A plasma torch based on electron cyclotron resonance and its simplified simulation method

Abstract

The present invention discloses a plasma torch based on electron cyclotron resonance and a simplified simulation method thereof, relating to the field of microwave plasma technology. The torch comprises a rectangular waveguide tube, two circular waveguide tubes symmetrically arranged on the rectangular waveguide tube, the circular waveguide tubes communicating with the interior of the rectangular waveguide tube, and a microwave plasma discharge tube. The microwave plasma discharge tube comprises a quartz tube extending through the rectangular waveguide tube and the two circular waveguide tubes, the quartz tube being wound with DC coils at equal intervals, and the interior of the quartz tube forming a plasma discharge zone. Based on a microwave plasma discharge model and incorporating the concept of electron cyclotron resonance, the present invention enhances the local electric field by introducing equally spaced coils in the electromagnetic field, thereby increasing the excitation efficiency of the plasma. Furthermore, providing DC power to the coils also introduces a constant magnetic field, thereby constraining the electron motion trajectory and improving the uniformity of the plasma.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave plasma technology, and more particularly 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 utilizes low-energy electromagnetic fields or microwaves to excite a plasma state. Common methods include capacitively coupled plasma, inductively coupled plasma, surface plasmon waves, helicon wave plasma, and microwave plasma. These methods have broad application potential in materials processing, surface modification, clean etching, nanomaterial synthesis, and environmental remediation. Low-temperature plasma technology, with its advantages of high efficiency, precise control, and environmental friendliness, is gaining increasing attention and adoption in scientific research and industrial applications.

[0003] Surface plasmon 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 that is trapped in the surface plasma oscillation waves. Surface plasmon waves have attracted widespread attention in fields such as nanophotonics, data storage, microscopy, and optical waveguides. Electromagnetic waves generated outside the plasma can propagate into the plasma or along the plasma surface until they are ultimately absorbed by the plasma. In these processes, the electromagnetic waves play a role in generating and maintaining plasma discharges and heating the electrons within the plasma.

[0004] Among them, microwave plasma (MWP) is an advanced processing technology that uses electromagnetic waves with microwave frequencies (2.45GHz or 915MHz) to excite the plasma state. By introducing microwave energy into a gas or liquid medium, its atoms or molecules are ionized, thereby forming a plasma. 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 walls of the reaction chamber. Changing conditions such as gas type, gas concentration, pressure, and input power can significantly change the plasma morphology, and the plasma load's ability to absorb microwaves can vary greatly, leading to significant reflections and low microwave-to-plasma efficiency. By adding a strong magnetic field to the discharge region, electrons can be caused to cyclotron around the magnetic field lines, increasing their movement path within the discharge region and strengthening the interaction between electrons and electromagnetic waves, which helps electrons absorb energy and improves plasma uniformity. However, in existing electron cyclotron resonance (ECR) plasmas, the magnetic field DC coil is located outside the microwave field, making it impossible to improve microwave-to-plasma efficiency. 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 an electron cyclotron resonance-based plasma torch, comprising a rectangular waveguide tube and two circular waveguide tubes symmetrically arranged on the rectangular waveguide tube, wherein the length direction of the rectangular waveguide tube is orthogonal to the centerline of the circular waveguide tube, and the circular waveguide tubes are connected to the interior of the rectangular waveguide tube. The microwave plasma discharge tube also comprises a quartz tube that passes through the rectangular waveguide tube and the two circular waveguide tubes, and a DC coil is wound around the quartz tube at equal intervals. The interior of the quartz tube contains a plasma discharge zone.

[0009] An adjustable short-circuit road 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 road 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 , microwave is fed into the input port of the rectangular waveguide, and 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 exactly 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 approach, based on a microwave plasma discharge model and incorporating the concept of electron cyclotron resonance, enhances the local electric field by introducing equally spaced DC coils within the electromagnetic field, thereby increasing plasma excitation efficiency. Furthermore, supplying DC power to the DC coils also introduces a constant magnetic field, constraining electron motion and improving plasma uniformity. Furthermore, modulating the current and voltage in the DC coils can improve plasma maintenance efficiency.

[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 distance between two adjacent turns are adjusted.

[0013] like Figure 3 As shown;

[0014] In one embodiment, one end of the rectangular waveguide tube is a microwave inlet, which is connected to the magnetron.

[0015] Specifically, a magnetron is an electric vacuum device used to generate microwave energy. Essentially, it's a diode placed in a constant magnetic field. Its function is to control the mutually perpendicular constant magnetic and electric fields, causing electrons inside the tube to interact with the high-frequency electromagnetic field, converting the energy gained from the constant electric field into microwave energy.

[0016] In one embodiment, the rectangular waveguide tube 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.

[0017] Specifically, the rectangular waveguide tube is a rectangular waveguide tube 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.

[0018] In one embodiment, a plurality of adjustment pins for adjusting impedance matching and improving transmission efficiency are provided on the rectangular waveguide tube located between the circular waveguide tube and the magnetron.

[0019] 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. Related references are as follows:

[0020] 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 the 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 can be reduced, the microwave distribution on the transmission line can be made more even, the impact of the reflected wave can be reduced, and the stable operation of the system can be ensured.

[0021] Fine-tuning the operating frequency: The operating frequency of the microwave system may be affected by environmental factors (such as temperature, humidity) or device aging and may shift. 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. Widening 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 broaden the application range of the system.

[0022] In one embodiment, the two ends of the DC coil are respectively connected to the positive and negative poles 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.

[0023] Specifically, a vacuum pump is used to provide the low-pressure environment required for plasma discharge (discharge can be performed with or without a vacuum pump; with a vacuum pump, discharge is at low pressure; without a vacuum pump, discharge is at atmospheric pressure).

[0024] 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 air. At 2.45 GHz, λg is approximately 171.8 mm.

[0025] In one embodiment, the thickness of the quartz tube is 2 mm, which serves as the discharge region of the plasma and can confine the plasma within the tube.

[0026] In one embodiment, the diameter of the circular waveguide is 32 mm.

[0027] 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 tube at this time.

[0028] 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 includes the following steps:

[0029] 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 determining 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;

[0030]

[0031] 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 vacuum;

[0032] 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:

[0033]

[0034] Where 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 and combining them with the Drude model to perform a three-dimensional simulation to study 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 calculating the influence of the DC coil and the magnetic field on the microwave plasma by bringing the medium magnetic field parameters and the medium electric field parameters into the joint simulation model.

[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 conducive to the excitation of plasma.

[0038] In addition, a plasma discharge device structure that places a DC coil in a microwave field, combined with the Comsol simulation program, achieves efficient excitation and maintenance of the plasma by modulating the electromagnetic field and 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.

[0039] Why simplify simulations? Self-consistent three-dimensional electron cyclotron resonance plasma models are computationally intensive, have poor convergence, and are computationally expensive. They also preclude wide-scale parameter sweeps and are difficult to use for guiding industrial production applications. This complex modeling process can be broken down into several simpler models, ultimately using single-term coupling to incorporate different variables into the same model, significantly reducing computational costs.

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

[0041] This invention is based on a microwave plasma discharge model and incorporates the concept of electron cyclotron resonance. By introducing equally spaced DC coils within the electromagnetic field, the local electric field is enhanced, thereby increasing plasma excitation efficiency. Furthermore, supplying DC power to the DC coils also introduces a constant magnetic field, constraining electron motion and improving plasma uniformity. Furthermore, by modulating the current and voltage in the DC coils, plasma maintenance efficiency can 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 is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0043] FIG1( a ) is a schematic diagram of the structure of a plasma torch based on electron cyclotron resonance;

[0044] Figure 1(b) is a detailed view of the local structure 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 diagram 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] Figure 9 It is the electron density distribution diagram during plasma excitation;

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

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

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

[0056] Figure 13 It 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 tube, 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 region, 10-DC power generator, 11-vacuum pump. DETAILED DESCRIPTION

[0058] To make the technical problems, technical solutions, and technical effects of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein 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 as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall 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. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. In addition, the terms "first," "second," etc. are used only to distinguish the descriptions and are not to 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 in use. 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. Therefore, they cannot be understood as limitations on the present invention.

[0062] Example 1

[0063] This embodiment provides a plasma torch based on electron cyclotron resonance, comprising a rectangular waveguide tube 2, two circular waveguide tubes 7 symmetrically arranged on the rectangular waveguide tube 2, the length direction of the rectangular waveguide tube 2 being orthogonal to the centerline of the circular waveguide tube 7, and the circular waveguide tube 7 and the interior of the rectangular waveguide tube 2 being connected, and a microwave plasma discharge tube 4, which penetrates a quartz tube 6 of the rectangular waveguide tube 2 and the two circular waveguide tubes 7, a DC coil 8 being wound around the quartz tube 6 at equal intervals, and a plasma discharge zone 9 being formed within the quartz tube 6;

[0064] An adjustable short-circuit path is slidably provided inside the rectangular waveguide tube 2 on a side away from the microwave inlet, and a position adjustment structure 5 for adjusting the position of the adjustable short-circuit path is provided at the end of the rectangular waveguide tube 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 , microwave is fed into the input port of rectangular waveguide 2, and it can be found that the TE10 mode of rectangular waveguide 2 presents the characteristics of standing wave distribution in the resonant cavity. At this time, the placement position of quartz tube 6 is exactly at the antinode position where the electric field is the strongest. The field strength value generated at this time is small, only 10 3 Order of magnitude.

[0066] This solution, based on a microwave plasma discharge model and incorporating the concept of electron cyclotron resonance, enhances the local electric field by introducing equally spaced DC coils (8) within the electromagnetic field, thereby increasing plasma excitation efficiency. Furthermore, supplying DC power to the DC coils (8) also introduces a constant magnetic field, constraining electron motion and improving plasma uniformity. Furthermore, by modulating the current and voltage in the DC coils (8), plasma maintenance efficiency can 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 distance between two adjacent turns are adjusted. Figure 3 shown.

[0068] Example 2

[0069] This embodiment is a further optimization based on the embodiment 1, specifically:

[0070] One end of the rectangular waveguide tube 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. Essentially, it's a diode placed in a constant magnetic field. Its function is to control the mutually perpendicular constant magnetic and electric fields, causing electrons inside the tube to interact with the high-frequency electromagnetic field, converting the energy gained from the constant electric field into microwave energy.

[0072] The rectangular waveguide tube 2 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.

[0073] Specifically, the rectangular waveguide tube 2 is a rectangular waveguide tube 2 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.

[0074] Example 3

[0075] This embodiment is further optimized based on embodiment 1 or embodiment 2, specifically:

[0076] The rectangular waveguide tube 2 located between the circular waveguide tube 7 and the magnetron is provided with a plurality of adjustment pins for adjusting impedance matching and improving transmission efficiency.

[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. Related references are 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 the 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 can be reduced, the microwave distribution on the transmission line can be made more even, the impact of the reflected wave can be reduced, and the stable operation of the system can be ensured.

[0079] Fine-tuning the operating frequency: The operating frequency of the microwave system may be affected by environmental factors (such as temperature, humidity) or device aging and may shift. 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. Widening 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 broaden the application range of the system.

[0080] Example 4

[0081] This embodiment is a further optimization based on any one of Embodiments 1 to 3, specifically:

[0082] The two ends of the DC coil 8 are respectively connected to the positive and negative poles 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 a low-pressure environment required for plasma discharge (discharge can be performed with or without the vacuum pump 11; with the vacuum pump 11, the discharge is low-pressure; without the vacuum pump 11, the discharge is atmospheric pressure).

[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, where n is a natural number and λg is the waveguide wavelength in air. At 2.45 GHz, λg is approximately 171.8 mm.

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

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

[0087] Specifically, in order to prevent electromagnetic waves from leaking from the circular waveguide tube 7, the size of the circular waveguide tube 7 needs to be limited. The diameter of the circular waveguide tube 7 in this device is 32 mm. Figure 2 It can be seen from the simulation that the microwave decays rapidly in the circular waveguide tube 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 determining 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 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] Where H is the magnetic field intensity, B is the magnetic induction density, A is the magnetic vector potential, and J is the current density;

[0096] Step S3, coupling the parameters in the electromagnetic simulation and combining them with the Drude model to perform a three-dimensional simulation to study the energy efficiency of microwaves to plasma before and after adding the DC coil;

[0097] Step S4: establishing a two-dimensional microwave-plasma coupling joint simulation model, and calculating the influence of the DC coil and the magnetic field on the microwave plasma by bringing the magnetic field parameters in step S2 and the electric field parameters in step S1 into the joint simulation model.

[0098] 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 conducive to the excitation of plasma.

[0099] In addition, a plasma discharge device structure that places a DC coil in a microwave field, combined with the Comsol simulation program, achieves efficient excitation and maintenance of the plasma by modulating the electromagnetic field and 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.

[0100] Why simplify simulations? Self-consistent three-dimensional electron cyclotron resonance plasma models are computationally intensive, have poor convergence, and are computationally expensive. They also preclude wide-scale parameter sweeps and are difficult to use for guiding industrial production applications. This complex modeling process can be broken down into several simpler models, ultimately using single-term coupling to incorporate different variables into the same model, significantly reducing computational costs.

[0101] A detailed description of the simplified simulation method for the plasma torch is as follows:

[0102] 1.1. DC coil structure optimization

[0103] In order to improve the electric field strength in the discharge chamber (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 the DC coils are adjusted. Figure 3 As shown,

[0104] 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 .

[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 (When the DC coil on the quartz tube has 0 turns, the maximum electric field strength inside the quartz tube is 1×10 3 When the DC coil on the quartz tube has 10 turns, the maximum electric field strength inside the quartz tube is 2×10 4 When the DC coil on the quartz tube has 15 turns, the maximum electric field strength inside the quartz tube is 4.9×10 3 When the DC coil on the quartz tube has 20 turns, the maximum electric field strength inside the quartz tube is 2.6×10 3 When the DC coil on the quartz tube has 25 turns, the maximum electric field strength inside the quartz tube is 2.7×10 3 ).

[0106] pass Figure 4It's not difficult to find that when the DC coil has fewer turns, electromagnetic waves can form a strong electric field between the gaps in the DC coil, which is more conducive to plasma excitation. As the number of turns increases, the energy of this enhanced electric field weakens, and the field strength in the quartz tube is almost the same as when there is no 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:

[0107] n = 100 / m;

[0108] □ = n × 0.001;

[0109] Where n is the DC coil proportional coefficient.

[0110] 1.2. Magnetic field DC coil simulation results

[0111] In the above simulation, the influence of the constant magnetic field generated by the DC current in the DC coil was 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 was moderately simplified and a two-dimensional axisymmetric model including the electromagnetic field-constant magnetic field-plasma was constructed. The schematic diagram of the model is as follows: Figure 5 .

[0112] When the DC coil power is 100W, the magnetic field distribution of the two-dimensional axisymmetric system is as follows: Figure 6 At this point, there is a strong magnetic field at the DC coil, as expected.

[0113] Magnetic field control microwave plasma process Figure 7 .

[0114] 1.3 Plasma simulation results

[0115] The principle of using the Drude equivalent model for plasma simulation is as follows:

[0116]

[0117]

[0118] 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 electron mass, q is the charge density, ε0 is the dielectric constant in vacuum, ε rp 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 reflect the absorption of the electromagnetic wave by the plasma. 11The parameters are defined as follows:

[0119]

[0120] Where Pref is the reflected power, Pin is the incident power, S 11 The smaller the value, the stronger the plasma's ability 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.

[0121] Table 1 Number of turns of DC coil, maximum electric field and S 11 Relationship table between

[0122] DC coil turns Field strength maximum S11 0 <![CDATA[1.84×10 3 ]]> -6.74 10 <![CDATA[2×10 4 ]]> -6.90 15 <![CDATA[4.9×10 3 ]]> -7.18 20 <![CDATA[2.6×10 3 ]]> -7.46 25 <![CDATA[4.7×10 3 ]]> -7.74 30 <![CDATA[5.8×10 3 ]]> -8.12

[0123] 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 the 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.

[0124] 1.4 Microwave-Plasma Joint Simulation Results

[0125] Multi-physics simulation of microwave and plasma was performed in Comsol software to study the effect 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 shown below: Figure 8 .

[0126] like Figure 9 As shown, with the increase of time, the electron density increases from 10 16 Increase to a maximum of 7×10 17 , and gradually converge, forming an electric field sheath near the plasma excitation area, preventing the electric field from penetrating the plasma. The simulation results reflect the limitations of microwave plasma, namely that plasma only appears in the discharge center, the plasma distribution is uneven, and the electron density gradient varies greatly.

[0127] The plasma simulation after adding the magnetic field is as follows Figure 10 、 Figure 11 shown.

[0128] contrast Figure 8 and Figure 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. Figure 9 and Figure 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 1019 , 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 initial strongest center and weaker ends to strong ends and weaker center. The electron density distribution on the central axis is as follows Figure 10 shown.

[0129] Figure 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 improve the uniformity of the plasma.

Claims

1. A plasma torch based on electron cyclotron resonance, comprising a rectangular waveguide tube (2), and two circular waveguide tubes (7) symmetrically arranged on the rectangular waveguide tube (2), wherein the length direction of the rectangular waveguide tube (2) is orthogonal to the center line of the circular waveguide tube (7), and the circular waveguide tube (7) is connected to the interior of the rectangular waveguide tube (2), characterized in that: It also includes a microwave plasma discharge tube (4), the microwave plasma discharge tube (4) passing through the rectangular waveguide tube (2) and the quartz tube (6) of the two circular waveguide tubes (7), a DC coil (8) being wound on the quartz tube (6) at equal intervals, and a plasma discharge zone (9) being located inside the quartz tube (6); An adjustable short-circuit surface is slidably provided inside the rectangular waveguide tube (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 provided at the end of the rectangular waveguide tube (2); The DC coil (8) is partially located in the rectangular waveguide tube (2), and the DC coil (8) is partially located in the circular waveguide tube (7); the current and voltage in the DC coil (8) are modulatable; The 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).

2. The plasma torch based on electron cyclotron resonance according to claim 1, characterized in that: One end of the rectangular waveguide tube (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 tube (2) 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.

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 provided on the rectangular waveguide tube (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 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 and λg is the waveguide wavelength in air.

6. 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.

7. 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.

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