Method and System for Electron Temperature Deduction from Optical Color inversion of Hollow Cathode Plumes

Abstract

This invention provides a method and system for inverting electron temperature from the optical color of a hollow cathode plume. It is applicable to the inversion and diagnosis of electron temperature distribution in hollow cathodes under on-orbit or other vacuum environments. The method is based on the extraction of optical color data from the hollow cathode plume, the two-dimensional processing of the plume optical color data, the establishment of a gridded optical color correlation database with electron temperature, and the inversion of electron temperature distribution using the gridded optical color. The electron temperature inversion data of this invention shows a trend consistent with Langmuir probe measurement data, with a diagnostic deviation within 30%. Based on this invention, researchers can directly and rapidly diagnose electron temperature distribution characteristics using hollow cathode plume photographs without physical contact.

Description

Technical Field

[0001] This invention relates to the field of computing, and more specifically, to a method and system for inverting electron temperature using the optical color of a hollow cathode plume. Background Technology

[0002] In the field of electric propulsion, hollow cathodes play a crucial role. They utilize thermionic emission mechanisms to greatly reduce the vacuum barrier for solid-state electron emission, not only supplying ignition and neutralization electrons to the thruster, but also being one of the decisive factors in the performance of electric thrusters.

[0003] The electron temperature characteristics inside a hollow cathode are of paramount importance, directly impacting electron emission capability and the cathode's operating mode. They are a crucial physical indicator indispensable for researchers designing and optimizing cathode structures. However, current technological limitations pose significant challenges to the study of electron temperature within hollow cathodes. Due to the small internal space of a hollow cathode, accurately measuring its internal electron temperature distribution using experimental methods is extremely difficult. This undoubtedly presents significant obstacles to in-depth exploration of the internal mechanisms and performance optimization of hollow cathodes, making non-contact diagnostics of the electron temperature inside hollow cathodes a current focus of research.

[0004] To date, among relevant studies, only the literature "Dan G, Kristina J, Ron W, et al. Hollow Cathode Theory and Experiment. I. Plasma Characterization Using Fast Miniature Scanning Probes. Journal of Applied Physics. 2005, 98: 1-9" attempted to diagnose the interior of a hollow cathode using a single Langmuir probe. This is a single fine needle with a diameter of only 0.5 mm. By using the probe to quickly enter and exit the cathode top hole area (wall probe abrasion) combined with voltage rapid scanning technology, the electron temperature inside the cathode can be obtained. However, the literature also mentions that this method can cause some damage to the electron movement inside the cathode, resulting in deviations in the measurement results and making it difficult to accurately reflect the true electron temperature inside the hollow cathode.

[0005] A patent search revealed invention patent CN118067401A, which discloses an on-orbit imaging monitoring device and method for the coupling state of a Hall thruster and cathode. This method first conducts an imaging monitoring experiment on the ground to obtain the electron temperature of the electron bridge in the coupling region of the Hall thruster under various operating conditions. Then, the electron temperature of the electron bridge in the coupling region is measured on a satellite. This measured electron temperature is compared with the electron temperature under the same operating conditions in the ground experiment. If the two are consistent, it indicates that the coupling state of the Hall thruster and cathode is good. If they are inconsistent, the voltage and current of the Hall thruster and the current of the hollow cathode are adjusted until they are consistent. This patent mainly focuses on the monitoring and adjustment methods for the coupling state of the Hall thruster and cathode, but it has shortcomings in the accurate correlation database of plume color and electron temperature, and in the precise capture of the electron temperature location.

[0006] In summary, given the problems of the existing technologies, researching a method and system for electron temperature inversion using the optical color of hollow cathode plumes has become a critical task that urgently needs to be addressed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for inverting electron temperature in hollow cathode plumes based on optical color.

[0008] A method for retrieving electron temperature from the optical color of a hollow cathode plume according to the present invention includes the following steps:

[0009] Step S1: Extract RGB data from the hollow cathode photograph, and perform grid difference fitting on the extracted RGB data to obtain the fitted RGB data;

[0010] Step S2: Perform two-dimensional profile separation on the fitted RGB data to obtain profile RGB data;

[0011] Step S3: Based on the profile RGB data, establish a correlation database of grid radiation color with different electron temperatures according to the atomic energy level transition rules;

[0012] Step S4: Based on the profile RGB data and the associated database, the electron temperature distribution is inverted.

[0013] Preferably, step S1 includes the following sub-steps:

[0014] Step S1.1: Based on the characteristics of the hollow cathode plume of electric propulsion, capture the brightest point of the plume, the cathode-plume boundary, the anode-plume boundary and the cathode central axis, obtain the envelope of the cathode plume region, and extract the RGB data within the envelope of the plume region;

[0015] Step S1.2: Perform differential fitting on the RGB data (based on the photo pixel grid) to the computational domain grid points to obtain the fitted RGB data, which presents a three-dimensional rotating body shape.

[0016] Preferably, in step S1.2, the difference method is area weight difference, that is, the larger the difference ratio, the greater the influence of the difference point on the grid node of the computational domain.

[0017] Preferably, step S2 includes the following sub-steps:

[0018] Step S2.1, first layer peeling: Based on the fitted RGB data, select the monochromatic point at the top of the three-dimensional plume that has not undergone color superposition, and use the monochromatic point to eliminate the color superposition caused by the first layer circle where the monochromatic point is located.

[0019] Step S2.2, second layer peeling: When the second monochrome dot appears at the top of the second layer of the feather, the second monochrome dot is used to eliminate the color superposition caused by the second layer of the feather.

[0020] Step S2.3, and so on, after n peelings, the light and color of the entire photo are processed into monochrome points to obtain the RGB data of the cross-section required for calculation.

[0021] Preferably, the peeling process includes: if a visual line is formed by superimposing the colors of m monochromatic points, the resulting color is (r1, g1, b1), and the color of a single monochromatic point is (r... p g p b p Based on rotational symmetry, among m monochrome points, two points (the visual foreground and background) have the same color as a single monochrome point; these are the actual color data of the peeled circumference. After peeling, the colors of the remaining (m-2) points on the visual line are superimposed, and the colors are denoted as (r2, g2, b2). The calculation formula is as follows:

[0022]

[0023] Preferably, in step S3, the atomic energy level transition rule considers eight transition lines from the high energy level to the low energy level of the Xe atom, specifically 8p→7p, 8p→6s1', 8p→6s1, 6p'→6s1', 6p'→6s1, 7p→6s1, 6s1'→1S0, and 6s1→1S0, with corresponding transition probabilities of 1 / 2500, 1 / 333, 1 / 333, 1 / 1690, 1 / 1450, 1 / 658, 1 / 3.79, and 1 / 3.17, respectively.

[0024] Preferably, in step S3, based on the electron scattering cross section and corresponding electron temperature of the 8 transition lines, and assuming that the background atom number density within the grid is uniformly distributed, the radiation color of the 8 transition lines of the gas discharge corresponding to the Xe central gas at different electron temperatures is obtained, and the radiated colors are superimposed so that any electron temperature within the grid corresponds to a unique grid background gas color, that is, "color" and "temperature" are in one-to-one correspondence, thereby establishing a correlation database.

[0025] Preferably, step S4 includes the following sub-steps:

[0026] Step S4.1: Based on the profile RGB data, use the associated database to determine the specific temperature value of the triggering light color electrons;

[0027] Step S4.2: The difference between the position where the atom undergoes an excited collision and the position where the atom emits a photon is the atomic path corresponding to the lifetime of the excited state. If the background atom number density distribution and velocity distribution are given, the position where the atom emits a photon is subtracted from the atomic path corresponding to the lifetime of the excited state to obtain the position where the atom undergoes an excited collision, which is the position corresponding to the electron temperature.

[0028] Step S4.3: Combine the specific temperature values ​​and the corresponding locations of the electron temperatures to obtain electron temperature distribution data.

[0029] Preferably, in step S4.2, the lifetime of the excited state of an atom is the reciprocal of the transition probability.

[0030] The present invention also provides a system for retrieving electron temperature from the optical color of a hollow cathode plume, comprising:

[0031] Module M1 extracts RGB data from the hollow cathode photograph and performs grid difference fitting on the extracted RGB data to obtain the fitted RGB data.

[0032] Module M2 performs two-dimensional profile separation on the fitted RGB data to obtain profile RGB data;

[0033] Module M3, based on profile RGB data, establishes a database relating grid radiation color to different electron temperatures according to atomic energy level transition rules;

[0034] Module M4, based on profile RGB data and associated database, inverts the electron temperature distribution.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. This invention performs inversion diagnosis on the electron temperature distribution of hollow cathodes in orbit or other vacuum environments. The electron temperature diagnosis data is consistent with the trend of Langmuir probe diagnosis data, and the diagnosis deviation is within 30%.

[0037] 2. This invention provides a non-contact diagnostic method for the internal electron temperature of a hollow cathode, which is beneficial for researchers to carry out the optimization design of cathode performance.

[0038] 3. This invention only requires hollow cathode plume photographs as input data, and can quickly analyze cathode performance data from photographs in literature, on-orbit or ground test photographs, laying the foundation for related image recognition technologies. Attached Figure Description

[0039] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0040] Figure 1 This is a schematic diagram of the two-dimensional cross-sectional separation process in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0042] This invention innovatively proposes a non-contact plume photochromic inversion electron temperature diagnostic method specifically for hollow cathodes. Focusing on cathode plume photographs, it first performs precise color data capture and meticulous data processing. Then, based on the principle of radiation energy level spectral lines and photochromic superposition, it cleverly calculates the atomic de-excitation energy levels corresponding to the photochromic colors, ultimately successfully retrieving the corresponding electron temperature data. This unique method integrates experimental photographic capture with numerical algorithms, belonging to a semi-theoretical, semi-experimental diagnostic mode. It opens up a new and effective technical path for the diagnosis of electron temperature distribution in hollow cathodes, fills the gap in existing technology, and greatly promotes the development and progress of hollow cathode-related research.

[0043] This invention is only applicable to hollow cathodes commonly used in electric propulsion, i.e., cathodes with features such as hollow ventilation, beam effect to increase ionization rate, and thermionic emission mechanism. If it is applied beyond this scope, uncertain diagnostic errors may occur.

[0044] Example 1:

[0045] This embodiment provides a method for retrieving electron temperature from the optical color of a hollow cathode plume, comprising the following steps:

[0046] Step S1: Extract RGB data from the hollow cathode photograph and perform grid difference fitting on the extracted RGB data to obtain the fitted RGB data.

[0047] Specifically, step S1 includes the following sub-steps:

[0048] Step S1.1: Based on the characteristics of the hollow cathode plume of electric propulsion, capture the brightest point of the plume, the cathode-plume boundary, the anode-plume boundary and the cathode central axis to obtain the envelope of the cathode plume region, and extract the RGB data within the envelope of the plume region.

[0049] Step S1.2: Perform differential fitting on the RGB data (based on the photo pixel grid) to the computational domain grid points to obtain the fitted RGB data, which presents a three-dimensional rotating body shape.

[0050] In this embodiment, the difference method is area-weighted difference, that is, the larger the difference ratio, the greater the influence of the difference point on the computational domain grid node.

[0051] Step S2: Perform two-dimensional profile separation on the fitted RGB data to obtain profile RGB data.

[0052] Figure 1 This is a schematic diagram of the two-dimensional cross-sectional separation process in an embodiment of the present invention.

[0053] like Figure 1 As shown, step S2 includes the following sub-steps:

[0054] Step S2.1, first layer peeling: Based on the fitted RGB data, select the monochromatic point at the top of the three-dimensional plume that has not undergone color superposition, and use the monochromatic point to eliminate the color superposition caused by the first layer circle where the monochromatic point is located.

[0055] Step S2.2, second layer peeling: When the second monochrome dot appears at the top of the second layer of the feather, the second monochrome dot is used to eliminate the color superposition caused by the second layer of the feather.

[0056] Step S2.3, and so on, after n peelings, the light and color of the entire photo are processed into monochrome points to obtain the RGB data of the cross-section required for calculation.

[0057] Specifically, the peeling process includes: if a visual line is formed by superimposing the colors of m monochromatic points, the resulting color is (r1, g1, b1), and the color of a single monochromatic point is (r... p g p b p Based on rotational symmetry, among m monochrome points, two points (the visual foreground and background) have the same color as a single monochrome point; these are the actual color data of the peeled circumference. After peeling, the colors of the remaining (m-2) points on the visual line are superimposed, and the colors are denoted as (r2, g2, b2). The calculation formula is as follows:

[0058]

[0059] Step S3: Based on the profile RGB data, establish a database of the correlation between grid radiation color and different electron temperatures according to the atomic energy level transition rules.

[0060] This embodiment takes Xe as an example and considers eight transition lines from the high energy level to the low energy level of the Xe atom, specifically 8p→7p, 8p→6s1', 8p→6s1, 6p'→6s1', 6p'→6s1, 7p→6s1, 6s1'→1S0 and 6s1→1S0, with corresponding transition probabilities of 1 / 2500, 1 / 333, 1 / 333, 1 / 1690, 1 / 1450, 1 / 658, 1 / 3.79 and 1 / 3.17, respectively.

[0061] Specifically, based on the electron scattering cross section and corresponding electron temperature of the eight transition lines, and assuming that the background atom number density within the grid is uniformly distributed, the radiation colors of the eight transition lines of the gas discharge corresponding to the Xe central gas at different electron temperatures are obtained. The radiated colors are then superimposed to ensure that any electron temperature within the grid corresponds to a unique grid background gas color, i.e., "color" and "temperature" are in one-to-one correspondence, thereby establishing a correlation database.

[0062] Step S4: Based on the profile RGB data and the associated database, the electron temperature distribution is inverted.

[0063] Step S4 includes the following sub-steps:

[0064] Step S4.1: Based on the profile RGB data, use the associated database to determine the specific temperature value of the triggering light color electrons.

[0065] Step S4.2: The difference between the position where the atom undergoes an excited collision and the position where the atom emits a photon is the atomic path corresponding to the lifetime of the excited state. Given the background atom number density distribution and velocity distribution, the position where the atom emits a photon is subtracted from the atomic path corresponding to the lifetime of the excited state to obtain the position where the atom undergoes an excited collision, which is the position corresponding to the electron temperature.

[0066] The lifetime of an excited state is the reciprocal of the transition probability.

[0067] Step S4.3: Combine the specific temperature values ​​and the corresponding locations of the electron temperatures to obtain electron temperature distribution data.

[0068] Example 2:

[0069] The present invention also provides a system for inverting electron temperature in a hollow cathode plume. The system for inverting electron temperature in a hollow cathode plume can be implemented by executing the process steps of a method for inverting electron temperature in a hollow cathode plume. That is, those skilled in the art can understand the method for inverting electron temperature in a hollow cathode plume as a preferred embodiment of the system for inverting electron temperature in a hollow cathode plume.

[0070] The system includes:

[0071] Module M1 extracts RGB data from the hollow cathode photograph and performs grid difference fitting on the extracted RGB data to obtain the fitted RGB data.

[0072] Module M2 performs two-dimensional profile separation on the fitted RGB data to obtain profile RGB data;

[0073] Module M3, based on profile RGB data, establishes a database relating grid radiation color to different electron temperatures according to atomic energy level transition rules;

[0074] Module M4, based on profile RGB data and associated database, inverts the electron temperature distribution.

[0075] The spirit and principles of this invention include: extracting RGB color data and performing data difference fitting on cathode plume photographs; then using a peeling method to separate the RGB data of the plume, which is in the form of a three-dimensional rotating body, into two-dimensional profile data; next, establishing a correlation database of grid radiation color with different electron temperatures; and based on this database and the atomic paths corresponding to the atomic excited-state lifetimes, retrieving electron temperature distribution data. All empirical coefficient corrections, cathode material substitutions, gas type substitutions, and formula equivalent transformations made within this spirit and principle should be included within the scope of protection of this invention.

[0076] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for inverting electron temperature in a hollow cathode plume, characterized in that, Includes the following steps: Step S1: Extract RGB data from the hollow cathode photograph, and perform grid difference fitting on the extracted RGB data to obtain the fitted RGB data; Step S2: Perform two-dimensional profile separation on the fitted RGB data to obtain profile RGB data; Step S3: Based on the RGB data of the profile, establish a database of the correlation between grid radiation color and different electron temperatures according to the atomic energy level transition rules; Step S4: Based on the profile RGB data and the associated database, invert the electron temperature distribution; Step S2 includes the following sub-steps: Step S2.1, first layer peeling: Based on the fitted RGB data, select the monochromatic point at the top of the three-dimensional plume that has not undergone color superposition, and use the monochromatic point to eliminate the color superposition caused by the first layer circumference where the monochromatic point is located; Step S2.2, second layer peeling: When the second monochrome dot appears at the top of the second layer of the feather, the second monochrome dot is used to eliminate the color superposition caused by the second layer of the feather. Step S2.3, and so on, after n peelings, the light and color of the entire photo are processed into monochrome points to obtain the RGB data of the cross-section required for calculation; The peeling process includes: if a certain visual line is... m The color is formed by superimposing the colors of several single-color dots, and the resulting color is ( ). r 1, g 1, b 1) The color of a single monochrome dot is ( r p , g p , b p According to rotational symmetry, the m Of the 10 monochrome points, 2 points have the same color as a single monochrome point; this is the actual color data of the peeled circumference. After peeling, the remaining visual line is ( m The colors of -2) points are superimposed, and the color is denoted as ( ). r 2, g 2, b 2) The calculation formula is as follows:

2. The method for electron temperature inversion of optical color in a hollow cathode plume according to claim 1, characterized in that, Step S1 includes the following sub-steps: Step S1.1: Based on the characteristics of the hollow cathode plume of electric propulsion, capture the brightest point of the plume, the cathode-plume boundary, the anode-plume boundary and the cathode central axis, obtain the envelope of the cathode plume region, and extract the RGB data within the envelope of the plume region; Step S1.2: Perform differential fitting on the RGB data to the grid points of the computational domain to obtain the fitted RGB data, which presents a three-dimensional rotating body shape.

3. The method for determining electron temperature in a hollow cathode plume based on optical color inversion according to claim 2, characterized in that, In step S1.2, the difference method is area weight difference, that is, the larger the difference ratio, the greater the influence of the difference point on the computational domain grid node.

4. The method for electron temperature inversion of optical color in a hollow cathode plume according to claim 1, characterized in that, In step S3, the atomic energy level transition rule considers eight transition lines from the high energy level to the low energy level of the Xe atom, specifically 8p→7p, 8p→6s1', 8p→6s1, 6p'→6s1', 6p'→6s1, 7p→6s1, 6s1'→1S0, and 6s1→1S0, with corresponding transition probabilities of 1 / 2500, 1 / 333, 1 / 333, 1 / 1690, 1 / 1450, 1 / 658, 1 / 3.79, and 1 / 3.17, respectively.

5. The method for electron temperature inversion of optical color in a hollow cathode plume according to claim 4, characterized in that, In step S3, based on the electron scattering cross section and corresponding electron temperature of the eight transition lines, and assuming that the background atom number density within the grid is uniformly distributed, the radiation colors of the eight transition lines of the gas discharge corresponding to the Xe central gas at different electron temperatures are obtained. The radiated colors are then superimposed to ensure that any electron temperature within the grid corresponds to a unique grid background gas color, i.e., the color and temperature are in one-to-one correspondence, thereby establishing a correlation database.

6. The method for electron temperature inversion of optical color in a hollow cathode plume according to claim 1, characterized in that, Step S4 includes the following sub-steps: Step S4.1: Based on the RGB profile data, determine the specific temperature value of the triggering light-color electrons using the associated database; Step S4.2: The difference between the position where the atom undergoes an excited collision and the position where the atom emits a photon is the atomic path corresponding to the lifetime of the excited state. Given the background atom number density distribution and velocity distribution, the position where the atom emits a photon is subtracted from the atomic path corresponding to the lifetime of the excited state to obtain the position where the atom undergoes an excited collision, i.e. the position corresponding to the electron temperature. Step S4.3: Combine the specific temperature value and the location corresponding to the electron temperature to obtain electron temperature distribution data.

7. The method for electron temperature inversion of optical color in a hollow cathode plume according to claim 6, characterized in that, In step S4.2, the lifetime of the excited state of the atom is the reciprocal of the transition probability.

8. A system for retrieving electron temperature from a hollow cathode plume, characterized in that, include: Module M1 extracts RGB data from the hollow cathode photograph and performs grid difference fitting on the extracted RGB data to obtain the fitted RGB data. Module M2 performs two-dimensional profile separation on the fitted RGB data to obtain profile RGB data; Module M3, based on the RGB data of the profile, establishes a database relating grid radiation color to different electron temperatures according to the atomic energy level transition rules; Module M4, based on the profile RGB data and the associated database, inverts the electron temperature distribution; The module M2 includes the following sub-steps: Module M2.1, first layer peeling: Based on the fitted RGB data, select the monochromatic point at the top of the three-dimensional plume that has not undergone color superposition, and use the monochromatic point to eliminate the color superposition caused by the first layer circumference where the monochromatic point is located; Module M2.2, second layer peeling: When the second monochrome point appears at the top of the second layer circumference of the plume, the color superposition caused by the second monochrome point is also eliminated. Module M2.3, and so on, after n peeling processes, the light and color of the entire photo are processed into monochrome points to obtain the RGB profile data required for calculation; The peeling process includes: if a certain visual line is... m The color is formed by superimposing the colors of several single-color dots, and the resulting color is ( ). r 1, g 1, b 1) The color of a single monochrome dot is ( r p , g p , b p According to rotational symmetry, the m Of the 10 monochrome points, 2 points have the same color as a single monochrome point; this is the actual color data of the peeled circumference. After peeling, the remaining visual line is ( m The colors of -2) points are superimposed, and the color is denoted as ( ). r 2, g 2, b 2) The calculation formula is as follows:

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