Development of Simple Diolution Refrigerators free from Cryogen refilling

稀释冰箱是一种非常低温的冰箱，可以连续工作到远低于1K，在极端情况下可以达到2毫开尔文。机器和操作的复杂性往往限制了这种冰箱的多功能性，它可以覆盖几百个左右的宽温度范围，而这对于许多领域的基础研究是必不可少的。制冷机的第一次简化是取消了用于循环3He冷凝的泵送He浴，而是将从蒸馏器中泵出的3He的焓用于JT预冷换热器[3]。我们已经使用了许多JT预冷稀释冰箱，其中一个被用于世界上最快旋转的实验，用于量子化漩涡的基础物理研究，因为冰箱的可靠性和简单性。第二个重要的简化是通过消除冷冻剂的使用来实现的。低温制冷机的发展使我们能够在没有冷冻剂[5]的情况下操作稀释制冷机，但振动限制了最终的低温和实验类型。我们已经实现了连续运行稀释冰箱，可以运行数周而无需重新填充冷冻剂，同时保持温度低于40mK。这是通过混合He制冷机的组合实现的，混合He制冷机由吉福德麦克马洪循环组成，第一级为固体置换器，第二级为双入口脉冲管制冷机，第二级为JT预冷稀释制冷机，没有1K锅和液体。为了获得在10mK以下进行实验的条件，正在对隔振与良好热接触的结合进行进一步的研究。

Dilution refrigerator is the very low temperature refrigerator continuously operable down to much below 1K and in the extreme case to 2 milli Kelvin [1]. The complication of the machine and the operation often limits the versatility of such a refrigerator covering the wide temperature range over a factor of a few hundred or so, which is essential for basic research in many fields [2].The first simplification of the refrigerator was brought about by the extinction of the pumped He bath for the condensation of the circulating 3He, instead the enthalpy of the 3He pumped out from the still is utilized in the JT precooling heat exchanger [3]. We have been using a number of JT precooled Dilution Refrigerators and One of them is being used for experiments under world fastest rotation for the fundamental study of physics of quantized vortices for years because of the reliability and the simplicity of the refrigerator [4].The second important simplification is achieved by the elimination of the cryogen usage. The development of the Cryocoolers enables us to operate a dilution refrigerator without cryogen [5], yet the viblation limits the ultimate low temperature as well as type of experiments.We have achieved continuously operating dilution refrigeraor which runs over many weeks without reffiling the cryogen while keeping the temperature below 40mK.This was made possible by combination of the hybrid He refrigerator, consists of Gifford McMahon cycle with solid displacer as the 1st stage and a double inlet pulse tube refrigerator as the second with a JT precooled dilution refrigerator which does not have 1K pot nor liq. ^4He bath. Further study of the combination of vibration isolation and good thermal contact is being carried out in order to obtain the condition to perform experiments below 10mK.