Multi-stage coaxial nested cold screen structure for dilution refrigerator

Abstract

The invention relates to a multistage coaxial nested cold shield structure for a dilution refrigerator, and relates to the technical field of refrigeration and low-temperature engineering, the multistage coaxial nested cold shield structure comprises a Dewar, the top of the Dewar is provided with a top plate in a sealing manner, and the Dewar is internally provided with a first-stage cold shield, a second-stage cold shield, a third-stage cold shield and a fourth-stage cold shield; the first-stage cold screen, the second-stage cold screen, the third-stage cold screen and the fourth-stage cold screen are coaxially arranged in a nested mode from outside to inside and from bottom to top, and the side walls of the first-stage cold screen, the second-stage cold screen, the third-stage cold screen and the fourth-stage cold screen are each provided with a plating layer and a heat insulation layer. The invention aims to gradually intercept radiation heat flow, minimize radiation heat loss of a low-temperature end, form a graded radiation heat flow barrier in a vacuum cavity of the dilution refrigerator, reduce heat leakage loss of each stage of structural component and guarantee efficient operation of dilution refrigeration cycle, and has the remarkable advantages of strong shielding effect, good thermal coupling with a system, compact structure and the like; and important positive significance is achieved for practical development of the dilution refrigerator.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration and cryogenic engineering, and particularly to a multi-stage coaxial nested cold shield structure for a dilution refrigerator. Background Art

[0002] As a low-interference refrigeration technology that can stably and continuously refrigerate in the millikelvin (mK) temperature range, the dilution refrigerator is widely used in frontier fields such as quantum computing and condensed matter physics experiments. In the dilution refrigerator, there is a temperature difference of nearly 300K along the way from the room temperature end to the extremely low temperature mixing chamber in the mK temperature range. Such a huge temperature gradient will cause various forms of irreversible heat losses (such as heat conduction of residual gas, heat conduction of structural components, radiative heat leakage, etc.). If these heat losses cannot be effectively suppressed, it will lead to a sharp decline in the overall performance of the refrigerator.

[0003] Among the above-mentioned irreversible heat losses, the heat leakage caused by radiative heat flux is one of the main sources of heat loss at the low temperature end of the refrigerator. The low temperature end in the mK temperature range is extremely sensitive to external tiny heat loads and is easily affected by the radiative heat flux from the high temperature region. In practice, people often use materials with low emissivity to make anti-radiation cold shields to effectively reduce the thermal radiation of the ambient temperature (such as the outer dewar) to the low temperature end.

[0004] The dilution refrigerator consists of multiple temperature regions, multiple stages of cold disks and a support structure. Excessive heat loss in any stage may lead to the attenuation of the overall refrigeration performance of the refrigerator, and even the cooling process cannot be realized. The conventional anti-radiation cold shield structure often ignores the structural characteristics of the dilution refrigerator and lacks pertinence for such a typical multi-stage structure of the dilution refrigerator. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a multi-stage coaxial nested cold shield structure for a dilution refrigerator to solve the problem that the existing cold shield structure lacks pertinence when reducing the heat loss of the dilution refrigerator.

[0006] The present invention is realized through the following technical solutions:

[0007] A multi-stage coaxial nested cold shield structure for a dilution refrigerator, including a dewar, a top plate is hermetically installed at the top of the dewar, and a first-stage cold shield, a second-stage cold shield, a third-stage cold shield and a fourth-stage cold shield are arranged inside the dewar. The first-stage cold shield, the second-stage cold shield, the third-stage cold shield and the fourth-stage cold shield are coaxially nested from outside to inside and from bottom to top, and coatings and insulating layers are provided on the side walls of the first-stage cold shield, the second-stage cold shield, the third-stage cold shield and the fourth-stage cold shield;

[0008] A pulse tube is installed on the top of the Dewar. The top of the pulse tube is connected through the top plate and extends above the top plate. There are two pulse tube cold heads on the pulse tube, and the two pulse tube cold heads are respectively connected to the tops of the first-stage cold shield and the second-stage cold shield.

[0009] Further, the first-stage cold shield includes a first-stage cold shield cylinder and a first-stage cold shield flange, the second-stage cold shield includes a second-stage cold shield cylinder and a second-stage cold shield flange, the third-stage cold shield includes a third-stage cold shield cylinder and a third-stage cold shield flange, and the fourth-stage cold shield includes a fourth-stage cold shield cylinder and a fourth-stage cold shield flange;

[0010] The first-stage cold shield cylinder, the second-stage cold shield cylinder, the third-stage cold shield cylinder, and the fourth-stage cold shield cylinder are all formed by rolling and welding a thin-walled metal material with high thermal conductivity, and are set as a hollow structure with one end open and the other end closed.

[0011] Further, the open end of the first-stage cold shield cylinder is welded to the first-stage cold shield flange, the open end of the second-stage cold shield cylinder is welded to the second-stage cold shield flange, the open end of the third-stage cold shield cylinder is welded to the third-stage cold shield flange, and the open end of the fourth-stage cold shield cylinder is welded to the fourth-stage cold shield flange.

[0012] Further, a first-stage cold disk, a second-stage cold disk, a third-stage cold disk, and a fourth-stage cold disk are respectively arranged above the first-stage cold shield cylinder, the second-stage cold shield cylinder, the third-stage cold shield cylinder, and the fourth-stage cold shield cylinder.

[0013] Further, the first-stage cold disk is detachably connected to the first-stage cold shield flange through multiple groups of bolts, the second-stage cold disk is detachably connected to the second-stage cold shield flange through multiple groups of bolts, the third-stage cold disk is detachably connected to the third-stage cold shield flange through multiple groups of bolts, and the fourth-stage cold disk is detachably connected to the fourth-stage cold shield flange through multiple groups of bolts;

[0014] The outer diameters of the first-stage cold disk, the second-stage cold disk, the third-stage cold disk, and the fourth-stage cold disk are respectively equal to the outer diameters of the corresponding first-stage cold shield flange, second-stage cold shield flange, third-stage cold shield flange, and fourth-stage cold shield flange.

[0015] Further, a mixing chamber is installed at the bottom of the fourth-stage cold shield. A mixing chamber cold disk is arranged below the mixing chamber, and both the mixing chamber and the mixing chamber cold disk are arranged inside the fourth-stage cold shield;

[0016] A delivery pipe and a circulation pipe communicating with its interior are respectively arranged at the top of the mixing chamber. A separated heat exchanger is communicated and arranged above the delivery pipe and the circulation pipe, and the separated heat exchanger is arranged inside the fourth-stage cold shield.

[0017] Further, both the delivery pipe and the circulation pipe are hermetically and penetratively connected to the fourth-stage cold disk, and continuous heat exchangers are respectively communicated and arranged at one ends of the delivery pipe and the circulation pipe extending into the third-stage cold shield;

[0018] The upper ends of two consecutive heat exchangers are jointly and communicatively provided with an evaporation chamber, and the evaporation chamber is arranged at the top inside the third-stage cold shield.

[0019] Furthermore, a JT heat exchanger is arranged inside the second-stage cold shield. The bottom of the outer tube of the JT heat exchanger penetrates through the third-stage cold disk and is communicatively connected with the inside of the evaporation chamber, and the top of the outer tube of the JT heat exchanger is connected through penetration with the second-stage cold disk.

[0020] Furthermore, a corrugated pipe is arranged between the first-stage cold disk and the second-stage cold disk. The bottom of the corrugated pipe is communicatively connected with the inside of the JT heat exchanger, and the top of the corrugated pipe is communicatively provided with a pumping pipeline. The top of the pumping pipeline is hermetically connected through penetration with the top plate and extends outside the Dewar.

[0021] Furthermore, a plurality of support rods are respectively arranged between the top plate, the first-stage cold shield, the second-stage cold shield, the third-stage cold shield and the fourth-stage cold shield, and the plurality of support rods are respectively detachably connected with the side walls of the first-stage cold disk, the second-stage cold disk, the third-stage cold disk and the fourth-stage cold disk corresponding in position.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. For the multi-stage coaxial nested cold shield structure for a dilution refrigerator, by adopting multi-stage thin-walled hollow cylinders arranged coaxially from outside to inside, and through mechanical fastening connections of each stage of cold shield with cold disks of different temperature grades in sequence, a radiation shielding system with a gradually decreasing axial temperature gradient is formed. Under the condition of strong radiative heat flux in the temperature range from room temperature to mK, a remarkable radiative heat flux shielding effect can be achieved, effectively suppressing the radiative heat load at the low-temperature end (especially the mixing chamber) of the dilution refrigeration system, and improving the thermal stability and the lowest temperature holding capacity of the system.

[0024] 2. In the present invention, each stage of cold shield is made of a thin-walled metal material with high thermal conductivity. Through grinding, polishing and gold plating treatment on the inner and outer surfaces, the emissivity is significantly reduced, and at the same time, the problem of emissivity deterioration caused by metal surface oxidation is suppressed. The radiation shielding performance remains stable during long-term operation, and it is applicable to a low-temperature physical experiment platform with high stability requirements.

[0025] 3. In the present invention, each stage of cold shield is coaxially and fixedly connected with the cold disks of each stage of the dilution refrigeration system through a flange structure with matching dimensions. The flange and the cylinder are formed by welding, and the flange and the cold disk are connected in a mechanical fastening manner, realizing efficient thermal coupling between the cold shield and the cold disks of each stage, and ensuring the temperature consistency and thermodynamic stability of the low-temperature shield body.

[0026] 4. In the present invention, the multi-stage cold shield structure is arranged in a longitudinal coaxial nested manner, and the outer diameter gradually decreases from top to bottom, which is completely matched with the axial layout of the cold disks of each stage of the system. The structure is compact and occupies a small space, and it is applicable to a complex dilution refrigeration system in a limited space.

[0027] 5. In the present invention, multi-layer thermal insulation materials are attached to the outer surfaces of cold shields at all levels and the surfaces of internal components thereof, which are composed of alternately stacked reflective layers and isolation layers, effectively reflecting and blocking the transfer of thermal radiation, further enhancing the heat insulation effect in the low-temperature section, and providing multiple guarantees in terms of thermal load management.

[0028] 6. By reasonably configuring the shielding structure and thermal coupling path, the present invention effectively reduces the steady-state thermal load of ultra-low temperature components such as the mixing chamber, improves the steady-state holding ability of the dilution refrigerator in the mK temperature range, and is applicable to experimental occasions with extremely high requirements for thermal stability and low noise background such as quantum computers, high-sensitivity detectors, and cryogenic heat capacity measurements, and has broad application prospects in the fields of quantum technology, cryophysics, and space science.

[0029] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0030] Figure 1 is the front view structural schematic diagram of the present invention;

[0031] Figure 2 is the schematic diagram of coaxial nesting of multi-stage cold shields in the present invention;

[0032] Figure 3 is the cross-sectional structural schematic diagram of the four-stage cold shield in the present invention;

[0033] Figure 4 is the installation flow chart of multi-stage coaxial nested cold shields in the present invention.

[0034] In the figure: 1, pulse tube cold head; 2, bellows; 3, JT heat exchanger; 4, evaporation chamber; 5, continuous heat exchanger; 6, separated heat exchanger; 7, mixing chamber; 8, dewar; 9, top plate; 10, pumping pipeline; 11, first-stage cold disk; 12, first-stage cold shield; 13, second-stage cold disk; 14, second-stage cold shield; 15, third-stage cold disk; 16, third-stage cold shield; 17, fourth-stage cold disk; 18, fourth-stage cold shield; 19, support rod; 20, mixing chamber cold disk; 21, first-stage cold shield cylinder; 22, second-stage cold shield cylinder; 23, third-stage cold shield cylinder; 24, fourth-stage cold shield cylinder; 25, first-stage cold shield flange; 26, second-stage cold shield flange; 27, third-stage cold shield flange; 28, fourth-stage cold shield flange; 29, coating; 30, thermal insulation layer. Detailed Description of the Invention

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention usually described and illustrated in the drawings here can be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0037] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not require further definition and explanation in subsequent drawings.

[0038] In the above description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "one side" and "the other side" is based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, terms such as "first" and "second" are only used for descriptive distinction and should not be construed as indicating or implying relative importance.

[0039] In addition, terms such as "identical" do not mean that the components are absolutely identical, but there may be slight differences. The term "perpendicular" merely means that the positional relationship between components is more perpendicular relative to "parallel", and does not mean that the structure must be completely perpendicular, but may be slightly inclined.

[0040] Please refer to Figure 1, the present invention provides a technical solution: a multi-stage coaxial nested cold shield structure for a dilution refrigerator, which includes a Dewar 8. A top plate 9 is hermetically installed at the top of the Dewar 8 to ensure the vacuum environment inside the Dewar 8 and reduce the interference of external gas heat conduction on the internal low-temperature environment. Inside the Dewar 8, there are a primary cold shield 12, a secondary cold shield 14, a tertiary cold shield 16, and a quaternary cold shield 18. The primary cold shield 12, secondary cold shield 14, tertiary cold shield 16, and quaternary cold shield 18 are coaxially nested from the outside to the inside and from the bottom to the top. It should be noted that the primary cold shield 12, as the outermost cold shield, directly faces the relatively high-temperature environment inside the Dewar 8 and the heat radiation from the outside. It first preliminarily blocks and absorbs heat. The secondary cold shield 14 is located inside the primary cold shield 12 and further reduces the temperature on the basis of the preliminary cooling of the primary cold shield 12. The tertiary cold shield 16 and quaternary cold shield 18 are arranged inward in sequence. Each stage of the cold shield further reduces the temperature on the basis of the previous stage, forming an effect of gradually decreasing the circumferential temperature gradient. Through the regular installation of each stage of the cold shield and the cooperation with the cold plates of different stability levels, a radiation shielding system with a gradually decreasing circumferential temperature gradient is formed, which has a good effect on transferring the radiation heat load of the mixing chamber 7 located in the innermost part, improving the thermal stability of the system and the ability to maintain the lowest temperature.

[0041] Refer to Figure 2 , the primary cold shield 12 includes a primary cold shield cylinder body 21 and a primary cold shield flange 25. The secondary cold shield 14 includes a secondary cold shield cylinder body 22 and a secondary cold shield flange 26. The tertiary cold shield 16 includes a tertiary cold shield cylinder body 23 and a tertiary cold shield flange 27. The quaternary cold shield 18 includes a quaternary cold shield cylinder body 24 and a quaternary cold shield flange 28. The primary cold shield cylinder body 21, secondary cold shield cylinder body 22, tertiary cold shield cylinder body 23, and quaternary cold shield cylinder body 24 are all formed by rolling and welding high-thermal-conductivity thin-walled metal materials, and are set as a hollow structure with one end open and the other end closed. During the operation of the dilution refrigerator, the cold quantity can be quickly transferred to each part through the cylinder body, greatly improving the refrigeration efficiency of the cold shield. The open end of the primary cold shield cylinder body 21 is welded to the primary cold shield flange 25. The open end of the secondary cold shield cylinder body 22 is welded to the secondary cold shield flange 26. The open end of the tertiary cold shield cylinder body 23 is welded to the tertiary cold shield flange 27. The open end of the quaternary cold shield cylinder body 24 is welded to the quaternary cold shield flange 28. The closed end enhances the overall structural strength of the cold shield, enabling it to withstand the pressure changes in the internal low-temperature environment and possible external mechanical stresses, preventing the cold shield from deforming or breaking. The welding of the open end to the corresponding flange ensures the sealing performance when the cold shields are connected to each other and to other components. The welding process can form a firm and seamless connection, effectively avoiding gas leakage, maintaining the vacuum environment inside the Dewar 8, thereby improving the thermal stability of the entire cold shield structure, and also facilitating the installation, disassembly, and maintenance of the cold shield. When the cold shield needs to be repaired or replaced, the operation can be carried out quickly and conveniently, reducing the downtime and improving the use efficiency of the equipment.

[0042] In addition, above the first-stage cold shield cylinder 21, the second-stage cold shield cylinder 22, the third-stage cold shield cylinder 23 and the fourth-stage cold shield cylinder 24, a first-stage cold disk 11, a second-stage cold disk 13, a third-stage cold disk 15 and a fourth-stage cold disk 17 are respectively arranged. The first-stage cold disk 11 is detachably connected to the first-stage cold shield flange 25 through multiple groups of bolts. The second-stage cold disk 13 is detachably connected to the second-stage cold shield flange 26 through multiple groups of bolts. The third-stage cold disk 15 is detachably connected to the third-stage cold shield flange 27 through multiple groups of bolts. The fourth-stage cold disk 17 is detachably connected to the fourth-stage cold shield flange 28 through multiple groups of bolts. The outer diameters of the first-stage cold disk 11, the second-stage cold disk 13, the third-stage cold disk 15 and the fourth-stage cold disk 17 are respectively equal to the outer diameters of the corresponding first-stage cold shield flange 25, second-stage cold shield flange 26, third-stage cold shield flange 27 and fourth-stage cold shield flange 28. It should be noted that while the bolt connection provides a stable mechanical connection to ensure good thermal coupling effect, it also forms an efficient heat conduction path. By reasonably controlling the tightening torque of the bolts, a uniform pressure can be applied on the contact surface between the cold disk and the flange, reducing the contact thermal resistance. High thermal conductivity silicone grease can also be applied between the cold disk and the flange to further fill the micro voids and reduce the thermal resistance, promoting the rapid transfer of cold quantity between the two. During the operation of the dilution refrigerator, the generated cold quantity can be quickly conducted to the cold shield through the cold disk, enabling the cold shield to quickly reach and maintain a low temperature state, effectively enhancing the shielding ability of the cold shield against radiant heat.

[0043] Specifically, a mixing chamber 7 is installed at the bottom of the fourth-stage cold shield 18. A mixing chamber cold disk 20 is arranged below the mixing chamber 7, and both the mixing chamber 7 and the mixing chamber cold disk 20 are arranged inside the fourth-stage cold shield 18. At the top of the mixing chamber 7, a delivery pipe and a circulation pipe communicating with its interior are respectively provided. Above the delivery pipe and the circulation pipe, a separated heat exchanger 6 is communicated and arranged, and the separated heat exchanger 6 is arranged inside the fourth-stage cold shield 18. Both the delivery pipe and the circulation pipe are hermetically and penetratingly connected to the fourth-stage cold disk 17, and the ends of the delivery pipe and the circulation pipe extending into the third-stage cold shield 16 are respectively communicated with a continuous heat exchanger 5. The upper ends of the two continuous heat exchangers 5 are jointly communicated with an evaporation chamber 4, and the evaporation chamber 4 is arranged at the top inside the third-stage cold shield 16. A JT heat exchanger 3 is arranged inside the second-stage cold shield 14. The bottom of the outer pipe of the JT heat exchanger 3 penetrates the third-stage cold disk 15 and is communicated with the interior of the evaporation chamber 4. The top of the outer pipe of the JT heat exchanger 3 is penetratingly connected to the second-stage cold disk 13. A corrugated pipe 2 is arranged between the first-stage cold disk 11 and the second-stage cold disk 13. The bottom of the corrugated pipe 2 is communicated with the interior of the JT heat exchanger 3. The top of the corrugated pipe 2 is communicated with a pumping pipeline 10. The top of the pumping pipeline 10 is hermetically and penetratingly connected to the top plate 9 and extends outside the Dewar 8. A pulse tube is installed at the top of the Dewar 8. The top of the pulse tube is penetratingly connected to the top plate 9 and extends above the top plate 9. Two pulse tube cold heads 1 are arranged on the pulse tube, and the two pulse tube cold heads 1 are respectively connected to the tops of the first-stage cold shield 12 and the second-stage cold shield 14.

[0044] It should be noted that since the dissolution entropy of 3He in 4He is lower than that of the pure 3He phase, heat is absorbed when 3He diffuses from the concentrated phase to the dilute phase, thus generating a refrigeration effect. The cold plate 20 of the mixing chamber is tightly coupled with the mixing chamber 7 through a highly thermally conductive connection, transferring the cold quantity to the fourth-stage cold shield 18 to maintain its low-temperature environment. Both the separated heat exchanger 6 and the continuous heat exchanger 5 adopt a countercurrent design, enabling the concentrated-phase 3He solution and the dilute-phase 3He solution to flow in opposite directions in adjacent pipelines, maximizing the heat exchange efficiency using the logarithmic mean temperature difference, recovering the cold quantity of the returned solution, reducing the temperature of the concentrated-phase 3He solution entering the evaporation chamber 4, and reducing the energy required for evaporation. In the evaporation chamber 4, the concentrated-phase 3He solution separates out 3He gas through evaporation, and the evaporation process absorbs heat to achieve further cooling. The evaporation chamber 4 is connected to the outer tube of the JT heat exchanger 3, and the 3He gas flows upward through the outer tube. After the 3He gas exchanges heat with the returned low-temperature 3He gas in the JT heat exchanger 3, it expands through a throttle valve (JT valve), generating additional cold quantity using the Joule-Thomson effect to pre-cool the gas in subsequent cycles. The evaporated 3He gas is pumped to the compressor outside the Dewar 8 through the bellows 2 and the pumping pipeline 10, and the compressed gas is re-cooled and returned to the system to form a closed cycle.

[0045] Furthermore, a plurality of support rods 19 are respectively provided between the top plate 9, the first-stage cold shield 12, the second-stage cold shield 14, the third-stage cold shield 16 and the fourth-stage cold shield 18, and the plurality of support rods 19 are respectively detachably connected to the side walls of the first-stage cold plate 11, the second-stage cold plate 13, the third-stage cold plate 15 and the fourth-stage cold plate 17 corresponding in position. The main body of the support rod 19 is made of a high-strength carbon fiber composite material, and a gradient material transition layer is adopted at the connection interface. Through the continuous change of composition and structure, the thermal stress generated by the difference in thermal expansion coefficients of the two materials is alleviated, avoiding an increase in thermal resistance caused by interface cracking. Even further, the two ends of the support rod 19 adopt a larger diameter to improve the connection strength with the cold plate, and the middle section is reduced to reduce the cross-sectional area of heat conduction, lower the heat flux density, and at the same time reduce the rigid constraint of mechanical connection.

[0046] Refer to Figure 3, on the side walls of the first-stage cold shield 12, the second-stage cold shield 14, the third-stage cold shield 16 and the fourth-stage cold shield 18, there are both a coating 29 and a thermal insulation layer 30. The coating 29 is made of a material with high reflectivity, such as a silver-plated or gold-plated layer, which can effectively reflect the external thermal radiation, reduce the heat absorbed by the cold shield itself, and lower the temperature rise rate of the cold shield. The thermal insulation layer 30 is made of a material with low thermal conductivity, such as multi-layer insulation material, which is laid in an alternating manner of an aluminum foil reflective layer and a polyimide heat insulation layer, with a thickness of about 0.5 - 2 mm. The multi-layer insulation material not only covers the outer surface of the cold shield cylinder, but also covers the outer surfaces of the cold plate connected to the cold shield and the structural components (such as the support rod 19, the mixing chamber 7, etc.) inside the cold shield, greatly reducing the heat transfer between the cold shields by conduction and convection, and further enhancing the heat insulation performance of the cold shield.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A multi-stage coaxial nested cold shield structure for a dilution refrigerator, including a Dewar (8), characterized in that: A top plate (9) is hermetically installed at the top of the Dewar (8). An inner stage cold shield (12), a second stage cold shield (14), a third stage cold shield (16) and a fourth stage cold shield (18) are arranged inside the Dewar (8). The inner stage cold shield (12), the second stage cold shield (14), the third stage cold shield (16) and the fourth stage cold shield (18) are coaxially nested from outside to inside and from bottom to top. Coatings (29) and heat insulation layers (30) are provided on the side walls of the inner stage cold shield (12), the second stage cold shield (14), the third stage cold shield (16) and the fourth stage cold shield (18). A pulse tube is installed at the top of the Dewar (8). The top of the pulse tube is connected through and extends above the top plate (9). Two pulse tube cold heads (1) are arranged on the pulse tube. The two pulse tube cold heads (1) are respectively connected to the tops of the inner stage cold shield (12) and the second stage cold shield (14).

2. The multi-stage coaxial nested cold screen structure for dilution refrigerators according to claim 1, wherein: The inner stage cold shield (12) includes an inner stage cold shield cylinder body (21) and an inner stage cold shield flange (25). The second stage cold shield (14) includes a second stage cold shield cylinder body (22) and a second stage cold shield flange (26). The third stage cold shield (16) includes a third stage cold shield cylinder body (23) and a third stage cold shield flange (27). The fourth stage cold shield (18) includes a fourth stage cold shield cylinder body (24) and a fourth stage cold shield flange (28). The inner stage cold shield cylinder body (21), the second stage cold shield cylinder body (22), the third stage cold shield cylinder body (23) and the fourth stage cold shield cylinder body (24) are all formed by rolling and welding thin-walled metal materials with high thermal conductivity, and are set as a hollow structure with one end open and the other end closed.

3. The multi-stage coaxial nested cold shield structure for dilution refrigerators according to claim 2, wherein: The open end of the inner stage cold shield cylinder body (21) is welded to the inner stage cold shield flange (25). The open end of the second stage cold shield cylinder body (22) is welded to the second stage cold shield flange (26). The open end of the third stage cold shield cylinder body (23) is welded to the third stage cold shield flange (27). The open end of the fourth stage cold shield cylinder body (24) is welded to the fourth stage cold shield flange (28).

4. The multi-stage coaxial nested cold shield structure for dilution refrigerator according to claim 3, characterized in that: An inner stage cold disk (11), a second stage cold disk (13), a third stage cold disk (15) and a fourth stage cold disk (17) are respectively arranged above the inner stage cold shield cylinder body (21), the second stage cold shield cylinder body (22), the third stage cold shield cylinder body (23) and the fourth stage cold shield cylinder body (24).

5. The multi-stage coaxial nested cold shield structure for a dilution refrigerator according to claim 4, characterized in that: The inner stage cold disk (11) is detachably connected to the inner stage cold shield flange (25) through multiple groups of bolts. The second stage cold disk (13) is detachably connected to the second stage cold shield flange (26) through multiple groups of bolts. The third stage cold disk (15) is detachably connected to the third stage cold shield flange (27) through multiple groups of bolts. The fourth stage cold disk (17) is detachably connected to the fourth stage cold shield flange (28) through multiple groups of bolts. The outer diameters of the inner stage cold disk (11), the second stage cold disk (13), the third stage cold disk (15) and the fourth stage cold disk (17) are respectively equal to the outer diameters of the corresponding inner stage cold shield flange (25), second stage cold shield flange (26), third stage cold shield flange (27) and fourth stage cold shield flange (28).

6. The multi-stage coaxial nested cold shield structure for dilution refrigerator according to claim 4, wherein: A mixing chamber (7) is installed at the bottom of the four-stage cold shield (18). A mixing chamber cold plate (20) is arranged below the mixing chamber (7), and both the mixing chamber (7) and the mixing chamber cold plate (20) are arranged inside the four-stage cold shield (18). A delivery pipe and a circulation pipe communicating with the inside of the mixing chamber (7) are respectively arranged at the top of the mixing chamber (7). A separated heat exchanger (6) is communicated and arranged above the delivery pipe and the circulation pipe, and the separated heat exchanger (6) is arranged inside the four-stage cold shield (18).

7. The multi-stage coaxial nested cold shield structure for dilution refrigerator according to claim 6, characterized in that: Both the delivery pipe and the circulation pipe are hermetically and penetratively connected to the four-stage cold plate (17), and one ends of the delivery pipe and the circulation pipe extending into the three-stage cold shield (16) are respectively communicated with a continuous heat exchanger (5). The upper ends of the two continuous heat exchangers (5) are jointly communicated with an evaporation chamber (4), and the evaporation chamber (4) is arranged at the top inside the three-stage cold shield (16).

8. The multi-stage coaxial nested cold shield structure for dilution refrigerators according to claim 7, characterized in that: A JT heat exchanger (3) is arranged inside the two-stage cold shield (14). The bottom of the outer pipe of the JT heat exchanger (3) penetrates through the three-stage cold plate (15) and is communicated with the inside of the evaporation chamber (4), and the top of the outer pipe of the JT heat exchanger (3) is penetratively connected to the two-stage cold plate (13).

9. The multi-stage coaxial nested cold shield structure for dilution refrigerator according to claim 8, characterized in that: A corrugated pipe (2) is arranged between the first-stage cold plate (11) and the two-stage cold plate (13). The bottom of the corrugated pipe (2) is communicated with the inside of the JT heat exchanger (3). The top of the corrugated pipe (2) is communicated with a pumping pipeline (10), and the top of the pumping pipeline (10) is hermetically and penetratively connected to the top plate (9) and extends outside the Dewar (8).

10. The multi-stage coaxial nested cold shield structure for a dilution refrigerator according to claim 1, characterized in that: A plurality of support rods (19) are respectively arranged between the top plate (9), the first-stage cold shield (12), the two-stage cold shield (14), the three-stage cold shield (16) and the four-stage cold shield (18), and the plurality of support rods (19) are respectively detachably connected to the side walls of the corresponding first-stage cold plate (11), two-stage cold plate (13), three-stage cold plate (15) and four-stage cold plate (17).

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