Ion thruster discharge chamber magnetic pole optimization method

Abstract

The invention relates to the technical field of space electric propulsion, in particular to an ion thruster discharge chamber magnetic pole optimization method, which obtains an optimized discharge chamber magnetic pole structure by researching plasma generation and evolution behaviors under a specific magnetic pole structure based on a plasma numerical simulation process. On one hand, plasma characteristic parameters which cannot be tested by a test are obtained by using a numerical simulation means and a basic discharge principle of a discharge chamber, and on the other hand, change relationships between electron motion behaviors and the magnetic field intensity of a cathode magnetic pole and the magnetic field intensity of a conical section magnetic field are established; the working process and the working mechanism in the discharge chamber when the ion thruster works are understood more deeply, and data support and technical support are provided for optimization design of the discharge chamber of the ion thruster.

Description

Technical Field

[0001] The present application relates to the field of space electric propulsion technology, and in particular to a method for optimizing the magnetic poles of an ion thruster discharge chamber. Background Art

[0002] Compared to chemical propulsion, the high specific impulse of ion thrusters can significantly increase spacecraft payloads and significantly reduce launch costs. However, the operating life of ion thrusters is a key factor limiting their wider application. Because ion thrusters have relatively low thrust, achieving their intended objectives while in orbit requires a longer operating life than other propulsion systems. This is especially true for long-range deep space exploration missions, which place even higher demands on the operating life of ion thrusters.

[0003] An ion thruster is a device that converts electrical energy into kinetic energy, and the plasma in it is the main source of kinetic energy. The discharge chamber is the main area where plasma is produced. The performance of the discharge chamber directly determines the thrust generated by the thruster and the time it can work to achieve the set goals. Therefore, the performance of the discharge chamber plays a vital role in the performance and service life of the ion thruster.

[0004] The magnetic topology and magnetic field distribution generated by the permanent magnet system within the discharge chamber determine the plasma's motion and density distribution. An optimal magnetic topology design results in better magnetic field confinement for electrons, resulting in longer retention time within the discharge chamber, a higher frequency of collisions between electrons and neutral atoms, and a greater probability of ion production. To better confine electrons, corresponding permanent magnets are designed at the cathode exit, cone, and column. However, because the primary electrons ejected from the cathode exit have lower energy and are less constrained by the magnetic field near the cathode exit, they easily escape the magnetic field and are absorbed by the anode, significantly increasing electron loss, increasing discharge losses, and degrading discharge chamber performance. Therefore, optimizing the magnetic poles at the cathode exit is key to reducing the primary electron loss rate.

[0005] However, since the performance of the discharge chamber also includes the density distribution of the plasma upstream of the screen along the radial direction of the discharge chamber, the more uniform the density distribution, the lower the plasma density in the center of the grid, the smaller the number of ions passing through the grid hole, and the longer the working life of the grid assembly, when considering the primary electron loss rate at the cathode outlet, the plasma distribution in the column section inside the discharge chamber must also be considered. This requires that the magnetic field-free area of ​​the column section be as large as possible, and this requires mutual cooperation and coordination among the cathode magnetic pole, the cone magnetic pole and the column magnetic pole, and comprehensive consideration of the primary electron loss rate, the collision of primary electrons and secondary electrons with neutral atoms, etc.

[0006] If the above results are obtained only by experimental tests to obtain the optimal magnetic pole position and size, it is necessary to constantly adjust the magnetic pole size and position and conduct a large number of experimental tests, which wastes manpower, material resources and financial resources, and cannot quickly obtain the results that designers want. Summary of the Invention

[0007] The present application provides a method for optimizing the magnetic poles of an ion thruster discharge chamber. On the one hand, it can obtain the microscopic characteristic parameters of the plasma inside the discharge chamber that cannot be measured experimentally, and on the other hand, it can help designers quickly obtain the most optimized magnetic pole configuration.

[0008] To achieve the above-mentioned objectives, the present application provides a method for optimizing the magnetic poles of an ion thruster discharge chamber, based on a plasma numerical simulation process, comprising the following steps: Step 1: Based on the performance index requirements of the ion thruster discharge chamber, using a theoretical analysis model of the discharge chamber, determining the magnetic induction intensity at the cathode outlet where the maximum magnetic field line is closed inside the discharge chamber; Step 2: Constructing a three-dimensional simulation calculation model of the discharge chamber according to the geometric structure of the discharge chamber; Step 3: Establishing a numerical simulation module for tracking electron motion trajectories; Step 4: Conducting numerical simulation of the discharge chamber plasma under a specific magnetic field structure to simulate the motion behavior and motion trajectory of electrons ejected from the cathode outlet; Step 5: Based on the magnetic induction intensity at the cathode outlet obtained by theoretical analysis, adjusting the geometric dimensions or positions of the cathode magnetic pole, cone magnetic pole, and column magnetic pole to obtain the magnetic induction intensity at the cathode outlet obtained by theoretical analysis; Step 6: Using the three-dimensional simulation calculation model of the discharge chamber, conducting numerical simulation of the discharge chamber plasma under the magnetic pole configuration, and comparing the calculation results with the results under the specific magnetic field structure; and Step 7: Determining and determining the optimized ion thruster discharge chamber magnetic pole geometry based on the comparison results and the performance optimization requirements of the ion thruster discharge chamber.

[0009] Furthermore, in step 1, the performance indicators of the ion thruster discharge chamber include discharge loss, discharge current, and density distribution of plasma upstream of the screen along the radial direction of the discharge chamber.

[0010] Furthermore, in step 1, the closure of the maximum magnetic field line inside the discharge chamber refers to a magnetic field line that has the largest magnetic field-free area in the column segment and is closed along the anode surface of the discharge chamber.

[0011] Furthermore, in step 2, the three-dimensional simulation calculation model of the discharge chamber includes a hollow cathode, an anode and a screen grid.

[0012] Furthermore, in step 3, the electrons are primary electrons ejected from the cathode outlet.

[0013] Furthermore, in step 7, the process of determining whether the magnetic pole geometry is optimal includes: comparing the plasma density distribution in the radial direction of the discharge chamber upstream of the screen, the thruster extraction beam, the discharge loss, and the anode current with the simulation results under a specific magnetic field structure; if the plasma density distribution is more uniform, the thruster extraction beam is more, the discharge loss is lower, the anode current is larger, and the performance parameters of the discharge chamber meet the design requirements, then the magnetic pole geometry is considered to be the optimal structure; otherwise, it is necessary to continue to adjust until the above requirements are met.

[0014] The present application provides a method for optimizing the magnetic poles of an ion thruster discharge chamber, which has the following beneficial effects:

[0015] On the one hand, this application uses numerical simulation methods and the basic discharge principles of the discharge chamber to obtain plasma characteristic parameters that cannot be tested experimentally. On the other hand, it establishes the relationship between electron motion behavior and the changing magnetic field strength of the cathode pole and the cone magnetic field, so as to have a deeper understanding of the working process and working mechanism inside the discharge chamber when the ion thruster is working, and provide data support and technical support for the optimized design of the ion thruster discharge chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings that constitute part of this application are used to provide a further understanding of this application and make other features, objects and advantages of this application more apparent. The illustrative embodiment drawings of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0017] Figure 1 1 is a schematic diagram of the steps of a method for optimizing the magnetic poles of an ion thruster discharge chamber according to an embodiment of the present application; DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0019] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0020] In this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0021] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to express a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0022] Additionally, the term "plurality" shall mean two or more.

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] like Figure 1 As shown, the present application provides a method for optimizing the magnetic poles of an ion thruster discharge chamber. Based on the process of plasma numerical simulation, the plasma generation and evolution behavior under a specific magnetic pole structure is studied to obtain the optimized discharge chamber magnetic pole structure. The method specifically includes the following steps:

[0025] Step 1: Based on the performance index requirements of the ion thruster discharge chamber, use the discharge chamber theoretical analysis model to determine the magnetic induction intensity at the cathode outlet with the maximum magnetic field line inside the discharge chamber;

[0026] Among them, the performance indicators of the ion thruster discharge chamber include discharge loss, discharge current, and the density distribution of the plasma upstream of the screen along the radial direction of the discharge chamber; the maximum magnetic field line closure inside the discharge chamber refers to the magnetic field line with the largest magnetic field-free area in the column section and closed along the anode surface of the discharge chamber;

[0027] The magnetic induction intensity at the cathode outlet is obtained according to the loss current of the primary electrons. The loss current of the primary electrons is expressed as the part that has been absorbed by the anode before participating in the collision with neutral atoms. The relationship between the loss current and the magnetic induction intensity is expressed as follows:

[0028]

[0029] Where: n p 、v p are the density and speed of the primary electrons respectively; e is the electron charge; B is the magnetic induction intensity at the cathode outlet; m e is the mass of the primordial electron; L c is the total length of the magnetic poles inside the discharge chamber.

[0030] Specifically, the primary electron loss current is required to be as small as possible. By comparing the primary electron loss current under different magnetic pole structures, the magnetic induction intensity in the above formula corresponding to the minimum primary electron loss current is obtained. This result is the magnetic induction intensity at the cathode outlet corresponding to the maximum magnetic field line closure inside the discharge chamber obtained by theoretical calculation.

[0031] Step 2: Based on the geometric structure of the discharge chamber, a three-dimensional simulation model of the discharge chamber is constructed. This model includes the hollow cathode, anode, and the upper surface of the screen grid. The hollow cathode acts as a solid body and emits a certain number of primary electrons into the discharge chamber.

[0032] Step 3: Establish a numerical simulation module for electron motion trajectory tracking; this module is mainly used to track the motion of primary electrons ejected from the hollow cathode outlet to obtain its motion trajectory.

[0033] Step 4: Carry out numerical simulation of the discharge chamber plasma under a specific magnetic field structure, simulate the motion behavior of the electrons ejected from the cathode outlet, and simulate their motion trajectory; carry out numerical simulation of the discharge chamber plasma under a specific magnetic field structure, and use the simulation module of electron motion trajectory tracking to obtain the motion path of the primary electrons under the specific magnetic field structure from a microscopic level.

[0034] Step 5: According to the magnetic induction intensity at the cathode outlet obtained by theoretical analysis, the geometric dimensions or positions of the cathode magnetic pole, the cone magnetic pole, and the column magnetic pole are adjusted to obtain the magnetic induction intensity at the cathode outlet obtained by theoretical analysis;

[0035] Specifically, according to the magnetic induction intensity at the cathode outlet obtained by theoretical analysis, the geometric dimensions or positions of the cathode magnetic pole, cone magnetic pole and column magnetic pole are adjusted, and then the magnetic field simulation calculations under different magnetic pole structures are carried out using ANSYS magnetic field simulation software. By comparing the magnetic induction intensity at the hollow cathode outlet with the results obtained by theoretical analysis in step 1, the geometric dimensions and positions of the cathode magnetic pole, cone magnetic pole and column magnetic pole are determined.

[0036] Step 6: Using the three-dimensional simulation model of the discharge chamber, perform numerical simulation of the discharge chamber plasma under this magnetic pole configuration and compare the calculation results with those under a specific magnetic field structure;

[0037] Step 7: Based on the comparison results and the performance optimization requirements of the ion thruster discharge chamber, determine and optimize the ion thruster discharge chamber magnetic pole geometry.

[0038] Specifically, the plasma density distribution in the radial direction of the discharge chamber upstream of the screen, the thruster-extracted beam, the discharge loss, and the anode current are compared with the simulation results under a specific magnetic field structure.

[0039] The thruster beam expression is:

[0040]

[0041] Where n i is the ion density; k is the Boltzmann constant; T e is the electron temperature; M is the ion mass; A s is the gate area; T s For ion transparency.

[0042] The discharge loss expression is:

[0043]

[0044] Where, I d is the anode current; V d is the anode voltage.

[0045] The anode current is the sum of the primary electron current, secondary electron current and ion current, and is expressed as:

[0046]

[0047] Where n e is the electron density; A a is the loss area of ​​ions and electrons on the anode wall; φ is the sheath potential of the plasma relative to the anode; A as is the anode area exposed to plasma; f c is the ion confinement factor.

[0048] According to the above formulas, if the obtained plasma density distribution is more uniform, the thruster-extracted beam is more, the discharge loss is lower, the anode current is larger, and the performance parameters of the discharge chamber (discharge loss, discharge current) meet the design requirements, then the geometric dimensions and positions of the cathode magnetic pole and the cone segment magnetic pole are considered to be the optimal structure, that is, the magnetic pole geometry is the optimal structure; otherwise, it is necessary to continue to adjust until the above requirements are met.

[0049] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for optimizing the magnetic poles of an ion thruster discharge chamber, characterized in that: The process based on plasma numerical simulation includes: Step 1: Based on the performance index requirements of the ion thruster discharge chamber, use the discharge chamber theoretical analysis model to determine the magnetic induction intensity at the cathode outlet with the maximum magnetic field line inside the discharge chamber; Step 2: Construct a three-dimensional simulation model of the discharge chamber based on the geometric structure of the discharge chamber; Step 3: Establish a numerical simulation module for electron motion trajectory tracking; Step 4: Conduct numerical simulation of the plasma in the discharge chamber under a specific magnetic field structure to simulate the motion behavior of electrons ejected from the cathode outlet and their motion trajectory; Step 5: According to the magnetic induction intensity at the cathode outlet obtained by theoretical analysis, the geometric dimensions or positions of the cathode magnetic pole, the cone magnetic pole, and the column magnetic pole are adjusted to obtain the magnetic induction intensity at the cathode outlet obtained by theoretical analysis; Step 6: Using the three-dimensional simulation model of the discharge chamber, perform numerical simulation of the discharge chamber plasma under this magnetic pole configuration and compare the calculation results with those under a specific magnetic field structure; Step 7: Based on the comparison results and the performance optimization requirements of the ion thruster discharge chamber, determine and optimize the ion thruster discharge chamber magnetic pole geometry.

2. The method for optimizing the magnetic poles of an ion thruster discharge chamber according to claim 1, wherein: In step 1, the performance indicators of the ion thruster discharge chamber include discharge loss, discharge current, and density distribution of plasma upstream of the screen along the radial direction of the discharge chamber.

3. The method for optimizing the magnetic poles of an ion thruster discharge chamber according to claim 2, wherein: In step 1, the closure of the maximum magnetic field line inside the discharge chamber refers to a magnetic field line with the largest magnetic field-free area in the column segment and closed along the anode surface of the discharge chamber.

4. The method for optimizing the magnetic poles of an ion thruster discharge chamber according to claim 3, wherein: In step 2, the three-dimensional simulation calculation model of the discharge chamber includes a hollow cathode, an anode and a screen grid.

5. The method for optimizing the magnetic poles of an ion thruster discharge chamber according to claim 4, wherein: In step 3, the electrons are primary electrons ejected from the cathode outlet.

6. The method for optimizing the magnetic poles of an ion thruster discharge chamber according to claim 5, wherein: In step 7, the process of determining whether the magnetic pole geometry is optimal includes: The plasma density distribution in the radial direction of the discharge chamber upstream of the screen, the thruster-extracted beam, the discharge loss, and the anode current are compared with the simulation results under a specific magnetic field structure. If the plasma density distribution is more uniform, the thruster-extracted beam is larger, the discharge loss is lower, the anode current is larger, and the performance parameters of the discharge chamber meet the design requirements, then the magnetic pole geometry is considered to be the optimal structure; Otherwise, continue to adjust until the above requirements are met.

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