Shuntable low loss variable current vapor cooled leads for superconductive loads

A shuntable low loss variable current vapor cooled lead (VCVCL) system for connecting an input power bus to a superconductive power bus, said system comprising:

• a plurality of shuntable low loss variable current vapor cooled lead (VCVCL) assemblies connected in parallel between said superconductive power bus and said input power bus, each of said VCVCL assemblies including:
• a superconductive material that is electrically connected between said input power bus and said output power bus,
• a containment jacket surrounding said superconductive material, and
• filling means for independently and selectively filling said containment jacket with a cryogenic liquid, so as to completely immerse said superconductive material,
• said superconductive material exhibiting superconducting properties when immersed within said cryogenic liquid, and not exhibiting superconducting properties when not immersed within said cryogenic liquid;
• and
• control means for selectively controlling each of said filling means as a function of how much current is flowing between said input power bus and said superconductive power bus;
• whereby the conduction properties of each of said VCVCL assemblies may be selectively controlled between either a superconducting state exhibiting virtually no resistance, or a non-superconducting state exhibiting a finite resistance, as a function of how much of said superconductive material of each VCVCL assembly is completely immersed within said cryogenic liquid by said filling means;
• or completely exposed out of said cryogenic liquid by said filling means;
• whereby the current flow within each of said VCVCL assemblies may be controlled by said filling means, with the current flow through a given VCVCL assembly that exhibits a finite resistance being effectively shunted to a parallel VCVCL assembly that exhibits a much lower resistance.

A method of delivering electrical currents to a superconductive load held in a dewar filled with a cryogenic liquid comprising the steps of:

• (a) forming a plurality of shuntable low loss variable current vapor cooled lead (VCVCL) assemblies, each of said VCVCL assemblies including:
• a superconductive material electrically connected between an input power bus connection and an output power bus connection, and means for independently immersing the superconductive material of a selected VCVCL assembly within a cryogenic liquid, the superconductive material in each VCVCL assembly being designed to have a specified operating current, I.sub.M, flow therethrough, the resistance of each of said VCVCL assemblies being a first value when said superconductive material is immersed within the cryogenic liquid, and being a second value, much greater than said first value, when not immersed within the cryogenic liquid;
• (b) connecting a plurality of the VCVCL assemblies formed in step (a) in parallel between a superconductive power bus within said dewar and an input power bus not within said dewar by connecting the output power bus connection of each VCVCL assembly to said superconductive power bus, and by connecting the input power bus connection of each VCVCL assembly to said input power bus, said superconductive power bus being connected to said superconductive load, and said input power bus being connected to a source of input power;
• (c) determining the load current, I.sub.L, required by the superconductive load and applying such load current to the input power bus;
• and then
• (d) immersing the superconductive material of n said VCVCL assemblies within a cryogenic liquid, where n is an integer that represents the number of VCVCL assemblies needed to provide the load current, I.sub.L, to the superconductive load, and by not immersing the superconductive material of any remaining VCVCL assemblies, whereby the load current, I.sub.L, is delivered to the superconductive load through those VCVCL assemblies that have their superconductive material immersed in the cryogenic liquid, while no significant current flows through the VCVCL assemblies not having their superconductive material immersed in the cryogenic liquid because the finite resistance of such non-immersed VCVCL assemblies automatically shunts the current to the parallel VCVCL assemblies having lower resistance;
• whereby each of said VCVCL assemblies that delivers current to said superconducting bus operates at near its specified operating current.