Plasma profile diagnosis method assisted by adjustable magnetic field

Abstract

The invention discloses a plasma profile diagnosis method assisted by an adjustable magnetic field, which comprises the following steps of: firstly deriving a dielectric constant of magnetized plasma from the electromagnetic property of the magnetized plasma, then substituting the dielectric constant into a calculation formula, exploring the influence of different magnetic fields on electromagnetic wave transmission, and aiming at a plasma model with relatively high electron density, calculating the dielectric constant of the magnetized plasma. The adjustable magnetic field is used for assisting in plasma parameter diagnosis. According to the method, the dielectric characteristics of the plasma can be changed by the external magnetic field, so that the reflection coefficient and the cut-off region range of the electromagnetic wave are changed, the information dimension of the reflection coefficient is increased by using the static magnetic field, the result accuracy is improved, and the required incident wave frequency band bandwidth is reduced; and a genetic algorithm is utilized to solve the problem that a complex mapping relation cannot be directly solved, and in-situ diagnosis of multiple physical quantities of plasma parameters is realized.

Description

Technical Field

[0001] The invention belongs to the field of microwave technology, and in particular relates to a plasma profile diagnosis method assisted by an adjustable magnetic field. 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 communication quality and may even cause radio interruption, i.e. the "black barrier" phenomenon. In order to solve the "black barrier" 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] Although the traditional microwave reflection method can reveal the distribution of electron density, it requires the existence of an obvious reflection interface in the electron density distribution, which limits its application scope to a certain extent; for the plasma sheath with a single-peak distribution, this method cannot diagnose the electron density distribution after the peak; at the same time, this method cannot obtain information on the collision frequency during the diagnosis process. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the adjustable magnetic field-assisted plasma profile diagnosis method provided by the present invention solves the problem that the traditional method is limited by the electron density distribution and cannot diagnose the electron density distribution after the peak, thereby realizing plasma profile diagnosis under complex antenna design.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a plasma profile diagnosis method assisted by an adjustable magnetic field, comprising the following steps:

[0007] S1, magnetizing the plasma by applying an external magnetic field;

[0008] S2, calculating the relative dielectric constant of the current magnetized plasma;

[0009] S3. Based on the calculated relative dielectric constant, the transmission characteristics of electromagnetic waves in the plasma are analyzed to determine whether the reflection coefficient corresponding to the incident wave frequency band of the current external magnetic field is the data required for plasma profile diagnosis;

[0010] If not, proceed to step S4;

[0011] If yes, proceed to step S5;

[0012] S4, adjusting the incident wave frequency band of the external magnetic field, re-magnetizing the plasma, and returning to step S2;

[0013] S5. The mapping relationship between different magnetic field intensities and reflection coefficients is analyzed by genetic algorithm to achieve plasma profile diagnosis.

[0014] Furthermore, in step S1, the layout of the external magnetic field of the magnetized plasma is as follows:

[0015] A wave-transmitting window is embedded in the surface of the aircraft, a permanent magnet is arranged on both sides of the wave-transmitting window inside the aircraft, and an antenna is arranged under the permanent magnet and directly facing the wave-transmitting window.

[0016] Furthermore, in step S1, the layout of the external magnetic field of the magnetized plasma is as follows:

[0017] A wave-transmitting window is embedded in the surface of the aircraft, and three electromagnetic coils and an antenna are arranged in sequence under the wave-transmitting window inside the aircraft.

[0018] Furthermore, the step S2 includes the following sub-steps:

[0019] S21. Calculate the electron motion equations of electrons in magnetized plasma under the combined action of electric and magnetic fields;

[0020] S22. When the electromagnetic wave propagates along the magnetic field direction, the conductivity of the magnetized plasma under the action of the left-hand circularly polarized wave and the right-hand circularly polarized wave is calculated according to the electron motion equation;

[0021] S23. Calculate the relative dielectric constant of the magnetized plasma according to the relationship between the electrical conductivity and the relative dielectric constant of the magnetized plasma.

[0022] Furthermore, in step S21, the electron motion equation of the electrons in the magnetized plasma under the combined action of the electric field and the magnetic field is:

[0023]

[0024] In the formula, m e represents the mass of the electron, v represents the velocity vector of the electron, and v e represents the frequency of electron collisions, e represents the electron charge, E represents the electric field strength, and B represents the external magnetic field strength.

[0025] Further, in step S22, the conductivity of the magnetized plasma is expressed as:

[0026]

[0027] In the formula, σ l represents the conductivity of the magnetized plasma under the action of left-handed circularly polarized waves, σ r represents the conductivity of the magnetized plasma under the action of right-hand circularly polarized waves, n e represents the electron density, e represents the electron charge, and v l represents the velocity of left-handed circularly polarized electrons, v r represents the speed of right-hand circularly polarized electrons, E l represents the electric field strength of left-hand circularly polarized wave, E r represents the electric field strength of right-hand circularly polarized wave, ε 0 represents the vacuum dielectric constant, ω p represents the characteristic frequency of the plasma, ω b represents the cyclotron angular frequency of the electron, and ω represents the incident frequency.

[0028] Furthermore, in step S23, the relationship between the conductivity and relative dielectric constant of the magnetized plasma is:

[0029]

[0030] In the formula, ε l,r represents the relative dielectric constant of the magnetized plasma, σ l,r represents the conductivity of the magnetized plasma, ω represents the incident frequency, and ε 0 represents the dielectric constant of vacuum;

[0031] The relative dielectric constant ε of the magnetized plasma l,r It is expressed as:

[0032]

[0033] In the formula, the subscript l and the “+” in ± represent left-hand circularly polarized waves, and r and “-” represent right-hand circularly polarized waves.

[0034] Furthermore, in step S3, when an external magnetic field is applied, the transmission characteristics of electromagnetic waves in the plasma are:

[0035] As the frequency of the incident electromagnetic wave increases, the reflection effect of the plasma on the electromagnetic wave weakens, and the frequency band where the reflection coefficient amplitude decreases fastest shifts to the left with the increase of the magnetic field strength. The greater the external magnetic field intensity, the lower the electromagnetic wave frequency band required for plasma profile diagnosis.

[0036] Furthermore, in step S4, the incident wave frequency band of the external magnetic field is adjusted, and a left-handed circularly polarized wave is used as the incident electromagnetic wave to re-magnetize the plasma.

[0037] Furthermore, in step S5, the mapping relationship of the reflection coefficient is:

[0038] R=F(ne(z),ve,B)

[0039] Where R is the reflection coefficient, F(·) is the function symbol, ne(z) is the electron density, ve is the collision frequency, and B is the magnetic field strength.

[0040] The beneficial effects of the present invention are:

[0041] (1) The key to the successful diagnosis of the plasma profile diagnosis method based on genetic algorithm is a certain amount of broadband reflection data information, especially for the diagnosis of plasma with high electron density, which usually requires a wider frequency band to be successfully diagnosed. However, in practical applications, the design of ultra-wideband antennas is relatively complex, and the size of antennas that can be carried during flight tests is also limited. Therefore, it is necessary to consider an optimization method to reduce the required bandwidth. Through a series of experiments, it is believed that the problem is caused by the electromagnetic wave transmission characteristics of the plasma, and it is difficult to solve this problem by changing the structural parameters of the genetic algorithm itself. In view of this problem, the present invention uses the influence of the adjustable magnetic field on the electromagnetic wave transmission characteristics to increase the amount of information at each frequency point, thereby reducing the frequency points of the frequency sweep while ensuring the total number of equations. First, the dielectric properties of the magnetized plasma are derived, and then the transmission characteristics of the electromagnetic wave under different magnetic field intensities are explored based on the derived results. Finally, the plasma profile diagnosis method based on the genetic algorithm is improved by using an external adjustable magnetic field, and a suitable external magnetic field is selected according to the diagnostic needs and actual conditions. The method is verified under plasma models with different parameters to verify the effectiveness of the method.

[0042] (2) The method of the present invention diagnoses the electron density profile of high-speed flying plasma based on broadband microwave reflection data. It considers using a static magnetic field to increase the information dimension of the reflection coefficient, thereby improving the accuracy of the results while reducing the required incident wave bandwidth. It also uses a genetic algorithm to solve the problem of being unable to directly solve complex mapping relationships, thereby realizing in-situ diagnosis of multiple physical quantities of plasma parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flow chart of the adjustable magnetic field-assisted plasma profile diagnostic method provided by the present invention.

[0044] Figure 2 This is a schematic diagram of the layout of the external magnetic field provided by the present invention.

[0045] Figure 3 The reflection coefficient amplitude-frequency curves of the left-hand circularly polarized wave and the right-hand circularly polarized wave provided by the present invention under the external magnetic field B of different intensities. DETAILED DESCRIPTION

[0046] 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.

[0047] The embodiment of the present invention provides a plasma profile diagnosis method assisted by an adjustable magnetic field, such as Figure 1 As shown, the following steps are included:

[0048] S1, magnetizing the plasma by applying an external magnetic field;

[0049] S2, calculating the relative dielectric constant of the current magnetized plasma;

[0050] S3. Based on the calculated relative dielectric constant, the transmission characteristics of electromagnetic waves in the plasma are analyzed to determine whether the reflection coefficient corresponding to the incident wave frequency band of the current external magnetic field is the data required for plasma profile diagnosis;

[0051] If not, proceed to step S4;

[0052] If yes, proceed to step S5;

[0053] S4, adjusting the incident wave frequency band of the external magnetic field, re-magnetizing the plasma, and returning to step S2;

[0054] S5. The mapping relationship between different magnetic field intensities and reflection coefficients is analyzed by genetic algorithm to achieve plasma profile diagnosis.

[0055] In step S1 of the embodiment of the present invention, a layout method of applying an external magnetic field is provided, such as Figure 2 As shown in (a), a wave-transmitting window is embedded in the surface of the aircraft, a permanent magnet is arranged on both sides of the wave-transmitting window inside the aircraft, and an antenna is arranged under the permanent magnet and directly opposite to the wave-transmitting window.

[0056] In step S1 of the embodiment of the present invention, another layout method of applying an external magnetic field is provided, such as Figure 2 As shown in (b), a wave-transmitting window is embedded in the surface of the aircraft, and three electromagnetic coils and an antenna are arranged in sequence under the wave-transmitting window inside the aircraft.

[0057] In step S2 of the embodiment of the present invention, the reasonable frequency is the maximum frequency that can be calculated within limited computing resources or the maximum frequency range supported by the hardware.

[0058] Step S2 in the embodiment of the present invention includes the following sub-steps:

[0059] S21. Calculate the electron motion equations of electrons in magnetized plasma under the combined action of electric and magnetic fields;

[0060] S22. When the electromagnetic wave propagates along the magnetic field direction, the conductivity of the magnetized plasma under the action of the left-hand circularly polarized wave and the right-hand circularly polarized wave is calculated according to the electron motion equation;

[0061] S23. Calculate the relative dielectric constant of the magnetized plasma according to the relationship between the electrical conductivity and the relative dielectric constant of the magnetized plasma.

[0062] In step S21 of this embodiment, the electron motion equation of the electrons in the magnetized plasma under the combined action of the electric field and the magnetic field is:

[0063]

[0064] In the formula, m e represents the mass of the electron, v represents the velocity vector of the electron, and v e represents the frequency of electron collisions, e represents the electron charge, E represents the electric field strength, and B represents the external magnetic field strength.

[0065] Specifically, assuming that the electromagnetic wave propagates along the +z direction, and the direction of the applied static magnetic field is consistent with the propagation direction of the electromagnetic wave, for the time-harmonic electromagnetic field, equation (1) can be expanded as follows:

[0066]

[0067] In the formula, ω b It represents the cyclotron angular frequency of the electron, in rad / s; v x 、v y 、v z Represents the components of the electron velocity vector in the x, y, and z directions; E x 、E y 、E z Represents the components of the electric field strength in the x, y, and z directions.

[0068] Write equation (2) in matrix form:

[0069]

[0070] According to Ohm's law, -n e ev=J=σE, so equation (4) can be converted to:

[0071]

[0072] Among them, J x , J y , J zThey represent the components of the current density vector J in the x, y, and z directions, respectively, and σ -1 From J=E and equation (5), we can see that the conductivity of the magnetized plasma is:

[0073]

[0074] The conductivity is converted into a tensor form and simplified as:

[0075]

[0076] in,

[0077]

[0078] Therefore, the relative dielectric tensor of the plasma is expressed as:

[0079]

[0080] Among them, I is the identity matrix, and other symbolic expressions are as follows:

[0081]

[0082] In the formula, ω p is the characteristic frequency of the plasma, in rad / s.

[0083] The electric field in the magnetized plasma is anisotropic. When electromagnetic waves propagate along the magnetic field, left-hand circularly polarized waves and right-hand circularly polarized waves will appear. The unit vectors of the two are expressed as:

[0084]

[0085] In the formula, the subscript l represents left-hand circularly polarized wave, r represents right-hand circularly polarized wave, and e x and e y are unit vectors in the x and y directions respectively.

[0086] The electron velocity in the plasma is also expressed as circular polarization:

[0087]

[0088] Under the action of circularly polarized radio waves, v l,r ×B can be simplified as:

[0089] v l,r ×B=v(e x ±je y )×Be z = ±jBv(e x ±je y )=±jBv l,r (17)

[0090] In the formula, the “+” in ± represents left-hand circularly polarized wave, and the “-” represents right-hand circularly polarized wave.

[0091] Substituting formula (17) into formula (1), we can obtain:

[0092]

[0093] Further calculations yield:

[0094]

[0095] Using Ohm's law J = σ l,r E l,r =-n e ev l,r And formula (19), the conductivity of the magnetized plasma in step S22 of this embodiment is expressed as:

[0096]

[0097] In the formula, σ l represents the conductivity of the magnetized plasma under the action of left-handed circularly polarized waves, σ r represents the conductivity of the magnetized plasma under the action of right-hand circularly polarized waves, n e represents the electron density, e represents the electron charge, and v l represents the velocity of left-handed circularly polarized electrons, v r represents the speed of right-hand circularly polarized electrons, E l represents the electric field strength of left-hand circularly polarized wave, E r represents the electric field strength of right-hand circularly polarized wave, ε 0 represents the vacuum dielectric constant, ω p represents the characteristic frequency of the plasma, ω b represents the cyclotron angular frequency of the electron, and ω represents the incident frequency.

[0098] In step S23 of this embodiment, the relationship between the conductivity and relative dielectric constant of the magnetized plasma is:

[0099]

[0100] In the formula, ε l,r represents the relative dielectric constant of the magnetized plasma, σ l,r represents the conductivity of the magnetized plasma, ω represents the incident frequency, and ε 0 represents the dielectric constant of vacuum.

[0101] Substituting equation (20) into equation (21), the relative dielectric constant of the magnetized plasma is obtained as:

[0102]

[0103] In the formula, the subscript l and the “+” in ± represent left-hand circularly polarized waves, and r and “-” represent right-hand circularly polarized waves.

[0104] In step S3 of the embodiment of the present invention, according to the derivation process of the formula of the relative dielectric constant, the externally applied electrostatic magnetic field will affect the relative dielectric constant of the plasma, and thus affect the transmission characteristics of the electromagnetic wave in the plasma; specifically, when the external magnetic field is applied, the transmission characteristics of the electromagnetic wave in the plasma are:

[0105] As the frequency of the incident electromagnetic wave increases, the reflection effect of the plasma on the electromagnetic wave weakens, and the frequency band where the reflection coefficient amplitude decreases fastest shifts to the left with the increase of the magnetic field strength. The greater the external magnetic field intensity, the lower the electromagnetic wave frequency band required for plasma profile diagnosis.

[0106] In a specific example of the present invention, Figure 3 As shown in the figure, the reflection coefficient amplitude-frequency curves of left-hand circular polarization wave and right-hand circular polarization wave under different strengths of external magnetic field B are given respectively ((a) is the relationship between the incident frequency and the reflection coefficient under left-hand circular polarization, and (b) is the relationship between the incident frequency and the reflection coefficient under right-hand circular polarization). Among them, the plasma is non-uniformly distributed, and the electron density conforms to the double Gaussian distribution model: Ne peak =5*10 18 m -3 , a 1 =2000,a 2 =1700, z 0 =0.035m, thickness is 0.1m, collision frequency is 1GHz.

[0107] Depend on Figure 3 (a) When the incident electromagnetic wave is a left-hand circularly polarized wave, the overall characteristics of the electromagnetic wave reflection coefficient are basically the same as when there is no external magnetic field: the reflection coefficient amplitude shows an overall downward trend, indicating that with the increase of the incident wave frequency, the reflection effect of the plasma on the electromagnetic wave gradually weakens, and the frequency band where the reflection coefficient amplitude decreases fastest gradually shifts to the left with the increase of the magnetic field strength. In the plasma profile diagnosis method based on genetic algorithm, the greater the intensity of the external magnetic field, the lower the frequency band required for diagnosis.

[0108] Depend on Figure 3(b) It can be seen that when the incident electromagnetic wave is a right-hand circularly polarized wave, when the magnetic field strength is small, the reflection coefficient characteristics are basically the same as when there is no magnetic field, and the frequency band where the reflection coefficient amplitude drops fastest shifts to the right. When the incident wave frequency is low, the reflection coefficient amplitude will have a "concave" area that first drops and then rises. After the magnetic field strength increases, this characteristic becomes more obvious, and the reflection coefficient has a significant drop in the lower frequency band, indicating that the magnetized plasma reflects very little incident waves in this frequency band, and some electromagnetic waves can penetrate the plasma. The greater the magnetic field strength, the lower the reflection coefficient amplitude in the "window" part, the wider the covered frequency band, and the better the electromagnetic wave penetration effect.

[0109] In step S4 of the embodiment of the present invention, the incident wave frequency band of the external magnetic field is adjusted, and a left-handed circularly polarized wave is used as the incident electromagnetic wave to re-magnetize the plasma.

[0110] Specifically, it is deduced that an external magnetic field will change the electromagnetic wave transmission characteristics of the plasma. At the same incident wave frequency, different external magnetic field strengths correspond to different reflection coefficient values. According to analysis, when an external magnetic field is applied to the plasma, the reflection ability of the plasma to the right-hand polarized wave is reduced. When diagnosing the plasma profile, the reflection data is used for diagnosis, so the right-hand polarized wave is not applicable. The left-hand polarized wave will shift the effective frequency band to the left, which just meets the requirement of reducing the incident frequency. Therefore, the left-hand polarized wave is used as the incident electromagnetic wave in this embodiment.

[0111] In step S5 of the embodiment of the present invention, the mapping relationship of the reflection coefficient is:

[0112] R=F(ne(z),ve,B)

[0113] Where R is the reflection coefficient, F(·) is the function symbol, ne(z) is the electron density, ve is the collision frequency, and B is the magnetic field strength.

[0114] The method of the present invention is a method that an external magnetic field can change the dielectric properties of plasma, thereby changing the reflection coefficient and cutoff range of electromagnetic waves; in the implementation process, the static magnetic field is considered to increase the information dimension of the reflection coefficient, improve the accuracy of the results, and reduce the required incident wave bandwidth. Starting from the electromagnetic properties of magnetized plasma, the dielectric constant expression of magnetized plasma is first derived, and then the expression is substituted into the calculation formula to explore the influence of different magnetic fields on electromagnetic wave transmission.

[0115] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0116] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A plasma profile diagnostic method assisted by an adjustable magnetic field, characterized in that: The following steps are involved: S1, magnetizing the plasma by applying an external magnetic field; S2, calculating the relative dielectric constant of the current magnetized plasma; S3. Based on the calculated relative dielectric constant, the transmission characteristics of electromagnetic waves in the plasma are analyzed to determine whether the reflection coefficient corresponding to the incident wave frequency band of the current external magnetic field is the data required for plasma profile diagnosis; If not, proceed to step S4; If yes, proceed to step S5; S4, adjusting the incident wave frequency band of the external magnetic field, re-magnetizing the plasma, and returning to step S2; S5. The mapping relationship between different magnetic field intensities and reflection coefficients is analyzed by genetic algorithm to achieve plasma profile diagnosis.

2. The adjustable magnetic field assisted plasma profile diagnostic method according to claim 1, characterized in that: In step S1, the layout of the external magnetic field of the magnetized plasma is as follows: A wave-transmitting window is embedded in the surface of the aircraft, a permanent magnet is arranged on both sides of the wave-transmitting window inside the aircraft, and an antenna is arranged under the permanent magnet and directly facing the wave-transmitting window.

3. The adjustable magnetic field assisted plasma profile diagnostic method according to claim 1, characterized in that: In step S1, the layout of the external magnetic field of the magnetized plasma is as follows: A wave-transmitting window is embedded in the surface of the aircraft, and three electromagnetic coils and an antenna are arranged in sequence under the wave-transmitting window inside the aircraft.

4. The adjustable magnetic field assisted plasma profile diagnostic method according to claim 1, characterized in that: The step S2 comprises the following sub-steps: S21. Calculate the electron motion equations of electrons in magnetized plasma under the combined action of electric and magnetic fields; S22. When the electromagnetic wave propagates along the magnetic field direction, the conductivity of the magnetized plasma under the action of the left-hand circularly polarized wave and the right-hand circularly polarized wave is calculated according to the electron motion equation; S23. Calculate the relative dielectric constant of the magnetized plasma according to the relationship between the electrical conductivity and the relative dielectric constant of the magnetized plasma.

5. The adjustable magnetic field assisted plasma profile diagnosis method according to claim 4, characterized in that: In step S21, the electron motion equation of the electrons in the magnetized plasma under the combined action of the electric field and the magnetic field is: In the formula, m e represents the mass of the electron, v represents the velocity vector of the electron, and v e represents the frequency of electron collisions, e represents the electron charge, E represents the electric field strength, and B represents the external magnetic field strength.

6. The adjustable magnetic field assisted plasma profile diagnosis method according to claim 5, characterized in that: In step S22, the conductivity of the magnetized plasma is expressed as: In the formula, σ l represents the conductivity of the magnetized plasma under the action of left-handed circularly polarized waves, σ r represents the conductivity of the magnetized plasma under the action of right-hand circularly polarized waves, n e represents the electron density, e represents the electron charge, and v l represents the velocity of left-handed circularly polarized electrons, v r represents the speed of right-hand circularly polarized electrons, E l represents the electric field strength of left-hand circularly polarized wave, E r represents the electric field strength of right-hand circularly polarized wave, ε0 represents the dielectric constant of vacuum, ω p represents the characteristic frequency of the plasma, ω b represents the cyclotron angular frequency of the electron, and ω represents the incident frequency.

7. The adjustable magnetic field assisted plasma profile diagnosis method according to claim 6, characterized in that: In step S23, the relationship between the conductivity and relative dielectric constant of the magnetized plasma is: In the formula, ε l,r represents the relative permittivity of the magnetized plasma, σ l,r represents the conductivity of magnetized plasma, ω represents the incident frequency, and ε0 represents the vacuum dielectric constant; The relative dielectric constant ε of the magnetized plasma l,r It is expressed as: In the formula, the subscript l and the "+" in ± represent left-hand circularly polarized waves, and r and "-" represent right-hand circularly polarized waves.

8. The adjustable magnetic field assisted plasma profile diagnosis method according to claim 1, characterized in that: In step S3, when an external magnetic field is applied, the transmission characteristics of electromagnetic waves in the plasma are: As the frequency of the incident electromagnetic wave increases, the reflection effect of the plasma on the electromagnetic wave weakens, and the frequency band where the reflection coefficient amplitude decreases fastest shifts to the left with the increase of the magnetic field strength. The greater the external magnetic field intensity, the lower the electromagnetic wave frequency band required for plasma profile diagnosis.

9. The adjustable magnetic field assisted plasma profile diagnosis method according to claim 1, characterized in that: In the step S4, the incident wave frequency band of the external magnetic field is adjusted, and the left-hand circularly polarized wave is used as the incident electromagnetic wave to re-magnetize the plasma.

10. The adjustable magnetic field assisted plasma profile diagnosis method according to claim 1, characterized in that: In step S5, the mapping relationship of the reflection coefficient is: R=F(ne(z),ve,B) Where R is the reflection coefficient, F(·) is the function symbol, ne(z) is the electron density, ve is the collision frequency, and B is the magnetic field strength.

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