Measurement of transport-current distribution and loss reduction in superconducting wires with transposed Bi-2223 filaments

Abstract

New superconducting wires with transposed Bi-2223 filaments were fabricated and tested to confirm both uniform transport-current distribution and loss reduction. Sample wires, 1 m length, were made of four multifilamentary pre-tapes, which were wrapped spirally, without any insulation, into two layers around a silver core wire. The wrapping direction and the pitch of the two layers can be changed easily, allowing both `opposite-' and `same-direction' wires to be prepared and tested. The sample parameters for the opposite-direction wire were chosen to achieve uniform distribution of transport currents. The wire obtained after heat treatment had relatively high critical currents of over 120 A at liquid nitrogen temperature with no external magnetic field. Where the current is greater than half the critical current, the observed hysteresis loss due to AC transport currents in the opposite-direction wire is about 60% as large as that in the same-direction wire. The experimental results for loss reduction and uniform current distribution in the opposite-direction wire agree closely with our theoretical predictions.