A torch tube structure that can excite an atmospheric pressure microwave nitrogen plasma

Abstract

The application discloses a microwave plasma torch structure capable of generating atmospheric microwave nitrogen plasma, and provides necessary parameter conditions for generating stable microwave nitrogen plasma based on the structure. The structure mainly comprises a three-tube coaxial distributed MPT torch tube, a porous concentric support necessary for ensuring coaxiality of the inner tube and the middle tube, a coupling ring for coupling microwave energy, a thin and straight quartz tube for improving the shielding gas flow rate, and a non-metallic straight tube such as a quartz tube or a ceramic tube for changing the material of the inner tube and the middle tube. The application can excite an atmospheric microwave nitrogen plasma torch, and can change the plasma shape and the discharge position by regulating parameters. The thin and straight quartz tube outside the middle tube improves the heat dissipation efficiency, and greatly reduces the operation cost of the device compared with argon commonly used for exciting plasma.

Description

Technical Field

[0001] This invention belongs to the field of analytical technology such as atomic spectroscopy, mass spectrometry, and combined colorimetry. More specifically, it relates to a torch tube structure that can excite atmospheric pressure microwave nitrogen plasma, a mechanism for regulating plasma morphology and discharge position, and a thin, straight quartz tube structure to improve the heat dissipation efficiency of the plasma torch. Background Technology

[0002] A microwave plasma torch (MPT) is a device that uses microwaves to generate plasma, which can be used for elemental analysis. It was invented by Professor Jin Qinhan et al. in 1985, with corresponding patent application number CN 94205428.8. The torch is a three-metal coaxial tube structure with one open end. Microwave energy enters the torch through a coaxial cable via capacitive and conductive coupling. When the cavity length is an odd multiple of 1 / 4λ, microwaves form a standing wave within the cavity, and plasma forms at the open end of the torch. Increasing the microwave input power in combination with a dual-resonant torch (patent number CN105072793A) improves the torch's excitation capability and stability, thereby enhancing the MPT's ability to detect elements.

[0003] Oxygen shielding gas is tangentially introduced into the outer tube of the MPT, argon maintaining gas (working gas) is introduced into the middle tube, and argon carrier gas is introduced into the inner tube. Compared with nitrogen plasma, argon plasma has a higher operating cost due to its high price, making it unsuitable for the cost requirements of industrial production processes. However, although the existing MPT structure can excite nitrogen plasma at high microwave power, the generated nitrogen plasma suffers from problems such as single-point discharge, metal tube ablation, rapid metal heating, low heat dissipation efficiency, and unstable discharge after ignition.

[0004] Existing atmospheric pressure microwave nitrogen plasma sources used in analytical fields mainly include:

[0005] (1) Based on the waveguide structure, a quartz tube is embedded in the position of the strongest electric field inside the waveguide, and nitrogen plasma is obtained by electric field breakdown.

[0006] (2) Surface wave plasma devices, such as the Okamoto cavity, generate a ring-shaped plasma in the gap between the upper surface of the inner conductor and the lower surface of the outer conductor. The field strength is the largest on the metal surface of the inner conductor, and it is an exponentially decaying field in the direction perpendicular to the interface.

[0007] (3) Based on circular waveguide resonant cavity structures, such as the Beenakker resonant cavity, the electromagnetic field is represented by TM. 010 The mode distribution involves exciting columnar plasma within a quartz tube located on the axis of the resonant cavity.

[0008] (4) Based on the Hammer resonant cavity principle, a quartz tube is embedded inside the waveguide. The quartz tube is located at the position of the strongest magnetic field and excites a ring plasma.

[0009] (1) Most waveguide-based plasma light sources are difficult to form a central channel. They are not tolerant to liquid aerosols at low power. After the sample is introduced, the light source is easily unstable, which is not conducive to reducing the detection limit. Long-term high-power operation will increase the operating cost. At the same time, since there is no extra heat dissipation mechanism, it is necessary to increase the working gas flow rate to remove excess heat, which reduces the residence time of the sample in the plasma, which is not conducive to the full excitation of the sample and will also increase the operating cost.

[0010] (2) Plasma light sources based on surface wave structures have high power requirements, generally greater than 1000W; at the same time, since there is no extra heat dissipation mechanism, it is necessary to increase the working gas flow rate to remove excess heat, generally 15-20L / min, which will also increase operating costs.

[0011] (3) Based on the Beenakker resonant cavity principle, the maximum power is 500W, which limits the detection limit of difficult-to-excite elements. There is no central channel that is conducive to sample introduction, so the liquid aerosol tolerance is low.

[0012] (4) The light source based on the Hammer resonant cavity principle has a maximum power limit of 1000W that is not adjustable, and requires a large working gas flow rate, generally greater than 20L / min, which increases the operating cost. This structure is sensitive to the waveguide resonant cavity and torch tube flow channel structure, which can easily cause flameout and torch tube burning problems. Summary of the Invention

[0013] To obtain a stable nitrogen plasma excitation source, and addressing the problems of single-point discharge, metal ablation, and low heat dissipation efficiency in existing MPT structures for exciting nitrogen plasma, this invention proposes a torch structure capable of exciting atmospheric pressure microwave nitrogen plasma. Based on existing torch structures, by altering the open ends of the middle and inner tubes and the material properties of the inner and outer walls, the electromagnetic field distribution is changed. Utilizing the adhesion and bonding phenomena of plasma to non-metals (such as quartz), the plasma discharge region is shifted from the metal surface to the surface of the non-metallic medium, or floats on the metal surface. This solves the problems of unstable discharge, metal ablation, and rapid metal thermal conductivity caused by nitrogen plasma contacting metal, thereby achieving control over the plasma morphology and discharge region position, further exciting N2MPT, and reducing device operating costs.

[0014] This invention can be achieved through the following technical solutions:

[0015] A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma includes an inner tube, a middle tube, and an outer tube that are independent and coaxially assembled. A porous concentric support is provided to ensure the coaxiality between the middle and inner tubes and to form a dual-resonance MPT structure. A coupling ring is used to couple microwave energy into the coaxial resonant cavity, and a sliding piston is used for cavity tuning. The height of the coupling ring from the sliding piston is an odd multiple of 1 / 4λ. A shielding gas inlet is provided on the outer tube, and a sustaining gas inlet is provided at the bottom between the inner and middle tubes. The middle tube has a metal + non-metal splicing structure, with a metal section at the bottom and a non-metal section at the top.

[0016] A torch structure capable of generating atmospheric pressure microwave nitrogen plasma includes an inner tube, a middle tube, and an outer tube that are independently and coaxially assembled. A porous concentric support is provided to ensure the coaxiality between the middle and inner tubes and to form a dual-resonance MPT structure. A coupling ring is used to couple microwave energy into a coaxial resonant cavity, and a sliding piston is used for cavity tuning. The height of the coupling ring from the sliding piston is an odd multiple of 1 / 4λ. The outer tube has a shielding gas inlet, and the bottom between the inner and middle tubes has a sustaining gas inlet. The inner surface of the upper open end of the middle tube has a non-metallic section, while the rest of the middle tube has a metallic surface. The bottom of the inner tube has a carrier gas inlet.

[0017] A torch structure capable of generating atmospheric pressure microwave nitrogen plasma includes an inner tube, a middle tube, and an outer tube, which are independently and coaxially assembled. A porous concentric support is provided to ensure the coaxiality between the middle and inner tubes, forming a dual-resonance MPT structure. A coupling ring is used to couple microwave energy into a coaxial resonant cavity, and a sliding piston is used for cavity tuning. The height of the coupling ring from the sliding piston is an odd multiple of 1 / 4λ. A shielding gas inlet is provided on the outer tube, and a sustaining gas inlet is provided at the bottom between the inner and middle tubes. The outer surface of the open end of the middle tube is a non-metallic section, and the height of the non-metallic section on the outer surface of the middle tube is higher than that of the inner metal section. The inner tube is positioned higher than the inner metal wall port of the middle tube. A carrier gas inlet is provided at the bottom of the inner tube.

[0018] Furthermore, the inner tube is a torch structure made of non-metallic material; the bottom of the inner tube is provided with a carrier gas inlet.

[0019] Furthermore, the inner tube is a torch structure with a metal conductor.

[0020] Furthermore, the inner tube is a torch tube structure consisting of metal and non-metal components, with the lower section being a metal section and the upper section being a non-metal section; a carrier gas inlet is provided at the bottom of the inner tube.

[0021] Furthermore, a non-metallic tube is provided outside the upper section of the middle tube. This thin, straight non-metallic tube is fixed to the outer tube with a sealing gasket to form a four-tube coaxial MPT structure. The upper end of the non-metallic tube is higher than the outer tube. The depth of the sealing gasket installation position inside the torch tube is higher than the tangential inlet of the shielding gas. A carrier gas inlet is provided at the bottom of the inner tube.

[0022] Furthermore, the non-metallic section of the middle tube is approximately 3-5 mm long, and the upper end of the non-metallic section is flush with or slightly higher than the opening end of the outer tube, but the height is less than 0.5 mm.

[0023] Furthermore, the metal segment is located inside the resonant cavity, approximately 2–5 mm below the opening end face of the outer tube.

[0024] Furthermore, the porous concentric support is located between the middle tube and the inner tube, at a depth of 3-30 mm from the opening end face of the metal segment.

[0025] Compared with existing methods that use an external magnetic field to control atmospheric pressure microwave nitrogen plasma, this invention has the following advantages:

[0026] 1) At room temperature and pressure, it can generate more stable nitrogen plasma and can control the plasma discharge position and plasma morphology, and the performance control is more stable and reliable;

[0027] 2) Higher heat dissipation efficiency, achieving higher shielded airflow velocity at lower gas flow rates;

[0028] 3) Compared with building a complex external magnetic field device with high magnetic field strength, the technical solution provided by this invention has lower improvement costs, is simpler to implement, and is more flexible in adjustment;

[0029] 4) Compared to the external strengthening magnetic field device that needs to be introduced, the torch structure provided by the present invention is simpler and more compact, and can generate stable microwave nitrogen plasma without introducing an additional heat dissipation device. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the torch tube structure in specific embodiment 1 of the present invention, where the central tube is a metal + non-metal splicing structure;

[0031] Figure 2 This is a schematic diagram of a torch tube structure in a specific embodiment 2 of the present invention, where the inner surface material of the central tube is changed to a non-metallic material (such as quartz material).

[0032] Figure 3 This is a schematic diagram of a torch tube structure in a specific embodiment 3 of the present invention, in which the outer surface material of the central tube is changed to a non-metallic material (such as quartz material);

[0033] Figure 4This is a schematic diagram of a torch tube structure in specific embodiment 4 of the present invention, where the middle tube is a metal + non-metal splicing structure and the inner tube is replaced with a non-metallic material.

[0034] Figure 5 This is a schematic diagram of a torch tube structure in specific embodiment 5 of the present invention, where the middle tube is a metal + non-metal splicing structure and the inner tube is replaced with an inner conductor.

[0035] Figure 6 This is a schematic diagram of a torch structure in specific embodiment 6 of the present invention, where the inner tube is replaced with a metal + non-metal splicing structure based on the middle tube being a metal + non-metal splicing structure.

[0036] Figure 7 This is a schematic diagram of a four-tube coaxial MPT structure with a metal + non-metal splicing structure in embodiment 7 of the present invention, with a thin straight quartz tube added to the outside of the middle tube;

[0037] Figure 8 This is a schematic diagram of the N2MPT generator in this invention.

[0038] Figure 9 Figure (a) is a schematic diagram of the plating scheme of the non-metallic tube with metal coating in this invention. Figure (b) is a schematic diagram of the plating scheme of the metal tube + non-metal splicing structure. Figure (c) is a schematic diagram of the plating scheme of the non-metallic tube with metal coating on the outer surface and metal coating on the inner surface.

[0039] Figure 10 Figure (a) is a schematic diagram of the metal pipe grooving scheme in this invention, and Figure (b) is a schematic diagram of the inner grooving of the metal pipe opening end.

[0040] The main components shown in the above diagram are explained below:

[0041] 1: Plasma flame;

[0042] 2: Multi-hole concentric support is used to ensure the coaxiality between the middle tube and the inner tube and to form a double-resonance MPT structure;

[0043] 3: Inner tube, mostly made of metal, but in some cases it can be made of non-metallic material, such as quartz;

[0044] 4: The middle tube is mostly made of metal, such as brass;

[0045] 5: Outer tube, mostly made of metal, such as brass;

[0046] 6: Coupling ring, used to couple microwave energy into the coaxial resonant cavity;

[0047] 7: Sliding piston, used for tuning the coaxial resonant cavity;

[0048] 8: Shielding gas;

[0049] 9: Maintain air supply;

[0050] 10: Carrier gas;

[0051] 11: Non-metallic straight pipe

[0052] 12: Metallic inner conductor with a pointed structure;

[0053] 13: Slim, straight quartz tube, used to increase the airflow velocity during shielding;

[0054] 14: Rubber / silicone sealing gasket, used to fix the thin straight quartz tube between the middle tube and the outer tube.

[0055] 15: Non-metallic pipes

[0056] 16: Coating Detailed Implementation

[0057] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Specific Implementation Example 1

[0059] like Figure 1 As shown, a torch structure capable of generating atmospheric pressure microwave nitrogen plasma includes: an independent inner tube 3, a middle tube 4, and an outer tube 5, made of commonly used metal materials such as brass and stainless steel; a porous concentric support 2 to ensure the coaxiality between the middle tube and the inner tube and form a double-resonant MPT structure; a coupling ring 6 for coupling microwave energy into the coaxial resonant cavity; a sliding piston 7 for resonant cavity tuning; and three gases: a shielding gas 8, a sustaining gas 9, and a carrier gas 10. A non-metallic straight tube 11 is spliced ​​to the upper open end face of the metal middle tube 4. The non-metallic tube material should meet the requirements of high temperature resistance, dimensional stability, good wave transmission performance, chemical corrosion resistance, wear resistance, and aging resistance, and is preferably a quartz tube. Figure 1 (1 in the middle is a plasma flame).

[0060] The outer tube 5, the middle tube 4, and the inner tube 3 are coaxially assembled; the height of the coupling ring 6 from the sliding piston 7 is an odd multiple of 1 / 4λ, preferably 30.6mm;

[0061] The shielding gas 8 enters tangentially between the middle and outer tubes; the sustaining gas 9 enters between the middle and inner tubes through the middle tube and is the working gas used to ignite the plasma; the carrier gas 10 passes through the inner tube.

[0062] Possible manufacturing processes for the central tube 4 structure include, but are not limited to, the following:

[0063] A. Non-metallic tube coating process, for example in this embodiment Figure 9 As shown in Figure (a), the inner and outer surfaces of the lower section of a non-metallic tube (such as a quartz tube or a ceramic tube) can be plated with gold, leaving a 3-5mm section unplated on both the inner and outer surfaces, so as to achieve a metal + non-metal structure for the middle tube; in terms of assembly, a sealing ring / sealing gasket can be selected to fix the middle tube in the venting interface.

[0064] B. Use conductive adhesive, conductive glue, metal foil, or other conductive tapes to splice non-metallic tubes with metal tubes.

[0065] The non-metallic section of the middle tube is approximately 3-5 mm long, and is flush with or slightly higher than the opening end of the outer tube, but less than 0.5 mm.

[0066] The aforementioned middle tube metal section is located inside the resonant cavity, approximately 2–5 mm below the opening end face of the outer tube; for the 3 / 4λ resonant cavity structure, the resonant cavity length is approximately 85–91 mm, and the length is continuously adjustable;

[0067] The porous concentric support is located between the middle tube and the inner tube, at a depth of 3 to 30 mm from the opening end face of the metal section of the middle tube, preferably 10 to 15 mm.

[0068] The gas switching method for generating N2MPT involves igniting with argon and then switching to nitrogen. The gas flow conditions before switching are characterized by an oxygen flow rate of less than 0.8 SLM for the shielding gas and an argon sustaining gas flow rate of 1.2–1.8 SLM. After switching, the oxygen shielding gas flow rate can be less than 0.5 SLM, and the nitrogen sustaining gas flow rate can be 1.2–1.5 SLM. Regarding the power conditions, nitrogen plasma excitation after switching can be achieved when the actual coupling power is greater than 400W. After switching, the N2MPT volume can be increased by increasing the microwave power and the nitrogen sustaining gas flow rate.

[0069] There are two types of gas switching processes. The first type involves first opening the nitrogen holding gas at 1.5–1.8 smol, then closing the argon holding gas. The second type involves directly switching using a pneumatic valve. Based on these gas switching processes, the N2MPT generator is as follows: Figure 8 As shown, nitrogen and argon are controlled by pneumatic valves with opposite states. Simultaneously operating the switch can connect argon and nitrogen at the same time.

[0070] This structure utilizes the phenomenon of plasma adhering to and sticking to non-metallic walls (such as quartz) to guide the plasma discharge region from the metal surface to the non-metallic dielectric surface, or to float on the metal surface. Specific Implementation Example 2

[0072] like Figure 2As shown, another structural schematic diagram according to the present invention is given, wherein the inner surface material of the middle tube 4 of the torch tube is changed to a non-metallic material (such as quartz material) torch tube structure, and the inner surface of the upper open end of the metal middle tube 4 is a non-metallic straight tube 11, preferably a quartz tube.

[0073] Possible manufacturing processes for the central tube 4 structure include, but are not limited to, the following:

[0074] A. Non-metallic tube coating process, for example in this embodiment Figure 9 As shown in Figure (b), a metal layer can be plated on the outer surface of the non-metallic tube 15 (such as a quartz tube) (as shown in Figure 16), while a 3-5 mm gap is left on the inner surface of the non-metallic tube without a metal layer, in order to achieve...

[0075] The inner surface material of the current central tube 4 has been changed to a non-metallic material (such as quartz) to form a torch tube structure;

[0076] B. Employs a metal central tube with four open ends and internal slotted structure, such as... Figure 10 As shown in Figure (a), the depth of the groove inside the metal tube 4 is 3-5 mm, and the height of the non-metal tube is 4-6 mm, which is slightly higher than the groove depth of the tube.

[0077] This structure incorporates insulating and high-temperature resistant materials such as quartz or ceramics between the two discharge electrodes of the middle tube and the inner tube, forming a dielectric barrier discharge and creating a hollow ring-shaped plasma in the region between the inner tube and the insulating material. Specific Implementation Example 3

[0079] like Figure 3 As shown, another structural schematic diagram according to the present invention is given, wherein the outer surface material of the middle tube 4 of the torch tube is changed to a non-metallic material (such as quartz material) torch tube structure, the outer surface of the upper opening end face of the metal middle tube 4 is a non-metallic straight tube 11, and the height of the non-metallic section of the outer wall of the metal middle tube 4 should be higher than the height of the inner wall metal section. The non-metallic tube is preferably a quartz tube; the inner tube 3 is higher than the metal inner wall of the middle tube 4.

[0080] Possible manufacturing processes for the central tube 4 structure include, but are not limited to, the following:

[0081] A. Gold plating process for non-metallic tubes, for example in this embodiment. Figure 9 As shown in Figure (c), a metal layer can be plated on the inner surface of a non-metallic tube (such as a quartz tube), while a 3-5 mm gap is left on the outer surface of the non-metallic tube without a metal layer, so as to realize the torch tube structure in which the outer surface material of the middle tube 4 is changed to a non-metallic material.

[0082] B. Employs a metal central tube with four open ends and internal slotted structure, such as... Figure 10 As shown in Figure (b), the depth of the groove on the outside of the metal tube 4 is 3-5 mm, and the height of the non-metal tube is 4-6 mm, which is slightly higher than the groove depth of the tube.

[0083] This structure utilizes the phenomenon of plasma adhering to and sticking to non-metallic walls to guide the position of the plasma discharge area from the surface of the inner metal wall of the middle tube 4 to floating on the upper end face of the inner metal wall of the middle tube 4, and the plasma adheres to the non-metallic inner wall. Specific Implementation Example 4

[0085] like Figure 4 As shown, a schematic diagram of another structure according to the present invention is given, in which the material properties of the inner / outer wall of the middle tube 4 are changed as in embodiments 1 to 3, and the inner tube is replaced with a non-metallic tube torch tube structure. Specific Implementation Example 5

[0087] like Figure 5 As shown, another structural schematic diagram according to the present invention is given. While the material properties of the inner / outer walls of the middle tube 4 are changed as in embodiments 1-3, the inner tube is replaced with a torch structure of a metal conductor. In this case, only two gas channels are needed, namely shielding gas 8 and maintaining gas 9; the upper port of the inner conductor 12 is preferably a needle tip structure. Specific Implementation Example 6

[0089] like Figure 6 As shown, another structural schematic diagram according to the present invention patent is given. While the material properties of the inner / outer wall of the middle tube 4 are changed as in embodiments 1 to 3, the inner tube is replaced with a torch tube structure with metal and non-metal splicing.

[0090] Because the outer diameter of the inner tube is relatively small and the tube wall is relatively thin, the preferred processing scheme for the inner tube structure 3 is... Figure 9 The non-metallic tube shown in Figure (a) is plated with a metal layer, wherein at least the lower part of the outer surface of the inner tube 3 is plated with a metal layer. Specific Implementation Example 7

[0092] like Figure 7 As shown, another structural schematic diagram according to the present invention patent is given. The material properties of the inner / outer wall of the middle tube 4 are changed as in Examples 1 to 3. The material properties and structure of the inner tube are changed as in Examples 4 to 6. A thin straight non-metallic tube 13 is added to the middle tube and the quartz tube is fixed with a sealing gasket 14 to form a four-tube coaxial MPT structure.

[0093] The selection of the thin, straight, high-temperature resistant non-metallic tube material should meet the following requirements: high temperature resistance, dimensional stability, good wave transmission performance, chemical corrosion resistance, wear resistance, and aging resistance. Quartz tube is preferred. The upper end of the non-metallic tube 13 is preferably higher than that of the outer tube 5.

[0094] The depth of the sealing gasket installed inside the torch tube should be higher than the tangential inlet of the shielding gas, preferably 25-35 mm;

[0095] The selection of sealing gasket materials includes, but is not limited to, commonly used sealing ring materials such as rubber, silicone, and PTFE.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma, characterized in that, The system includes an inner tube, a middle tube, and an outer tube that are independent and coaxially assembled. A porous concentric support is used to ensure the coaxiality between the middle and inner tubes and to form a dual-resonance MPT structure. A coupling ring is used to couple microwave energy into the coaxial resonant cavity, and a sliding piston is used for cavity tuning. The height of the coupling ring from the sliding piston is an odd multiple of 1 / 4λ. A shielding gas inlet is provided on the outer tube, and a maintenance gas inlet is provided at the bottom between the inner and middle tubes. The middle tube has a metal and non-metal splicing structure, with a metal section at the bottom and a non-metal section at the top.

2. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma, characterized in that, The system includes an inner tube, a middle tube, and an outer tube that are independent and coaxially assembled. A porous concentric support is used to ensure the coaxiality between the middle and inner tubes and to form a dual-resonance MPT structure. A coupling ring is used to couple microwave energy into the coaxial resonant cavity. A sliding piston is used for resonant cavity tuning. The height of the coupling ring from the sliding piston is an odd multiple of 1 / 4λ. A shielding gas inlet is provided on the outer tube, and a sustaining gas inlet is provided at the bottom between the inner and middle tubes. The inner surface of the upper open end of the middle tube has a non-metallic section, while the rest of the middle tube's surface is metallic. A carrier gas inlet is provided at the bottom of the inner tube.

3. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma, characterized in that, The system comprises an inner tube, a middle tube, and an outer tube, which are independent and coaxially assembled. A porous concentric support is used to ensure the coaxiality between the middle and inner tubes and to form a dual-resonance MPT structure. A coupling ring is used to couple microwave energy into the coaxial resonant cavity. A sliding piston is used for resonant cavity tuning. The height of the coupling ring from the sliding piston is an odd multiple of 1 / 4λ. A shielding gas inlet is provided on the outer tube, and a sustaining gas inlet is provided at the bottom between the inner and middle tubes. The outer surface of the open end of the middle tube is a non-metallic section, and the height of this non-metallic section is higher than the height of the inner metal section. The inner tube is positioned higher than the inner metal wall port of the middle tube. A carrier gas inlet is provided at the bottom of the inner tube.

4. The torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to claim 1, characterized in that, The inner tube is a torch tube structure made of non-metallic material; the bottom of the inner tube is provided with a carrier gas inlet.

5. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to claim 1, characterized in that, The inner tube is a torch structure with a metallic conductor.

6. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to claim 1, characterized in that, The inner tube is a torch tube structure consisting of metal and non-metal components, with the lower section being a metal section and the upper section being a non-metal section; a carrier gas inlet is provided at the bottom of the inner tube.

7. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to claim 3, characterized in that, The upper section of the middle tube is provided with a non-metallic tube, which is fixed to the outer tube with a sealing gasket to form a four-tube coaxial MPT structure; the upper end of the non-metallic tube is higher than the outer tube; the depth of the sealing gasket installation position inside the torch tube is higher than the shielding gas tangential flow inlet; the bottom of the inner tube is provided with a carrier gas inlet.

8. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to any one of claims 1-7, characterized in that, The non-metallic section of the middle tube is 3-5mm long. The upper end of the non-metallic section is flush with or slightly higher than the opening end of the outer tube, but the height is less than 0.5mm.

9. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to any one of claims 1-7, characterized in that, The metal segment is located inside the resonant cavity, 2-5 mm below the opening end face of the outer tube.

10. A torch structure capable of exciting atmospheric pressure microwave nitrogen plasma according to any one of claims 1-7, characterized in that, The porous concentric support is located between the middle tube and the inner tube, at a depth of 3~30 mm from the opening end face of the metal section.

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