A broadband atmospheric microwave plasma torch

Abstract

The present application relates to the field of microwave plasma technology, and more particularly to a wideband atmospheric microwave plasma torch, which mainly comprises an outer conductor, an inner conductor, an RF joint and a discharge device. The inner conductor comprises a first tapered end, a cylinder and a second tapered end. The cylinder is connected between the first tapered end and the second tapered end. The first tapered end is connected with the RF joint, and the second tapered end is connected with the discharge device. Through the above structure, the second tapered end at the end of the inner conductor (electrode) is enlarged to increase the electric flux and expand the excitation area of the plasma torch, so that the stable excitation of the large-flow and large-volume plasma flame can be realized. The increase of the electrode will cause the impedance mismatching to be unbalanced. Two gradually changing impedance matching structures are added to the design of the torch body to achieve good matching between the electrode end disc and the coaxial structure.

Description

Technical Field

[0001] This invention relates to the field of microwave plasma technology, and more specifically, to a broadband atmospheric pressure microwave plasma torch. Background Technology

[0002] Microwave plasma is characterized by high electron density, high efficiency, and high electron temperature. Therefore, microwave plasma torches are widely used in surface treatment, chemical engineering, materials processing, and other fields.

[0003] The widespread application of plasma torches in materials synthesis, thin film preparation, directional etching, spraying, and fusion welding has attracted considerable attention from both academia and industry. High-flow-rate plasma jets, in particular, have become a hot topic in plasma research due to their large gas flow rate, large flame volume, and ability to process larger quantities of material in a single pass. To achieve high-flow-rate gas excitation, resonant structures are often a good choice. These structures allow as much microwave power as possible to propagate into the cavity, generating a strong electric field that deposits power into the plasma. However, this also results in a relatively small excitation region in conventional resonant cavity structures, preventing the generation of a large plasma flame. Furthermore, the excitation region is further compressed after plasma ignition. Therefore, conventional coaxial resonant cavity plasma jets produce thinner and shorter flames, which is clearly disadvantageous for large-volume material surface treatment. Thus, the research and design of devices capable of generating high-flow-rate, large-volume plasma jets under the same conditions has become an urgent requirement. Summary of the Invention

[0004] The purpose of this invention is to provide a broadband atmospheric pressure microwave plasma torch to solve the above-mentioned problems in the prior art.

[0005] This invention is achieved through the following technical solution: A broadband atmospheric pressure microwave plasma torch includes an outer conductor, an inner conductor, a radio frequency connector, and a discharge device. The inner conductor is disposed inside the outer conductor, with one end connected to the radio frequency connector and the other end connected to the discharge device. The radio frequency connector and the discharge device are respectively connected to the two ends of the outer conductor. The inner conductor includes a first conical end, a column, and a second conical end. The column is connected between the first conical end and the second conical end. The first conical end is connected to the radio frequency connector, and the second conical end is connected to the discharge device. The maximum bottom area of ​​the first conical end is less than or equal to the minimum bottom area of ​​the second conical end.

[0006] Preferably, the discharge device includes an air inlet device, a quartz tube, and a mesh cylinder. The bottom of the mesh cylinder is detachably connected to the outer conductor. The quartz tube is disposed inside the mesh cylinder, with one end connected to the inner conductor. The air inlet device is disposed at the connection between the quartz tube and the inner conductor.

[0007] Preferably, the air intake device includes two air intake pipes, one end of which is connected to the quartz tube.

[0008] Preferably, through holes are provided on both sides of the outer conductor, and the air inlet pipe passes through the through holes to penetrate the outer conductor.

[0009] Preferably, the two air intake pipes are connected to the two sides of the quartz tube in a rotationally symmetrical manner, and the angle between the two air intake pipes and the horizontal direction is 15 degrees.

[0010] Preferably, the side of the mesh cylinder has several through holes.

[0011] Preferably, one end of the mesh tube is detachably connected to the outer conductor by bolts.

[0012] Preferably, the RF connector includes a connector base and threads disposed on the connector base.

[0013] Preferably, the outer conductor has a through hole on the side near the RF connector, for one end of the inner conductor to pass through the outer conductor and connect to the RF connector.

[0014] Preferably, one end of the second conical end is provided with a groove, and one end of the quartz tube is provided with a protrusion, the protrusion being disposed within the groove.

[0015] The technical solution of the present invention has at least the following advantages and beneficial effects: The structure provided by this invention mainly includes an outer conductor, an inner conductor, a radio frequency connector, and a discharge device. The inner conductor includes a first conical end, a column, and a second conical end. The column is connected between the first and second conical ends. The first conical end is connected to the radio frequency connector, and the second conical end is connected to the discharge device. Through this structure, the enlargement of the inner conductor (electrode) end, i.e., the second conical end, increases the electric field flux and expands the excitation region of the plasma torch, enabling stable excitation of a high-flow-rate, large-volume plasma flame. The enlargement of the electrode can cause impedance matching imbalance. Therefore, two gradually changing impedance matching structures are added to the torch design to achieve good matching between the electrode end disk and the coaxial structure. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a cross-sectional structural diagram of the present invention; Figure 3 For the present invention Figure 1 The left view; Figure 4 This is a cross-sectional schematic diagram of the inner conductor of the present invention; Figure 5 This is a schematic diagram of the structure of the inner conductor of the present invention; Figure 6 This is a cross-sectional schematic diagram of the outer conductor of the present invention; Figure 7 This is a schematic diagram of the structure of the outer conductor of the present invention; Figure 8 This is a schematic diagram of the structure of the mesh tube of the present invention; Figure 9 This is a top view of the mesh tube of the present invention; Figure 10 This is a cross-sectional schematic diagram of the mesh tube of the present invention; Figure 11 This is a schematic diagram of the structure of the present invention without the outer conductor; Figure 12 This is a schematic diagram of the gas flow direction at the air intake of the present invention; Figure 13 The distribution variation of the microwave electric field (V / m) at different times is shown in the present invention. Figure 14 This represents the distribution variation of electron number density (1 / m³) at different times in this invention.

[0018] Icons: 1-RF connector, 2-outer conductor, 3-inlet pipe, 4-mesh tube, 5-inner conductor, 6-quartz tube. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Please refer to Figures 1-11 The present invention provides a broadband atmospheric pressure microwave plasma torch, comprising an outer conductor 2, an inner conductor 5, a radio frequency connector 1, and a discharge device. The inner conductor 5 is disposed inside the outer conductor 2, with one end connected to the radio frequency connector 1 and the other end connected to the discharge device. The radio frequency connector 1 and the discharge device are respectively connected to the two ends of the outer conductor 2. Specifically, the outer conductor 2 is a hollow cylindrical structure with one end open. One open end is connected to the discharge device, and the other end is connected to the radio frequency connector 1. The radio frequency connector 1 is used to connect to the input of an external microwave source.

[0021] The inner conductor 5 includes a first conical end, a column, and a second conical end. The column is connected between the first conical end and the second conical end. The first conical end is connected to the radio frequency connector 1, and the second conical end is connected to the discharge device. The maximum bottom area of ​​the first conical end is less than or equal to the minimum bottom area of ​​the second conical end.

[0022] Specifically, the inner conductor 5 is usually used as a high-voltage electrode (positive or negative) to form a strong electric field with the external electrode (such as a nozzle or grounding electrode), and ionizes the working gas (such as argon, nitrogen or air) through high-voltage discharge to generate plasma.

[0023] The first conical end, the column, and the second conical end are integrated into a single structure. From the first conical end to the second conical end, the cross-sectional area of ​​the inner conductor 5 gradually increases. Both the first and second conical ends are approximately truncated cones. The upper and lower surface areas of the truncated cones constitute the two base areas of the truncated cones. The smallest base area of ​​the first conical end, i.e., the top of the first conical end, is connected to the RF connector 1. The largest base area of ​​the first conical end constitutes one end face of the column. The other end face of the column constitutes the end face of the smallest base area of ​​the second conical end. The largest base area of ​​the second conical segment constitutes the base surface of the entire structure of the inner conductor 5. Through the gradually increasing shape of the inner conductor 5 from one end to the other, a gradually transitioning impedance matching structure is formed, which can reduce reflection and improve microwave energy efficiency.

[0024] The structure provided by this invention mainly includes an outer conductor 2, an inner conductor 5, an RF connector 1, and a discharge device. The inner conductor 5 includes a first conical end, a column, and a second conical end. The column is connected between the first and second conical ends. The first conical end is connected to the RF connector 1, and the second conical end is connected to the discharge device. Through the above structure, the enlargement of the end of the inner conductor 5 (electrode), i.e., the second conical end, increases the electric field flux and expands the excitation area of ​​the plasma torch, enabling the stable excitation of a high-flow-rate, large-volume plasma flame. The enlargement of the electrode will cause impedance matching imbalance. Therefore, two gradually changing impedance matching structures are added to the torch design to achieve good matching between the electrode end disk and the coaxial structure.

[0025] In this invention, the jet is considered a narrow-bandwidth and resonant-frequency filter, directly fed through a coaxial structure, and its maximum efficiency is achieved through impedance matching. From an electrical perspective, the impedance matching structure is highly sensitive to minute changes in the electrical load (e.g., plasma). The plasma is ignited at a frequency and operated under the influence of resonant-frequency changes caused by variations in plasma impedance. Therefore, the operating network within the jet is termed bistable (ignition and operation). This is achieved by adding a short matching line between the jet (inactive plasma) and the inner coaxial conductor 5.

[0026] Another effect is the variation in impedance matching, which is influenced by the presence of conductive materials. If the matching wire is wide enough, it acts as part of the electromagnetic wave radiated by the antenna, resulting in a large electric flux at the open circuit of the resonant cavity, significantly improving the efficiency of plasma excitation. Of course, this also affects impedance matching. Ignition of the plasma further increases the complexity of the system. Variations in the electrical length of the matching disk are expected to cause a shift to lower frequencies, but due to complex interactions, it is impossible to calculate the exact amount. These variations can be approximated through system simulation.

[0027] In one exemplary embodiment of the present invention, the discharge device includes an air inlet device, a quartz tube 6 and a mesh cylinder 4. The bottom of the mesh cylinder 4 is detachably connected to the outer conductor 2. The quartz tube 6 is disposed inside the mesh cylinder 4, with one end connected to the inner conductor 5. The air inlet device is disposed at the connection between the quartz tube 6 and the inner conductor 5.

[0028] Specifically, the quartz tube 6 is a hollow cylindrical structure with one open end and one closed end. A protrusion is located at the closed end, and a groove is located at the bottom of the second conical end of the inner conductor 5. The quartz tube 6 connects to the groove at the second conical end via the protrusion. The quartz tube 6 physically isolates the inner conductor 5 (high-voltage electrode) from the outer electrode (such as a grounding nozzle or reaction chamber), preventing direct short circuits and ensuring that high-voltage discharge occurs only through the gaseous medium. The quartz tube 6 acts as a dielectric barrier, facilitating dielectric barrier discharge. Its insulating properties confine the discharge to the inside or outer surface of the tube, forming a uniform low-temperature plasma and preventing the intense energy concentration of arc discharge.

[0029] Secondly, the air intake device includes two air intake pipes 3, one end of which is connected to the quartz tube 6.

[0030] Through holes are provided on both sides of the outer conductor 2. The air inlet pipe 3 passes through the through holes and penetrates the outer conductor 2. The two air inlet pipes 3 are connected to both sides of the quartz tube 6 in a rotationally symmetrical manner. Furthermore, the angle between the two air inlet pipes 3 and the horizontal direction is 15 degrees, and the gas feed tangential direction is staggered with the axis of the cylinder. Figure 12It can be seen that this air intake method can generate a spiraling upward airflow, improving the uniformity of airflow in the glass tube.

[0031] In one exemplary embodiment of the present invention, the side of the mesh cylinder 4 is provided with a plurality of through holes, and one end of the mesh cylinder 4 is detachably connected to the outer conductor 2 by bolts.

[0032] In addition, the RF connector 1 includes a connector base and a thread provided on the connector base. The outer conductor 2 has a through hole on the side near the RF connector 1, for one end of the inner conductor 5 to pass through the outer conductor 2 and connect to the RF connector 1.

[0033] Based on the structure described above in this invention, plasma simulations were performed, and additional simulations were conducted in the finite element simulator COMSOL to evaluate whether the principle can be applied to active plasmas.

[0034] To better illustrate the state of plasma within the glass tube, rotational symmetry is used. From Figure 14 It is known that microwave power generation breakdown first occurs at the edge of the matching disk, which is the open-circuit point of the coaxial resonant cavity, where microwave energy concentrates. Over time, the discharge region concentrates towards the center of the glass tube, gradually increasing in volume. When the discharge time reaches... At 100 seconds, the discharge tends to stabilize, and the shape of the plasma column no longer changes over time.

[0035] Figure 13 This demonstrates the changes in the microwave electric field distribution during the discharge process. At the initial time... The electron number density per second is The number density per m³ is far less than the critical number density of microwave plasma. Units / m³. In the initial state, because the equivalent coaxial line of the open circuit will cause total microwave reflection, the microwaves are only in the cavity and near the open circuit point.

[0036] like Figure 14 As shown, when the electron number density exceeds a critical value, the plasma exhibits metallic properties and shields electromagnetic waves. A thin quartz tube 6 exists between the plasma and the metal wall; this acts as a two-conductor transmission line for electromagnetic propagation. Electromagnetic waves propagate along the glass tube wall, eventually dissipating within the plasma.

[0037] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A broadband atmospheric pressure microwave plasma torch, characterized in that, It includes an outer conductor (2), an inner conductor (5), a radio frequency connector (1), and a discharge device. The inner conductor (5) is disposed inside the outer conductor (2), with one end connected to the radio frequency connector (1) and the other end connected to the discharge device. The radio frequency connector (1) and the discharge device are respectively connected to the two ends of the outer conductor (2). The inner conductor (5) includes a first conical end, a column and a second conical end. The column is connected between the first conical end and the second conical end. The first conical end is connected to the radio frequency connector (1) and the second conical end is connected to the discharge device. The maximum bottom area of ​​the first conical end is less than or equal to the minimum bottom area of ​​the second conical end.

2. The broadband atmospheric pressure microwave plasma torch according to claim 1, characterized in that, The discharge device includes an air inlet device, a quartz tube (6) and a mesh tube (4). The bottom of the mesh tube (4) is detachably connected to the outer conductor (2). The quartz tube (6) is disposed inside the mesh tube (4), and one end of it is connected to the inner conductor (5). The air inlet device is disposed at the connection between the quartz tube (6) and the inner conductor (5).

3. The broadband atmospheric pressure microwave plasma torch according to claim 2, characterized in that, The air intake device includes two air intake pipes (3), one end of which is connected to the quartz tube (6).

4. The broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that, The outer conductor (2) has through holes on both sides, and the air inlet pipe (3) passes through the through holes to penetrate the outer conductor (2).

5. A broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that, The two air intake pipes (3) are connected to the two sides of the quartz tube (6) in a rotationally symmetrical manner, and the angle between the two air intake pipes (3) and the horizontal direction is 15 degrees.

6. A broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that, The side of the mesh cylinder (4) has several through holes.

7. A broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that, One end of the mesh tube (4) is detachably connected to the outer conductor (2) by bolts.

8. A broadband atmospheric pressure microwave plasma torch according to claim 1, characterized in that, The radio frequency connector (1) includes a connector and threads disposed on the connector.

9. A broadband atmospheric pressure microwave plasma torch according to claim 1, characterized in that, The outer conductor (2) has a through hole on the side near the radio frequency connector (1) for one end of the inner conductor (5) to pass through the outer conductor (2) and connect to the radio frequency connector (1).

10. A broadband atmospheric pressure microwave plasma torch according to claim 2, characterized in that, One end of the second conical end is provided with a groove, and one end of the quartz tube (6) is provided with a protrusion, which is disposed in the groove.

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