HTS Current Leads for the NHMFL Series-Connected Hybrid Magnet

A design for the current leads for the National High Magnetic Field Laboratory series-connected hybrid magnet is described. The leads are comprised of a nitrogen vapor cooled resistive heat exchanger section, operating between 296 and 79 K. The heat exchanger uses the “pierced jelly roll” lead technology proven at the National High Magnetic Field Laboratory. A conduction-cooled high-temperature superconducting (HTS) section, operating between 79 and 6 K, uses Sumitomo Type G Bi-2223/Ag5%Au conductors, stacked and soldered into a stainless steel and copper shunt brazement. The leads are located in close proximity to the magnet, and the magnitude of the fringe field on the HTS tapes is 0.37 tesla. The configuration of the HTS section is determined by careful analysis of the self-field and fringe field at the warm end of the HTS section, and by findings from a program of conductor testing.