Pulse type electromagnetic thruster plume characteristic analysis system and method

Abstract

The invention discloses a pulse type electromagnetic thruster plume characteristic analysis system and method, and the system employs a vacuum chamber, a current monitoring system, a multi-probe data collection device, an ion current measurement circuit, and a data collection and processing system. The multi-probe data acquisition device is used for acquiring plume plasma saturated ion current of the pulse type electromagnetic thruster and outputting the plume plasma saturated ion current as a voltage signal; the ion current measuring circuit is used for converting the voltage signal acquired by the multi-probe data acquisition device into an ion current signal; and the data acquisition and processing system is used for collecting the voltage signal output by the multi-probe data acquisition device and the ion current signal converted by the ion current measuring circuit, converting the ion current signal into a digital signal, performing fitting processing on the ion current signal, and analyzing plume characteristics of the pulse type electromagnetic thruster with multiple ion groups superposed. According to the method, a more accurate theoretical basis is provided for performance optimization of the thruster.

Description

Technical Field

[0001] The invention relates to the field of aerospace technology, and in particular discloses a multi-ion group superposition pulse electromagnetic thruster plume characteristic analysis system and method. Background Art

[0002] As an advanced space propulsion technology, pulsed electromagnetic thrusters have been widely used in aerospace fields such as satellite attitude control and orbit transfer. The working principle of the thruster involves complex multi-physical field coupling phenomena, including electromagnetic fields, plasma dynamics, and material ablation. The thruster working fluid produces ionized components with different ionization degrees and different compositions during discharge ions, so there are also ion groups with various ionization degrees and compositions in its plume. These ion groups have different charge states, generation times, and velocity distribution characteristics. A deep understanding of the characteristics of the thruster plume plasma is of vital importance to mastering the working principle of the thruster, optimizing performance, and improving propulsion efficiency.

[0003] At present, the research on the characteristics of pulsed electromagnetic thruster plume plasma mainly relies on experimental diagnostic techniques, such as Langmuir probe, optical emission spectroscopy and mass spectrometry diagnostic techniques. These techniques can provide key information about plasma parameters, chemical composition and particle velocity distribution. However, these techniques have certain limitations in describing the composition and characteristics of ion groups in plume plasma. For example, optical emission spectroscopy is the superposition integral of the spectral lines of multiple ion components in space, which is prone to errors in identifying and quantitatively analyzing the emission lines of specific ions. The mass spectrometer has limited selectivity in distinguishing ions with similar mass-to-charge ratios, and some ion signals may be lost due to differences in ionization efficiency; in addition, its sampling representativeness is poor, it is greatly affected by position and time, and the experimental conditions in high vacuum environment are more demanding. As a traditional technology in the field of plasma diagnosis, the Langmuir probe can analyze the electron density, temperature and movement speed of plasma in a specific area. However, in the study of pulsed electromagnetic thruster plume diagnosis, the plasma parameters provided by the Langmuir probe are usually only the macroscopic average values ​​of the parameters. For example, patent CN202310686912.8 mentions that through time-of-flight (ToF) technology, the peak or other features in the probe signal can be used to determine the ion velocity. However, ToF technology can only provide the "average" speed of the plume plasma and cannot distinguish the motion characteristics of different ion groups. Patent CN202111465016.6 proposes the use of a multi-probe layout for plasma diagnosis, but does not involve parameterized model fitting, and cannot quantify microscopic characteristic parameters such as thermal diffusion and divergence rate of the ion group.

[0004] In summary, the existing technologies have not effectively solved the problem of the superposition effect of multiple ion groups in the plasma plume, and cannot accurately reflect the key characteristics such as the structure, velocity distribution, thermal diffusion, and divergence of the ion groups. The inability to accurately analyze the superposition effect of multiple ion groups leads to significant errors in performance evaluation, making it more difficult to deeply understand the physical mechanism in the process of the thruster plume plasma movement. Summary of the Invention

[0005] The present invention provides a system and method for analyzing the plume characteristics of a pulsed electromagnetic thruster, aiming to solve at least one defect existing in the above-mentioned existing technologies.

[0006] One aspect of the present invention relates to a system for analyzing the plume characteristics of a pulsed electromagnetic thruster, including a vacuum chamber, a current monitoring system, a multi-probe data acquisition device, an ion current measurement circuit, and a data acquisition and processing system. Among them, The vacuum chamber is used to provide a space simulation working environment for the operation of the pulsed electromagnetic thruster; The current monitoring system is arranged in the vacuum chamber and is used to monitor the main discharge current waveform of the pulsed electromagnetic thruster in real time; The multi-probe data acquisition device is arranged in the vacuum chamber and is used to collect the saturated ion current of the plasma plume of the pulsed electromagnetic thruster and output it as a voltage signal; The ion current measurement circuit is connected to the multi-probe data acquisition device and is used to convert the voltage signal collected by the multi-probe data acquisition device into an ion current signal; The data acquisition and processing system is respectively connected to the multi-probe data acquisition device and the ion current measurement circuit, and is used to collect the voltage signal output by the multi-probe data acquisition device and the ion current signal converted by the ion current measurement circuit, convert the ion current signal into a digital signal, and is responsible for fitting and processing the ion current signal to analyze the plume characteristics of the pulsed electromagnetic thruster with the superposition of multiple ion groups.

[0007] Further, the multi-probe data acquisition device includes a probe body, and the probe body takes a single Langmuir probe as the core. The Langmuir single probe is made of tungsten wire with a diameter of 50μm - 200μm.

[0008] Further, the system for analyzing the plume characteristics of the pulsed electromagnetic thruster further includes an insulating support. The insulating support is processed into a tubular or columnar shape, and the Langmuir single probe is sleeved inside the insulating support. The length of the insulating support is 3mm - 6mm.

[0009] Further, the multi-probe data acquisition device includes multiple probes arranged at equal intervals along the spatial angular axis of the plume of the pulsed electromagnetic thruster, and the tips of the probes are perpendicular to the plasma ejection direction.

[0010] Furthermore, the pulsed electromagnetic thruster plume characteristics analysis system also includes a bias power supply, which is connected to the multi-probe data acquisition device and is used to load a sufficiently high and constant negative bias voltage to the ground on the probe to form an ion sheath on the probe surface, repel electrons and receive ions, thereby collecting the ion saturation current.

[0011] Furthermore, the pulse electromagnetic thruster plume characteristics analysis system also includes a protective cover, which is arranged outside the probe.

[0012] Furthermore, the data acquisition and processing system includes a data acquisition card, which is connected to the ion current measurement circuit and is used to convert the ion current signal output by the ion current measurement circuit into a digital signal.

[0013] Another aspect of the present invention relates to a pulse electromagnetic thruster plume characteristics analysis method, which is applied to the above-mentioned pulse electromagnetic thruster plume characteristics analysis method. The pulse electromagnetic thruster plume characteristics analysis method comprises the following steps: Construct a multi-ion group superposition distribution model; As the plasma is ejected from the thruster nozzle to form a plume, the plasma sheet expands in the form of a cone in the horizontal direction. According to the multi-ion group superposition distribution model, the current density generated by the charge amount passing through the unit area of ​​the i-th ion group is obtained. ; According to the current density , add the current densities of the n ion groups superimposed to obtain the total ion current density ; Based on the total ion current density , get the kth Langmuir probe position and process the theoretical ion current ; Get the k Experimental measurement of ionic current at a Langmuir probe , the optimization objective is used to perform parameter fitting so that the theoretical ion current Fitting the experimentally measured ion currents , obtain the optimal pulsed electromagnetic thruster plume characteristic parameters.

[0014] Further, in the step of constructing a multi-ion group superposition distribution model, each ion group distribution in the multi-ion group superposition distribution model is independently characterized as shown in the following formula:

[0015] in, x is the axial position of the ion group during its axial motion, is the axial velocity of the ion group, describing the speed of the ions moving in the axial direction of the thruster; is the average axial velocity of the ion group, representing the average movement speed of the ion group; is the axial thermal velocity of the ion group, reflecting the distribution of thermal motion velocity of the ion group in the axial direction; It is the charge per unit area of ​​the ion group, which represents the charge density of the ion group; is the Dirac delta function, which is used to represent the spatial localization of the ion group; is the thruster nozzle position, is the time it takes for the ion group to move to the thruster nozzle position, It is The distribution function of an ion group.

[0016] Furthermore, according to the current density , add the current densities of the n ion groups superimposed to obtain the total ion current density In the step, the current density for:

[0017] The total ion current density j(x, t) is:

[0018] in, is the time difference, For ion clusters Location, At time, it moves from the thruster exit position to The speed of the position; For ion clusters Location, At time, it moves from the thruster exit position to x The speed of the position; is the current density expression, is the axial position of the ion group during axial motion, is the thruster nozzle position, The ion group moves to The time at the location, is the time it takes for the ion group to move to the thruster exit position, , ; is the number of ion group superpositions.

[0019] The beneficial effects achieved by the present invention are: The present invention provides a pulse electromagnetic thruster plume characteristics analysis system and method. The system adopts a vacuum chamber, a current monitoring system, a multi-probe data acquisition device, an ion current measurement circuit and a data acquisition and processing system. The vacuum chamber is used to provide a space simulation working environment for the pulse electromagnetic thruster; the current monitoring system is used to monitor the main discharge current waveform of the pulse electromagnetic thruster in real time; the multi-probe data acquisition device is used to collect the saturated ion current of the pulse electromagnetic thruster plume plasma and output it as a voltage signal; the ion current measurement circuit is used to convert the voltage signal collected by the multi-probe data acquisition device into an ion current signal; the data acquisition and processing system is used to collect the voltage signal output by the multi-probe data acquisition device and the ion current signal converted by the ion current measurement circuit, convert the ion current signal into a digital signal, and is responsible for fitting the ion current signal to analyze the pulse electromagnetic thruster plume characteristics of multiple ion groups superimposed. The pulse electromagnetic thruster plume characteristics analysis system and method provided by the present invention have the following beneficial effects: 1. Improved accuracy Compared with the traditional ToF (Time-of-Flight) technology, the plume plasma reconstruction method of the present invention can more accurately describe the characteristics of the ion group in the pulsed electromagnetic thruster plume, including the structure of the ion group, and the average velocity, thermal diffusion, cone expansion vertex position and generation time of each ion group. The movement and distribution characteristics. This helps to deeply understand the physical mechanism of plasma in the plume and provide a more accurate theoretical basis for the performance optimization of the thruster.

[0020] 2. Deepening of physical understanding Through detailed analysis of ion groups, the present invention can reveal the physical processes of plasma generation, acceleration, transmission and interaction during the operation of pulsed electromagnetic thrusters, and guide the optimization of thruster electrode geometry by quantifying thermal diffusion and divergence rate, providing important theoretical support for further improving the design and performance of thrusters. It also helps to discover the deficiencies in existing thruster plume simulation models, provide directions for the improvement and perfection of the models, and promote the development of pulsed electromagnetic thruster technology.

[0021] 3. Improved application value The method of the present invention can be applied to the fields of design, optimization and fault diagnosis of pulsed electromagnetic thrusters, and provides engineers with an effective tool to help them better understand the working characteristics of thrusters and improve the performance and reliability of thrusters.

[0022] Compared with the prior art, the present invention can provide more comprehensive and accurate information on the characteristics of plume plasma, which is helpful for developing more efficient and reliable pulsed electromagnetic thrusters and contributing to the development of the aerospace field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of an embodiment of a method for analyzing plume characteristics of a pulsed electromagnetic thruster according to the present invention; Figure 2 A schematic diagram of the probe distribution in the thruster plume region in a pulsed electromagnetic thruster plume characteristic analysis system of the present invention; Figure 3 A schematic diagram of changes in the distribution of plume ion groups in a pulsed electromagnetic thruster plume characteristic analysis system of the present invention; Figure 4 It is a schematic diagram of the ion current waveform detected by a probe in a pulsed electromagnetic thruster plume characteristic analysis system of the present invention; Figure 5 A graph showing the relationship between the discharge current waveform and the plasma density and temperature measured by the Langmuir probe in a pulsed electromagnetic thruster plume characteristic analysis system of the present invention; Figure 6 The ion current collected by a probe in a pulsed electromagnetic thruster plume characteristic analysis system of the present invention is fitted and decomposed into three different ion group currents. DETAILED DESCRIPTION

[0024] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] like Figures 1 to 6 As shown, the first embodiment of the present invention proposes a pulse electromagnetic thruster plume characteristic analysis system, including a vacuum chamber, a current monitoring system, a multi-probe data acquisition device, an ion current measurement circuit and a data acquisition and processing system, wherein the vacuum chamber is used to provide a space simulation working environment for the pulse electromagnetic thruster; the current monitoring system is arranged in the vacuum chamber, and is used to monitor the main discharge current waveform of the pulse electromagnetic thruster in real time; the multi-probe data acquisition device is arranged in the vacuum chamber, and is used to collect the saturated ion current of the pulse electromagnetic thruster plume plasma and output it as a voltage signal; the ion current measurement circuit is connected to the multi-probe data acquisition device, and is used to convert the voltage signal collected by the multi-probe data acquisition device into an ion current signal; the data acquisition and processing system is respectively connected to the multi-probe data acquisition device and the ion current measurement circuit, and is used to collect the voltage signal output by the multi-probe data acquisition device and the ion current signal converted by the ion current measurement circuit, convert the ion current signal into a digital signal, and is responsible for fitting the ion current signal to analyze the pulse electromagnetic thruster plume characteristics of multiple ion groups superimposed.

[0026] Further, see Figures 1 to 6, this embodiment proposes a pulse electromagnetic thruster plume characteristics analysis system, which also includes a bias power supply and a protective cover. The multi-probe data acquisition device includes a probe body, the probe body is centered on a single Langmuir single probe, and the Langmuir single probe uses a tungsten wire with a diameter of 50μm-200μm. The pulse electromagnetic thruster plume characteristics analysis system also includes an insulating support, the insulating support is processed into a tubular or cylindrical shape, the Langmuir single probe is sleeved in the insulating support, and the length of the insulating support is 3mm to 6mm. The multi-probe data acquisition device includes a plurality of probes arranged at equal intervals along the spatial angle axis of the pulse electromagnetic thruster plume, and the tips of the probes are perpendicular to the plasma ejection direction. The bias power supply is connected to the multi-probe data acquisition device, and is used to form an ion sheath on the probe surface by loading a sufficiently high constant negative bias to the ground on the probe, repelling electrons and receiving ions, thereby collecting ion saturation current. The pulse protective cover is arranged outside the probe. The data acquisition and processing system includes a data acquisition card, which is connected to the ion current measurement circuit and is used to convert the ion current signal output by the ion current measurement circuit into a digital signal. The pulse electromagnetic thruster plume characteristic analysis system proposed in the present invention realizes real-time monitoring and data acquisition of the pulse plasma thruster plume plasma characteristics, improves the efficiency and accuracy of experimental research; by reconstructing and processing the probe data, it can accurately describe the structure, velocity distribution, charge state, thermal diffusion, divergence rate and other characteristics of the ion group in the thruster plume, and provide a reliable theoretical basis for the design, optimization and performance evaluation of the thruster.

[0027] like Figures 1 to 6 As shown, the working principle of the impulse electromagnetic thruster plume characteristics analysis system provided in this embodiment is as follows: A pulse electromagnetic thruster plume characteristic analysis system comprises a vacuum chamber, a DC power supply, a trigger controller, a voltage monitoring system, a pulse electromagnetic thruster (electric thrusters using capacitive energy storage such as pulse plasma thrusters, laser electromagnetic induced plasma thrusters, and magnetic plasma thrusters), a plasma diagnostic system, and a data acquisition and processing system.

[0028] Vacuum chamber (vacuum degree <1×10 -3 Pa), providing a space-simulated working environment for the thrusters.

[0029] The positive and negative outputs of the DC power supply are connected to the two poles of the energy storage capacitor of the pulse electromagnetic thruster through a transmission line, and the energy storage capacitor is charged.

[0030] The current monitoring system uses Rogowski coil to monitor the thruster main discharge current waveform in real time.

[0031] The multi-probe data acquisition device includes a probe body: a single Langmuir single probe is used as the core, and the probe can use a tungsten wire with a diameter of 50μm-200μm. While ensuring the mechanical strength of the probe, it also reduces the disturbance to the plasma and ensures the accuracy of the measurement data.

[0032] Insulation support: To prevent short circuit and ensure stability, ceramic, quartz and other insulating and high temperature resistant materials are used to process into a tube or column, and the tungsten wire is placed in the center to isolate it from the surrounding conductors. The length of the exposed insulation support of the tungsten wire of each probe is 3mm to 6mm, and the diameter and exposed length of all probes used in the experiment are the same to ensure that the exposed area of ​​each probe is equal.

[0033] Protective cover: Because there are high-speed particles and strong electromagnetic fields in the pulsed electromagnetic thruster plume, a stainless steel protective cover is set outside the probe. Small holes are opened on its surface to allow particles to enter and interact with the tungsten wire, while blocking high-energy particles from impacting. The aperture size is optimized according to experimental requirements and plasma characteristics to balance protection effect and measurement accuracy.

[0034] Probe layout: Probes are distributed along the spatial angle axis at each grid coordinate point in the thruster plume space. The tip of the probe is perpendicular to the plasma ejection direction. To avoid the influence of mutual shadows between probes, the relative position and spacing of the probes should be reasonably set to cover the plume plasma area that needs diagnostic measurement.

[0035] Bias power supply: During measurement, a sufficiently high constant negative bias voltage to the ground must be applied to the probe to form an ion sheath on the probe surface, which repels electrons and receives ions, thereby collecting the ion saturation current. The bias power supply uses an adjustable DC power supply with an output voltage range of -50V to -100V. Under different thruster parameter settings, the voltage is adjusted to ensure that the probe works in the ion saturation zone.

[0036] Ion current measurement circuit: A 20Ω~50Ω sampling resistor is connected in series to the Langmuir single probe measurement circuit. The ion current is measured using a low-noise, high-sensitivity voltage-current conversion circuit, and the voltage collected on the sampling resistor is converted into an ion current signal. To improve accuracy, a low-pass filter with a cutoff frequency of 1kHz~100kHz is added to filter out the high-frequency noise introduced by the thruster discharge.

[0037] Data acquisition and processing system: The ion current signal output by the ion current measurement circuit is connected to the data acquisition card, converted into a digital signal and transmitted to the computer's data acquisition and processing system. The data acquisition and processing system is responsible for fitting the collected plasma current signal according to the pulse electromagnetic thruster plume characteristic program with multiple ion groups superimposed.

[0038] See Figures 1 to 6, this embodiment relates to a method for analyzing the plume characteristics of a pulsed electromagnetic thruster. Applied to the above method for analyzing the plume characteristics of a pulsed electromagnetic thruster, the method for analyzing the plume characteristics of a pulsed electromagnetic thruster includes the following steps: Step S100, construct a superposition distribution model of multiple ion groups.

[0039] During the discharge process of the pulsed electromagnetic thruster, the working medium of the thruster generates ions with different ionization degrees and compositions under the ionization effect. Under the combined action of the electric field and magnetic field, they will form independent groups and maintain the relative stability of their charge states and masses during the movement after exiting the thruster. Therefore, the plume of the pulsed electromagnetic thruster is composed of the superposition of multiple independent ion groups, and each ion group has a unified charge state and mass. These ion groups each occupy a specific distribution range in space and exhibit different generation and evolution processes in time.

[0040] Based on the principles of plasma physics and the results of plasma diagnostic research, it can be assumed that the plasma of the thruster plume contains n ion groups ( i = 1, 2, 3......n), and the movement of each ion group along the axial direction of the thruster follows the truncated Maxwell charge distribution law. The i th ion group is a plasma sheet at the exit of the thruster nozzle. The distribution of each ion group can be independently characterized as shown in formula (1): At the exit of the thruster nozzle (1) In formula (1), x is the axial position during the axial movement of the ion group, is the axial velocity of the ion group, describing the movement velocity of the ion in the axial direction of the thruster; is the axial average velocity of the ion group, representing the average movement velocity of the ion group; is the axial thermal velocity of the ion group, reflecting the thermal movement velocity distribution of the ion group in the axial direction; is the charge per unit area of the ion group, characterizing the charge density of the ion group; is the Dirac δ function, used to represent the locality of the ion group in space; is the position of the thruster nozzle, is the time when the ion group moves to the position of the thruster nozzle, is the th ion group's distribution function.

[0041] (2) This distribution function describes well the movement behavior of the ion group under the action of the electromagnetic field, and at the same time takes into account the thermal movement and spatial distribution characteristics of the ions.

[0042] Step S200: As the plasma is ejected from the thruster nozzle to form a plume, the plasma sheet expands in the form of a cone in the horizontal direction. According to the multi-ion group superposition distribution model, the current density generated by the charge amount passing through the unit area of ​​the i-th ion group is obtained. .

[0043] like Figure 3 As shown, when t>t s As the plasma ejects from the thruster nozzle to form a plume, the plasma sheet expands along the thruster axis due to thermal diffusion and expands in the lateral direction in the form of a cone. The apex of the lateral expansion of the cone is located at x s Upstream h s Location.

[0044] Therefore, during the axial movement of the ion group, the cross-sectional area at different axial positions x will change due to axial thermal diffusion and lateral conical expansion, which will cause the ion charge distribution per unit area to change, and then the current density distribution changes with the lateral expansion of the ion group.

[0045] Principle of axial thermal diffusion: ions themselves have thermal motion characteristics, which originates from the theory of molecular thermal motion in statistical mechanics. Plasma is composed of a large number of ions and electrons. After obtaining energy, the ions will be in a state of continuous thermal motion. During the axial movement of the ion group along the thruster, due to the differences in the thermal motion speeds of different ions, ions with higher thermal speeds will gradually diffuse to areas with lower speeds, causing the plasma sheet to gradually expand in the axial direction. This phenomenon conforms to Fick's diffusion law. From the perspective of microscopic interactions within the plasma, there are Coulomb interactions between ions, and frequent collisions occur during the movement. The collisions cause the ions to exchange energy and momentum, further exacerbating the axial diffusion of the ions and causing the plasma sheet to continue to extend.

[0046] Principle of lateral conical expansion: This phenomenon is related to the principle of jet expansion in fluid mechanics. When plasma is ejected from the thruster, it can be regarded as a special fluid jet. In the absence of external constraints, the jet will be affected by the surrounding environment. When the plasma is ejected outward, there is a pressure difference between its edge and the surrounding gas or vacuum environment. In order to achieve pressure balance, the plasma at the edge will diffuse in all directions. Since the diffusion trends in all directions in the lateral direction are similar, and driven by the axial movement, a form that expands in the form of a cone is formed. In terms of the characteristics of the plasma itself, it has certain conductivity and magnetism. Under the action of the magnetic field and the induced magnetic field generated by itself, the movement trajectory of the ions will be affected, making the lateral diffusion present a cone-shaped feature as a whole.

[0047] This makes x>x s The distribution function of the ion population at φ introduces a cone expansion factor reflects the change in charge per unit area due to the lateral cone expansion, where is the cone expansion factor, h s It is the distance between the apex of the cone's lateral extension and the nozzle position. x is the axial position of the ion group during axial motion, x s is the thruster nozzle position. i The distribution function of the ion group is .

[0048] Thus, the i Ion clusters at position x at The current density generated by the amount of charge passing through a unit area in a given time , can be obtained by formula (3): (3) In formula (3), is the time difference, For ion clusters Location, At time, it moves from the thruster exit position to The speed of the position; For ion clusters Location, At time, it moves from the thruster exit position to x The speed of the position; is the current density expression, is the axial position of the ion group during axial motion, is the thruster nozzle position, The ion group moves to The time at the location, is the time it takes for the ion group to move to the thruster exit position, , .

[0049] Step S300: According to the current density ,right n The current density of each ion group is added to obtain the total ion current density. .

[0050] The sum of the current densities of n ion groups is the total ion current density. , as shown in formula (4): (4) In formula (4), is the integral calculation result, is the axial position of the ion group during axial motion, is the thruster nozzle position, The ion group moves to x The time at the location, is the time it takes for the ion group to move to the thruster exit position, , ; is the number of ion group superpositions.

[0051] Step S400: According to the total ion current density , get the kth Langmuir probe position and process the theoretical ion current .

[0052] The theoretical ion current at the kth Langmuir probe position is ,in, is the theoretical ion current at the kth Langmuir probe position, is the total ion current collected by the kth probe, is the effective collection area of ​​the Langmuir probe, and the effective collection area of ​​all Langmuir probes is the same, that is, .

[0053] Step S500: Obtain the experimentally measured ion current at the kth Langmuir probe , the optimization objective is used for parameter fitting, so that the theoretical ion current Fitting experimentally measured ion currents , obtain the optimal pulsed electromagnetic thruster plume characteristic parameters.

[0054] Parameter fitting: The ion current actually detected at the kth Langmuir probe is In order to fit the experimentally measured ion current, the normalized least squares error is defined as As the optimization objective, it is shown in formula (5): (5) In formula (5), is the normalized least squares error, For the k The normalized least squares error between the theoretical ion current of each probe and the total ion current collected by the probe. is the theoretical ion current at the kth Langmuir probe position, is the ion current actually detected at the kth Langmuir probe.

[0055] In this embodiment, the normalized least squares error is used As an optimization target, fitting the experimentally measured ion current has statistical and mathematical principles as well as practical application considerations. The following is a detailed introduction: 1. Theoretical basis Principle of least squares method: The least squares method is a classic mathematical optimization technique. Its core idea is to find the best function match for the data by minimizing the sum of squares of errors. In the ion current fitting problem, there is an error between the experimentally measured ion current and the ion current calculated by the model. By summing the squares of the errors, the errors in all probe positions and the entire time window can be comprehensively considered. The squaring operation can avoid the mutual cancellation of positive and negative errors, highlight the impact of larger errors on the overall results, and make the fitting results more inclined to reduce the errors of those data points with larger deviations, thereby obtaining fitting parameters that are more in line with the actual situation.

[0056] Statistical significance of normalization: In practical applications, the amplitudes of ion currents measured by different probes may vary greatly. If the square sum of errors is used directly for optimization, the errors corresponding to currents with larger amplitudes will dominate the sum, while the errors of currents with smaller amplitudes may be ignored, resulting in the fitting results not being able to reflect the characteristics of all data well. Through normalization, the square sum of errors of each probe can be relativized, so that current errors of different amplitudes have equal weight in the optimization target. This can more fairly consider the impact of each probe data on the fitting results and improve the accuracy and versatility of the fitting.

[0057] 2. Practical Application Considerations Data stability and reliability: Experimental measured data often have certain noise and uncertainty. Normalized least squares error can reduce the impact of these noise and uncertainty on the fitting results to a certain extent. Because it comprehensively considers the overall characteristics of the data, rather than just focusing on the errors of individual data points, it makes the fitting process more robust and the obtained fitting parameters more representative and reliable.

[0058] Facilitates model evaluation and comparison: Using the normalized least squares error as the optimization target provides a unified evaluation standard for different fitting models or different parameter settings. By comparing the values ​​in different situations, you can intuitively determine which model or parameter combination can better fit the experimental data, thereby facilitating model screening and optimization. For example, when trying different initial values ​​of ion group parameters or changing the number of ion groups, you only need to compare the corresponding values, you can quickly determine which setting is better.

[0059] Meet the actual needs of engineering: In actual engineering applications, a model that can accurately describe the characteristics of ion current is needed, and the parameters of the model must have certain physical meaning and interpretability. The normalized least squares error optimization method can match the obtained model parameters with the actual physical process while meeting the fitting accuracy requirements, providing a reliable foundation for subsequent research and application. For example, in the design and optimization of plasma thrusters, an accurate ion current fitting model can help engineers better understand the working principle of the thruster and thus improve the performance of the thruster.

[0060] Furthermore, the ion current detected by the first probe The relationship diagram with time is as follows Figure 4 For example, we first need to determine the time integration interval based on the probe detection signal window. This interval is the probe collection ion current time window to ensure that all ion currents passing through can be collected within this time period. Based on the first probe measurement data, this example is , is the error for each probe, determined by calculating the difference between the ion current detected by each probe and the ion current calculated by the model.

[0061] Furthermore, appropriate initial values ​​of the model parameters are set. According to the magnitude of experimental measurement data, the initial values ​​of the average velocity, thermal diffusion velocity, cone expansion vertex position, generation time, and initial surface charge density multiplied by the effective probe collection area are set.

[0062] Further, parameter fitting is performed. An optimization algorithm (such as Levenberg-Marquardt nonlinear least squares method, Newton method, gradient descent method, etc.) is used to iteratively solve the model parameters of formula (4), with the goal of minimizing the error between the current signal calculated by the model and the current signal measured experimentally, which is generally Stop iterative solution so that the ion current calculated by the model can better fit the ion current data obtained from experimental measurements.

[0063] In this way, the optimal pulsed electromagnetic thruster plume characteristic parameters can be obtained. The optimal pulsed electromagnetic thruster plume characteristic parameters include the average velocity of each ion group, the thermal diffusion velocity, the position of the cone expansion apex, the initial moment of plume plasma generation, and the surface charge density multiplied by the effective probe collection area.

[0064] Note: The following is a brief description of the algorithm: Taking the simple gradient descent method as an example, the implementation steps are as follows: 1. Parameter initialization: Assign initial values ​​to the parameters to be adjusted in the model, such as the axial average velocity of the ion group, axial thermal velocity, lateral extension vertex distance, initial time, and the product of unit area charge and effective collection area. These initial values ​​can be based on experience, previous experimental results or random settings.

[0065] 2. Calculate the error gradient: According to the current parameter value, calculate the partial derivative of the normalized least squares error with respect to each parameter to obtain the error gradient. In the ion current curve fitting, it is necessary to obtain the expressions of these partial derivatives through derivative operations based on the ion current model formula.

[0066] 3. Update parameters: According to the rule of gradient descent, use the learning rate α to adjust the parameter value. The parameter update formula is the updated parameter value. The learning rate controls the step size of each parameter update, and its value is critical. If it is too large, it may cause excessive parameter updates, miss the optimal solution, or even increase the error; if it is too small, it will slow down the convergence speed and increase the calculation time.

[0067] 4. Iterative optimization: Repeat steps 2 and 3, continuously calculate the error gradient and update the parameters until the stopping condition is met. The stopping condition can be that the error change is less than a certain threshold, indicating that the error has converged; or the parameter change is less than a certain threshold, which means that the parameter is close to the optimal value; or it can be that the maximum number of iterations set in advance is reached. In practical applications, variants of gradient descent methods such as stochastic gradient descent (SGD) and mini-batch gradient descent (Mini-Batch GD) can also be used. Each time they update the parameters, they do not calculate the gradient based on all the data, but based on a randomly selected sample (SGD) or a small batch of samples (Mini-Batch GD), which can speed up the calculation and reduce memory usage.

[0068] 3. Model Complexity In order to avoid overfitting, by selecting an appropriate model complexity, the amount of calculation and model complexity can be reduced while ensuring the accuracy of the model, thereby improving the practicality of the model. Figure 5 As shown, according to the discharge current oscillation waveform, corresponding to the three discharge current peaks, three types of ion groups are generated, so the maximum number of ion groups is set to 3, and the initial positions of all ion groups are set to the thruster exit position.

[0069] like Figures 1 to 6 In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods: The pulsed plasma thruster is used as the embodiment body. The thruster is a thruster using parallel copper electrodes, with a channel size of 4.5 cm (length) × 1.5 cm (height) × 1 cm (width), and a polytetrafluoroethylene ablation block with a thickness of 15 mm. =4.5cm.

[0070] Debug and calibrate the discharge current detection system and plasma diagnostic system to ensure that they can work properly and accurately measure the discharge current and plasma current signals.

[0071] Connect data acquisition and processing systems to ensure real-time data transmission and storage.

[0072] 1. Parameter settings Set the working parameters of the pulsed plasma thruster, including the capacitance of the capacitor bank, the initial discharge voltage, the discharge frequency, etc. The capacitance value of the capacitor is 6 μF , the capacitor charging voltage is 1000V and the discharge frequency is set to 1Hz.

[0073] The parameters of the Langmuir probe were set, such as the diameter, length, and tip shape of the probe, and the bias voltage was set to -50 V to ensure that the probe worked under ion saturation.

[0074] 2. Experimental Measurement Depend on Figure 5 As shown, discharge current measurement - there are three main discharge peaks in the pulsed plasma thruster discharge current, and a main type of ion group will be generated corresponding to each peak. Therefore, it is assumed that three main ion groups are generated in the discharge with different plasma densities and temperatures.

[0075] 3. Plasma Measurement In the embodiment, it is arranged along the axial centerline of the propeller, see Figure 2 , three Langmuir probes, with axial points of 8, 12, and 16 cm probes and a slight lateral offset of about 0.5 mm to avoid obstruction.

[0076] 4. Data Processing and Analysis 1. Data preprocessing Furthermore, the collected voltage and plasma current signals are preliminarily processed, including noise removal, filtering and amplification, to improve the quality of the signals.

[0077] Furthermore, the integrity and accuracy of the signal are checked, and abnormal data and interference signals are eliminated to ensure the reliability of subsequent analysis.

[0078] 2. Model Fitting Figure 6 As shown in the figure, the ion current collected by a probe is fitted and decomposed into three different ion group currents (IG1 IG 2 IG 3 ).

[0079] Furthermore, appropriate initial values ​​of model parameters are selected. According to the magnitude of experimental measurement data, the initial values ​​of average velocity, thermal diffusion velocity, cone expansion vertex position, generation time, and initial surface charge density multiplied by the effective probe collection area are set.

[0080] Furthermore, the optimization algorithm is used to iteratively solve the model parameters. By continuously adjusting the parameter values, the error between the current signal calculated by the model and the current signal measured experimentally is minimized to achieve , stop iterative solution, and get the best model parameter value. And the ion current collected by a certain probe can be decomposed into the superposition of three different ion groups, such as Figure 6 shown.

[0081] 5. Results Analysis According to the fitted ion group parameters, the average velocity, thermal diffusion, cone expansion vertex position and generation time of each ion group are analyzed. The characteristic differences between different ion groups can be compared to understand the structure and movement law of ion groups. On this basis, the following analysis is further carried out: 1. Analysis of plume plasma characteristics The overall characteristics of the pulsed plasma thruster plume plasma are obtained by comprehensively considering the characteristics of the ion group. The variation of the plume plasma characteristics with the pulsed electromagnetic thruster operating parameters (such as capacitor bank capacitance, discharge initial voltage, discharge frequency, etc.) is explored, and the plume plasma characteristics under different experimental conditions are compared.

[0082] 2. Trend analysis By analyzing the changing trends of ion group parameters and plume plasma characteristics with capacitor capacitance and initial discharge voltage, and constructing a mathematical model to describe the relationship between these parameters, trend analysis can provide guidance for the design and optimization of pulsed plasma thrusters, helping engineers optimize operating parameters and improve thruster performance and efficiency.

[0083] 3. Model support By introducing the truncated Maxwell charge distribution function, the total ion current density model proposed in the present invention is not only simple and practical, but also can effectively describe the motion behavior of ions under the action of electric and magnetic fields. It also takes into account the thermal motion and spatial distribution characteristics of ions, with relatively low calculation cost, and is easy to apply in practical engineering. Therefore, this model provides more reliable theoretical support for the design, optimization and performance evaluation of pulsed plasma thrusters.

[0084] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A pulse electromagnetic thruster plume characteristics analysis system, characterized in that: It includes a vacuum chamber, a current monitoring system, a multi-probe data acquisition device, an ion current measurement circuit and a data acquisition and processing system, among which: The vacuum chamber is used to provide a space-simulated working environment for the pulsed electromagnetic thruster; The current monitoring system is arranged in the vacuum chamber and is used to monitor the main discharge current waveform of the pulse electromagnetic thruster in real time; The multi-probe data acquisition device is arranged in the vacuum chamber and is used to collect the saturated ion current of the pulsed electromagnetic thruster plume plasma and output it as a voltage signal; The ion current measurement circuit is connected to the multi-probe data acquisition device and is used to convert the voltage signal output by the multi-probe data acquisition device into an ion current signal; The data acquisition and processing system is respectively connected to the multi-probe data acquisition device and the ion current measurement circuit, and is used to collect the voltage signal output by the multi-probe data acquisition device and the ion current signal converted by the ion current measurement circuit, convert the ion current signal into a digital signal, and is responsible for fitting the ion current signal to analyze the plume characteristics of the pulsed electromagnetic thruster with multiple ion groups superimposed.

2. The pulse electromagnetic thruster plume characteristics analysis system according to claim 1, characterized in that: The multi-probe data acquisition device comprises a probe body, wherein the probe body is based on a single Langmuir probe, and the Langmuir probe is a tungsten wire with a diameter of 50 μm-200 μm.

3. The pulsed electromagnetic thruster plume characteristics analysis system according to claim 2, characterized in that: The pulse electromagnetic thruster plume characteristic analysis system also includes an insulating support, which is processed into a tubular or columnar shape, and the Langmuir single probe is sleeved in the insulating support, and the length of the insulating support is 3 mm to 6 mm.

4. The pulse electromagnetic thruster plume characteristics analysis system according to claim 3, characterized in that: The multi-probe data acquisition device comprises a plurality of probes arranged at equal intervals along the spatial angular axis of the pulsed electromagnetic thruster plume, and the tips of the probes are perpendicular to the plasma ejection direction.

5. The pulse electromagnetic thruster plume characteristics analysis system according to claim 4, characterized in that: The pulsed electromagnetic thruster plume characteristics analysis system also includes a bias power supply, which is connected to the multi-probe data acquisition device and is used to load a negative bias voltage to the ground on the probe to form an ion sheath on the probe surface, repel electrons and receive ions, thereby collecting ion saturation current.

6. The pulse electromagnetic thruster plume characteristics analysis system according to claim 5, characterized in that: The pulse electromagnetic thruster plume characteristic analysis system further comprises a protective cover, which is arranged outside the probe.

7. The pulse electromagnetic thruster plume characteristics analysis system according to claim 6, characterized in that: The data acquisition and processing system comprises a data acquisition card, which is connected to the ion current measurement circuit and is used for converting the ion current signal output by the ion current measurement circuit into a digital signal.

8. A pulse electromagnetic thruster plume characteristics analysis method, applied to the pulse electromagnetic thruster plume characteristics analysis method as claimed in any one of claims 1 to 7, characterized in that: The pulse electromagnetic thruster plume characteristics analysis method comprises the following steps: Construct a multi-ion group superposition distribution model; As the plasma is ejected from the thruster nozzle to form a plume, the plasma sheet expands in the form of a cone in the horizontal direction. According to the multi-ion group superposition distribution model, the current density generated by the charge amount passing through the unit area of ​​the i-th ion group is obtained. ; According to the current density , add the current densities of the n ion groups superimposed to obtain the total ion current density ; According to the total ion current density , get the kth Langmuir probe position and process the theoretical ion current ; Get the k Experimental measurement of ionic current at a Langmuir probe , the optimization objective is used to perform parameter fitting so that the theoretical ion current Fitting the experimentally measured ion currents , obtain the optimal pulsed electromagnetic thruster plume characteristic parameters.

9. The method for analyzing the plume characteristics of a pulsed electromagnetic thruster according to claim 8, characterized in that: In the step of constructing a multi-ion group superposition distribution model, each ion group distribution in the multi-ion group superposition distribution model is independently characterized as shown in the following formula: in, x is the axial position of the ion group during its axial motion, is the axial velocity of the ion group, describing the speed of the ions moving in the axial direction of the thruster; is the average axial velocity of the ion group, representing the average movement speed of the ion group; is the axial thermal velocity of the ion group, reflecting the distribution of thermal motion velocity of the ion group in the axial direction; It is the charge per unit area of ​​the ion group, which represents the charge density of the ion group; It's Dirac Function, used to represent the spatial localization of the ion group; is the thruster nozzle position, is the time it takes for the ion group to move to the thruster nozzle position, It is The distribution function of an ion group.

10. The method for analyzing the plume characteristics of a pulsed electromagnetic thruster according to claim 8, wherein: According to the current density , add the current densities of the n ion groups superimposed to obtain the total ion current density j ( x , t ) step, the current density for: The total ion current density j ( x , t )for: in, is the time difference, For ion clusters Location, At time, it moves from the thruster exit position to The speed of the position; For ion clusters Location, At time , the speed from the thruster exit position to the x position; is the current density expression, is the axial position of the ion group during axial motion, is the thruster nozzle position, The ion group moves to The time at the location, is the time it takes for the ion group to move to the thruster exit position, , ; is the number of ion group superpositions.

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