Current Leads for Conduction-Cooled Magnets at 20-30 K

Cryogenic current leads are designed and tested for conduction-cooled superconducting magnets operating at 20-30 K. These magnets are under development in Korea for electrical machinery with MgB 2 wires or YBCO tapes. Since a single-stage cryocooler is employed, the current leads are made of metal over the entire length. Different sizes of copper conductor are fabricated for 80-100 A level and experimentally tested with a commercial Gifford-McMahon cryocooler. Temperature is measured at the coldhead and several axial locations along the conductor in order to estimate the cryogenic load. A geometric condition to minimize the cooling load is clearly demonstrated by the experiment. An analytical model is also presented to explain the optimal condition, taking into account the properties of copper and the refrigeration capacity of cryocooler.