AC operating test results for a conduction-cooled HTS coil

We fabricated a conduction-cooled HTS coil wound with the conductors composed of four Ag-sheathed Bi2223 tapes, which have no insulator, and a CuNi tape coated with polyimide for reinforcement and insulation. Using the HTS coil we measured AC loss and investigated thermal stability of the conduction-cooled HTS coil. The coil is composed of 12 single-pancake coils and impregnated with epoxy resin. The inner diameter of the coil is φ100 mm, the outer diameter is φ190 mm and the height is 90 mm. The HTS coil carried 800 A at 20 K as designed and generated 2.9 T at the central point of the coil. Sinusoidal currents were supplied to the HTS coil at 20-50 K and AC losses were measured using the electrical method. The AC losses per cycle of the HTS coil increased with increasing the frequency of the current, which indicates the coupling losses would generate between Ag-sheathed Bi2223 tapes in addition to the hysteresis losses. Sinusoidal waveform current of 100 A and 1.32 Hz was continuously supplied to the coil in order to investigate the thermal stability of the coil in AC operations. Although the coil generated an AC loss of 125.6 W, the temperature of the coil became stable approximately 200 sec after starting operation, which indicates that Ag-sheathed Bi2223 coils have high thermal stability in AC operations and are suitable for AC applications.