A method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model

Abstract

The present invention discloses a method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model. The method comprises: using SPIS simulation software, based on the PIC algorithm, and introducing macroparticles to calculate a plume distribution model diagram according to the operating state of a Hall thruster; extracting the plume density of each grid in the plume distribution model diagram, converting the color image of the plume distribution model into a grayscale image, and drawing isodensity lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths; using the Drude model to represent the relative dielectric constant based on collisions in the plume; dividing the same relative dielectric constant into layers, using a layered structure to construct an electromagnetic wave transmission model in the plume, performing an electromagnetic solution, and obtaining the characteristic parameters of electromagnetic wave transmission. The present invention efficiently and accurately obtains the characteristic parameters of electromagnetic waves in the plume propagation path, thereby improving the research and application of Hall thrusters.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave transmission characteristics in a Hall thruster plume, and in particular relates to a method for extracting characteristic parameters of an electromagnetic field in a plume propagation path based on a visualization model. Background Art

[0002] A plume, a term used in fluid mechanics, also refers to a Taoist priest. A plume has four key elements: first, a fluid with momentum, Flow 1; second, a fluid medium, Flow 2, which does not have momentum; third, the density difference between Flow 1 and Flow 2 must be small, but they must also be non-homogeneous, so that the boundary between them is indistinguishable; and fourth, Flow 1 must be unimpeded by anything outside of Flow 2—that is, Flow 1 must flow entirely within Flow 2.

[0003] Hall thrusters, also known as Hall effect thrusters, are thrusters in which propellant is accelerated by an electric field. Hall thrusters confine electrons in a magnetic field and use the electrons to ionize the propellant, accelerating the ions to generate thrust and neutralizing the ions in the plume.

[0004] Hall thruster is an advanced electric propulsion device, which is widely used in the field of satellite position keeping and attitude control. 3 s order of magnitude) and high efficiency (up to 60% or more) make it one of the preferred propulsion devices for future spacecraft.

[0005] Currently, there are two main methods for studying the transmission characteristics of electromagnetic waves in Hall thruster plumes: experimental measurement and numerical simulation. The experimental measurement method requires simulating the Hall thruster plume environment on the ground and transmitting and receiving electromagnetic waves to measure the characteristics of the electromagnetic waves passing through the plume. However, the experimental measurement method is not only expensive and time-consuming, but also difficult to accurately simulate the real environment in some cases. In contrast, the numerical simulation method uses a combination of mathematical methods and physical models to calculate the amplitude and phase changes of electromagnetic waves in the plume, which has the advantages of low cost and fast calculation speed.

[0006] In numerical simulation, researchers at home and abroad commonly use methods such as the finite difference method (FDTD), the finite element method (FEM), and geometric optics (reference: He Wusheng, N. de Mejanes, and Yu Bo). While these methods can simulate the propagation characteristics of electromagnetic waves in plumes to a certain extent, they still suffer from high computational complexity and slow performance. For example, performing dynamic particle calculations on all particles in the plume individually is computationally intensive and time-consuming. To overcome these shortcomings, simplifying the plume model to achieve more accurate simulation results has become an inevitable trend.

[0007] The existing technology still lacks an efficient and accurate simulation method when dealing with the electromagnetic wave transmission characteristics in plumes. Summary of the Invention

[0008] The purpose of the present invention is to overcome the defects of the prior art and propose a method for extracting characteristic parameters of the electromagnetic field in the plume propagation path based on a visualization model.

[0009] To achieve the above objectives, the present invention proposes a method for extracting characteristic parameters of the electromagnetic field in the plume propagation path based on a visualization model, comprising:

[0010] Step 1) According to the working state of the Hall thruster, SPIS simulation software is used, based on the PIC algorithm, macro particles are introduced, and a plume distribution model diagram is obtained through calculation;

[0011] Step 2) extracting the plume density of each grid in the plume distribution model image, converting the color image of the plume distribution model into a grayscale image, and drawing isodensity lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths;

[0012] Step 3) Based on the collision in the plume, the Drude model is used to represent the relative dielectric constant;

[0013] Step 4) Divide the layers with the same relative dielectric constant into a layer, use a layered structure to build a transmission model of electromagnetic waves in the plume, perform electromagnetic solutions, and obtain characteristic parameters of electromagnetic wave transmission.

[0014] Preferably, the working state of the Hall thruster in step 1) includes: divergence angle, ionization rate, thrust and mass flow.

[0015] Preferably, in step 1), based on the PIC algorithm, macro particles are introduced to establish a plume distribution model; comprising:

[0016] Macro particles are introduced, and the movement of the macro particles is used to replace the actual movement of charged particles. The volume of each macro particle falling in the grid is used as the weight assigned to the grid, and a plume distribution model is established. The weight is used to represent the density and frequency of the macro particles.

[0017] The grid of the macro particles is a cone of different sizes.

[0018] Preferably, in step 2), the color image of the plume distribution model is converted into a grayscale image, and isodensity lines are drawn on the color image by distinguishing the grayscale levels of the image, including:

[0019] The color image of the plume distribution model is converted into a 256-level grayscale image, the maximum and minimum pixel values ​​are identified, and the pixel values ​​within the maximum and minimum pixel value range are divided into several levels. The positions of the same pixel value are smoothly connected to obtain the isodensity lines.

[0020] Preferably, the relative dielectric constant ε in step 3) is r (ω) is:

[0021]

[0022] in, is the plume plasma frequency, ω is the electromagnetic wave frequency, v c is the plume collision frequency, j represents the imaginary part, n e is the plasma electron density, e is the unit charge, e=1.6×10 -19 C, ε0 is the dielectric constant of vacuum, ε0=8.85×10 -12 F / m,m e is the mass of the electron, m e =9.11×10 -31 kg.

[0023] Preferably, performing electromagnetic solution to obtain characteristic parameters of electromagnetic wave transmission includes:

[0024] The CST electromagnetic calculation tool is introduced, and the FIT algorithm is used to numerically solve the Maxwell equations. By discretizing space and time, the time-varying behavior of the electromagnetic field is calculated to obtain the characteristic parameters of electromagnetic wave transmission, including the transmission coefficient and reflection coefficient.

[0025] Preferably, performing electromagnetic solution to obtain characteristic parameters of electromagnetic wave transmission includes: introducing finite difference method, finite element method or geometric optics method to calculate the time-varying behavior of the electromagnetic field to obtain characteristic parameters of electromagnetic wave transmission, including: transmission coefficient and reflection coefficient.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] This invention introduces a visual model extraction method to effectively address the existing challenges of high computational effort, slow execution, and insufficient simulation accuracy in research on the electromagnetic wave transmission characteristics of Hall thruster plumes. By processing plume distribution images generated by SPIS software simulation, the present invention reduces computational costs while improving computational speed and ensuring the accuracy of simulation results. This method efficiently and accurately captures the characteristic parameters of electromagnetic waves along the plume propagation path, thereby enhancing the effectiveness of Hall thruster-related research and applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1is the plume distribution model obtained by SPIS simulation;

[0029] Figure 2 This is a schematic diagram of the SPIS macroparticle grid;

[0030] Figure 3 It is a schematic diagram of the plume density of each grid extracted from SPIS simulation;

[0031] Figure 4 It is a schematic diagram of the plume isopycnal lines;

[0032] Figure 5 It is a schematic diagram of the electromagnetic wave transmission model;

[0033] Figure 6 It is a flow chart of the method for extracting characteristic parameters of the electromagnetic field in the plume propagation path based on the visualization model of the present invention. DETAILED DESCRIPTION

[0034] The present invention proposes a method for extracting characteristic parameters of the electromagnetic field in the plume propagation path based on a visualization model. By processing the plume distribution image obtained by software simulation, accurate simulation results can be obtained at a lower computing cost and faster speed, effectively making up for the shortcomings of the existing technology.

[0035] The purpose of this invention is to provide a method for extracting characteristic parameters of the electromagnetic field along the plume propagation path based on a visualization model. This method addresses the existing challenges of high computational effort, slow execution, and insufficient simulation accuracy in the study of electromagnetic wave transmission characteristics within Hall thruster plumes. By processing plume distribution images obtained through SPIS software simulation, this method reduces computational costs while improving computational speed and ensuring the accuracy of simulation results. This method allows for efficient and precise extraction of characteristic parameters of electromagnetic waves along the plume propagation path, such as the transmission coefficient S21 and the reflection coefficient S22, thereby enhancing the effectiveness of Hall thruster-related research and applications.

[0036] 1. The plume model is calculated using SPIS (Spacecraft Plasma Interaction Software) developed by the European Space Agency. By setting the divergence angle, ionization rate, thrust, mass flow and other parameters of the Hall thruster, the PIC (Particle-In-Cell) algorithm is used to introduce the concept of macro particles. Macro particles represent all the physical properties of all particles in a volume, including density and frequency. The volume of each macro particle falling on the grid is used as the weight assigned to the grid to represent the density and frequency of the macro particles. The plume distribution model is obtained by replacing the actual movement of charged particles with the movement of a part of the macro particles. Figure 1 shown.

[0037] 2. If Figure 2As shown in the figure, the grids of the macro particles are all cones of different sizes. There are many grids and there is no clear relationship between the grids, which makes it difficult to build a plume model. In addition, the plume density of each grid obtained by SPIS simulation is extracted as follows: Figure 3 As shown in the figure, there is no accurate position information given to each grid, and manual extraction of the density of each grid is a lot of work. Therefore, the SPIS simulation results cannot be directly converted into characteristic parameters of the electromagnetic field in the plume propagation path.

[0038] 3. Based on Figure 1 Visualization model, extract density information from plume, Figure 1 The color image is converted to a grayscale image, and isodensity lines are drawn on the color image by distinguishing the grayscale levels. Specifically, the color image is converted to a 256-level grayscale image. By identifying the maximum and minimum pixel values, the pixel values ​​within the range are evenly divided into six levels. Positions with the same pixel value are smoothly connected, and these system lines are used as isodensity lines. The propagation path of the electromagnetic wave in the plume varies for different antenna and Hall thruster layouts. For example, for an electromagnetic wave penetrating the plume 10 cm from the thruster outlet, the system parameter settings in its transmission path are represented by the value of the isodensity line layer traversed at that location, and the value of the corresponding isodensity line layer is taken as the average value of each level.

[0039] like Figure 4 As shown, the density parameters of the plume in different transmission paths are obtained.

[0040] 4. In plumes, the most common type of collision is elastic collision. Since the mass of Xe (xenon) atoms is much greater than that of electrons, the speed of Xe atoms is much lower than that of electrons and can be considered almost stationary. Therefore, in plumes, collisions between electrons and Xe atoms meet the conditions of the Drude model. To simplify the description of the plume model, we can use the Drude model to express its relative dielectric constant:

[0041]

[0042] in, is the plume plasma frequency, ω is the electromagnetic wave frequency, v c is the plume collision frequency. n e is the plasma electron density, e is the unit charge, and is e = 1.6×10 -19 C, ε0 is the dielectric constant of vacuum, which is ε0 = 8.85 × 10 -12 F / m,m e is the mass of the electron, m e =9.11×10 -31kg. In the above formula, except for the plasma electron density, all other values ​​are constant. Therefore, the plasma frequency is determined by its electron density. The Drude model follows the classical collision model and classical electromagnetic field theory. Compared to other models, the Drude model's mathematical expression is relatively simple, resulting in higher computational efficiency.

[0043] 5. Combination Figure 4 , the same relative dielectric constant is divided into a layer, and a layered structure is used to build a transmission model of electromagnetic waves in the plume, such as Figure 5 This electromagnetic wave transmission model is then introduced into various electromagnetic calculation tools to obtain the corresponding electromagnetic wave transmission characteristics. Here, the CST electromagnetic calculation tool is introduced, using the FIT algorithm and the numerical solution of Maxwell's equations to calculate the time-varying behavior of the electromagnetic field by discretizing space and time.

[0044] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0045] Example

[0046] like Figure 6 As shown, an embodiment of the present invention proposes a method for extracting characteristic parameters of an electromagnetic field in a plume propagation path based on a visualization model, comprising:

[0047] Step 1) According to the working state of the Hall thruster, SPIS simulation software is used, based on the PIC algorithm, macro particles are introduced, and a plume distribution model diagram is obtained through calculation;

[0048] Step 2) extracting the plume density of each grid in the plume distribution model image, converting the color image of the plume distribution model into a grayscale image, and drawing isodensity lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths;

[0049] Step 3) Based on the collision in the plume, the Drude model is used to represent the relative dielectric constant;

[0050] Step 4) Divide the layers with the same relative dielectric constant into a layer, use a layered structure to build a transmission model of electromagnetic waves in the plume, perform electromagnetic solutions, and obtain characteristic parameters of electromagnetic wave transmission.

[0051] The innovation of this invention lies in the introduction of a visual model extraction method, which effectively solves the problems of large computational complexity, slow operation speed, and insufficient simulation accuracy in the existing research on the electromagnetic wave transmission characteristics of Hall thruster plumes. The specific innovations are as follows:

[0052] 1. Using SPIS to simulate plume model:

[0053] The present invention adopts SPIS software, sets the divergence angle, ionization rate, thrust, mass flow and other parameters of the Hall thruster, uses the PIC algorithm, introduces the concept of macroparticles, replaces the actual motion of charged particles by the motion of a part of macroparticles, and represents the actual situation of macroparticles by weight, thus obtaining an accurate plume distribution model.

[0054] 2. Simplify the complexity of the plume model:

[0055] Traditional plume models are difficult to construct due to the large number of macroparticle meshes and the lack of clear relationships between them. By extracting the plume density of each mesh obtained from SPIS simulation and converting it into an easily processable grayscale image, the complexity of the plume model is effectively simplified and the efficiency of model construction is improved.

[0056] 3. Density extraction method based on visualization model:

[0057] This method processes simulated plume distribution images, converting them into grayscale images. By distinguishing the image's grayscale levels and drawing isodensity lines, the density parameters of the plume along different transmission paths are obtained. Compared to manually extracting density for each grid, this method significantly reduces workload and improves accuracy and efficiency.

[0058] 4. Conversion from simulation results to characteristic parameters:

[0059] The present invention proposes a new method that can convert the plume distribution image in the SPIS simulation results into the characteristic parameters of the electromagnetic field on the plume propagation path, overcoming the problem in the prior art that the simulation results cannot be directly converted into practical application parameters.

[0060] Alternatives:

[0061] Traditional numerical simulation methods such as the Finite Difference Method (FDTD), Finite Element Method (FEM), and Geometric Optics can serve as alternatives to step 4. By incorporating the Drude model into these algorithms and then calculating the electromagnetic properties, we can utilize various electromagnetic computational tools to obtain corresponding electromagnetic wave transmission characteristics, thereby validating and optimizing the method of the present invention.

[0062] Step 1: Input the thruster's divergence angle, ionization rate, thrust, mass flow and other working state parameters into the SPIS software to obtain the density distribution model of each particle in the plume;

[0063] Step 2: Input the plume collision frequency and the electron density obtained by SPIS into the Drude model to simplify the plume model;

[0064] Step 3: Input the discretized plume model and electromagnetic wave frequency band into the electromagnetic solver, and obtain the transmission characteristics of the electromagnetic wave: the closer the propagation path of the electromagnetic wave is to the thruster outlet, the greater its attenuation; and the attenuation of the electromagnetic wave has no obvious connection with the angle of its incident plume, and is more affected by the area with higher particle density in the plume.

[0065] The present invention adopts a density extraction method based on a visualization model. By converting the plume distribution image obtained by simulation into a grayscale image and drawing isodensity lines by distinguishing the grayscale levels of the image, it brings significant beneficial effects. Specifically, this method simplifies the complexity of the plume model and improves the efficiency and accuracy of model construction. In addition, by introducing a hierarchical structure to build a transmission model of electromagnetic waves in the plume, the simulation accuracy of the electromagnetic wave transmission characteristics is further improved. Combined with different electromagnetic calculation tools, the characteristic parameters of electromagnetic waves in the plume propagation path can be obtained efficiently and accurately, significantly reducing the calculation cost and time, and improving the reliability and practicality of the simulation results.

[0066] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model, comprising: Step 1) Based on the working state of the Hall thruster, SPIS simulation software is used to introduce macro particles based on the PIC algorithm and calculate the plume distribution model diagram; Step 2) Extract the plume density of each grid in the plume distribution model image, convert the color image of the plume distribution model into a grayscale image, and draw isodensity lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths; Step 3) Based on the collision in the plume, the Drude model is used to represent the relative dielectric constant; Step 4) Divide the layers with the same relative permittivity into a layer, use the layered structure to build a model of electromagnetic wave transmission in the plume, perform electromagnetic solution, and obtain the electromagnetic wave transmission characteristic parameters; In step 1), macro particles are introduced based on the PIC algorithm to establish a plume distribution model; the steps include: Macro particles are introduced, and the movement of the macro particles is used to replace the actual movement of charged particles. The volume of each macro particle falling in the grid is used as the weight assigned to the grid, and a plume distribution model is established. The weight is used to represent the density and frequency of the macro particles. The grid of the macro particles is composed of cones of different sizes; In step 2), the color image of the plume distribution model is converted into a grayscale image, and isodensity lines are drawn on the color image by distinguishing the grayscale levels of the image, including: The color image of the plume distribution model is converted into a 256-level grayscale image, the maximum and minimum pixel values ​​are identified, and the pixel values ​​within the maximum and minimum pixel value range are divided into several levels. The positions of the same pixel value are smoothly connected to obtain the isodensity lines; The electromagnetic solution is performed to obtain the electromagnetic wave transmission characteristic parameters, including: The CST electromagnetic calculation tool is introduced, and the FIT algorithm is used to numerically solve the Maxwell equations. By discretizing space and time, the time-varying behavior of the electromagnetic field is calculated to obtain the characteristic parameters of electromagnetic wave transmission, including the transmission coefficient and reflection coefficient.

2. The method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model according to claim 1, characterized in that: The working states of the Hall thruster in step 1) include: divergence angle, ionization rate, thrust and mass flow.

3. The method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model according to claim 1, characterized in that: The relative dielectric constant in step 3) for: ； in, is the plume plasma frequency, is the electromagnetic wave frequency, is the plume collision frequency, j represents the imaginary part, is the plasma electron density, is the unit charge, , is the dielectric constant of vacuum, , is the electron mass, .

4. The method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model according to claim 1, characterized in that: The electromagnetic solution is performed to obtain the characteristic parameters of electromagnetic wave transmission, including: introducing a finite difference method, a finite element method or a geometric optics method to calculate the time-varying behavior of the electromagnetic field to obtain the characteristic parameters of electromagnetic wave transmission, including: a transmission coefficient and a reflection coefficient.

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