Reduction of transport current losses in Bi-Sr-Ca-Cu-O wires with transposed filaments

A new type of high temperature superconducting wire with transposed filaments is fabricated and tested to confirm reduction of transport current losses. Sample wires of 1 meter long are made of four Bi2223 multifilamentary pre-tapes which are wrapped spirally into two layers around the silver core wire without any insulation. The wrapping direction and pitch for the two layers can be changed easily so that both the opposite and the same direction wires are prepared for the present experiment. The sample parameters are chosen to achieve uniform distribution of transport currents inside the opposite-direction wire. These wires, obtained after heat treatment, have relatively high critical currents of 99-122 amperes in liquid nitrogen in no external magnetic fields. In the range of currents higher than a half of 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 one. This experimental result for the loss reduction agrees closely with our theoretical prediction