTIFILAMENTARY WIRES FOR AC USE DEVELOPED BY THE BRONZE PROCESS USING DIFFUSION BARRIER TECHNIQUES

Nb3Sn multifilamentary superconducting wires for a.c. use were develop ed by the bronze method using Cu diffusion barrier techniques. To redu ce a.c. losses, the filament diameter was designed to be less than 0.5 mu m and the final resistivity of the bronze matrix was increased usi ng a Cu alloy diffusion barrier with the addition of Si and Mn element s around the filaments. As a result, interfilamentary proximity coupli ng could be prevented until a filament spacing of 0.3 mu m and hystere sis losses for the wires reached lower values, from 1.75 kJ m(-3) to 1 2.18 kJ m(-3) at a magnetic field amplitude of 0.5 T under controlled reaction heat treatment. The perpendicular resistivity of the matrix b etween the filaments estimated from the coupling loss was about 2.5 x 10(-8) Ohm m, which was considerably less than the resistivity value o f the matrix estimated after the reaction. This was thought to be due to an extreme reduction in Sn concentration between the filaments. Fur thermore, a small a,c. coil was fabricated by winding a stranded cable fabricated in this way. The a.c. loss of the coil at 50 Hz in a centr al magnetic field of 0.5 T was 178 kW m(-3) and the a.c. quench curren t at 50 Hz was 195 A, which is about 10% lower than the critical curre nt on the load line. This degradation was due to the temperature rise in the cable caused by a.c. loss.