Development of 100 kA current leads for superconductor critical current measurement

Abstract

To measure the critical current of superconductors for the Large Helical Device (LHD), a large current of about 100 kA is required. For this purpose we have made short-time rated 100 kA current leads and successfully tested them up to 75 kA, the maximum current capacity of existing power supplies. Prior to the design of 100 kA lead, we constructed a pair of leads of smaller capacity, 30 kA short-time rating, and tested in transient operation. We have also developed transient analysis computer program for vapor-cooled current leads and utilized the same for design of the leads. On the basis of this smaller model results and calculations, we designed the 100 kA leads. In the transient operation of the leads, we raised the current up to 75 kA in 5 min, kept it at 75 kA for 10 min and reduced down to zero in 5 min. Temperature and voltage rise were small during the operation. Thus, we can expect from the test results that the current leads can feed 100 kA to the superconductor to measure its critical current.