Non-uniform plasma parameter diagnosis method based on microwave local penetration effect

Abstract

The invention provides a non-uniform plasma parameter diagnosis method based on a microwave local penetration effect, relates to the technical field of electromagnetism and plasma diagnosis, and comprises combined diagnosis of plasma profile electron density distribution and collision frequency. According to the method, the peak left side plasma is modeled in a layering manner, and an iterative optimization distribution result is realized; the peak value of the plasma electron density is derived by using the maximum value of the reflection coefficient amplitude slope; the method comprises the following steps: modeling a plurality of distribution models aiming at the peak right side plasma, and determining the model through an attenuation coefficient; meanwhile, the maximum value of the amplitude of the reflection coefficient is utilized to complete the diagnosis of the collision frequency. According to the invention, the problem of non-uniform plasma profile parameter diagnosis is solved.

Description

Technical Field

[0001] The invention belongs to the technical fields of electromagnetics and plasma diagnosis, and in particular relates to a method for diagnosing parameters of non-uniform plasma based on the local penetration effect of microwaves. Background Art

[0002] When an aircraft flies at a supersonic speed between 20 and 100 kilometers above the ground, its head surface will rub against the air violently to form a plasma sheath, which will cause attenuation and phase shift of electromagnetic waves, seriously affecting the quality of communication and may even cause radio interruption, i.e. the "blackout" phenomenon. In order to predict, evaluate and even alleviate the "blackout" phenomenon, it is necessary to diagnose the plasma sheath parameters, which generally include electron density and collision frequency.

[0003] Microwave diagnosis is one of the main methods of plasma diagnosis, which includes two types: invasive and non-invasive. Invasive microwave diagnosis mainly uses probes, including microwave resonance probes, plasma impedance probes, plasma absorption probes, etc. Non-invasive microwave diagnosis can be divided into microwave reflection method and microwave transmission method. Microwave reflection method uses the amplitude and phase obtained by the reflection of electromagnetic waves on the plasma interface to diagnose plasma parameters, and microwave transmission method uses the attenuation of electromagnetic waves through the plasma to infer the electron density and collision frequency.

[0004] Existing plasma diagnostic technology has the following disadvantages:

[0005] Electrostatic probes and microwave probes are invasive diagnostic methods that can interfere with the plasma flow field, such as changing the flow pattern and forming a space charge sheath, and are generally unable to diagnose collision frequencies;

[0006] Although the microwave transmission method does not interfere with the plasma being measured, it requires multiple transmitting and receiving channels, and generally has a low spatial resolution, and cannot accurately diagnose the distribution of plasma electron density;

[0007] The traditional microwave reflection method is based on the total reflection of electromagnetic waves at different positions in the plasma, and the electron density is estimated from the incident frequency to diagnose the profile. This method ignores the influence of the plasma layer near the reflection surface on the reflection amplitude and phase, and the diagnostic accuracy is insufficient. Summary of the invention

[0008] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for diagnosing parameters of non-uniform plasma based on the local penetration effect of microwaves, which solves the problem of diagnosing parameters of non-uniform plasma profiles.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is: a method for diagnosing parameters of non-uniform plasma based on the local penetration effect of microwaves, comprising the following steps:

[0010] S1. Obtaining an amplitude and phase curve of a plasma reflection coefficient, wherein the phase curve of the plasma reflection coefficient is used to query an actual reflection coefficient phase according to an incident frequency;

[0011] S2, searching for the maximum value of the slope of the amplitude decrease of the swept-frequency plasma reflection coefficient to determine the peak electron density, wherein the frequency of the maximum value is the cutoff frequency fc corresponding to the peak electron density;

[0012] S3, dividing the plasma with a thickness of d to be diagnosed into N spatial resolution units according to non-uniformity, and additionally introducing the 0th layer before L is 1 layer, wherein the thickness of each spatial resolution unit is divided according to the cutoff frequency fc corresponding to the peak electron density and the 1 / 3 of the wavelength corresponding to the maximum value of the incident frequency finc;

[0013] S4, setting the initial value of the collision frequency inversion to a number close to 0;

[0014] S5, iteratively inverting the plasma density rising edge profile based on the local penetration effect and non-uniform partitioning results;

[0015] S6, at the initial inversion frequency f 1 At , the collision frequency is gradually increased until the reflection coefficient amplitude of the inversion profile along the rising edge at this frequency point is close to the reflection coefficient amplitude of the measured curve. This value is the collision frequency inversion value, and the collision frequency diagnosis is completed; wherein, this value is the collision frequency that makes the reflection coefficient amplitude of the inversion profile along the rising edge close to the reflection coefficient amplitude of the measured curve;

[0016] S7. Based on the collision frequency diagnosis results, multiple distribution models are modeled, the attenuation coefficient is determined by the amplitude of the plasma reflection coefficient, and the reflection coefficient amplitude curve is obtained by sweeping the attenuation coefficient;

[0017] S8. Compare the reflection coefficient amplitude curve with the standard amplitude curve to determine whether the second inflection point of the reflection coefficient amplitude curve is closest to the standard amplitude curve. If so, complete the falling edge distribution diagnosis; otherwise, return to step S7.

[0018] The beneficial effects of the present invention are as follows: the present invention proposes a plasma electron density distribution diagnosis method based on the local penetration characteristics of plasma, including the joint diagnosis of plasma profile electron density distribution and collision frequency. In the present invention, the plasma on the left side of the peak is modeled in layers and the distribution result is iteratively optimized; the present invention uses the maximum value of the reflection coefficient amplitude slope to derive the plasma electron density peak; the present invention models multiple distribution models for the plasma on the right side of the peak, and determines the model by the attenuation coefficient; at the same time, the present invention uses the maximum value of the reflection coefficient amplitude to complete the diagnosis of the collision frequency. The present invention solves the problem of non-uniform plasma profile parameter diagnosis.

[0019] Furthermore, the expression of the electron density is as follows:

[0020]

[0021] Among them, p represents the electron density of the plasma, f represents the plasma cutoff frequency, m e represents the mass of the electron, ε 0 represents the dielectric constant of vacuum, and e represents the charge of an electron.

[0022] Furthermore, step S5 includes the following steps:

[0023] S501, according to the actual test obtained by the sweep reflection coefficient phase, by determining the initial reflection phase Get the initial inversion frequency f 1 and the corresponding electron density ne 1 ,in, Indicates the maximum value of the reflection phase;

[0024] S502, start i=1 round of iteration, invert the plasma electron density of L=1 layer, when the plasma passes through the 0th layer thickness d 0 After total reflection, the thickness d corresponding to the density of the 0th layer is inverted according to the initial phase of the reflection. 0 ;

[0025] S503, the thickness d 0 Divide into and Two floors, and An infinite metal boundary is placed behind, where Δd represents the diagnostic spatial resolution, which is divided into two layers according to the peak electron density corresponding to the cutoff frequency fc and the maximum value of the incident frequency finc corresponding to 1 / 3 of the wavelength;

[0026] S504: Based on the setting result of step S503, the reflection coefficient phase is calculated using an equivalent transmission line model. And repeatedly adjust The position of the reflection coefficient phase Close to the actual reflection coefficient phase, determine the first layer of plasma position;

[0027] S505, continue i=1 rounds of iteration, invert the plasma electron density of L=2 layers, and calculate the reflection coefficient phase using the equivalent transmission line model And repeatedly adjust The position of the reflection coefficient phase Close to the actual reflection coefficient phase, repeat step S505 until the peak electron density is reached to determine the position of the second layer of plasma; wherein this round of inversion is three layers of plasma plus the metal boundary, and the density of the three layers of plasma is ne 0 、ne 1 and 2 The cutoff frequencies of the first and second plasma layers are f 1 and f 2 , the locations are and

[0028] S506: Determine whether the arrive If yes, then go to step S6, otherwise, add 1 to the value of i and return to step S502 to iteratively invert the plasma density rising edge profile, wherein each round adds a layer of local penetrable thickness, that is, in the i-th round, when determining the thickness of the l-th layer of electron density, a metal plate is placed after the l+i-1 layer, arrive The value remains unchanged from the previous inversion result. The value of the reflection coefficient phase Closest to the actual reflection coefficient phase, complete the arrive Iterative update of , where represents the position of the 0th layer in the i-th round, represents the first layer position in the i-th round, represents the second-layer position in the i-th round, Indicates the position of the N-i+1th layer in the i-th round, and They represent the l+1th layer position and the l+i-1th layer position in the i-th round respectively.

[0029] The beneficial effect of the above further scheme is that the position of each layer of plasma is continuously corrected through multiple rounds of iterative inversion, making the inversion result more accurate.

[0030] Furthermore, the thickness d 0 The expression is as follows:

[0031]

[0032] Among them, k 0 represents the free space wave number.

[0033] The beneficial effect of the above further scheme is: through the above formula, the thickness of the 0th layer is determined for plasma inversion, and on this basis, the 0th layer is divided to form the 1st layer, laying the foundation for plasma inversion.

[0034] Furthermore, the expression of the equivalent transmission line model is as follows:

[0035]

[0036] Among them, R l and R l+1 They represent the reflection coefficients of the lth layer and the l+1th layer in the equivalent transmission line model, respectively. l and k l+1 denote the wave vectors along the incident direction in the lth layer and the l+1th layer, j denotes the imaginary unit, μ l and μ l+1 Represent the magnetic permeability of the lth layer and the magnetic permeability of the l+1th layer, R l(l+1) and P l(l+1) Both represent two intermediate parameters, R 0 It represents the final reflection coefficient of the equivalent transmission line model to the outside. represents the reflection coefficient phase, d l Represents the position coordinates of the lth layer.

[0037] The beneficial effect of the above further solution is: providing theoretical support for the calculation of the reflection coefficient and providing a basis for the subsequent calculation of the plasma layer position. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The figure is a flow chart of the method of the present invention.

[0039] Figure 2 It is a schematic diagram of the original reflection coefficient amplitude curve.

[0040] Figure 3 Schematic diagram of the original reflection coefficient phase curve.

[0041] Figure 4 This is the plasma inversion result on the left side of the peak.

[0042] Figure 5 This is a schematic diagram of the amplitude curve when the attenuation coefficient a=1400.

[0043] Figure 6 Schematic diagram of the plasma electron density distribution inversion results. DETAILED DESCRIPTION

[0044] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0045] Example

[0046] Based on the above, the present invention provides a method for inverting the electron density distribution of the plasma profile and diagnosing the collision frequency at the same time, which is specifically divided into the diagnosis of the electron density peak, the diagnosis of the distribution on the left side of the peak, the diagnosis of the distribution on the right side of the peak, and the diagnosis of the collision frequency. Figure 1 As shown, a method for diagnosing parameters of non-uniform plasma based on the local penetration effect of microwaves is implemented as follows:

[0047] S1. Obtaining an amplitude and phase curve of a plasma reflection coefficient, wherein the phase curve of the plasma reflection coefficient is used to query an actual reflection coefficient phase according to an incident frequency;

[0048] S2, searching for the maximum value of the slope of the amplitude decrease of the swept-frequency plasma reflection coefficient to determine the peak electron density, wherein the frequency of the maximum value is the cutoff frequency fc corresponding to the peak electron density;

[0049] In this embodiment, the peak electron density is determined by searching for the maximum value of the slope of the sweep reflection coefficient amplitude. The frequency of this point is the cutoff frequency corresponding to the peak electron density. The electron density can be converted by formula (1) according to the cutoff frequency. Then, within this order of magnitude, the electron density is divided into

[0050]

[0051] Among them, p represents the electron density of the plasma, f represents the plasma cutoff frequency, m e represents the mass of the electron, ε 0 represents the dielectric constant of vacuum, and e represents the charge of an electron.

[0052] S3, dividing the plasma with a thickness of d to be diagnosed into N spatial resolution units according to non-uniformity, and additionally introducing the 0th layer before L is 1 layer, wherein the thickness of each spatial resolution unit is divided according to the cutoff frequency fc corresponding to the peak electron density and the 1 / 3 of the wavelength corresponding to the maximum value of the incident frequency finc;

[0053] In this embodiment, the plasma with a thickness of d to be diagnosed is divided into 1, 2, ..., N spatial resolution units according to the inhomogeneity. For iterative inversion, an additional layer 0 is introduced before the L = 1 layer. In particular, the thickness of each spatial resolution unit can be divided according to the peak electron density corresponding to the cutoff frequency fc and the maximum value of the incident frequency finc corresponding to 1 / 3 of the wavelength.

[0054] S4, setting the initial value of the collision frequency inversion to a number close to 0, for example, it can be set to 1e-30;

[0055] S5. Based on the local penetration effect and the non-uniform partitioning results, iteratively invert the plasma density rising edge profile, and the implementation method is as follows:

[0056] S501, according to the actual test obtained by the sweep reflection coefficient phase, by determining the initial reflection phase Get the initial inversion frequency f 1 and the corresponding electron density ne 1 ,in, Indicates the maximum value of the reflection phase;

[0057] In this embodiment, the initial reflection phase is determined based on the swept frequency reflection coefficient phase obtained in actual testing. The initial inversion frequency f is determined by 1 , The closer to 180 degrees, the lower the initial inversion frequency, and the smaller the plasma density at the starting position of the corresponding plasma profile. The actual corresponding cutoff frequency is f 1 The electron density of can also be obtained by formula (1), denoted as ne 1 , and invert the position corresponding to this density

[0058] S502, start i=1 round of iteration, invert the plasma electron density of L=1 layer, when the plasma passes through the 0th layer thickness d 0 After total reflection, the thickness d corresponding to the density of the 0th layer is inverted according to the initial phase of the reflection. 0 ;

[0059] S503, the thickness d 0 Divide into and Two floors, and An infinite metal boundary is placed behind, where Δd represents the diagnostic spatial resolution, which is divided into two layers according to the peak electron density corresponding to the cutoff frequency fc and the maximum value of the incident frequency finc corresponding to 1 / 3 of the wavelength;

[0060] S504: Based on the setting result of step S503, the reflection coefficient phase is calculated using an equivalent transmission line model. And repeatedly adjust The position of the reflection coefficient phase Close to the actual reflection coefficient phase, determine the first layer of plasma position;

[0061] In this embodiment, the iteration of round i=1 is started. First, the plasma electron density of layer L=1 is inverted. Specifically, it is assumed that the electron density of layer 0 is ne 0 = 0, the plasma passes through the layer thickness d 0 After total reflection occurs, the thickness corresponding to the density of layer 0 is inverted according to the initial phase of the reflection, which can be converted according to the following formula:

[0062]

[0063] Among them, k 0 represents the free space wave number. 0 It is divided into two layers, denoted as Δd is the diagnostic spatial resolution, which can be divided according to the peak electron density corresponding to the cutoff frequency fc and the maximum value of the incident frequency finc corresponding to 1 / 3 of the wavelength. An infinite metal boundary is placed behind it. The local penetration effect of plasma is defined as the plasma reflection phase is no longer affected by the electron density behind it after passing through a few resolution units of the plasma cutoff frequency. Therefore, placing a metal boundary will not affect the reflection phase. At this time, the inversion model is frequency f 1 Under the irradiation of the incident wave, the reflection of the two-layer plasma and the metal boundary can be obtained by using the equivalent transmission line model. The equivalent transmission line model formula is as follows:

[0064]

[0065]

[0066]

[0067]

[0068] Among them, R l and R l+1 They represent the reflection coefficients of the lth layer and the l+1th layer in the equivalent transmission line model, respectively. l and k l+1 denote the wave vectors along the incident direction in the lth layer and the l+1th layer, j denotes the imaginary unit, μ l and μ l+1Represent the magnetic permeability of the lth layer and the magnetic permeability of the l+1th layer, R l(l+1) and P l(l+1) Both represent two intermediate parameters, R 0 It represents the final reflection coefficient of the equivalent transmission line model to the outside. represents the reflection coefficient phase, d l Represents the position coordinates of the lth layer. R can be inversely deduced from the reflection coefficient of the last layer by formula (2): 0 The value of .

[0069] Repeated adjustment The position until Approximate the reflection coefficient phase of the real inhomogeneous plasma at this frequency. At this time, the electron density is ne 1 The corresponding position is Determine the location of the first plasma layer. In particular, if Far deviation d 0 , the resolution unit size needs to be readjusted.

[0070] S505, continue i=1 rounds of iteration, invert the plasma electron density of L=2 layers, and calculate the reflection coefficient phase using the equivalent transmission line model And repeatedly adjust The position of the reflection coefficient phase Close to the actual reflection coefficient phase, repeat step S505 until the peak electron density is reached to determine the position of the second layer of plasma; wherein this round of inversion is three layers of plasma plus the metal boundary, and the density of the three layers of plasma is ne 0 、ne 1 and 2 The cutoff frequencies of the first and second plasma layers are f 1 and f 2 , the locations are and

[0071] In this embodiment, the second layer electron density position is determined according to the above steps. The inversion is continued for i=1 iteration, and the inversion of L=2 layers of electron density. At this time, the inversion model is a three-layer plasma plus a metal boundary. The density of the three layers of plasma is known, which are ne 0 、ne 1 and 2 The cutoff frequencies of the first plasma and the second plasma are f 1 and f 2 , the locations are and Among them, only is the unknown position that needs to be inverted. The reflection coefficient phase of the model can be obtained by using the equivalent transmission line model. Repeated adjustment The position until Approximate the reflection coefficient phase of the real inhomogeneous plasma at this frequency. Repeat this step until the peak electron density is reached, completing the first round of iteration.

[0072] S506: Determine whether the arrive If yes, then go to step S6, otherwise, add 1 to the value of i and return to step S502 to iteratively invert the plasma density rising edge profile, wherein each round adds a layer of local penetrable thickness, that is, in the i-th round, when determining the thickness of the l-th layer of electron density, a metal plate is placed after the l+i-1 layer, arrive The value remains unchanged from the previous inversion result. The value of the reflection coefficient phase Closest to the actual reflection coefficient phase, complete the arrive Iterative update of , where represents the position of the 0th layer in the i-th round, represents the first layer position in the i-th round, represents the second-layer position in the i-th round, Indicates the position of the N-i+1th layer in the i-th round, and They represent the l+1th layer position and the l+i-1th layer position in the i-th round respectively.

[0073] In this embodiment, steps S502 to S504 are repeated to start the subsequent rounds of iterative inversion. In each round, a layer of local penetrable thickness is added. That is, in the i-th round, when determining the thickness of the l-th layer of electron density, a metal plate is placed after the l+i-1th layer. arrive The value of remains unchanged from the previous inversion result. The value of Closest to the actual reflection coefficient phase, complete the arrive Iterative updates.

[0074] In this embodiment, the subsequent rounds of iterative inversion are started, and each round adds a layer of local penetrable thickness. Instead of placing a metal border directly behind this layer, place the first round After the corresponding electron density, the metal boundary is placed. At this time, adjust and The positions of the two layers make it possible to re-satisfy the consistency between the inversion phase and the real phase of the electron density below the cutoff frequency of this layer; similarly, in order to invert Instead of putting a metal border directly behind this layer, put a round behind it. After the layer corresponds to the electron density, the metal boundary is placed. At this time, adjust The positions of the two layers are such that the inversion phase of the electron density below the cutoff frequency of the layer is consistent with the true phase.

[0075] In this embodiment, the inversion of the plasma electron density rising edge profile is based on the plasma local penetration effect, that is, after passing through a few resolution units of the plasma cutoff frequency, the plasma reflection phase is no longer affected by the subsequent electron density. Therefore, placing a metal boundary will not affect the reflection phase.

[0076] In this embodiment, multiple rounds of iterations are performed on the inversion of the profile along the rising edge of the plasma electron density, taking into account the influence of the subsequent plasma layer on the reflection phase of the current inverted layer.

[0077] S6, at the initial inversion frequency f 1 At , the collision frequency is gradually increased until the reflection coefficient amplitude of the inversion profile along the rising edge at this frequency point is close to the reflection coefficient amplitude of the measured curve. This value is the collision frequency inversion value, and the collision frequency diagnosis is completed; wherein, this value is the collision frequency that makes the reflection coefficient amplitude of the inversion profile along the rising edge close to the reflection coefficient amplitude of the measured curve;

[0078] S7. Based on the collision frequency diagnosis results, multiple distribution models are modeled, the attenuation coefficient is determined by the amplitude of the plasma reflection coefficient, and the reflection coefficient amplitude curve is obtained by sweeping the attenuation coefficient;

[0079] S8. Compare the reflection coefficient amplitude curve with the standard amplitude curve to determine whether the second inflection point of the reflection coefficient amplitude curve is closest to the standard amplitude curve. If so, complete the falling edge distribution diagnosis; otherwise, return to step S7.

[0080] In this embodiment, the collision frequency is a parameter that needs to be diagnosed. The plasma falling edge is modeled based on the result of the collision frequency to complete the diagnosis of the falling edge profile distribution.

[0081] In this embodiment, the plasma profile at the falling edge is inverted. For distribution models such as double Gaussian, parabola, and exponential decay, the value of the attenuation coefficient is adjusted, and the frequency sweep is applied to the fitted falling edge model and the obtained rising edge distribution model, and the obtained reflection coefficient amplitude curve is compared with the standard amplitude curve to find the attenuation coefficient that makes the second inflection point of the curve closest to the standard curve, thereby determining the falling edge distribution.

[0082] Double Gaussian distribution model formula:

[0083]

[0084] Parabolic distribution model formula:

[0085] ne i =-a(x i -thick p ) 2 +ne p (8)

[0086] Exponential decay distribution model formula:

[0087]

[0088] Among them, x i represents the location of the plasma layer i, ne i represents the electron density of the i-th layer of plasma, thick p Indicates the location of the peak value of plasma electron density, ne p Represents the plasma peak electron density, and a represents the attenuation coefficient of the model. For each distribution model, adjust the value of the attenuation coefficient a, and sweep the frequency incident for the distribution model on the right side of the peak and the distribution model on the left side of the equal peak obtained by inversion, and compare the obtained reflection coefficient amplitude curve with the standard amplitude curve to observe whether the second inflection point of the curve is closest to the standard curve. If so, the right distribution model at this time is determined to be the original plasma peak right distribution. Otherwise, change the value of a, adjust the model, and repeat this step until the plasma peak right distribution diagnosis is completed.

[0089] In this embodiment, multiple modeling assumptions are made for the falling edge profile, and the attenuation coefficient is determined by the second inflection point of the reflection coefficient amplitude curve being closest to the standard curve.

[0090] Diagnostic Examples:

[0091] Establish a multilayer plasma model and set the plasma model parameters as follows: peak electron density ne p 1*10 18 cm 3 The electron density distribution conforms to the double Gaussian distribution, the attenuation coefficient a on the right side of the peak is 1500, and the collision frequency v e 1.2*10 8 Hz, the total thickness of the plasma is 0.1m. The reflection coefficient amplitude and phase are obtained by sweeping the frequency from 4 to 18 GHz for the plasma. Figure 2 , Figure 3 shown.

[0092] According to the plasma electron density distribution diagnosis method provided by the present invention, firstly, using Figure 2 The peak electron density ne of the plasma is obtained at the maximum slope of the amplitude curve p is 1.0048*10 18 cm 3 Then, according to this method, the layered modeling was carried out on the left side of the peak, and after three iterative inversions, the plasma electron density distribution on the left side of the peak and the diagnostic results after interpolation processing were obtained, such as Figure 4 As shown; then, the plasma collision frequency v is obtained by comparing the reflection coefficient amplitude curve with the original amplitude curve. e 1.25*10 8 Hz, the attenuation coefficient a distributed on the right side of the peak is 1400. At this time, the reflection coefficient amplitude curve and the plasma electron density distribution inversion result are as follows: Figure 5 , Figure 6 After calculation, the electron density distribution obtained by the layer-by-layer inversion of electron density distribution and collision frequency diagnosis method based on the local penetration characteristics of plasma is very close to the original distribution, and the relative error of collision frequency diagnosis is 4.2%.

[0093] In summary, the present invention takes into account the local penetration characteristics of electromagnetic waves in plasma when performing plasma electron density distribution inversion, making the diagnosis result more accurate. The present invention is applicable to the diagnosis of plasma model parameters with various different distributions, including double Gaussian distribution, parabolic distribution, exponential distribution, etc. The plasma parameter diagnosis method of the present invention can diagnose the electron density distribution and collision frequency at the same time, making the diagnosis more efficient.

Claims

1. A method for diagnosing parameters of non-uniform plasma based on microwave local penetration effect, characterized in that: The following steps are involved: S1. Obtaining an amplitude and phase curve of a plasma reflection coefficient, wherein the phase curve of the plasma reflection coefficient is used to query an actual reflection coefficient phase according to an incident frequency; S2, searching for the maximum value of the slope of the amplitude decrease of the swept-frequency plasma reflection coefficient to determine the peak electron density, wherein the frequency of the maximum value is the cutoff frequency fc corresponding to the peak electron density; S3, dividing the plasma with a thickness of d to be diagnosed into N spatial resolution units according to non-uniformity, and additionally introducing the 0th layer before L is 1 layer, wherein the thickness of each spatial resolution unit is divided according to the cutoff frequency fc corresponding to the peak electron density and the 1 / 3 of the wavelength corresponding to the maximum value of the incident frequency finc; S4, setting the initial value of the collision frequency inversion to a number close to 0; S5, iteratively inverting the plasma density rising edge profile based on the local penetration effect and non-uniform partitioning results; S6. At the initial inversion frequency f1, gradually increase the collision frequency until the reflection coefficient amplitude of the rising edge inversion profile at this frequency point is close to the reflection coefficient amplitude of the measured curve. This value is the collision frequency inversion value, and the collision frequency diagnosis is completed; wherein, this value is the collision frequency that makes the reflection coefficient amplitude of the rising edge inversion profile close to the reflection coefficient amplitude of the measured curve; S7. Based on the collision frequency diagnosis results, multiple distribution models are modeled, the attenuation coefficient is determined by the amplitude of the plasma reflection coefficient, and the reflection coefficient amplitude curve is obtained by sweeping the attenuation coefficient; S8. Compare the reflection coefficient amplitude curve with the standard amplitude curve to determine whether the second inflection point of the reflection coefficient amplitude curve is closest to the standard amplitude curve. If so, complete the falling edge distribution diagnosis; otherwise, return to step S7.

2. The method for diagnosing inhomogeneous plasma parameters based on microwave local penetration effect according to claim 1, characterized in that: The expression of the electron density is as follows: Among them, p represents the electron density of the plasma, f represents the plasma cutoff frequency, m e represents the mass of the electron, ε0 represents the dielectric constant of vacuum, and e represents the charge of the electron.

3. The method for diagnosing inhomogeneous plasma parameters based on microwave local penetration effect according to claim 1, characterized in that: The step S5 comprises the following steps: S501, according to the actual test obtained by the sweep reflection coefficient phase, by determining the initial reflection phase Get the initial inversion frequency f1 and the corresponding electron density ne1, where, Indicates the maximum value of the reflection phase; S502, start i=1 round of iteration, invert the plasma electron density of L=1 layer, when the plasma passes through the 0th layer with thickness d0, total reflection occurs, and the thickness d0 corresponding to the 0th layer density is inverted according to the initial phase of reflection; S503, divide the thickness d0 into and Two floors, and An infinite metal boundary is placed behind, where Δd represents the diagnostic spatial resolution, which is divided into two layers according to the peak electron density corresponding to the cutoff frequency fc and the maximum value of the incident frequency finc corresponding to 1 / 3 of the wavelength; S504: Based on the setting result of step S503, the reflection coefficient phase is calculated using an equivalent transmission line model. And repeatedly adjust The position of the reflection coefficient phase Close to the actual reflection coefficient phase, determine the first layer of plasma position; S505, continue i=1 rounds of iteration, invert the plasma electron density of L=2 layers, and calculate the reflection coefficient phase using the equivalent transmission line model And repeatedly adjust The position of the reflection coefficient phase Close to the actual reflection coefficient phase, repeat step S505 until the peak electron density is reached to determine the position of the second layer of plasma; wherein this round of inversion is three layers of plasma plus a metal boundary, the three layers of plasma density are ne0, ne1 and ne2, the first layer of plasma and the second layer of plasma correspond to the cutoff frequencies f1 and f2, and the positions are and S506: Determine whether the arrive If yes, then go to step S6, otherwise, add 1 to the value of i and return to step S502 to iteratively invert the plasma density rising edge profile, wherein each round adds a layer of local penetrable thickness, that is, in the i-th round, when determining the thickness of the l-th layer of electron density, a metal plate is placed after the l+i-1 layer, arrive The value remains unchanged from the previous inversion result. The value of the reflection coefficient phase Closest to the actual reflection coefficient phase, complete the arrive Iterative update of , where represents the position of the 0th layer in the i-th round, represents the first layer position in the i-th round, represents the second-layer position in the i-th round, Indicates the position of the N-i+1th layer in the i-th round, and They represent the l+1th layer position and the l+i-1th layer position in the i-th round respectively.

4. The method for diagnosing inhomogeneous plasma parameters based on microwave local penetration effect according to claim 3, characterized in that: The thickness d0 is expressed as follows: Here, k0 represents the free space wave number.

5. The method for diagnosing inhomogeneous plasma parameters based on microwave local penetration effect according to claim 3, characterized in that: The expression of the equivalent transmission line model is as follows: Among them, R l and R l+1 They represent the reflection coefficients of the lth layer and the l+1th layer in the equivalent transmission line model, respectively. l and k l+1 denote the wave vectors along the incident direction in the lth layer and the l+1th layer, j denotes the imaginary unit, μ l and μ l+1 Represent the magnetic permeability of the lth layer and the magnetic permeability of the l+1th layer, R l(l+1) and P l(l+1) Both represent two intermediate parameters, R0 represents the final reflection coefficient of the equivalent transmission line model to the outside, represents the reflection coefficient phase, d l Represents the position coordinates of the lth layer.

Images