Design of a 60-kA HTS current lead for fusion magnets and its R&D

A 60kA HTS current lead has been designed for large fusion magnets such as ITER magnet. The actual refrigeration input power required to cool the curr ent lead is specified to be reduced to one third that of the conventional c opper lead. The HTS part of the 60 kA lead consists of 48 units installed w ith cylindrical array into the enter surface of a stainless steel tube with a diameter of 145 mm, Each unit is composed of six Bi2223/Ag-10at%Au tapes , and its cross-sectional dimension is 6.5 mm x 2.7 mm. The HTS part is coo led by conduction, and the warm and cold end temperature conditions of the HTS part are 50 K and 4.5 K, respectively. The copper part is cooled by hel ium gas, a flow rate of 3.9 g/s and the inlet temperature of 35 kA. The 60- kA lead has been designed in consideration of safety under the long dischar ge time condition of ITER-TF coil with a detection time of 2 sec. and a dis charge time constant of 15 sec. For the purpose of verifying the reliabilit y of the design for the lung discharge time, one unit sample has been fabri cated and tested. The result indicates that the maximum temperature rise of the HTS part is less than 150 k for the ITER like-discharge from 1.25 kA. corresponding to 60 kA of the full lead with 48 units.