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

研制了一种不使用液氦的氦-氦稀释制冷机。商用两级Gifford-McMahon制冷机（SRDK-408DA, Sumitomo Heavy Industries, ltd.）用于冷却稀释装置和低温恒温器屏蔽的辐射屏蔽。在稀释制冷过程中设计了一个焦耳-汤姆逊循环，用于将^3He-^4He气体混合物冷凝到稀释装置中。GM冰箱可将DR机组冷却至3.05K。这个低温足以运行焦耳-汤姆逊循环和稀释制冷过程。研制了一种具有标准管中式换热器和逆流式焦耳-汤姆逊膨胀式换热器的稀释装置，并通过了氦泄漏试验。研制了自动循环^3He-^4He气体控制系统并进行了测试。稀释装置已与通用冰箱结合使用。气体控制系统的几个连接件已通过氦气泄漏试验。温度计和电加热器附在稀释装置上。本文研究了焦耳-汤姆逊循环中混合气体的冷凝过程。最终制冷试验计划在冷凝试验后不久进行。

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.