Device and method for measuring time-varying ion energy distribution of Hall thruster

Abstract

The invention discloses a device and a method for measuring time-varying ion energy distribution of a Hall thruster. The invention relates to a device and a method for measuring time-varying ion energy distribution of a Hall thruster. Ionic current samples are collected by using an RPA group and an oscilloscope, a thruster state set is defined, and a training set is created to obtain a mapping relation. By using the data, a current sample is reproduced and an I-V curve is fitted, so that ion energy distribution is obtained. According to the method, the change of ion energy distribution along with time can be accurately measured, the limitation of the prior art is solved, and a more accurate technical means is provided for researching the magnetic shielding Hall thruster.

Description

Technical Field

[0001] The present invention relates to the technical field of electric propulsion, and particularly to an apparatus and method for measuring the time-varying ion energy distribution of a Hall thruster. Background Art

[0002] For decades, Hall thrusters have been the preferred method of electric propulsion in space applications. With power limits continuously breaking new highs, the research on Hall thrusters remains crucial in the field of electric propulsion. In recent years, significant progress has been made in Hall thruster-related technologies, one of which is magnetic shielding technology, a technique used to reduce the erosion of the channel walls caused by high-speed ion bombardment. The erosion of the channel walls is the main life-limiting factor of traditional stationary plasma thruster Hall thrusters. After magnetic shielding is achieved by adjusting the magnetic field inside the Hall thruster channel, the channel erosion rate can be significantly reduced.

[0003] Adding magnetic shielding changes the positions of the ionization region and the acceleration region. In a Hall thruster without magnetic shielding, the acceleration region forms at the channel exit and coincides with the position of the maximum magnetic field. By manipulating the magnetic field lines, the acceleration region of a magnetic shielding Hall thruster is shifted to the outside of the channel. This shift can generate a new ion energy distribution that does not exist in a Hall thruster without magnetic shielding. The changes caused by magnetic shielding, especially the emergence of the new ion distribution, highlight the importance of studying the ion energy distribution.

[0004] There are several diagnostic methods for measuring the time-average of the ion energy in the plume, including laser-induced fluorescence (LIF), E×B probes, and retarding potential analyzers (RPA). However, since Hall thrusters are dynamic systems, it is very important to study the time variation of ion energy. In order to capture the required dynamics in the Hall thruster plume, time-varying diagnostic techniques are needed. Existing methods, such as time-resolved laser-induced fluorescence (TRLIF), have successfully demonstrated their ability to create time-varying ion velocity distributions in Hall thrusters. Although TRLIF provides an effective means to study the time variation of ion velocity or energy, these devices are costly, complex in structure, difficult to transport between different facilities, and not suitable for implementation on spacecraft.

[0005] The Chinese patent authorization document with the publication number CN106596112A owned by Harbin Institute of Technology discloses a method and system for measuring the ion energy distribution of a Hall thruster. Using a multi-grid probe as the measurement tool, by measuring the curve of ion current changing with time at different suppression voltages of the multi-grid probe, obtaining the current values corresponding to different suppression voltages at the same moment, getting the function relationship between current and voltage at this moment, then obtaining the average ion velocity at this moment, and further obtaining the ion energy at this moment; obtaining the ion energy at other moments within the oscillation period at a set time interval, and fitting the ion energies at different moments in chronological order to obtain the curve of the ion energy distribution changing with time within the low-frequency oscillation period.

[0006] Since the above measurement system uses a multi-grid probe, the measurement result of its ion current may be affected by factors such as probe contamination and secondary electron emission, resulting in measurement errors; in addition, its data processing method uses the discharge current as the indication signal, and selects the ion current at the same discharge current in different oscillation periods to fit the I-V curve. This is essentially a physical time alignment, which may bring errors in the results. Given the inconvenience of implementing TRLIF and the measurement errors of the above patent, a device and method that are convenient to implement and can achieve high-precision measurement of ion energy distribution are needed. Summary of the Invention

[0007] The present invention provides a device and method for measuring the time-varying ion energy distribution of a Hall thruster with high implementable measurement accuracy, which can obtain the relationship between the ion energy distribution in the plume and time, and provides a more accurate technical means for studying the ion energy distribution of a magnetic shield Hall thruster and the relationship between discharge oscillation and ion energy distribution.

[0008] The technical solution of the present invention is as follows:

[0009] A device for measuring the time-varying ion energy distribution of a Hall thruster, the device includes:

[0010] A current acquisition module, specifically including an RPA group composed of three RPAs integrated together, used to simultaneously acquire three groups of ion currents and positive bias voltages that constitute the I-V curve; each RPA is composed of four layers of gates. The first layer of gate is suspended to reduce plasma perturbation; the second layer of gate is negatively biased to block the collection of electrons; the third layer of gate is at a positive bias voltage to allow ions with selected energy to pass through; the fourth layer of gate is negatively biased to block the secondary electrons emitted by the collector.

[0011] A current amplification module, specifically including three transimpedance amplifiers TIA, connected between the RPA group and the oscilloscope, used to allow the measurement of high-speed current.

[0012] The data acquisition module specifically includes an oscilloscope, which is used to collect the ion current and thruster discharge current at three sets of positive bias voltages collected by the RPA group, facilitating the subsequent reproduction of the ion current and the fitting of the I-V curves at each representative moment during the entire measurement period.

[0013] A method for measuring the time-varying ion energy distribution of a Hall thruster, the method comprising:

[0014] The data acquisition method no longer obtains the I-V curve by scanning the voltage using a single standard RPA. Instead, it uses an RPA group integrated by three RPAs. At positive bias voltages starting from zero, a certain sample depth is collected, and then the voltage is increased by a certain voltage step, and a certain sample depth or a specific period of time is collected. This process is repeated until the entire voltage range is collected;

[0015] There is a correlation between the selected voltage step and the specific number of voltage increases, specifically including: the number of voltage increases = voltage step × 3. For example, initially, the positive bias voltages of the three RPAs are 0V, 1V, and 2V respectively, and the voltage step is 1V. Then the number of voltage increases for each RPA is 3V. Thus, in the next stage, the positive bias voltages of the three RPAs are 3V, 4V, and 5V respectively;

[0016] For example, the current acquisition rate is 500 MS / s, the positive bias voltage range is 0 - 250V, and the initial positive bias voltages of the RPA group are 0V, 2V, and 4V. When a sample depth of 1.5 MS is collected, the RPA group increases the voltage by a voltage increase of 6V and rises to 6V, 8V, and 10V respectively, and continues to collect a sample depth of 1.5 MS. This process is repeated until the entire voltage range of 0 - 250V is collected.

[0017] The data processing method is a method of using partial prediction to reproduce the whole. In essence, it is a statistical method. This method ensures that the ion currents at the same moment selected for fitting the I-V curve at a certain representative moment all come from the most general thruster state, reducing the measurement error of the ion current caused by the instability of the thruster state. Specifically:

[0018] Define a set, define the state of a Hall thruster during a certain period as a set M, and the elements in it can be specifically embodied as ion current samples at a certain sample depth at a certain moment under a certain positive bias voltage;

[0019] Create a training set and obtain a mapping relationship. Before the formal test starts, first create a training set. The training set covers the ion current samples at each moment under each positive bias voltage, and a diffeomorphism mapping f: M → M is obtained by training on this training set;

[0020] Replicate the sample from the collected sample and the mapping relationship. During formal testing, based on an ion current sample at a certain sample depth at a certain moment under a certain positive bias voltage and the mapping relationship, the current sample under a certain positive bias voltage throughout the entire time period can be replicated;

[0021] Fit the sample points to obtain the I-V curve. According to the required time-varying scale, in the entire current samples under each positive bias voltage, sample points at the same moment are intercepted respectively, and these sample points are recombined to form the I-V curve at this moment;

[0022] Obtain the time-varying ion energy distribution. From the I-V curve at a certain moment, the ion velocity distribution at this moment is obtained, and then the ion energy distribution at this moment is obtained. The ion energy distributions at each moment are integrated to obtain the time-varying ion energy distribution.

[0023] For example, according to the ions in the data acquisition method, the current acquisition rate is 500 MS / s, the sample depth is 1.5 MS, and the positive bias voltage range is 0 - 250 V. It is calculated that the acquisition time corresponding to each sample with a sample depth of 1.5 MS is 3 ms. Since the RPA group is composed of three RPAs integrated, the sample duration for collecting the entire voltage range is 250÷2÷3×3 = 125 ms. Before formal testing, training is first carried out. The positive bias voltage starts from 0 V, with a voltage step of 2 V. At each voltage, several current samples with a duration of 5 s are collected. The acquisition trigger uses the discharge current as the indication signal. When the discharge current reaches a certain value, the acquisition starts. These current samples are used as the elements of the training set, and a diffeomorphic mapping f: M→M is trained. During formal testing, the short current samples with a duration of 3 ms and a sample depth of 1.5 MS under each positive bias voltage obtained from the test are replicated through the mapping relationship to obtain the complete 125-ms long current samples of the history and future relative to this short current sample, that is, 125 long current samples with a duration of 125 ms under the positive bias voltages of 0 V, 2 V, 4 V... 250 V. Sample points at the same moment are taken from these 125 long current samples and fitted to form the I-V curve at this moment. From this, the ion velocity distribution at this moment is obtained, and then the ion energy distribution at this moment is obtained. The ion energy distributions at each moment are integrated to obtain the time-varying ion energy distribution. Description of the Drawings

[0024] Figure 1 Flowchart of the method for measuring time-varying ion energy of the Hall thruster of the present invention

[0025] Figure 2 Schematic diagram of the RPA of the device for measuring time-varying ion energy of the Hall thruster of the present invention

[0026] Figure 3 Installation layout diagram of the device for measuring time-varying ion energy of the Hall thruster of the present invention

[0027] Figure 4 Rear view and upper and lower isometric axonometric views of an RPA group formed by integrating three RPAs

[0028] Figure 5 Schematic diagram of the principle of sample reproduction of the data processing method for the time-varying ion energy method of the Hall thruster of the present invention

[0029] Figure 6 Schematic diagram of the I-V curve and ion energy distribution at a certain moment of the data processing method for the time-varying ion energy of the Hall thruster of the present invention Specific implementation manners

[0030] To enable those skilled in the art to better understand the technical solutions in this patent application of the present invention, the technical solutions in this application will be clearly and completely described below with reference to the accompanying drawings in this application. Obviously, the described implementation manners are only a part of the implementation manners of this application, rather than all of them. All other implementation manners obtained by those of ordinary skill in the art based on the implementation manners in this application without creative efforts should fall within the scope of protection of this application.

[0031] Figure 1 Flowchart of the method for measuring the time-varying ion energy of the Hall thruster of the present invention. As Figure 1 shown, the method includes: a data acquisition method and a data processing method.

[0032] Among them, the data acquisition method specifically includes:

[0033] Using an oscilloscope to collect ion current samples at each positive bias voltage. At a positive bias voltage starting from zero, a certain sample depth is collected, then the voltage is increased by a certain voltage step, and a certain sample depth or a specific period of time is collected, and this process is repeated until the entire voltage range is collected;

[0034] There is a correlation between the selection of the voltage step and the specific number of voltage increases. Specifically, it includes: the number of voltage increases = voltage step × 3. For example, initially, the positive bias voltages of the three RPAs are 0V, 1V, and 2V respectively, and the voltage step is 1V, then the number of voltage increases for each RPA is 3V. Thus, in the next stage, the positive bias voltages of the three RPAs are 3V, 4V, and 5V respectively.

[0035] The data processing method specifically includes:

[0036] Define a set, and define the state of the Hall thruster in a certain period as a set M, and the elements in it can be specifically embodied as ion current samples with a certain sample depth at a certain moment under a certain positive bias voltage;

[0037] Create a training set and obtain the mapping relationship. Before the formal test starts, first create a training set that covers the ion current samples at each moment under various positive bias voltages. Train a diffeomorphic mapping f: M → M on this training set;

[0038] Replicate the sample from the collected sample and the mapping relationship. During the formal test, based on an ion current sample at a certain moment and a certain sample depth under a certain positive bias voltage and the mapping relationship, the current sample under a certain positive bias voltage for the entire time period can be replicated;

[0039] Fit the sample points to obtain the I-V curve. According to the required time-varying scale, intercept the sample points at the same moment from the entire current samples under various positive bias voltages, and recombine these sample points to form the I-V curve at that moment;

[0040] Obtain the time-varying ion energy distribution. Take the negative derivative of the I-V curve at a certain moment to obtain the ion energy distribution at that moment, and integrate the ion energy distributions at each moment to obtain the time-varying ion energy distribution.

[0041] Figure 2 This is the schematic diagram of the RPA principle for the time-varying ion energy measurement device of the Hall thruster of the present invention. Grid1 to Grid4 are four layers of grids respectively. The first layer of grid Grid1 is floating to reduce plasma perturbation; the second layer of grid Grid2 is negatively biased to block the collection of electrons; the third layer of grid Grid3 is positively biased to allow ions with selected energy to pass through; the fourth layer of grid Grid4 is negatively biased to block the secondary electrons emitted by the collector; Collector is the collector electrode used to collect the ion current.

[0042] Figure 3 This is the schematic diagram of the installation layout of the time-varying ion energy measurement device of the Hall thruster of the present invention. 301 represents the Hall thruster, 302 represents the integrated RPA group, 303 represents the central axis of the Hall thruster channel, 304 represents the electrical wiring, 305 represents the transimpedance amplifier TIA, 306 represents the oscilloscope, and 307 represents the vacuum facility.

[0043] Figure 4 This is the RPA group integrated by three RPAs. The upper figure is the rear view, and the lower figure is the upper and lower isometric axonometric view. 401 represents the RPA, 402 represents the integrated storage device, and 403 represents the grid of the RPA.

[0044] Figure 5 This is the schematic diagram of the sample replication principle of the data processing method for the time-varying ion energy method of the Hall thruster of the present invention.

[0045] 501 represents the ion current samples collected by the oscilloscope. a represents the voltage step, which can be flexibly selected according to the resolution required by the time-varying ion energy distribution.

[0046] 502 represents the current samples at 0V positive bias voltage during the entire time period reproduced through the mapping relationship from the ion current samples collected at 0V positive bias voltage. The thick line part represents the actually collected ion current samples, and the thin line part represents the reproduced ion current samples.

[0047] 503 - 505 respectively represent the current samples at 0V positive bias voltage during the entire time period reproduced through the mapping relationship from the ion current samples collected at aV, 2aV, and NaV positive bias voltages. The thick line part represents the actually collected ion current samples, and the thin line part represents the reproduced ion current samples, obtaining a total of N + 1 current samples.

[0048] Figure 6 It is a schematic diagram of the I-V curve and ion energy distribution at a certain moment for the method of processing time-varying ion energy data of the Hall thruster of the present invention.

[0049] The Figure 5 Obtain N + 1 current samples, take the sample points at a certain moment on each current sample, and fit to obtain the I-V curve at this moment, as shown in 601; take the negative value of the derivative of this I-V curve, and the ion energy distribution at this moment can be obtained, as shown in 602, where the vertical axis represents the relative magnitude of the number of ions at each ion energy.

[0050] Only one moment is selected in this article. Take multiple representative moments and repeat the above processing. Fit the ion energy distributions at each moment obtained, and the time-varying ion energy distribution can be obtained.

[0051] The foregoing only illustrates some embodiments of the present invention. Changes, modifications, additions, or variations can be made without departing from the scope and essence of the disclosed embodiments. This embodiment is illustrative rather than restrictive. At the same time, for those of ordinary skill in the art, there will be changes in the specific embodiments and application scopes according to the idea of the present invention. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A device for measuring the time-varying ion energy distribution of a Hall thruster, characterized in that: The device comprises: a current acquisition module, a current amplification module and a data acquisition module.

2. The device for measuring the time-varying ion energy distribution of a Hall thruster according to claim 1, characterized in that: The current acquisition module specifically includes: an RPA group formed by integrating three RPAs.

3. The device for measuring the time-varying ion energy distribution of a Hall thruster according to claim 1, characterized in that: The current measurement module specifically includes: three transimpedance amplifiers TIA.

4. The device for measuring the time-varying ion energy distribution of a Hall thruster according to claim 1, characterized in that: The data acquisition module specifically includes: an oscilloscope.

5. The device for measuring the time-varying ion energy distribution of a Hall thruster according to claim 2, characterized in that: The RPA is composed of four layers of gates. The first layer of gates is suspended to reduce plasma disturbances; the second layer of gates is negatively biased to block the collection of electrons; the third layer of gates is positively biased to allow ions with selected energy to pass through; the fourth layer of gates is negatively biased to block secondary electrons emitted by the collector.

6. The device for measuring the time-varying ion energy distribution of a Hall thruster according to claim 2, characterized in that: The RPA group is integrated through a storage device to simultaneously obtain three sets of ion currents and positive bias voltages constituting IV curves.

7. The device for measuring the time-varying ion energy distribution of a Hall thruster according to claim 3, characterized in that: The transimpedance amplifier allows high-speed current measurement.

8. A method for measuring the time-varying ion energy distribution of a Hall thruster, characterized in that: The method comprises: a data collection method and a data processing method.

9. A method for measuring time-varying ion energy distribution of a Hall thruster according to claim 8, characterized in that: The data acquisition method no longer uses a single standard RPA to obtain an IV curve by scanning voltage, but instead uses an RPA group integrated by three RPAs to collect a certain sample depth under a positive bias voltage starting from zero, obtain the ion current at a certain sample depth, and then increase the voltage at a certain voltage step to collect a certain sample depth. This process is repeated until the entire voltage range is collected.

10. The method for measuring the time-varying ion energy distribution of a Hall thruster according to claim 8, characterized in that: The voltage step selection and the specific boost number are correlated, specifically including: boost number = voltage step × 3. For example, initially, the positive bias voltages of the three RPAs are 0V, 1V, and 2V, respectively, and the voltage step is 1V. Then, the boost number of each RPA is 3V. Therefore, the positive bias voltages of the three RPAs in the next acquisition stage are 3V, 4V, and 5V, respectively.

11. A method for measuring time-varying ion energy distribution of a Hall thruster according to claim 8, characterized in that: The data processing method is essentially a statistical method, which ensures that the ion currents at the same time selected for fitting the IV curve at a representative time are all from the most general thruster state, reducing the ion current measurement error caused by the instability of the thruster state, specifically including: Define a set, define the state of the Hall thruster in a certain period of time as a set M, the elements of which can be concretized as ion current samples at a certain sample depth at a certain moment under a certain positive bias voltage; Create a training set and obtain the mapping relationship. Before the formal test begins, first create a training set that covers the ion current samples at each time under each positive bias voltage. A differential homeomorphism mapping f:M→M is obtained by training on this training set. The sample is reproduced by the collected sample and the mapping relationship. During the formal test, the current sample under a certain positive bias voltage in the entire time period can be reproduced through the ion current sample and mapping relationship at a certain sample depth at a certain moment under a certain positive bias voltage; The IV curve is obtained by fitting the sample points. According to the required time-varying scale, the sample points at the same moment are intercepted in the entire current sample under each positive bias voltage. These sample points are recombined to form the IV curve at that moment. The time-varying ion energy distribution is obtained by taking the negative derivative of the IV curve at a certain moment to obtain the ion energy distribution at that moment, and the ion energy distribution at each moment is integrated to obtain the time-varying ion energy distribution.

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