Electric power losses of current input into superconducting devices cooled by supercritical helium

This paper deals with the methods and results of calculations to minimize power losses in cryogenic installations related to current input into superconducting systems with forced supercritical helium cooling. Different schemes and modes of cooling the current leads with a superconducting region at the cold end are examined. Optimum helium flow rate and minimum power losses in an idealized and an actual cryogenic unit are defined. The calculations were made within the working temperature range of 5-18 K. The paper shows that the choice of the current lead cooling scheme allowing for minimum power losses depends on the relation between the temperatures of the superconducting device and of the superconducting transition in the superconducting region of the current lead. The value of minimum power losses decreases with the growth of the transient temperature in the superconducting region.