An MPD cathode temperature monitoring system and method based on infrared radiation imaging

Abstract

The present invention discloses an MPD cathode temperature monitoring system and method based on infrared radiation imaging. The monitoring system includes a notch filter, a photodetector, a measurement and control system, and a camera. The notch filter is used to shield the plume radiation light in the cathode radiation light of the MPD, and is respectively arranged on two windows of the vacuum chamber where the MPD works during operation. The monitoring method is as follows: the cathode radiation light is received by the photodetector after passing through the notch filter, and the photodetector outputs the light intensity signal to the measurement and control system to obtain the expected value of the camera exposure time, and then controls the exposure time of the camera. The camera receives the cathode radiation light and generates an infrared radiation photo. The measurement and control system obtains the MPD cathode temperature according to the infrared radiation photo. The present invention effectively eliminates the radiation interference of the plasma plume, controls the camera exposure time in real time, realizes the measurement of the surface temperature and morphology of the MPD cathode, and has the advantages of accurate results and strong applicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, relates to a test method for a magnetoplasma thruster, and particularly relates to an MPD cathode temperature monitoring system and method based on infrared radiation imaging. Background Art

[0002] The magnetoplasma thruster (MPD) is a type of electric propulsion system that adopts a completely different design concept from chemical rockets. Its thrust mainly relies on the combined acceleration of electromagnetic force and aerodynamic force to generate plasma. Compared with other electric propulsion technologies, the magnetoplasma thruster has the advantages of high thrust density and specific impulse, and has great application prospects in interstellar missions. However, one of the key parameters of the thruster - the service life is severely restricted by the ablation problem of the cathode. Due to the extremely high cathode temperature (>3000K), the existing contact temperature measurement methods are difficult to achieve real-time monitoring of the cathode surface temperature and surface ablation morphology, and a more intuitive and non-interfering test technology is needed. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above defects and provide an MPD cathode temperature monitoring system and method based on infrared radiation imaging. The monitoring system of the present invention includes a notch filter, a photodetector, a measurement and control system, and a camera; the notch filter is used to shield the plume radiation light in the radiation light of the MPD cathode, including a first notch filter and a second notch filter; the first notch filter and the second notch filter are respectively arranged on two windows of the vacuum chamber where the MPD works; the monitoring method is that the cathode radiation light is received by the photodetector after passing through the first notch filter, and the photodetector outputs the light intensity signal of the cathode radiation light to the measurement and control system; the measurement and control system calculates the expected value of the camera exposure time according to the light intensity signal, and outputs an exposure time control signal to the camera according to the expected value of the camera exposure time; the camera adjusts the exposure time according to the exposure time control signal, and receives the cathode radiation light passing through the second notch filter to generate an infrared radiation photo; the measurement and control system obtains the MPD cathode temperature according to the infrared radiation photo. The present invention effectively eliminates the radiation interference of the plasma plume, controls the camera exposure time in real time, realizes the measurement of the MPD cathode surface temperature and morphology, and has the advantages of accurate results and strong applicability.

[0004] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0005] An MPD cathode temperature monitoring system based on infrared radiation imaging, including a notch filter, a photodetector, a measurement and control system, and a camera;

[0006] The notch filter is used to shield the plume radiation light in the cathode radiation light of the MPD, and includes a first notch filter and a second notch filter; the first notch filter and the second notch filter are respectively arranged on two windows of the vacuum chamber where the MPD works;

[0007] The cathode radiation light is received by the photodetector after passing through the first notch filter, and the photodetector outputs the light intensity signal of the cathode radiation light to the measurement and control system; the measurement and control system calculates the expected value of the camera exposure time according to the light intensity signal, and outputs an exposure time control signal to the camera according to the expected value of the camera exposure time; the camera adjusts the exposure time according to the exposure time control signal, and receives the cathode radiation light passing through the second notch filter to generate an infrared radiation photo; the measurement and control system obtains the MPD cathode temperature according to the infrared radiation photo.

[0008] Further, the above monitoring system further includes a spectral measurement mechanism, which is used to obtain the plume radiation light in the vacuum chamber and determine the strong radiation band and weak radiation band in the plume radiation light according to the radiation power. The specific method is to judge whether the radiation intensity of the adjacent band of a certain band A is below 5% of the radiation intensity of band A. If so, band A is taken as the strong radiation band, and if not, band A is taken as the weak radiation band.

[0009] The notch filter shields the strong radiation band and transmits the weak radiation band.

[0010] Further, the spectral measurement mechanism in the above monitoring system includes a spectrometer, an optical fiber and an optical fiber probe. The optical fiber probe is installed at the head of the optical fiber, and the tail of the optical fiber is connected to the spectrometer.

[0011] Further, the acquisition frequency of the photodetector in the above monitoring system > 1MHz;

[0012] The two windows of the vacuum chamber where the MPD works are quartz windows with a transmittance ≥ 80% in the wavelength range of 200 - 2000nm.

[0013] A method for monitoring the MPD cathode temperature based on infrared radiation imaging, implemented by using the above monitoring system, includes the following steps:

[0014] S1 The cathode radiation light is received by the photodetector after passing through the first notch filter, and the photodetector outputs the light intensity signal of the cathode radiation light to the measurement and control system;

[0015] S2 The measurement and control system calculates the expected value of the camera exposure time according to the light intensity signal, and outputs an exposure time control signal to the camera according to the expected value of the camera exposure time;

[0016] The S3 camera adjusts the exposure time according to the exposure time control signal, and receives the cathode radiation light passing through the second notch filter to generate an infrared radiation photo;

[0017] The S4 measurement and control system obtains the MPD cathode temperature based on the infrared radiation photo.

[0018] Further, in step S2 of the above monitoring method, the calculation formula for the expected value of the camera exposure time obtained by the measurement and control system according to the light intensity signal is as follows:

[0019] t = cW 0c / I d

[0020] where t is the expected value of the camera exposure time, I d is the light intensity signal output by the photodetector, W 0c is the irradiance corresponding to the camera's full well, and c is the correction coefficient.

[0021] Further, in step S4 of the above monitoring method, the measurement and control system obtains the MPD cathode temperature based on the calibration curve of the relationship between the gray value output by the camera and the temperature and the gray value of the infrared radiation photo;

[0022] The calibration curve of the relationship between the gray value output by the camera and the temperature is obtained through a calibration experiment;

[0023] In the calibration experiment, the object photographed by the camera is the MPD cathode heated in a programmable muffle furnace. There is the same window and notch filter between the MPD cathode and the camera as in step S3. The photographing conditions of the camera and the spatial relationship between the MPD cathode and the camera are exactly the same as in step S3. According to the gray value of the photo obtained in the calibration experiment and the temperature of the programmable muffle furnace, the calibration curve of the relationship between the gray value output by the camera and the temperature is obtained.

[0024] Further, in the calibration experiment of the above monitoring method, a protective cover for shielding the luminescence of the corundum tube in the programmable muffle furnace is provided outside the MPD cathode.

[0025] Further, in step S4 of the above monitoring method, it also includes establishing a general relationship formula between the gray value N output by the camera and the temperature T according to the calibration curve of the relationship between the gray value output by the camera and the temperature obtained through the calibration experiment. The specific steps are as follows:

[0026] S4.1 Establish the calibration formula between the output gray value N and the temperature T:

[0027]

[0028] where c1 is the first radiation constant, and its value is 3.742×10 -16 W·m 2, c2 is the second radiation constant, with a value of 1.4388×10 -2 m·K, λ is the central wavelength passing through the notch filter, and Δt is the camera exposure time; the calibration coefficient A = CεΔλΔS, where C is the energy conversion coefficient of the camera, ε is the emissivity of the material, Δλ is the bandwidth of the notch filter, and ΔS is the surface element on the MPD cathode surface;

[0029] S4.2 Calibrate the calibration coefficient A according to the calibration curve of the relationship between the output gray value of the camera and the temperature obtained from the calibration experiment, and obtain the general relationship between the output gray value N of the camera and the temperature T.

[0030] Furthermore, in step S4 of the above monitoring method, when the temperature control range t1~t2 of the programmable muffle furnace in the calibration experiment is less than the MPD cathode temperature range, the MPD cathode temperature within the range of t1~t2 is determined according to the calibration curve of the relationship between the output gray value of the camera and the temperature, and the MPD cathode temperature outside the range of t1~t2 is determined according to the general relationship between the output gray value N of the camera and the temperature T.

[0031] The present invention has the following beneficial effects compared with the prior art:

[0032] (1) The present invention fully eliminates the influence of strong plume radiation interference, and realizes the measurement of the surface temperature and morphology of the MPD cathode by using the high-temperature radiation characteristics of the MPD cathode. It has the advantage of non-contact and can provide key data for thruster development and ground performance analysis;

[0033] (2) The method of the present invention fully considers practicality. For the complex environment of a large vacuum chamber and a small window, all test equipment is installed outside the vacuum chamber, and a single camera is used, maximizing the applicability to the complex environment;

[0034] (3) The present invention designs the filtering characteristics of the notch filter according to the plume radiation spectrum, uses the notch filter to shield the strong radiation spectrum of the plume in the cathode radiation light, and transmits other bands, effectively shortening the exposure time and improving the dynamic measurement performance;

[0035] (4) The present invention, based on the practical problems that the cathode radiation light intensity changes greatly during the arc starting and working condition changes in the MPD working process, controls the exposure time of the camera based on the signal intensity of the photodetector, realizes the dynamic exposure of the camera, and the test system of the present invention is particularly suitable for use in a changing environment. Brief Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the MPD cathode temperature monitoring system based on infrared radiation imaging of the present invention;

[0037] Figure 2Flowchart of the MPD cathode temperature monitoring method based on infrared radiation imaging according to the present invention;

[0038] Figure 3 Infrared radiation photograph of the MPD cathode taken by the camera according to the present invention;

[0039] Figure 4 Variation diagram of the cathode end face temperature with time according to the present invention;

[0040] Figure 5 Relationship curve between radiation energy and the surface temperature of an object;

[0041] Figure 6 Schematic diagram of the calibration experiment according to the present invention;

[0042] Figure 7 Relationship curve between the output gray value of the camera and the temperature obtained from the calibration experiment according to the present invention. Detailed implementation manner

[0043] The following provides a detailed description of the present invention, and the features and advantages of the present invention will become clearer and more definite along with these descriptions.

[0044] Here, the special term "exemplary" means "serving as an example, embodiment, or illustration". Any embodiment described as "exemplary" here does not necessarily have to be interpreted as superior to or better than other embodiments. Although various aspects of the embodiments are shown in the drawings, unless otherwise specified, the drawings do not have to be drawn to scale.

[0045] The present invention combines a notch filter and a CCD camera to completely eliminate the interference of the plume radiation spectrum, enabling clear imaging of the MPD cathode. Based on the imaging gray value, the surface temperature of the cathode can be obtained.

[0046] Such as Figure 1 , the MPD cathode temperature monitoring system based on infrared radiation imaging according to the present invention includes a spectrometer, an optical fiber, an optical fiber probe, a notch filter, a photodetector, a measurement and control system, and a camera.

[0047] The spectrometer is connected to the optical fiber, and an optical fiber probe is installed at the head of the optical fiber. The optical fiber probe is an optical coupler that receives parallel light, collects the plume radiation light into the optical fiber, and transmits it to the spectrometer. The spectrometer analyzes the spectral characteristics of the plume and extracts the weak wavelength band of the plume spectrum for designing the notch filter.

[0048] The notch filter is installed at two inclined windows of the vacuum chamber. The window material is quartz, which can ensure high transmittance in a wide spectrum range of 200 - 2000 nm. A high-frequency photodetector and a camera are respectively installed behind the two notch filters.

[0049] The light intensity signal output by the high-frequency photodetector is collected by the measurement and control system, and the exposure time of the camera is obtained through calculation; the measurement and control system outputs a signal to control the exposure time of the camera, reads the photos taken by the camera, and the taken photos enter the measurement and control system for processing and calculation, and are finally stored in the hard disk of the server.

[0050] The above system realizes the dynamic exposure control of the camera through the combination of the photodetector, the measurement and control system and the camera, so that the measurement system can be applied to the situation where the luminous intensity changes abruptly.

[0051] Such as Figure 2 , the steps of the MPD cathode temperature monitoring method based on infrared radiation imaging of the present invention are as follows:

[0052] Step 1, use a spectrometer to collect the characteristic spectrum of the MPD plume, analyze the intensity distribution characteristics of the spectrum, and evaluate the range boundary of the weaker spectral band; judge whether the radiation intensity of the adjacent band of a certain band A is below 5% of the radiation intensity of band A. If so, then take band A as the strong spectral band. If not, then take band A as the weak spectral band.

[0053] Step 2, design a total of 2 notch filters and install them at the front ends of the camera and the high-frequency photodetector respectively;

[0054] Step 3, align the optical axes and imaging positions of the camera and the high-frequency photodetector with the cathode of the MPD;

[0055] Step 4, the measurement and control system collects the output light intensity signal of the high-frequency photodetector and judges the radiation intensity of the MPD cathode;

[0056] Step 5, the measurement and control system outputs a control signal to control the exposure time of the camera, or simultaneously controls the gate width and the opening moment during exposure to realize imaging of the cathode;

[0057] Step 6, the measurement and control system collects the output photos of the camera, processes and analyzes the gray value distribution in the photos, and obtains the temperature distribution through comparison with the calibration data;

[0058] Step 7, the measurement and control system saves the collected photos and the temperature distribution to the server hard disk;

[0059] Step 8, the measurement and control system starts collecting again, repeats steps 4-7, and realizes long-time dynamic continuous collection of the MPD cathode.

[0060] The calibration data in the above step 6 is obtained through a calibration experiment, Figure 6 gives a schematic diagram of the calibration experiment, which mainly includes two parts:

[0061] (1) The CCD camera and the optical acquisition system include the CCD camera, quartz window, notch filter, etc. used in the MPD cathode temperature monitoring system based on infrared radiation imaging. All the devices and working distances in the calibration system should be the same as those in the above monitoring system;

[0062] (2) The programmable muffle furnace. The maximum temperature of the existing muffle furnace is 1700 °C. The object to be measured should be the MPD cathode used in the experiment, or other structures with a temperature higher than 800 °C, such as the anode and the high-temperature part of the magnetic coil, etc. That is, the temperature monitoring device and method of the present invention are not only applicable to the MPD cathode temperature monitoring, but also applicable to the temperature detection of structures such as the anode and the high-temperature part of the magnetic coil.

[0063] Two points should be noted in the calibration experiment: (1) The spatial relationship (distance, pitch angle, etc.) between the position of the CCD camera and the object to be measured should be the same as that in the MPD cathode temperature monitoring system; (2) At high temperatures, the inner surface of the corundum tube in the furnace also has strong radiation and luminescence. Therefore, a protective cover is required around the material to be measured to avoid the luminescence of other materials.

[0064] Figure 7 The calibration curve of the output gray level of the typical CCD camera and the temperature is given. In the figure, N represents the gray level, and the gray level and the reciprocal of the temperature are linearly related under the logarithmic coordinates. According to this curve, the temperature at the measuring point can be obtained by using the gray level (with the same gain and shooting position) acquired by the CCD camera. When the exposure time of the photo in the calibration experiment is different from that of the infrared radiation photo obtained during real-time monitoring, the gray level of the infrared radiation photo can be converted into the corresponding gray level at the exposure time of the photo in the calibration experiment according to the ratio of the exposure times of the two, and then the MPD cathode temperature can be obtained according to the calibration curve.

[0065] The monochromatic thermometry method refers to using the relationship between the radiant energy of a single wavelength and the temperature for temperature measurement. According to Planck's law, the spectral radiant exitance E bλ of an actual object and the temperature T is as follows:

[0066]

[0067] ε(λ,T) is the monochromatic emissivity of the object, which varies with the wavelength and temperature of the object. In this article, it is assumed that the objects to be measured are all gray bodies, that is, the monochromatic emissivity and the directional emissivity ε(θ) on the surface of the object to be measured are equal, that is, ε(λ,T) = ε(θ) = ε.

[0068] In the formula: E bλ is the spectral radiant exitance, with the unit of W / m 3 ;

[0069] λ is the wavelength, with the unit of m;

[0070] T is the thermodynamic temperature in black body, with the unit of K;

[0071] e is the base of the natural logarithm;

[0072] c1 is the first radiation constant, with a value of 3.742×10 -16 W·m 2 ;

[0073] c2 is the second radiation constant, with a value of 1.4388×10 -2 m·K;

[0074] θ is the angle with the normal direction of the radiation surface;

[0075] ε is the emissivity of the material.

[0076] Actually, the monochromatic temperature measurement method realizes temperature measurement based on the relationship between the radiant energy in a narrow band and the temperature. When the band is narrow, it can be considered that the spectral radiant intensity within the band is equal.

[0077] According to the spectral radiant intensity E bλ we can obtain Figure 5 the radiation energy Φ-T curve as shown, for the surface of an object with a surface area of 1 cm 2 after 0.01 s, the relationship between the radiation energy and the temperature within a certain band (780 nm) is as Figure 5 shown.

[0078] According to the above monochromatic temperature measurement method, the radiation energy Φ can be expressed as:

[0079]

[0080] Corresponding to the specific situation during the MPD cathode temperature test, the meanings of the physical quantities in the above formula are: c1 is the first radiation constant, with a value of 3.742×10 -16 W·m 2 , c2 is the second radiation constant, with a value of 1.4388×10 -2 m·K, λ is the central wavelength passing through the notch filter, Δt is the camera exposure time, ε is the emissivity of the material, T is the MPD cathode temperature, Δλ is the notch filter bandwidth, and ΔS is the surface element of the MPD cathode surface.

[0081] Since the radiation energy is proportional to the gray value N of the image captured by the CCD camera, the relationship can be expressed as:

[0082] N = CΦ;

[0083] where C is the energy conversion coefficient of the camera. Combining with formula (2), we can obtain:

[0084]

[0085] Combine the parameters of the above formula so that the calibration coefficient A = C * ε * Δλ * ΔS, and the calibration formula can be obtained:

[0086]

[0087] For the experimental setup described in this patent, Δλ, ΔS, and ε all remain unchanged, where A is the calibration coefficient containing C and the above three parameters.

[0088] In the present invention, the key technology of monochromatic temperature measurement is to calibrate the relationship between the gray value (corresponding to the radiation energy) output by the camera and the temperature. After calibrating A using the above calibration curve, a general relationship between the gray value N and the temperature T that is also applicable outside the temperature control range of the programmable muffle furnace can be obtained. For example Figure 7 As shown, the fitting formula can also be established first According to the data obtained from the calibration experiment, directly determine the fitting coefficients A' and B' in the fitting formula, and a general relationship between the gray value N and the temperature T that is applicable both inside and outside the temperature control range of the programmable muffle furnace can also be established.

[0089] Based on the high-temperature surface radiation characteristics of materials, the present invention designs a suitable spectral band and testing equipment to achieve dynamic imaging of the radiation on the cathode surface in the infrared band, which can minimize the exposure time and effectively eliminate the radiation interference of the plasma plume; achieve precise control of the camera exposure time, and can capture the dynamic characteristics of the surface temperature. This process is crucial for optimizing the cathode design of the thruster and improving the overall life of the thruster.

[0090] Example 1:

[0091] As Figure 1 shown, an MPD cathode temperature monitoring system based on infrared radiation imaging according to the present invention includes a spectrometer, an optical fiber, an optical fiber probe, a notch filter, a high-frequency photodetector, a measurement and control system, and a camera.

[0092] The spectrometer (AvaSpec-ULS4096CL-EVO fiber spectrometer) is connected to the optical fiber (multimode optical fiber, core diameter 400um). An optical fiber probe is installed at the head of the optical fiber. The optical fiber probe is an optical coupler (Thorlabs, F950SMA-A) that receives parallel light, collects the plume radiation light into the optical fiber, and transmits it to the spectrometer. The spectrometer analyzes the spectral characteristics of the plume, divides the spectral band of the plume radiation light into a strong spectral band and a weak spectral end, and is used to design a notch filter so that the notch filter shields the plasma luminescence in the plume. The radiation passing through the notch filter is mainly thermal radiation, which can improve the accuracy of imaging temperature measurement.

[0093] The notch filter used in this embodiment has a transmission band of 800 - 950 nm, which blocks strong plume radiation spectral bands such as 811 nm and 840 nm. The notch filter is installed at two inclined windows where the MPD operates. The window material is quartz, which can ensure high transmittance in the wide spectral range of 200 - 2000 nm.

[0094] In the present invention, the surface of the MPD cathode is measured. The surface temperature range of the MPD cathode is from several hundred K to about 3000 K. The surface radiance is proportional to the fourth power of the temperature. That is, the irradiance received by the camera changes by more than 1000 times. If real-time exposure is not performed, the camera will be underexposed or overexposed, both of which will lead to data distortion (the intensity response of the camera has a non-linear response region in both weak light and strong light). In this case, it is impossible to use the gray output of the camera to convert the cathode temperature.

[0095] Therefore, in the present invention, high-frequency photodetectors above MHz and cameras are respectively installed behind the two notch filters to control the exposure time of the camera in real time, so that the photos taken can best reflect the infrared radiation distribution of the MPD cathode.

[0096] The optical intensity signal output by the high-frequency photodetector (Thorlabs DET10A2) is collected by the measurement and control system (NI 6115 multifunctional acquisition card and virtual instrument software), and the expected value of the exposure time of the camera (DMK 33UX273) is obtained through calculation. The specific calculation formula is as follows:

[0097] t = cW 0c / I d

[0098] where t is the expected value of the camera exposure time, I d is the optical intensity signal output by the photodetector, W 0c is the irradiance corresponding to the full well of the camera, and c is the correction coefficient, which is obtained by pre-calibrating with a standard tungsten light source.

[0099] The measurement and control system outputs a signal to control the exposure time of the camera, and reads the photos taken by the camera as Figure 3 shown. The taken photos enter the measurement and control system for processing and calculation to obtain the MPD cathode temperature as Figure 4 , and finally saved in the hard disk of the server (Lenovo SR550). A larger hard disk (>100TB) ensures that the test system can run and save data for a long time.

[0100] The present invention has been described in detail above in connection with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions of the present invention and their implementation manners, and these all fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

[0101] The content not detailedly described in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. An MPD cathode temperature monitoring system based on infrared radiation imaging, characterized in that, It includes a notch filter, a photodetector, a measurement and control system, and a camera; The notch filter is used to shield the strong radiation band in the plume radiation light of the cathode radiation light of the magnetoplasma thruster MPD, and includes a first notch filter and a second notch filter; the first notch filter and the second notch filter are respectively arranged on two windows of the vacuum chamber where the magnetoplasma thruster MPD works; The cathode radiation light is received by the photodetector after passing through the first notch filter, and the photodetector outputs the light intensity signal of the cathode radiation light to the measurement and control system; the measurement and control system calculates the expected value of the camera exposure time according to the light intensity signal, and outputs an exposure time control signal to the camera according to the expected value of the camera exposure time; the camera adjusts the exposure time according to the exposure time control signal, and receives the cathode radiation light passing through the second notch filter to generate an infrared radiation photo; the measurement and control system obtains the cathode temperature of the magnetoplasma thruster MPD according to the infrared radiation photo.

2. The MPD cathode temperature monitoring system based on infrared radiation imaging according to claim 1, characterized in that, It also includes a spectral measurement mechanism, which is used to obtain the plume radiation light in the vacuum chamber and determine the strong radiation band and weak radiation band in the plume radiation light according to the radiation power. The specific method is to judge whether the radiation intensity of the adjacent band of a certain band A is below 5% of the radiation intensity of band A. If so, band A is regarded as the strong radiation band. If not, band A is regarded as the weak radiation band; The notch filter shields the strong radiation band and transmits the weak radiation band.

3. The MPD cathode temperature monitoring system based on infrared radiation imaging according to claim 2, characterized in that, The spectral measurement mechanism includes a spectrometer, an optical fiber, and an optical fiber probe. The optical fiber probe is installed at the head of the optical fiber, and the tail of the optical fiber is connected to the spectrometer.

4. The MPD cathode temperature monitoring system based on infrared radiation imaging according to claim 1, characterized in that, The acquisition frequency of the photodetector > 1 MHz; The two windows of the vacuum chamber where the magnetoplasma thruster MPD works are quartz windows with a transmittance ≥ 80% in the wavelength range of 200 - 2000 nm.

5. An MPD cathode temperature monitoring method based on infrared radiation imaging, characterized in that, It is implemented by using a magnetoplasma thruster MPD cathode temperature monitoring system based on infrared radiation imaging according to any one of claims 1 - 4, and includes the following steps: S1 The cathode radiation light is received by the photodetector after passing through the first notch filter, and the photodetector outputs the light intensity signal of the cathode radiation light to the measurement and control system; S2 The measurement and control system calculates the expected value of the camera exposure time according to the light intensity signal, and outputs an exposure time control signal to the camera according to the expected value of the camera exposure time; S3 The camera adjusts the exposure time according to the exposure time control signal, and receives the cathode radiation light passing through the second notch filter to generate an infrared radiation photo; S4 The measurement and control system obtains the cathode temperature of the magnetoplasma thruster MPD according to the infrared radiation photo.

6. The MPD cathode temperature monitoring method based on infrared radiation imaging according to claim 5, characterized in that, In step S2, the calculation formula for the measurement and control system to calculate the expected value of the camera exposure time according to the light intensity signal is as follows: t = cW 0c / I d wherein, t is the expected value of the camera exposure time, I d is the optical intensity signal output by the photodetector, W 0c is the irradiance corresponding to the camera full well, c is the correction coefficient.

7. The MPD cathode temperature monitoring method based on infrared radiation imaging according to claim 5, characterized in that, In step S4, the measurement and control system obtains the cathode temperature of the magnetoplasma thruster MPD according to the calibration curve based on the relationship between the gray value output by the camera and the temperature and the gray value of the infrared radiation photo; The calibration curve of the relationship between the gray value output by the camera and the temperature is obtained through a calibration experiment; In the calibration experiment, the object photographed by the camera is the MPD cathode of a magnetoplasma thruster heated in a programmable muffle furnace. A window and a notch filter identical to those in step S3 are provided between the MPD cathode of the magnetoplasma thruster and the camera. The shooting conditions of the camera and the spatial relationship between the MPD cathode of the magnetoplasma thruster and the camera are exactly the same as those in step S3. According to the gray value of the obtained photos in the calibration experiment and the temperature of the programmable muffle furnace, a calibration curve of the relationship between the gray value output by the camera and the temperature is obtained.

8. The MPD cathode temperature monitoring method based on infrared radiation imaging according to claim 7, characterized in that, In the calibration experiment, a protective cover for shielding the luminescence of the corundum tube in the programmable muffle furnace is provided outside the MPD cathode of the magnetoplasma thruster.

9. The MPD cathode temperature monitoring method based on infrared radiation imaging according to claim 7, characterized in that, In the step S4, it further includes establishing a general relationship formula between the camera output gray value N and the temperature T according to the calibration curve of the relationship between the camera output gray value and the temperature obtained from the calibration experiment. The specific steps are as follows: S4.1 Establish the output gray value N Calibration formula with temperature T: ； Among them, is the first radiation constant, and its value is 3.742×10 -16 W·m 2 , is the second radiation constant, and its value is 1.4388×10 -2 m·K, is the central wavelength passing through the notch filter, is the camera exposure time; the calibration coefficient , where C is the energy conversion coefficient of the camera, ε is the emissivity of the material, is the notch filter bandwidth, is the surface element of the MPD cathode surface of the magnetoplasma thruster; S4.2 Calibrate the calibration coefficient A according to the calibration curve of the relationship between the gray value output by the camera and the temperature obtained from the calibration experiment, and obtain the general relationship between the gray value output by the camera N and the temperature T.

10. A method for monitoring the temperature of an MPD cathode based on infrared radiation imaging according to claim 9, characterized in that, In the step S4, when the temperature control range t1~t2 of the programmable muffle furnace in the calibration experiment is less than the temperature range of the MPD cathode of the magnetoplasma thruster, the temperature of the MPD cathode of the magnetoplasma thruster within the range of t1~t2 is determined according to the calibration curve of the relationship between the gray value output by the camera and the temperature, and the temperature of the MPD cathode of the magnetoplasma thruster outside the range of t1~t2 is determined according to the gray value output by the camera N and the general relational expression with the temperature T.

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