Plasma thrust testing method and device

Abstract

The invention discloses a plasma thrust testing method and device, and the method comprises the steps: carrying out the calibration of a stepped force applied to a target plate, building a thrust-voltage linear model based on a voltage signal fed back by a displacement sensor, applying the instantaneous force of an analog pulse to the target plate, and carrying out the calibration of the thrust-voltage linear model. The dynamic response speed of the displacement sensor is verified, the propeller is triggered to discharge in a vacuum environment, the target plate swings after being impacted by plasma, the axial displacement of the target plate at different moments is obtained by the displacement sensor and converted into voltage signals at corresponding moments, and the voltage signals sent by the displacement sensor are collected based on an oscilloscope. The transient thrust of the plasma is inverted, and a transient thrust-discharge voltage-time curve is obtained through data fitting based on discharge parameters of the propeller at different moments. After step force is applied to the target plate for calibration, transient thrust is inverted through output voltage of the displacement sensor, and high-precision microsecond transient thrust inversion is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric propulsion, and particularly relates to a method and device for testing plasma thrust. Background Art

[0002] A pulsed plasma thruster (PPT) is an electric propulsion device that generates plasma by means of pulsed discharge and accelerates the plasma through electromagnetic force to generate thrust. Its basic working principle is to initiate gas ionization in the discharge channel through a high-voltage pulse to form a high-temperature and high-pressure plasma, and then accelerate and eject the plasma through the action of an electromagnetic field to generate thrust. The pulsed plasma thruster has the characteristics of high efficiency, low thrust, and no need for a large amount of fuel. High efficiency: Compared with traditional chemical thrusters, the pulsed plasma thruster has a higher specific impulse (the ratio of thrust to consumed fuel), making it suitable for long-duration, low-thrust missions. Low thrust: The thrust generated by the pulsed plasma thruster is relatively small, usually applicable to spacecraft orbit correction or attitude control tasks that require fine adjustment. No need for a large amount of fuel: Compared with chemical propulsion, the pulsed plasma thruster uses less gas, so it has lower fuel consumption. Precise control: The pulsed propulsion method makes the generation of thrust more controllable, enabling precise adjustment of the spacecraft's orbit and attitude. The pulsed plasma thruster plays an important role in the fields of orbit correction and attitude control, deep space exploration, and satellite orbit management. In terms of orbit correction and attitude control, the pulsed plasma thruster is often used for the fine adjustment and attitude control of spacecraft, especially important in satellites and space probes. In deep space exploration, due to its high specific impulse and low fuel consumption, the PPT performs excellently in deep space exploration missions, being able to provide continuous small thrust for a long time to help the spacecraft perform orbit transfer. In satellite orbit management, for example, satellites in low Earth orbit (LEO) can use PPT to maintain their orbits or perform orbit decay after the mission is completed. Moreover, the PPT has the advantages of simple structure, small volume, and light weight, and is particularly suitable for attitude control and orbit adjustment tasks of small satellites. Therefore, the pulsed plasma thruster (coaxial gun) has important applications in the fields of space propulsion, material processing, etc.

[0003] The working principle of the pulsed plasma thruster can be divided into several main steps: plasma generation, plasma acceleration, and pulsed ejection. Plasma generation: The thruster is filled with gas (such as xenon or other inert gases), and a high-voltage pulse is applied through a power supply to excite the gas to form plasma (i.e., charged particles). Plasma acceleration: Under the action of an electric field or magnetic field, the electrons and ions in the plasma are accelerated, and their speeds continue to increase. Pulsed ejection: Under the action of a high-voltage pulse, the plasma is instantaneously accelerated and ejected at high speed through the nozzle to generate thrust.

[0004] Coaxial gun discharge pulse plasma thrusters have important applications in the field of space propulsion due to their high specific impulse, simple structure, etc. Their thrust performance directly depends on discharge parameters (voltage, current, gas working medium, etc.). Existing research focuses on plasma characteristic diagnosis. Thrust is essentially a macroscopic manifestation of plasma momentum change, and plasma momentum is directly related to its microscopic parameters (such as density, velocity, temperature, etc.). By measuring these parameters and combining with physical models, the thrust value can be deduced. However, the plasma discharge time is short (in the microsecond to millisecond range) and the thrust is transient, making it difficult to accurately calculate the plasma thrust value through plasma characteristic diagnosis methods. Summary of the Invention

[0005] The present invention provides a plasma thrust test method and device, which can solve the problem in the background technology that it is difficult to accurately calculate the plasma thrust value due to the short plasma discharge time and transient thrust.

[0006] A plasma thrust test method includes: Calibrate by applying a stepped force to the target plate, and based on the voltage signal fed back by the displacement sensor, establish a thrust-voltage linear model; Apply an instantaneous force simulating a pulse to the target plate to verify the dynamic response speed of the displacement sensor; Trigger the thruster discharge in a vacuum environment. After the target plate is impacted by the plasma and swings, the axial displacement of the target plate at different times is acquired by the displacement sensor and converted into a voltage signal corresponding to the time. Based on the oscilloscope collecting the voltage signal sent by the displacement sensor, the transient thrust of the plasma is inversely calculated in combination with the thrust-voltage linear model; Based on the discharge parameters of the thruster at different times and the transient thrust of the plasma, through data fitting, obtain a transient thrust-discharge voltage-time curve to analyze the variation law of the transient thrust.

[0007] Preferably, a push-pull gauge is used to apply the stepped force to the target plate. The stepped force is a known force, and the stepped force uses 0.5N as the unit step size.

[0008] Preferably, the formula of the thrust-voltage linear model is F = k×V + C; In the formula: k is a coefficient; V is the voltage signal fed back by the displacement sensor; C is a constant.

[0009] Preferably, before the displacement sensor acquires the axial displacement of the target plate, an initial zero position needs to be preset. The initial zero position is the distance between the target plate and the displacement sensor.

[0010] Preferably, the distance detected by the displacement sensor between it and the target plate at the current moment is recorded as the current distance. At the current moment, the axial displacement of the target plate is the difference between the initial zero position and the current distance.

[0011] Preferably, the discharge parameters include discharge voltage and discharge current.

[0012] A plasma thrust test device applicable to the plasma thrust test method described above includes: a target plate, the target plate is connected to a suspension support system, and the suspension support system is used to adjust the position of the target plate; On one side of the target plate, there is a displacement sensor for real-time measurement of the axial displacement of the target plate. The displacement sensor is electrically connected to an oscilloscope, and the oscilloscope is used to collect the voltage signal of the displacement sensor.

[0013] Preferably, the target plate is a composite plate structure formed by welding a molybdenum plate and a copper plate.

[0014] Preferably, the suspension support system includes a steel wire rope. One end of the steel wire rope is connected to the target plate, and the other end is connected to a bearing.

[0015] Preferably, the displacement sensor includes a preamplifier. The preamplifier is provided with a probe, and the preamplifier is connected to an extension cable.

[0016] Advantages of the present invention: (1) In the present invention, after calibrating by applying a stepped force to the target plate, the transient thrust is inversely calculated through the output voltage of the displacement sensor, realizing high-precision microsecond-level transient thrust inversion.

[0017] (2) In the present invention, the displacement of the target plate is measured non-contact by the displacement sensor, which can avoid the electromagnetic sensitivity problem of traditional strain gauges. During the measurement process, the height of the target plate 3 and the distance between the displacement sensors 6 can be adjusted, and it can adapt to experiments with different plasma parameters.

[0018] (3) In the present invention, compared with the measurement by the laser interferometry method, the present application can complete the measurement of more accurate transient thrust at a lower cost. During the measurement of transient thrust, the change law of the transient thrust can also be analyzed to evaluate the transient thrust characteristics of plasma discharge. Description of the Drawings

[0019] Figure 1 It is a flowchart of a plasma thrust test method provided by the present invention; Figure 2 It is a structural schematic diagram of a plasma thrust test device provided by the present invention; Figure 3Schematic structural diagram of a plasma thrust test device provided by the present invention in a thrust measurement state; Figure 4 Side view of the three-dimensional structure of a plasma thrust test device provided by the present invention.

[0020] Explanation of reference numerals: 1. Bearing; 2. Steel wire rope; 3. Target plate; 4. Thruster; 5. Plasma jet; 6. Displacement sensor; 61. Probe; 62. Pre-amplifier; 63. Extension cable; 7. First bracket; 8. Oscilloscope; 9. Second bracket. Specific embodiments

[0021] The following describes the specific embodiments of the present invention in detail, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0022] In the prior art, it is difficult to accurately obtain the actual thrust of the plasma both in the measurement and calculation processes when deriving the thrust value. The plasma discharge time is short, reaching the microsecond to millisecond level, and the thrust will undergo transient changes. It is difficult to accurately calculate the thrust value of the plasma through the diagnostic method of plasma characteristics. The plasma thrust is also one of the important parameters of the coaxial gun discharge pulse plasma thruster, and its thrust characteristics directly affect the propulsion efficiency.

[0023] The inventor found that there is a lack of precise measurement means for transient thrust in the μs-ms magnitude in the art. In the prior art, the conventional pendulum device is large in size, low in response frequency, and easily affected by high-temperature plasma sputtering. The traditional strain gauge force measurement platform has a low response frequency, usually <1 kHz, and cannot capture the transient process of pulsed discharge. The piezoelectric sensor is easily affected by electromagnetic interference and requires a rigid connection, which affects the swing freedom. Using the laser interferometry method has the problems of high cost and being sensitive to vibration, which is likely to cause measurement errors.

[0024] As Figure 2 , Figure 4 shown, the present invention provides a plasma thrust test device, and the entire device is arranged in an acrylic vacuum chamber, and the vacuum chamber is adapted to the plasma experimental environment. The plasma thrust test device includes: a target plate 3, and the target plate 3 is a composite plate structure welded by a molybdenum plate and a copper plate, with a size of 30 cm × 30 cm × 0.2 cm. The molybdenum plate faces the thruster 4, and the copper plate faces away from the thruster 4. The thruster 4 is a discharge pulse plasma thruster. In this embodiment, the thruster 4 uses a coaxial gun. The center of the target plate 3 needs to be aligned with the outlet of the thruster 4, and the axial distance is within 25 cm to ensure that the plasma can completely impact the target plate 3.

[0025] Among them, the molybdenum plate serves as the anti-sputtering layer of the target plate 3, which can reduce the sputtering of the material caused by the plasma jet 5 emitted by the thruster 4 when bombarding the target plate 3. The copper plate serves as the signal coupling layer, which can enhance the eddy current signal response. The method of using the target plate 3 welded by the molybdenum plate and the copper plate for anti-sputtering has the characteristics of vacuum compatibility, anti-interference, and high precision, and is suitable for the thrust characteristic research of the pulsed plasma thruster 4 in the laboratory environment and the transient plasma thrust measurement in the vacuum environment.

[0026] The target plate 3 is connected to a suspension support system, and the suspension support system is used to adjust the position of the target plate 3. The suspension support system includes a steel wire rope 2. The target plate 3 is connected to the bearing 1 through the steel wire rope 2 to reduce friction interference and allow the target plate 3 to swing freely. One end of the steel wire rope 2 is connected to the target plate 3, and the other end is connected to the bearing 1. The bearing 1 is a linear bearing, and the bearing 1 is installed on the second bracket 9. The second bracket 9 can move horizontally through the track inside the vacuum chamber, facilitating the adjustment of the distance between the target plate 3 and the thruster 4 to meet the tests at different distances. The upper part of the second bracket 9 is provided with a slidable rail for supporting the adjustment of the target plate 3 within a height range of ±50 mm. A rod is also installed on the rail, and the bearing 1 can move horizontally on the rod.

[0027] A displacement sensor 6 for real-time measurement of the axial displacement of the target plate 3 is provided on one side of the target plate 3. The displacement sensor 6 uses an eddy current sensor. The eddy current sensor uses the eddy current principle to measure the position change of an object. During the induction process, the sensor emits high-frequency signals, and the interaction with the measured object generates eddy current changes, thereby measuring the displacement. This process itself has a certain isolation effect from the interference of external electromagnetic waves, so that the displacement sensor 6 has the characteristic of anti-electromagnetic interference. The circuit of the displacement sensor 6 is led out through the interface on the vacuum chamber. The displacement sensor 6 is electrically connected to an oscilloscope 8, and the oscilloscope 8 is used to collect the voltage signal of the displacement sensor 6.

[0028] Specifically, the displacement sensor 6 is fixedly installed on the first bracket 7. The first bracket 7 can move horizontally, so that the displacement sensor 6 can be adjusted according to the position of the target plate 3 before the experiment. The first bracket 7 is made of insulating material to avoid electromagnetic interference. The displacement sensor 6 includes a preamplifier 62. The preamplifier 62 is fixed on the first bracket 7. The preamplifier 62 is provided with a probe 61 and is connected with an extension cable 63. Among them, the distance between the probe 61 and the target plate 3 is 1 mm - 13 mm, which is convenient for real-time measurement of the axial displacement of the target plate 3 and outputting a voltage signal to the oscilloscope 8.

[0029] Such as Figure 2As shown, before the test, the target plate 3 and the wire rope 2 are in the same vertical plane. Adjust the position of the target plate 3 so that the center thereof is aligned with the outlet of the thruster 4. Then adjust the position of the displacement sensor 6 so that the probe 61 is coaxial with the center of the target plate 3.

[0030] As Figure 3 shown, during the test, the thruster 4 emits a plasma jet 5 towards the target plate 3. Under the bombardment of the plasma jet 5, the target plate 3 is subjected to a thrust force and swings. During the swinging process, the target plate 3 undergoes an axial displacement. The probe 61 of the displacement sensor 6 detects the axial displacement of the target plate 3 and converts it into a voltage signal for transmission to the oscilloscope 8, and the oscilloscope 8 collects the voltage signal emitted by the displacement sensor 6.

[0031] In this plasma thrust test device, except that the first bracket 7 is made of insulating material and the target plate 3 is a composite plate structure welded by a molybdenum plate and a copper plate, the rest of the components are made of metal materials, including but not limited to copper and aluminum materials, to meet the requirements of vacuum experiments.

[0032] This device has a simple structure and a small volume, and has the characteristics of high temperature resistance and anti-electromagnetic interference, and can avoid the electromagnetic sensitivity problem of traditional strain gauges.

[0033] In one embodiment, as Figure 1 shown, the present invention also provides a plasma thrust test method, which uses a plasma thrust test device for testing.

[0034] This plasma thrust test method includes static calibration and dynamic calibration.

[0035] The static calibration method is: applying a stepped force to the target plate 3 for calibration, and based on the voltage signal fed back by the displacement sensor 6, establishing a thrust-voltage linear model.

[0036] The formula of the thrust-voltage linear model is F = k×V + C.

[0037] In the formula: k is a coefficient; V is the voltage signal fed back by the displacement sensor 6; C is a constant.

[0038] During calibration, a push-pull force gauge is used to apply a stepped force to the target plate 3. The stepped force is a known force (0 - 10N controllable), and the stepped force takes 0.5N as the unit step size. When applying the stepped force, record the output voltage of the displacement sensor 6 corresponding to each stepped force. Calibrate the relationship curve between the output voltage of the displacement sensor 6 and the axial displacement of the target plate 3, and calculate the sensitivity and linear error.

[0039] Dynamic calibration is as follows: applying an instantaneous force of a simulated pulse to the target plate 3 to verify the dynamic response speed of the displacement sensor 6. This helps ensure that the displacement sensor 6 can have a response speed at the microsecond level and is suitable for the measurement of pulsed thrust.

[0040] Static calibration and dynamic calibration can be carried out both before and after assembling the plasma thrust test device, and the operation sequence is not unique. In some embodiments, after assembling the plasma thrust test device, static calibration and dynamic calibration are carried out.

[0041] Assemble the plasma thrust test device. First, hang the target plate 3 on the bearing 1 through the steel wire rope 2, adjust the height so that the center of the target plate 3 is aligned with the axis of the thruster 4, and adjust the height of the bearing 1 so that the steel wire rope 2 is in the vertical initial state (as Figure 2 shown). Install the displacement sensor 6, and an initial zero position needs to be preset. The initial zero position is the distance between the target plate 3 and the displacement sensor 6. In this embodiment, the distance between the probe 61 of the displacement sensor 6 and the target plate 3 is set to 5 mm (i.e., the initial zero position). Fix the entire plasma thrust test device in the vacuum chamber.

[0042] Among them, the distance detected by the displacement sensor 6 between it and the target plate 3 at the current moment is recorded as the current distance. At the current moment, the axial displacement of the target plate 3 is the difference between the initial zero position and the current distance.

[0043] As Figure 3 shown, start the experiment to measure the transient thrust. First, evacuate the vacuum chamber until the target air pressure, then trigger the discharge of the thruster 4. The plasma jet 5 is ejected from the outlet of the thruster 4, and the target plate 3 swings after being impacted by the plasma. The axial displacement of the target plate 3 at different moments is acquired by the displacement sensor 6 and converted into a voltage signal at the corresponding moment. Based on the oscilloscope 8 collecting the voltage signal sent by the displacement sensor 6, the transient thrust of the plasma is inversely calculated in combination with the thrust-voltage linear model.

[0044] Based on the discharge parameters of the thruster 4 at different moments and the transient thrust of the plasma, where the discharge parameters include discharge voltage and discharge current, through data fitting, the transient thrust-discharge voltage-time curve is obtained to analyze the variation law of the transient thrust.

[0045] The specific steps of this plasma thrust test method are as follows: S1. Apply a stepped force (in steps of 0.5 N) to the center of the target plate 3 using a push-pull gauge, record the output voltage of the displacement sensor 6, and the axial displacement of the target plate 3 detected by the displacement sensor 6 corresponds to different output voltages. Based on the voltage signal feedback by the displacement sensor 6, establish a thrust-voltage linear model.

[0046] S2. Apply an instantaneous force of a simulated pulse to the target plate 3 to verify the dynamic response speed of the displacement sensor 6.

[0047] S3. Assemble the plasma thrust test device.

[0048] First, suspend the target plate 3 on the bearing 1 through the steel wire rope 2, adjust the height so that the center of the target plate 3 aligns with the axis of the thruster 4, and adjust the height of the bearing 1 so that the steel wire rope 2 is in the vertical initial state. Install the displacement sensor 6 and set the distance between the probe 61 of the displacement sensor 6 and the target plate 3 to 5 mm (i.e., the initial zero position). Fix the entire plasma thrust test device in the vacuum chamber.

[0049] S4. First, evacuate the vacuum chamber until the target air pressure, then trigger the discharge of the thruster 4. The plasma jet 5 is ejected from the outlet of the thruster 4, and the target plate 3 swings after being impacted by the plasma.

[0050] During this process, the axial displacement of the target plate 3 at different times is acquired by the displacement sensor 6 and converted into a voltage signal corresponding to the time. Based on this, a voltage-time curve can be plotted.

[0051] S5. The oscilloscope 8 collects the voltage signal sent by the displacement sensor 6 and inversely calculates the transient thrust of the plasma.

[0052] The inversion logic is: By combining the thrust-voltage linear model in S1 with the voltage-time curve in S4, a transient thrust-time curve and a transient thrust-voltage-time curve can be obtained.

[0053] S6. Based on the discharge parameters (discharge voltage and discharge current) of the thruster 4 at different times, a discharge voltage / discharge current-time curve can be plotted. Through data fitting, a transient thrust-discharge voltage-time curve is obtained to analyze the variation law of the transient thrust.

[0054] Specifically, by combining the transient thrust-time curve in S5 with the discharge voltage / discharge current-time curve in S6, a transient thrust-discharge voltage-time curve can be obtained, and then the characteristics of the transient thrust can be analyzed.

[0055] In this application, the displacement of the target plate 3 is measured non-contact by the displacement sensor 6. This not only avoids the electromagnetic sensitivity problem of traditional strain gauges, but also, after combining with the method of applying a stepped force to the target plate 3 for calibration, the transient thrust is inversed through the output voltage of the displacement sensor 6, thus realizing the inversion of microsecond-level transient thrust with high precision. During the measurement process, the height of the target plate 3 and the spacing of the displacement sensor 6 can be adjusted to adapt to experiments with different plasma parameters. Moreover, the swing of the target plate 3 is not restricted during the experiment, making the inversion measurement of the transient thrust more accurate. Compared with the measurement by laser interferometry, this application can achieve more accurate measurement of the transient thrust at a lower cost. During the measurement of the transient thrust, the variation law of the transient thrust can also be analyzed to evaluate the transient thrust characteristics of plasma discharge.

[0056] The above are only several specific embodiments of the present invention disclosed. However, the embodiments of the present invention are not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A plasma thrust testing method, characterized in that Including: Calibrate the target plate (3) by applying a stepped force, and establish a linear thrust-voltage model based on the voltage signal fed back by the displacement sensor (6). Apply an instantaneous force simulating a pulse to the target plate (3) to verify the dynamic response speed of the displacement sensor (6). Trigger the discharge of the thruster (4) in a vacuum environment. After the target plate (3) is impacted by the plasma and swings, the axial displacement of the target plate (3) at different moments is acquired by the displacement sensor (6) and converted into a voltage signal at the corresponding moment. Based on the oscilloscope (8) collecting the voltage signal sent by the displacement sensor (6), the transient thrust of the plasma is deduced by combining the thrust-voltage linear model. Based on the discharge parameters of the thruster (4) at different moments and the transient thrust of the plasma, obtain the transient thrust-discharge voltage-time curve through data fitting to analyze the variation law of the transient thrust.

2. The plasma thrust test method according to claim 1, wherein Apply the stepped force to the target plate (3) using a push-pull gauge. The stepped force is a known force, and the stepped force has a unit step of 0.5 N.

3. A plasma thrust test method according to claim 1, characterized in that The formula of the thrust-voltage linear model is F = k×V + C. Wherein: k is a coefficient; V is the voltage signal fed back by the displacement sensor (6); C is a constant.

4. A plasma thrust testing method according to claim 1, characterized in that, Before the displacement sensor (6) acquires the axial displacement of the target plate (3), an initial zero position needs to be preset. The initial zero position is the distance between the target plate (3) and the displacement sensor (6).

5. The plasma thrust testing method according to claim 4, characterized in that, The distance detected by the displacement sensor (6) between it and the target plate (3) at the current moment is recorded as the current distance. At the current moment, the axial displacement of the target plate (3) is the difference between the initial zero position and the current distance.

6. The plasma thrust testing method according to claim 1, characterized in that The discharge parameters include discharge voltage and discharge current.

7. A plasma thrust test device applicable to the plasma thrust test method according to any one of claims 1-6, characterized in that, Including: A target plate (3), the target plate (3) is connected to a suspension support system, and the suspension support system is used to adjust the position of the target plate (3). On one side of the target plate (3), there is a displacement sensor (6) for real-time measurement of the axial displacement of the target plate (3). The displacement sensor (6) is electrically connected to an oscilloscope (8), and the oscilloscope (8) is used to collect the voltage signal of the displacement sensor (6).

8. The plasma thrust testing device according to claim 7, characterized in that, The target plate (3) is a composite plate structure welded by a molybdenum plate and a copper plate.

9. The plasma thrust test device according to claim 7, characterized in that, The suspension support system includes a steel wire rope (2). One end of the steel wire rope (2) is connected to the target plate (3), and the other end is connected to a bearing (1).

10. A plasma thrust testing device according to claim 7, characterized in that, The displacement sensor (6) includes a preamplifier (62). The preamplifier (62) is provided with a probe (61), and the preamplifier (62) is connected to an extension cable (63).

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