A tunable magnetic field assisted plasma profile diagnostic method

Abstract

The application discloses a tunable magnetic field assisted plasma profile diagnosis method, which is characterized in that the dielectric constant of magnetized plasma is derived from the electromagnetic characteristics of the magnetized plasma, and then the dielectric constant is substituted into a calculation formula to explore the influence of different magnetic fields on electromagnetic wave transmission, and the tunable magnetic field assistance is used to diagnose the plasma parameters for the plasma model with high electron density. The application is a method in which an external magnetic field can change the dielectric characteristics of plasma, and then change the reflection coefficient of electromagnetic waves and the range of the cutoff region, the information dimension of the reflection coefficient is increased by using a static magnetic field, the result accuracy is improved, the required incident wave frequency band bandwidth is reduced, the problem that a complex mapping relationship cannot be directly solved is solved by using a genetic algorithm, and in-situ diagnosis of multiple physical quantities of plasma parameters is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of microwave technology, and particularly relates to a method for diagnosing a plasma profile with adjustable magnetic field assistance. BACKGROUND

[0002] When an aircraft flies at supersonic speed between 20 to 100 kilometers from the ground surface, the head surface of the aircraft will rub against air to form a plasma sheath, which will cause attenuation and phase shift of electromagnetic waves, and thus seriously affect the communication quality, and even cause radio interruption, i.e., the "blackout" phenomenon. In order to solve the "blackout" phenomenon, the parameters of the plasma sheath need to be diagnosed, and the parameters generally include electron density and collision frequency.

[0003] The microwave diagnosis method is one of the main existing plasma diagnosis methods, which includes invasive and non-invasive methods. The invasive microwave diagnosis mainly uses a probe, and mainly includes a microwave resonance probe, a plasma impedance probe, a plasma absorption probe, etc. The non-invasive microwave diagnosis can be divided into a microwave reflection method and a microwave transmission method. The microwave reflection method uses the amplitude and phase of electromagnetic waves reflected on the plasma interface to diagnose the plasma parameters, and the microwave transmission method uses the attenuation of electromagnetic waves through the plasma to inversely deduce the electron density and the collision frequency.

[0004] The traditional microwave reflection method can reveal the distribution of the electron density, but requires that the electron density distribution has a clear reflection interface, which limits the application range to a certain extent. For a single-peak distributed plasma sheath, the method cannot diagnose the electron density distribution after the peak. Meanwhile, the method cannot obtain the collision frequency information in the diagnosis process. SUMMARY

[0005] In view of the above problems in the prior art, the method for diagnosing a plasma profile with adjustable magnetic field assistance provided by the application solves the problem that the traditional method is limited by the electron density distribution and cannot diagnose the electron density distribution after the peak, and realizes the plasma profile diagnosis under complex antenna design.

[0006] In order to achieve the above-mentioned purposes, the application adopts the technical scheme of a method for diagnosing a plasma profile with adjustable magnetic field assistance, comprising the following steps:

[0007] S1, magnetizing the plasma by 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, analyzing the transmission characteristics of electromagnetic waves in the plasma, and then determining whether the reflection coefficient corresponding to the incident wave frequency band of the current external magnetic field is the required data for realizing the plasma profile diagnosis.

[0010] If no, go to step S4;

[0011] If yes, go to step S5;

[0012] S4, adjust the incident wave frequency band of the applied magnetic field, remagnetize the plasma, and return to step S2;

[0013] S5, analyze the mapping relationship between different magnetic field strengths and reflection coefficients through a genetic algorithm to realize plasma profile diagnosis.

[0014] Further, in step S1, the layout of the applied magnetic field for magnetizing the plasma is:

[0015] The wave-transparent window is embedded in the surface of the aircraft, and one permanent magnet is arranged on each side of the wave-transparent window inside the aircraft, and an antenna is arranged opposite the wave-transparent window below the permanent magnet.

[0016] Further, in step S1, the layout of the applied magnetic field for magnetizing the plasma is:

[0017] The wave-transparent window is embedded in the surface of the aircraft, and three electromagnetic coils and an antenna are sequentially arranged below the wave-transparent window inside the aircraft.

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

[0019] S21, calculate the electron motion equation of the electrons in the magnetized plasma under the joint action of the electric field and the magnetic field;

[0020] S22, according to the electron motion equation, calculate the electrical conductivity of the magnetized plasma under the action of left-handed circularly polarized waves and right-handed circularly polarized waves when the electromagnetic wave propagates along the magnetic field direction;

[0021] S23, according to the relationship between the electrical conductivity and the relative permittivity of the magnetized plasma, calculate the relative permittivity of the magnetized plasma.

[0022] Further, in step S21, the electron motion equation of the electrons in the magnetized plasma under the joint 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 electron motion velocity vector, v e represents the electron collision frequency, e represents the electron charge, E represents the electric field strength, and B represents the applied magnetic field strength.

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

[0026]

[0027] wherein σ l represents the conductivity of the magnetized plasma under the action of the left-handed circularly polarized wave, σ r represents the conductivity of the magnetized plasma under the action of the right-handed circularly polarized wave, n e represents the electron density, e represents the electron charge, v l represents the left-handed circularly polarized electron velocity, v r represents the right-handed circularly polarized electron velocity, E l represents the left-handed circularly polarized wave electric field intensity, E r represents the right-handed circularly polarized wave electric field intensity, ε0 represents the vacuum permittivity, ω p represents the characteristic frequency of the plasma, ω b represents the cyclotron frequency of the electron, ω represents the incident frequency.

[0028] Further, in the step S23, the relationship between the conductivity of the magnetized plasma and the relative permittivity is:

[0029]

[0030] wherein ε l,r represents the relative permittivity of the magnetized plasma, σ l,r represents the conductivity of the magnetized plasma, ω represents the incident frequency, and ε0 represents the vacuum permittivity.

[0031] The relative permittivity ε l,r of the magnetized plasma is:

[0032]

[0033] wherein the subscript "+" in the subscripts l and ± represents the left-handed circularly polarized wave, and r and "-" represent the right-handed circularly polarized wave.

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

[0035] With the increase of the incident electromagnetic wave frequency, the reflection effect of the plasma on the electromagnetic wave is weakened, the frequency band in which the reflection coefficient amplitude drops fastest is left shifted with the increase of the magnetic field strength, and the stronger the external magnetic field strength, the lower the electromagnetic wave frequency band required for the plasma profile diagnosis.

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

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

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

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

[0040] The present application has the following advantages:

[0041] (1) The key to the success of the plasma profile diagnosis method based on the genetic algorithm is a certain amount of broadband reflection data information, especially for the diagnosis of high electron density plasma, which usually requires a wider frequency band to be diagnosed successfully. However, in actual application, the design of the ultra-wideband antenna is relatively complex, and the size of the antenna that can be carried during flight test is also limited, so it is necessary to consider the optimization method to reduce the required frequency band width. Through a series of experiments, it is believed that this problem is caused by the electromagnetic wave transmission characteristics of the plasma, and it is difficult to solve this problem by changing the structure parameters of the genetic algorithm itself; the present application uses the influence of the controllable magnetic field on the electromagnetic wave transmission characteristics to increase the information quantity at each frequency point, thereby reducing the frequency points 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 strengths are explored according to the derived results. Finally, the controllable magnetic field is used to improve the plasma profile diagnosis method based on the genetic algorithm, and the appropriate external magnetic field is selected according to the diagnosis needs and actual conditions, and the method is verified under different parameters of the plasma model, which verifies the effectiveness of the method.

[0042] (2) The present application method is based on broadband microwave reflection data to carry out the diagnosis of high-speed flying plasma electron density profile, considers using static magnetic field to increase the information dimension of the reflection coefficient, improves the accuracy of the results while reducing the required incident wave frequency band width, and uses genetic algorithm to solve the problem of complex mapping relationship that cannot be directly solved, and realizes the in-situ diagnosis of multiple physical quantities of plasma parameters. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The controllable magnetic field assisted plasma profile diagnosis method flowchart provided by the present application.

[0044] Figure 2 The external magnetic field layout schematic diagram provided by the present application.

[0045] Figure 3 The reflection coefficient amplitude-frequency curve of the left-handed circularly polarized wave and the right-handed circularly polarized wave under different strengths of the external magnetic field B provided by the present application. DETAILED DESCRIPTION

[0046] The specific embodiments of the present application are described below to enable those skilled in the art to understand the present application, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, any changes that are obvious within the spirit and scope of the present application defined and determined by the appended claims are included in the protection of the present application.

[0047] The embodiment of the present application provides a tunable magnetic field assisted plasma profile diagnosis method, as shown in the figure, comprising the following steps: Figure 1

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

[0049] S2, calculate the relative permittivity of the current magnetized plasma;

[0050] S3, based on the calculated relative permittivity, analyze the transmission characteristics of electromagnetic waves in the plasma, and then determine whether the reflection coefficient corresponding to the incident wave frequency band of the current external magnetic field is the required data for realizing plasma profile diagnosis;

[0051] If not, go to step S4;

[0052] If yes, go to step S5;

[0053] S4, adjust the incident wave frequency band of the external magnetic field, re-magnetize the plasma, and return to step S2;

[0054] S5, analyze the mapping relationship between different magnetic field strengths and reflection coefficients by genetic algorithm to realize plasma profile diagnosis.

[0055] In step S1 of the embodiment of the present application, a layout mode of an external magnetic field is provided, as shown in Figure 2 (a) The wave-transparent window is embedded in the surface of the aircraft, and one permanent magnet is arranged on each side of the wave-transparent window inside the aircraft, and an antenna is arranged opposite the wave-transparent window below the permanent magnet.

[0056] In step S1 of the embodiment of the present application, another layout mode of an external magnetic field is provided, as shown in Figure 2 (b) The wave-transparent window is embedded in the surface of the aircraft, and three electromagnetic coils and an antenna are sequentially arranged below the wave-transparent window inside the aircraft.

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

[0058] Step S2 in the embodiment of the present application comprises the following sub-steps: ​

[0059] S21, calculating an electron motion equation of an electron in the magnetized plasma under the joint action of an electric field and a magnetic field;

[0060] S22, calculating the conductivity of the magnetized plasma under the action of left circularly polarized waves and right circularly polarized waves according to the electron motion equation when the electromagnetic wave propagates along the magnetic field direction;

[0061] S23, calculating the relative permittivity of the magnetized plasma according to the relationship between the conductivity of the magnetized plasma and the relative permittivity.

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

[0063]

[0064] In the formula, m e represents the mass of the electron, v represents the velocity vector of the electron, v e represents the collision frequency of the electron, e represents the electric quantity of the electron, E represents the electric field intensity, and B represents the intensity of the applied magnetic field.

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

[0066]

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

[0068] Formula (2) is written in matrix form as:

[0069]

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

[0071]

[0072] In the formula, J x , J y , J zrespectively, are the components of the current density vector J in the x, y, z directions, and σ -1 ·J = E and formula (5) can be known that the conductivity of the magnetized plasma is:

[0073]

[0074] The conductivity becomes a tensor form, which is written as:

[0075]

[0076] wherein,

[0077]

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

[0079]

[0080] wherein, I is a unit matrix, and other symbols are expressed as follows:

[0081]

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

[0083] The electric field in the magnetized plasma is anisotropic, and when the electromagnetic wave propagates along the magnetic field direction, left-handed circularly polarized wave and right-handed circularly polarized wave appear, and the unit vectors of the two are represented as:

[0084]

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

[0086] The electron velocity in the plasma is also represented as a circular polarization mode:

[0087]

[0088] Under the action of the circularly polarized electric wave, 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, "+" in "+" indicates a left-handed circularly polarized wave, and "-" indicates a right-handed circularly polarized wave.

[0091] Substituting formula (17) into formula (1) gives:

[0092]

[0093] Further calculation gives:

[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 the present embodiment is expressed as:

[0096]

[0097] In the formula, σ l represents the conductivity of the magnetized plasma under the action of a left-handed circularly polarized wave, σ r represents the conductivity of the magnetized plasma under the action of a right-handed circularly polarized wave, n e represents the electron density, e represents the electron charge, v l represents the velocity of a left-handed circularly polarized electron, v r represents the velocity of a right-handed circularly polarized electron, E l represents the electric field intensity of a left-handed circularly polarized wave, E r represents the electric field intensity of a right-handed circularly polarized wave, ε0 represents the vacuum permittivity, and ω p represents the characteristic frequency of the plasma, and ω b represents the cyclotron frequency of the electron, and ω represents the incident frequency.

[0098] In step S23 of the present embodiment, the relationship between the conductivity of the magnetized plasma and the relative permittivity is:

[0099]

[0100] In the formula, ε l,r represents the relative permittivity of the magnetized plasma, σ l,r represents the conductivity of the magnetized plasma, ω represents the incident frequency, and ε0 represents the vacuum permittivity.

[0101] Substituting formula (20) into formula (21) gives the relative permittivity of the magnetized plasma as:

[0102]

[0103] In the formula, the subscript ''+'' in l and + represents left-handed circularly polarized wave, and r and ''-'' represent right-handed circularly polarized wave.

[0104] In step S3 of the embodiment of the application, according to the derivation process of the above formula of the relative permittivity, the applied electrostatic electromagnetic field has an influence on the relative permittivity of the plasma, and further influences the transmission characteristics of the electromagnetic wave in the plasma; specifically, when the magnetic field is applied, the transmission characteristics of the electromagnetic wave in the plasma are as follows:

[0105] With the increase of the frequency of the incident electromagnetic wave, the reflection of the plasma to the electromagnetic wave is weakened, the frequency band in which the reflection coefficient amplitude drops fastest is shifted left with the increase of the magnetic field strength, and the stronger the applied magnetic field strength is, the lower the frequency band required for the plasma profile diagnosis is.

[0106] In a specific example of the application, as shown in Figure 3 , the amplitude-frequency curves of the reflection coefficient of the left-handed circularly polarized wave and the right-handed circularly polarized wave under different intensities of the applied magnetic field B are respectively given ((a) is the relationship between the incident frequency and the reflection coefficient under the left-handed circularly polarized wave, and (b) is the relationship between the incident frequency and the reflection coefficient under the right-handed circularly polarized wave). 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 , a1 = 2000, a2 = 1700, z0 = 0.035 m, the thickness is 0.1 m, and the collision frequency is 1 GHz.

[0107] From Figure 3 (a), when the incident electromagnetic wave is the left-handed circularly polarized wave, the overall characteristics of the electromagnetic wave reflection coefficient are basically the same as those without the applied magnetic field: the reflection coefficient amplitude as a whole shows a downward trend, indicating that with the increase of the incident wave frequency, the reflection of the plasma to the electromagnetic wave is gradually weakened, and the frequency band in which the reflection coefficient amplitude drops fastest is gradually shifted left with the increase of the magnetic field strength. In the plasma profile diagnosis method based on the genetic algorithm, the stronger the applied magnetic field strength is, the lower the required frequency band is.

[0108] From Figure 3 (b), it can be seen that when the incident electromagnetic wave is the right-handed circularly polarized wave, the reflection coefficient characteristics basically remain unchanged when the magnetic field strength is small, the frequency band in which the reflection coefficient amplitude drops fastest is shifted right, and when the incident wave frequency is low, the reflection coefficient amplitude will appear a ''concave'' region which first drops and then rises. After the magnetic field strength increases, this characteristic is more obvious, and the reflection coefficient has a significant drop in a low frequency band, indicating that the magnetized plasma reflects little incident wave in this frequency band, and part of the electromagnetic wave can penetrate the plasma. The stronger the magnetic field strength is, the lower the reflection coefficient amplitude of the ''window'' part is, the wider the covered frequency band is, and the better the electromagnetic wave penetration effect is.

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

[0110] Specifically, according to the deduction that the applied magnetic field changes the electromagnetic wave transmission characteristics of the plasma, at the same incident wave frequency point, different applied magnetic field strengths correspond to different reflection coefficient values. According to the analysis, when the applied magnetic field is applied to the plasma, the reflection ability of the plasma to the right-handed polarized wave is reduced, and when the plasma profile is diagnosed, the reflection data is used for diagnosis, so the right-handed polarized wave is not suitable. The left-handed polarized wave will make the effective frequency band left-shift, which exactly meets the requirement of reducing the incident frequency, therefore, the left-handed polarized wave is used as the incident electromagnetic wave in the embodiment.

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

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

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

[0114] The method of the present application is a method in which the applied magnetic field can change the medium characteristics of the plasma, and further change the reflection coefficient and the cutoff region range of the electromagnetic wave; in the implementation process, 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. Starting from the electromagnetic characteristics of the magnetized plasma, the permittivity expression of the magnetized plasma is first derived, and then the expression is substituted into the calculation formula to explore the influence of different magnetic fields on the electromagnetic wave transmission.

[0115] The principles and implementation manners of the present application are described by using specific embodiments in the present application, and the above embodiment descriptions are only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges will be changed, and the above descriptions should not be understood as limitations of the present application.

[0116] Those skilled in the art will realize that the embodiments described herein are for the purpose of helping the reader to understand the principles of the present application, and should be understood as the protection scope of the present application not being limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations according to the technical inspirations disclosed in the present application without departing from the essence of the present application, and these modifications and combinations are still within the protection scope of the present application.

Claims

1. A tunable magnetic field assisted plasma profile diagnostic method, comprising: The method comprises the following steps: S1, magnetizing the plasma by an external magnetic field; S2, calculating the relative permittivity of the current magnetized plasma; S3, analyzing the transmission characteristics of the electromagnetic wave in the plasma based on the calculated relative permittivity, and determining whether the reflection coefficient corresponding to the incident wave frequency band of the current external magnetic field is the required data for plasma profile diagnosis; If not, go to step S4; If yes, go 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, analyzing the mapping relationship between different magnetic field strengths and reflection coefficients by using a genetic algorithm to realize plasma profile diagnosis.

2. The tunable magnetic field assisted plasma profile diagnostic method of claim 1, wherein, In the step S1, the layout mode of the external magnetic field for magnetizing the plasma is: Embed a wave-transparent window in the surface of the aircraft, and arrange an antenna below the wave-transparent window in the aircraft.

3. The tunable magnetic field assisted plasma profiling diagnostic method of claim 1, wherein, In the step S1, the layout mode of the external magnetic field for magnetizing the plasma is: Embed a wave-transparent window in the surface of the aircraft, and arrange three electromagnetic coils and an antenna in sequence below the wave-transparent window in the aircraft.

4. The tunable magnetic field assisted plasma profiling diagnostic method of claim 1, wherein, The step S2 comprises the following sub-steps: S21, calculating the electron motion equation of the electrons in the magnetized plasma under the joint action of the electric field and the magnetic field; S22, calculating the conductivity of the magnetized plasma under the action of the left circularly polarized wave and the right circularly polarized wave according to the electron motion equation when the electromagnetic wave propagates along the magnetic field direction; S23, calculating the relative permittivity of the magnetized plasma according to the relationship between the conductivity of the magnetized plasma and the relative permittivity.

5. The tunable magnetic field assisted plasma profiling diagnostic method of claim 4, wherein, In the step S21, the electron motion equation of the electrons in the magnetized plasma under the joint action of the electric field and the magnetic field is: where m e represents the electron mass, v represents the electron velocity vector, v e represents the electron collision frequency, e represents the electron charge, E represents the electric field strength, and B represents the applied magnetic field strength.

6. The tunable magnetic field assisted plasma profiling diagnostic method of claim 5, wherein, In the step S22, the conductivity of the magnetized plasma is represented as: where σ l represents the conductivity of the magnetized plasma under the action of the left-handed circularly polarized wave, σ r represents the conductivity of the magnetized plasma under the action of the right-handed circularly polarized wave, n e represents the electron density, e represents the electron charge, v l represents the left-handed circularly polarized electron velocity, v r represents the right-handed circularly polarized electron velocity, E l represents the left-handed circularly polarized wave electric field intensity, E r represents the right-handed circularly polarized wave electric field intensity, ε0 represents the vacuum permittivity, ω p represents the characteristic frequency of the plasma, ω b represents the cyclotron frequency of the electron, ω represents the incident frequency.

7. The tunable magnetic field assisted plasma profiling diagnostic method of claim 6, wherein, In the step S23, the relationship between the conductivity of the magnetized plasma and the relative permittivity is: where ε l,r represents the relative permittivity of the magnetized plasma, σ l,r represents the conductivity of the magnetized plasma, ω represents the incident frequency, and ε0represents the vacuum permittivity; The relative permittivity ε of the magnetized plasma l,r is represented as: In the formula, the "+" in the subscripts l and ± represents the left circularly polarized wave, and r and "-" represent the right circularly polarized wave.

8. The tunable magnetic field assisted plasma profiling diagnostic method of claim 1, wherein, In the step S3, when the external magnetic field is applied, the transmission characteristics of the electromagnetic wave in the plasma are: As the frequency of the incident electromagnetic wave increases, the reflection effect of the plasma on the electromagnetic wave weakens, the frequency band with the fastest decline in the amplitude of the reflection coefficient shifts left with the increase of the magnetic field strength, and the stronger the external magnetic field strength, the lower the electromagnetic wave frequency band required for plasma profile diagnosis.

9. The tunable magnetic field assisted plasma profiling diagnostic method of claim 1, wherein, In the step S4, the incident wave frequency band of the external magnetic field is adjusted, and the left circularly polarized wave is used as the incident electromagnetic wave to re-magnetize the plasma.

10. The tunable magnetic field assisted plasma profiling diagnostic method of claim 1, wherein, In the step S5, the mapping relationship of the reflection coefficient is: R=F(ne(z),ve,B) In the formula, R represents the reflection coefficient, F(·) is a function symbol, ne(z) represents the electron density, ve represents the collision frequency, and B represents the magnetic field strength.

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