3He/4He dilution refrigerator with high cooling capacity and direct pulse tube pre-cooling |
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| Authors: | Kurt Uhlig |
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| Affiliation: | 1. Institute for Particle Physics, ETH Zürich, CH-8093 Zürich, Switzerland;2. Laboratory for High Energy Physics, Albert Einstein Center for Fundamental Physics, University of Bern, CH-3012 Bern, Switzerland;3. Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland;1. State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yutian Road, Shanghai 200083, China;2. Shanghai Research Center for Quantum Sciences, Shanghai 201315, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. Shanghai Boreas Cryogenics Co., Ltd, Shanghai 201802, China;1. CSNSM, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, 91405 Orsay, France;2. Univ Lyon, Université Lyon 1, CNRS/IN2P3, IPN-Lyon, F-69622 Villeurbanne, France;3. Massachussets Institute of Technology, Laboratory for Nuclear Science, 77 Massachusetts Avenue Cambridge, MA 02139-4307, USA;1. Department of Mechanical Engineering, University of Wisconsin – Madison, 1500 Engineering Drive, ERB – Room 1335, Madison, WI 53706, USA;2. Department of Mechanical Engineering, University of Wisconsin – Madison, 1500 Engineering Drive, ERB – Room 1341, Madison, WI 53706, USA |
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| Abstract: | In the article, a 3He/4He dilution refrigerator (DR) is described which is pre-cooled by a commercial two-stage pulse tube refrigerator (PTR); cryo-liquids are not necessary with this type of milli-kelvin refrigerator. The simple design of the condensation stage of this so-called dry DR is novel and explained in detail. In most dry DRs the circulating 3He gas is cooled by a two-stage PTR to a temperature of about 4 K. In the next cooling step, the 3He flow is cooled and partially liquefied in a Joule–Thomson circuit, before it is run to the dilution refrigeration unit. The counterflow heat exchanger of the Joule–Thomson circuit is cooled by the cold 3He gas pumped from the still of the DR. In the DR described here, the heat exchanger of the Joule–Thomson stage was omitted entirely; in the present design, the 3He gas is cooled by the PTR in three different heat exchangers, with the first one mounted on the first stage of the PTR, the second one on the regenerator of the second stage, and the third one on the cold end of the second stage. The heat load caused by the 3He flow is mostly absorbed by the first two heat exchangers. Thus the 3He flow presents only a small heat load to the second stage of the PTR, which therefore operates close to its base temperature of 2.5 K at all times. A pre-cooling temperature of 2.5 K of the 3He flow is sufficiently low to run a DR without further pre-cooling. The simplified condensation system allows for a shorter, compacter and more economical design of the DR. Additionally, the pumping speed of the turbo pump is no longer obstructed by the counterflow heat exchanger of the Joule Thomson stage as in our earlier DR design. |
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