Superconducting microparticle composite wire

Abstract

A novel concept of a ductile composite wire which incorporates filaments made of brittle superconductor powders was proposed and experimentally demonstrated. Unsintered, submicron NbC powders were encapsulated in copper tubes. These were fabricated down to single filament wires without sintering or high temperature annealing. Multifilamentary composites with up to 3000 filaments were then formed by successive rebundling of tubes into sealed billets and their mechanical reduction. Due to the fluid-like behavior of the unsintered powder core, the composites were ductile and resistant to filament fracture. The wire critical temperature was 10 to 11 K, the upper critical field was 2 ± 0.2 tesla and the superconductor self-field critical current density attained 6 × 108amps/m2. The critical current showed a remarkable tolerance of uniaxial and bending strains. While the NbC superconductor is not of great technical interest, it permitted one to prove the new concept. The subsequent use of NbCN powders confirmed that the observed wire behavior is also obtained in high magnetic fields, up to 15 tesla.