Low-vibration desktop type liquid-helium-free dilution refrigerating machine and application thereof

Abstract

The invention discloses a low-vibration desktop type liquid-helium-free dilution refrigerator, which is characterized in that a DR dilution unit and a pulse tube refrigerator are respectively arranged in two mutually independent vacuum containers, and the vacuum containers are connected through a corrugated pipe; and mechanical decoupling between the two is realized. In addition, the DR dilution unit is connected with an air extractor outside the vacuum container; the pulse tube refrigerator is connected with a compressor outside the vacuum container; the high vibration device is separated from the DR dilution unit and the pulse tube refrigerator, so that a vibration source can be effectively isolated, and the vibration reduction effect is improved. A small part of helium is shunted from a helium circulation loop of the pulse tube refrigerator, and the shunted helium cooling loop is connected with the radiation shielding layer after being pre-cooled for multiple times so as to cool the radiation shielding layer; mixed gas in the dilution refrigeration loop enters the DR dilution unit after being pre-cooled for multiple times, deep refrigeration is conducted on a mixing chamber of the dilution unit, and thermal coupling between the DR dilution unit and the mixing chamber is achieved. The low-vibration desktop type dilution refrigerator can be suitable for low-temperature experimental equipment sensitive to vibration, such as STM and AFM.

Description

Technical Field

[0001] This invention relates to the field of cryogenic refrigeration technology, and in particular to a low-vibration, cryogenic refrigerant-free desktop dilution refrigerator, which can be applied to vibration-sensitive cryogenic experimental equipment such as scanning tunneling microscopes (STM) and atomic force microscopes (AFM). Background Technology

[0002] Desktop dilution refrigerators, due to their mixing chamber mounting plate, offer advantages such as omnidirectional accessibility and short cooling times, making them widely used in scientific research. Traditional desktop dilution refrigerators require pre-cooling with liquid helium (LHe), resulting in cumbersome operation and high operating costs. Furthermore, many existing refrigerators employ a structure where the pulse tube refrigerator is directly coupled to the dilution unit, making it easy for vibrations generated during refrigerator operation to be transmitted to the mixing chamber, affecting the accuracy of precision experiments.

[0003] Existing pulse tube refrigerators (PTCs) have the advantages of no cryogenic refrigerant, high efficiency, and convenient operation. However, when combining them with desktop dilution refrigerators, how to achieve effective thermal coupling between the two, suppress vibration transmission, and ensure convenient access to the mixing chamber has become an urgent technical problem to be solved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application proposes a low-vibration desktop liquid helium-free dilution refrigerator and its application. This application places the dilution unit of the dilution refrigerator and the pulse tube refrigerator (PTC) in separate vacuum containers, and connects them through stainless steel bellows to form a remote thermal coupling structure. Combined with a dual cooling circuit design, it achieves low-vibration, cryogenic refrigerant-free refrigeration.

[0005] The technical solution adopted in this invention is as follows: A low-vibration desktop liquid-free helium dilution refrigerator includes: Two independent vacuum containers are connected by a bellows. A vacuum container is provided with multiple radiation shielding layers and a DR dilution unit placed inside the radiation shielding layers. The DR dilution unit is connected to a vacuum pump outside the vacuum container via a flexible hose. A pulse tube refrigerator is installed inside another vacuum container, and the pulse tube refrigerator is connected to a compressor outside the vacuum container via a high-pressure helium tube; The pulse tube refrigerator and the DR dilution unit are placed in separate vacuum containers, and the pumping device and compressor are also separated from the DR dilution unit and the pulse tube refrigerator and placed separately to achieve mechanical decoupling and reduce vibration. A helium cooling circuit is diverted from the helium circulation loop of the pulse tube refrigerator. After multiple cooling cycles, the helium cooling circuit is connected to the radiation shielding layer to cool the radiation shielding layer. After cooling, the helium gas returns to the pulse tube refrigerator. The dilution cooling circuit is connected to the DR dilution unit after being cooled multiple times in the pulse tube refrigerator, and performs deep cooling on the mixing chamber of the dilution unit.

[0006] Furthermore, the helium cooling circuit includes a counter-current heat exchanger, a PTC first-stage heat exchanger, a PTC second-stage regenerator heat exchanger, a PTC second-stage heat exchanger, a cooling medium transmission pipeline, a secondary heat sink, a primary heat sink, a cooling medium recovery pipeline, and the counter-current heat exchanger, connected in sequence; the working medium of the helium cooling circuit is helium. 4 He.

[0007] Furthermore, the operating pressure of the helium cooling circuit is always higher than... 4 The critical pressure of He keeps helium in a supercritical state.

[0008] Furthermore, the dilution cooling circuit includes a PTC-side activated carbon collector e, a PTC-side heat exchanger, a second-stage regenerator heat exchanger, and another heat exchanger connected in sequence. It is connected to the DR dilution unit via a dilution cooling channel. The working medium of the dilution cooling circuit is a mixture of helium and helium-4 gas (³He / ) 4 He.

[0009] Furthermore, the cooling medium transmission pipeline, cooling medium recovery pipeline, and dilution cooling channel are all placed inside the corrugated pipe.

[0010] Furthermore, the cooling medium transmission pipeline is wrapped with ultra-high insulation material, the cooling medium recovery pipeline is located inside the shielding layer installed on the cooling medium transmission pipeline, and the dilution cooling channel is located inside the shielding layer installed on the cooling shut-off recovery pipeline.

[0011] Furthermore, the surface of the radiation shielding layer is gold-plated.

[0012] Furthermore, the corrugated pipe is made of stainless steel.

[0013] The beneficial effects of this invention are: In the structural design of this invention, the PTC and DR dilution units are placed in two independent vacuum containers with no direct mechanical connection between them. In addition, high-vibration components such as the compressor on the PTC side are also placed outside the vacuum chamber, and the pumping components on the DR dilution unit side are also placed outside the vacuum chamber. This can block the vibration transmission path from the source and achieve mechanical decoupling between the two.

[0014] 2. The present invention flexibly connects two independent units through a corrugated pipe, which can effectively attenuate the vibration generated during the operation of PTC and prevent the vibration from being transmitted to the DR dilution unit through the pipeline, thereby further suppressing the transmission of vibration.

[0015] 3. Because the present invention decouples the PTC and DR dilution unit in terms of structure, the pulse tube refrigerator 10 and the DR dilution unit 6 are connected by a dual cooling circuit; wherein, the multi-channel radiation screen of the DR dilution unit is cooled by the helium cooling circuit to reduce external radiative heat leakage; the DR dilution unit is deeply cooled by the dilution cooling circuit; thus realizing remote thermal coupling between the two.

[0016] 4. The helium in the helium cooling circuit is always in a supercritical state, with no bubbles generated, eliminating additional vibrations caused by phase transition.

[0017] 5. Since this invention can effectively reduce vibration, it can be applied to vibration-sensitive low-temperature experimental equipment such as scanning tunneling microscopes (STM) and atomic force microscopes (AFM), further expanding the application scenarios and improving the accuracy of low-temperature experiments.

[0018] Figure 1 This is a schematic diagram of a low-vibration desktop liquid-free helium dilution refrigerator.

[0019] In the diagram, 1. Second vacuum container; 2. Primary cold shield; 3. Secondary cold shield; 4. Secondary heat sink; 5. Primary heat sink; 6. DR dilution unit; 7. Bellows; 8. First vacuum container; 9. Cooling medium transfer pipeline; 10. Pulse tube refrigerator; 11. Cooling medium recovery pipeline. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0021] Combined with appendix Figure 1 This invention proposes a low-vibration desktop liquid-free helium dilution refrigerator, comprising two independent vacuum containers, namely a first vacuum container 8 and a second vacuum container 1; wherein, the first vacuum container 8 contains a pulse tube refrigerator 10 (abbreviated as PTC); the pulse tube refrigerator 10 is connected to a compressor outside the vacuum container through a high-pressure helium tube.

[0022] The second vacuum container 1 is equipped with a DR dilution unit 6; the DR dilution unit 6 is connected to the pumping device outside the vacuum container through a flexible hose.

[0023] Structurally, this application places the pulse tube refrigerator 10 and the DR dilution unit 6 in two independent vacuum containers, and the compressor connected to the pulse tube refrigerator 10 is also placed outside the vacuum container; the pumping device connected to the DR dilution unit 6 is also placed outside the vacuum container; thereby isolating the main vibration-generating components outside the vacuum container, and structurally achieving mechanical decoupling and suppressing vibration transmission.

[0024] The first vacuum container 8 and the second vacuum container 1 are connected by a flexible connection component; and the pulse tube refrigerator 10 inside the vacuum container is connected to the DR dilution unit 6 through a dual cooling circuit, which can achieve physical connection and medium transmission while attenuating vibration transmission.

[0025] In this embodiment, the flexible connection component uses a bellows 7 to connect the first vacuum container 8 and the second vacuum container 1.

[0026] The specific structure and connection relationships of each unit are as follows: Two radiation shielding layers are nested in the second vacuum container 1, namely, a primary cold shield 2 and a secondary cold shield 3 from the outside to the inside. The DR dilution unit 6 is placed in the secondary cold shield 3. A secondary heat sink 4 is set outside the secondary cold shield 3, and a primary heat sink 5 is set outside the primary cold shield 2.

[0027] In the first vacuum container 8, a helium cooling circuit is diverted from the helium circulation loop of the pulse tube refrigerator 10. After multiple cooling cycles, the helium cooling circuit is connected to the radiation shielding layer to cool the radiation shielding layer. After cooling, the helium cooler returns to the pulse tube refrigerator 10.

[0028] The helium cooling circuit specifically includes, in sequence, a counter-current heat exchanger c, a PTC first-stage heat exchanger f, a PTC second-stage regenerator heat exchanger g, a PTC second-stage heat exchanger h, a cooling medium transmission pipeline 9, a secondary heat sink 4, a primary heat sink 5, a cooling medium recovery pipeline 11, and the counter-current heat exchanger c. The working medium of this helium cooling circuit is helium (…). 4 He).

[0029] The working process of helium in the helium cooling circuit is as follows: Helium ( 4Helium gas (H) is compressed by compressor (b) and enters countercurrent heat exchanger (c), where it is pre-cooled by the returning cold helium. The pre-cooled helium then flows sequentially through PTC first-stage heat exchanger (f), second-stage regenerator (g), and second-stage heat exchanger (h), gradually cooling to a base temperature below 4K (preferably 3.6K). The low-temperature helium then enters the second vacuum container via cooling medium transmission pipeline (9), exchanging heat with the second-stage heat sink (4) to cool the second-stage cold shield (3). The low-temperature helium flowing out of the second-stage heat sink (4) flows into the first-stage heat sink (5), exchanging heat with it to cool the first-stage cold shield (2), thus providing cooling for the two radiation shielding layers outside the DR dilution unit (6). The heated helium flowing out of the second-stage heat sink (4) returns to the first vacuum container via cooling medium recovery pipeline (11) and re-enters countercurrent heat exchanger (e) to complete the cycle.

[0030] It should be noted that both the cooling medium transmission pipeline 9 and the cooling medium recovery pipeline 11 are placed inside the corrugated pipe 7.

[0031] In this embodiment, the bellows 7 is made of stainless steel.

[0032] In this embodiment, the operating pressure of the helium cooling circuit is always higher than that of the helium cooling circuit. 4 The critical pressure of He keeps helium in a supercritical state, preventing bubble vibrations that occur when the liquid phase transforms into the gas phase.

[0033] The dilution cooling circuit includes a PTC-side activated carbon collector e, a PTC-side heat exchanger f', a second-stage regenerator heat exchanger g, a heat exchanger h', and a DR dilution unit 6 connected in sequence. After undergoing multiple cooling cycles within the pulse tube refrigerator 10, the dilution cooling circuit connects to the DR dilution unit 6 to deeply cool the mixing chamber of the dilution unit 6. The working medium of this dilution cooling circuit is a mixture of helium and helium-4 gas (³He / ) 4 He.

[0034] Helium mixed in the dilution cooling circuit (³He / ) 4 The working process of He is as follows: the mixed helium first enters the activated carbon collector e on the PTC side to remove impurities and achieve purification; the purified mixed helium flows through three cascaded heat exchangers (f'-g-h') on the PTC side in sequence and is cooled to a base temperature below 4K; the cooled mixed helium enters the dilution unit 6 in the second vacuum container DR1 through the conveying channel in the bellows 7, and finally achieves a deep cooling of 100mK level in the mixing chamber of the dilution unit 6.

[0035] In this embodiment, multiple radiation shielding layers are provided outside the DR dilution unit 6, such as the secondary cold screen 3 located in the inner layer and the primary cold screen 2 located in the outer layer; and the two radiation screens are cooled by heat exchange using a helium cooling circuit, which can effectively reduce external radiation heat leakage.

[0036] In this embodiment, the surface of the radiation shielding layer is gold-plated (absorption rate ε≤0.01) and wrapped with ultra-high thermal insulation material; the radiation shielding openings at both ends of the stainless steel corrugated pipe are sealed with ultra-high thermal insulation material to minimize heat loss.

[0037] In this embodiment, the pulse tube refrigerator 10 is selected as a high-power pulse tube refrigerator or a GM refrigerator, preferably with a first-stage cooling power >45W@45K and a second-stage cooling power >1.5W@4.2K, to ensure the cooling power requirements of the helium cooling circuit, and its second-stage cooling temperature ≤4K.

[0038] In this embodiment, the second-stage regenerator heat exchanger g adopts a dual heat exchanger structure, with the capillary tube directly brazed to the regenerator tube body.

[0039] In this embodiment, the length of the bellows 7 can be adjusted according to actual needs (up to 5m).

[0040] In the above embodiments, the dilution refrigeration machine is a pulse tube refrigeration machine as an example. It can also be replaced with a GM refrigeration machine to further reduce equipment costs.

[0041] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A low-vibration desktop liquid-free helium dilution refrigerator, characterized in that, include: Two independent vacuum containers are connected by a bellows (7); A vacuum container is provided with multiple radiation shielding layers and a DR dilution unit (6) placed inside the radiation shielding layers. The DR dilution unit (6) is connected to the pumping device outside the vacuum container through a flexible hose. A pulse tube refrigerator (10) is installed in another vacuum container, and the pulse tube refrigerator (10) is connected to a compressor outside the vacuum container through a high-pressure helium tube; The pulse tube refrigerator (10) and the DR dilution unit (6) are placed in separate vacuum containers, and the pumping device and compressor are also separated from the DR dilution unit (6) and the pulse tube refrigerator (10) and placed separately to complete mechanical decoupling and reduce vibration. A helium cooling circuit is diverted from the helium circulation loop of the pulse tube refrigerator (10). After multiple pre-cooling and temperature reductions, the helium cooling circuit is connected to the radiation shielding layer to cool the radiation shielding layer. After cooling, it returns to the pulse tube refrigerator (10). After being pre-cooled multiple times in the pulse tube refrigerator (10), the dilution cooling circuit is connected to the DR dilution unit (6) to perform deep cooling on the mixing chamber of the dilution unit (6).

2. The low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The helium cooling circuit includes a counter-current heat exchanger, a PTC first-stage heat exchanger, a PTC second-stage regenerator heat exchanger, a PTC second-stage heat exchanger, a cooling medium transmission pipeline (9), a secondary heat sink (4), a primary heat sink (5), a cooling medium recovery pipeline (11), and the counter-current heat exchanger, connected in sequence. The working medium of the helium cooling circuit is helium. 4 He.

3. The low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The operating pressure of the helium cooling circuit is always higher than 4 The critical pressure of He keeps helium in a supercritical state.

4. The low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The dilution cooling circuit includes a PTC-side activated carbon collector, a PTC-side heat exchanger, a second-stage regenerator heat exchanger, and another heat exchanger connected in sequence. It is connected to the DR dilution unit (6) via a dilution cooling channel. The working medium of the dilution cooling circuit is a mixture of helium-3 and helium-4 gas (³He / ) 4 He.

5. A low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The cooling medium transmission pipeline (9), the cooling medium recovery pipeline (11), and the dilution cooling channel are all placed inside the corrugated pipe (7).

6. A low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The cooling medium transmission pipeline (9), the cooling medium recovery pipeline (11), and the dilution cooling channel are all wrapped with ultra-high insulation material.

7. A low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The surface of the radiation shielding layer is gold-plated.

8. A low-vibration desktop liquid-free helium dilution refrigerator according to claim 1, characterized in that, The corrugated pipe (7) is made of stainless steel.

9. An application of a low-vibration desktop liquid-free helium dilution refrigerator, characterized in that, The low-vibration desktop liquid-free helium dilution refrigerator described in any one of claims 1-9 is used for low-temperature experiments in scanning tunneling microscopes and atomic force microscopes.

Images