A dual-channel transient plasma parameter measurement system

Abstract

This invention relates to the field of plasma detection technology, and particularly to a dual-channel transient plasma parameter measurement system. The dual-channel transient plasma parameter measurement system includes an axial Faraday probe and multiple circumferentially distributed energy level selection probes. The Faraday probe is used to measure the total ion current. Each energy level selection probe includes, radially from the inside out, an unconnected inner shield, a collecting electrode, and an outer shield. A positive bias voltage is applied to the inner and outer shields. The collecting electrode is connected to a positive bias voltage with the same bias voltage value as its two external shields. The positive bias voltages connected to the multiple energy level selection probes along the axial direction increase sequentially in an arithmetic sequence. This invention provides a composite probe system that integrates multiple measurement capabilities and offers a faster response.

Description

Technical Field

[0001] This invention relates to the field of plasma detection technology, and in particular to a dual-channel transient plasma parameter measurement system. Background Technology

[0002] Plasma probes can be widely used in plume studies and rapid acquisition of ion parameters under high vacuum conditions such as ion thrusters, Hall thrusters, and magnetohydrodynamic thrusters. They are particularly suitable for ion flow measurement and energy spectrum analysis under pulsed discharge, unsteady excitation, or high-frequency disturbance environments.

[0003] While existing technologies can measure ion current density or energy distribution separately, they cannot simultaneously meet the requirements of "fast transient response" and "strong energy spectrum integrity". Especially under pulsed, modulated or unstable excitation conditions in electric thruster operation, single probe structures suffer from serious problems such as data lag, distortion and difficulty in synchronous comparison. There is an urgent need for a composite probe system that integrates multiple measurement capabilities and has a faster response. Summary of the Invention

[0004] This invention provides a dual-channel transient plasma parameter measurement system, which offers a structurally integrated, rapidly responding, and highly consistent dual-channel transient plasma parameter measurement system. It can simultaneously acquire ion current density and energy distribution under pulsed or unsteady-state discharge conditions, and is particularly suitable for real-time diagnosis and data acquisition during high-frequency excitation, transient plumes, and the dynamic operation of electric thrusters.

[0005] This invention provides a dual-channel transient plasma parameter measurement system, comprising an axial Faraday probe and multiple circumferentially distributed energy level selection probes. The Faraday probe is used to measure the total ion current. Each energy level selection probe includes, from the inside to the outside, an unconnected inner shield, a collecting electrode, and an outer shield. The inner and outer shields are positively biased. The collecting electrode is connected to a positive bias with the same bias value as the two external shields. The positive biases of the multiple energy level selection probes connected axially increase sequentially in an arithmetic sequence.

[0006] In one possible design, the Faraday probe includes an inner core and a shielding barrel that is sleeved outside the inner core but not in contact with it. The inner core and the shielding barrel are respectively connected to two negative bias voltages of the same voltage. An electron retardation gate is disposed outside the circumferentially selected energy level probe. The electron retardation gate is connected to the negative bias voltage. The negative bias voltage applied by the electron retardation gate and the Faraday probe is used to shield electrons.

[0007] In one possible design, the inner core and the sleeve are biased at -30V.

[0008] In one possible design, the collector is connected to a high-speed differential acquisition circuit to acquire the current values ​​received by the different energy level selection probes.

[0009] In one possible design, there are 106 independent bias voltages, ranging from +50V to +1100V, with each group of independent bias voltages spaced 10V apart. Each independent bias voltage has one bias voltage connected to the inner shield and the outer shield of the energy level selection probe, and another bias voltage connected to the collector. The independent bias voltages and the energy level selection probes correspond one-to-one.

[0010] In one possible design, the method of using the system includes: After power-on, a bias voltage is applied to the energy level selection probe; When the plasma plume is injected to the front end of the system, the probes at different energy levels collect ions and output transient current changes through a differential circuit; Meanwhile, the Faraday probe measures the total current in real time; The transient energy spectrum is determined based on the current collected by multiple energy level selection probes and the Faraday probe to analyze the transient effects of energy drift or current density fluctuation during pulse discharge.

[0011] In one possible design, the transient energy spectrum is obtained through a transient ion distribution function, which is: IEDF Sk (t) = { J sta …, J k J k+1 ,…, J end} Among them, IEDF Sk (t) is the transient ion distribution function, J k J is the current density at the probe for the energy level selection. sta J is the current density of the energy level selection probe to apply the minimum bias voltage. end The current density of the probe is selected to apply the maximum bias voltage to the energy level.

[0012] In one possible design, the current density at the energy level selection probe is calculated using the following formula: J k =δI k / S k Where, δI k = I k+1 - I k I k S is the current at the collector electrode. k The area of ​​the collecting electrode is denoted as .

[0013] In one possible design, after obtaining the transient ion distribution function, it is calibrated using the current density measured by a Faraday probe to obtain the calibrated transient ion distribution function IEDF(t): IEDF(t) = IEDF Sk (t)*J f / ΣJ k Among them, J f The surface ion current density of the Faraday probe is given.

[0014] In one possible design, the ion current density on the Faraday probe surface is calculated using the following formula: J f = I f / S f Among them, I f S is the current sampled by the core of the Faraday probe. f It is the area of ​​the core of the Faraday probe.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Simultaneous measurement of two parameters results in more consistent data: The integrated design of the Faraday probe and RPA probe enables simultaneous measurement of ion current density and energy distribution, avoiding the spatial error and time asynchrony problems caused by traditional dual-probe alternating measurements.

[0016] 2. Faster measurement response, adaptable to transient scenarios: By replacing RPA voltage scanning with a multi-channel static bias array and in conjunction with a high-speed differential circuit, the system can acquire energy spectrum changes at the microsecond level, making it suitable for transient conditions such as pulse discharge, unsteady plume, and electric propulsion modulation.

[0017] 3. Strong anti-interference, compact structure, and easy integration: Differential acquisition effectively suppresses electromagnetic interference and improves measurement stability. The entire probe structure is small in size and highly modular, making it suitable for integration into experimental platforms or small spaceborne devices, and possesses good engineering applicability.

[0018] Compared with traditional Faraday or RPA probes, this invention is not only more comprehensive in function and faster in measurement, but also has better data consistency and system robustness, which can significantly improve the accuracy and efficiency of plasma plume diagnosis. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a system cross-sectional structure provided in an embodiment of the present invention; Figure 2 This is a system assembly diagram provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of probe distribution on a system collection board provided in an embodiment of the present invention; Figure 4 This is a circuit diagram provided in an embodiment of the present invention.

[0021] In the figure, 1. Electronic retardation grid; 2. Collecting plate; 3. Ceramic mounting base; 4. Limiting baffle; 5. Outer shell; 6. Base plate; 7. Shielded cable; 11. Inner core; 12. Shielding barrel; 21-Inner shielding electrode; 22-Collecting electrode; 23-Outer shielding electrode. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] In the description of the embodiments of the present invention, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or stated, the term "multiple" refers to two or more; the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0024] In this specification, it should be understood that the directional terms such as "upper" and "lower" used in the description of the embodiments of the present invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of the present invention. Furthermore, in the context, it should also be understood that when it is mentioned that one element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0025] As mentioned above, the prior art has the following drawbacks: Background Technology 1: Traditional Faraday Probe A Faraday probe is a basic device used to measure the total ion current density in plasma. Its typical structure consists of a metal collecting electrode, an insulating shell, and a bias circuit. Its working principle is as follows: Collect the ion flow in front of the probe; The current value is read by a current measurement system, and then the current density is calculated.

[0026] This probe has a simple structure and fast response speed, making it suitable for measuring the flow intensity distribution in steady-state or quasi-steady-state ion plumes. It is widely used in laboratory and ground-based vacuum testing systems.

[0027] shortcoming: Unable to provide energy distribution information for ions; It is not sensitive to changes in ion characteristics under pulse / transient discharge; Sampling locality bias exists in spatially non-uniform plumes.

[0028] In summary, Faraday probes can only measure ion current density and cannot provide information on the energy distribution of ions. This limitation stems from the fact that their structure is essentially a current collector, lacking energy selectivity; ions of all energies are collected simultaneously, making energy resolution impossible.

[0029] Therefore, when the plasma plume contains multiple energy components (such as bimodal distribution and tail-accelerated ions), this probe cannot distinguish the ion energy level structure, leading to distorted or insufficient measurement results. This has significant limitations for scenarios such as thruster plume diagnosis and ion acceleration process analysis.

[0030] Background Technology 2: Retarding Potential Analyzer (RPA) RPA probes consist of multi-stage electrodes (typically shielding grids, meshes, and collecting electrodes). By adjusting the bias voltage, they intercept ions of different energies, thereby reconstructing the ion energy spectrum. The principle is as follows: Set the scan voltage; Integrate the collected current under different voltages; Inverse the ion energy distribution function (IEDF).

[0031] shortcoming: Slow response: Each data point corresponds to a scanning voltage, which usually takes tens to hundreds of milliseconds, making it difficult to capture sub-millisecond or even microsecond-level changes in plasma parameters; Asynchronous error: Since the scanning period may differ from the plume fluctuation period, phase error or time drift can be easily introduced, resulting in an inaccurate energy spectrum after inversion; High circuit complexity: The multi-stage bias control circuit has high requirements for anti-interference design and is prone to potential instability in high-frequency plumes; Unable to output flow density information simultaneously: RPA focuses on energy analysis and lacks direct feedback on total flow intensity.

[0032] In summary, although existing technologies can measure ion current density or energy distribution separately, they cannot simultaneously meet the requirements of "fast transient response" and "strong energy spectrum integrity". Especially under the conditions of pulsed, modulated or unstable excitation of electric thrusters, single probe structures have serious problems such as data lag, distortion and difficulty in synchronous comparison. There is an urgent need for a composite probe system that integrates multiple measurement capabilities and has a faster response.

[0033] Furthermore, single-probe measurement schemes suffer from data coupling and spatial displacement errors. To obtain ion current density and energy spectrum simultaneously, many laboratories use a "dual-probe alternation measurement" method (i.e., measuring the current first at the same location, then measuring the energy spectrum). However, this method has the following drawbacks: Misaligned measurement points cannot guarantee that the two probes are collecting the same ion plume; The state of the ion source may change between two measurements, making the data incomparable. It increases mechanical complexity and testing costs, making it difficult to integrate into compact systems.

[0034] In summary, existing Faraday probes and RPA probes have significant shortcomings in terms of functionality, timeliness, and data consistency, making it difficult to meet the requirements for high-resolution and synchronous measurements in pulsed excitation, modulated discharge, or unsteady plasma systems, thus limiting their application in next-generation electric propulsion plume diagnostics.

[0035] To solve the above problem, please refer to Figures 1 to 4This invention provides a dual-channel transient plasma parameter measurement system, including an axial Faraday probe and multiple circumferentially distributed energy level selection probes. The Faraday probe is used to measure the total ion current. Each energy level selection probe includes, from the inside to the outside, an unconnected inner shield 21, a collector 22, and an outer shield 23. The inner shield 21 and the outer shield 23 are positively biased. The collector 22 is connected to a positive bias with the same bias value as the two outer shields. The positive biases of the multiple energy level selection probes connected along the axial direction increase sequentially in an arithmetic sequence.

[0036] This invention innovatively integrates a Faraday probe and an electrostatic energy analyzer (RPA) composed of energy level-selective probes into a single probe device, enabling simultaneous measurement of ion current density and energy distribution. This structure effectively avoids the measurement position inconsistencies and time deviations present in traditional multi-probe systems, significantly improving the spatial consistency and data reliability of measurements. This invention uses a fixed bias array instead of the voltage scanning method of traditional RPAs, and introduces a differential acquisition circuit. Using the Faraday channel as a reference channel, it performs parallel differential processing on transient current signals at multiple energy levels, thereby significantly improving the system's temporal resolution and response speed, meeting the requirements for real-time energy spectrum reconstruction of microsecond-level dynamic plumes.

[0037] Specifically, a positive voltage with the same potential is applied to both the inner and outer shielding layers to selectively sieve the kinetic energy of the incident ions. Only when the ion kinetic energy is higher than the potential barrier formed by the electric field of the shielding layer can the ion penetrate the shielding layer and finally reach the collector 22. The ion current density within the corresponding energy range can be obtained by measuring the collection current. The Faraday probe can measure the total current density, and by combining the ion current densities of different energy ranges, a current density energy spectrum can be constructed instantaneously. A high-speed differential acquisition circuit is configured to compare the current of each energy level channel with the Faraday reference signal and output the differential current signal in real time. A fixed bias array structure is used instead of the traditional RPA scanning method; and the time resolution (microsecond level) is significantly improved through parallel differential signal acquisition technology.

[0038] In this embodiment, the Faraday probe and the energy level selection probe are fixed on the collection plate 2, the collection plate 2 is mounted on the ceramic mounting base 3, the bottom of the ceramic mounting base 3 is provided with a limiting baffle 4, the outer shell 5 is covered, the bottom of the shell 5 is connected to the base plate 6, and the shielded cable 7 is connected on the system axis.

[0039] This system has a compact structure and clear modules, and can be directly integrated into vacuum experimental platforms, micro-miniature electric thruster testing systems, or on-orbit diagnostic equipment. It is also compatible with common controllers (such as STM32, FPGA, etc.), and has good anti-interference capabilities, data consistency, and adaptability to complex electromagnetic environments. It is suitable for high-precision measurement tasks under unsteady-state, modulated, or pulsed discharge plasma conditions.

[0040] In some embodiments of the present invention, the Faraday probe includes an inner core 11 and a shielding barrel 12 that is sleeved outside the inner core 11 but does not contact it. The inner core 11 and the shielding barrel 12 are respectively connected to two negative bias voltages of the same voltage. An electron retardation gate 1 is provided outside the circumferential energy level selection probe. The electron retardation gate 1 is connected to the negative bias voltage. The electron retardation gate 1 and the negative bias voltage applied by the Faraday probe are used to shield electrons.

[0041] In some embodiments of the present invention, the bias voltage applied to the inner core 11 and the sleeve is -30V.

[0042] In some embodiments of the present invention, the collector 22 is connected to a high-speed differential acquisition circuit to acquire the current values ​​received by the different energy level selection probes.

[0043] In some embodiments of the present invention, 106 independent bias voltages are included, ranging from +50V to +1100V, with a 10V interval between each group of independent bias voltages. Each independent bias voltage is connected to the inner shield 21 and outer shield 23 of the energy level selection probe, and the other bias voltage is connected to the collector 22. The independent bias voltages and the energy level selection probes correspond one-to-one.

[0044] In some embodiments of the present invention, the method of using the system includes: After power-on, a bias voltage is applied to the energy level selection probe; When the plasma plume is injected to the front end of the system, different energy level selective probes collect ions and output transient current changes through differential circuits; Meanwhile, the Faraday probe measures the total current in real time; The transient energy spectrum is determined by collecting currents from multiple energy level selection probes and Faraday probes to analyze the transient effects of energy drift or current density fluctuations during pulsed discharge.

[0045] In some embodiments of the present invention, the transient energy spectrum is obtained through a transient ion distribution function, which is: IEDF Sk (t) = { J sta …, J k J k+1 ,…, J end} Among them, IEDF Sk (t) is the transient ion distribution function, J k To select the current density at the probe for the energy level, J sta To select the current density of the probe for the energy level to which the minimum bias voltage is applied, J end The current density of the probe is selected to apply the maximum bias voltage to the energy level.

[0046] In some embodiments of the present invention, the current density at the energy level selection probe is calculated using the following formula: J k =δI k / S k Where, δI k = I k+1 - I k I k To collect the current at electrode 22, S k To collect the area of ​​pole 22.

[0047] In some embodiments of the present invention, after obtaining the transient ion distribution function, it is calibrated using the current density measured by a Faraday probe to obtain the calibrated transient ion distribution function IEDF(t): IEDF(t) = IEDF Sk (t)*J f / ΣJ k Among them, J f The surface ion current density of the Faraday probe is given.

[0048] In some embodiments of the present invention, the surface ion current density of the Faraday probe is calculated using the following formula: J f = I f / S f Among them, I f The current S collected by the core 11 of the Faraday probe f It is the area of ​​the Faraday probe core 11.

[0049] The specific theoretical process is as follows: A Faraday probe, comprising an inner core 11 and a shielding barrel 12, is positioned at the center of the probe. The bias voltage of the probe inner core 11 is U. f The current in the inner core 11 is measured as If. The shielding barrel 12 is connected to the shielding circuit, and the bias voltage is U. f ', and U f = U f The density of the ion current at the probe surface was calculated to be: J f = I f / S f S f It is the area of ​​the Faraday probe core 11 The Sk electrode consists of three parts: an inner shield 21, a collector 22, and an outer shield 23. The bias voltage of the collector 22 is U. k Measure the current I within the collector 22k The inner shield 21 and the outer shield 23 are connected to the shielding circuit, and the bias voltage is U. k ', and U k = U k '); Similarly, at adjacent electrodes S k+1 The bias voltage of collector 22 is U k+1 Measure the current I within the collector 22 k+1 The inner shield 21 and the outer shield 23 are connected to the shielding circuit, and the bias voltage is U. k+1 ', and U k+1 = U k+1 '); The voltage difference between adjacent electrodes is dU = U k+1 - U k Calculate the current difference δI between adjacent electrodes. k = I k+1 -I k The calculated ion current density at the probe surface is: J k =δI k / S k At time t, all S k Electrode (S) sta ~ S end The collected current density J f (t) is integrated (shown as sta=5, end=110, voltage resolution 10V), and the transient ion energy distribution function IEDF can be obtained. Sk (t): IEDF Sk (t) = { J sta …, J k J k+1 ,…, J end} The ion energy distribution function at time t is normalized and calibrated using the current density measured by a Faraday probe to obtain the transient ion energy distribution function IEDF. IEDF(t) = IEDF Sk (t)*J f / ΣJ k .

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-channel transient plasma parameter measurement system, characterized in that, It includes an axial Faraday probe and multiple circumferentially distributed energy level selection probes. The Faraday probe is used to measure the total current of ions. Each energy level selection probe includes, from the inside to the outside, an unconnected inner shield, a collector, and an outer shield. The inner and outer shields are positively biased. The collector is connected to a positive bias with the same bias value as the two outer shields. The positive biases of the multiple energy level selection probes connected along the axial direction increase sequentially in an arithmetic sequence.

2. The system according to claim 1, characterized in that, The Faraday probe includes an inner core and a shielding barrel that is sleeved outside the inner core but not in contact with it. The inner core and the shielding barrel are respectively connected to two negative bias voltages of the same voltage. The circumferentially distributed energy level selection probes are provided with an electron retardation gate outside. The electron retardation gate is connected to a negative bias voltage. The negative bias voltage applied by the electron retardation gate and the Faraday probe is used to shield electrons.

3. The system according to claim 2, characterized in that, The bias voltage applied to the inner core and the shielding barrel is -30V.

4. The system according to claim 1, characterized in that, The collector is connected to a high-speed differential acquisition circuit to acquire the current values ​​received by the probes at different energy levels.

5. The system according to claim 1, characterized in that, It includes 106 independent bias voltages, ranging from +50V to +1100V, with a 10V interval between each group of independent bias voltages. Each independent bias voltage has one bias voltage connected to the inner shield and the outer shield of the energy level selection probe, and the other bias voltage connected to the collector. The independent bias voltages and the energy level selection probes correspond one-to-one.

6. The system according to claim 1, characterized in that, The method of using the system includes: After power-on, a bias voltage is applied to the energy level selection probe; When the plasma plume is injected to the front end of the system, the probes at different energy levels collect ions and output transient current changes through a differential circuit; Meanwhile, the Faraday probe measures the total current in real time; The transient energy spectrum is determined based on the current collected by multiple energy level selection probes and the Faraday probe to analyze the transient effects of energy drift or current density fluctuation during pulse discharge.

7. The system according to claim 6, characterized in that, The transient energy spectrum was obtained through a transient ion distribution function, which is: IEDF Sk (t) = { J sta …, J k J k+1 ,…, J end } Among them, IEDF Sk (t) is the transient ion distribution function, J k J is the current density at the probe for the energy level selection. sta J is the current density of the energy level selection probe to apply the minimum bias voltage. end The current density of the probe is selected to apply the maximum bias voltage to the energy level.

8. The system according to claim 7, characterized in that, The formula for calculating the current density at the energy level selection probe is as follows: J k =δI k / S k Where, δI k = I k+1 - I k I k S is the current at the collector electrode. k The area of ​​the collecting electrode is denoted as .

9. The system according to claim 7, characterized in that, After obtaining the transient ion distribution function, it is calibrated using the current density measured by a Faraday probe to obtain the calibrated transient ion distribution function IEDF(t): IEDF(t) = IEDF Sk (t)*J f / ΣJ k Among them, J f The surface ion current density of the Faraday probe is given.

10. The system according to claim 9, characterized in that, The surface ion current density of the Faraday probe is calculated using the following formula: J f = I f / S f Among them, I f S is the current sampled by the core of the Faraday probe. f It is the area of ​​the core of the Faraday probe.

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