Refrigerator system

Abstract

The refrigerating machine system comprises a compressor and a refrigerating machine, the low-pressure input end of the compressor is connected with a low-pressure gas outlet of the refrigerating machine, and the high-pressure output end of the compressor is connected with a high-pressure gas inlet of the refrigerating machine; the compressor comprises a compressor main body connected between a low-pressure input end and a high-pressure output end, and the compressor main body absorbs low-pressure helium from the refrigerator and continuously outputs high-pressure helium to the refrigerator; the low-pressure suction pressure of the compressor body ranges from 0.8 Mpa to 1.4 Mpa, and the high-pressure exhaust pressure of the compressor body does not exceed 2.8 Mpa. The operating parameters required by the first temperature zone and the second temperature zone can be considered, so that the performance of the refrigerator is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a cryogenic refrigerator, in particular to a refrigerator system. BACKGROUND

[0002] In a cryogenic system, GM (Gifford-McMahon) refrigerator is commonly used to cool a target object, such as a superconducting magnet. The refrigerator generally adopts a two-stage form, the first stage cold head provides cooling capacity for the magnet cold shield to be cooled down, generally in the temperature range of 20-60K, and the second stage cold head provides cooling capacity for the magnet itself, generally in the liquid helium temperature range. It is worth noting that the operating parameter requirements of the two temperature ranges of the two-stage refrigerator are inconsistent, such as frequency, pressure, etc. In order to improve the refrigeration capacity in the second temperature range, the operating frequency of the refrigerator is generally 1-1.2Hz. But this is not suitable for the parameters required for the first temperature range, that is, in the high temperature range, the first temperature range does not fully exert its performance because it is not running in the appropriate parameter state. The way to improve the refrigeration capacity of the first temperature range is to increase the operating frequency of the refrigerator, but this is contradictory to the operating frequency required by the second temperature range, because too fast operating frequency will result in insufficient residence time of the refrigerant in the second displacer, which will result in insufficient heat exchange between the refrigerant and the heat exchange material in the second displacer, leading to performance degradation of the second temperature range. SUMMARY

[0003] The purpose of the present application is to provide a refrigerator system that can take into account the operating parameters required by the first and second temperature ranges and improve the performance of the refrigerator.

[0004] Technical scheme: The refrigerator system of the present application comprises a compressor and a refrigerator, the low-pressure input end of the compressor is connected to the low-pressure gas outlet of the refrigerator, and the high-pressure output end of the compressor is connected to the high-pressure gas inlet of the refrigerator; the compressor comprises a compressor main body connected between the low-pressure input end and the high-pressure output end, which absorbs low-pressure helium gas from the refrigerator and continuously outputs high-pressure helium gas to the refrigerator;

[0005] The refrigerator comprises a cylinder, a first cold head and a second cold head, wherein the cylinder comprises a first stage cylinder body and a second stage cylinder body; the first stage cylinder body and the second stage cylinder body are coaxially arranged, the first cold head is connected between the first stage cylinder body and the second stage cylinder body, and the second cold head is arranged at the end of the second stage cylinder body; the operating temperature range of the first cold head is 20-60K, and the operating temperature range of the second cold head is 2-5K; the difference between the lower limit value of the helium gas permeation depth range corresponding to the low pressure provided by the compressor main body and the upper limit value of the helium gas permeation depth range corresponding to the high pressure provided by the compressor main body is not more than 2 times the difference between the upper and lower limit values of the helium gas permeation depth range corresponding to the low pressure.

[0006] Further, the upper limit of the helium permeation depth range is the thermal permeation depth of helium, and the lower limit of the helium permeation depth range is the viscous permeation depth of helium.

[0007] Further, the low-pressure suction pressure of the compressor body ranges from 0.8 to 1.4 Mpa, and the high-pressure exhaust pressure is not more than 2.8 Mpa.

[0008] Further, the ratio of the high-pressure provided by the compressor body to the low-pressure ranges from 2 to 3.5.

[0009] Further, different types of heat exchange materials are arranged in the first-stage push piston and the second-stage push piston.

[0010] Further, the compressor comprises a frequency converter connected to the compressor body, a controller connected to the frequency converter, a second pressure sensor arranged on the low-pressure flow path of the compressor, and a first pressure sensor arranged on the high-pressure flow path of the compressor; the first pressure sensor and the second pressure sensor are connected to the controller.

[0011] Further, the first pressure sensor is used to measure the pressure of the high-pressure helium on the high-pressure flow path of the compressor and send it to the controller, and the second pressure sensor is used to measure the pressure of the low-pressure helium on the low-pressure flow path of the compressor and send it to the controller.

[0012] Further, when the controller determines that the pressure of the high-pressure helium exceeds 2.8 Mpa or the pressure of the low-pressure helium is not within the range of 0.8 to 1.4 Mpa, the controller sends an instruction to the frequency converter to adjust the operating frequency of the compressor body, and the frequency converter adjusts the operating frequency of the compressor body in real time according to the instruction until the pressure of the high-pressure helium is not more than 2.8 Mpa and the pressure of the low-pressure helium is within the range of 0.8 to 1.4 Mpa.

[0013] Further, the low-pressure suction pressure of the compressor body (61) ranges from 1 to 1.2 Mpa, and the high-pressure exhaust pressure ranges from 2.5 to 2.8 Mpa.

[0014] Further, the compressor body is a variable-frequency compression package or a fixed-frequency compression package.

[0015] Advantages: Compared with the prior art, the significant technical effects of the present application are as follows: by optimizing the operating pressure parameters, the present application makes the permeation depths of helium in the high-pressure and low-pressure states close to each other and comparable to the equivalent diameter of the heat exchange material, so that the heat exchange efficiency of the heat exchange material in the operating cycle is improved, and the performance of the refrigerator is improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structural schematic diagram of the present application;

[0017] Figure 2 It is the specific heat capacity curve of helium and heat exchange material;

[0018] Figure 3 This is a graph showing the penetration depth of helium in the 40K temperature range of the present invention;

[0019] Figure 4 This is a graph showing the penetration depth of helium in different temperature zones according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods and the accompanying drawings.

[0021] like Figure 1 As shown, the refrigerator system of the present invention involves the following components: a compressor 1, a first metal hose 2, a second metal hose 3, a refrigerator 4, a cylinder 11, a first-stage cylinder body 111, a second-stage cylinder body 112, a push piston 12, a first-stage push piston 121, a second-stage push piston 122, a cover body 21, a connecting rod 22, a drive mechanism 23, a switching valve 24, a refrigerator motor 25, a first cold head 31, a second cold head 32, a high-pressure gas inlet 51, a low-pressure gas outlet 52, a compressor body 61, a frequency converter 62, a controller 63, a first pressure sensor 64, a second pressure sensor 65, a high-pressure output end 69, and a low-pressure input end 70.

[0022] The low-pressure input end 70 of the compressor 1 is connected to the low-pressure gas outlet 52 of the refrigerator 4 via the second metal hose 3, and the high-pressure output end 69 of the compressor 1 is connected to the high-pressure gas inlet 51 of the refrigerator 4 via the first metal hose 2. The compressor 1 includes a compressor body 61, a frequency converter 62, a controller 63, a first pressure sensor 64, and a second pressure sensor 65. The compressor body 61 is connected between the low-pressure input end 70 and the high-pressure output end 69. The compressor body 61 absorbs low-pressure helium from the refrigerator 4 and continuously outputs high-pressure helium to the refrigerator 4. In this embodiment, the compressor body 61 uses a variable-frequency scroll compressor. The variable-frequency scroll compressor also includes a frequency converter 62 and a control unit 63. The frequency converter 62 is connected to the compressor body 61, and the controller 63 is connected to the frequency converter 62. The second pressure sensor 64 is set in the high-pressure flow path of the compressor 1 to measure the pressure of the high-pressure working gas. The first pressure sensor 65 is set in the low-pressure flow path of the compressor 1 to measure the pressure of the low-pressure working gas. The first pressure sensor 64 and the second pressure sensor 65 are connected to the controller 63 .

[0023] The first pressure sensor 64 is used to measure the pressure of the high-pressure helium gas on the high-pressure flow path of the compressor 1 and send it to the controller 63 . The second pressure sensor 65 is used to measure the pressure of the low-pressure helium gas on the low-pressure flow path of the compressor 1 and send it to the controller 63 .

[0024] The refrigerator 4 is a two-stage refrigerator, comprising a cylinder 11, a displacement piston 12, a driving mechanism 23, a switching valve 24, a refrigerator motor 25, a first cold head 31, and a second cold head 32. The cylinder 11 comprises a first-stage cylinder body 111 and a second-stage cylinder body 112, which are coaxially arranged (the "up-down" direction is defined by the axis direction of the cylinder 111 in the figure), and the displacement piston 12 comprises a first-stage displacement piston 121 and a second-stage displacement piston 122. The cylinder 11 is a two-stage cylinder, the body of which is made of 304 stainless steel. The first-stage cylinder body 111 and the second-stage cylinder body 112 are coaxially arranged, the first cold head 31 is welded between the first-stage cylinder body 111 and the second-stage cylinder body 112, and the second cold head 32 is arranged at the end of the second-stage cylinder body 112. The first cold head 31 serves as a high-temperature cold head, and the second cold head 32 serves as a low-temperature cold head. The inner diameter of the second-stage cylinder body 112 is smaller than that of the first-stage cylinder body 111. Both the first cold head 31 and the second cold head 32 are made of copper. The first-stage displacement piston 121 is arranged inside the first-stage cylinder body 111, and the second-stage displacement piston 122 is arranged inside the second-stage cylinder body 112. The first-stage displacement piston 121 and the second-stage displacement piston 122 are coaxially connected. The inner diameter of the second-stage displacement piston 122 is smaller than that of the first-stage displacement piston 121. The driving mechanism 23 is arranged inside the cover 21 and connected with the first-stage displacement piston 121. The first-stage displacement piston 121 and the second-stage displacement piston 122 move up and down in the cylinder 11 under the driving of the driving mechanism 23. The first-stage cylinder body 111 has a first-stage expansion chamber 113 at the lower end inside, and the second-stage cylinder body 112 has a second-stage expansion chamber 123 at the lower end inside. When the first-stage displacement piston 121 and the second-stage displacement piston 122 move upwards in the figure, the volumes of the first-stage expansion chamber 113 and the second-stage expansion chamber 123 increase. Conversely, the corresponding expansion volumes decrease.

[0025] The refrigerator motor 25 and the switching valve 24 are accommodated in the cover 21 of the refrigerator 4. The refrigerator motor 25 serves as the driving source of the first-stage displacement piston 121, the second-stage displacement piston 122, and the switching valve 24. The refrigerator motor 25 drives the driving mechanism 23 to move up and down along the axis of the cylinder 11 through the eccentric cam 26, so that the first-stage displacement piston 121 and the second-stage displacement piston 122 can move back and forth in the first-stage cylinder body 11a and the second-stage cylinder body 11b, respectively. The switching valve 24 is used to periodically switch the flow path of the working gas. The refrigerator 4 can be a regenerative ultra-low-temperature refrigerator such as a Gifford-McMahon refrigerator (so-called GM refrigerator), or a pulse tube refrigerator or a Stirling refrigerator.

[0026] The refrigerator 4 can provide cooling capacity, which requires the compressor 1 to provide a certain pressure difference, that is, there is a certain pressure difference between the first-stage expansion chamber and the second-stage expansion chamber of the refrigerator 4. Generally, the pressure difference between the high-pressure working gas and the low-pressure working gas is between 1.4 and 2.0 MPa, and the optimal pressure difference is selected between 1.6 and 1.7 MPa.

[0027] The high-pressure helium gas output by the compressor body 61 enters the refrigerator 4, passes through the switching valve 24 provided in the cover body 21, passes through the first-stage push piston 121 and the second-stage push piston 122 in sequence, and exchanges heat with the heat exchange material in the first-stage push piston 121 and the second-stage push piston 122. The cooled helium gas expands in the first-stage expansion chamber 113 and the second-stage expansion chamber 123, and then returns along the original path, passes through the second-stage push piston 122 and the first-stage push piston 121 in sequence, and is heated by the heat exchange material in the second-stage push piston 122 and the first-stage push piston 121. After passing through the switching valve 24, it returns to the low-pressure input end 70 of the compressor 1, completing a cycle.

[0028] The operating temperature range of the first cold head 31 is 20-60 K (first temperature range), and the operating temperature range of the second cold head 32 is 2-5 K (second temperature range). For a two-stage refrigerator that can reach the liquid helium temperature range, the operating temperature range of the first cold head 31 is generally between 30-50 K.

[0029] Different types of heat exchange materials are set in the first stage push piston 121 and the second stage push piston 122. The selection basis of heat exchange materials is: the larger the ratio of the volume specific heat capacity of the heat exchange material to the volume specific heat capacity of helium, the better, so as to improve the heat exchange efficiency between the heat exchange material and helium. Figure 2 As shown, Figure 2 Figure (a) is a volumetric specific heat capacity curve of heat transfer material and helium; Figure 2 Figure (b) is the volume specific heat capacity curve of heat transfer materials and helium below 10K temperature range. Figure 2 As shown in Figure (a), the heat exchange material in the first-stage push piston 121 can be stainless steel (SS), phosphor bronze (Brass), or wire mesh or pellets made of lead, because the volume specific heat of general metal materials in the temperature range of 20-60K is much greater than the volume specific heat of helium; the heat exchange material in the second-stage push piston 122 is, from top to bottom (from the hot end to the low temperature end), generally non-magnetic cold storage material, magnetic cold storage material, such as pellets made of holmium copper (HoCu2) and gadolinium oxysulfide (GOS), Figure 2 As shown in Figure (b).

[0030] In addition to selecting the type of heat exchange material, in order to improve the heat transfer efficiency between the heat exchange material and helium, the more critical thing is to select the specifications of the heat exchange material. The specifications of the heat exchange material must meet the following conditions:

[0031] δ ν <Di<δ κ

[0032] wherein, D i is the hydraulic diameter of the heat exchange material, δ κ is the thermal penetration depth of helium, δ ν is the viscous penetration depth of helium.

[0033] the thermal penetration depth of helium λ is the thermal diffusivity of helium, and ω is the angular frequency corresponding to the heat exchange period of helium in the pusher piston 12; the viscous penetration depth of helium ν is the kinematic viscosity of helium, and ω is the angular frequency corresponding to the heat exchange period of helium in the pusher piston 12.

[0034] When the specification of the heat exchange material satisfies δ ν <Di<δ κ , the refrigeration working medium helium can fully exchange heat with the heat exchange material, and at the same time, the flow resistance of helium is not too large, which maintains the necessary pressure difference required for expansion.

[0035] As Figure 3 shown, when the first cold head 31 is in the 40K temperature zone, the low-pressure suction pressure is 0.4MPa, and the hydraulic diameter of the heat exchange material in the first-stage pusher piston 121 is preferably in the range of 0.61-0.72mm, but when the system high-pressure exhaust pressure is 2MPa, the preferred hydraulic diameter of the heat exchange material in the first pusher piston 121 is in the range of 0.31-0.35mm, and the range of the above two is quite different. In the running process of the refrigerator 4, the low-pressure suction pressure is generally 0.4-0.6MPa, and the high-pressure exhaust pressure is generally 2.0-2.3MPa. In this state, the hydraulic diameter of the heat exchange material in the first-stage pusher piston 121 is difficult to consider the range of the helium penetration depth under the two pressures, so that the heat exchange effect or flow resistance between the heat exchange material and helium cannot be considered, resulting in that the refrigeration efficiency of the refrigerator 4 is not optimal.

[0036] The present application provides a refrigerator system running mode to solve the above problems.

[0037] The compressor body 61 runs in the following manner: the difference between the lower limit value of the helium penetration depth range corresponding to the low pressure provided by the compressor body 61 and the upper limit value of the helium penetration depth range corresponding to the high pressure provided by the compressor body 61 is not more than 2 times the difference between the upper and lower limit values in the helium penetration depth range corresponding to the low pressure. Among them, the upper limit value of the helium penetration depth range is the thermal penetration depth of helium, and the lower limit value of the helium penetration depth range is the viscous penetration depth of helium.

[0038] like Figure 3 As shown. The thermal penetration depth of helium δ κ and the viscous penetration depth of helium δ ν (The solid line in the figure is the thermal penetration depth of helium, and the dotted line is the viscous penetration depth) changes with the pressure of the system. In the 40K temperature range, when the helium pressure is at a low state, the thermal penetration depth of helium δ κ and the viscous penetration depth of helium δ ν , with the pressure change rate is large. When the helium pressure is greater than 1.2MPa, as the pressure increases, the above heat penetration depth δ κ and the viscous penetration depth of helium δ ν As the pressure change rate becomes larger, it gradually becomes gentler.

[0039] and, Figure 3 The figure also shows the helium penetration depth in the liquid helium temperature range (4.2K) as a function of pressure (the solid line is the thermal penetration depth, and the dashed line is the viscous penetration depth). As can be seen from the figure, the range from the viscous penetration depth to the thermal penetration depth does not change significantly with varying pressure, which provides a convenience for the implementation of the present invention. That is, during implementation, the focus only needs to be on the temperature range of the first cold head 31 (above 20K) and select the appropriate operating pressure.

[0040] When implementing it specifically, Figure 4 The figure shows the helium penetration depth ranges for the three temperature zones of 20K, 40K, and 60K. The solid line at the edge of the shaded portion of the figure represents the thermal penetration depth of helium, the dashed line represents the viscous penetration depth, and the shaded portion represents the range of selectable hydraulic diameters for the heat exchange material. The chiller system operates in the following manner: the difference δ between the lower limit of the helium penetration depth range α corresponding to the selected low-pressure suction pressure and the upper limit of the helium penetration depth range α corresponding to the selected high-pressure exhaust pressure does not exceed twice the difference between the upper and lower limits of the helium penetration depth range α corresponding to the selected low-pressure suction pressure.

[0041] The low-pressure intake pressure of the priority compressor body 61 is in the range of 0.8 MPa to 1.4 MPa.

[0042] Specifically, the temperature of the first cold head 31 is 60K. In the past, the low-pressure intake of the compressor body 61 was generally 0.4MPa, and the high-pressure exhaust was around 2.2MPa. The helium penetration depth range α under low-pressure conditions is in the range of 0.86 to 1mm, and the helium penetration depth range α under high-pressure conditions is in the range of 0.38 to 0.44mm. The difference between the lower limit of the helium penetration depth range α under low-pressure conditions and the upper limit of the helium penetration depth range α under high-pressure conditions is 0.42mm, which is more than three times the helium penetration depth range α of 0.86 to 1mm (the range difference is 0.14mm) under low-pressure conditions. In this case, it is difficult to select the specifications of the heat exchange material, and the refrigeration system cannot fully exert the performance of the heat exchange material.

[0043] In the above embodiment, the low-pressure suction pressure can be selected as 1.4 MPa. Considering safety, the high-pressure exhaust pressure does not exceed 2.8 MPa. The high-pressure to low-pressure pressure ratio is 2, and the pressure difference is 1.4 MPa, which can meet the operating requirements of the refrigerator 4. At 1.4 MPa, the helium penetration depth range under the low-pressure state (the arrow interval corresponding to α1 is 0.46 to 0.55 mm) has a lower limit of 0.46 mm and an upper limit of 0.4 mm corresponding to the high pressure of 2.8 MPa. The difference δ1 between the two (the lower limit of the helium penetration depth range corresponding to the low pressure and the upper limit of the helium penetration depth range corresponding to the high pressure) is only 0.06 mm, which does not exceed twice the difference between the upper and lower limits in α1 (0.09 mm). Therefore, the heat exchange material can better play its advantages compared to the previous operating mode.

[0044] like Figure 4 As shown, the temperature range of the first cold head 31 is 40K. The low-pressure intake pressure is preferably above 1.2 MPa, and the corresponding helium penetration depth range α2 is 0.36-0.46 mm, with a lower limit of 0.36 mm. The upper limit of the high-pressure helium penetration depth range corresponding to a high-pressure exhaust pressure of 2.8 MPa is 0.29 mm. The difference δ2 between the lower limit of the low-pressure helium penetration depth range and the upper limit of the high-pressure helium penetration depth range is 0.07 mm, which does not exceed twice the difference between the upper and lower limits of the interval range α2, which is 0.1 mm.

[0045] like Figure 4 As shown, when the temperature range of the first cold head 31 is 20K, the low-pressure suction pressure is preferably above 0.8 MPa, and the corresponding helium penetration depth range α3 is 0.25-0.29 mm, with a lower limit of 0.25 mm. The upper limit of the high-pressure helium penetration depth range corresponding to the high-pressure state of 2.8 MPa is 0.17 mm. The difference δ3 between the lower limit of the low-pressure helium penetration depth range and the upper limit of the high-pressure helium penetration depth range is 0.08 mm, which does not exceed twice the difference of 0.0.4 mm in the range α2.

[0046] The ratio of the high pressure to the low pressure is 3.5, and the pressure difference reaches 2 MPa. The selected high pressure can be appropriately reduced, and the pressure difference of 1.7 MPa is a relatively optimal value, and the high pressure can be selected as 2.5 MPa, and the corresponding upper limit value is 0.18 mm, and the corresponding difference value δ3 is 0.07 mm.

[0047] In the implementation process, the ratio of the high pressure discharge pressure to the low pressure suction pressure of the compressor body 61 is preferably set to be 2-3.5. The lower the refrigeration temperature of the first cold head 31, the greater the pressure difference requirement provided by the compressor body 61. Therefore, according to the selected temperature range, the high pressure discharge pressure is preferably 2.5 MPa or more.

[0048] In the present application, the upper limit of the low pressure suction pressure is set to be 1.4 MPa. In fact, when the low pressure suction pressure is greater than 1.4 MPa, the high pressure discharge pressure corresponding to the penetration depth interval range and the low pressure suction pressure corresponding to the helium penetration interval range are closer. However, due to the structural limitation of the compressor body 61 of the compressor 1, the high pressure discharge pressure is generally not more than 2.8 MPa, and therefore the low pressure suction pressure cannot be too large, otherwise the pressure difference provided by the compressor body 61 will be small.

[0049] The present application sets the low pressure suction pressure to be 0.8-1.4 MPa, and the high pressure discharge pressure is not more than 2.8 MPa, so as to improve the performance of the refrigerator, and the pressure ratio of the compressor 1 can be set to be 2.0-3.5. For example, when the suction pressure is 1.4 MPa, the high pressure is set to be 2.8 MPa, and the pressure difference is also 1.4 MPa, which meets the needs of the refrigerator 4. When the low pressure suction pressure is set to be 0.8 MPa, the high pressure discharge pressure can be set to be 2.5 MPa, and the pressure difference can reach 1.7 MPa. If the low pressure suction pressure is set to be too large, in addition to the insufficient pressure difference, from the (a) figure in FIG. 1, it can be seen that the volume specific heat of helium is relatively large, and the volume specific heat of the heat exchange material is relatively small compared with the volume specific heat of helium, which is not conducive to heat exchange. Figure 2

[0050] The low pressure suction pressure is preferably 1.0-1.2 MPa, and the high pressure discharge pressure is preferably 2.5-2.8 MPa. When the low pressure suction pressure is 0.8-1.4 MPa, compared with 0.4 MPa, from the (b) figure in FIG. 1, it can be seen that the volume specific heat of helium is slightly smaller, which improves the heat exchange efficiency of the second stage push piston 122. Figure 2

[0051] ​​The compressor 1 can be operated at a constant pressure selected or the pressure value can be adjusted during operation. When the compressor 1 is selected to operate with the pressure value adjusted during operation, the compressor 1 operates in a manner that the above-mentioned range corresponding to the high pressure is closest to the above-mentioned range corresponding to the low pressure.

[0052] The compressor body 61 is a variable frequency compressor, and can also be implemented as a fixed frequency compressor. During implementation, the pressure of the matched refrigeration machine 4 is adjusted by setting the static charging pressure value, so that the pressure change of the compressor body 61 during the entire operation process is within the set target value change range (the range of the low-pressure suction pressure is 0.8-1.4 Mpa, and the high-pressure discharge pressure is not more than 2.8 Mpa), rather than controlling the high-pressure helium pressure and the low-pressure helium pressure to be constant by the frequency converter 62. Although there can be a change range of the low-pressure suction pressure during the entire process, the low-pressure suction pressure and the high-pressure discharge pressure can still be within the set range.

Claims

1. A refrigerator system, characterized in that: The invention comprises a compressor (1) and a refrigerator (4), wherein a low-pressure input end (70) of the compressor (1) is connected to a low-pressure gas outlet (52) of the refrigerator (4), and a high-pressure output end (69) of the compressor (1) is connected to a high-pressure gas inlet (51) of the refrigerator (4); The compressor (1) includes a compressor body (61) connected between a low-pressure input end (70) and a high-pressure output end (69), wherein the compressor body (61) absorbs low-pressure helium from the refrigerator (4) and continuously outputs high-pressure helium to the refrigerator (4); The refrigerator (4) comprises a cylinder (11), a first cold head (31) and a second cold head (32), wherein the cylinder (11) comprises a first-stage cylinder body (111) and a second-stage cylinder body (112); The first-stage cylinder (111) and the second-stage cylinder (112) are coaxially arranged, the first cold head (31) is connected between the first-stage cylinder (111) and the second-stage cylinder (112), and the second cold head (32) is arranged at the end of the second-stage cylinder (112); The operating temperature range of the first cold head (31) is 20-60K, and the operating temperature range of the second cold head (32) is 2-5K; The compressor body (61) operates in such a manner that the difference between the lower limit of the helium penetration depth range corresponding to the low pressure provided by it and the upper limit of the helium penetration depth range corresponding to the high pressure provided by it does not exceed twice the difference between the upper and lower limits in the helium penetration depth range corresponding to the low pressure.

2. The refrigerator system according to claim 1, wherein: The upper limit of the helium penetration depth range is the thermal penetration depth of helium, and the lower limit of the helium penetration depth range is the viscous penetration depth of helium.

3. The refrigerator system according to claim 1, wherein: The low-pressure suction pressure of the compressor body (61) ranges from 0.8 to 1.4 MPa, and the high-pressure exhaust pressure does not exceed 2.8 MPa.

4. The refrigerator system according to claim 1, wherein: The ratio of the high pressure to the low pressure provided by the compressor body (61) is 2 to 3.

5.

5. The refrigerator system according to claim 1, wherein: Different types of heat exchange materials are arranged in the first-stage pushing piston (121) and the second-stage pushing piston (122).

6. The refrigerator system according to claim 1, wherein: The compressor (1) includes a frequency converter (62) connected to a compressor body (61), a controller (63) connected to the frequency converter (62), a second pressure sensor (65) provided on a low-pressure flow path of the compressor (1), and a first pressure sensor (64) provided on a high-pressure flow path of the compressor (1); the first pressure sensor (64) and the second pressure sensor (65) are connected to the controller (63).

7. The refrigerator system according to claim 6, wherein: The first pressure sensor (64) is used to measure the pressure of the high-pressure helium gas on the high-pressure flow path of the compressor (1) and send it to the controller (63), and the second pressure sensor (65) is used to measure the pressure of the low-pressure helium gas on the low-pressure flow path of the compressor (1) and send it to the controller (63).

8. The refrigerator system according to claim 6, wherein: When the controller (63) determines that the pressure of the high-pressure helium gas exceeds 2.8 MPa, or the pressure of the low-pressure helium gas is not within the range of 0.8 to 1.4 MPa, the controller (63) sends an instruction to the frequency converter (62) to adjust the operating frequency of the compressor body (61), and the frequency converter (62) adjusts the operating frequency of the compressor body (61) in real time according to the instruction until the pressure of the high-pressure helium gas does not exceed 2.8 MPa and the pressure of the low-pressure helium gas is within the range of 0.8 to 1.4 MPa.

9. The refrigerator system according to claim 1, wherein: The compressor body (61) is a variable frequency compressor or a fixed frequency compressor.

10. The refrigerator system according to claim 3, wherein: The low-pressure suction pressure of the compressor body (61) ranges from 1 to 1.2 MPa, and the high-pressure exhaust pressure ranges from 2.5 to 2.8 MPa.

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