High-temperature superconducting current lead incorporating operation in the current-sharing mode

This paper describes a high-temperature superconducting (HTS) current lead, in which, over a short length at the warm end (e.g., 80 K), the lead, comprised of paralleled BSCCO-2223/Ag-Au tapes, is operated in the current-sharing mode. Because our leads rely on cooling by the effluent helium vapor, they are applicable only to devices such as superconducting magnets that operate in a bath of liquid helium. The current-sharing mode operation results in a significant saving of the superconducting materials (BSCCO, Ag, and Au) needed to construct our leads as compared with a `fully-superconducting' HTS lead of the same configuration that is rated for the same transport current and operates over the same temperature range. Detailed analysis of our four leads, each rated 6-kA and comprised of 240 paralleled BSCCO-2223/Ag-Au tapes, demonstrates that the cold-end heat input of each of our leads is equal to or can be optimized to be smaller than that of a completely superconducting counterpart comprised of 480 paralleled tapes. The paper also shows that a protection criterion under fault mode or heat exchange consideration ultimately determines the extent to which the material saving can be achieved in our leads.