Fabrication and Test of a 60-kA HTS Current Lead for Fusion Magnet System

A 60-kA HTS current lead was fabricated and tested in the frame of the R and D work for large fusion magnets such as the ITER magnet. The design of the current lead was characterized by its safe thermal protection for the current decay of about ten seconds after quench as well as lower electrical power consumption for its cryogenic equipment. The 60-kA current lead is composed of a lower temperature HTS part using HTS and a high temperature copper part using a conventional copper cable. The HTS part consists of 48 HTS units installed in the cylindrical array into the grooves provided on the outer surface of a stainless steel cylinder with a diameter of 146 mm. The unit was composed of six Bi2223/Ag-10at%Au tapes and its cross-sectional dimension is 6.5 mm x 2.7 mm. The stainless steel cylinder and Ag alloy sheath have a share in thermal protection for quench. The current lead was tested under the cooling condition that the bottom of the HTS part was immersed into 4.2 K liquid helium, and the bottom of the copper part was forced cooled with a helium gas of 3.2 g/s at 20 K. The lead was successfully operated at 60 kA without quench. Heat load to liquid helium was 4.8 W. The total electrical power consumption for the cryogenic equipment was estimated as 37 % of that of conventional copper current lead