Method for maintaining high vacuum under extraction of high-speed neutral particle flow field

Abstract

This application discloses a method for maintaining high vacuum under high-speed neutral particle flow field extraction, belonging to the field of low-Earth orbit space environment simulation technology. The method involves coarsely pumping the vacuum container to reduce the pressure below a first pressure value; activating the container's cryogenic pump and the transition section's cryogenic pump to reduce the pressure below a second pressure value, establishing a high-vacuum background environment; activating the gas-helium refrigeration system to cool the cryogenic cold plate, lowering its temperature below a first temperature threshold and its pressure below a third pressure value, forming high-pumping-rate vacuum maintenance conditions; allowing a neutral particle source to extract a high-speed neutral particle flow field through the transition section; and continuously evacuating the introduced gas molecules during the continuous extraction of the particle flow using the container's cryogenic pump, the transition section's cryogenic pump, and the cryogenic cold plate to maintain the pressure below a fourth pressure value. This application solves the technical problem of maintaining high vacuum in a container under high-speed neutral particle flow field extraction.

Description

Technical Field

[0001] This application relates to the field of spacecraft low-Earth orbit space environment simulation technology, and more specifically to a method for maintaining high vacuum under high-speed neutral particle flow field extraction. Background Technology

[0002] With the rapid development of commercial space technology, countries around the world have launched low-Earth orbit (LEO) satellite constellation deployment plans, and my country has also simultaneously carried out research and development work on LEO satellite technology. The operating space environment for LEO satellites is more complex than that for high-Earth orbit satellites, and solar activity is low during years with a particle number density of 4.53 × 10⁻⁶. / High solar activity year: particle number density of 12.96 × / Average value: Particle number density is 7.9 × / The ambient gas molecule density is relatively high, and its main components include nitrogen and atomic oxygen. Taking the ultra-low Earth orbit environment as an example, the typical gas molecule density can reach 5 × 10⁻⁶. indivual / The satellite's orbital speed is approximately 7.8 km / s. Under these conditions, different satellite configurations will generate different aerodynamic drag. Therefore, it is necessary to simulate the low-Earth orbit space environment on the ground to complete the aerodynamic drag test of the satellite configuration.

[0003] In ground-based simulation tests of aerodynamic drag, the test specimen remains stationary, and a neutral particle source blows out a directional particle wind with a velocity equivalent to that of the satellite. The particle number density must match the low Earth orbit (LEO) space environment. For safety reasons, neon is typically used as the simulation gas because it is an inert gas, chemically inert, and has a molecular weight close to that of nitrogen and atomic oxygen. During the test, the neutral particle source continuously ejects a high-speed particle stream into the vacuum container, which is equivalent to actively releasing a large amount of gas into the vacuum container. This places extremely high demands on the performance of the vacuum system.

[0004] In existing technologies, vacuum containers typically employ a dry pump unit for rough evacuation, followed by a cryogenic pump to achieve a high vacuum environment. For containers with a volume of not less than 80... A large experimental space can be obtained — Vacuum levels on the order of Pa. However, under orbital ambient temperatures of 850 K, the corresponding pressure in the low Earth orbit space environment is approximately 6 × 10⁻⁶ Pa. Pa, the experimental requirement is that the container's base pressure must be less than this value. More importantly, once the neutral particle source is activated, a large amount of gas is continuously introduced into the vacuum container, causing a significant increase in pressure inside the container. According to the formula for calculating the steady-state pressure of a vacuum system, the steady-state pressure of the container is directly proportional to the total gas load of the system and inversely proportional to the effective pumping speed of the system. The total gas load of the system includes the system's outgassing and leakage. With a conventional vacuum pump configuration, the system's effective pumping speed is limited, making it impossible to maintain the container pressure at the required level under the dynamic condition of continuous outgassing from the particle source.

[0005] To address these issues, some existing technologies attempt to increase pumping speed by adding cryogenic cold plates inside the vacuum container. However, the cooling methods and structural designs of traditional cryogenic cold plates are typically only suitable for static high-vacuum environments, with limited pumping speed enhancement capabilities, and they are difficult to maintain a stable high vacuum under dynamic conditions where a high-speed neutral particle flow field is continuously extracted.

[0006] Therefore, how to effectively establish and maintain a high vacuum inside a vacuum container under dynamic conditions where a large amount of gas is continuously released into the container from a high-speed neutral particle flow field, especially to meet the stringent vacuum requirements of low-Earth orbit space environment simulation experiments, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this application is to provide a method for maintaining high vacuum under high-speed neutral particle flow field extraction, which can solve at least one of the technical problems mentioned above. The specific solution is as follows: This application provides a method for maintaining high vacuum under high-speed neutral particle flow field extraction, including: The vacuum container is subjected to rough evacuation to reduce the pressure inside the vacuum container to below the first pressure value, thereby obtaining an initial low vacuum environment. In the initial low vacuum environment, the container cryogenic pump installed on the wall of the vacuum container and the transition section cryogenic pump installed on the wall of the transition section are started to remove the residual gas in the vacuum container and the gas entering through the transition section, so that the pressure in the vacuum container is reduced to below the second pressure value, and a high vacuum background environment is established. In the high vacuum background environment, the gas-helium refrigeration system is started to cool the low-temperature cold plate set in the vacuum container, so that the low-temperature cold plate reaches the target low temperature state, and the gas in the vacuum container is condensed and evacuated through the low-temperature cold plate until the temperature of the low-temperature cold plate is lower than the first temperature threshold, so that the pressure in the vacuum container is lower than the third pressure value, and a high pumping speed vacuum maintenance condition is formed in the vacuum container. Under the high-pumping-speed vacuum maintenance condition, the neutral particle source is led out into the vacuum container through a transition section that coincides with the axis of the vacuum container. During the continuous extraction of the high-speed neutral particle flow field, the introduced gas molecules are continuously evacuated by the container cryogenic pump, the transition section cryogenic pump, and the cryogenic cold plate, so that the pressure inside the vacuum container is maintained below the fourth pressure value, thereby achieving high vacuum maintenance under the low-orbit space environment simulation conditions.

[0008] Furthermore, the cryogenic pump is positioned at the center of the vacuum container wall to evacuate the gas within the main space of the vacuum container.

[0009] Furthermore, the cryogenic pump of the transition section is arranged circumferentially along the transition section, and the axis of the transition section is aligned with the axis of the vacuum container to evacuate the gas in the path of the high-speed neutral particle flow field.

[0010] Furthermore, the cryogenic cold plate is cooled by the helium gas refrigeration system, which outputs cryogenic helium gas to cool the cryogenic cold plate and maintain the cryogenic cold plate at the target low temperature.

[0011] Furthermore, the outer surface area of ​​the cryogenic cold plate is matched to the cooling capacity of the gaseous-helium refrigeration system so that the heat load of the cryogenic cold plate is adapted to the cooling capacity of the gaseous-helium refrigeration system.

[0012] Furthermore, the cryogenic cold plate is configured to include two cold plates, which are arranged opposite each other in the vacuum container along the propagation direction of the high-speed neutral particle flow field, and a particle flow channel is formed between the two cold plates.

[0013] Furthermore, a stainless steel tube is used as the helium flow channel for the cryogenic cold plate, and copper fins are welded to the outer surface of the stainless steel tube. The copper fins are arranged in a staggered and discontinuous manner to form an optically sealed structure.

[0014] Furthermore, the outer surface of the low-temperature cold plate is polished to form a low-emissivity surface, and a metal coating is formed on the polished outer surface to reduce radiative heat transfer.

[0015] Furthermore, an adsorption material is provided on the inner surface of the low-temperature cold plate to form a gas molecule adsorption layer on the inner surface of the low-temperature cold plate.

[0016] Furthermore, the extraction conditions of the high-speed neutral particle flow field are set according to the low-Earth orbit space environment, so that the pressure maintained in the vacuum container matches the gas load introduced by the high-speed neutral particle flow field, so that the gas environment in the vacuum container is close to the state of the low-Earth orbit space environment.

[0017] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects: 1. This application discloses a method for maintaining high vacuum under high-speed neutral particle flow field extraction. First, the vacuum container is coarsely pumped to reduce the pressure below a first pressure value, obtaining an initial low vacuum environment. Then, the container cryogenic pump and the transition section cryogenic pump are activated to remove residual gas and gas entering through the transition section, reducing the pressure below a second pressure value and establishing a high vacuum background environment. Based on this, a gas-helium refrigeration system is activated to cool the cryogenic cold plate, lowering its temperature below a first temperature threshold and its pressure below a third pressure value, forming high-pumping-speed vacuum maintenance conditions. Finally, during the continuous extraction of the high-speed neutral particle flow field, the introduced gas molecules are continuously evacuated by the container cryogenic pump, the transition section cryogenic pump, and the cryogenic cold plate, maintaining the pressure inside the vacuum container below a fourth pressure value. This method, through coarse pumping, a high vacuum background, deep cryogenic cold plates, staged pumping, and gradual pressure reduction, achieves stable maintenance of high vacuum under dynamic conditions of continuous particle source release, effectively solving the problem of a sharp drop in vacuum caused by active release in existing technologies. 2. This application discloses a method for maintaining high vacuum under high-speed neutral particle flow field extraction. When setting up the cryogenic cold plate, it comprises two cold plates arranged opposite each other along the propagation direction of the high-speed neutral particle flow field. This maximizes the contact opportunity between gas molecules and the cold plate surface while ensuring the passage of particle flow. By using a stainless steel tube as the helium flow channel and welding copper fins to the outer surface of the stainless steel tube, the copper fins are arranged in a staggered and discontinuous manner to form an optically sealed structure, effectively preventing radiative heat from entering the interior of the cold plate. Polishing the outer surface of the cryogenic cold plate and forming a metal coating significantly reduces radiative heat transfer; and by placing adsorption material on the inner surface of the cryogenic cold plate, the adsorption capacity for gas molecules is significantly enhanced. This allows the cryogenic cold plate to achieve higher pumping efficiency under the same cooling power, providing a reliable technical guarantee for maintaining high vacuum under high-speed neutral particle flow field extraction conditions.

[0018] 3. This application discloses a method for maintaining high vacuum under the extraction of a high-speed neutral particle flow field. The extraction conditions of the high-speed neutral particle flow field are set according to the low-Earth orbit (LEO) space environment, ensuring that the pressure maintained within the vacuum container matches the gas load introduced by the high-speed neutral particle flow field. This allows the gas environment within the vacuum container to approximate the LEO space environment. Specifically, it enables the background pressure within the vacuum container to be lower than a third pressure value, and maintains the pressure below a fourth pressure value under the dynamic condition of continuous extraction of the high-speed neutral particle flow field. This pressure index is compatible with the pressure requirements corresponding to the LEO space environment. This allows aerodynamic drag testing of satellite configurations to be conducted under vacuum conditions close to the actual LEO space environment, resulting in more reliable and valuable test results, providing reliable experimental support for the research and development of LEO satellite technology. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a schematic flowchart illustrating a method for maintaining high vacuum under high-speed neutral particle flow field extraction, as provided in an embodiment of this application.

[0020] Figure 2 This is a schematic diagram of a device for maintaining high vacuum under high-speed neutral particle flow field extraction, provided in an embodiment of this application.

[0021] Figure 3 This is a schematic diagram of the structure and cross-section of a low-temperature cold plate provided in an embodiment of this application.

[0022] Figure 4 This is a schematic diagram showing the position settings of the two low-temperature cold plates provided in the embodiments of this application.

[0023] Explanation of reference numerals in the attached figures: Vacuum container 1, transition section 2, neutral particle source 3, container cryogenic pump 4, cryogenic cold plate 5, first cryogenic cold plate 501, second cryogenic cold plate 502, oil removal and gas management system 6, cold box 7, turbine expander 8, helium tank 9. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the product or device that includes that element.

[0026] The following detailed description, in conjunction with the accompanying drawings, illustrates a method for maintaining high vacuum under high-speed neutral particle flow field extraction, as described in this application. This embodiment uses a low-Earth orbit space environment simulation experiment as its application scenario, specifically simulating the directional particle wind environment encountered by a low-Earth orbit satellite during its on-orbit operation, in order to complete the aerodynamic drag test of the satellite configuration.

[0027] This application provides a method for maintaining high vacuum under high-speed neutral particle flow field extraction, and a schematic diagram of the method flow is shown below. Figure 1 As shown; a device for maintaining high vacuum under high-speed neutral particle flow field extraction, such as... Figure 2 and Figure 3 As shown.

[0028] In this embodiment of the application, a method for maintaining high vacuum under high-speed neutral particle flow field extraction includes: S1. Perform a rough evacuation on vacuum container 1 to reduce the pressure inside vacuum container 1 to below the first pressure value, thereby obtaining an initial low vacuum environment.

[0029] The vacuum container 1 used in this embodiment is a space environment simulator with a volume of not less than 80 cubic meters. It is used to contain the test specimen and provide a simulated space environment. The vacuum container 1 is connected to the neutral particle source 3 through the transition section 2. The axis of the transition section 2 coincides with the axis of the vacuum container 1 to ensure that the high-speed neutral particle flow field is introduced along the axial direction of the container.

[0030] Before proceeding, the vacuum container 1 is first subjected to rough evacuation. In this embodiment, a dry pump unit is used for rough evacuation, which includes a screw pump and a Roots pump. The dry pump unit is started to perform rough evacuation on the vacuum container 1, reducing the pressure inside the vacuum container 1 to below a first pressure value. In this embodiment, the first pressure value is 10 Pa, thus obtaining an initial low vacuum environment.

[0031] S2. Under the initial low vacuum environment, start the container cryogenic pump 4 installed on the wall of vacuum container 1 and the transition section 2 cryogenic pump installed on the wall of transition section 2 to remove the residual gas in vacuum container 1 and the gas entering through transition section 2, so that the pressure in vacuum container 1 is reduced to below the second pressure value, and a high vacuum background environment is established.

[0032] Under initial low vacuum conditions, the container cryogenic pump 4, located on the wall of vacuum container 1, and the transition section 2 cryogenic pump, located on the wall of transition section 2, are activated. Container cryogenic pump 4 is a large-diameter cryogenic pump, positioned at the center of the wall of vacuum container 1, used to evacuate the gas within the main space of vacuum container 1. Transition section 2 cryogenic pump is positioned circumferentially along transition section 2, with the axis of transition section 2 coinciding with the axis of vacuum container 1, used to evacuate the gas along the path of the high-speed neutral particle flow field.

[0033] Both the container cryogenic pump 4 and the transition section cryogenic pump 2 utilize GM refrigerators to obtain pumping capacity. Their main components include a helium compressor and a two-stage cold head. After startup, the container cryogenic pump 4 and the transition section cryogenic pump 2 evacuate residual gas from the vacuum container 1, as well as gas entering through the transition section 2, reducing the pressure inside the vacuum container 1 to below a second pressure value. In this embodiment, the second pressure value is 1× Pa, thereby establishing a high vacuum background environment.

[0034] The technical solution of this application embodiment achieves all-round suction of gas in the high-speed neutral particle flow field introduction path by setting the cryogenic pump of the transition section 2 around the circumference of the transition section 2 and aligning the axis of the transition section 2 with the axis of the vacuum container 1. This effectively prevents the gas ejected from the particle source from flowing back or accumulating before entering the vacuum container 1, ensuring the cleanliness of the introduced particle flow field.

[0035] S3. In a high vacuum background environment, start the gas-helium refrigeration system to cool the low-temperature cold plate 5 set in the vacuum container 1, so that the low-temperature cold plate 5 reaches the target low temperature state, and condense and evacuate the gas in the vacuum container 1 through the low-temperature cold plate 5 until the temperature of the low-temperature cold plate 5 is lower than the first temperature threshold, so that the pressure in the vacuum container 1 is lower than the third pressure value, so that a high pumping speed vacuum maintenance condition is formed in the vacuum container 1.

[0036] Under high vacuum conditions, the gaseous helium refrigeration system is activated to cool the cryogenic cold plate 5 located inside the vacuum container 1. The gaseous helium refrigeration system includes a helium compression unit and a cooling unit, specifically consisting of a helium compressor, an oil removal and gas management system, a cold box 7, a helium storage tank, and cold plates.

[0037] The helium compressor serves as the system's power source, supplying high-pressure helium. High-purity helium stored in the intermediate-pressure tank, along with compressor oil, is compressed into a high-pressure helium-oil mixture within the compressor. After passing through an oil removal and gas management system, oil and helium are separated. The oil returns to the compressor via a return oil pipe, ensuring that the oil content of the helium entering the cold box 7 is within the specified range (non-helium components below 10 PPM). The high-pressure helium is cooled by a heat exchanger inside the external cold box 7, and then expanded and cooled by a turbine expander 8, becoming cryogenic helium (temperature below 10 K), which serves as the cooling medium to provide cryogenic temperatures for the cryogenic cold plate 5.

[0038] The cryogenic cold plate 5 is cooled by outputting cryogenic helium gas from the helium-gas refrigeration system, bringing it to the target low temperature. The cryogenic cold plate 5 also condenses and evacuates the gas inside the vacuum container 1. In this embodiment, the outer surface area of ​​the cryogenic cold plate 5 is matched to the refrigeration capacity of the helium-gas refrigeration system, ensuring that the heat load of the cold plate 5 is compatible with the refrigeration capacity of the system, and guaranteeing that the total heat load of the cold plate is less than the effective refrigeration power of the system.

[0039] In this embodiment, the heat sink is cooled to below 100K by a liquid nitrogen system, and the cryogenic cold plate 5 is cooled to below 10K by a gaseous helium refrigeration system. Due to the large temperature difference between the cryogenic cold plate 5 and the heat sink, radiative heat transfer becomes one of the main heat loads of the cryogenic cold plate 5. To ensure that the heat load of the cryogenic cold plate 5 is compatible with the cooling capacity of the gaseous helium refrigeration system, the radiative heat transfer needs to be quantitatively calculated.

[0040] In this embodiment, the radiative heat transfer of the liquid nitrogen-cooled heat sink to the cryogenic cold plate 5 is calculated according to the following formula: in, The heat radiated by the heat sink to the low-temperature cold plate 5 is expressed in W. This represents the outer surface area of ​​the low-temperature cold plate 5, in units of... ; This represents the internal surface area of ​​the heat sink, in units of... ; This indicates the emissivity of the outer surface of the low-temperature cold plate 5; Indicates the emissivity of the inner surface of the heat sink; This indicates the temperature of the low-temperature cold plate 5, in Kelvin (K). This indicates the temperature of the heat sink, expressed in Kelvin (K).

[0041] Based on the above calculation results, the outer surface area of ​​the cryogenic cold plate 5 can be matched and set so that the total heat load of the cryogenic cold plate 5 is less than the effective cooling power of the gas-helium refrigeration system at 10K, thereby ensuring that the cryogenic cold plate 5 can stably maintain the target low temperature state and provide sufficient pumping capacity for maintaining high vacuum under the conditions of high-speed neutral particle flow field extraction.

[0042] In this embodiment, the cryogenic cold plate 5 is cooled to below 10K by a gas-helium refrigeration system, and its total heat load includes three parts: radiative heat transfer, conductive heat leakage, and gas condensation heat. Radiative heat transfer mainly originates from the radiative heat from the liquid nitrogen-cooled heat sink to the cryogenic cold plate 5; conductive heat leakage mainly originates from solid-state heat conduction between the cryogenic cold plate 5 and surrounding components, including heat conduction through the cold plate support structure and heat leakage at pipe connections; and gas condensation heat originates from the latent heat of phase change released when gas molecules in a high-speed neutral particle flow field condense on the surface of the cryogenic cold plate 5.

[0043] The sum of the three heat loads mentioned above constitutes the total cooling power required by the gas-helium refrigeration system. Calculations and analysis show that in this embodiment, conductive heat leakage and gas condensation heat are relatively small, while radiative heat transfer accounts for the majority of the total heat load. Therefore, reducing the radiative heat transfer coefficient of the outer surface of the cryogenic cold plate 5 is key to reducing the total heat load and improving refrigeration efficiency.

[0044] Based on the above analysis, this embodiment polishes the outer surface of the cryogenic cold plate 5 and forms a metal coating to reduce the emissivity of the outer surface, thereby reducing radiative heat transfer. Simultaneously, the outer surface area of ​​the cryogenic cold plate 5 is matched to the cooling capacity of the gas-helium refrigeration system, ensuring that the total heat load of the cryogenic cold plate 5 is less than the effective cooling power of the gas-helium refrigeration system at 10K. This ensures that the cryogenic cold plate 5 can stably maintain the target low temperature state and provides sufficient pumping capacity for maintaining high vacuum under conditions of high-speed neutral particle flow field extraction.

[0045] The cryogenic cold plate 5 comprises two cold plates, a first cryogenic cold plate 501 and a second cryogenic cold plate 502, arranged opposite each other within the vacuum container 1 along the propagation direction of the high-speed neutral particle flow field, forming a particle flow channel between the two cold plates. The distance between the two cold plates is not less than 5 cm. A stainless steel tube is used as the helium flow channel for the cryogenic cold plate 5, and copper fins are welded to the outer surface of the stainless steel tube. The copper fins are arranged in a staggered and discontinuous manner to form an optically sealed structure. The first cryogenic cold plate 501 and the second cryogenic cold plate 502 are arranged opposite each other, together forming an opposing optically sealed space. This space can effectively prevent external radiant heat from directly entering the interior of the cold plates, while ensuring the smooth passage of the high-speed neutral particle flow field.

[0046] The outer surface of the low-temperature cold plate 5 is polished to form a low-emissivity surface. A metal coating is then formed on the polished outer surface, achieved by vacuum evaporation of an aluminum film or electroplating of a nickel film, to reduce radiative heat transfer. An adsorbent material is placed on the inner surface of the low-temperature cold plate 5, achieved by spraying black paint and attaching activated carbon, to form a gas molecule adsorption layer on the inner surface of the low-temperature cold plate 5. In this embodiment, the adsorbent material is activated carbon.

[0047] The technical solution of this application embodiment uses a stainless steel tube as a helium flow channel and welds copper fins to its outer surface. The copper fins are arranged in a staggered and discontinuous manner to form an optically sealed structure. This ensures effective cooling of the cold plate while preventing radiant heat from directly entering the interior of the cold plate, thus reducing the heat load. Polishing the outer surface of the low-temperature cold plate 5 and forming a metal coating significantly reduces the radiative heat transfer coefficient of the outer surface, decreasing radiative heat exchange between the cold plate and the surrounding environment and improving the cooling efficiency. By setting an adsorbent material on the inner surface of the low-temperature cold plate 5 to form a gas molecule adsorption layer, the physical adsorption capacity for gas molecules is significantly enhanced, increasing the gas pumping speed per unit area of ​​the cold plate and enabling the cold plate to achieve higher pumping performance with the same condensation area.

[0048] Refrigeration continues until the temperature of the cryogenic cold plate 5 drops below a first temperature threshold (10K in this embodiment), causing the pressure inside the vacuum container 1 to drop below a third pressure value (1×K in this embodiment). Pa creates a high-speed vacuum maintenance condition inside vacuum container 1.

[0049] During this process, the expression for the pumping speed on the surface of the low-temperature cold plate 5 is: in, This indicates the pumping speed of the cold plate surface, in units of... ; This represents the theoretical volumetric pumping speed per unit area of ​​the condensation surface, in units of... ; This indicates the condensation coefficient of the cold plate surface; This indicates the condensation area of ​​the cold plate, in units of... .

[0050] S4. Under the condition of maintaining a high pumping speed vacuum, the neutral particle source 3 is led out into the vacuum container 1 through the transition section 2 which coincides with the axis of the vacuum container 1 to form a high-speed neutral particle flow field.

[0051] Under high-pumping-speed vacuum maintenance conditions, the neutral particle source 3 is led out into the vacuum container 1 through the transition section 2, which coincides with the axis of the vacuum container 1, to form a high-speed neutral particle flow field. In this embodiment, the extraction conditions of the high-speed neutral particle flow field are set according to the low-Earth orbit space environment, so that the pressure maintained inside the vacuum container 1 matches the gas load introduced by the high-speed neutral particle flow field, thereby making the gas environment inside the vacuum container 1 close to the low-Earth orbit space environment state.

[0052] Specifically, the embodiments of this application simulate typical operating conditions in a low-Earth orbit space environment: the particle number density is 5× / The satellite's orbital speed is 7.8 km / s, the orbital ambient temperature is 850 K, and the corresponding ambient pressure is approximately 6 × 10⁻⁶ km / s. Pa. In the embodiments of this application, neon is used as the simulated gas because it is an inert gas, chemically inert, and its molecular weight is close to that of nitrogen and atomic oxygen.

[0053] S5. During the continuous extraction of the high-speed neutral particle flow field, the introduced gas molecules are continuously pumped in through the container cryogenic pump 4, the transition section 2 cryogenic pump and the cryogenic cold plate 5, so that the pressure inside the vacuum container 1 is maintained below the fourth pressure value, thereby achieving high vacuum maintenance under the low orbit space environment simulation conditions.

[0054] During the continuous extraction of the high-speed neutral particle flow field, the introduced gas molecules are continuously evacuated by the container cryogenic pump 4, the transition section cryogenic pump 2, and the cryogenic cold plate 5, so that the pressure inside the vacuum container 1 is maintained below the fourth pressure value. In this embodiment, the fourth pressure value is 1× Pa enables the maintenance of high vacuum under simulated low-Earth orbit space environment conditions.

[0055] During this dynamic process, the steady-state pressure of the container is calculated using the following expression: Where P represents the container pressure under steady state, and the unit is Pa; Indicates the system leakage rate, in units of ; This indicates the system's venting volume, in units of... ; Indicates the effective pumping speed of the system, in units of .

[0056] By establishing a high vacuum background environment through the cryogenic pump 4 in the container and the cryogenic pump in the transition section 2, and by providing an extremely high pumping speed through the cryogenic cold plate 5 cooled by the gas-helium refrigeration system, the embodiments of this application can effectively counteract the atmospheric load generated by the continuous introduction of a high-speed neutral particle flow field, thus maintaining the pressure inside the container stably at 1× under dynamic conditions. Below Pa, it meets the vacuum requirements for low-Earth orbit space environment simulation tests.

[0057] This application provides a method for maintaining high vacuum under high-speed neutral particle flow field extraction. The method achieves dynamic high vacuum maintenance under continuous high-speed neutral particle flow field extraction conditions through a staged evacuation process. First, a coarse evacuation process is used to obtain an initial low-vacuum environment. Then, a high-vacuum background environment is established using a cryogenic pump 4 in the container and a cryogenic pump in the transition section 2. Next, a high-pumping-rate vacuum maintenance condition is formed by cooling the cryogenic cold plate 5 using a gas-helium refrigeration system. Finally, during the continuous extraction of the particle flow, a three-stage evacuation assembly continuously evacuates the introduced gas. This solves the technical problem in the prior art where a large amount of gas is actively released from the particle source, causing a sharp drop in vacuum level. It achieves stable pressure maintenance within the vacuum container 1 below the required pressure value under dynamic operating conditions.

[0058] This application also provides a device for maintaining high vacuum under high-speed neutral particle flow field extraction. The device in this application is used for low-Earth orbit space environment simulation experiments, specifically to simulate the directional particle wind environment encountered by low-Earth orbit satellites during on-orbit operation, in order to complete the aerodynamic drag test of the satellite configuration. Figure 2 and Figure 3 As shown, the apparatus includes: a vacuum container 1, a transition section 2, a container cryogenic pump 4, a transition section 2 cryogenic pump, a gaseous-helium refrigeration system, a cryogenic cold plate 5, and a roughing pump unit. The vacuum container 1 is used to contain the test specimen, with a volume of not less than 80 cubic meters. The transition section 2 connects the vacuum container 1 and the neutral particle source 3, with the axis of the transition section 2 coinciding with the axis of the vacuum container 1. The roughing pump unit uses a dry pump unit, including a screw pump and a Roots pump, for roughing the vacuum container 1.

[0059] The cryogenic pump 4 is located at the center of the wall of the vacuum container 1. It is a large-diameter cryogenic pump used to evacuate the gas within the main space of the vacuum container 1. The cryogenic pump 4 obtains its pumping capacity through a GM refrigerator, and its main components include a helium compressor and a two-stage cold head.

[0060] The cryogenic pump in transition section 2 is arranged circumferentially along transition section 2, and the axis of transition section 2 coincides with the axis of vacuum container 1. It is used to evacuate the gas in the path introduced by the high-speed neutral particle flow field. The cryogenic pump in transition section 2 is also a large-diameter cryogenic pump, and its pumping capacity is obtained through a GM refrigerator.

[0061] During the rough evacuation, the dry pump unit is started to perform a rough evacuation of vacuum container 1, reducing the pressure inside vacuum container 1 to below 10 Pa. Subsequently, the container cryogenic pump 4 and the transition section cryogenic pump 2 are started to reduce the pressure inside vacuum container 1 to 1 × 10 Pa. A high vacuum background environment is established below Pa.

[0062] The gaseous-helium refrigeration system is used to refrigerate the cryogenic cold plate 5, and includes a helium compression unit and a cooling unit. Specifically, the gaseous-helium refrigeration system consists of a helium compressor, an oil removal and gas management system, a cold box 7, a helium tank 9, and connecting pipelines.

[0063] Helium tank 9 is used to store high-purity helium, which serves as the working fluid source for the refrigeration system. The helium compressor, as the power source of the system, draws helium from helium tank 9 and compresses it. The high-purity helium stored in helium tank 9, together with compressor oil, is compressed into a high-pressure helium-oil mixture within the helium compressor. This mixture is then transported through pipelines to the oil removal and gas management system.

[0064] The oil removal and gas management system is used to separate oil and helium from the mixture of high-pressure helium and oil, ensuring that the oil content of the helium entering the cold box 7 is within a specified range. In this embodiment, the non-helium component is less than 10 PPM. The separated oil returns to the helium compressor through the oil return pipeline, and the separated pure high-pressure helium enters the cold box 7.

[0065] The cold chamber 7 is equipped with a helium regenerative heat exchanger, a cryogenic adsorber, a turbine expander 8, cryogenic valves, and sensors. High-pressure helium gas is first pre-cooled by the helium regenerative heat exchanger inside the cold chamber 7, and then enters the turbine expander 8 for expansion and cooling. The turbine expander 8 lowers the temperature of the helium gas through expansion, transforming it into cryogenic helium. The helium gas, after expansion and cooling by the turbine expander 8, has a temperature below 10K and is used as a cooling medium to be transported through pipelines to the cryogenic cold plate 5 inside the vacuum container 1, providing cryogenic cooling for the cryogenic cold plate 5.

[0066] During the cooling process, a cooling water system is used to cool the helium compressor, ensuring that it operates within its normal operating temperature range. The cooling water system is connected to the helium compressor and circulates to remove the heat generated during compression.

[0067] This application embodiment also includes a heat sink and a liquid nitrogen system for establishing a cold background environment. The heat sink is located inside the vacuum container 1 and connected to the liquid nitrogen system. The liquid nitrogen system operates in a single-phase closed-loop liquid nitrogen circulation mode. After startup, it cools the heat sink, reducing its average temperature to below 100K, thereby establishing a cold background environment and reducing the impact of thermal radiation on the temperature field inside the vacuum container 1.

[0068] The cryogenic cold plate 5 is installed inside the vacuum container 1, such as... Figure 4 As shown, it consists of a first cryogenic cold plate 501 and a second cryogenic cold plate 502. The two cryogenic cold plates 501 are arranged opposite each other in the direction of propagation of the high-speed neutral particle flow field inside the vacuum container 1, forming a particle flow channel between the two cryogenic cold plates 502. The distance between the two cryogenic cold plates 502 is not less than 5 cm.

[0069] The outer surface area of ​​the cryogenic cold plate 5 is matched with the effective cooling power of the gas-helium refrigeration system at 10K, so that the heat load of the cryogenic cold plate 5 is adapted to the cooling capacity of the gas-helium refrigeration system, and the total heat load of the cold plate is less than the effective cooling power of the system.

[0070] The cryogenic cold plate 5 uses stainless steel tubes as helium flow channels, with the stainless steel tubes located on the inner side. Copper fins are welded to the outer surface of the stainless steel tubes, with the copper fins located on the outer side. The copper fins are arranged in a staggered and discontinuous manner, and the copper fins welded to adjacent stainless steel tubes must not be continuous, in order to form an optically sealed structure. The cryogenic helium gas output from the gaseous helium refrigeration system cools the cryogenic cold plate 5 through the stainless steel tube channels.

[0071] The outer surface of the low-temperature cold plate 5 is polished to form a low-emissivity surface, and a metal coating is formed on the polished outer surface. In this embodiment, it is a vacuum-deposited aluminum film or an electroplated nickel film to reduce radiative heat transfer. The inner surface of the low-temperature cold plate 5 is sprayed with black paint and activated carbon is attached to it to form a gas molecule adsorption layer on the inner surface of the low-temperature cold plate 5.

[0072] The shape of the cryogenic cold plate 5 can be modified to suit the test environment; there are no fixed shape requirements. The projected area of ​​the outer surface of the cryogenic cold plate 5 shall not exceed half the cross-sectional area of ​​the vacuum container 1.

[0073] The working process of a device for maintaining high vacuum under high-speed neutral particle flow field extraction according to an embodiment of this application is as follows: First, start the dry pump unit to perform a rough pumping process on vacuum container 1, so that the pressure inside vacuum container 1 is reduced to below 10Pa, and an initial low vacuum environment is obtained.

[0074] Under initial low vacuum conditions, the cryogenic pump 4 located at the center of the wall of vacuum container 1 and the cryogenic pump 2 located circumferentially along the transition section 2 are activated to remove residual gas in vacuum container 1 and gas entering through the transition section 2, reducing the pressure inside vacuum container 1 to 1× A high vacuum background environment is established below Pa.

[0075] Under a high vacuum background, the liquid nitrogen system is activated to cool the heat sink, lowering its average temperature to below 100K and establishing a cold background environment. Simultaneously, the gaseous helium refrigeration system is activated. Helium tank 9 provides high-purity helium, which is compressed by the helium compressor to form a high-pressure mixture of helium and oil. After oil removal and purification by the gas management system, the mixture enters the cold chamber 7, where it is expanded and cooled by the turbine expander 8 to become cryogenic helium. This cryogenic helium is then output to the stainless steel pipe channel of the cryogenic cold plate 5 to cool it. Refrigeration continues until the temperature of the cryogenic cold plate 5 drops below 10K, reducing the pressure inside the vacuum container 1 to below 1× Pa creates a high-speed vacuum maintenance condition inside vacuum container 1.

[0076] Under high-pumping-speed vacuum maintenance conditions, the neutral particle source 3 is led out into the vacuum container 1 through the transition section 2 which coincides with the axis of the vacuum container 1 to form a high-speed neutral particle flow field, which is used to simulate the directional particle wind encountered by the low-orbit satellite during its operation.

[0077] During the continuous extraction of the high-speed neutral particle flow field, the introduced gas molecules are continuously evacuated by the container cryogenic pump 4, the transition section cryogenic pump 2, and the cryogenic cold plate 5, maintaining the pressure inside the vacuum container 1 at 1× Below Pa, high vacuum maintenance can be achieved under simulated low-Earth orbit space environment conditions.

[0078] This embodiment establishes a high-vacuum background environment through a cryogenic pump 4 in the container and a cryogenic pump in the transition section 2. A cryogenic cold plate 5, cooled by a gas-helium refrigeration system, provides an extremely high pumping speed, enabling the system to maintain a high vacuum state even under dynamic conditions of continuous extraction of a high-speed neutral particle flow field. The gas-helium refrigeration system employs mechanical cooling, obtaining deep-temperature helium gas through a turbine expander 8 to provide stable and reliable cooling for the cold plate. The cryogenic cold plate 5 utilizes a stainless steel tube and copper fin structure with different surface treatments on its inner and outer surfaces, effectively improving pumping efficiency. This embodiment provides a device for maintaining high vacuum under high-speed neutral particle flow field extraction, meeting the stringent vacuum requirements of low-Earth orbit space environment simulation experiments and solving the problem of maintaining high vacuum under high-speed neutral particle flow field extraction conditions.

[0079] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0080] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for maintaining high vacuum under high-speed neutral particle flow field extraction, characterized in that, include: The vacuum container is subjected to a rough evacuation process to reduce the pressure inside the vacuum container to below the first pressure value, thereby obtaining an initial low vacuum environment. In the initial low vacuum environment, the container cryogenic pump installed on the wall of the vacuum container and the transition section cryogenic pump installed on the wall of the transition section are started to remove the residual gas in the vacuum container and the gas entering through the transition section, so that the pressure in the vacuum container is reduced to below the second pressure value, and a high vacuum background environment is established. In the high vacuum background environment, the gas helium refrigeration system is started to cool the low-temperature cold plate set in the vacuum container, so that the low-temperature cold plate reaches the target low temperature state, and the gas in the vacuum container is condensed and evacuated through the low-temperature cold plate until the temperature of the low-temperature cold plate is lower than the first temperature threshold, so that the pressure in the vacuum container is lower than the third pressure value, and a high pumping speed vacuum maintenance condition is formed in the vacuum container. Under the high-pumping-speed vacuum maintenance condition, the neutral particle source is led out into the vacuum container through a transition section that coincides with the axis of the vacuum container. During the continuous extraction of the high-speed neutral particle flow field, the introduced gas molecules are continuously evacuated by the container cryogenic pump, the transition section cryogenic pump, and the cryogenic cold plate, so that the pressure inside the vacuum container is maintained below the fourth pressure value, thereby achieving high vacuum maintenance under the low-orbit space environment simulation conditions.

2. The method according to claim 1, characterized in that, The cryogenic pump is positioned at the center of the vacuum container wall to evacuate the gas within the main space of the vacuum container.

3. The method according to claim 1, characterized in that, The cryogenic pump in the transition section is arranged circumferentially along the transition section, and the axis of the transition section is aligned with the axis of the vacuum container to evacuate the gas in the path of the high-speed neutral particle flow field.

4. The method according to claim 1, characterized in that, The cryogenic cold plate is cooled by the gas helium refrigeration system described above. The cryogenic cold plate is cooled by outputting cryogenic helium gas, so that the cryogenic cold plate maintains the target low temperature state.

5. The method according to claim 4, characterized in that, The outer surface area of ​​the cryogenic cold plate is matched to the cooling capacity of the gas-helium refrigeration system so that the heat load of the cryogenic cold plate is adapted to the cooling capacity of the gas-helium refrigeration system.

6. The method according to claim 1, characterized in that, The cryogenic cold plate is configured to include two cold plates, which are arranged opposite each other in the vacuum container along the propagation direction of the high-speed neutral particle flow field, and a particle flow channel is formed between the two cold plates.

7. The method according to claim 6, characterized in that, A stainless steel tube is used as the helium flow channel for the cryogenic cold plate. Copper fins are welded to the outer surface of the stainless steel tube and arranged in a staggered and discontinuous manner to form an optically sealed structure.

8. The method according to claim 6, characterized in that, The outer surface of the low-temperature cold plate is polished to form a low-emissivity surface, and a metal coating is formed on the polished outer surface to reduce radiative heat transfer.

9. The method according to claim 6, characterized in that, An adsorption material is provided on the inner surface of the low-temperature cold plate to form a gas molecule adsorption layer on the inner surface of the low-temperature cold plate.

10. The method according to claim 1, characterized in that, The extraction conditions of the high-speed neutral particle flow field are set according to the low-Earth orbit space environment, so that the pressure maintained in the vacuum container matches the gas load introduced by the high-speed neutral particle flow field, so that the gas environment in the vacuum container is close to the state of the low-Earth orbit space environment.

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