Uniform plasma generator based on multi-electrode structure

Abstract

The invention belongs to the technical field of discharge plasma application, and discloses a uniform plasma generator based on a multi-electrode structure, which comprises a positive direct-current high-voltage power supply system, a negative direct-current high-voltage power supply system, an annular air inlet channel, an ellipsoidal electrode, an annular grounding electrode tightly attached to the inner wall, a circular-truncated-cone-shaped first discharge cavity, an ellipsoidal second discharge cavity and a horn-shaped opening, and an annular air outlet group. Layered anions are generated through negative polarity self-periodic discharge in the first discharge cavity and are pushed by airflow to a positive discharge area of the second discharge cavity to generate plasma for neutralization, and potential discharge self-constriction and discharge mode conversion are reduced through real-time ionization working medium replacement, so that the uniformity and stability of the generated plasma are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of discharge plasma, and particularly relates to a uniform plasma generator based on a multi-electrode structure. Background Art

[0002] Uniform discharge refers to the stable, continuous, and evenly distributed release process of charges or currents in a specific medium or space, which is the core basis for the practical application of plasma technology in the field of industrial manufacturing. Its importance lies in that the uniformity directly determines the efficiency, stability, and controllability of the discharge process. For example, in scenarios such as semiconductor etching, material surface modification, and new energy battery manufacturing, uniform discharge can ensure consistent processing accuracy, stable material properties, and avoid equipment damage or product defects caused by local overheating or energy concentration. The application scope covers industries (such as plasma cleaning, thin film deposition), energy (such as fuel cells, lithium battery formation), medical (such as plasma disinfection, tumor treatment), and environmental protection (such as waste gas treatment) and other fields. However, in practice, the phenomenon of non-uniform discharge is widespread. The main reasons include the distortion of the electric field distribution (local electric field enhancement caused by electrode shape or voltage fluctuation), environmental interference (temperature and pressure changes affecting the ionization balance), and the inherent characteristics of the discharge mode (such as the self-shrinking effect of arc discharge easily forming local high-temperature channels). These factors together lead to the concentration of energy in space or time, thereby destroying the uniformity and restricting the reliability and large-scale development of technology applications. Therefore, designing a stable long-term uniform discharge cavity is of great significance for the practical application of plasma technology.

[0003] A common way to maintain discharge uniformity is to reduce the air pressure, use rare gases with low ionization energy as discharge working media, and cover the metal electrodes with insulating media. For example, a magnetic levitation electrode dielectric barrier dispersion discharge plasma generating device introduced in CN201711107912.9, but its gas working medium and air pressure environment limit its application scope. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a uniform plasma generator based on a multi-electrode structure, which solves the conversion of discharge from uniform to filamentous caused by the self-shrinking of the discharge plasma channel, and avoids the problem of reduced processing effect caused by local overheating or energy concentration of the plasma in practical applications.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A uniform plasma generator based on a multi-electrode structure includes a negative DC high-voltage power supply system 1, a positive DC high-voltage power supply system 9, a horn-shaped opening 6, a first discharge cavity 5, and a second discharge cavity 10, wherein the first discharge cavity 5 is located at the bottom of the second discharge cavity 10;

[0007] An annular intake passage 2 for the gas working medium for negative ionization is opened on the bottom surface of the first discharge chamber 5; a first ellipsoidal electrode 3 is arranged at the bottom of the first discharge chamber 5, and the first ellipsoidal electrode 3 is connected to the negative DC high-voltage power supply system 1; the inner wall of the first discharge chamber 5 is closely attached to the first annular grounding electrode 4;

[0008] An annular air outlet hole group 8 for guiding the working medium replacement is opened at the top of the second discharge chamber 10; a second ellipsoidal electrode 11 is arranged at the top of the second discharge chamber 10, and the second ellipsoidal electrode 11 is connected to the positive DC high-voltage power supply system 9; the inner wall of the second discharge chamber 10 is closely attached to the second annular grounding electrode 7;

[0009] The second discharge chamber 10 is isolated from the first discharge chamber 5 through a flared opening 6; the negative DC high-voltage power supply system 1 and the positive DC high-voltage power supply system 9 are respectively arranged outside the first discharge chamber 5 and the second discharge chamber 10; the voltage amplitude of the positive DC high-voltage power supply system 9 is lower than the voltage amplitude of the negative DC high-voltage power supply system 1.

[0010] The area of the first annular grounding electrode 4 is smaller than that of the second annular grounding electrode 7.

[0011] The first discharge chamber 5 is frustum-shaped, the radius of the top surface of the frustum is 110 mm, and the radius of the bottom surface is 60 mm; the second discharge chamber 10 is ellipsoidal, and the length of the major semi-axis of the ellipsoid is 200 mm.

[0012] The first ellipsoidal electrode 3 and the second ellipsoidal electrode 11 are made of copper, and the length of the major axis of the two ellipsoidal electrodes is 25 mm, and the lengths of the middle semi-axis and the minor semi-axis are both 10 mm.

[0013] The first annular grounding electrode 4 and the second annular grounding electrode 7 are made of copper, and the second annular grounding electrode 7 is subjected to surface smoothing treatment.

[0014] 6. A uniform plasma generator based on a multi-electrode structure according to claim 1, characterized in that the inclination angle of the flared opening 6 is 45 degrees and it is made of polytetrafluoroethylene.

[0015] Both the first discharge chamber 5 and the second discharge chamber 10 are made of polytetrafluoroethylene.

[0016] The pore radius of the annular air outlet hole group 8 is 4 mm, the minimum radius of the position where it is located is 60 mm, the pores are arranged radially from the inside to the outside and the mutual spacing is 1 mm.

[0017] The maximum radius of the annular intake passage 2 is 25 mm; the gas flow rate of the annular intake passage 2 is adjusted according to the voltage amplitudes of the negative DC high-voltage power supply system 1 and the positive DC high-voltage power supply system 9.

[0018] The linear distance between the first ellipsoidal electrode 3 and the first annular ground electrode 4 in the first discharge chamber 5 is not less than half of the linear distance between the second ellipsoidal electrode 11 and the second annular ground electrode 7 in the second discharge chamber 10.

[0019] The present invention realizes the method of maintaining uniform and diffuse discharge in a large-range discharge chamber under atmospheric pressure by designing the intake air, the geometric structures and distributions of the electrodes in the chamber. Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The uniform plasma generator based on a multi-electrode structure disclosed by the present invention includes upper and lower discharge chambers, two sets of high-voltage DC power supplies with different amplitudes of positive and negative polarities, and ellipsoidal electrodes. After a negative corona is generated on the first ellipsoidal electrode in the first discharge chamber, under the action of the electric field generated by the small-area annular electrode and the first ellipsoidal electrode, negative ions will be attracted upward and distributed in layers along with the self-period of the discharge. Under the action of the air flow, they will be gradually pushed to the second discharge chamber through the trumpet-shaped opening. However, due to the geometric shapes and distributions of the lower annular electrode and the trumpet-shaped opening, the negative ions will be evenly distributed in an arch shape in the second discharge chamber, and this arch-shaped distribution to a certain extent prevents the generation of filamentous plasma caused by the potential discharge self-shrinking effect.

[0021] Furthermore, as the negative ions are distributed in the second discharge chamber, they will mix with the positive ions generated by the positive-polarity discharge with a lower amplitude and move evenly in all directions under the electric field formed between the large-area annular electrode and the second ellipsoidal electrode, thereby forming a uniform plasma in space. At the same time, because the annular intake and outlet continuously replace the gas working medium in the upper part of the discharge and the first discharge chamber, it avoids the increase in the plasma temperature caused by potential gas heating. Through the special electrode structure design, the charge neutralization of the discharge plasma inside the second discharge chamber is realized, effectively generating a uniform plasma under atmospheric pressure, and the ion energy in this plasma completely depends on the amplitudes of the positive and negative DC high-voltage power supplies, which can be adjusted according to requirements while avoiding the plasma from shrinking into filaments, thereby reducing the application efficiency of the plasma. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of the uniform plasma generator based on a multi-electrode structure of the present invention;

[0023] Figure 2 It is a schematic structural diagram of the annular air outlet group of the present invention;

[0024] Figure 3 It is the laser Thomson diagnostic result of the plasma electron density generated by the present invention;

[0025] Figure 4 It is a schematic diagram of the first annular ground electrode;

[0026] Figure 5 Schematic diagram of the second annular grounding electrode;

[0027] Figure 6 Schematic diagram showing that the linear distance between the first ellipsoidal electrode and the first annular grounding electrode is not less than half of the linear distance between the second ellipsoidal electrode and the second annular grounding electrode;

[0028] Figure 7 Measurement result graph of the electron density of the plasma in the cavity using the laser Thomson scattering method.

[0029] Wherein, 1 is the negative DC high-voltage power supply system, 2 is the annular intake channel, 3 is the first ellipsoidal electrode, 4 is the first annular grounding electrode, 5 is the frustum-shaped inner wall of the first discharge cavity, 6 is the flared opening, 7 is the second annular grounding electrode, 8 is the annular gas outlet group, 9 is the positive DC high-voltage power supply system, 10 is the second discharge cavity, and 11 is the second ellipsoidal electrode. Specific implementation mode

[0030] The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations rather than limitations of the present invention.

[0031] As Figure 1 shown, a uniform plasma generator based on a multi-electrode structure provided by the present invention includes a negative DC high-voltage power supply system 1, an annular intake channel 2, a first ellipsoidal electrode 3, a first annular grounding electrode 4, a first discharge cavity 5, a flared opening 6, a second annular grounding electrode 7, an annular gas outlet group 8, a positive DC high-voltage power supply system 9, a second discharge cavity 10, and a second ellipsoidal electrode 11.

[0032] During operation, the working medium for discharge needs to continuously enter the first discharge cavity 5 through the annular intake channel 2. The schematic diagram of the annular intake channel is as Figure 2 shown, and its specific flow rate depends on the applied voltages of the negative DC high-voltage power supply system 1 and the positive DC high-voltage power supply system 9. The specific correlation is V1 is the applied negative voltage, V2 is the applied positive voltage (unit: kV), R is the total gas flow rate of the annular intake passage (unit: mL / min), K is the fitting coefficient of the response curve. For example, when applying a -8 kV negative voltage and a 5 kV positive voltage, the required gas flow rate is 55 ml / min. The radius of the top surface of the frustum of the first discharge chamber 5 is 110 mm, and the radius of the bottom surface is 60 mm. The major axis length of the ellipsoidal electrode 3 is 25 mm, and the middle semi-axis and minor semi-axis lengths are both 10 mm. It is connected to the negative DC high-voltage power supply system 1 and forms an electric field with the first annular grounding electrode 4 to ionize the incoming working medium, generating a layer-distributed plasma. Under the push of the gas working medium, negative ions are pushed to the second discharge chamber 10. The shape of the second discharge chamber 10 is ellipsoidal, with the major semi-axis length of the ellipsoid being 200 mm, and the middle semi-axis and minor semi-axis lengths both being 80 mm. The positive DC high-voltage power supply system 9 ionizes the gas working medium in the second discharge chamber 10 to generate positive ions, which combine with negative ions and generate a uniformly distributed plasma in the electric field generated by the smooth second annular grounding electrode 7, ultimately achieving the uniform distribution of the plasma.

[0033] As Figure 3 shown, the annular outlet hole group 8 distributed radially in a ring can better guide the replacement of the gas working medium in the second discharge chamber 10. The radius of the air hole is 4 mm, and the distance between adjacent outlet holes is 1 mm. At the same time, because it is closer to the position where the uniform plasma is generated, it can replace the working medium in time before the plasma self-heating, further maintaining the uniformity of the plasma. The horn-shaped opening 6 made of polytetrafluoroethylene has the characteristics of good heat insulation, low high-temperature expansion coefficient, and resistance to plasma corrosion. The horn-shaped opening is 45 degrees, which is conducive to the negative ions generated in the first discharge chamber to be distributed in a layered arch shape, and can greatly avoid the discharge mode transition caused by the direct connection of the upper and lower parts of the plasma.

[0034] The first and second discharge chambers are divided into upper and lower parts, both made of polytetrafluoroethylene. The inner wall is required to be smooth and without obvious burrs to avoid the development of plasma along the surface and local hot spots in the sheath region. The overall thickness is 3 mm. The first annular grounding electrode 4 and the second annular grounding electrode 7 are required to be close to the inner wall, and their schematic diagrams are respectively as Figure 4 and Figure 5 shown. Among them, the straight-line distance between the first annular grounding electrode 4 and the first ellipsoidal electrode 3 should not be less than the major semi-axis length of the first ellipsoidal electrode to avoid the further generation of plasma before the negative ions are pushed away.

[0035] The self-periodic negative discharge frequency f (unit: Hz) generated on the first ellipsoidal electrode 3 in the lower first discharge chamber 5 is related to the applied negative voltage V1 (unit: kV), and its empirical formula can be characterized as where \(l\) is the straight-line distance between the first ellipsoidal electrode 3 and the first annular ground electrode 4 (unit: m), \(R\) is the gas flow rate of the annular intake passage (unit: mL / min), and \(K\) and \(C\) are the fitting coefficients of the response curve. Under the influence of this self-periodic characteristic, the stratification period of negative ions will remain consistent and, under the influence of the annular intake passage 2, will be pushed above the flared opening 6 to neutralize the positive ions generated when the positive DC high-voltage power supply system 9 ionizes the working medium. Also, since the voltage amplitude of the positive DC high-voltage source is less than the amplitude of \(V1\), and since the straight-line distance between the first ellipsoidal electrode 3 and the first annular ground electrode 4 in the first discharge chamber 5 is not less than half of the straight-line distance between the second ellipsoidal electrode and the second annular ground electrode 7 in the second discharge chamber 10, as shown in Figure 6 shown, this can ensure that no positive corona discharge will be converted into streamer or even spark discharge during the generation process of the neutralized plasma, thereby ensuring the uniformity of the discharge. The measurement results of the electron density of the plasma in the cavity using the laser Thomson scattering method are as shown in Figure 7 shown. In the center of the second discharge chamber 10, the plasma density is relatively uniform, and its electron density is between \(10^{10}\) 18 and \(10^{12}\) 20 m\(^{-3}\), -3 and the measurement consistency is good, and the measurement is also repeatable. In contrast, the filamentous discharge generated during the generation of plasma using a single electrode has poor repeatability, and the plasma density varies greatly at different positions, as shown in Figure 7 shown.

[0036] In summary, the present invention can generate uniform and stable plasma in a large cavity range at atmospheric pressure and ensure that the plasma parameters will not deteriorate further due to the operation time, and can be widely applied to fields such as waste gas treatment and plasma disinfection.

Claims

1. A uniform plasma generator based on a multi - electrode structure, characterized in that, It includes a negative DC high-voltage power supply system (1), a positive DC high-voltage power supply system (9), a flared opening (6), a first discharge chamber (5) and a second discharge chamber (10), wherein the first discharge chamber (5) is located at the bottom of the second discharge chamber (10); An annular intake passage (2) for the gas working medium for negative-polarity ionization to enter is opened on the bottom surface of the first discharge chamber (5); a first ellipsoidal electrode (3) is arranged at the bottom of the first discharge chamber (5), and the first ellipsoidal electrode (3) is connected to the negative DC high-voltage power supply system (1); the inner wall of the first discharge chamber (5) is closely attached to the first annular grounding electrode (4); An annular gas outlet hole group (8) for guiding the working medium replacement is opened at the top of the second discharge chamber (10); a second ellipsoidal electrode (11) is arranged at the top of the second discharge chamber (10), and the second ellipsoidal electrode (11) is connected to the positive DC high-voltage power supply system (9); the inner wall of the second discharge chamber (10) is closely attached to the second annular grounding electrode (7); The second discharge chamber (10) is isolated from the first discharge chamber (5) by the flared opening (6); the negative DC high-voltage power supply system (1) and the positive DC high-voltage power supply system (9) are respectively arranged outside the first discharge chamber (5) and the second discharge chamber (10); the voltage amplitude of the positive DC high-voltage power supply system (9) is lower than that of the negative DC high-voltage power supply system (1).

2. The uniform plasma generator based on a multi-electrode structure according to claim 1, characterized in that, The area of the first annular grounding electrode (4) is smaller than that of the second annular grounding electrode (7).

3. A uniform plasma generator based on a multi-electrode structure according to claim 1, characterized in that, The first discharge chamber (5) is frustum-shaped, the radius of the top surface of the frustum is 110 mm, and the radius of the bottom surface is 60 mm; the second discharge chamber (10) is ellipsoidal, and the length of the major semi-axis of the ellipsoid is 200 mm.

4. A uniform plasma generator based on a multi - electrode structure according to claim 1, characterized in that, The first ellipsoidal electrode (3) and the second ellipsoidal electrode (11) are made of copper, and the length of the major axis of the two ellipsoidal electrodes is 25 mm, and the lengths of the middle semi-axis and the minor semi-axis are both 10 mm.

5. A uniform plasma generator based on a multi - electrode structure according to claim 1, characterized in that, The first annular grounding electrode (4) and the second annular grounding electrode (7) are made of copper, and the surface of the second annular grounding electrode (7) is smoothed.

6. A uniform plasma generator based on a multi-electrode structure according to claim 1, characterized in that, The inclination angle of the flared opening (6) is 45 degrees and it is made of polytetrafluoroethylene.

7. A uniform plasma generator based on a multi - electrode structure according to claim 1, characterized in that, Both the first discharge chamber (5) and the second discharge chamber (10) are made of polytetrafluoroethylene.

8. A uniform plasma generator based on a multi-electrode structure according to claim 1, characterized in that, The radius of the air holes of the annular gas outlet hole group (8) is 4 mm, the minimum radius of the position where it is located is 60 mm, and the air holes are radially arranged from the inside to the outside and the distance between each other is 1 mm.

9. A uniform plasma generator based on a multi-electrode structure according to claim 1, wherein The maximum radius of the annular intake passage (2) is 25 mm; the gas flow rate of the annular intake passage (2) is adjusted according to the voltage amplitudes of the negative DC high-voltage power supply system (1) and the positive DC high-voltage power supply system (9).

10. A uniform plasma generator based on a multi - electrode structure according to claim 1, characterized in that, The linear distance between the first ellipsoidal electrode (3) and the first annular grounding electrode (4) in the first discharge chamber (5) is not less than half of the linear distance between the second ellipsoidal electrode (11) and the second annular grounding electrode (7) in the second discharge chamber (10).

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