Characteristics of multifilamentary wires for a.c. use developed by the bronze process using diffusion barrier techniques

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Abstract
Multifilamentary superconducting wires for a.c. use were developed by the bronze method using Cu diffusion barrier techniques. To reduce a.c. losses, the filament diameter was designed to be less than and the final resistivity of the bronze matrix was increased using a Cu alloy diffusion barrier with the addition of Si and Mn elements around the filaments. As a result, interfilamentary proximity coupling could be prevented until a filament spacing of and hysteresis losses for the wires reached lower values, from to at a magnetic field amplitude of 0.5 T under controlled reaction heat treatment. The perpendicular resistivity of the matrix between the filaments estimated from the coupling loss was about , which was considerably less than the resistivity value of the matrix estimated after the reaction. This was thought to be due to an extreme reduction in Sn concentration between the filaments. Furthermore, 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 central magnetic field of 0.5 T was and the a.c. quench current at 50 Hz was 195 A, which is about 10% lower than the critical current on the load line. This degradation was due to the temperature rise in the cable caused by a.c. loss.