An optimized rotating helium-recondensing system using Roebuck refrigerators

Abstract

This paper describes an optimized design of the helium-recondensing system utilizing cascade Roebuck refrigerators. A superconducting generator or motor has a superconducting held winding in its rotor that should be continuously cooled by cryogen. Liquid helium transfer from the stationary system to the rotor of the LTS (Low Temperature Superconductor) superconducting generator has been problematic, cumbersome, and inefficient. The novel concept of a rotating helium-recondensing system is contrived. The vaporized cold helium inside the rotor is isothermally compressed by centrifugal force and recondensed to 4.2 K reservoir through the expansion process. There is no helium coupling between the rotor and the stationary liquid helium storage. Thermodynamic analysis of the cascade refrigeration system is performed to determine the optimum key design parameters. The loss mechanisms are also described to point out the sources that might reduce the system performance. (C) 1999 Elsevier Science Ltd. All rights reserved.