Ac loss properties of a 4 kJ conduction-cooled pulse coil wound with a Bi2223 6-strand parallel conductor for SMES

We designed and fabricated a 4 kJ conduction-cooled superconducting pulse coil with a 6-strand interlayer-transposed parallel conductor composed of B12223 multifilamentary tapes. We adopted the helium gas forced-flow cooling system where the helium gas flowed inside a copper pipe soldered with the flanges of brass. We succeeded in the continuous pulse operation with an amplitude of 500 A-1.6 T at a sweep rate of 140 A/s at 30 K as designed. Even in the ac operation with an ac loss of 120 W, the difference in temperature inside the winding was only 5 K and it was possible to hold the coil temperature around 30 K. In this paper, we report the design and the test results of the coil system from the aspect of ac loss and thermal properties.