Development of high current vapor-cooled current leads for large superconductor critical current measuring

Several programs to develop superconducting magnets for Large Helical Device (LHD) are under way at the National Institute for Fusion Science in Japan. The development of large scale superconductors for use in superconducting magnets is an important goal of these programs. To measure the critical current of such large scale superconductors the authors have to supply a very high current of up to 100 kA. For this purpose the authors have developed very large current capacity, vapor-cooled current leads. As a first step in this development the authors have made and tested a pari of current leads with a short-time rated current of 30 kA. The authors have also developed an analytical program to calculate the time dependent characteristics of vapor-cooled current leads and compared the results of our calculations with the experimental results obtained with 30 kA current leads. This paper describes the development of vapor-cooled current leads, the test results obtained with them and a comparison of their measured and calculated characteristics