Microwave plasma enhancement method based on metal pillars

Abstract

The present invention relates to the field of plasma enhancement technology, specifically a microwave plasma enhancement method based on a metal column, and the most suitable size is explored by analyzing four influencing parameters, namely, the height h of the metal column, the distance d between the axis of the metal column and the glass flow guide tube, the diameter R of the metal column, and the angle angle. The electric field intensity concentrated in the glass flow guide tube area of ​​the optimized structure is about doubled compared with the original structure, which effectively strengthens the concentration of the electric field. Further focusing optimization of the electric field intensity is carried out to increase the electric field intensity in the quartz discharge tube area, thereby better ionizing and breaking down the working gas, and making the generated microwave plasma torch more stable.

Description

Technical Field

[0001] The invention relates to the field of plasma enhancement technology, in particular to a microwave plasma enhancement method based on metal columns. Background Art

[0002] Microwave plasma has the advantages of no electrodes, high electron density, high electron temperature and high energy efficiency. It is widely used in daily life, energy, chemical industry, materials and other fields.

[0003] The conventional microwave plasma torch mainly includes a glass flow tube, into which the gas to be ionized is introduced, and the corresponding microwave is applied to ionize it. However, in actual use, it is found that although the microwave plasma torch can generate microwave plasma well when the working gas is argon, when the working gas is compressed air, the microwave plasma generated is small and unstable, and the temperature of the glass flow tube wall is too high. It can be seen that the microwave plasma torch currently used is applicable to a small number of gas types, and there is still a lot of room for improvement. Summary of the invention

[0004] In order to avoid and overcome the technical problems existing in the prior art, the present invention provides a microwave plasma enhancement method based on metal pillars. The present invention can effectively improve the stability of the generated microwave plasma.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The microwave plasma enhancement method based on metal pillars comprises the following steps:

[0007] S1. Two or more metal columns are arranged in an array on the outer circumference of the glass flow guide tube and are used to guide microwaves to flow along the axial direction of the glass flow guide tube to form a plasma torch model for simulation;

[0008] S2. During the simulation process, the gas and microwaves to be ionized are loaded into the plasma torch model, and the electric field intensity distribution state in the glass flow tube is obtained;

[0009] S3, changing the position distribution of each metal column outside the glass guide tube in the plasma torch model to obtain the electric field intensity distribution state in the glass guide tube under various position distributions;

[0010] S4. Divide the electric field intensity distribution in the glass flow guide tube into an upper distribution state, a middle distribution state and a lower distribution state in sequence, wherein the middle distribution state is the optimal distribution state; compare the various electric field intensity distribution states to obtain an electric field intensity distribution state that satisfies the optimal distribution state.

[0011] As a further solution of the present invention: the process of establishing a plasma torch model in the simulation software COMSOL is as follows:

[0012] S11. In the simulation software COMSOL, a hollow cylindrical glass guide tube is selected, and the glass guide tube is arranged vertically on a horizontal base surface, and the height of the glass guide tube is H;

[0013] S12. Two or more metal columns are evenly arranged in sequence around the axis of the glass guide tube on the outside of the glass guide tube to form a circular array distribution; the metal columns are vertically arranged on the horizontal base plane, the height of the metal columns is h, the circular angle between two adjacent metal columns is angle, and the diameter of the metal columns is R; along the radial direction of the glass guide tube, the distance from the axis of the metal column to the nearest outer side surface of the glass guide tube is d.

[0014] As a further solution of the present invention: in the process of loading the gas and microwaves to be ionized into the plasma torch model, the variable control method is adopted, that is, any three physical quantities among h, angle, R and d are controlled to remain unchanged, and only the remaining physical quantity is changed; and in the process of changing the remaining physical quantity, the value of the physical quantity is changed by an isogradient transformation method.

[0015] As a further solution of the present invention: the requirements for dividing the electric field intensity distribution state in the glass guide tube are set as follows: first, the glass guide tube is equally divided into six sections along the axial direction of the glass guide tube, and when 80% of the plasma in the glass guide tube is distributed in the lower three sections of the glass guide tube, it is defined as the lower layer distribution state;

[0016] When 80% of the plasma in the glass flow tube is evenly distributed in the middle four sections of the glass flow tube, it is defined as the middle layer distribution state;

[0017] When 80% of the plasma in the glass flow tube is distributed in the upper three sections of the glass flow tube, it is defined as the upper distribution state;

[0018] The middle distribution state is the optimal distribution state.

[0019] As a further solution of the present invention: the glass flow guide tube and the metal columns arranged outside the glass flow guide tube are arranged in a microwave cavity in which microwaves are distributed; the addition of the metal columns converts the electric field mode in the microwave cavity from the TM mode to the TEM mode; the distribution of the microwave electric field in the microwave cavity can be calculated by the Helmholtz equation, which is expressed as follows:

[0020]

[0021] in, represents the Hamiltonian operator; μr Represents the relative magnetic permeability of the medium, air is 1, and plasma is also 1; represents the electric field vector; k 0 represents the microwave beam; ε r represents the relative dielectric constant of the medium, which is 1 for air and 1 for plasma; ω represents the angular frequency of microwaves; ε 0 represents the dielectric constant of vacuum; jσ represents the electrical conductivity.

[0022] As a further solution of the present invention: the electron density of the plasma in the glass flow tube is calculated by the following formula:

[0023]

[0024] Among them, n e represents the plasma electron density; represents the plasma electron flux; Represents the electron vector velocity; R e Represents the electron source; μ e represents electron mobility; represents the electron diffusion coefficient.

[0025] As a further solution of the present invention: the electric field coupling of plasma refers to the mechanism of transferring microwave energy to plasma through electric field interaction, using plasma conductivity as a bridge to achieve microwave plasma electric field coupling, the formula is as follows:

[0026] σ p =n e e 2 / m e (v m -jω)

[0027] Among them, σ p represents electric field coupling; e represents the amount of electron charge; m e represents the mass of the electron; v m represents the electron collision frequency; jω represents the microwave angular frequency.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] After the metal column is added, the present invention has a higher electric field focusing effect in the center of the discharge area, so that the microwave plasma torch can better ionize and penetrate different types of working gases, thereby improving the uniformity of plasma distribution in the glass guide tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the main operating steps of the present invention.

[0031] Figure 2It is a structural schematic diagram of the plasma torch model in the present invention.

[0032] Figure 3 It is a structural schematic diagram of the end face of the plasma torch model in the present invention.

[0033] Figure 4 Schematic diagram of the electric field intensity distribution when the height h is between 40 mm and 80 mm in the present invention.

[0034] Figure 5 Schematic diagram of the electric field intensity distribution when the height h is between 90 mm and 120 mm in the present invention.

[0035] Figure 6 It is a schematic diagram of the relationship between the distance d and the electric field intensity focusing in the present invention.

[0036] Figure 7 Graph showing the relationship between the electric field intensity on the center section line and the distance between the metal column and the glass flow guide tube in the present invention.

[0037] Figure 8 Graph showing the relationship between the angle angle and the electric field intensity focusing in the present invention.

[0038] Fig. 9 This is a diagram showing the relationship between the diameter R and the electric field intensity focusing in the present invention.

[0039] Fig.10 Graph showing the relationship between the electric field intensity on the center section line and the radius R of the metal column in the present invention.

[0040] In the figure: 10, glass guide tube; 20, metal column. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0042] See also Figure 1 In the embodiment of the present invention, the microwave plasma enhancement method based on the metal column 20 mainly includes the following contents.

[0043] 1. Establish a plasma torch model.

[0044] like Figure 2 and Figure 3 As shown, in the simulation software COMSOL, a hollow cylindrical glass flow guide tube 10 is selected, and the glass flow guide tube 10 is vertically arranged on a horizontal base surface, and the height of the glass flow guide tube 10 is H (mm).

[0045] Two or more metal pillars 20 are evenly arranged in sequence around the axis of the glass guide tube 10 on the outside of the glass guide tube 10 to form a circular array distribution; the metal pillars 20 are arranged vertically on the horizontal base plane, the height of the metal pillars 20 is h (mm), the circular angle between two adjacent metal pillars 20 is angle, and the diameter of the metal pillars 20 is R (mm); along the radial direction of the glass guide tube 10, the distance from the axis of the metal pillar 20 to the outer side surface of the glass guide tube 10 closest to it is d (mm). The metal pillars 20 are made of metal copper material.

[0046] like Figure 3 As shown, during the simulation process, the height h (mm) of the metal pillar 20, the distance d (mm) between the axis of the metal pillar 20 and the glass flow guide tube 10, the diameter R (mm) of the metal pillar 20, and the gap between the metal pillars 20 are mainly adjusted parameterically. Since the metal pillars 20 are set as an array structure during geometric modeling, the setting is performed by adjusting the angle angle.

[0047] 2. Change the height h of the metal pillar 20.

[0048] A metal column 20 is placed in a ring around the glass guide tube 10, the input working power is 1 kW, the frequency is set at 2.45 GHz, the outer diameter of the glass guide tube 10 is 15 mm, and the height H of the glass guide tube 10 is 120 mm.

[0049] The distance d between the axis of the metal column 20 and the glass flow guide tube 10 is set to 2.5mm, the diameter R of the metal column 20 is 3mm, and the array angle angle is 28 degrees. The height h of the metal column 20 has a step length of 10mm, and the value range of the height h is 40mm to 120mm. It can be seen from the simulation results that when the height h is 40mm, there is a focusing effect, but the effect is not obvious. As the height h is increased, when the height h ranges from 60mm to 70mm, there is an obvious electric field focusing effect in the glass flow guide tube 10 area, but the focusing effect at this time is mainly concentrated in the lower half of the glass flow guide tube 10, that is, the lower layer distribution state. As the height h further increases, the electric field in the glass flow guide tube 10 still has a focusing effect, but it decreases compared to the range of 60mm to 70mm. Until the height h reaches 100mm, it can be seen that the electric field focusing effect in the entire glass flow guide tube 10 is relatively uniform and is in a middle layer distribution state. When the height h reaches 120 mm, the electric field in the glass flow guide tube 10 is mainly focused in the coupled upper semi-cylindrical cavity, which belongs to the upper layer distribution state.

[0050] In order to more intuitively observe the electric field focusing effect of different parameters on the glass guide tube 10 area, a three-dimensional section line is set on the axis of the glass guide tube 10, and the length is consistent with the glass guide tube 10, which is 120 mm. The electric field strength curve on this section line can be drawn through the section line, such as Figure 4 and Figure 5 As shown. Figure 4 It can be seen intuitively that when h is 40 mm to 70 mm, the electric field is focused on the lower half of the glass flow guide tube 10; when h is 80 mm, 90 mm and 120 mm, the electric field strength is mainly concentrated in the upper half of the glass flow guide tube 10; when h is 100 mm and 110 mm, the electric field strength is more evenly concentrated in the glass flow guide tube 10.

[0051] 3. Change the distance d.

[0052] Next, we analyze the relationship between the distance d between the axis of the metal column 20 and the glass guide tube 10 and the electric field intensity focusing of the plasma torch model. The diameter R of the simulated metal column 20 is 3 mm, the array angle angle is 28 degrees, and the height h of the metal column 20 is 120 mm. For easy observation, the cross-sectional electric field of the center area of ​​the glass guide tube 10 is viewed in COMSOL. The relationship between the distance d and the electric field intensity focusing of the plasma torch model is shown in the figure. Figure 6 As shown in FIG. 1 , the interval length of d from (a) to (f) is 2 mm, from d = 0 mm to d = 10 mm. The relationship between the electric field strength on the center section line and the distance between the metal column 20 and the glass guide tube 10 is as follows: Figure 7 As shown. Figure 6 and Figure 7 It can be seen that the closer the metal pillar 20 is to the glass flow guide tube 10, the better the focusing effect. The best focusing effect is at a distance d between 2 mm and 4 mm, and the maximum electric field strength can reach 1.2x105 V / m. When the distance d reaches 6 mm as shown in (d), the electric field focusing effect decreases significantly. As the distance d continues to increase, when d=10 mm, the maximum electric field focusing effect in the glass flow guide tube 10 is only about 35000 V / m.

[0053] 4. Change the angle.

[0054] Next, we analyze the relationship between the gap between the metal pillars 20 and the electric field intensity focus. The diameter R of the metal pillar 20 simulated is 3 mm, the height h of the metal pillar 20 is 120 mm, and the distance d between the radius of the metal pillar 20 and the glass guide tube 10 is 2.5 mm. For easy observation, only the cross-sectional electric field of the central area of ​​the glass guide tube 10 is selected in COMSOL, and the relationship between the array angle angle and the electric field intensity focus is as follows: Figure 8 As shown, from Figure 8The angle interval from (a) to (c) is 10 degrees, from angle = 20 degrees to angle = 40 degrees. Figure 8 From (a), (b), and (c), we can see that when the array angle is between 20 and 30 degrees, the electric field energy concentration effect is the best. So we continue to simulate angle = 24 degrees, angle = 26 degrees, and angle = 28 degrees. Figure 8 As shown in (d), (e), and (f), it can be seen that the electric field focusing effect is best when the array angle is between 20 and 30 degrees, and the maximum can reach 1.3x10 5 V / m, wherein when angle=24 degrees, the electric field strength has the best focusing effect in the glass flow guide tube 10 .

[0055] 5. Change the diameter R of the metal column 20.

[0056] Finally, the relationship between the diameter R of the metal column 20 and the electric field intensity focusing of the structure is analyzed. The height h of the metal column 20 simulated is 120 mm, the array angle angle = 28 degrees, and the distance d between the axis of the metal column 20 and the glass guide tube 10 is 2.5 mm. For easy observation, select the section electric field of the central area of ​​the glass guide tube 10 in COMSOL, and adjust the relationship between the diameter R of the metal column 20 and the electric field intensity focusing of the structure as shown in the figure. Fig. 9 As shown, it can be seen that Fig. 9 In (a), when R = 2 mm, the focusing effect of the electric field is relatively poor. When the diameter is R = 3 mm to R = 3.5 mm, the focusing effect of the electric field in the glass flow guide tube 10 is the best. The relationship between the electric field intensity on the central section and the radius of the metal column 20 is shown in FIG. Fig.10 As shown in the figure, it can be seen that when the diameter R = 1.75 mm, the metal column 20 has the best electric field focusing effect on the glass flow guide tube 10 area, and the maximum electric field can reach 1.3x10 5 V / m.

[0057] The most suitable size is explored by analyzing the four influencing parameters, namely, the height h of the metal column 20, the distance d between the axis of the metal column 20 and the glass flow tube 10, the diameter R of the metal column 20, and the angle angle. The electric field intensity concentrated in the glass flow tube 10 area of ​​the optimized structure is about doubled compared with the original structure, which effectively strengthens the concentration of the electric field. Further focusing optimization of the electric field intensity is carried out to increase the electric field intensity in the quartz discharge tube area, so as to better ionize and break down the working gas, making the generated microwave plasma torch more stable.

[0058] Introducing a cylindrical metal column 20 into a microwave cavity will cause an electric field mode conversion in the region, usually from a TM mode to a TEM mode electric field. The TEM mode electric field has the distribution characteristics of the electric field strength on the surface of the inner conductor, so the electric field in a specific region can be enhanced by introducing multiple metal columns 20.

[0059] Microwave electric field enhancement: The microwave electric field passes through the metal cylinder, which can form a larger electric field area with more uniform field strength in the plasma excitation area. Since the electron density of the plasma is directly related to the electric field distribution, the plasma will be enhanced under this field strength distribution.

[0060] Water cooling system: Due to the high ionization degree and strong chemical activity of microwave plasma, the enhanced plasma is usually higher in temperature and larger in volume. It will etch and melt the quartz tube after long-term operation, so a cooling system is needed to cool the quartz tube. Based on the existing structure, the water cooling system of the device can be directly implemented in the metal column 20. The original solid metal column 20 can be replaced with a heat-conducting metal copper tube, which not only realizes the function of enhancing the electric field, but also completes the water cooling effect.

[0061] Plasma enhancement: This structure increases the electric field strength in the plasma excitation area, so under the same microwave input power, the microwave plasma system using this structure can generate more plasma. At the same time, compared with the traditional system, the plasma is easier to be excited after using this structure, and the excited plasma is more stable.

[0062] The electron density of microwave plasma directly affects the conductivity, dielectric constant, plasma frequency, plasma wavelength and other characteristics of plasma. It is closely related to the processes of plasma energy transmission, plasma reaction and interaction between plasma and external field, and the electron density of microwave plasma is directly determined by the electric field.

[0063] Electric field coupling of microwave plasma refers to the mechanism of transferring microwave energy to plasma through electric field interaction. Plasma conductivity is usually used as a bridge to achieve microwave plasma electric field coupling, and plasma conductivity is directly related to plasma electron density and is positively correlated.

[0064] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. Microwave plasma enhancement method based on metal pillars, It is characterized in that The following steps are involved: S1. Two or more metal pillars (20) are arranged in an array on the outer circumference of the glass flow guide tube (10) and are used to guide microwaves to flow along the axial direction of the glass flow guide tube (10) to form a plasma torch model for simulation; S2. During the simulation process, the gas and microwaves to be ionized are loaded into the plasma torch model, and the electric field intensity distribution state in the glass flow guide tube (10) is obtained; S3, changing the position distribution of each metal column (20) outside the glass flow guide tube (10) in the plasma torch model to obtain the electric field intensity distribution state in the glass flow guide tube (10) under each position distribution; S4, dividing the electric field intensity distribution in the glass flow guide tube (10) into an upper distribution state, a middle distribution state and a lower distribution state in sequence, the middle distribution state being the optimal distribution state; comparing the various electric field intensity distribution states to obtain an electric field intensity distribution state that satisfies the optimal distribution state; The process of establishing a plasma torch model in the simulation software COMSOL is as follows: S11. In the simulation software COMSOL, a hollow cylindrical glass flow guide tube (10) is selected, and the glass flow guide tube (10) is arranged vertically on a horizontal base surface, and the height of the glass flow guide tube (10) is H; S12. Two or more metal columns (20) are evenly arranged in sequence on the outside of the glass flow guide tube (10) around the axis of the glass flow guide tube (10) to form a circular array distribution; the metal columns (20) are arranged vertically on a horizontal base plane, the height of the metal columns (20) is h, the circular angle between two adjacent metal columns (20) is angle, and the diameter of the metal columns (20) is R; along the radial direction of the glass flow guide tube (10), the distance from the axis of the metal column (20) to the outer side surface of the glass flow guide tube (10) closest to it is d.

2. The microwave plasma enhancement method based on metal pillars according to claim 1, It is characterized in that In the process of loading the gas and microwaves to be ionized into the plasma torch model, the variable control method is adopted, that is, any three physical quantities among h, angle, R and d are kept unchanged, and only the remaining physical quantity is changed; and in the process of changing the remaining physical quantity, the value of the physical quantity is changed by an isogradient transformation method.

3. The microwave plasma enhancement method based on metal pillars according to claim 2, It is characterized in that The requirements for dividing the electric field intensity distribution state in the glass flow guide tube (10) are set as follows: the glass flow guide tube (10) is equally divided into six sections along the axial direction of the glass flow guide tube (10); when 80% of the plasma in the glass flow guide tube (10) is distributed in the lower three sections of the glass flow guide tube (10), it is defined as a lower layer distribution state; When 80% of the plasma in the glass flow guide tube (10) is evenly distributed in the middle four sections of the glass flow guide tube (10), it is defined as a middle layer distribution state; When 80% of the plasma in the glass flow guide tube (10) is distributed in the upper three sections of the glass flow guide tube (10), it is defined as an upper layer distribution state; The middle distribution state is the optimal distribution state.

4. The microwave plasma enhancement method based on metal pillars according to any one of claims 1 to 3, It is characterized in that The glass flow guide tube (10) and the metal columns (20) arranged outside the glass flow guide tube (10) are arranged in a microwave cavity in which microwaves are distributed; the addition of the metal columns (20) causes the electric field mode in the microwave cavity to be converted from the TM mode to the TEM mode; the distribution of the microwave electric field in the microwave cavity can be calculated by the Helmholtz equation, which is expressed as follows: in, represents the Hamiltonian operator; μ r Represents the relative magnetic permeability of the medium, air is 1, and plasma is also 1; represents the electric field vector; k 0 represents the microwave beam; ε r represents the relative dielectric constant of the medium, which is 1 for air and 1 for plasma; ω represents the angular frequency of microwaves; ε 0 represents the dielectric constant of vacuum; jσ represents the electrical conductivity.

5. The microwave plasma enhancement method based on metal pillars according to claim 4, It is characterized in that The electron density of the plasma in the glass flow tube (10) is calculated by the following formula: Among them, n e represents the plasma electron density; represents the plasma electron flux; Represents the electron vector velocity; R e Represents the electron source; μ e represents electron mobility; represents the electron diffusion coefficient.

6. The microwave plasma enhancement method based on metal pillars according to claim 5, It is characterized in that The electric field coupling of plasma refers to the mechanism of transferring microwave energy to plasma through electric field interaction, using plasma conductivity as a bridge to achieve microwave plasma electric field coupling. The formula is as follows: σ p =n e teacher 2 / m e (v m -jω) Among them, σ p represents electric field coupling; e represents the electron charge; m e represents the electron mass; v m represents the electron collision frequency; jω represents the microwave angular frequency.

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