A method for establishing a variable boundary simulation model of a grid assembly of an ion thruster

Abstract

This application relates to the field of space electric propulsion technology, specifically to a method for establishing a variable boundary simulation model of an ion thruster gate assembly. The method includes: Step 1: dividing the gate into regions; Step 2: selecting the object to be studied within each region; Step 3: calculating the upstream ion density of each object; Step 4: calculating the corresponding Debye length and determining the maximum values ​​of the calculation region in the lateral and radial directions; Step 5: handling collisions between atoms; Step 6: establishing a simulation calculation model; Step 7: calculating the gate morphology; Step 8: correcting the gate simulation calculation model; and Step 9: completing the establishment of the variable boundary simulation model of the ion thruster gate assembly. This application utilizes the sputtering etching morphology obtained from simulation calculations to update and improve the simulation calculation model in real time, enabling more accurate prediction of the thruster's operational lifespan, significantly shortening the product development cycle and reducing development costs.

Description

Technical Field

[0001] This application relates to the field of space electric propulsion technology, and more specifically, to a method for establishing a variable boundary simulation model of an ion thruster gate assembly. Background Technology

[0002] The propulsion system is one of the essential core systems of any spacecraft, and the demands on propulsion systems have undergone significant changes in recent military aerospace technology development. High-capacity, long-life military communication, data relay, navigation, and positioning satellites require high-specific-impulse on-orbit propulsion systems to significantly increase the satellite's payload ratio, extend its operational life, and reduce launch costs. Ion and Hall-type electric propulsion systems have become the preferred choice to meet these requirements.

[0003] Compared to Hall thrusters, ion thrusters offer significant advantages such as ultra-high specific impulse, long lifespan, and precisely adjustable thrust, making them the optimal choice for future on-orbit missions. However, the relatively low thrust of ion thrusters necessitates efficient and reliable operation for tens of thousands of hours. Extensive experimental results have shown that the gate assembly is a weak point in ion thrusters. High-energy ion bombardment and sputtering of the gate assembly during thruster operation can lead to structural failure, and in severe cases, thruster failure.

[0004] While experimental testing can verify the long lifespan of a thruster, it is time-consuming and labor-intensive. Numerical simulation, on the other hand, can estimate the thruster's operational lifespan by simulating the movement and bombardment sputtering processes of high-energy ions, or determine the correctness of the design values ​​for the geometric or electrical parameters of the gate assembly. The bombardment sputtering of high-energy ions on the gate hole wall or surface is a dynamic process, and current numerical simulation models are all static, making it impossible to accurately correct the simulation model in real time, thus hindering accurate prediction of the thruster's operational lifespan. Summary of the Invention

[0005] This application provides a method for establishing a variable boundary simulation model of an ion thruster gate assembly. By using numerical simulation technology and combining experimental measurement results, the working life of the thruster can be predicted more accurately.

[0006] To achieve the above objectives, this application provides a method for establishing a variable boundary simulation model of an ion thruster gate assembly, comprising the following steps: Step 1: Divide the gate into regions based on the beam ion density distribution obtained from experimental measurements; Step 2: Select the objects to be studied within each region according to the research needs; Step 3: Calculate the upstream ion density of each research object using the relationship between the beam ion density and the upstream ion density of the gate; Step 4: Calculate the corresponding Debye length based on the upstream ion density of the gate, and determine the maximum values ​​of the calculation region in the lateral and radial directions; Step 5: Process collisions between atoms to obtain the neutral gas density distribution at each grid node within the calculation region; Step 6: Establish the simulation... The computational model uses the particle cloud method to simulate the acceleration, focusing, and extraction process of the beam ions, handles the collisions between the beam ions and neutral gas, and simulates the generation of high-energy ions and the sputtering etching process on the gate hole walls and surfaces during the collisions. Step 7: The simulation system automatically calculates the gate morphology after every 1000 time steps based on the sputtering etching rate of a single ion. Step 8: The simulation calculation model is corrected by comparing the gate corrosion results calculated in the simulation with those measured in the experiment, based on the gate morphology measured in the experiment. Step 9: The simulation calculation model is corrected every 1000 time steps until the change in electric field distribution on the grid nodes in the calculation area is ≤0.05%, at which point the calculation ends, and the establishment of the variable boundary simulation model of the ion thruster gate assembly is completed.

[0007] Furthermore, in step 1, the gate is divided into three regions: the gate center region, the gate edge region, and the other regions of the gate.

[0008] Furthermore, in step 2, selecting the objects to be studied within each region includes the following steps:

[0009] Step 2.1: Select one-quarter of each of the two gate apertures with the highest beam ion density in the gate center region as the research object of the gate center region; Step 2.2: Select one-quarter of each of the two gate apertures with the lowest beam ion density in the gate edge region as the research object of the gate edge region; Step 2.3: Select one-quarter of each of the two gate apertures corresponding to the average beam ion density in other regions of the gate as the research object of other regions of the gate.

[0010] Furthermore, the research focused on the gate assembly of an electrostatic ion thruster.

[0011] Furthermore, in step 5, the direct Monte Carlo collision method is used to process collisions between atoms to obtain the neutral gas density distribution on each grid node within the computational region.

[0012] Furthermore, in step 6, the collision types between the beam ions and the neutral gas include elastic collisions and charge exchange collisions.

[0013] The present invention provides a method for establishing a variable boundary simulation model of an ion thruster gate assembly, which has the following beneficial effects:

[0014] This application utilizes sputtering etching morphology obtained through simulation calculations to update and improve the simulation calculation model in real time. This enables more accurate prediction of the thruster's service life and rapid judgment of the correctness of the thruster's design parameters. It proposes a new approach to thruster design optimization, which can significantly shorten the product development cycle and reduce development costs. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings:

[0016] Figure 1 This is a flowchart of a method for establishing a variable boundary simulation model of an ion thruster gate assembly according to an embodiment of this application;

[0017] Figure 2 This is a schematic diagram of the beam ion density measurement value according to the method for establishing a variable boundary simulation model of the ion thruster gate assembly provided in the embodiments of this application.

[0018] Figure 3 This is a gate simulation region diagram based on the method for establishing a variable boundary simulation model of an ion thruster gate assembly provided in the embodiments of this application;

[0019] Figure 4 The image shows the accelerated gate corrosion morphology obtained experimentally based on the method for establishing a variable boundary simulation model of the ion thruster gate assembly according to the embodiments of this application.

[0020] Figure 5 This is a schematic diagram showing the correction of the simulation calculation region between the gate center region and other regions in the method for establishing a variable boundary simulation model of an ion thruster gate assembly according to the embodiments of this application.

[0021] Figure 6 This is a schematic diagram of the simulation calculation region correction for the gate edge region according to the method for establishing a variable boundary simulation model of an ion thruster gate assembly provided in the embodiments of this application. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0023] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0024] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0025] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0026] In addition, the term "multiple" should mean two or more.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] Specifically, the gate assembly is one of the key components of the ion thruster. While its structure is simple—a dual-gate ion optical system consists of two gate assemblies, and a triple-gate ion optical system consists of three—the actual process of ions moving between the gate assemblies is extremely complex. This is because the gate is composed of two or three convex lenses, whose function is not only to extract and accelerate ionized ions within the discharge chamber, but also to focus the extracted ions to ensure they are ejected with the smallest possible beam divergence angle, minimizing losses. Due to the uneven plasma density distribution upstream of the gate, the maximum beam current extracted from the central and edge regions differs significantly. Under the influence of space charge, abnormal focusing can cause unnecessary beam ions to be intercepted by the gate. When ions with a certain energy directly impact the gate surface, they bombard the surface. Prolonged bombardment can cause sputtering of the gate material, altering the gate structure. When the grooves and pits formed between two or three gate holes break, the gate fails. Traditionally, the long-life verification of ion thrusters is carried out through experimental testing, but this method requires a lot of manpower, material resources, and financial resources. The emergence of numerical simulation has successfully solved this problem. The simulation calculation method is used to simulate the generation process, focusing process, and bombardment sputtering etching process of high-energy ions. Based on the simulation calculation results, the life of the thruster is predicted. Since the sputtering etching process of ions on the gate surface or hole wall is related to the thruster's operating time, but the sputtering morphology is related to the sputtering rate, it is necessary to establish an accurate ion thruster life prediction model in order to accurately predict the thruster performance.

[0029] This application establishes a variable boundary simulation model for the gate assembly of an ion thruster. This model primarily targets the gate assembly of an electrostatic ion thruster. Utilizing numerical simulation techniques and combining experimental measurement results, the model is continuously refined based on the sputtering etching rate of high-energy ions on the gate surface or via walls during thruster operation. This achieves the goal of accurately predicting the thruster's operational lifespan. Specifically, the model includes the following steps:

[0030] Step 1: Based on the beam ion density distribution obtained from the experiment, the gate is divided into regions, namely the gate center region, the gate edge region, and other regions of the gate;

[0031] Step 2: Select the subjects to be studied within each region according to the needs of the research:

[0032] The study focuses on the two gate holes with the highest beam ion density in the gate center region. Since the beam ion density in the gate center region is almost constant in the radial direction, the simulation object for this region is the gate hole at the very center of the gate assembly. Considering the interaction between holes, the study focuses on the two adjacent gate holes with the highest beam ion density in the gate center region.

[0033] The study focuses on the two gate apertures with the lowest beam ion density at the gate edge region. Since the beam ion density is lower in the gate edge region compared to other regions, overfocusing is more likely to occur during beam extraction. Therefore, to ensure that all gates can extract the beam effectively, it is necessary to ensure that the beam in the gate aperture with the lowest beam ion density can also be properly focused. Thus, the gate aperture with the lowest beam ion density is selected as the simulation object for this region. Similarly, considering the interaction between gate apertures, the adjacent gate aperture with the lowest beam ion density is selected as the simulation object for the gate edge region. Finally, considering the computation time and accuracy of the simulation results, each of these apertures is selected as the numerical simulation object.

[0034] Two quarters of the beam ion density in other regions of the gate are selected as the research objects of the other regions of the gate. The beam ion density in other regions of the gate gradually decreases along the radial direction of the thruster. Therefore, the gate hole corresponding to the average beam ion density in this region is selected as the research object of the simulation calculation. Similarly, considering the interaction between the holes, as well as the calculation time and calculation accuracy, the gate holes adjacent to the research object are selected. One quarter of the two gate holes are selected as the numerical simulation research objects of this region.

[0035] Step 3: Calculate the upstream ion density of the grating for each research object by using the relationship between the beam ion density and the upstream ion density of the grating.

[0036] Step 4: Based on the upstream ion density of the screen, calculate the corresponding Debye length and determine the maximum values ​​in the horizontal and radial directions of the calculation region. The relationship between the upstream ion density and the Debye length is shown in the following formula:

[0037]

[0038] Where n i ε0 is the upstream ion density of the grating, ε0 is the vacuum permittivity, k is the Boltzmann constant, and T is the T0. e Here, e represents the electron temperature, and e represents the electron charge.

[0039] Step 5: Use the direct Monte Carlo collision method to handle collisions between atoms and obtain the neutral gas density distribution on each grid node in the computational domain;

[0040] Step 6: Establish a simulation calculation model, use the particle cloud method to simulate the acceleration, focusing and extraction process of the beam ions, use the Monte Carlo method to handle the elastic collision and charge exchange collision process between the beam ions and the neutral gas, and simulate the generation of high-energy ions and the sputtering etching process on the gate hole wall and surface during the charge exchange collision process.

[0041] Step 7: The simulation system automatically calculates the gate morphology after 1000 working time steps based on the sputtering etching rate of a single ion. The expression for the sputtering etching depth is as follows:

[0042]

[0043] Where J is the current intercepted at the gate surface; Y is the sputtering yield; M Mo ρ Mo These represent the atomic mass and density of molybdenum, the gate material, respectively.

[0044] Step 8: Compare the gate corrosion results obtained from simulation calculations and experimental measurements, and revise the gate simulation calculation model based on the gate morphology obtained from experimental measurements;

[0045] Step 9: Correct the simulation model every 1000 time steps until the change in electric field distribution on the grid nodes in the calculation area is ≤0.05%. The calculation ends, and the simulation model of the variable boundary of the ion thruster gate assembly is established.

[0046] More specifically, taking a 30cm ion thruster as an example, its grid assembly uses a variable aperture grid, and the specific area division is obtained based on the experimentally measured beam ion density. For example... Figure 2 The figure shows the beam ion density at different radial positions measured in the experiment, with a beam current of 2.1 A. Based on the relationship between beam ion density and beam current:

[0047]

[0048] Among them: I b For beam current, A; e is electron charge, C; k is Boltzmann constant, J / K; T e Electron temperature (K); M is ion mass (kg); A s m is the gate area. -2 ;T s Ion transparency, 0.7.

[0049] The calculated average beam current density is 1.38 × 10⁻⁶. 17 m -3 The beam flatness of the 30cm ion thruster was 0.8, and the maximum and minimum beam ion densities were 1.73 × 10⁻⁶. 17 m -3 1.1×10 17 m -3 Therefore, 1.73 × 10 17 m -3 1.38×10 17 m -3and 1.1×10 17 m -3 These represent the average beam ion densities in the central region, other regions, and edge regions of the 30cm ion thruster grid. The beam ion density in the central region of the grid remains essentially constant at 1.73 × 10⁻⁶. 17 m -3 The beam ion density corresponds to the central aperture of the gate; the beam ion density of the outermost gate aperture in the gate edge region is about 1 to 2 orders of magnitude smaller than the average beam density. Considering that the beam is not over-focused, 1.1 × 10⁻⁶ is chosen. 15 m -3 The simulated object is the beam ion density corresponding to the gate edge region; the simulated object for other regions of the gate is the gate aperture corresponding to the average beam ion density, i.e., a beam ion density of 1.38 × 10⁻⁶. 17 m -3 The simulation regions of each quarter of the two adjacent gate vias are shown in the figure. Figure 3 As shown, the simulation calculation areas for the gate center region, edge region, and other regions are all as follows. Figure 3 As shown.

[0050] Then calculate the Debye length using the following formula:

[0051]

[0052] The calculated plasma density is 1.73 × 10⁻⁶. 17 m -3 1.38×10 17 m -3 and 1.1×10 15 m -3 The Debye lengths of the three regions of the gate are 5.0 × 10⁻⁶. -5 m, 4.5×10 -5 m and 5.0×10 -4 m.

[0053] The maximum horizontal value of the computational domain is: 10 × λ D +t s +2×l g +t a +100×λ D , where 10×λ D To calculate the distance from the left boundary of the region to the upstream surface of the screen, t s +2×l g +t a The region from the upstream surface of the screen grid to the downstream surface of the deceleration grid, 100×λ D t is the distance from the downstream surface of the deceleration gate to the right boundary of the computational region. s t a These are the thicknesses of the screen grid and the acceleration grid, respectively;g This represents the grid spacing.

[0054] The maximum radial value of the computational region is: r s +l cc / 2; where r s Let l be the radius of the screen grid. cc This refers to the spacing between the screen apertures.

[0055] Then, a simulation model was established, using the particle cloud method to simulate the acceleration, focusing, and extraction process of the beam ions. The Monte Carlo method was used to handle the elastic collisions and charge exchange collisions between the beam ions and the neutral gas, simulating the generation of high-energy ions during charge exchange collisions and the sputtering etching process on the gate hole walls and surfaces. The morphology of the accelerated gate corrosion was shown in the figure. Figure 4 As shown, from left to right, the corrosion morphology of the ion thruster after 0 hours, 13042 hours, and 29240 hours of operation is shown.

[0056] Finally, the simulation calculation model was corrected. According to the experimental measurement results, the beam ions in the central region of the gate and other regions were focused normally. The accelerating gate was mainly bombarded by charge-exchange ions, and the thickness of the accelerating gate changed. However, in the edge region, due to the over-focusing of beam ions and the simultaneous bombardment of charge-exchange ions, the aperture and thickness of the accelerating gate changed. Therefore, the simulation calculation model was corrected in two ways.

[0057] (1) Gate center region and other regions

[0058] Based on the measured changes in the acceleration gate thickness of the simulated object in two regions, the simulation model was revised, specifically as follows: Figure 5 As shown, where dt a The change in the grid thickness is accelerated after the thruster has been operating for N hours.

[0059] (2) Gate edge region

[0060] Based on the experimentally measured changes in the aperture and thickness of the gate's outermost edge aperture, the simulation model was revised, specifically as follows: Figure 6 As shown.

[0061] Where dt a dr a The changes in the thickness and radius of the acceleration grid after the thruster has been operating for N hours are described. Since the radius of the acceleration grid aperture varies at different radial positions, the specific aperture size is determined based on experimental measurement results.

[0062] The simulation model of each region of the gate is corrected every 1000 time steps according to the above method until the change in electric field distribution on the grid nodes in the calculation area is ≤0.05%, and the calculation ends, thus completing the establishment of the variable boundary simulation model of the ion thruster gate assembly.

[0063] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for establishing a variable boundary simulation model of an ion thruster gate assembly, characterized in that, Includes the following steps: Step 1: Divide the gate region according to the beam ion density distribution obtained from the experiment; Step 2: Select the subjects to be studied within each region according to the needs of the research; Step 3: Calculate the upstream ion density of the grating for each research object by using the relationship between the beam ion density and the upstream ion density of the grating. Step 4: Calculate the corresponding Debye length based on the upstream ion density of the screen, and determine the maximum value of the calculation area in the horizontal and radial directions; Step 5: Process the collisions between atoms to obtain the neutral gas density distribution on each grid node in the computational domain; Step 6: Establish a simulation calculation model, use the particle cloud method to simulate the acceleration, focusing and extraction process of the beam ions, handle the collision between the beam ions and the neutral gas, simulate the generation of high-energy ions during the collision process and the sputtering etching process on the gate hole wall and surface. Step 7: The simulation system automatically calculates the gate morphology after 1000 working time steps based on the sputtering etching rate of a single ion. Step 8: Compare the gate corrosion results obtained from simulation calculations and experimental measurements, and revise the gate simulation calculation model based on the gate morphology obtained from experimental measurements; Step 9: Correct the simulation model every 1000 time steps until the change in electric field distribution on the grid nodes in the calculation area is ≤0.05%. The calculation ends, and the establishment of the variable boundary simulation model of the ion thruster gate assembly is completed.

2. The method for establishing a variable boundary simulation model of an ion thruster gate assembly according to claim 1, characterized in that, In step 1, the gate is divided into three regions: the gate center region, the gate edge region, and the other regions of the gate.

3. The method for establishing a variable boundary simulation model of an ion thruster gate assembly according to claim 2, characterized in that, Step 2 involves selecting the objects to be studied within each region, including the following steps: Step 2.1: Select one-quarter of each of the two gate holes with the highest beam ion density in the gate center region as the research object of the gate center region; Step 2.2: Select one-quarter of each of the two gate apertures with the lowest beam ion density in the gate edge region as the research object of the gate edge region; Step 2.3: Select one-quarter of each of the two gate holes corresponding to the average beam current ion density of other regions of the gate as the research object of other regions of the gate.

4. The method for establishing a variable boundary simulation model of an ion thruster gate assembly according to claim 3, characterized in that, The research object is the gate assembly of an electrostatic ion thruster.

5. The method for establishing a variable boundary simulation model of an ion thruster gate assembly according to claim 1, characterized in that, In step 5, the direct Monte Carlo collision method is used to handle collisions between atoms and obtain the neutral gas density distribution on each grid node in the computational region.

6. The method for establishing a variable boundary simulation model of an ion thruster gate assembly according to claim 5, characterized in that, In step 6, the collision types between the beam ions and the neutral gas include elastic collisions and charge exchange collisions.

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