Design and testing of a high temperature superconducting current lead

The high critical temperature and low thermal conductivity of the ceramic superconductor Y-Ba-Cu-O were utilized to reduce the Joule heating and the heat leak in a vapor-cooled current lead design of nominally 1-kA capacity. The lead consists of a lower superconducting part and an upper normal metal (copper) part. The superconducting part is an assembly of 20 rectangular bars fabricated from a composite of Y-Ba-Cu-O and Ag (15% vol.). This part is designed to operate below the critical temperature of the ceramic superconductor. The copper part, consisting of 20 copper wires, extends outside of the cryostat and interfaces to the room-temperature power supply. The lead was successfully tested in a liquid-helium cryostat for currents up to 2 kA. At the optimum operating currents of 1.7-1.8 kA, the helium boil-off measurements show heat leak reduction of approximately 40% from the conventional designs. Details of the design, fabrication issues, and the testing are presented.