Method and device for auxiliary excitation of microwave plasma

Abstract

The invention discloses a method and a device for auxiliary excitation of microwave plasma, and relates to the technical field of plasma excitation. The method comprises the following steps: reducing the air pressure in a reaction cavity to 5-10kPa, and introducing pure CO2 gas; applying microwaves into the reaction cavity to excite initial plasmas; increasing the air pressure in the reaction cavity to normal pressure, and adjusting microwave frequency to match impedance change; when the air pressure in the reaction cavity is larger than or equal to 80 kPa, inert gas is injected into the reaction cavity, and a mixed gas environment is formed; increasing the concentration ratio of CO2 in the reaction cavity to be greater than or equal to 95%, and dynamically adjusting the microwave power through spectrum feedback; and when the CO2 concentration in the reaction cavity reaches 90%, microwave pulse modulation is activated, and plasma oscillation is inhibited. Through multi-parameter dynamic coupling control, stable excitation of the plasma can be achieved under the low-power condition, the reaction activity is remarkably improved, and the method is suitable for various industrial scenes such as microwave kilns and heating kilns.

Description

Technical Field

[0001] The present invention relates to the field of plasma excitation technology, and in particular to a method and device for assisting in exciting microwave plasma. Background Art

[0002] Microwave-assisted ignition (MII) technology significantly improves ignition efficiency by coupling microwave energy with spark plug plasma, becoming a key approach to breaking the lean burn limit. Its core mechanism lies in the selective deposition of microwave energy in the plasma, which triggers nonequilibrium ionization kinetics, thereby accelerating the initiation and propagation of the combustion chain reaction. Ikeda et al. demonstrated the engineering feasibility of this technology in the development of a plasma combustion engine. Experiments showed that microwave energy injection can improve combustion efficiency by over 18% (SAE 2009-1-1049). This technology stems from the mass difference between electrons and other particles in the plasma. Due to their extremely low mass, electrons efficiently absorb microwave energy, accelerating them to high energy states of 5-10 eV within picoseconds, forming a non-equilibrium plasma. These high-energy electrons, through impact ionization, dissociation, and excitation, generate a large number of reactive free radicals (such as O, H, and OH) within nanoseconds, significantly reducing the activation energy barrier for the ignition reaction. Hwang's team quantified the enhancement effect of this technology in constant-volume combustion experiments on acetylene-air mixtures (Combu Flame 2016, 167:86-96). Compared with conventional spark ignition, microwave-assisted ignition extended the lean burn limit from 0.6 to 0.5 equivalence ratio and increased the laminar flame speed by 43%. Notably, the microwave enhancement effect decayed exponentially when the ambient pressure exceeded 0.5 MPa, attributed to the reduced energy deposition efficiency caused by the shortened electron mean free path under high pressure. For the methane-air system, Wolk et al. used high-speed schlieren imaging to reveal the microscopic mechanism of microwave-assisted ignition (Combu Flame 2013, 160:1225-1234). Their research demonstrated that microwave energy injection not only enhances free radical production through electron collisions (chemical kinetic enhancement) but also induces Kelvin-Helmholtz instabilities in the plasma, generating microscale turbulent wrinkles in the flame front and effectively increasing the reaction surface area. The synergistic effect of these two factors increases the initial temperature generation rate of the fire core by 2.1 times, successfully extending the lean combustion limit of methane to an equivalence ratio of 0.55.

[0003] Current research confirms that microwave-assisted ignition technology has a universally effective enhancement effect on the lean combustion of active hydrocarbon fuels such as acetylene and methane. However, the environmental impact of CO2 contamination remains. Based on this, Heeseon Kim et al. demonstrated that microwave plasma can effectively promote the decomposition of the inert gas CO2, and that CO2 ignition can be achieved with the help of microwave-assisted excitation. Furthermore, Spencer and Gallimore used a 2.45 GHz, 2 kW magnetron, a straight quartz tube with silica gel cooling, and a CO2 / Ar mixture to maintain a stable plasma. They achieved a CO2 conversion efficiency of 10% and an energy efficiency of 20% at a specific energy input (SEI) of 1.5 eV / molecule. However, the high dependence on an Ar auxiliary gas content of >70% to maintain plasma stability led to low CO2 conversion efficiency, resulting in high costs and resource constraints that hinder large-scale application. Furthermore, the spatial distribution of the plasma destabilizes under turbulent conditions, causing the CO2 dissociation efficiency to drop to 35% of the atmospheric pressure level at 1 MPa.

[0004] Therefore, it is an urgent problem for those skilled in the art to propose a method and device for assisting in exciting microwave plasma to solve the difficulties existing in the prior art. Summary of the Invention

[0005] In view of this, the present invention provides a method and device for assisting the excitation of microwave plasma. Through multi-parameter dynamic coupling control, it can achieve stable plasma excitation under low-power conditions and significantly improve reaction activity. It is suitable for industrial scenarios such as microwave kiln heating kilns.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for assisting the excitation of microwave plasma, which achieves low-power excitation of microwave plasma of high ionization energy gas by dynamically adjusting gas pressure and gas composition under the action of microwaves, comprising:

[0008] S1. Reduce the pressure in the reaction chamber to 5-10 kPa and introduce pure CO2 gas;

[0009] S2, applying microwaves to the reaction chamber to excite initial plasma;

[0010] S3, gradually increasing the pressure in the reaction chamber to normal pressure at a rate of 0.5-2 kPa / s, while adjusting the microwave frequency to match the impedance change;

[0011] S4. When the pressure in the reaction chamber is ≥80 kPa, inject inert gas He or Ar into the reaction chamber to form a He / CO2 or Ar / CO2 mixed gas environment;

[0012] S5. Increase the CO2 concentration in the reaction chamber to ≥95% at a rate of 0.5% / s-2% / s, and dynamically adjust the microwave power through spectral feedback with an adjustment range of ±10%;

[0013] S6. When the CO2 concentration in the reaction chamber reaches 90%, microwave pulse modulation is activated to suppress plasma oscillation.

[0014] In the above method, optionally, in S1 , the pressure in the reaction chamber is reduced by vacuuming.

[0015] In the above method, optionally, the microwave power applied in S2 is 1.8 kW to 2.2 kW and the frequency is 2.40 GHz to 2.48 GHz.

[0016] In the above method, optionally, in S3, the microwave frequency matching impedance change is adjusted to satisfy the following relationship:

[0017]

[0018] Where Δf is the frequency offset in MHz; ΔP is the pressure change in kPa; ΔP0 is the initial pressure in kPa; and k is the adjustment coefficient in the range of 0.05-0.15 in MHz.

[0019] In the above method, optionally, in the mixed gas environment formed in S4, the mixing volume ratio of the inert gas to CO2 is 4:1 to 2:1.

[0020] In the above method, optionally, when the inert gas is injected into the reaction chamber in S4, the pressure difference between the inert gas channel and the CO2 channel is maintained at ≥ 20 kPa, and the gas replacement rate is:

[0021] Q CO2 =Q total ·(1-e -t / τ )

[0022] Among them, Q total is the total flow rate, the value range is 5-15, the unit is L / min; τ is the time constant, the value range is 30-60, the unit is s; t is the replacement time, the unit is s.

[0023] In the above method, optionally, in S6, the microwave pulse modulation frequency is 1-10 kHz, and the duty cycle is 40-80%.

[0024] A device for assisting in exciting microwave plasma, performing any of the above methods for assisting in exciting microwave plasma, comprising:

[0025] Reaction chamber, microwave source, waveguide transmission line, ceramic manifold, microwave resonant cavity, ventilation system, dual-channel connector, buffer chamber and air pressure-gas coordinated control module;

[0026] The ventilation system is connected to the dual-channel connector, buffer chamber and reaction chamber in sequence. When the pressure in the reaction chamber drops to 5-10kPa, pure CO2 gas is introduced. When the pressure in the reaction chamber is ≥80kPa, inert gas He or Ar is injected into the reaction chamber.

[0027] The microwave source is connected to the reaction cavity through a waveguide transmission line, and microwaves are applied to the reaction cavity to excite the initial plasma;

[0028] The microwave resonant cavity, the ceramic diverter plate and the air pressure-gas coordinated control module are located in the reaction cavity.

[0029] The above device can be optionally provided with a microwave resonant cavity, the inner wall of which is coated with an Al2O3-Y2O3 composite coating with a coating thickness of 50-100 μm and a dielectric constant temperature coefficient value range of 2×10 -4 / ℃ to 4×10 -4 / ℃;

[0030] The air pressure-gas coordinated control module includes: a capacitive vacuum gauge with a range of 0.1Pa-200kPa and an accuracy of ≤0.5% FS; a spectral feedback unit equipped with a 519nm narrowband filter and a photomultiplier tube;

[0031] Dual-channel connector, flow resolution 0.1sccm;

[0032] Microwave automatic tuner, matching time ≤ 50ms, voltage standing wave ratio VSWR ≤ 1.3;

[0033] The buffer tank is connected to the dual-channel connector, and the volume of the buffer tank is 8-15% of the volume of the reaction chamber;

[0034] A porous ceramic diverter plate with a porosity of 60-80% is set inside the buffer tank.

[0035] It can be seen from the above technical solution that compared with the prior art, the present invention provides a method and device for assisting the excitation of microwave plasma, which has the following beneficial effects: the present invention realizes stable excitation of CO2 plasma at low power through the coordinated control of low gas pressure regulation and gas composition transition; the CO2 excitation power is reduced from 4.2kW ​​to below 2kW (a decrease of 56%), and the steady-state maintenance power is only 2kW (fluctuation of ±7.5%), saving 32% energy; the stability is significantly improved, and the tolerance to gas pressure fluctuations reaches ±5kPa; the industrial applicability is enhanced, supporting gas circulation recovery, and the electrodeless design avoids metal contamination; it has strong scalability and can be adapted to Ar / CO2 mixed systems, N2 / CO2 and other mixed gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0037] Figure 1 A flow chart of a method for assisting in exciting microwave plasma provided by the present invention;

[0038] Figure 2 A structural diagram of a device for assisting in exciting microwave plasma provided by the present invention; DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] In this application, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or apparatus comprising the element.

[0041] Reference Figure 1 As shown, the present invention discloses a method for assisting the excitation of microwave plasma, which realizes low-power excitation of microwave plasma of high ionization energy gas by dynamically adjusting gas pressure and gas composition under the action of microwaves, including:

[0042] S1. Reduce the pressure in the reaction chamber to 5-10 kPa and introduce pure CO2 gas;

[0043] S2, applying microwaves to the reaction chamber to excite initial plasma;

[0044] S3, gradually increasing the pressure in the reaction chamber to normal pressure at a rate of 0.5-2 kPa / s, while adjusting the microwave frequency to match the impedance change;

[0045] S4. When the pressure in the reaction chamber is ≥80 kPa, inject inert gas He or Ar into the reaction chamber to form a He / CO2 or Ar / CO2 mixed gas environment; utilize the Penning effect of He to reduce the actual ionization energy of CO2;

[0046] S5. Increase the CO2 concentration in the reaction chamber to ≥95% at a rate of 0.5% / s-2% / s. Dynamically adjust the microwave power through spectral feedback (519nm CO molecular spectral line intensity) with an adjustment range of ±10%;

[0047] S6. When the CO2 concentration in the reaction chamber reaches 90%, microwave pulse modulation is activated to suppress plasma oscillation.

[0048] Furthermore, in S1, the reaction chamber is evacuated to 5-10 kPa (the CO2 breakdown field strength is reduced to 2.8-3.5 kV / cm).

[0049] Furthermore, the microwave power applied in S2 is 1.8kW-2.2kW and the frequency is 2.40GHz-2.48GHz, and the low pressure environment is used to reduce the breakdown threshold and generate initial plasma.

[0050] Furthermore, the microwave frequency matching impedance change is adjusted in S3 to satisfy the following relationship:

[0051]

[0052] Where Δf is the frequency offset in MHz; ΔP is the pressure change in kPa; ΔP0 is the initial pressure in kPa; and k is the adjustment coefficient in the range of 0.05-0.15 in MHz.

[0053] Furthermore, in the mixed gas environment formed in S4, the mixing volume ratio of the inert gas to CO2 is 4:1 to 2:1.

[0054] Furthermore, when the inert gas is injected into the reaction chamber in S4, the pressure difference between the inert gas channel and the CO2 channel is maintained at ≥20 kPa, and the gas replacement rate is:

[0055] Q CO2 =Q total ·(1-e -t / τ )

[0056] Among them, Q totalis the total flow rate, the value range is 5-15, the unit is L / min; τ is the time constant, the value range is 30-60, the unit is s; t is the replacement time, the unit is s.

[0057] Furthermore, the microwave pulse modulation frequency in S6 is 1-10 kHz, and the duty cycle is 40-80%.

[0058] Reference Figure 2 As shown, a device for assisting in exciting microwave plasma, performing any of the above methods for assisting in exciting microwave plasma, comprising:

[0059] Reaction chamber, microwave source, waveguide transmission line, ceramic manifold, microwave resonant cavity, ventilation system, dual-channel connector, buffer chamber and air pressure-gas coordinated control module;

[0060] The ventilation system is connected to the dual-channel connector, buffer chamber and reaction chamber in sequence. When the pressure in the reaction chamber drops to 5-10kPa, pure CO2 gas is introduced. When the pressure in the reaction chamber is ≥80kPa, inert gas He or Ar is injected into the reaction chamber.

[0061] The microwave source is connected to the reaction cavity through a waveguide transmission line, and microwaves are applied to the reaction cavity to excite the initial plasma;

[0062] The microwave resonant cavity, ceramic manifold and pressure-gas coordinated control module are located in the reaction cavity;

[0063] Furthermore, the inner wall of the microwave resonant cavity is coated with an Al2O3-Y2O3 composite coating with a coating thickness of 50-100 μm and a dielectric constant temperature coefficient value range of 2×10 -4 / ℃ to 4×10 -4 / ℃;

[0064] The air pressure-gas coordinated control module includes: a capacitive vacuum gauge with a range of 0.1Pa-200kPa and an accuracy of ≤0.5% FS; a spectral feedback unit equipped with a 519nm narrowband filter and a photomultiplier tube;

[0065] Dual-channel connector, flow resolution 0.1sccm;

[0066] Microwave automatic tuner, matching time ≤ 50ms, voltage standing wave ratio VSWR ≤ 1.3;

[0067] The buffer tank is connected to the dual-channel connector, and the volume of the buffer tank is 8-15% of the volume of the reaction chamber;

[0068] A porous ceramic diverter plate with a porosity of 60-80% is set inside the buffer tank.

[0069] In specific embodiment 1, combined Figure 2 In the microwave plasma excitation apparatus shown, during the low-pressure plasma ignition phase, the vacuum pump was activated to evacuate the reaction chamber to an absolute pressure of 5 kPa. Pure CO₂ gas was introduced via a mass flow controller at a flow rate of 8 L / min for 30 seconds until the gas purity in the chamber reached >99.5% (confirmed by online monitoring with a mass spectrometer). The microwave source was activated with an output power of 1.5 kW and a frequency of 2.45 GHz. The microwaves were transmitted via a waveguide to the Al₂O₃-Y₂O₃ composite-coated resonant cavity, where they excited a purple plume of plasma. The plasma core temperature was measured by an infrared thermal imager at 785±15°C. Pressure gradient loading and microwave dynamic matching were employed by injecting CO₂ into the cavity at a rate of 1.5 kPa / s, increasing the pressure gradient to ambient pressure (101 kPa). When the pressure reached 50 kPa, the frequency was adjusted to 2.46 GHz. Upon reaching ambient pressure, the frequency was adjusted back to 2.44 GHz. The voltage standing wave ratio (VSWR) decreased to 1.15, as confirmed by a vector network analyzer. Dynamic replacement control of gas components When the gas pressure is stable at 80 kPa, the dual-channel gas supply system is started: N2 is injected into channel I at a flow rate of 10 L / min; CO2 is injected into channel II at a flow rate of 5 L / min to form a mixed gas of N2:CO2=2:1; the pressure difference between the channels is maintained at 20 kPa by the pressure differential controller, and the gas replacement rate satisfies Q_CO2=15×(1-e -t / 40 )(t is the time variable). High-purity phase maintenance and pulse energy regulation When the mass spectrometer detects a CO2 concentration of 92%, the microwave pulse modulation module is activated: pulse frequency 5kHz, duty cycle 60% (pulse width 120μs); the spectral feedback unit monitors the 519nm characteristic spectral line intensity and dynamically adjusts the power in the range of 1.38-1.62kW (±8%). After 8 hours of continuous operation, the plasma temperature stabilized at 3980±30K (measured by thermocouple), and gas chromatography analysis showed that the CO2 decomposition rate reached 14.8%.

[0070] In specific embodiment 2, the Ar / CO2 system is industrial-grade and highly efficient. The reaction chamber is pre-evacuated to 6-10 kPa, CO2 is introduced to a pressure of 10 kPa, and a 1.8 kW @ 2.48 GHz microwave is applied to excite the plasma. The initial electron density is measured by Langmuir probe to be 2.1 × 10 15 m -3. Rapid pressure increase and flow field cooperate to increase the pressure to normal pressure at a rate of 2kPa / s, and synchronously adjust the frequency according to Δf=0.15×(P-10) / 10 (P is the real-time gas pressure). When the gas pressure reaches 80kPa, it is switched to Ar / CO2=3:1 mixed gas, and the gas distribution uniformity is greater than 92% (verified by PIV flow field test) through the porous ceramic diverter plate (406) (porosity 70%, average pore size 50μm). In the energy efficiency optimization stage, the CO2 proportion is increased to 95% at a rate of 2vol% / s. When the 519nm spectral intensity decreases by 5%, the power compensation mechanism is triggered to increase the power to 2.2kW. After the CO2 purity reaches 95%, 10kHz pulse modulation (duty cycle 40%) is enabled. At this time: the instantaneous peak power of the microwave is 2.4kW, and the average power consumption is 1.44kW; the mass spectrometry detection CO2 decomposition energy efficiency reaches 25.3% (an increase of 10.5 percentage points compared with Example 1).

[0071] In specific Example 3, the extreme operating conditions of the pure CO2 system were verified; the reaction chamber was evacuated to 0.1kPa (near vacuum), CO2 was introduced to 10kPa, and a 2.0kW@2.48GHz microwave-excited plasma was applied, shortening the breakdown delay time to 120ms (1 / 3 of that in Example 1). High-pressure tolerance verification maintained CO2 purity >99% and gradually increased the gas pressure to 200kPa: when the pressure was >150kPa, the adaptive frequency sweep mode was activated (2.40-2.48GHz step 10MHz); under the 200kPa operating condition, the CO2 decomposition rate was still measured at 9.7%, and the power efficiency was maintained at 18.2%.

[0072] In specific embodiment 4, a turbulent flow enhanced mass transfer system (industrial kiln integrated application) is used; the method is implemented in a microwave high-temperature kiln: a cyclone (407) is installed at the gas inlet in a swirl field coupling design to make the tangential velocity of the He / CO2 mixed gas reach 15m / s (Reynolds number Re=8500), and the formation of a stable Taylor vortex structure is confirmed by PIV testing. Anti-disturbance dynamic adjustment When the cavity pressure fluctuates by ±5kPa, the microwave frequency adjustment coefficient k is dynamically adjusted to 0.12MHz / kPa through feedback from a capacitive vacuum gauge (402), so that the electron density in the plasma core region is stabilized at (1.2±0.3)×101 6 m -3 (Microwave interferometry measurement). Industrial performance verification compared with traditional methods: Under the same gas flow rate, the flame propagation speed increased from 12.3m / s to 17.2m / s (+39.8%); NOx emission concentration increased from 286mg / Nm 3 Reduced to 108mg / Nm 3 (-62.2%); the density of kiln products increased from 92.1% to 94.4%.

[0073] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple. For relevant parts, refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without expending creative work.

[0074] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for assisting the excitation of microwave plasma, characterized in that: Under the action of microwaves, microwave plasma with high ionization energy gas is achieved by dynamically adjusting gas pressure and gas composition, including: S1. Reduce the pressure in the reaction chamber to 5-10 kPa and introduce pure CO2 gas; S2, applying microwaves to the reaction chamber to excite initial plasma; S3, gradually increasing the pressure in the reaction chamber to normal pressure at a rate of 0.5-2 kPa / s, while adjusting the microwave frequency to match the impedance change; S4. When the pressure in the reaction chamber is ≥80 kPa, inject inert gas He or Ar into the reaction chamber to form a He / CO2 or Ar / CO2 mixed gas environment; S5. Increase the CO2 concentration in the reaction chamber to ≥95% at a rate of 0.5% / s-2% / s, and dynamically adjust the microwave power through spectral feedback with an adjustment range of ±10%; S6. When the CO2 concentration in the reaction chamber reaches 90%, microwave pulse modulation is activated to suppress plasma oscillation.

2. The method for assisting in exciting microwave plasma according to claim 1, wherein: In S1, the pressure in the reaction chamber is reduced by vacuuming.

3. The method for assisting in exciting microwave plasma according to claim 1, characterized in that: The microwave power applied in S2 is 1.8kW-2.2kW, and the frequency is 2.40GHz-2.48GHz.

4. The method for assisting in exciting microwave plasma according to claim 1, wherein: The microwave frequency matching impedance change in S3 is adjusted to satisfy the following relationship: Where Δf is the frequency offset in MHz; ΔP is the pressure change in kPa; ΔP0 is the initial pressure in kPa; and k is the adjustment coefficient in the range of 0.05-0.15 in MHz.

5. The method for assisting in exciting microwave plasma according to claim 1, characterized in that: In the mixed gas environment formed in S4, the volume ratio of the inert gas to CO2 is 4:1 to 2:

1.

6. The method for assisting in exciting microwave plasma according to claim 1, characterized in that: When inert gas is injected into the reaction chamber in S4, the pressure difference between the inert gas channel and the CO2 channel is maintained at ≥20kPa, and the gas replacement rate is: Q CO2 =Q total ·(1-e -t / τ ) Among them, Q total is the total flow rate, the value range is 5-15, the unit is L / min; τ is the time constant, the value range is 30-60, the unit is s; t is the replacement time, the unit is s.

7. The method for assisting in exciting microwave plasma according to claim 1, characterized in that: The microwave pulse modulation frequency in S6 is 1-10kHz and the duty cycle is 40-80%.

8. A device for assisting in exciting a microwave plasma, comprising: Reaction chamber, microwave source, waveguide transmission line, ceramic manifold, microwave resonant cavity, ventilation system, dual-channel connector, buffer chamber and air pressure-gas coordinated control module; The ventilation system is connected to the dual-channel connector, buffer chamber and reaction chamber in sequence. When the pressure in the reaction chamber drops to 5-10kPa, pure CO2 gas is introduced. When the pressure in the reaction chamber is ≥80kPa, inert gas He or Ar is injected into the reaction chamber. The microwave source is connected to the reaction cavity through a waveguide transmission line, and microwaves are applied to the reaction cavity to excite the initial plasma; The microwave resonant cavity, the ceramic diverter plate and the air pressure-gas coordinated control module are located in the reaction cavity.

9. The device for assisting in exciting microwave plasma according to claim 8, characterized in that: The inner wall of the microwave resonant cavity is coated with Al2O3-Y2O3 composite coating with a coating thickness of 50-100μm and a dielectric constant temperature coefficient value range of 2×10 -4 / ℃ to 4×10 -4 / ℃; The air pressure-gas coordinated control module includes: a capacitive vacuum gauge with a measuring range of 0.1Pa-200kPa and an accuracy of ≤0.5% FS; Spectral feedback unit, equipped with 519nm narrowband filter and photomultiplier tube; Dual-channel connector, flow resolution 0.1sccm; Microwave automatic tuner, matching time ≤ 50ms, voltage standing wave ratio VSWR ≤ 1.3; The buffer tank is connected to the dual-channel connector, and the volume of the buffer tank is 8-15% of the volume of the reaction chamber; A porous ceramic diverter plate with a porosity of 60-80% is set inside the buffer tank.

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