Abstract
For the refrigeration of pressurized He II at 1.8K, 3He refrigerator with a Joule-Thomson expansion system is expected to have about one order of magnitude larger refrigeration capacity than the conventional 4He method, provided that the same pumping system is used. This is because the saturated vapor pressure of liquid 3He is about one order of magnitude larger than that of liquid 4He at 1.8K. In order to verify this idea, we have constructed a small refrigeration system for pressurized He II. The refrigerator was designed for about 1W cooling capacity using a evacuation pump of 500l/min and 3He gas of 70l at NTP. The system worked stably for a stationary heat load, and it is found that there exists a critical pressure (about 1.9atm) above which the system does not reach to a steady state. The maximum refrigeration capacity was 0.78W at 1.7K of liquid 3He, where the temperature difference between liquid 3He and pressurized He II was 0.124K. The results show the usefulness of this system for refrigeration of pressurized He II.
