Development of liquid He free dilution refrigerator with Gifford-McMahon refrigerator.

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A ^3He-^4He dilution refrigerator is developed to operate without using liquid helium. A commercial two-stage Gifford-McMahon refrigerator(SRDK-408DA, Sumitomo Heavy Industries, ltd.)is used to cool the dilution unit and the radiation shield of shield of the cryostat. A Joule-Thomson cycle for condensation of the ^3He-^4He gas mixture into the dilution unit is designed to built in the dilution refrigeration process.1. The GM refrigerator can cool the DR unit down to 3.05K.This low temperature is enough to operate Joule-Thomson cycle and the dilution refrigeration process.2. A dilution unit with a standard tube-in-tube type heat exchanger and a counter flow type heat exchanger for Joule-Thomson expansion has been made and passed on the helium leak test.3. Automatic circulation ^3He-^4He gas control system has been made and tested.4. The dilution unit has been combined with the GM refrigerator. Leak test with helium gas has been passed on several connection parts to the gas control system.5. Thermometers and electrical heaters are attached to the dilution unit.6. A condensation process of the mixture gas in a Joule-Thomson cycle is under examination. Final refrigeration test is planed soon just after the condensation test.