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

A 60 kA HTS current lead has been designed for large fusion magnets such as the ITER magnet. The actual refrigeration input power required to cool the current lead is specified to be reduced to one third that of the conventional copper lead. The HTS part of the 60 kA lead consists of 48 units installed with cylindrical array into the outer surface of a stainless steel tube with a diameter of 146 mm. Each unit is composed of six Bi2223/Ag-10at%Au tapes, and its cross-sectional dimension is 6.5 mm/spl times/2.7 mm. The HTS part is cooled 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 helium gas, a flow rate of 3.9 g/s and the inlet temperature of 35 K. The 60-kA lead has been designed in consideration of safety under the long discharge time condition of ITER-TF coil with a detection time of 2 sec, and a discharge time constant of 15 sec. For the purpose of verifying the reliability of the design for the long discharge time, one unit sample has been fabricated 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.