A SMES Shuntable Vapor-Cooled Current Lead Array Reduces Liquid Helium Usage and Improves Reliability

Abstract

In a conventionally designed vapor-cooled current lead, the geometry is governed by the criterion that the cryogen heat input is minimized at the maximum design current. At lower currents, the heat input due to conduction gives rise to a performance penalty in a SMES device because of its variable current duty cycle. A new design has been tested that uses an array of parallel current leads with independent liquid helium level control which significantly reduces the time-averaged cryogen heat load in a superconducting magnet that operates at variable currents. At reduced magnet currents, one or more leads can be “shunted out” by lowering the liquid helium level in those leads. Test data indicates that an order of magnitude reduction in cryogen heat load is possible at zero current compared to conventionally optimized leads, and about a factor of two reduction is achievable for a typical SMES operating cycle.