Demonstration of a 67 kA vapor-cooled current lead with improved thermal efficiency

Conventionally designed vapor-cooled leads used in superconducting magnetic energy storage device (SMES) must be optimized at the maximum current. The standard optimization practice, which minimizes the sum of the Joule and conduction heat inputs, incurs a penalty for a diurnal 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 (LHe) level control which significantly reduces the cryogen heat load in a superconducting magnet that operates at variable currents. At reduced magnet currents, one or more parallel leads in the array is “shunted out” by lowering the LHe levels. The increased electrical and thermal resistance of those leads reduces the total LHe boil-off of the array. Test results on a 67 kA lead are presented, showing an 80% reduction in LHe consumption at zero current when compared to a conventional lead