Moire deflection-based long gap pilot discharge channel temperature measurement system and method

Abstract

A long-gap pilot discharge channel temperature measurement system and method based on moire deflection belong to the technical field of high-voltage long-gap discharge plasma diagnosis, solve the problem of large error in pilot channel moire fringe imaging by using the traditional moire deflection optical path caused by the certain spacing between the grating and the discharge electrode in the traditional moire deflection optical path; by adopting the conjugate optical system composed of two first imaging lenses with the same parameters and the second imaging lens between the high-voltage discharge electrode and the Langley grating group in the moire deflection optical path, and making the pilot discharge channel image at the reference grating of the Langley grating group, the interference of the Langley grating group on the formation and development process of the pilot discharge channel is eliminated, the problem of large error in pilot channel moire fringe imaging by using the traditional moire deflection optical path is solved, and the accurate measurement of long-gap pilot discharge channel temperature can be realized.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage long-gap discharge plasma diagnostic technology, and relates to a long-gap leader discharge channel temperature measurement system and method based on Moiré deflection. Background Technology

[0002] Leader discharge is the dominant physical process in the breakdown of long air gaps, and the positive leader discharge characteristics are a crucial foundation for the insulation coordination of overvoltage operations in ultra-high voltage / extra-high voltage power transmission and transformation systems and for lightning protection technology for high-target objects on the ground. The leader channel is a thermal plasma formed by the thermal ionization of air molecules. The gas temperature is not only an indicator of the translational kinetic energy of neutral particles but also a macroscopic parameter characterizing the degree of participation of complex thermal ionization processes within the channel. Channel temperature is closely related to key parameters such as electric field, electron density, and conductivity, and is a fundamental parameter determining the characteristics of the channel plasma. Simultaneously, channel temperature directly affects the energy dissipation rates of heat conduction and convection, playing a crucial role in the evolution of channel morphology and size. Therefore, research on the evolution law of gas temperature in leader discharge channels is of significant scientific importance and engineering application value for revealing the physical mechanism of leader discharge and for the insulation coordination of supporting equipment and lightning shielding design.

[0003] In laboratory positive-polarity long air gap discharges, the radial dimension of the channel is typically in the sub-mm range, while the radial temperature gradient can reach thousands of K / mm. During the initial current injection phase, the channel undergoes isochoric heating, with the temperature change rate at the channel center exceeding 2000 K / initial phase, demanding high time resolution from the measurement system. However, during the streamer-leader conversion dark region, the channel center temperature is usually only a few hundred K, requiring high sensitivity from the measurement system. In the laboratory, leader discharges typically last tens or even hundreds of microseconds, and the formation time and development path of the leader discharge channel exhibit strong randomness and complex variations. For temperature measurement of long air gap leader discharge channels, current plasma temperature diagnostic methods struggle to simultaneously meet the requirements of non-invasiveness, fast response, high sensitivity, high spatiotemporal resolution, and continuous time-domain measurement.

[0004] For measuring the gas temperature in atmospheric pressure discharge channels, current methods mainly employ emission spectroscopy and Rayleigh laser scattering, which offer advantages such as μ-level spatial resolution and nanosecond-level transient measurement capabilities. However, due to the rapid temperature changes in the leader channel, with radial temperature gradients reaching thousands of K / mm, and the non-repeatability of leader discharges, these methods are difficult to apply to measuring the temperature distribution in leader discharge channels. For long-gap leader discharge processes, current methods primarily utilize long-path optical flow field display techniques to achieve non-invasive quantitative reconstruction of leader channel temperature parameter distributions. These include Mach-Zehnder (MZ) laser interferometry, quantitative schlieren imaging, and moiré deflection. The MZ laser interferometry uses fringe imaging to detect channel parameters, and the fringe offset is positively correlated with the absolute value of the gas density change. However, for dark channels, the gas density change is very small, and the fringes have a certain width, making the MZ laser interferometry unsuitable for completely measuring the temperature of leader discharge channels. Quantitative schlierenography and moiré deflection methods utilize image grayscale changes and fringe shifts to reflect the magnitude of light deflection angles, respectively. Both grayscale changes and fringe shifts are positively correlated with the first derivative of the gas refractive index distribution. Even when the absolute change in refractive index in the leader discharge channel is small, a larger spatial refractive index gradient is more favorable for detection. However, quantitative schlierenography relies on grayscale changes in the schlieren image for parameter inversion. These grayscale changes are easily affected by interference from discharge self-luminescence and noise from imaging components. Furthermore, the improvement in temporal and spatial resolution of the quantitative schlieren system is limited by the intensity of the LED light source, resulting in certain limitations in its application in transient temperature measurement of leader discharge channels. In contrast, moiré deflection uses a laser source as the sensing light source. Due to the high luminous intensity of the laser, the temporal and spatial resolution of the system can be significantly improved while maintaining the contrast of the fringe image. Simultaneously, moiré deflection technology uses fringe imaging, giving the entire system strong resistance to environmental noise and vibration, making it a promising application for transient temperature measurement of gases in leader discharge channels.

[0005] In previous long-gap leader channel temperature measurement optical paths based on moiré deflection technology, the Langqi grating assembly was typically placed close to the high-voltage discharge electrode to reduce the distance between the reference grating and the discharge channel. This distance was usually less than 10 cm. However, the proximity of the grating to the high-voltage discharge electrode affected the electric field distribution around the electrode, ultimately impacting the number and development path of the leader discharge channels. This resulted in the inability to guarantee that the discharge channel parameters met the coaxial symmetry assumption required for the inverse Abel transform. Simultaneously, the gap between the reference grating and the discharge channel caused the light deflection range at the reference grating to be larger than that at the actual discharge channel, leading to a larger radial offset range in the obtained moiré fringe image. This, in turn, caused errors in the extraction of the light deflection angle distribution, ultimately resulting in errors in the inversion of the gas temperature distribution in the leader discharge channel. In summary, in a traditional moiré deflection optical path, the grating close to the high-voltage discharge electrode will cause the discharge to generate an irregular development path in the pilot channel. At the same time, the gap between the grating and the discharge channel will introduce errors in the extraction of the light deflection angle distribution, making it difficult to accurately measure the transient temperature of the gas in the long-gap pilot discharge channel using a traditional moiré deflection optical path.

[0006] In summary, current methods for continuous time-domain measurement of transient gas temperature in long-gap pilot discharge channels still have the following problems:

[0007] (1) Due to the non-repeatability of long-gap leader discharge, emission spectroscopy and Rayleigh laser scattering methods are difficult to apply to the measurement of temperature distribution in the leader discharge channel.

[0008] (2) The offset of Mach-Zehnder (MZ) laser interference fringes is positively correlated with the absolute value of the gas density change. However, the gas density change in the dark channel is very small, and the fringes have a certain width, making it difficult to fully apply the MZ laser interference method to the measurement of the temperature of the pilot discharge channel.

[0009] (3) The grayscale changes of quantitative schlieren images are easily affected by interference such as discharge self-luminescence and noise of imaging components, and the improvement of system time and space resolution is limited by the light intensity of LED light source, which leads to certain limitations in its application in the field of transient temperature measurement of pilot discharge channel.

[0010] In a traditional moiré deflection optical path, the grating close to the high-voltage discharge electrode will cause the discharge to generate an irregular development path in the pilot channel. At the same time, the gap between the grating and the discharge channel will introduce errors in the extraction of the light deflection angle distribution. As a result, it is difficult to accurately measure the transient temperature of the gas in the long-gap pilot discharge channel using a traditional moiré deflection optical path. Summary of the Invention

[0011] The purpose of this invention is to design a long-gap pilot discharge channel temperature measurement method and system based on moiré deflection, so as to solve the problem of large imaging error of pilot channel moiré fringes caused by the existence of a certain gap between the grating and the discharge electrode in the traditional moiré deflection optical path.

[0012] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0013] A long-gap pilot discharge channel temperature measurement system based on Moiré deflection includes: a high-power solid-state laser, a spatial filter, a collimating lens, a high-voltage discharge electrode, a first imaging lens, a second imaging lens, a Langie grating group, a converging lens, a slit, a filter, a high-speed camera, a data storage computer, an oscilloscope, an electro-optic converter, and a photoelectric converter. The high-power solid-state laser is used to generate laser light. The spatial filter is positioned at the focal point of the collimating lens to generate a parallel beam with uniform intensity distribution as the system's probe light, used to homogenize the laser beam and allow only zero-frequency light to pass through while eliminating other frequency light. The collimating lens has a circular light-transmitting surface. The high-power solid-state laser emits a parallel beam, which serves as the probe light passing through the pilot discharge channel. The high-voltage discharge electrode is positioned between the collimating lens and the first imaging lens, at the focal point of the first imaging lens. The distance between the high-voltage discharge electrode and the collimating lens is greater than the discharge gap size. A lightning or operational impulse voltage waveform is applied to the high-voltage discharge electrode according to experimental requirements, generating a pilot channel density and refractive index gradient field at the electrode tip. The first and second imaging lenses are convex lenses with the same focal length, forming a conjugate optical system. The distance between the first and second imaging lenses is twice the imaging distance. The focal length of the lens; the Langevin grating group consists of two Langevin gratings with a certain included angle, namely a reference grating and a detection grating, and the distance between the reference grating and the detection grating is an integer multiple of the Talbot distance, wherein the reference grating is placed at the focal point of the second imaging lens, and the Langevin grating group is used to form moiré fringes with a certain offset at the detection grating by the probe light obtained through the discharge channel perturbation; the slit only allows ± image-level fringes to pass through to eliminate the influence of grating diffraction, and is placed at the focal point of the converging lens, which focuses the parallel beam of light at the slit for moiré fringe imaging; the distance between the converging lens and the detection grating in the Langevin grating and The distance between the converging lens and the imaging plane of the high-speed camera is twice the focal length of the converging lens to ensure the spatial resolution of the moiré fringe image. The filter is used to eliminate the influence of discharge self-emission and improve the monochromaticity of the laser beam, thereby improving the imaging quality of the moiré fringes. The data storage computer is used for storing the moiré fringe image and extracting and analyzing the fringe data. The oscilloscope is used to measure and store the impulse voltage waveform applied to the high-voltage discharge electrode. The oscilloscope's AUX interface outputs a TTL signal, which is converted by an electro-optic converter and a photoelectric converter, transmitted to the high-speed camera, and synchronously triggered to achieve time synchronization of the entire measurement system.

[0014] Furthermore, the high-power solid-state laser is a continuous laser, and it generates a solid-state laser with a wavelength of 532 nm and an emission power ≥ optical power ≥ solid-state power.

[0015] Furthermore, the filter is a narrow-bandpass filter with a center wavelength of 532nm.

[0016] Furthermore, the collimating lens is a convex lens with a light-transmitting aperture of 10cm and a focal length of 1.0m, and the distance between the high-voltage discharge electrode and the collimating lens is greater than 1.0m.

[0017] Furthermore, the light transmission dimensions and focal length parameters of the first and second imaging lenses are the same as those of the collimating lens.

[0018] Furthermore, the frequency of the Langqi grating group is selected to be 20Hz, and the angle between the reference grating and the detection grating does not exceed 10°. - 2 rad.

[0019] Furthermore, the distance between the reference grating and the detection grating is 3 times the Tuber distance.

[0020] Furthermore, the converging lens is a convex lens with a light-transmitting aperture of 10cm and a focal length of 0.5m, while the detection grating and the imaging plane of the high-speed camera are respectively placed at a distance of 1.0m from the converging lens.

[0021] Furthermore, the high-speed camera employs a lensless direct projection imaging method to obtain the maximum spatial resolution of the moiré fringe image.

[0022] A measurement method for the temperature measurement system of the long gap pilot discharge channel based on Moiré deflection, comprising the following steps:

[0023] S1. A positive polarity impulse voltage is applied to the high-voltage discharge electrode to generate a pilot discharge channel;

[0024] S2. The impulse voltage waveform is measured, displayed and stored using an oscilloscope. The oscilloscope generates a trigger pulse signal, which is then used to trigger the high-speed camera in the moiré deflection optical path via an electro-optic converter and a photoelectric converter, thereby achieving synchronous acquisition of the time-resolved moiré deflection image of the pilot channel.

[0025] S3. The laser beam generated by the high-power solid-state laser is homogenized by a spatial filter and only zero-frequency light passes through. It is then further collimated by a collimating lens to form a parallel laser beam of the same size as the mirror. When the parallel laser beam passes through the refractive index gradient change region of the pilot discharge channel, it will be deflected outward.

[0026] S4. The parallel laser beam and the deflected light beam that has passed through the discharge will converge through the first imaging lens, and then pass through the second imaging lens to produce a mirror image of the light beam that is deflected at the discharge channel at the reference grating in the Rankine grating group; the deflected light beam passes through the Rankine grating group and produces a moiré fringe with a certain displacement at the detection grating, and then passes through the converging lens to form a multi-level light spot at the slit, wherein the slit only allows ± its level of fringes to pass through in order to eliminate the diffraction effect of the grating;

[0027] S5. The converging lens images the moiré fringes generated at the detection grating onto the high-speed camera, and the moiré fringes image is stored on the data storage computer.

[0028] S6. Based on the acquired moiré fringe image of the pilot discharge channel, the radial distribution of the number of offset pixels of the moiré fringe is extracted. Combined with the spatial resolution of the moiré image, the grating frequency, and the spacing between the reference grating and the detection grating, the radial distribution of the deflection angle generated by the parallel laser beam passing through the discharge channel is obtained.

[0029] S7. Based on the obtained radial distribution of light deflection angle and the coaxial symmetric distribution of pilot channel parameters, the radial distribution of the magnitude of refractive index of the discharge channel is obtained by combining the inverse Abel transform formula. The radial distribution data of transient gas temperature in the pilot channel can be obtained by using the Glaston-Dale formula and the ideal gas law.

[0030] The advantages of this invention are:

[0031] The technical solution of this invention employs a conjugate optical system consisting of a first imaging lens and a second imaging lens with the same parameters between the high-voltage discharge electrode and the Rankine grating group in the moiré deflection optical path. This system images the leader discharge channel onto the reference grating of the Rankine grating group, eliminating the interference of the Rankine grating group on the formation and development process of the leader discharge channel. This solves the problem of large imaging errors of the leader channel moiré fringes using the traditional moiré deflection optical path, and enables accurate measurement of the temperature of the long-gap leader discharge channel. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the long gap pilot discharge channel temperature measurement system based on Moiré deflection according to Embodiment 1 of the present invention.

[0033] Figure 2 This is a schematic diagram showing the deflection of parallel light as it passes through the leader discharge channel generated around the high-voltage discharge electrode. Detailed Implementation

[0034] 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 in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0036] Example 1

[0037] like Figure 1 As shown, the long-gap pilot discharge channel temperature measurement system based on moiré deflection in this embodiment of the invention includes: a high-power solid-state laser 11, a spatial filter 12, a collimating lens 13, a high-voltage discharge electrode 14, a first imaging lens 15, a second imaging lens 16, a Langie grating group 17, a converging lens 18, a slit 19, a filter 20, a high-speed camera 21, a data storage computer 22, an oscilloscope 23, an electro-optic converter 24, and a photoelectric converter 25.

[0038] The high-power solid-state laser 11 is used to generate a laser with a wavelength of 532 nm, a luminous power ≥ 100 Hz, and is a continuous laser.

[0039] The spatial filter 12 is positioned at the focal point of the collimating lens 13 to generate a parallel beam with uniform intensity distribution as the system's probe light. This beam homogenizes the laser beam and allows only zero-frequency light to pass through while eliminating other frequency light, effectively improving the quality of the moiré fringes and further enhancing the accuracy of the discharge channel gas temperature inversion.

[0040] The collimating lens 13 has a circular light-transmitting mirror surface, which makes the light emitted by the high-power solid-state laser 11 form a parallel beam and serve as the probe light passing through the pilot discharge channel.

[0041] The high-voltage discharge electrode 14 is disposed between the collimating lens 13 and the first imaging lens 15, and is located at the focal point of the first imaging lens 15. The distance between the high-voltage discharge electrode 14 and the collimating lens 13 is greater than the size of the discharge gap to meet the insulation safety distance requirements. Lightning or operational impulse voltage waveforms are applied to the high-voltage discharge electrode 14 according to experimental requirements. By applying the impulse voltage waveform, a leader channel density and refractive index gradient field are generated at the electrode end.

[0042] The first imaging lens 15 and the second imaging lens 16 are convex lenses with the same focal length to form a conjugate optical system, and the distance between the first imaging lens 15 and the second imaging lens 16 is twice the focal length of the imaging lens.

[0043] The Langzi grating group 17 is composed of two Langzi gratings with a certain included angle, namely a reference grating and a detection grating. The distance between the reference grating and the detection grating is an integer multiple of the Talbot distance. The reference grating is placed at the focal point of the second imaging lens 16. The entire Langzi grating group 17 is used to form a moiré fringe with a certain offset at the detection grating by the detection light obtained by the discharge channel disturbance.

[0044] The slit 19 allows only ± grade fringes to pass through to eliminate the effect of grating diffraction, and is placed at the focal point of the converging lens 18. The converging lens 18 focuses the parallel beam of light onto the slit 19 for moiré fringe imaging. The distance between the converging lens 18 and the detection grating in the Langzi grating group 17, as well as the distance between the converging lens 18 and the imaging plane of the high-speed camera 11, are both twice the focal length of the converging lens 18 to ensure the spatial resolution of the moiré fringe image.

[0045] The filter 20 is a narrow-bandpass filter with a center wavelength of 532nm to eliminate the influence of discharge self-luminescence and to improve the monochromaticity of the laser beam in order to improve the imaging quality of moiré fringes.

[0046] The data storage computer 22 is used for storing moiré fringe images and extracting and analyzing fringe data;

[0047] The oscilloscope 23 is used to measure and store the impulse voltage waveform applied to the high-voltage discharge electrode 14. The AUX interface of the oscilloscope 23 outputs a TTL signal, which is converted by the electro-optic converter 24 and the photoelectric converter 25 and transmitted to the high-speed camera 21 for synchronous triggering to achieve time synchronization of the entire measurement system.

[0048] The workflow of the long-gap pilot discharge channel temperature measurement system based on Moiré deflection in this invention is as follows:

[0049] Step 1: Apply a positive polarity impulse voltage to the high-voltage discharge electrode 14. As the amplitude of the impulse voltage applied to the high-voltage discharge electrode 14 continues to increase, when the electric field distribution near the electrode meets the initiation conditions for the streamer, the streamer discharge is generated, which then injects energy into the channel and heats the air molecules. When the gas temperature in the discharge channel reaches the critical temperature for triggering unstable thermal ionization, the discharge channel will complete the transformation from streamer to leader discharge. A single initial discharge channel with a vertical development perpendicular to the ground is generated at the electrode end. The refractive index in the discharge channel gradually increases from the center to the outside.

[0050] Step 2: Use oscilloscope 23 to measure, display and store the impulse voltage waveform, and oscilloscope 23 generates a trigger pulse signal, which is then used by electro-optic converter 24 and photoelectric converter 25 to trigger the high-speed camera 21 in the moiré deflection optical path, so as to realize the synchronous acquisition of the time-resolved moiré deflection image of the pilot channel.

[0051] Step 3: In the Moiré deflection measurement optical path, the laser beam generated by the high-power solid-state laser 11 is homogenized by the spatial filter 12 and only the zero-frequency light passes through. It is then further collimated by the collimating lens 13 to form a parallel laser beam of the same size as the mirror surface.

[0052] Step 4: When the parallel laser beam passes through the refractive index gradient change region of the pilot discharge channel, it will be deflected outwards, such as... Figure 2 As shown, the moiré deflection technique measures the distribution of the light deflection angle α at the corresponding position by detecting the fringe offset, and finally realizes the inversion calculation of the gas temperature distribution in the pilot discharge channel.

[0053] Step 5: The parallel laser beam and the deflected light beam that has passed through the discharge will converge through the first imaging lens 15 in the conjugate optical system, and further pass through the second imaging lens 16 to generate a mirror image of the light beam deflected at the discharge channel at the reference grating in the Langzi grating group 17.

[0054] Step 6: The deflected light passes through the Langqi grating group 17, generating a moiré fringe with a certain displacement at the detection grating, and further passes through the converging lens 18 to form a multi-level light spot at the slit 19, wherein the slit 19 only allows ± level fringes to pass through in order to eliminate the diffraction effect of the grating.

[0055] Step 7: The converging lens 18 images the moiré fringes generated at the detection grating onto the high-speed camera 21. The high-speed camera 21 uses a lensless direct projection imaging method to obtain the maximum spatial resolution of the moiré fringes image, and the moiré fringes image is stored on the computer.

[0056] Step 8: Based on the acquired pilot discharge channel moiré fringe image, the radial distribution of the number of offset pixels of the moiré fringe is extracted. Combined with parameters such as the spatial resolution of the moiré image, the grating frequency, and the spacing between the reference grating and the detection grating, the radial distribution of the deflection angle generated by the parallel laser beam passing through the discharge channel is obtained.

[0057] Step 9: Based on the obtained radial distribution of light deflection angle and the assumption of coaxial symmetry distribution of pilot channel parameters, the radial distribution of refractive index of discharge channel can be obtained by combining the inverse Abel transform formula, and the radial distribution data of transient gas temperature of pilot channel can be obtained by using the Glaston-Dale formula and ideal gas law.

[0058] Step 10: By changing the axial distribution cross section of the pilot channel, repeating steps 8 and 9, the radial temperature distribution on different axial cross sections of the discharge channel can be obtained; by continuously analyzing multiple moiré fringe images, the temporal evolution law of the temperature distribution of the pilot discharge channel can be obtained.

[0059] To ensure the quality of the moiré fringe image, the high-power solid-state laser 11 in the moiré deflection optical path should have a power greater than 100mW to ensure image brightness and facilitate accurate extraction of the moiré fringe offset. In conducting a positive polarity 1.0m rod-plate gap impulse discharge experiment, to balance the system's observation space and optical path length, and considering the difficulty of lens fabrication, the collimating lens 13 is a convex lens with a 10cm aperture and a 1.0m focal length. The high-voltage discharge electrode 14 is positioned 1.0m away from the collimating lens to prevent discharge. Simultaneously, the first imaging lens 15 and the second imaging lens 16 have the same aperture and focal length as the collimating lens 13 to ensure the optical path's insulation safety under high-voltage experimental conditions. To balance system sensitivity and the actual moiré fringe spacing, the frequency of the Langqi grating group 17 is selected as 20Hz, and the angle between the reference grating and the detection grating does not exceed 10°. -2 The distance between the two gratings can be selected as 3 times the Tuber distance. In order to shorten the optical path length and ensure the spatial resolution of the moiré fringe image, the converging lens 18 adopts a convex lens with a light-passing diameter of 10cm and a focal length of 0.5m. At the same time, the detection grating and the imaging plane of the high-speed camera 21 are respectively placed at a distance of 1.0m from the converging lens to ensure that the image spatial resolution is greater than 20 and the resolution is greater than the image spatial resolution.

[0060] The key point of the long-gap leader discharge channel temperature measurement system and method based on moiré deflection proposed in this invention lies in the use of a conjugate optical system between the high-voltage discharge electrode 14 and the Langevin grating group 17, consisting of a first imaging lens 15 and a second imaging lens 16 with identical parameters. This system images the leader discharge channel onto the Langevin grating group 17, eliminating the interference of the Langevin grating group 17 on the formation and development process of the leader discharge channel. This solves the problem of large imaging errors in the leader channel moiré fringes using traditional moiré deflection optical paths, enabling accurate measurement of the temperature of the long-gap leader discharge channel. Therefore, using the aforementioned conjugate optical system to achieve a spatial mirror image of the discharge channel, and based on various optical flow field display technologies, such as quantitative schlieren and Mach-Zehnder (MZ) laser interferometry, can achieve some of the functions of this invention, and are therefore considered alternatives to this application.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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. Such 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 temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection, characterized in that, include: The system comprises a high-power solid-state laser (11), a spatial filter (12), a collimating lens (13), a high-voltage discharge electrode (14), a first imaging lens (15), a second imaging lens (16), a Langzier grating group (17), a converging lens (18), a slit (19), a filter (20), a high-speed camera (21), a data storage computer (22), an oscilloscope (23), an electro-optic converter (24), and a photoelectric converter (25). The high-power solid-state laser (11) is used to generate laser light. The spatial filter (12) is positioned at the focal point of the collimating lens (13) to generate a parallel beam with uniform intensity distribution as the system's probe light, used to homogenize the laser beam and make only zero-frequency light the probe beam. Light passes through while eliminating other frequencies of light; the collimating lens (13) has a circular light-transmitting mirror surface, which makes the light emitted by the high-power solid-state laser (11) form a parallel beam and serve as the probe light passing through the pilot discharge channel; the high-voltage discharge electrode (14) is disposed between the collimating lens (13) and the first imaging lens (15), and is placed at the focal point of the first imaging lens (15), and the distance between the high-voltage discharge electrode (14) and the collimating lens (13) is greater than the size of the discharge gap; lightning or operational impulse voltage waveforms are applied to the high-voltage discharge electrode (14) according to experimental requirements, and the pilot channel density and refractive index gradient field are generated at the electrode end by applying the impulse voltage waveform; the first imaging... The first imaging lens (15) and the second imaging lens (16) are convex lenses with the same focal length, forming a conjugate optical system. The distance between the first imaging lens (15) and the second imaging lens (16) is twice the focal length of the imaging lens. The Langzi grating group (17) is composed of two Langzi gratings with a certain included angle, namely a reference grating and a detection grating. The distance between the reference grating and the detection grating is an integer multiple of the Talbot distance. The reference grating is placed at the focal point of the second imaging lens (16). The Langzi grating group (17) is used to form moiré fringes with a certain offset at the detection grating by the detection light obtained through the discharge channel disturbance. The slit (19) only allows ± grade fringes to pass through to eliminate light. The influence of grating diffraction is mitigated, and the beam is placed at the focal point of the converging lens (18), which focuses the parallel beam at the slit (19) for moiré fringe imaging. The distance between the converging lens (18) and the detection grating in the Langzi grating group (17), as well as the distance between the converging lens (18) and the imaging plane of the high-speed camera (11), are both twice the focal length of the converging lens (18) to ensure the spatial resolution of the moiré fringe image. The filter (20) is used to eliminate the influence of discharge self-luminescence and improve the monochromaticity of the laser beam, thereby improving the imaging quality of the moiré fringes. The data storage computer (22) is used for storing the moiré fringe image and extracting and analyzing the fringe data.The oscilloscope (23) is used to measure and store the impulse voltage waveform applied to the high-voltage discharge electrode (14). The AUX interface of the oscilloscope (23) outputs a TTL signal, which is converted by an electro-optic converter (24) and a photoelectric converter (25) and transmitted to the high-speed camera (21) for synchronous triggering to achieve timing synchronization of the entire measurement system.

2. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The high-power solid-state laser (11) is a continuous laser and generates a laser with a wavelength of 532 nm and a wavelength of 532 nm. The laser's emission power is greater than or equal to the laser's emission power.

3. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The filter (20) is a narrow-bandpass filter with a center wavelength of 532nm.

4. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The collimating lens (13) is a convex lens with a light-transmitting aperture of 10cm and a focal length of 1.0m, and the distance between the high-voltage discharge electrode (14) and the collimating lens (13) is greater than 1.0m.

5. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The light transmission size and focal length parameters of the first imaging lens (15) and the second imaging lens (16) are the same as those of the collimating lens (13).

6. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The frequency of the Langqi grating group (17) is selected to be 20Hz, and the angle between the reference grating and the detection grating does not exceed 10°. -2 rad.

7. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The distance between the reference grating and the detection grating is 3 times the Tuber distance.

8. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The converging lens (18) is a convex lens with a light-transmitting aperture of 10cm and a focal length of 0.5m. The imaging planes of the detection grating and the high-speed camera (21) are respectively placed at a distance of 1.0m from the converging lens (18).

9. The temperature measurement system for a long-gap pilot discharge channel based on Moiré deflection according to claim 1, characterized in that, The high-speed camera (21) uses a lensless direct projection imaging method to obtain the maximum spatial resolution of the moiré fringe image.

10. A measurement method for the temperature measurement system of a long-gap pilot discharge channel based on moiré deflection as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. A positive polarity impulse voltage is applied to the high voltage discharge electrode (14) to generate a pilot discharge channel; S2. The impulse voltage waveform is measured, displayed and stored using an oscilloscope (23). The oscilloscope (23) generates a trigger pulse signal, which is then used to trigger the high-speed camera (21) in the moiré deflection optical path via an electro-optic converter (24) and a photoelectric converter (25), thereby realizing the synchronous acquisition of the time-resolved moiré deflection image of the pilot channel. S3. The laser beam generated by the high-power solid-state laser (11) is homogenized by the spatial filter (12) and only the zero-frequency light passes through. It is further collimated by the collimating lens (13) to form a parallel laser beam of the same size as the mirror. When the parallel laser beam passes through the refractive index gradient change region of the pilot discharge channel, it will be deflected outward. S4, the parallel laser beam and the deflected light beam that has passed through the discharge will converge through the first imaging lens (15), and further pass through the second imaging lens (16) and generate a mirror image of the light beam deflected at the reference grating in the Langzi grating group (17); the deflected light beam passes through the Langzi grating group (17) and generates a moiré fringe with a certain displacement at the detection grating, and further passes through the converging lens (18) to form a multi-level light spot at the slit (19), wherein the slit (19) only allows ± level fringes to pass through in order to eliminate the diffraction effect of the grating; S5. The converging lens (18) images the moiré fringes generated at the detection grating onto the high-speed camera (21), and the moiré fringes image is stored on the data storage computer (22). S6. Based on the acquired moiré fringe image of the pilot discharge channel, the radial distribution of the number of offset pixels of the moiré fringe is extracted. Combined with the spatial resolution of the moiré image, the grating frequency, and the spacing between the reference grating and the detection grating, the radial distribution of the deflection angle generated by the parallel laser beam passing through the discharge channel is obtained. S7. Based on the obtained radial distribution of light deflection angle and the coaxial symmetric distribution of pilot channel parameters, the radial distribution of the magnitude of refractive index of the discharge channel is obtained by combining the inverse Abel transform formula. The radial distribution data of transient gas temperature in the pilot channel can be obtained by using the Glaston-Dale formula and the ideal gas law.

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