Plasma torch based on electron cyclotron resonance and simplified simulation method thereof

Abstract

The invention discloses a plasma torch based on electron cyclotron resonance and a simplified simulation method thereof, and relates to the technical field of microwave plasmons.The plasma torch comprises a rectangular waveguide tube, two round waveguide tubes symmetrically arranged on the rectangular waveguide tube and communicated with the interior of the rectangular waveguide tube and further comprises a microwave plasma discharge tube. The microwave plasma discharge tube penetrates through the rectangular waveguide tube and the quartz tubes of the two round waveguide tubes, direct current coils are wound on the quartz tubes at equal intervals, and a plasma discharge area is arranged in the quartz tubes. On the basis of a microwave plasma discharge model and in combination with the thought of electron cyclotron resonance, a local electric field can be improved by introducing coils at equal intervals into an electromagnetic field, so that the excitation efficiency of plasma is improved; in addition, a constant magnetic field can be introduced by providing direct current for the coil, so that the electron motion trail is restrained, and the uniformity of the plasma is improved.

Description

Technical Field

[0001] The invention relates to the technical field of microwave plasma, and more specifically to the technical field of a plasma torch based on electron cyclotron resonance and a simplified simulation method thereof. Background Art

[0002] Low-temperature plasma technology is an advanced processing and application technology that uses low-energy electromagnetic fields or microwaves to excite the plasma state. Common methods include capacitively coupled plasma, inductively coupled plasma, surface plasma waves, helicon wave plasma and microwave plasma. These methods have broad application potential in material processing, surface modification, clean etching, nanomaterial synthesis and environmental governance. Low-temperature plasma technology has the advantages of high efficiency, precise control and environmental protection, so it is increasingly being paid attention to and adopted in scientific research and industrial applications.

[0003] Surface plasma waves (SPWs) are electromagnetic surface waves that propagate near the surface of metals. These waves are generated by the interaction between free electrons and photons on the metal surface, forming an electron concentration gradient distribution and being bound in the plasma oscillation waves on the surface. Surface plasma waves have attracted extensive attention in the fields of nano-optoelectronics, data storage, microscopy, optical waveguides, etc. Electromagnetic waves generated outside the plasma can propagate into the plasma or propagate along the plasma surface until they are finally absorbed by the plasma. In these processes, the role of electromagnetic waves is to generate and maintain plasma discharge and heat the electrons in the plasma.

[0004] Among them, microwave plasma (MWP) is an advanced processing technology that uses electromagnetic waves of microwave frequency (2.45GHz or 915MHz) to excite the plasma state. Plasma is formed by introducing microwave energy into a gas or liquid medium to ionize its atoms or molecules. This technology has attracted much attention because it can achieve precise local heating and volume heating. Microwave plasma has shown broad application prospects in the fields of material synthesis, energy development and environmental governance. Electron cyclotron resonance (ECR) microwave plasma Electron cyclotron resonance (ECR) microwave plasma is a plasma generated by the combined action of high-frequency microwaves and a constant magnetic field provided by a DC coil, causing electrons to cyclotron in the magnetic field and be excited by microwave energy. The plasma generated by this technology has a high density and temperature and is widely used in the fields of high-energy processing and fine material processing.

[0005] Existing microwave plasma devices have poor robustness, low electron energy density, and are prone to etching the outer wall of the reaction chamber. When changing conditions such as gas type, gas concentration, pressure, and input power, the plasma morphology is prone to significant changes, the plasma load's ability to absorb microwaves varies greatly, and it is easy to produce large reflections, and the efficiency of microwaves to plasma is low. By adding a strong magnetic field to the discharge region, electrons can be made to cyclotron around the magnetic lines of force, increasing the movement path of electrons in the discharge region, making the interaction between electrons and electromagnetic waves stronger, which is more conducive to electrons absorbing energy and improving plasma uniformity. However, in the existing electron cyclotron resonance plasma (ECR), the magnetic field DC coil is located outside the microwave field, which cannot improve the efficiency of microwaves to plasma. Summary of the invention

[0006] The purpose of the present invention is to solve the above technical problems and provide a plasma torch based on electron cyclotron resonance and a simplified simulation method thereof.

[0007] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0008] One aspect of the present invention provides a plasma torch based on electron cyclotron resonance, comprising a rectangular waveguide tube, two circular waveguide tubes symmetrically arranged on the rectangular waveguide tube, wherein the length direction of the rectangular waveguide tube is orthogonal to the center line of the circular waveguide tube, and the circular waveguide tube is connected to the inside of the rectangular waveguide tube, and further comprising a microwave plasma discharge tube, wherein the microwave plasma discharge tube is a quartz tube that passes through the rectangular waveguide tube and the two circular waveguide tubes, a DC coil is wound on the quartz tube at equal intervals, and the inside of the quartz tube is a plasma discharge zone;

[0009] An adjustable short-circuit surface is slidably arranged on one side of the rectangular waveguide tube away from the microwave inlet, and a position adjustment structure for adjusting the position of the adjustable short-circuit surface is arranged at the end of the rectangular waveguide tube.

[0010] Specifically, in the case of microwave input (the power of the microwave source is 1W), the electric field distribution in the system without a DC coil is as follows: Figure 2 , microwaves are fed into the input port of the rectangular waveguide. It can be found that the TE10 mode of the rectangular waveguide presents the characteristics of standing wave distribution in the resonant cavity. At this time, the placement position of the quartz tube is just at the antinode position where the electric field is the strongest. The field strength generated at this time is small, only 10 3 Order of magnitude.

[0011] This scheme is based on the microwave plasma discharge model and the idea of ​​electron cyclotron resonance. It increases the local electric field by introducing equally spaced DC coils in the electromagnetic field, thereby increasing the excitation efficiency of the plasma. In addition, providing DC power to the DC coil can also introduce a constant magnetic field, thereby constraining the trajectory of electron movement and improving the uniformity of the plasma. In addition, by modulating the current and voltage in the DC coil, the maintenance efficiency of the plasma can also be improved.

[0012] In order to improve the electric field strength in the quartz tube, a DC coil is added to the above structure and optimized, and the number of turns of the DC coil and the spacing between two adjacent turns are adjusted. Figure 3 As shown;

[0013] In one embodiment, one end of the rectangular waveguide is a microwave inlet, and the microwave inlet is connected to the magnetron.

[0014] Specifically, a magnetron is an electric vacuum device used to generate microwave energy. It is essentially a diode placed in a constant magnetic field. Its function is to make the electrons in the tube interact with the high-frequency electromagnetic field under the control of the mutually perpendicular constant magnetic field and constant electric field, and convert the energy obtained from the constant electric field into microwave energy.

[0015] In one embodiment, the rectangular waveguide has a starting frequency of 1.72 GHz, an ending frequency of 2.61 GHz, a cross-sectional length of 109.22 mm, and a width of 54.61 mm.

[0016] Specifically, the rectangular waveguide is a rectangular waveguide of the Chinese standard BJ22, with a starting frequency of 1.72 GHz, an end frequency of 2.61 GHz, a cross-sectional length of 109.22 mm, and a width of 54.61 mm.

[0017] In one embodiment, a plurality of adjustment pins for adjusting impedance matching and improving transmission efficiency are provided on the rectangular waveguide between the circular waveguide and the magnetron.

[0018] Specifically, the main functions of the adjustment pins include adjusting impedance matching, improving transmission efficiency, fine-tuning the operating frequency, and widening the frequency response range. The relevant reference content is as follows:

[0019] Impedance matching to improve transmission efficiency: Microwave systems are usually composed of multiple components with different characteristics, and there may be impedance mismatches between different components. By adjusting the position and depth of the adjustment pin in the transmission line, the equivalent impedance of the transmission line can be changed, thereby achieving impedance matching with the previous and next stage circuits or devices. When the system reaches an impedance matching state, microwave energy can be transmitted from one component to another to the maximum extent, reducing reflection and energy loss and improving transmission efficiency. Reduce standing wave ratio: Impedance mismatch will cause microwaves to generate standing waves on the transmission line. The standing wave ratio is an indicator to measure the degree of standing waves. The larger the standing wave ratio, the stronger the reflected wave in the system and the worse the transmission effect. The adjustment pin can adjust the standing wave. By adjusting the parameters of the pin, the standing wave ratio is reduced, the microwave distribution on the transmission line is more uniform, the influence of reflected waves is reduced, and the stable operation of the system is ensured.

[0020] Fine-tune the operating frequency: The operating frequency of the microwave system may be offset by environmental factors (such as temperature, humidity) or device aging. The adjustment pins can fine-tune the frequency characteristics of the system to return it to the designed operating frequency. By changing the position of the three pins in the cavity, the resonant frequency of the cavity can be adjusted, thereby achieving the adjustment of the operating frequency of the entire microwave system. Widen the frequency response range: In some applications, the microwave system is required to have a certain frequency response range. The adjustment pins can change the frequency response characteristics of the system to a certain extent, so that it can adapt to microwave signal inputs of different frequencies and widen the application range of the system.

[0021] In one embodiment, two ends of the DC coil are respectively connected to the positive and negative electrodes of the DC power generator through wires, one end of the quartz tube is an air inlet, and the other end is connected to a vacuum pump.

[0022] Specifically, the vacuum pump is used to provide the low-pressure environment required for plasma discharge (discharge can be performed with or without a vacuum pump, discharge with a vacuum pump is low-pressure discharge, and discharge without a vacuum pump is atmospheric pressure).

[0023] In one embodiment, the position adjustment structure can adjust the distance between the short-circuit surface and the microwave plasma discharge tube. When the distance is (2*n+1)*λg / 4, the electric field is maximum, where n is a natural number and λg is the waveguide wavelength in the air. At 2.45 GHz, λg is approximately 171.8 mm.

[0024] In one embodiment, the quartz tube has a thickness of 2 mm and is the discharge region of the plasma, which can confine the plasma within the tube.

[0025] In one embodiment, the diameter of the circular waveguide is 32 mm.

[0026] Specifically, in order to prevent electromagnetic waves from leaking from the circular waveguide, the size of the circular waveguide needs to be limited. The diameter of the circular waveguide in this device is 32 mm. Figure 2 From the simulation, we can see that the microwave decays rapidly in the circular waveguide at this time.

[0027] Another aspect of the present invention provides a simplified simulation method for analyzing an electron cyclotron resonance plasma torch, which is applicable to the above-mentioned electron cyclotron resonance-based plasma torch, and comprises the following steps:

[0028] Step S1, based on the Helmholtz equation of the electric field, a three-dimensional electric field model is established to analyze the electric field distribution, specifically to determine the length of the rectangular waveguide, the diameter and length of the circular waveguide, the number of turns of the DC coil and the spacing between the DC coils;

[0029]

[0030] Where E is the electric field strength, μ r is the relative magnetic permeability, k0 is the electromagnetic wave number, ε r is the relative dielectric constant, σ is the conductivity, ω is the angular frequency of the electromagnetic wave, and ε0 is the dielectric constant in a vacuum;

[0031] Step S2: Establish a two-dimensional axisymmetric magnetic field model, bring the DC coil parameters into the magnetic field model, and calculate the magnetic induction intensity generated under different input powers:

[0032]

[0033]

[0034] Among them, H is the magnetic field intensity, B is the magnetic induction density, A is the magnetic vector potential, and J is the current density;

[0035] Step S3, coupling the parameters in the electromagnetic simulation, combining the Drude model to perform a three-dimensional simulation, and studying the energy efficiency of microwaves to plasma before and after adding the DC coil;

[0036] Step S4, establishing a two-dimensional microwave-plasma coupling joint simulation model, and bringing the medium magnetic field parameters and the medium electric field parameters into the joint simulation model to calculate the influence of the DC coil and the magnetic field on the microwave plasma.

[0037] Specifically, there is currently no design for a plasma device that places a magnetic field DC coil in a microwave field. This design can overcome the uneven discharge phenomenon of microwave plasma. At the same time, the DC coil has a focusing effect on the electromagnetic field, which is beneficial to the excitation of plasma.

[0038] In addition, a plasma discharge device structure in which a DC coil is placed in a microwave field is combined with the Comsol simulation program to achieve efficient excitation and maintenance of the plasma by modulating the electromagnetic field and the static magnetic field (i.e., the current in the DC coil or the voltage across the DC coil), thereby improving the uniformity of the plasma through the above structure.

[0039] Why do we need to simplify the simulation? The self-consistent three-dimensional electron cyclotron resonance plasma model has a large amount of calculation, poor convergence, high calculation cost, and cannot be used for large-scale parameter scanning, and it is difficult to guide industrial production applications. The complex modeling process can be divided into several simple models, and finally the different variables can be reflected in the same model using a single coupling method, which greatly reduces the model calculation cost.

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

[0041] The present invention is based on the microwave plasma discharge model and the idea of ​​electron cyclotron resonance. It increases the local electric field by introducing equally spaced DC coils in the electromagnetic field, thereby increasing the excitation efficiency of the plasma. In addition, providing DC power to the DC coil can also introduce a constant magnetic field, thereby constraining the electron motion trajectory and improving the uniformity of the plasma. In addition, by modulating the current and voltage in the DC coil, the maintenance efficiency of the plasma can also be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] FIG. 1( a ) is a schematic diagram of the structure of a plasma torch based on electron cyclotron resonance;

[0044] Figure 1(b) is a local structural refinement diagram of Figure 1(a);

[0045] Figure 2 This is the electric field simulation diagram when there is no coil;

[0046] Figure 3 This is the simulation diagram after adding the coil;

[0047] Figure 4 This is a graph showing the effect of the number of coil turns on the electric field distribution;

[0048] Figure 5 This is the boundary condition diagram in the coil magnetic field simulation;

[0049] Figure 6is the magnetic field distribution diagram in the two-dimensional axisymmetric model of magnetic field;

[0050] Figure 7 This is the workflow diagram of magnetic field regulation of microwave plasma;

[0051] Figure 8 It is the electric field distribution diagram during plasma excitation;

[0052] Fig. 9 It is the electron density distribution diagram during plasma excitation;

[0053] Fig.10 It is the electric field distribution diagram during plasma excitation after adding a constant magnetic field;

[0054] Fig.11 It is the electron density distribution diagram during plasma excitation after adding a constant magnetic field;

[0055] Fig.12 This is a diagram of the central electron density distribution under different discharge conditions;

[0056] Fig.13 is a flow chart of a simplified simulation method of an electron cyclotron resonance plasma torch;

[0057] Figure numerals: 1-microwave generator, 2-rectangular waveguide, 3-adjustable pin, 4-microwave plasma discharge tube, 5-position adjustment structure, 6-quartz tube, 7-circular waveguide tube, 8-DC coil, 9-plasma discharge zone, 10-DC power generator, 11-vacuum pump. DETAILED DESCRIPTION

[0058] In order to make the technical problems, technical solutions and technical effects of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0059] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In addition, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0061] In the description of the embodiments of the present invention, it should be noted that the terms "inside", "outside", "upper", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0062] Example 1

[0063] The present embodiment provides a plasma torch based on electron cyclotron resonance, comprising a rectangular waveguide 2, two circular waveguide tubes 7 symmetrically arranged on the rectangular waveguide 2, the length direction of the rectangular waveguide 2 being orthogonal to the center line of the circular waveguide tube 7, the circular waveguide tube 7 being connected to the inside of the rectangular waveguide 2, and a microwave plasma discharge tube 4, the microwave plasma discharge tube 4 passing through a quartz tube 6 of the rectangular waveguide 2 and the two circular waveguide tubes 7, a DC coil 8 being equally spaced around the quartz tube 6, and a plasma discharge zone 9 being inside the quartz tube 6;

[0064] An adjustable short-circuit surface is slidably arranged inside the rectangular waveguide 2 on a side away from the microwave inlet, and a position adjustment structure 5 for adjusting the position of the adjustable short-circuit surface is arranged at the end of the rectangular waveguide 2.

[0065] Specifically, in the case of microwave input (the power of the microwave source is 1W), the electric field distribution in the system without the DC coil 8 is as follows: Figure 2 , microwaves are fed into the input port of rectangular waveguide 2. It can be found that the TE10 mode of rectangular waveguide 2 shows the characteristics of standing wave distribution in the resonant cavity. At this time, the placement position of quartz tube 6 is just at the antinode position of the strongest electric field. The field strength generated at this time is small, only 10 3 Order of magnitude.

[0066] This scheme is based on the microwave plasma discharge model and the idea of ​​electron cyclotron resonance. By introducing equally spaced DC coils 8 in the electromagnetic field, the local electric field is improved, thereby increasing the excitation efficiency of the plasma. In addition, providing DC power to the DC coils 8 can also introduce a constant magnetic field, thereby constraining the electron motion trajectory and improving the uniformity of the plasma. In addition, by modulating the current and voltage in the DC coils 8, the maintenance efficiency of the plasma can also be improved.

[0067] In order to improve the electric field strength in the quartz tube 6, a DC coil 8 is added to the above structure and optimized, and the number of turns of the DC coil 8 and the spacing between two adjacent turns are adjusted. Figure 3 shown.

[0068] Example 2

[0069] This embodiment is further optimized on the basis of embodiment 1, specifically:

[0070] One end of the rectangular waveguide 2 is a microwave inlet, which is connected to the magnetron.

[0071] Specifically, a magnetron is an electric vacuum device used to generate microwave energy. It is essentially a diode placed in a constant magnetic field. Its function is to make the electrons in the tube interact with the high-frequency electromagnetic field under the control of the mutually perpendicular constant magnetic field and constant electric field, and convert the energy obtained from the constant electric field into microwave energy.

[0072] The starting frequency of rectangular waveguide 2 is 1.72 GHz, the ending frequency is 2.61 GHz, the cross-sectional length is 109.22 mm, and the width is 54.61 mm.

[0073] Specifically, the rectangular waveguide 2 tube is a rectangular waveguide 2 tube of the Chinese standard BJ22, with a starting frequency of 1.72 GHz, a stop frequency of 2.61 GHz, a cross-sectional length of 109.22 mm, and a width of 54.61 mm.

[0074] Example 3

[0075] This embodiment is further optimized on the basis of Embodiment 1 or Embodiment 2, specifically:

[0076] A plurality of adjustment pins for adjusting impedance matching and improving transmission efficiency are arranged on the rectangular waveguide 2 located between the circular waveguide tube 7 and the magnetron.

[0077] Specifically, the main functions of the adjustment pins include adjusting impedance matching, improving transmission efficiency, fine-tuning the operating frequency, and widening the frequency response range. The relevant reference content is as follows:

[0078] Impedance matching to improve transmission efficiency: Microwave systems are usually composed of multiple components with different characteristics, and there may be impedance mismatches between different components. By adjusting the position and depth of the adjustment pin in the transmission line, the equivalent impedance of the transmission line can be changed, thereby achieving impedance matching with the previous and next stage circuits or devices. When the system reaches an impedance matching state, microwave energy can be transmitted from one component to another to the maximum extent, reducing reflection and energy loss and improving transmission efficiency. Reduce standing wave ratio: Impedance mismatch will cause microwaves to generate standing waves on the transmission line. The standing wave ratio is an indicator to measure the degree of standing waves. The larger the standing wave ratio, the stronger the reflected wave in the system and the worse the transmission effect. The adjustment pin can adjust the standing wave. By adjusting the parameters of the pin, the standing wave ratio is reduced, the microwave distribution on the transmission line is more uniform, the influence of reflected waves is reduced, and the stable operation of the system is ensured.

[0079] Fine-tune the operating frequency: The operating frequency of the microwave system may be offset by environmental factors (such as temperature, humidity) or device aging. The adjustment pins can fine-tune the frequency characteristics of the system to return it to the designed operating frequency. By changing the position of the three pins in the cavity, the resonant frequency of the cavity can be adjusted, thereby achieving the adjustment of the operating frequency of the entire microwave system. Widen the frequency response range: In some applications, the microwave system is required to have a certain frequency response range. The adjustment pins can change the frequency response characteristics of the system to a certain extent, so that it can adapt to microwave signal inputs of different frequencies and widen the application range of the system.

[0080] Example 4

[0081] This embodiment is further optimized on the basis of any one of Embodiments 1 to 3, specifically:

[0082] Two ends of the DC coil 8 are respectively connected to the positive and negative electrodes of the DC power generator 10 through wires. One end of the quartz tube 6 is an air inlet, and the other end is connected to a vacuum pump 11.

[0083] Specifically, the vacuum pump 11 is used to provide the low-pressure environment required for plasma discharge (discharge can be performed with or without the vacuum pump 11; discharge with the vacuum pump 11 is low-pressure discharge, and discharge without the vacuum pump 11 is atmospheric pressure discharge).

[0084] The position adjustment structure 5 adjusts the distance between the adjustable short-circuit surface and the microwave plasma discharge tube 4. When the distance is (2*n+1)*λg / 4, the electric field is maximum, wherein n is a natural number, λg is the waveguide wavelength in the air, and at 2.45 GHz, λg is approximately 171.8 mm.

[0085] The thickness of the quartz tube 6 is 2 mm, and it is the discharge area of ​​the plasma, and can confine the plasma in the tube.

[0086] The diameter of the circular waveguide 7 is 32 mm.

[0087] Specifically, in order to prevent electromagnetic waves from leaking from the circular waveguide 7, the size of the circular waveguide 7 needs to be limited. The diameter of the circular waveguide 7 in the device is 32 mm. Figure 2 It can be seen from the simulation that the microwave decays rapidly in the circular waveguide 7 at this time.

[0088] Example 5

[0089] This embodiment provides a simplified simulation method for analyzing an electron cyclotron resonance plasma torch, which is applicable to the above-mentioned electron cyclotron resonance-based plasma torch, and includes the following steps:

[0090] Step S1, based on the Helmholtz equation of the electric field, a three-dimensional electric field model is established to analyze the electric field distribution, specifically to determine the length of the rectangular waveguide, the diameter and length of the circular waveguide, the number of turns of the DC coil and the spacing between the DC coils;

[0091]

[0092] Where E is the electric field strength, μ r is the relative magnetic permeability, k0 is the electromagnetic wave number, ε r is the relative dielectric constant, σ is the conductivity, ω is the angular frequency of the electromagnetic wave, and ε0 is the dielectric constant in a vacuum;

[0093] Step S2: Establish a two-dimensional axisymmetric magnetic field model, bring the DC coil parameters into the magnetic field model, and calculate the magnetic induction intensity generated under different input powers:

[0094]

[0095]

[0096] Among them, H is the magnetic field intensity, B is the magnetic induction density, A is the magnetic vector potential, and J is the current density;

[0097] Step S3, coupling the parameters in the electromagnetic simulation, combining the Drude model to perform a three-dimensional simulation, and studying the energy efficiency of microwaves to plasma before and after adding the DC coil;

[0098] Step S4, establishing a two-dimensional microwave-plasma coupling joint simulation model, by bringing the magnetic field parameters in step S2 and the electric field parameters in step S1 into the joint simulation model to calculate the influence of the DC coil and the magnetic field on the microwave plasma.

[0099] Specifically, there is currently no design for a plasma device that places a magnetic field DC coil in a microwave field. This design can overcome the uneven discharge phenomenon of microwave plasma. At the same time, the DC coil has a focusing effect on the electromagnetic field, which is beneficial to the excitation of plasma.

[0100] In addition, a plasma discharge device structure in which a DC coil is placed in a microwave field is combined with the Comsol simulation program to achieve efficient excitation and maintenance of the plasma by modulating the electromagnetic field and the static magnetic field (i.e., the current in the DC coil or the voltage across the DC coil), thereby improving the uniformity of the plasma through the above structure.

[0101] Why do we need to simplify the simulation? The self-consistent three-dimensional electron cyclotron resonance plasma model has a large amount of calculation, poor convergence, high calculation cost, and cannot be used for large-scale parameter scanning, and it is difficult to guide industrial production applications. The complex modeling process can be divided into several simple models, and finally the different variables can be reflected in the same model using a single coupling method, which greatly reduces the model calculation cost.

[0102] A detailed description of the simplified simulation method of the plasma torch is as follows:

[0103] 1.1. DC coil structure optimization

[0104] In order to improve the electric field strength in the discharge chamber (quartz tube), a DC coil is added and optimized based on the above structure, and the number of turns of the DC coil and the spacing between the DC coils are adjusted. Figure 3 As shown,

[0105] The DC coil is evenly wound around the quartz tube. At this time, the small gap between the DC coils is similar to a slot antenna, which has a focusing effect on microwaves. Under the premise of keeping the total length unchanged, the number of turns of the DC coil and the spacing between the DC coils are changed. The electric field distribution in the quartz tube area is as follows: Figure 4 .

[0106] The DC coil is evenly wound around the quartz tube. At this time, the small gap between the DC coils is similar to a slot antenna, which has a focusing effect on microwaves. Under the premise of keeping the total length unchanged, the number of turns of the DC coil and the spacing between the DC coils are changed. The electric field distribution in the quartz tube area is as follows: Figure 4 (When the DC coil on the quartz tube has 0 turns, the maximum electric field strength in the quartz tube is 1×10 3 When the DC coil on the quartz tube has 10 turns, the maximum electric field strength in the quartz tube is 2×10 4 When the DC coil on the quartz tube has 15 turns, the maximum electric field strength in the quartz tube is 4.9×10 3 When the DC coil on the quartz tube has 20 turns, the maximum electric field strength in the quartz tube is 2.6×10 3When the DC coil on the quartz tube has 25 turns, the maximum electric field strength in the quartz tube is 2.7×10 3 ).

[0107] pass Figure 4 It is not difficult to find that when the number of turns of the DC coil is small, the electromagnetic wave can form a strong electric field between the gaps of the DC coil, which is more conducive to the excitation of plasma. As the number of turns increases, the energy of this enhanced electric field becomes weaker, and the field strength in the quartz tube is almost the same as the field strength without the DC coil. Therefore, the number of turns of the DC coil is required to be smaller. The number of turns m (turns) of the DC coil and the spacing h (mm) of the DC coil are described by the following formula:

[0108] n = 100 / m;

[0109] □ = n × 0.001;

[0110] Where n is the DC coil proportional coefficient.

[0111] 1.2. Magnetic field DC coil simulation results

[0112] In the above simulation, the influence of the constant magnetic field generated by the DC current in the DC coil is not considered. However, the three-dimensional electromagnetic field-constant magnetic field-plasma interaction full coupling simulation takes a long time to calculate and has poor convergence. Therefore, the model is moderately simplified and a two-dimensional axisymmetric model including electromagnetic field-constant magnetic field-plasma is constructed. The schematic diagram of the model is as follows Figure 5 .

[0113] When the DC coil power is 100W, the magnetic field distribution of the two-dimensional axisymmetric system is as follows: Figure 6 At this time, there is a strong magnetic field at the DC coil, as expected.

[0114] Magnetic field control microwave plasma process Figure 7 .

[0115] 1.3 Plasma simulation results

[0116] The principle of using the Drude equivalent model for plasma simulation is as follows:

[0117]

[0118]

[0119] Among them, σ p is the plasma conductivity, n e is the electron density, v m is the collision frequency, ω is the angular frequency, ω p is the electron frequency, m e is the mass of the electron, q is the charge density, ε0 ​​is the dielectric constant in vacuum, εrp is the relative dielectric constant of the plasma. By defining the above parameters, the interaction between the excited plasma and the electromagnetic wave can be simulated. The S11 parameter can be used to reflect the absorption of the electromagnetic wave by the plasma. 11 The parameters are defined as follows:

[0120]

[0121] Where Pref is the reflected power, Pin is the incident power, S 11 The smaller the value, the stronger the ability of plasma to absorb electromagnetic waves, the less electromagnetic waves are reflected, and the number of turns of the DC coil, the maximum value of the electric field and S 11 The relationship between them is shown in Table 1.

[0122] Table 1 DC coil turns, electric field maximum and S 11 The relationship table between

[0123]

[0124]

[0125] It is not difficult to see from Table 1 that after adding the DC coil, the maximum field strength increases by 2 to 10 times, which is more conducive to exciting plasma. At the same time, as the number of turns of the DC coil increases, the reflected electromagnetic waves continue to decrease, the efficiency of microwave to plasma energy transfer is improved, and the power absorbed by the plasma is enhanced.

[0126] 1.4 Microwave-plasma joint simulation results

[0127] The multi-physics field simulation of microwave and plasma was carried out in Comsol software to study the influence of magnetic field on plasma distribution. Under the conditions of input power of 200W, reaction gas of argon and working pressure of 1Torr, the simulation results of plasma are as follows: Figure 8 .

[0128] like Fig. 9 As shown, with the increase of time, the electron density increases from 10 16 Up to 7×10 17 , and gradually gather together. At this time, a sheath of electric field is formed in the area near the plasma excitation, and the electric field cannot further penetrate the plasma. The simulation results reflect the limitations of microwave plasma, that is, there is plasma only in the discharge center area, the plasma distribution is uneven, and the electron density gradient changes greatly.

[0129] The plasma simulation after adding the magnetic field is as follows Fig.10 , Fig.11 shown.

[0130] contrast Figure 8and Fig.10 It can be found that the electric field is increased by two orders of magnitude, and higher field strength makes it easier to excite plasma. Fig. 9 and Fig.11 It can be found that the electron density has undergone a significant change. First, the maximum value of the electron density has increased significantly from 10 17 Increased to 10 19 , higher electron density means stronger plasma, which is more conducive to plasma reaction; in addition, the distribution of plasma has also changed significantly, from the strongest center and weak ends to strong ends and weak center. The electron density distribution on the central axis is as follows Fig.10 shown.

[0131] Fig.12 The central electron density distribution under different discharge conditions. Through comparative analysis, it can be found that after adding the magnetic field (blue), the uniformity of the plasma in the entire quartz tube is significantly improved. Without adding the magnetic field (green), the plasma decays rapidly on the left and right sides. Adding a magnetic field helps to improve the uniformity of the plasma.

Claims

1. A plasma torch based on electron cyclotron resonance, comprising a rectangular waveguide (2) tube, and two circular waveguide tubes (7) symmetrically arranged on the rectangular waveguide (2) tube, wherein the length direction of the rectangular waveguide (2) tube is orthogonal to the center line of the circular waveguide tube (7), and the circular waveguide tube (7) is connected to the inside of the rectangular waveguide (2) tube, characterized in that: It also comprises a microwave plasma discharge tube (4), the microwave plasma discharge tube (4) passing through the rectangular waveguide (2) and the quartz tubes (6) of the two circular waveguide tubes (7), a DC coil (8) being wound at equal intervals on the quartz tube (6), and a plasma discharge zone (9) being located inside the quartz tube (6); An adjustable short-circuit surface is slidably arranged inside the rectangular waveguide (2) tube on a side away from the microwave inlet, and a position adjustment structure (5) for adjusting the position of the adjustable short-circuit surface is arranged at the end of the rectangular waveguide (2) tube.

2. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: One end of the rectangular waveguide (2) is a microwave inlet, and the microwave inlet is connected to the magnetron.

3. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: The rectangular waveguide (2) tube has a starting frequency of 1.72 GHz, a stopping frequency of 2.61 GHz, a cross-sectional length of 109.22 mm, and a width of 54.61 mm.

4. The plasma torch based on electron cyclotron resonance according to claim 2, characterized in that: A plurality of adjustment pins for adjusting impedance matching and improving transmission efficiency are arranged on the rectangular waveguide (2) located between the circular waveguide tube (7) and the magnetron.

5. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: The two ends of the DC coil (8) are respectively connected to the positive and negative electrodes of a DC power generator (10) via wires; one end of the quartz tube (6) is an air inlet, and the other end is connected to a vacuum pump (11).

6. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: The position adjustment structure (5) adjusts the distance between the adjustable short-circuit surface and the microwave plasma discharge tube (4), and the electric field is maximum when the distance is (2*n+1)*λg / 4, wherein n is a natural number and λg is the waveguide wavelength in air.

7. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: The quartz tube (6) has a thickness of 2 mm and is the discharge area of ​​the plasma.

8. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: The diameter of the circular waveguide tube (7) is 32 mm.

9. A simplified simulation method for a plasma torch for analyzing electron cyclotron resonance, characterized in that: An electron cyclotron resonance-based plasma torch suitable for use in any one of claims 1 to 8.

10. A simplified simulation method for a plasma torch for analyzing electron cyclotron resonance according to claim 9, characterized in that: The steps include: Step S1, based on the Helmholtz equation of the electric field, a three-dimensional electric field model is established to analyze the electric field distribution, specifically to determine the length of the rectangular waveguide, the diameter and length of the circular waveguide, the number of turns of the DC coil and the spacing between the DC coils; Where E is the electric field strength, μ r is the relative magnetic permeability, k0 is the electromagnetic wave number, ε r is the relative dielectric constant, σ is the conductivity, ω is the angular frequency of electromagnetic waves, and ε0 is the dielectric constant in vacuum; Step S2: Establish a two-dimensional axisymmetric magnetic field model, bring the DC coil parameters into the magnetic field model, and calculate the magnetic induction intensity generated under different input powers: Among them, H is the magnetic field intensity, B is the magnetic induction density, A is the magnetic vector potential, and J is the current density; Step S3, coupling the parameters in the electromagnetic simulation, combining with the Drude model to perform a three-dimensional simulation, and studying the energy efficiency of microwave to plasma before and after adding the DC coil; Step S4, establishing a two-dimensional microwave-plasma coupling joint simulation model, and bringing the medium magnetic field parameters and the medium electric field parameters into the joint simulation model to calculate the influence of the DC coil and the magnetic field on the microwave plasma.

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