He I-He II electrical lead transition

The authors address a new lead concept. This design would apply to electrical leads between superfluid helium (He II) baths and ordinary 4.2-K He I baths. The lead consists of a plug made of alternating copper/stainless steel (SS) thin laminates with attached superconducting strands. The laminates minimize thermal conduction from 4.2 K to He II and provide large heat capacity for protection compared to a solid SS transition. The authors have constructed and tested a 50-kA transition lead that is fully stable up to about 35 kA. Between 35 and 55 kA, the lead will have a stable temperature profile if it becomes normal. Between 55 and 75 kA, its temperature will increase slowly enough with time following a disturbance so that the protection circuit can turn off the connected power supply.<>