Design and Test of a 1.8K Liquid Helium Refrigerator

Abstract

A liquid helium refrigeration system is being developed that will be capable of testing superconducting specimens at temperatures down to 1.8 K, currents up to 15 kA, and magnetic fields from 0 to 5 Tesla. The superconducting specimens will be immersed in a bath of subcooled, superfluid helium at atmospheric pressure. Subcooled superfluid helium is an ideal coolant for superconductors as it has an exceptionally high thermal conductivity, high heat capacity, and will not readily evaporate. These characteristics allow superconducting specimens to be tested at a constant temperature and therefore allow precise measurement of the critical surface associated with the sample. Argonne National Laboratory (ANL) has requested the design and fabrication of this liquid helium refrigeration system in order to characterize Niobium-Titanium superconducting wires and coils that will be installed in the Advanced Photon Source (APS). The low temperature, high current and high magnetic field requirements make this refrigeration system unique and not readily available within ANL or its contractors.

This thesis describes the design, fabrication, and an initial test run of the refrigeration system. The proof-of-concept test demonstrated that the system was capable of producing subcooled, superfluid helium, verified the integrity of the cryostat components and instrumentation at cryogenic temperatures, and identified several system enhancements that can be made in order to improve the refrigerator's performance during future testing.