AC Loss Measurement of High-Tc Superconducting Coils Wound With Stacked Conductors

In order to elucidate the ac loss characteristics of high-T_c superconducting coils wound with stacked conductors, we measured ac losses of Bi-2223 sample coils under the various electromagnetic conditions by a nitrogen boil-off method. The sample coils were wound with stacked conductors, which were composed of two Bi-2223 tapes. Each tape of stacked conductors was wrapped with polyimide tape, and the ends were made into the open circuit or short circuit. The coils with transposition and the coils without transposition were prepared as sample coils. We measured the magnetic amplitude dependence and the frequency dependence of ac losses of sample coils under external magnetic fields, and evaluated the magnetization losses and coupling current losses. Measured data were compared with theoretical values. Based on the obtained results, ac loss characteristics of high-T_c superconducting coils wound with stacked conductors under external magnetic fields were discussed.