Microwave plasma excitation device and parameter optimization method thereof

Abstract

This invention discloses a microwave plasma excitation device and its parameter optimization method. The excitation device includes a waveguide cavity comprising a first cavity, a second cavity, and a third cavity connected sequentially. A quartz tube passes through the first cavity, and an auxiliary excitation conductor is nested on the inner wall of the quartz tube at the junction with the first cavity. A connecting sleeve is provided at one end of the quartz tube, and the connecting sleeve is connected to a carrier gas heat dissipation module. The carrier gas heat dissipation module is also connected to the third cavity. A magnetron is provided inside the carrier gas heat dissipation module, and the output shaft of the magnetron extends into the interior of the third cavity. The carrier gas heat dissipation module can input a heat dissipation medium for cooling the magnetron into the quartz tube. The parameter optimization method combines finite element parametric scanning analysis technology and multivariate regression equation fitting. The excitation device of this invention reduces the complexity of the equipment and improves the integration between various functional modules.

Description

Technical Field

[0001] This invention belongs to the field of microwave plasma technology, specifically relating to a microwave plasma excitation device and its optimization method. Background Technology

[0002] Microwave plasma technology is a technique that uses microwaves to excite and ionize a gas to form plasma. Microwave discharge can generate large-volume plasma at atmospheric pressure. Compared with other plasma excitation methods, it has advantages such as lower excitation power, no need for electrodes, and the ability to operate over a wider pressure range. Simultaneously, microwave plasma has concentrated energy, a high reaction temperature, and abundant high-energy electrons, charged particles, and active free radicals, and is now widely used in fields such as solid waste treatment, new material preparation, metal refining, and microcircuit manufacturing.

[0003] Existing small-scale microwave plasma excitation devices mainly consist of functional modules such as a magnetron, magnetron heat dissipation assembly, waveguide cavity, carrier gas supply assembly, and plasma reaction cavity. Due to the low integration of each functional module, they are often complex in structure and large in size, which limits the further promotion of microwave plasma technology in industrial applications. For example, in the field of microwave plasma welding, to achieve rapid and flexible welding of complex precision workpieces, the plasma excitation module / device on the welding machine must be sufficiently lightweight and compact. Therefore, large, low-integration microwave plasma devices can no longer meet the requirements.

[0004] The plasma reaction chamber is the location where plasma is generated. During the excitation and maintenance of plasma, it needs to withstand extremely high temperatures. Therefore, existing technologies, such as Chinese patents CN109874221A, CN104507249A, CN112996209A, and CN101378615A, all use quartz tubes with high melting points as the reaction chamber. The plasma excitation and maintenance process causes vibrations in the quartz tube, necessitating a tight fit. However, under tight fit conditions, due to the difference in thermal expansion coefficients between the quartz tube and the mounting components, and the quartz tube's high brittleness, the radial thermal expansion force of the quartz tube cannot be released under high-temperature operating conditions due to the constraint of the mounting components. This easily leads to cracks on the surface of the quartz tube, thus affecting its service life.

[0005] The waveguide cavity connects the plasma reaction cavity (quartz tube) and the microwave source (magnetron), serving as a device for microwave energy transfer. Its structural characteristics directly affect the efficiency of microwave transmission from the microwave source to the reaction cavity, determining the plasma's energy utilization rate and thus its excitation effect. Optimization of the waveguide cavity structure should aim to maximize microwave transmission efficiency within the cavity, thereby maximizing the electric field strength within the reaction cavity to achieve a better plasma excitation state. Existing waveguide cavity structure optimization methods, such as those using High Frequency Simulator Structure software for parameter scanning analysis, involve finite element analysis of the waveguide cavity within a given size variation range. This obtains the electric field strength at the reaction cavity location under different size combinations, with the goal of maximizing the electric field strength. The size combination corresponding to the maximum electric field strength is then selected as the optimal solution for the waveguide cavity structure. However, these optimization methods can only obtain the optimal solution for waveguide cavity structures within a fixed size range in a single iteration. They cannot predict the optimal solution for waveguide cavity structures outside the size variation range. When the allowable size variation range of the waveguide cavity changes during the design process, the size variation range needs to be reset in the computer for recalculation, making the optimization process cumbersome and complex, and unsuitable for optimizing waveguide cavity structures with frequently changing size variation ranges. For example, traditional methods can obtain the optimal solution for the waveguide cavity structure within the size variation range [50mm-100mm]. When the design requirements change and the allowable size variation range of the waveguide cavity is changed to [80mm-120mm], the waveguide cavity optimization needs to be repeated for the new size variation range, which will increase the optimization design time. At the same time, the finite element analysis in each optimization process consumes a lot of computer memory resources, resulting in long analysis times and further reducing optimization efficiency. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a microwave plasma excitation device that solves the problems of complex structure, low integration, and easily broken quartz tubes in existing microwave plasma excitation devices. This invention also provides a parameter optimization method for microwave plasma excitation devices that solves the problems of cumbersome and inefficient existing optimization methods.

[0007] The technical solution of this invention is as follows:

[0008] A microwave plasma excitation device includes a waveguide cavity comprising a first cavity, a second cavity, and a third cavity connected in sequence. The cross-sectional area of ​​the first cavity is smaller than that of the third cavity, and the cross-sectional area of ​​the second cavity gradually increases from the first cavity to the third cavity. A quartz tube passes through the first cavity, and an auxiliary excitation conductor is nested on the inner wall of the quartz tube at the junction with the first cavity. One end of the quartz tube is provided with a connecting sleeve, which is connected to a carrier gas heat dissipation module. The carrier gas heat dissipation module is also connected to the third cavity. A magnetron is provided inside the carrier gas heat dissipation module, and the output shaft of the magnetron extends into the interior of the third cavity. The microwaves generated by the magnetron are transmitted through the waveguide cavity and enter the interior of the quartz tube to form a microwave electric field. The auxiliary excitation conductor excites a microwave plasma torch. The carrier gas heat dissipation module can input a heat dissipation medium for cooling the magnetron into the quartz tube.

[0009] Preferably, an elastic clamping assembly is installed on the quartz tube on the other side of the first cavity opposite to the connecting sleeve. The elastic clamping assembly includes an installation tube and a clamp. The installation tube is located on the outside of the quartz tube, and the clamp is located between the quartz tube and the installation tube.

[0010] Preferably, the elastic clamping assembly further includes a clamping screw and a fixing cap. The number of clamping screws is at least two, and the clamping screws are evenly distributed and installed on the mounting tube. The inner end of the clamping screw passes through the side wall of the mounting tube and is clamped against the clamp. The fixing cap is threaded to the end of the mounting tube away from the first cavity. The fixing cap is provided with a through hole communicating with the inside of the quartz tube.

[0011] Preferably, the elastic clamping assembly further includes a base plate, which is welded and fixed to the waveguide cavity. The base plate is used to install and fix the microwave plasma excitation device in the corresponding application scenario, and the end of the mounting tube near the first cavity is welded to the base plate.

[0012] Preferably, the clamp consists of a telescopic part and mounting parts located at both ends of the telescopic part. The clamp is nested in the inner wall of the mounting tube, and the clamp is coaxially installed with the mounting tube through the mounting parts. The longitudinal section of the telescopic part is W-shaped, and the telescopic part is provided with multiple evenly distributed strip openings along the circumference.

[0013] Preferably, the telescopic part has an outwardly convex surface in the middle, and the inner end of the clamping screw is directly opposite the convex surface in the middle of the telescopic part.

[0014] Preferably, the carrier gas heat dissipation module includes a protective cover, a centrifugal fan, a flow guide shell, a three-way valve, and a connector. The protective cover is fixed on the third cavity, and the magnetron is located inside the protective cover. The protective cover is also connected to the centrifugal fan, and the air outlet of the centrifugal fan is aligned with the magnetron. The flow guide shell is fixed on the other side of the protective cover opposite to the centrifugal fan. The three-way valve has a first passage, a second passage, and a third passage. The three-way valve is connected to the flow guide shell through the first passage and to the connector through the second passage. The connector is connected to the connecting sleeve. Valves are respectively provided on the first passage and the third passage.

[0015] Preferably, the auxiliary excitation conductor is spring-shaped and made of tungsten wire.

[0016] A method for optimizing the parameters of a microwave plasma excitation device includes the following steps:

[0017] S1. Establish the original three-dimensional model of the waveguide cavity and analyze the factors affecting the microwave transmission efficiency of the waveguide cavity. The waveguide cavity includes a first cavity, a second cavity, and a third cavity that are connected in sequence. The first cavity passes through a quartz tube. Select several dimensional parameters of the first cavity, the second cavity, and the third cavity in the waveguide cavity as variables to participate in the structural optimization, which are called the parameters to be optimized.

[0018] S2. Determine the value range of each parameter to be optimized based on the actual working conditions;

[0019] S3. Import the original three-dimensional model of the waveguide cavity into the finite element analysis software for parametric scanning analysis to obtain the electric field intensity of the waveguide cavity at the quartz tube under different combinations of parameters to be optimized.

[0020] S4. Analyze the influence of the interaction between the parameters to be optimized on the electric field strength, and summarize the corresponding response laws;

[0021] S5. Establish the functional relationship between the parameters to be optimized and the electric field intensity, and fit the multiple regression equation of the electric field intensity relative to the parameters to be optimized.

[0022] S6. Perform goodness-of-fit and significance tests on the multiple regression equation. If the goodness-of-fit and significance of the equation meet the requirements, it means that the equation is correctly fitted. Then, proceed to step S7. If the goodness-of-fit and significance of the equation do not meet the requirements, return to step S5 until the requirements for goodness-of-fit and significance are met.

[0023] S7. Given the value range of each parameter to be optimized, use step S6 to fit the correct equation, with the optimization objective being to maximize the electric field strength at the quartz tube. Calculate the combination of values ​​of the parameters to be optimized under the optimization objective, which is called the optimal parameter value combination. Record the electric field strength corresponding to the optimal parameter value combination, which is called the optimal solution.

[0024] S8. Based on the response pattern summarized in step S4, estimate the value range of each parameter to be optimized under the optimization objective, which is called the response range. Determine whether the optimal parameter value combination calculated in step S7 is within the response range. If the optimal parameter value combination is within the response range, it means that the optimal parameter value combination is correct, and jump to step S9. If the optimal parameter value combination is not within the response range, it means that the optimal parameter value combination is incorrect, and jump back to step S7 until the optimal parameter value combination is within the response range.

[0025] S9. Reconstruct the three-dimensional model of the waveguide cavity using the optimal parameter value combination; this is called the verification model.

[0026] S10. Perform finite element analysis on the test model and obtain the electric field strength obtained from the finite element analysis, which is called the test value.

[0027] S11. Set the inspection standard and calculate the difference between the optimal solution in step S7 and the inspection value in step S10. If the standard is met, it proves that the optimal solution in step S7 is calculated correctly and the optimization process ends. If the standard is not met, it proves that the optimal solution in step S7 is calculated incorrectly and the process jumps back to step S5 until the inspection standard in step S11 is met.

[0028] Preferably, the length of the first cavity of the waveguide cavity is equal to the length of the third cavity, and the parameters to be optimized in step S1 are the length of the first cavity and the length of the second cavity.

[0029] The beneficial effects of this invention are:

[0030] (1) The present invention improves the integration between the functional modules of the excitation device. The present invention integrates the carrier gas supply component and the magnetron heat dissipation component in the excitation device into a unified carrier gas heat dissipation module. The heat dissipation airflow of the magnetron is used as the working carrier gas of the plasma, which reduces the complexity of the equipment, promotes the miniaturization of the overall equipment, and expands the application scenarios of the equipment.

[0031] (2) The present invention also designed an adjustable elastic clamping assembly. This structure can effectively absorb the radial thermal expansion force of the quartz tube and prevent the quartz tube from breaking in the high-temperature working environment. At the same time, the clamping force of the elastic clamping is adjustable, which can avoid the loosening problem caused by insufficient clamping force of the quartz tube.

[0032] (3) This invention also combines finite element parametric scanning analysis technology and the idea of ​​multivariate regression equation fitting to create a parameter optimization method for microwave plasma excitation device. This method can establish a functional relationship between the structural size parameters of the waveguide cavity and the local electric field intensity, and rely on this functional relationship to achieve joint optimization of the size parameters and the local electric field intensity. Traditional methods can only optimize the waveguide cavity within a fixed size variation range. The optimization method of this invention can optimize the waveguide cavity within any size variation range. Moreover, no matter how many times the allowable size variation range of the waveguide cavity is changed, only one finite element parametric scanning analysis is needed. The optimization process is simple and efficient. Attached Figure Description

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0034] Figure 1 This is a front view of the overall structure of the excitation device of the present invention;

[0035] Figure 2 This is a three-dimensional view of the overall structure of the excitation device of the present invention;

[0036] Figure 3 This is a perspective view of the excitation device behind the concealed protective cover of the present invention;

[0037] Figure 4 This is a perspective view of the excitation device of the present invention with the mounting tube, base plate and fixing cap concealed;

[0038] Figure 5 This is a top view of the overall structure of the excitation device of the present invention;

[0039] Figure 6 yes Figure 5 A cross-sectional view along the AA direction;

[0040] Figure 7 yes Figure 6 Enlarged view of point I in the middle;

[0041] Figure 8 This is a perspective view of the fixture of the present invention;

[0042] Figure 9 It is the original waveguide cavity and its parameters to be optimized;

[0043] Figure 10 It is a response contour map;

[0044] Figure 11 It is a three-dimensional response surface plot;

[0045] Figure 12 It is the prediction error of the multiple regression equation.

[0046] The diagram is marked as follows:

[0047] 1. Waveguide cavity; 1.1. First cavity; 1.2. Second cavity; 1.3. Third cavity; 2. Elastic clamping assembly; 2.1. Mounting tube; 2.2. Base plate; 2.3. Clamp; 2.3.1. Mounting part; 2.3.2. Telescopic part; 2.4. Clamping screw; 2.5. Fixing cap; 3. Connecting sleeve; 4. Carrier gas heat dissipation module; 4.1. Protective cover; 4.2. Centrifugal fan; 4.3. Guide shell; 4.4. Three-way valve; 4.5. Connector; 5. Magnetron; 6. Quartz tube; 7. Auxiliary excitation conductor. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0049] like Figures 1 to 6 As shown, a microwave plasma excitation device includes a waveguide cavity 1, an elastic clamping assembly 2, a connecting sleeve 3, a carrier gas heat dissipation module 4, a magnetron 5, a quartz tube 6, and an auxiliary excitation conductor 7. The waveguide cavity 1 includes a first cavity 1.1, a second cavity 1.2, and a third cavity 1.3 connected in sequence. The cross-sectional area of ​​the first cavity 1.1 is smaller than that of the third cavity 1.3. The cross-sectional area of ​​the second cavity 1.2 gradually increases along the direction from the first cavity 1.1 to the third cavity 1.3. The first cavity 1.1 is through which the quartz tube 6 passes. An auxiliary excitation conductor 7 is nested in the inner wall of the quartz tube 6 at the junction with the first cavity 1.1. The auxiliary excitation conductor 7 is spring-shaped and made of tungsten wire. One end of the quartz tube 6 is provided with a connecting sleeve 3. The connecting sleeve 3 is tubular in shape and has a round hole and an inner tube thread hole respectively. The connecting sleeve 3 is welded and fixed to the first cavity 1.1 of the waveguide cavity 1. The lower part of the quartz tube 6 passes through the first cavity 1.1 and abuts against the round hole of the connecting sleeve 3. The connecting sleeve 3 is installed between the waveguide cavity 1 and the carrier gas heat dissipation module 4. The connecting sleeve 3 is threadedly connected to the connector 4.5 in the carrier gas heat dissipation module 4 through the inner tube thread hole. The carrier gas heat dissipation module 4 is also connected to the third cavity 1.3. The magnetron 5 is completely wrapped by the protective cover 4.1 in the carrier gas heat dissipation module 4, and its output shaft extends into the interior of the third cavity 1.3. During operation, the output shaft of the magnetron 5 continuously generates microwaves inside the waveguide cavity 1. After being transmitted through the waveguide cavity 1, the microwaves enter the quartz tube 6 to form a microwave electric field. The microwave plasma torch is excited by the auxiliary excitation conductor 7 embedded in the quartz tube 6. At the same time, the carrier gas heat dissipation module 4 inputs the heat dissipation medium that cools the magnetron 5 into the quartz tube 6 as a carrier gas to maintain the shape of the plasma torch.

[0050] The carrier gas heat dissipation module 4 includes a protective cover 4.1, a centrifugal fan 4.2, a flow guide shell 4.3, a three-way valve 4.4, and a connector 4.5. The protective cover 4.1 is fixedly installed on the third cavity 13 by screws. The protective cover 4.1 is a metal shell and is also provided with metal heat sinks. The magnetron 5 is located inside the protective cover 4.1, which completely encloses it, providing a safe and stable working environment. The protective cover 4.1 is also connected to a centrifugal fan 4.2, with its outlet aimed at the heating element of the magnetron 5. A guide shell 4.3 is fixed to the other side of the protective cover 4.1, opposite the centrifugal fan 4.2. A three-way valve 4.4 has a first passage, a second passage, and a third passage. The three-way valve 4.4 is connected to the guide shell 4.3 through the first passage and to the connector 4.5 through the second passage. The connector 4.5 is a pipe fitting with internal threads at both ends, threadedly connected to the three-way valve 4.4 and the connecting sleeve 3, respectively. Valves are installed on the first and third passages to control the airflow entering the three-way valve 4.4, thereby regulating the carrier gas flow rate into the quartz tube 6, which in turn helps to adjust the size of the plasma torch after excitation. Additionally, from... Figures 1 to 6 As can be seen, the third passage is connected to the external open environment. A valve on the third passage controls its opening and closing, and this design helps release excess carrier gas to the outside, thus regulating the carrier gas flow rate. The centrifugal fan 4.2 uses its high-speed rotating impeller to accelerate outside air into the protective cover 4.1, thereby dissipating heat from the magnetron 5. The main functions of the guide shell 4.3, the three-way valve 4.4, and the connector 4.5 are to direct the cooling airflow from the centrifugal fan 4.2 into the connecting sleeve 3 and the quartz tube 6 connected to the connecting sleeve 3, converting the cooling airflow into carrier gas for plasma excitation, while simultaneously controlling the carrier gas flow rate. In existing plasma excitation devices, the magnetron 5 cooling module and the plasma carrier gas supply module are completely independent, with no interaction between them. In this embodiment, the carrier gas cooling module 4 integrates these two functional modules, eliminating the need for an additional independent carrier gas supply device. This effectively reduces the structural complexity of the device, promotes overall miniaturization, and expands the application scenarios of the device.

[0051] Quartz tube 6 is a tubular structure made of high-temperature resistant quartz. The installation method of the quartz tube is as follows: Figure 6 and Figure 7As shown, an elastic clamping assembly 2 is installed on the quartz tube 6 on the other side of the first cavity 1.1 opposite to the connecting sleeve 3. The elastic clamping assembly 2 includes a mounting tube 2.1, a base plate 2.2, a clamp 2.3, a clamping screw 2.4, and a fixing cap 2.5. The mounting tube 2.1 is a circular tube with external threads machined on the upper part and symmetrically threaded holes in the middle. One end of the mounting tube 2.1 near the first cavity 1.1 is welded to the base plate 2.2. The base plate 2.2 is a rectangular plate and is welded and fixed to the waveguide cavity 1. The base plate 2.2 has through holes around its perimeter for installing and fixing the microwave plasma excitation device in the corresponding application scenario. The mounting tube 2.1 is located on the outside of the quartz tube 6, and the clamp 2.3 is located between the quartz tube 6 and the mounting tube 2.1. The structure of the clamp 2.3 is as follows. Figure 8As shown, the clamp 2.3 consists of a telescopic part 2.3.2 and mounting parts 2.3.1 located at both ends of the telescopic part 2.3.2. The clamp 2.3 is nested in the inner wall of the mounting tube 2.1, and the clamp 2.3 is coaxially mounted with the mounting tube 2.1 through the mounting parts 2.3.1. The telescopic part 2.3.2 is a metal spring with a W-shaped longitudinal cross section, and a convex surface protruding outward in the middle. The telescopic part 2.3.2 has multiple evenly distributed strip openings along the circumference. In addition, there are at least two clamping screws 2.4. These are ordinary hexagonal head screws, installed in the threaded holes in the middle of the mounting tube 2.1. The clamping screws 2.4 are evenly distributed on the mounting tube 2.1. The inner end of each clamping screw 2.4 passes through the side wall of the mounting tube 2.1 and is pressed against the clamp 2.3. A fixing cap 2.5 is threaded to the end of the mounting tube 2.1 away from the first cavity 1.1. The fixing cap 2.5 is generally round with threads on its inner wall and a through hole communicating with the inside of the quartz tube 6. The main function of the elastic clamping assembly 2 is to achieve elastic clamping of the quartz tube 6, preventing it from breaking due to the inability to release thermal expansion forces under high temperatures, while ensuring that the quartz tube 6 is securely installed and will not loosen during operation. The elastic clamping steps for the quartz tube 6 are as follows: First, nest the clamp 2.3 inside the inner wall of the mounting tube 2.1, and rely on the mounting part 2.3.1 of the clamp 2.3 to ensure coaxial installation between the clamp 2.3 and the mounting tube 2.1. At this time, the clamping screws 2.4 on both sides of the mounting tube 2.1 are directly opposite the convex surface of the telescopic part 2.3.2 in the middle of the clamp 2.3. Next, nest the quartz tube 6 into the clamp 2.3, adjust the position of the clamping screws 2.4, and adjust the radial clamping force of the quartz tube 6 by squeezing / releasing the clamp 2.3. At the same time, the bottom of the quartz tube 6 abuts against the connecting sleeve 3. Finally, rotate the fixing cap 2.5 to axially clamp the quartz tube 6.Compared with the traditional clamping method for quartz tube 6, the clamping method provided in this embodiment has the following characteristics: When the clamp 2.3 is not under stress, its inner diameter is smaller than the outer diameter of the quartz tube 6. After the quartz tube 6 is inserted into the clamp 2.3, the inner diameter of the telescopic part 2.3.2 of the clamp 2.3 expands due to the compression of the quartz tube 6. Simultaneously, the clamp 2.3 is forced to elongate axially. The telescopic part 2.3.2 in the clamp 2.3 automatically provides radial clamping force to the quartz tube 6. If the clamping force on the quartz tube 6 is insufficient / excessive due to machining / installation errors, the clamping force can be increased / decreased by adjusting the clamping screw 2.4. Tightening force; After successful plasma excitation, the quartz tube 6 expands due to heat (mainly radial thermal expansion). In the traditional "rigid" installation method, the quartz tube 6 is in close contact with the surrounding metal mounting surface, which causes the expansion force of the quartz tube 6 to be unable to be released and thus break. However, if the clamping method of the quartz tube 6 provided in this embodiment is used, after the quartz tube 6 expands radially, the quartz tube 6 will again radially compress the telescopic structure of the clamp 2.3. At the same time, the clamp 2.3 will be forced to extend axially again, automatically adjusting the clamping force on the quartz tube 6. This can effectively absorb the thermal expansion force of the quartz tube 6 and prevent the quartz tube 6 from breaking.

[0052] The waveguide cavity structure is optimized to improve microwave transmission efficiency within the cavity, maximize the electric field strength within the quartz tube, and achieve a better plasma excitation state. In this embodiment, the auxiliary mounting structures unrelated to microwave transmission efficiency in the aforementioned waveguide cavity 1 are removed, and a simplified original waveguide cavity to be optimized is established, such as... Figure 9 As shown, the parameter optimization method of this invention is used to optimize the structure of the original waveguide cavity, obtaining the optimal parameter combination and optimal solution for the waveguide cavity. The finite element analysis software used in this invention is COMSOL, and the data processing software is Design Expert. The specific optimization steps are as follows:

[0053] S1. Establish the original three-dimensional model of the waveguide cavity and analyze the factors affecting the microwave transmission efficiency of the waveguide cavity, such as... Figure 9 As shown, the waveguide cavity includes a first cavity, a second cavity, and a third cavity connected in sequence. The first cavity passes through a quartz tube. The length of the first cavity is equal to the length of the third cavity. The lengths L1 of the first cavity and L2 of the second cavity are selected as variables for structural optimization and are called the parameters to be optimized.

[0054] S2. Determine the value range of each parameter to be optimized based on the actual working conditions, where L1∈[60,100]mm and L2∈[10,140]mm;

[0055] S3. Import the original three-dimensional model of the waveguide cavity into the finite element analysis software for parametric scanning analysis, obtain the finite element analysis results under some parameter value combinations, and export the electric field intensity E of the waveguide cavity at the quartz tube under different combinations of parameter values ​​to be optimized (a total of 70 groups), as shown in Table 1.

[0056] Table 1. Electric field intensity of waveguide cavity at quartz tube under different combinations of parameters to be optimized.

[0057]

[0058]

[0059] S4. Analyze the influence of the interaction between the parameters to be optimized on the electric field strength, and obtain the contour plot of the response of the parameter values ​​to the electric field strength. Figure 10 ) and three-dimensional response surface plot ( Figure 11 The corresponding response patterns can be summarized as follows: under the combination of larger L1 and smaller L2 values, the analyzed E is larger; under the combination of smaller L1 and smaller L2 values, the analyzed E is smaller.

[0060] S5. Establish the functional relationship between the parameter to be optimized and the electric field intensity, and fit the multiple regression equation of the electric field intensity with respect to the parameter to be optimized as follows:

[0061] E = 0.001L2 4 -0.038L1 4 -0.007L1L2 3 +0.044L1 3 L2+0.013L1 2 L2 2 +9.3L1 3 +0.253L2 3 -0.025L1L2 2 -11L1 2 L2-44L2 2 -608L1 2 +896L1L2-20163L2+4783L1+402446

[0062] S6. Perform goodness-of-fit and significance tests on the multiple regression equations to obtain the analysis of variance table of the multiple regression equations, as shown in Table 2. In Table 2, R0... 2 R is the coefficient of determination, which measures the goodness of fit. 2 The closer the value is to 1, the better the regression equation fits the observed values. The R-squared value of the above regression equation... 2 The value is 0.9723, which proves that the regression equation has a good fit.

[0063] In Table 2, the p-value represents the minimum confidence level required to reject the hypothesis of the regression equation, determining whether the regression method is significant. Generally, to prove the significance of the regression equation, the p-value should be less than 0.05. The p-value of the above regression equation is less than 0.0001, proving that the equation is relatively significant. Using this multiple regression equation, the electric field strength E′ under different parameter combinations in Table 1 is calculated, which is called the predicted value. The difference between the predicted value E′ and the actual analysis result E in Table 1 is compared to obtain the prediction error. Figure 12 , Figure 12 The data points in the graph represent the predicted E′ of the multiple regression equation under different combinations of parameters to be optimized. The graph also contains a straight line with a slope of 1; the closer the data points are to this line, the smaller the prediction error of the regression equation. Figure 12 The positions of the vast majority of data points are close to a straight line, indicating that the overall prediction error of the above multiple regression equation is small and the fit is high.

[0064] Table 2. Analysis of Variance Table for Multiple Regression Equations

[0065]

[0066] S7. Given the value ranges of each parameter to be optimized, the value ranges of L1 and L2 change to [50, 200] mm and [5, 80] mm, respectively. Use the correct equation fitted in step S6 to maximize the electric field strength at the quartz tube as the optimization objective. Calculate the combination of L1 and L2 values ​​under the optimization objective as (7.9 mm, 110.8 mm), which is called the optimal parameter value combination. Record the electric field strength E″ = 299402 V / m corresponding to the optimal parameter value combination, which is called the optimal solution. It should be noted that the value ranges of each parameter to be optimized in this step are not limited by the value range determined in step S2, and can be different from or even exceed the value range determined in step S2.

[0067] S8. Based on the response pattern summarized in step S4, estimate the value ranges of each parameter to be optimized under the optimization objective: L1∈[0,20]mm, L2∈[90,200]mm, which are called the response ranges. It is determined that the optimal parameter value combinations calculated in step S7, L1=7.9mm, L2=110.8mm, are both within this response range, indicating that the optimal parameter value combinations are correct.

[0068] S9. Reconstruct the three-dimensional model of the waveguide cavity using the optimal parameter value combination; this is called the verification model.

[0069] S10. Perform finite element analysis on the test model and obtain the electric field strength obtained from the finite element analysis, which is called the test value.

[0070] S11. Set the inspection standard and calculate the difference between the optimal solution in step S7 and the inspection value in step S10. If the standard is met, it proves that the optimal solution in step S7 is calculated correctly and the optimization process ends. If the standard is not met, it proves that the optimal solution in step S7 is calculated incorrectly and the process jumps back to step S5 until the inspection standard in step S11 is met.

[0071] This invention combines finite element parametric scanning analysis technology with the concept of multivariate regression equation fitting to create a parameter optimization method for microwave plasma excitation devices. This method can establish a functional relationship between the structural size parameters of the waveguide cavity and the local electric field intensity, and achieve joint optimization of the size parameters and the local electric field intensity based on this functional relationship. Traditional methods can only optimize the waveguide cavity within a fixed size variation range. The optimization method of this invention can optimize the waveguide cavity within any size variation range, and no matter how many times the allowable size variation range of the waveguide cavity is changed, only one finite element parametric scanning analysis is needed. The optimization process is simple and efficient.

[0072] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A microwave plasma excitation device, characterized in that, The device includes a waveguide cavity comprising a first cavity, a second cavity, and a third cavity connected in sequence. The cross-sectional area of ​​the first cavity is smaller than that of the third cavity. The cross-sectional area of ​​the second cavity gradually increases along the direction from the first cavity to the third cavity. A quartz tube passes through the first cavity. An auxiliary excitation conductor is nested on the inner wall of the quartz tube at the junction with the first cavity. One end of the quartz tube is provided with a connecting sleeve, which is connected to a carrier gas heat dissipation module. The carrier gas heat dissipation module is also connected to the third cavity. A magnetron is provided inside the carrier gas heat dissipation module. The output shaft of the magnetron extends into the interior of the third cavity. The carrier gas heat dissipation module can input a heat dissipation medium for cooling the magnetron into the quartz tube.

2. The microwave plasma excitation device according to claim 1, characterized in that, An elastic clamping assembly is installed on the quartz tube on the other side of the first cavity opposite to the connecting sleeve. The elastic clamping assembly includes an installation tube and a clamp. The installation tube is located on the outside of the quartz tube, and the clamp is located between the quartz tube and the installation tube.

3. The microwave plasma excitation device according to claim 2, characterized in that, The elastic clamping assembly further includes clamping screws and fixing caps. The number of clamping screws is at least two, and the clamping screws are evenly distributed and installed on the mounting tube. The inner end of the clamping screw passes through the side wall of the mounting tube and is clamped against the clamp. The fixing cap is threaded to the end of the mounting tube away from the first cavity. The fixing cap is provided with a through hole communicating with the inside of the quartz tube.

4. The microwave plasma excitation device according to claim 3, characterized in that, The elastic clamping assembly also includes a base plate, which is welded and fixed to the waveguide cavity. The base plate is used to install and fix the microwave plasma excitation device in the corresponding application scenario. The end of the mounting tube near the first cavity is welded to the base plate.

5. A microwave plasma excitation device according to claim 3, characterized in that, The clamp consists of a telescopic part and mounting parts located at both ends of the telescopic part. The clamp is nested in the inner wall of the mounting tube, and the clamp is coaxially installed with the mounting tube through the mounting parts. The longitudinal section of the telescopic part is W-shaped, and the telescopic part has multiple evenly distributed strip openings along the circumference.

6. A microwave plasma excitation device according to claim 5, characterized in that, The telescopic part has an outwardly protruding convex surface in the middle, and the inner end of the clamping screw is directly opposite the convex surface in the middle of the telescopic part.

7. A microwave plasma excitation device according to claim 1, characterized in that, The carrier gas heat dissipation module includes a protective cover, a centrifugal fan, a flow guide shell, a three-way valve, and a connector. The protective cover is fixed on the third cavity, and the magnetron is located inside the protective cover. The protective cover is also connected to the centrifugal fan, and the air outlet of the centrifugal fan is aligned with the magnetron. The flow guide shell is fixed on the other side of the protective cover opposite to the centrifugal fan. The three-way valve has a first passage, a second passage, and a third passage. The three-way valve is connected to the flow guide shell through the first passage and to the connector through the second passage. The connector is connected to the connecting sleeve. Valves are respectively provided on the first passage and the third passage.

8. A microwave plasma excitation device according to claim 1, characterized in that, The auxiliary excitation conductor is spring-shaped and made of tungsten wire.

9. A method for optimizing the parameters of a microwave plasma excitation device, characterized in that, Includes the following steps: S1. Establish the original three-dimensional model of the waveguide cavity and analyze the factors affecting the microwave transmission efficiency of the waveguide cavity. The waveguide cavity includes a first cavity, a second cavity, and a third cavity that are connected in sequence. The first cavity passes through a quartz tube. Select several dimensional parameters of the first cavity, the second cavity, and the third cavity in the waveguide cavity as variables to participate in the structural optimization, which are called the parameters to be optimized. S2. Determine the value range of each parameter to be optimized based on the actual working conditions; S3. Import the original three-dimensional model of the waveguide cavity into the finite element analysis software for parametric scanning analysis to obtain the electric field intensity of the waveguide cavity at the quartz tube under different combinations of parameters to be optimized. S4. Analyze the influence of the interaction between the parameters to be optimized on the electric field strength, and summarize the corresponding response laws; S5. Establish the functional relationship between the parameters to be optimized and the electric field intensity, and fit the multiple regression equation of the electric field intensity relative to the parameters to be optimized. S6. Perform goodness-of-fit and significance tests on the multiple regression equation. If the goodness-of-fit and significance of the equation meet the requirements, it means that the equation is correctly fitted. Then, proceed to step S7. If the goodness-of-fit and significance of the equation do not meet the requirements, return to step S5 until the requirements for goodness-of-fit and significance are met. S7. Given the value range of each parameter to be optimized, use step S6 to fit the correct equation, with the optimization objective being to maximize the electric field strength at the quartz tube. Calculate the combination of values ​​of the parameters to be optimized under the optimization objective, which is called the optimal parameter value combination. Record the electric field strength corresponding to the optimal parameter value combination, which is called the optimal solution. S8. Based on the response pattern summarized in step S4, estimate the value range of each parameter to be optimized under the optimization objective, which is called the response range. Determine whether the optimal parameter value combination calculated in step S7 is within the response range. If the optimal parameter value combination is within the response range, it means that the optimal parameter value combination is correct, and jump to step S9. If the optimal parameter value combination is not within the response range, it means that the optimal parameter value combination is incorrect, and jump back to step S7 until the optimal parameter value combination is within the response range. S9. Reconstruct the three-dimensional model of the waveguide cavity using the optimal parameter value combination; this is called the verification model. S10. Perform finite element analysis on the test model and obtain the electric field strength obtained from the finite element analysis, which is called the test value. S11. Set the inspection standard and calculate the difference between the optimal solution in step S7 and the inspection value in step S10. If the standard is met, it proves that the optimal solution in step S7 is calculated correctly and the optimization process ends. If the standard is not met, it proves that the optimal solution in step S7 is calculated incorrectly and the process jumps back to step S5 until the inspection standard in step S11 is met.

10. The parameter optimization method for the microwave plasma excitation device according to claim 9, characterized in that, The length of the first cavity of the waveguide cavity is equal to the length of the third cavity, and the parameters to be optimized in step S1 are the length of the first cavity and the length of the second cavity.

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