A method and system for on-line diagnosis of plasma density of a hypersonic vehicle

Abstract

The application discloses a kind of hypersonic vehicle plasma density on-line diagnosis method, including the current of probe zero position acquisition is obtained to obtain the current of modified probe plasma acquisition;In the current of modified probe plasma acquisition, effective data is selected, and is divided into n sections;The I-V curve of each section data in n section data is obtained;According to I-V curve, electron temperature and saturated ion current are obtained, and then the electron density of n section data is obtained;Edge effect and collision effect correction are carried out to the electron density, and the plasma density of plasma flow field is obtained.The application also discloses a kind of hypersonic vehicle plasma density on-line diagnosis system, including power supply module, power conversion module, triangular wave conversion module, signal conditioning module, acquisition and frequency adjustment module, probe and data processing equipment.The application improves plasma measurement data processing efficiency and accuracy under real environment, and can be used to guide basic theory research, predict model correction and support reliable measurement and control communication research.

Description

Technical Field

[0001] This invention belongs to the field of online plasma electron density diagnostic technology, and relates to a method and system for online diagnosis of plasma density in hypersonic vehicles. Background Technology

[0002] To investigate the impact of plasma on spacecraft telemetry, tracking, and communication during hypersonic (>5 Ma) flight, research on plasma density diagnostic technology is being conducted. Considering the highly complex plasma environment, the difficulty of measurement, and the current limited understanding in actual flight conditions, achieving online plasma density diagnostics and acquiring plasma density data under actual flight conditions can improve our understanding and refine theoretical research methods and measurement techniques.

[0003] Currently, various plasma diagnostic methods have been developed on the ground. Probes, as one of these methods, are widely used in ground tests, but have not yet been verified in real flight environments. Real flight environments place high demands on the heat resistance, strength, and reliability of probes, and existing solutions are not suitable for use in long-term aerodynamic high-temperature environments. Unlike existing ground acquisition systems, flight systems have limited telemetry code rates, and to capture plasma density electrical signals, a certain sampling period and sampling frequency must be ensured. Due to environmental interference and circuit acquisition errors, data acquired in real environments cannot be directly fitted to a standard volt-ampere characteristic curve, and error correction is required for the data. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned shortcomings and provide an online diagnostic method and system for plasma density in hypersonic vehicles. This solves the technical problem of low efficiency and accuracy in plasma diagnostics due to the inability to fit standard current-voltage characteristic curves to data collected in real-world environments. This invention improves data processing efficiency and accuracy and can be used to guide fundamental theoretical research, predict model correction, and support reliable telemetry and control communication research.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for online diagnosis of plasma density in hypersonic vehicles includes:

[0007] S1 places the probe in an air environment to obtain the probe zero-position sampling current I0;

[0008] S2 places the probe in the plasma flow field, and the probe plasma collection current I(t) is obtained;

[0009] S3 uses the zero-position acquisition current I0 to correct the plasma acquisition current I(t), and obtains the corrected probe plasma acquisition current I'(t);

[0010] S4 selects valid data from the corrected probe plasma acquisition current I'(t);

[0011] S5 divides the valid data into n segments, resulting in n segments of data; n > 1;

[0012] S6 uses the scanning voltage of the probe to obtain the IV curve of each segment of data in n segments;

[0013] S7 obtains the electron temperature T based on the IV curves of each data segment. e and saturated ion current I io ;

[0014] S8 is based on the electronic temperature T of n segments of data. e and saturated ion current I io Obtain the electron density of n data segments;

[0015] S9 corrects the electron density of n segments of data for edge and collision effects to obtain the plasma density of the plasma flow field during flight.

[0016] Furthermore, step S2 involves placing the probe in the plasma flow field, and the method for obtaining the probe plasma collection current I(t) is as follows:

[0017] When I(t) < I1, the sampling frequency is set to ≤1kHz;

[0018] When I(t)≥I1, the sampling frequency is set to ≥30kHz;

[0019] I1 is set according to the sampling error and is used to determine whether the sampled current signal is a valid signal.

[0020] Furthermore, in step S1, the probe zero-position acquisition current I0 is the average value of the current within 2 seconds before the probe enters the plasma flow field.

[0021] Furthermore, in step S3, I'(t) = I(t) - I0.

[0022] Furthermore, in step S4, the valid data contains m periods, where m ≥ 1, and simultaneously satisfies the following conditions:

[0023] The amplitude of m cycles is greater than I1; I1 is set according to the sampling error and is used to determine whether the sampled current signal is a valid signal;

[0024] The maximum value of valid data is greater than or equal to I1;

[0025] Valid data must change in accordance with the period of the triangular wave voltage;

[0026] The effective data shows a continuous changing trend.

[0027] Furthermore, in step S5, the value of n is determined based on the number of valid data periods m;

[0028] Each data segment contains at least one cycle. The larger m is, the closer the plasma density of the plasma flow field during flight obtained in step S9 is to the real environment.

[0029] In step S8, the electron density of the n data segments corresponds to the electron density at different times during the flight.

[0030] Furthermore, in step S6, each of the n data segments contains at least >1 period, and the IV curve of each data segment is the average value of the IV curves of each period in each data segment.

[0031] Furthermore, in step S7, the electron temperature T is obtained based on the IV curves of each data segment. e and saturated ion current I io The method involves smoothing, filtering, and fitting the IV curve for each data segment, and then using the maximum current value on the positive half-axis of the fitted IV curve as the saturated ion current I. io The electron temperature T is obtained from the slope of the IV curve at the zero-crossing point after fitting. e .

[0032] A hypersonic vehicle plasma density online diagnostic system is provided to implement the above-mentioned hypersonic vehicle plasma density online diagnostic method. The system includes a power supply module, a power conversion module, a triangular wave conversion module, a signal conditioning module, an acquisition and frequency adjustment module, a probe, and a data processing device.

[0033] The power conversion module converts the first voltage signal input from the power supply module into a second voltage signal with a predetermined peak value, and outputs the second voltage signal to the triangular wave conversion module;

[0034] The triangular wave conversion module receives the second voltage signal input from the power conversion module, converts the second voltage signal into a triangular wave driving voltage signal for driving the probe, and acquires the current signal of the probe, converts the current signal of the probe into a voltage signal, and outputs the converted voltage signal to the signal conditioning module.

[0035] The signal conditioning module receives the converted voltage signal input from the triangular wave transformation module and conditions the converted voltage signal into a third voltage signal of 1 to 5V.

[0036] The acquisition and frequency adjustment module samples the third voltage signal according to the set sampling frequency to obtain I0 and I(t);

[0037] The data processing equipment obtains the plasma density of the plasma flow field based on I0 and I(t) and combined with the triangular wave voltage signal.

[0038] Furthermore, in the aforementioned hypersonic vehicle plasma density online diagnostic system, the probe is a dual-flat probe, which is mounted on the vehicle using a support housing.

[0039] The probe electrode is made of niobium-tungsten alloy that can withstand temperatures above 2000℃;

[0040] The supporting shell is made of ceramic material that can withstand temperatures above 1500℃;

[0041] The dual flat-mounted probes are isolated from the aircraft using insulating gaskets.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] (1) This invention creatively proposes an online diagnostic method for plasma density, which improves data processing efficiency and accuracy by distinguishing effective data and processing effective data in segments;

[0044] (2) The present invention forms a diagnostic error correction method for real test data. The diagnostic error is within one order of magnitude, and the difference between the corrected result and the predicted result is within 50%.

[0045] (3) Under conditions of limited bandwidth resources, this invention, by dynamically adjusting the sampling frequency in real time, can maximize the saving of telemetry bandwidth resources and obtain effective measurement data compared to existing methods of direct high-speed sampling on the ground, and can adapt to 10e 10 cm -3 up to 10e 14 cm -3 Measurement of plasma density within a range;

[0046] (4) This invention is applicable to plasma density measurement in aerodynamically complex high-temperature (greater than 800°C) and highly reliable real flight environments. The design of the probe body takes into account structural strength and material characteristics, and the design of the drive circuit takes into account the effective data acquisition cycle and sampling frequency, thus ensuring the reliability, effectiveness and applicability of the design. Attached Figure Description

[0047] Figure 1 This is a block diagram of the hypersonic vehicle plasma density online diagnostic system of the present invention;

[0048] Figure 2 This is a schematic diagram of the dual flat-mounted probe structure of the present invention;

[0049] Figure 3 This is a schematic diagram of the installation of the double flat probe of the present invention, wherein (a) is a schematic diagram of the mounting flange and gasket, and (b) and (c) are schematic diagrams of the two gaskets respectively;

[0050] Figure 4 This is a flowchart of the online plasma density diagnosis method for hypersonic vehicles according to the present invention;

[0051] In the figure, 1-insulating sleeve, 2-electrode, 3-support housing, 4-mounting flange, 5-plug connector, 6-cable, 7-first insulating gasket, 8-second insulating gasket. Detailed Implementation

[0052] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0053] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0054] This invention is designed for real-time online plasma density diagnosis under actual flight conditions. It establishes an online plasma density diagnosis system under flight conditions, and develops a method for correcting errors in real plasma density diagnosis data and an experimental database. This invention can be used to guide basic theoretical research, predict model correction, and support research on reliable measurement, control, and communication.

[0055] like Figure 1 The core component of the hypersonic vehicle plasma density online diagnostic system of the present invention is the probe and conversion circuit. The conversion circuit performs power conversion and outputs a triangular wave voltage to drive the probe to collect data through conditioning and then perform telemetry encoding.

[0056] The probe employs a dual-flat probe structure. Since the probe's outer surface is exposed, structural strength and high-temperature resistance designs were incorporated into the probe electrodes and support housing. The probe electrodes are made of niobium-tungsten alloy, capable of withstanding temperatures above 2000℃, while the support housing can be made of alumina high-temperature resistant ceramic material, capable of withstanding temperatures above 1500℃. To ensure that external electrostatic interference does not affect the aircraft's internal structure, the diagnostic system is isolated from the telemetry system. This isolation is achieved using insulating gaskets, ensuring the probe is insulated from the aircraft. Figure 2 and Figure 3Electrode 2, support housing 3, and insulating sleeve 1 are in direct contact with the measurement environment. The electrode material is selected from high-temperature resistant and highly conductive materials, such as tungsten, molybdenum, or tungsten-molybdenum alloys, which are good conductors and resistant to high temperatures. The insulating sleeve is selected from materials with good insulation, high temperature resistance, and high hardness, which have good insulation performance in high-temperature environments, such as high-temperature resistant ceramic materials. The support housing 3 is selected from high-temperature resistant materials, and the most direct way is to select the same material as the electrode. Considering the actual flight environment, thermal sealing needs to be considered. High-temperature adhesive can be applied between the electrode and the insulating sleeve, and between the insulating sleeve and the outer shell. Connector 5 and cable 6 are used to connect to the conversion circuit. The cable protective sleeve should be resistant to high temperatures, and the connection between the cable and the electrode should be a combination of crimping and screwing. Because the outer surface of the dual flat-mounted probes is exposed in a real flight environment, in order to ensure that external static electricity and other interferences do not affect the interior of the aircraft, the probes should be isolated from the system. The installation steps of the dual flat-mounted probes and the aircraft are as follows: the first insulating gasket 7 and the second insulating gasket 8 are assembled with the mounting flange 4 by adhesive bonding; the second insulating gasket is located at the working end of the dual flat-mounted probe body; the probes are fixed to the metal shell of the aircraft using M4 screws; high-temperature sealant is applied between the probe shell and the aircraft during installation to ensure heat sealing and heat protection.

[0057] The conversion circuit section includes a power supply module (power supply and isolation module), a power conversion module, a triangular wave conversion module, a signal conditioning module, and a sampling frequency adjustment module. The triangular wave frequency determines the effective data acquisition period, and the sampling frequency determines the error magnitude of the effective data. Unlike ground measurement systems, actual aircraft systems often cannot guarantee high sampling frequencies and system bandwidth. The conversion circuit section has integrated the triangular wave frequency and sampling frequency to ensure that as much effective data as possible is acquired, while also ensuring reliable data acquisition under limited bandwidth.

[0058] Specifically, the isolation module performs current limiting, filtering, and isolation of the input voltage, and prevents reverse power connection from affecting the equipment; the power conversion module performs boosting, bucking, and current limiting on the isolated output voltage, providing a peak voltage signal of ±50V to the triangular wave conversion module; the triangular wave conversion module generates a triangular wave voltage, driving a triangular wave drive voltage signal with a peak output of ±50V, a drive load of not less than 3A, and a frequency of not less than 200Hz; the triangular wave drive voltage signal is output to the probe to drive the probe to generate a plasma current signal, and also samples the plasma drive current signal through a sampling resistor and outputs it to the signal conditioning module. The signal conditioning module conditions and outputs a 0-5V voltage signal to the acquisition and frequency adjustment module for processing, and finally outputs the data for telemetry framing.

[0059] The power management module isolates and converts the externally input DC power (28V±4V), providing high voltage and high load current to the triangular wave drive module and powering all circuits. The triangular wave drive module first generates a triangular wave using a dedicated triangular wave chip. A triangular wave drive amplifier circuit then generates a triangular wave voltage with a peak value of ±50V. This signal is input to the power amplifier drive circuit, ultimately outputting a triangular wave drive voltage signal with a peak value of ±50V, a drive load of at least 3A, and a frequency of at least 200Hz. Under the influence of the triangular wave drive voltage, the probe generates a current signal, which is output to the signal conditioning module. Simultaneously, the triangular wave drive voltage is also led out and input to the signal conditioning module. The signal conditioning module samples the current signal and conditions it into a 0-5V voltage signal for system acquisition.

[0060] The triangular wave driver module consists of an analog triangular wave generator circuit, a power amplifier driver circuit, and a signal sampling resistor. The analog triangular wave generator circuit uses a dedicated triangular wave chip to generate a 200Hz frequency and an output amplitude of -1V to +1V, outputting the signal to the power amplifier driver circuit. A current signal sampling resistor is designed in the signal output path to convert the current signal into a voltage signal of a few millivolts to tens of millivolts, which is then output to the signal conditioning module. The signal conditioning module conditions the multiple acquired signals into 0-5V signals for system acquisition. The amplification factor is designed according to the magnitude of the input differential voltage, ensuring that the amplified voltage meets the input voltage requirements of the external system.

[0061] Based on the plasma density ranging from the 10th to the 14th power, corresponding to currents ranging from a few milliamps to a few amperes, with a dynamic range of 83.5 dB, the real-time online acquisition system divides the conditioning circuit into different ranges to achieve the acquisition of a large dynamic signal range. The conditioning paths are divided according to the 10-mA range (1mA to tens of milliamps), the 100-mA range (tens of milliamps to hundreds of milliamps), and the ampere range (several amperes). This can cover plasma density measurements from the 10th to the 14th power, and the signal resolution can reach tens of microamps. It is applied to plasma density measurements in the first real flight environment.

[0062] Preferably, the output frequency of the triangular wave generator is between 100Hz and 200Hz to ensure an effective acquisition period;

[0063] Preferably, the sampling frequency is switched between low frequency (not greater than 1kHz) and high frequency (not less than 30kHz) to ensure that the telemetry bitstream stores valid data and reduce invalid data transmission.

[0064] Preferably, data collected in real-world environments often cannot be directly fitted to a standard current-voltage characteristic curve. This invention corrects data errors, which, compared to existing methods of direct and simple filtering and fitting, corrects the acquisition errors.

[0065] Dual flat probes can reduce disturbances to the measured plasma to some extent. The probe consists of two electrodes with similar surface areas. A bias voltage is applied between the two probes, which are suspended as a whole. By measuring the change in the operating current between the two probes as a function of the scanning voltage, the current-voltage characteristic curve can be obtained.

[0066] like Figure 4 The present invention provides an online diagnostic method for plasma density in hypersonic vehicles, comprising:

[0067] (1) Raw data cleaning

[0068] Before the actual test, the probe was placed in normal air, and the theoretical sampling current of the probe converter was zero. However, in the actual acquisition system, due to the influence of the surrounding environment, the sampling current may not be zero. Zero-point correction of the data is required to eliminate the effects of "zero drift".

[0069] Assuming the probe current data is represented as I(t), calculate the measured average value I0 when the current signal is stable before entering the flow field (calculate the average value in the range of 2s before entering the flow field). The probe current after zero-position correction can be expressed as I'(t)=I(t)-I0.

[0070] (2) Selecting valid data segments

[0071] During online measurement, the voltage scanning frequency of the probe converter is 200Hz and the sampling frequency is 1MHz, resulting in a large amount of actual data collected, and a lot of invalid data. It is necessary to select valid data that can reflect the true flow field from the original experimental data for subsequent processing.

[0072] Select data that are greater than a certain threshold range and have a clear periodic pattern as valid data; ensure that the selected segment has a large signal amplitude and good signal stability.

[0073] (3) Effective data segmentation and averaging

[0074] Based on the number of valid data periods, select the number of segments n. Average all periods in each segment to obtain the average IV curve for that segment, ultimately resulting in n average IV curves. The subsequent processing method for each IV curve is consistent, ultimately yielding n plasma densities.

[0075] (4) IV curve smoothing and filtering

[0076] Compared to the current values ​​measured by dual flat probes, the IV curves exhibit smaller values ​​and are more susceptible to environmental influences. The IV curves also show numerous spikes and significant oscillations, making it impossible to further determine the electron temperature and saturation electron current. Therefore, smoothing and filtering of the IV curves are necessary to eliminate spikes and oscillations. The number of smoothing points and the selection of the filtering method need to be determined based on the specific data.

[0077] (5) IV curve fitting

[0078] In subsequent calculations, the IV curve needs to be differentiated. Even after smoothing and filtering, the IV curve is still not a monotonic curve and cannot be further processed. Therefore, curve fitting is required, and the fitted curve is used for subsequent calculations. Theoretically, the transition segment of the dual-probe IV curve rises exponentially and approaches horizontal in the saturated flow regions at both ends, forming an overall S-shaped curve. Therefore, a suitable fitting function needs to be selected based on the curve's shape during fitting.

[0079] (6) Calculate the saturation ion current

[0080] When calculating the saturation ion current of a dual-plane probe, the maximum current in the IV curve is generally selected. Observing the actual characteristics of dual-plane probe test data in real experiments, the negative half-axis curve usually exhibits greater fluctuations; therefore, the maximum current on the positive half-axis is generally chosen as the saturation ion current.

[0081] (7) Calculate the electron temperature

[0082] According to theoretical derivation, the slope of the IV curve of the dual flat probe at the zero point is inversely proportional to the electron temperature. Therefore, the electron temperature can be obtained by calculating the slope of the curve at the zero point.

[0083] The specific formula is as follows:

[0084]

[0085] The current between the two electrodes is I. D The voltage between the two electrodes is V. D e is the electron charge, I io The saturated ion current is (equivalent to the maximum value of I'(t) after correction above), k is the Boltzmann constant, and T is the saturated ion current. e It represents the electron temperature.

[0086] The electron temperature can be obtained from the above formula.

[0087] (8) Calculate electron density

[0088] Since the dual probes can only collect ion saturation flow, the ion density is calculated as the plasma density.

[0089] Ion density is obtained from ion saturation current:

[0090]

[0091] Where, n e For electron density, n i This represents the ion density. A sThe probe collection area is expressed in meters (m²). 2 m i denoted as ion mass in kg, Te as electron temperature in K, k as Boltzmann constant in J / K, and e as elementary charge in coulombs.

[0092] (9) Correcting edge effects and collision effects

[0093] Based on Formulas 3 and 4, the edge effect and collision effect are corrected respectively to obtain the corrected dual-flat probe ion collection flow, which is used to calculate the final measured plasma density.

[0094] The effective collection area of ​​the probe can be calculated based on the special configuration and boundary conditions of the dual planar probe, and the ion collection flux I after edge effect correction of the dual planar probe can be obtained. i,mea1 The relation is:

[0095]

[0096] Where e is the elementary charge, k is the Boltzmann constant, and T e V is the electron temperature. D Let be the potential between the two electrodes. a and b are parameters obtained from simulations of the physical state of the plasma. r p Let λ be the electrode radius, and λ0 be the unperturbed Debye length. φ p I represents the electromotive force of the plasma at the electrode. i The actual ion flow is equivalent to the probe plasma collection current I(t) in this invention.

[0097] Formula 3 is applicable to the following situations: 5<η p <50, where r p λ is the electrode radius of the probe. D The length of the Debye.

[0098] Based on relevant equations and boundary conditions, the formula for ion current correction and appropriate parameters can be derived, resulting in the collision effect-corrected dual-plane probe ion acquisition current I0. i,mea2 The relation is:

[0099]

[0100] Where α=λ D / λ i λ D λ is the Debye length. i Let b be the ion collision frequency, b = 0.8, c = 12.9. Let e ​​be the elementary charge, k be the Boltzmann constant, and T be the ion collision frequency. eV is the electron temperature. D The potential between the two electrodes is denoted as .

[0101] When edge effect and collision effect corrections are applied sequentially, I in Equation 4 i The ion flow is corrected for each process.

[0102] This invention provides a diagnostic error correction method for real experimental data. The diagnostic error is within one order of magnitude, and the corrected result differs from the predicted result by less than 50%.

[0103] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0104] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for online diagnosis of plasma density in hypersonic vehicles, characterized in that, include: S1 places the probe in an air environment to obtain the probe zero-position sampling current I0; S2 places the probe in the plasma flow field and obtains the probe plasma collection current I(t); S3 uses the zero-position acquisition current I0 to correct the plasma acquisition current I(t), and obtains the corrected probe plasma acquisition current I'(t); S4 Selects valid data from the corrected probe plasma acquisition current I'(t); S5 divides the valid data into n Section, obtained n Segment data; n >1; S6 Based on the probe's scanning voltage, obtain n IV curves for each segment of data in the segment data; S7 Obtains the electron temperature based on the IV curves of each data segment. and saturated ion current ; S8 According to n electronic temperature of segment data and saturated ion current get n Electron density of segment data; S9 pairs n The electron density of the segment data is corrected for edge and collision effects to obtain the plasma density of the plasma flow field during flight.

2. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, Step S2 involves placing the probe in the plasma flow field. The method for obtaining the probe plasma sampling current I(t) is as follows: When I(t) < I1, the sampling frequency is set to ≤1kHz; When I(t)≥I1, the sampling frequency is set to ≥30kHz; I1 is set according to the sampling error and is used to determine whether the sampled current signal is a valid signal.

3. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, In step S1, the probe zero-position acquisition current I0 is the average value of the current within 2 seconds before the probe enters the plasma flow field.

4. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, In step S3, I'(t) = I(t) - I0.

5. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, In step S4, the valid data includes m One cycle, m ≥1, and simultaneously satisfy the following conditions: m The amplitude of each cycle is greater than I1; I1 is set according to the sampling error and is used to determine whether the sampled current signal is a valid signal; The maximum value of valid data is greater than or equal to I1; Valid data must change in accordance with the period of the triangular wave voltage; The effective data shows a continuous changing trend.

6. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, In step S5, based on the number of periods of valid data m Sure n The value; Each data segment contains at least one period. m The larger the value, the closer the plasma density of the plasma flow field obtained in step S9 during flight is to the real environment; In step S8, n The electron density of the segment data corresponds to the electron density at different times during the flight.

7. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, In step S6, n Each data segment contains at least one period, and the IV curve of each data segment is the average of the IV curves of each period in each data segment.

8. The method for online diagnosis of plasma density in a hypersonic vehicle according to claim 1, characterized in that, In step S7, the electron temperature is obtained based on the IV curves of each data segment. and saturated ion current The method involves smoothing, filtering, and fitting the IV curve for each data segment, and then using the maximum current value on the positive half-axis of the fitted IV curve as the saturated ion current. The electron temperature is obtained from the slope of the IV curve at the zero-crossing point after fitting. .

9. An online diagnostic system for plasma density in hypersonic vehicles, characterized in that, The method for online diagnosis of plasma density of hypersonic vehicles according to any one of claims 1-8 includes a power supply module, a power conversion module, a triangular wave conversion module, a signal conditioning module, an acquisition and frequency adjustment module, a probe, and a data processing device. The power conversion module converts the first voltage signal input from the power supply module into a second voltage signal with a predetermined peak value, and outputs the second voltage signal to the triangular wave conversion module; The triangular wave conversion module receives the second voltage signal input from the power conversion module, converts the second voltage signal into a triangular wave driving voltage signal for driving the probe, and acquires the current signal of the probe, converts the current signal of the probe into a voltage signal, and outputs the converted voltage signal to the signal conditioning module. The signal conditioning module receives the converted voltage signal from the triangular wave conversion module and conditions the converted voltage signal into a third voltage signal of 1~5V. The acquisition and frequency adjustment module samples the third voltage signal according to the set sampling frequency to obtain I0 and I(t); The data processing equipment obtains the plasma density of the plasma flow field based on I0 and I(t) and combined with the triangular wave voltage signal.

10. The hypersonic vehicle plasma density online diagnostic system according to claim 9, characterized in that, The probe is a dual-flat probe, which is mounted on the aircraft using a support housing. The probe electrode is made of niobium-tungsten alloy that can withstand temperatures above 2000℃; The supporting shell is made of ceramic material that can withstand temperatures above 1500℃; The dual flat-mounted probes are isolated from the aircraft using insulating gaskets.

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