Closed-Cycle Neon Refrigerator for High-Temperature Superconducting Magnets

Abstract

A closed-cycle refrigerator using neon as a working fluid has been designed and is under construction at the Applied Superconductivity Center of the University of Wisconsin-Madison. The refrigerator is intended for use in testing small superconducting magnets formed from BSCCO and other high temperature superconducting materials. A hybrid design is used, with a helium cryocooler operating on the Gifford-McMahon cycle precooling a separate neon stream. The neon stream is driven by a rotary vane compressor that provides a flow rate of 0.4 g/s between high and low side pressures of 450 kPa and 50 kPa, respectively. The high and low sides are separated by a Joule-Thomson metering valve, which maintains low side pressure, and thus cold end temperature via a closed-loop PID controller. The refrigerator is designed to provide a cooling capacity of 10 Watts at 25 K. At the cold end, the neon will be partially condensed into a two-phase fluid which is transferred out of the refrigerator vessel to a separate magnet test vessel. The liquid fraction will be available for an isothermal convective interface with the magnet. This paper details the considerations and constraints that went into the design, and discusses the hardware chosen to perform the required processes. Special emphasis is placed on design and testing of the tube-in-tube and cable-in-conduit heat exchangers that have been built, or are presently being built for this project.