CN110708853B - Waveguide feed-in type microwave coupling plasma generating device - Google Patents
Waveguide feed-in type microwave coupling plasma generating device Download PDFInfo
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- CN110708853B CN110708853B CN201910982248.5A CN201910982248A CN110708853B CN 110708853 B CN110708853 B CN 110708853B CN 201910982248 A CN201910982248 A CN 201910982248A CN 110708853 B CN110708853 B CN 110708853B
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- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
- H05H1/461—Microwave discharges
- H05H1/4622—Microwave discharges using waveguides
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Abstract
The invention relates to a waveguide feed-in type microwave coupling plasma generating device, belonging to the technical field of microwave energy application. The waveguide-coaxial resonant cavity consists of a waveguide part and a coaxial resonant cavity part; the waveguide part comprises a standard waveguide (2), a waveguide-coaxial conversion cone (11), a short-circuit piston (12) and an adjusting rod (13); the coaxial resonant cavity part comprises an outer conductor (1), an inner conductor (3), a middle pipe (4), an inner pipe (5), a sample pipe (6), a sample inlet (7), an inner layer gas inlet (8), a middle layer gas inlet (9), an outer layer gas inlet (10), a cooling ring (14) and an impedance matching cone (15). The device of the invention has no power input limit of the radio frequency coaxial connector and the microwave antenna, and has the advantages of large feed-in power, long stable working time, high microwave energy coupling efficiency and the like.
Description
Technical Field
The invention belongs to the technical field of Microwave energy application, and particularly relates to a waveguide feed-in type Microwave Coupled Plasma generator, in particular to a Microwave Coupled Plasma (MCP for short) generator suitable for power input of kilowatt level or above.
Background
The microwave resonant cavity for excitation light source of Microwave Plasma Torch (MPT) spectrometer is a resonant cavity based on that the inner core of radio frequency coaxial connector is connected with microwave antenna, and the microwave energy is fed into the resonant cavity via the microwave antenna, for example, CN 94205428.8. The resonant cavity adopts an L16-KF type radio frequency coaxial connector, and the average power of the long-time stable and reliable work is only below 200W. Further, as in patent CN 106304602A, the highest average power of stable and reliable operation for a long time is not even about 1000 w when L29-KF type rf coaxial connector is used to connect microwave antenna. When a microwave antenna is connected by using a radio frequency coaxial connector of the type L16-KF or L29-KF, the microwave power fed into the cavity is limited, and there are also two problems:
1) when the feed-in power is too high, the polytetrafluoroethylene supporting piece supporting the inner core of the coaxial connector is deformed due to the heating of the antenna, so that the position of the antenna deviates from the normal size, the local microwave antenna is further overheated, and the microwave antenna is burnt finally;
2) when the feed power is too high, partial discharge sometimes occurs near the antenna before the end face of the resonant cavity, and the microwave antenna is more easily burnt by the partial discharge, so that the resonant cavity cannot work normally.
In addition, when the antenna feeds microwave energy, a radio frequency coaxial connector and a microwave antenna need to be installed on a hole formed in the side surface of the outer conductor of the resonant cavity. The local opening of the side surface of the outer conductor can destroy the uniform distribution of the microwave electromagnetic field of the whole resonant cavity, and especially when the opening is formed at the position with the maximum electric field intensity, the microwave energy coupling efficiency of the coaxial resonant cavity can be reduced.
In the document CN103269561A, a waveguide direct-fed microwave plasma torch device is proposed, in which a waveguide portion employs a graded waveguide and a narrow-edge compression waveguide to transmit microwave energy from a standard waveguide to a coaxial resonant cavity. Both the graded waveguide and the narrow-edge compression waveguide belong to non-standard parts and need special processing and manufacturing.
Disclosure of Invention
The invention aims to overcome the defects in the background technology and provide a waveguide feed-in type MCP generating device, which utilizes a standard waveguide and a waveguide-coaxial conversion cone to directly feed microwave energy into a coaxial resonant cavity.
The specific technical scheme of the invention is as follows:
a waveguide feed-in type microwave coupling plasma generating device is composed of a waveguide part and a coaxial resonant cavity part; the waveguide part comprises a standard waveguide 2, a waveguide-coaxial conversion cone 11, a short-circuit piston 12 and an adjusting rod 13; the coaxial resonant cavity part comprises an outer conductor 1, an inner conductor 3, a middle tube 4, an inner tube 5, a sample tube 6, a sample inlet 7, an inner layer gas inlet 8, a middle layer gas inlet 9, an outer layer gas inlet 10, a cooling ring 14 and an impedance matching cone 15;
the first port of the standard waveguide 2 is connected with a microwave generation system, an outer conductor 1 and a waveguide-coaxial conversion cone 11 of a coaxial resonant cavity are vertically arranged in the length direction between the first port and the second port of the standard waveguide 2, the central axis of the cone is superposed with the central axis of the outer conductor 1, and the waveguide-coaxial conversion cone 11 is a hollow circular truncated cone or a hollow trapezoid; the second port of the standard waveguide 2 is closed by a short-circuit piston 12, and the short-circuit piston 12 is connected with an adjusting rod 13;
the outer conductor 1, the inner conductor 3, the middle tube 4, the inner tube 5 and the sample tube 6 are sequentially nested and coaxial from outside to inside, the sample tube 6, the inner tube 5, the middle tube 4 and the inner conductor 3 are flush at the outlet end face of the formed resonant cavity, the sample tube 6, the inner tube 5, the middle tube 4, the inner conductor 3 and the outer conductor 1 form a microwave resonant cavity of a nested coaxial structure, and the characteristic impedance range of the resonant cavity is 50-80 ohms;
the outer conductor 1 is between the first port and the second port of the standard waveguide 2, and perpendicularly intersects with the length direction of the standard waveguide 2, when the waveguide-coaxial conversion cone 11 is a single-side cone, the height of the outer conductor 1 is (2n +1)/4 times of the wavelength of the used microwave, wherein n is 0, 1, 2 or 3; when the waveguide-coaxial conversion cone 11 is a bilateral cone, the outer conductor 1 is divided into an upper part and a lower part, the bottom surface of the upper half part of the outer conductor 1 is coincided with the lower bottom surface of the upper cone of the waveguide-coaxial conversion cone 11, the top surface of the lower half part of the outer conductor 1 is coincided with the upper bottom surface of the lower cone of the waveguide-coaxial conversion cone 11, the upper cone and the lower cone of the waveguide-coaxial conversion cone 11 are two hollow round tables which are vertically symmetrical along the central axis of the standard waveguide 2, the sum of the heights is less than the height of the standard waveguide 2, the distance between the lowest surface of the inner cavity of the outer conductor 1 and the central axis of the standard waveguide 2 is 1/4 times of the used microwave wavelength, the distance between the lowest surface of the inner cavity of the outer conductor 1 and the highest surface of the inner cavity is (2n +1)/4 times of the used microwave wavelength, wherein n is 1, 2 or 3, and the outer conductor 1 is, the material is preferably metal with resistivity less than 30n omega m;
when the waveguide-coaxial conversion cone 11 is a single-side cone, the inner conductor 3 is directly fastened with the bottom of the standard waveguide 2 through the waveguide-coaxial conversion cone 11; when the waveguide-coaxial conversion cone 11 is a double-sided cone, the inner conductor 3 is fastened and sealed with the bottom of the outer conductor 1; the inner conductor 3 is a hollow cylinder, and the material thereof is preferably metal with resistivity less than 30n omega m;
the outer wall of the middle pipe 4 and the inner conductor 3 are closed at the lower part of the inner conductor 3 to form an annular gap for laminar flow of the outer layer with the closed bottom end and the open top end face; the middle tube 4 is a hollow cylinder, and the material of the middle tube is preferably metal with the resistivity less than 30n omega m.
The outer wall of the inner pipe 5 and the middle pipe 4 are sealed at the lower part of the middle pipe 4 to form an annular gap with a closed bottom end and an open top end face for laminar flow of middle-layer gas; the inner tube 5 is a hollow cylindrical body, and is preferably made of a metal having a resistivity of less than 30n Ω · m.
The outer wall of the sample tube 6 and the inner tube 5 are closed at the lower part of the inner tube 5 to form an annular gap for laminar flow of inner layer gas with a closed bottom end and an open top end face; the sample tube 6 is a cylinder with a hollow inner part, and the material of the sample tube can be metal, and can also be nonmetal such as ceramic, graphite, quartz and the like.
The sample inlet 7 is positioned at the bottom end axis position of the sample tube 6, a sample enters the sample tube 6 through the sample inlet 7, flows out of the end face of the outlet side of the coaxial resonant cavity, enters the plasma, and is excited and ionized by the plasma;
the inner layer gas inlet 8 is positioned at the radial position of the lower part of the inner pipe 5 close to the bottom end of the inner pipe 5 and adopts a radial gas inlet mode; the inner layer gas is introduced into an annular gap formed by the inner surface of the inner tube 5 and the outer surface of the sample tube 6, flows out at the end face of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms inner layer plasma after ionization;
the middle layer gas inlet 9 is positioned at the radial position of the lower part of the middle pipe 4 close to the bottom end of the middle pipe 4 and adopts a radial gas inlet mode; the middle layer gas is introduced into an annular gap formed by the inner surface of the middle pipe 4 and the outer surface of the inner pipe 5, flows out at the end face of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms middle layer plasma after ionization;
the outer layer gas inlet 10 is positioned at the radial position of the lower part of the inner conductor 3 close to the bottom end of the inner conductor 3 and adopts a radial gas inlet mode; the outer layer gas is introduced into an annular gap between the inner surface of the inner conductor 3 and the outer surface of the middle pipe 4, flows out at the end face of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms outer layer plasma after ionization;
the inner layer gas, the middle layer gas and the outer layer gas are ionized to jointly form a three-layer plasma torch, the volume of the torch is suitable for the requirement of high-power application, the bottom of the plasma is slightly separated from the end face between the inner conductor 3 and the sample tube 6, and the end face is prevented from being ablated by heat generated by the high-power plasma.
The inner layer gas, the middle layer gas and the outer layer gas can work by selecting argon, helium or nitrogen, different types of plasmas are obtained respectively, and the plasma generating device is suitable for different application occasions. The inner layer gas, the middle layer gas and the outer layer gas can also be xenon or krypton gas and other gases which are easy to ionize. The inner layer gas, the middle layer gas and the outer layer gas can be selected from the same kind of gas to work, and can also be selected from different kinds of gas to work.
The cooling ring 14 is arranged at the interval position below the upper end surface of the outer conductor 1, and the cooling ring 14 is tightly contacted with the outer conductor 1; the cooling ring 14 cools the outer conductor 1 by adopting a water cooling or compressed air cooling mode to reduce the temperature of a cavity body near the plasma torch and ensure that the coaxial resonant cavity can normally work for a long time;
the impedance matching cone 15 is arranged on the upper end face of the outer conductor 1 and is tightly connected with the upper end face of the outer conductor 1; the size of the lower opening of the impedance matching cone 15 is the same as the inner diameter of the outer conductor 1, the inner surface of the impedance matching cone 15 can be a conical surface, a spherical surface or a rotating parabolic curved surface, and the height of the inner surface is greater than or equal to 1/4 times of the used microwave wavelength.
The working process of the waveguide feed-in type MCP generating device is as follows:
when the microwave power output is started, the microwave is transmitted in the standard waveguide 2 in the transverse electric mode TE10, and a reflected wave is formed on the inner surface of the short-circuit piston end 12, and the reflected wave is superimposed with the incident wave to form a standing wave inside the waveguide. The distance between the inner surface of the short circuit piston 12 and the central axis of the coaxial resonant cavity outer conductor 1 is adjusted by the adjusting rod 13, so that the central axis of the coaxial resonant cavity outer conductor 1 is at the maximum position of the standing wave electric field intensity in the standard waveguide 2. At this time, the distance between the center axis of the outer conductor 1 and the inner surface of the shorting piston 12 is about 1/4 times or 3/4 times the wavelength of the waveguide. The electromagnetic wave in the standard waveguide 2 is smoothly transited from the TE10 mode to the TEM mode under the action of the waveguide-coaxial transition cone 11, and the TEM mode electromagnetic wave is transmitted into the coaxial resonant cavity through the inner conductor 3 to form another standing wave. The standing wave electric field intensity reaches maximum at the upper outlet end face of the coaxial resonant cavity. Gas is properly regulated on the end face of the outlet side of a triple annular gap formed between an inner conductor 3 and a middle tube 4, between the middle tube 4 and an inner tube 5 and between the inner tube 5 and a sample tube 6 of the coaxial resonant cavity, and a microwave electric field ionizes triple laminar flow uniform gas at the same time to form MCP.
The invention has the advantages that:
1. the waveguide feed-in type MCP generating device provided by the invention has no power input limit of a radio frequency coaxial connector and a microwave antenna, is particularly suitable for feeding microwave power above kilowatt level, works stably and reliably for a long time, and can obtain stable high-temperature high-density plasma under the condition of atmospheric pressure.
2. The invention adopts the waveguide-coaxial conversion cone to realize the conversion of the microwave transmission mode, avoids using the gradual change type waveguide and the narrow-edge compression waveguide, and has more convenient processing of the cone and lower cost compared with the two special waveguides.
3. The invention can solve the problem of incomplete distribution of the local electromagnetic field on the inner surface of the outer conductor generated by the cavity at the entrance of the antenna when the microwave energy is fed in by the antenna mode, and the waveguide feeding mode ensures that the whole electromagnetic field between the inner conductor and the outer conductor of the coaxial resonant cavity is uniformly distributed and the coupling efficiency of the microwave energy is higher.
Description of the drawings:
fig. 1 is a schematic structural diagram of a single-cone MCP generator according to embodiment 1 of the present invention.
Fig. 2 is a schematic structural diagram of a double-cone MCP generating device according to embodiment 2 of the present invention.
Detailed Description
The following detailed description is made with reference to the accompanying drawings and examples. The drawings illustrate only preferred embodiments of the invention and are not to be considered limiting of its scope. The invention may admit to other equally effective embodiments.
Example 1
Referring to fig. 1, a waveguide feed-in MCP generator is mainly composed of a waveguide section and a coaxial resonant cavity section.
The waveguide part comprises a standard waveguide 2, a waveguide-coaxial transition cone 11, a short-circuit piston 12 and an adjusting rod 13.
The first port of the standard waveguide 2 is connected with a microwave generating system, the outer wall of the upper part in the length direction between the first port and the second port of the standard waveguide 2 is vertically provided with a coaxial resonant cavity outer conductor 1, the inner wall of the lower part in the length direction of the standard waveguide 2 is provided with a waveguide-coaxial conversion cone 11, and the central axis of the cone is superposed with the central axis of the outer conductor 1. The second port corresponding to the first port of the standard waveguide 2 is closed by a short-circuit piston 12, the short-circuit piston 12 is connected with an adjusting rod 13, and the position of the short-circuit piston 12 in the standard waveguide 2 is adjusted by the adjusting rod 13.
In this example, the standard waveguide 2 is a rectangular waveguide of the BJ26 type, and has cross-sectional dimensions of 86.4mm wide and 43.2mm high. Of course, other sized waveguides, such as BJ22 or BZ26 rectangular waveguides, may be used. The inner wall of the waveguide and the inner wall of the short-circuit piston are plated with copper or silver.
The waveguide-coaxial conversion cone 11 is a truncated cone type single-sided cone, and the cone angle is 40 degrees. The upper bottom surface of the cone is sealed with the inner conductor 3, and the lower bottom surface of the cone is sealed with the outer wall of the lower part of the standard waveguide 2.
The microwave is transmitted in the transverse electric mode TE10 inside the standard waveguide 2, and a reflected wave is formed on the inner surface of the short-circuited piston end 12, and the reflected wave is superimposed with the incident wave to form a standing wave inside the waveguide. In order to feed microwave energy into the coaxial resonant cavity to the maximum extent, reduce microwave reflection power and facilitate exciting plasma, the distance between the inner surface of the short-circuit piston 12 and the central axis of the coaxial resonant cavity outer conductor 1 needs to be adjusted by the adjusting rod 13, so that the central axis of the coaxial resonant cavity outer conductor 1 is at the maximum position of the standing wave electric field intensity in the standard waveguide 2. In this example, the distance between the central axis of the outer conductor 1 and the inner surface of the short-circuiting piston 12 is 1/4 times or 3/4 times the wavelength of the waveguide.
The electromagnetic wave in the standard waveguide 2 smoothly transits from the TE10 mode to the TEM mode through the waveguide-coaxial transition cone 11, and the TEM mode electromagnetic wave is transmitted into the coaxial resonant cavity through the inner conductor 3 to form another standing wave. The standing wave electric field intensity is extremely high at the upper outlet end face of the coaxial resonant cavity, and if the gas adjustment is proper at the outlet end face, MCP is easily formed.
The coaxial resonant cavity part comprises an outer conductor 1, an inner conductor 3, a middle tube 4, an inner tube 5, a sample tube 6, a sample inlet 7, an inner layer gas inlet 8, a middle layer gas inlet 9, an outer layer gas inlet 10, a cooling ring 14 and an impedance matching cone 15. Wherein, the inner conductor 3 is designed in the outer conductor 1, the middle tube 4 is designed in the inner conductor 3, the inner tube 5 is designed in the middle tube 4, and the sample tube 6 is designed in the inner tube 5. The central axis of the sample tube 6 coincides with the central axis of the coaxial resonant cavity, the sample tube 6 is coaxial with the inner tube 5, the inner tube 5 is coaxial with the middle tube 4, the middle tube 4 is coaxial with the inner conductor 3, the inner conductor 3 is coaxial with the outer conductor 1, and the sample tube 6, the inner tube 5, the middle tube 4 and the inner conductor 3 are flush with each other on the outlet end face of the resonant cavity. The sample tube 6, the inner tube 5, the middle tube 4, the inner conductor 3 and the outer conductor 1 form a microwave resonant cavity of a nested coaxial structure, and the characteristic impedance range of the coaxial resonant cavity is 50-80 ohms.
The outer conductor 1 is arranged between the first port and the second port of the standard waveguide 2 and perpendicular to the length direction of the standard waveguide 2, and the central axis of the outer conductor 1 is coincident with the central axis of the waveguide-coaxial transition cone 11. The outer conductor 1 is a hollow cylinder with an inner diameter of 35-60 mm. The upper end face of the outer conductor is 90-100 mm away from the outer wall of the standard waveguide 2. The outer conductor 1 is made of high-conductivity and low-loss metal, such as oxygen-free copper, red copper or high-purity aluminum, or is processed by copper alloy or aluminum alloy, and the inner surface of the outer conductor is plated with silver to improve the Q value of the cavity. The inner surface of the outer conductor is subjected to rust prevention and corrosion prevention treatment.
The inner conductor 3 is directly fastened to the bottom of the standard waveguide 2 via a waveguide-coaxial transition taper 11 and protrudes from the lower inner wall of the standard waveguide 2. The inner conductor 3 is a cylinder with a hollow inner part, and a middle tube 4, an inner tube 5 and a sample tube 6 are arranged in the inner conductor. In this example, the inner conductor has an outer diameter of 10 to 18mm and an inner diameter of 9 to 16 mm. The inner conductor 3 can be made of high-conductivity and low-loss metal materials, such as pure copper materials of oxygen-free copper, red copper and the like or high-purity aluminum, copper alloy and aluminum alloy, the outer surface of the inner conductor is plated with silver, and rust-proof and corrosion-proof treatment is adopted.
The middle pipe 4 and the inner conductor 3 are sealed at the lower part of the inner conductor 3 to form an annular gap with one end sealed and the other end opened at the end face of the coaxial resonant cavity outlet side for laminar flow of outer layer gas. The middle tube 4 is a hollow cylinder, and is made of high-conductivity and low-loss metal.
The inner pipe 5 and the middle pipe 4 are sealed at the lower part of the middle pipe 4 to form an annular gap with one end sealed and the other end opened at the end face of the coaxial resonant cavity outlet side for laminar flow of the middle layer gas. The inner tube 5 is a cylinder with a hollow inner part and is made of metal with high conductivity and low loss.
The sample tube 6 and the inner tube 5 are closed at the lower part of the inner tube 5 to form an annular gap with one closed end and the other open end at the end face of the coaxial resonant cavity outlet side for laminar flow of inner layer gas. The sample tube 6 is also a cylinder with a hollow inner part, and the material of the sample tube can be metal, and can also be nonmetal such as ceramic, graphite, quartz and the like.
The sample inlet 7 is positioned at the axial position of the tail end of the sample tube 6, and the aerosol sample enters the sample tube 6 through the sample inlet 7, flows out from the end face of the outlet side of the coaxial resonant cavity, enters the central channel of the plasma, and is excited and ionized.
The inner layer gas inlet 8 is positioned at the radial position of the lower part of the inner pipe 5 close to the tail end of the inner pipe 5 and adopts a radial gas inlet mode. The inner layer gas is introduced into an annular gap formed by the inner surface of the inner tube 5 and the outer surface of the sample tube 6, flows out at the end face of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms inner layer plasma after ionization.
The middle layer gas inlet 9 is positioned at the radial position of the lower part of the middle pipe 4 close to the tail end of the middle pipe 4 and adopts a radial gas inlet mode. The middle layer gas is introduced into an annular gap formed by the inner surface of the middle pipe 4 and the outer surface of the inner pipe 5, flows out from the end face of the outlet side of the resonant cavity in a laminar flow state, and forms middle layer plasma after ionization.
The outer gas inlet 10 is located at the lower part of the inner conductor 3 and close to the radial position of the tail end of the inner conductor 3, and adopts a radial gas inlet mode. The outer layer gas is introduced into an annular gap between the inner surface of the inner conductor 3 and the outer surface of the middle pipe 4, flows out from the end face of the outlet side of the resonant cavity in a laminar flow state, and forms outer layer plasma after ionization.
The inner layer gas, the middle layer gas and the outer layer gas are ionized to jointly form a three-layer plasma torch, the volume of the torch is suitable for the requirement of high-power application, the bottom of the plasma is slightly separated from the end face between the inner conductor 3 and the sample tube 6, and the end face is prevented from being ablated by heat generated by the high-power plasma.
The inner layer gas, the middle layer gas and the outer layer gas can work by selecting argon, helium or nitrogen, different types of plasmas are obtained respectively, and the plasma generating device is suitable for different application occasions. The inner layer gas, the middle layer gas and the outer layer gas can also be xenon or krypton gas and other gases which are easy to ionize.
The inner layer gas, the middle layer gas and the outer layer gas can be selected from the same kind of gas to work, and can also be selected from different kinds of gas to work.
The cooling ring 14 is installed at a position of a lower section of the upper end surface of the outer conductor 1, and the cooling ring 14 is in close contact with the outer conductor 1. The cooling ring 14 cools the outer conductor 1 by adopting a water cooling or compressed air cooling mode to reduce the temperature of a cavity body near the plasma torch and ensure that the coaxial resonant cavity can normally work for a long time. The cooling pipe is connected with the refrigeration radiator through an air pump or a water pump, and the air pump or the water pump provides cooling power or circulating power to enable air or water to circulate between the refrigeration radiator and the water cooling device so as to realize the function of cooling.
An impedance matching cone 15 is mounted on the upper end face of the outer conductor 1 and is closely connected thereto. The size of the lower opening of the impedance matching cone 15 is the same as the inner diameter of the outer conductor 1, the inner surface of the impedance matching cone can be a conical surface, a spherical surface or a rotating parabolic curved surface, and the height of the impedance matching cone is greater than or equal to 1/4 times of the used microwave wavelength. The impedance matching cone 15 is used for realizing approximate matching between the characteristic impedance of the coaxial resonant cavity and the impedance of the free space, reducing the reflected power, stabilizing the torch flame, preventing the microwave leakage and protecting the normal and stable work of the microwave generation system.
The brief working process of the embodiment 1 of the invention is as follows:
1, starting a water cooling or compressed air cooling system;
2, starting a power supply of the microwave control system to preheat;
3, opening a steel cylinder valve, adjusting the gas flow of the outer layer gas, the middle layer gas and the inner layer gas, for example, 1.5L/min of the outer layer gas, 1.0L/min of the middle layer gas and 1.0L/min of the inner layer gas, performing pipeline purging, and discharging air accumulated in the cavity;
4 starting microwave output, and generating microwave with frequency of 2.45GHz and power above kilowatt level by using magnetron (not shown). The microwave is transmitted in the transverse electric mode TE10 inside the standard waveguide 2, and a reflected wave is formed on the inner surface of the short-circuited piston end 12, and the reflected wave is superimposed with the incident wave to form a standing wave inside the waveguide. The distance between the inner surface of the short circuit piston 12 and the central axis of the coaxial resonant cavity outer conductor 1 is adjusted by the adjusting rod 13, so that the axis of the coaxial resonant cavity outer conductor 1 is at the maximum position of the standing wave electric field intensity in the standard waveguide 2. At this time, the distance between the center axis of the outer conductor 1 and the inner surface of the shorting piston 12 is about 1/4 times or 3/4 times the wavelength of the waveguide. The electromagnetic wave in the standard waveguide 2 is smoothly transited from the TE10 mode to the TEM mode under the action of the waveguide-coaxial transition cone 11, and the TEM mode electromagnetic wave is transmitted into the coaxial resonant cavity through the inner conductor 3 to form another standing wave. The standing wave electric field intensity reaches maximum at the upper outlet end face of the coaxial resonant cavity. When the outlet side end face of the triple annular gap formed between the inner conductor 3 and the middle tube 4, between the middle tube 4 and the inner tube 5 and between the inner tube 5 and the sample tube 6 of the coaxial resonant cavity is properly adjusted, the igniter simultaneously acts to release initial electrons to cause the gas near the end face to generate electron avalanche reaction, the microwave electric field ionizes the triple laminar flow uniform gas simultaneously, and the MCP torch flame is ignited at the outlet end face.
Example 2
Referring to fig. 2, the generating means is mainly composed of a waveguide portion and a coaxial cavity portion.
The waveguide part comprises a standard waveguide 2, a waveguide-coaxial transition cone 11, a short-circuit piston 12 and an adjusting rod 13. The standard waveguide 2, the short-circuit piston 12 and the adjusting rod 13 are the same as those in embodiment 1, and only the waveguide-coaxial conversion cone 11 is different from that in embodiment 1.
The waveguide-coaxial conversion cone 11 is two parts with the same size, which are respectively arranged on the upper side and the lower side of the inner wall of the standard waveguide 2, and the central axis of the cone is superposed with the central axis of the outer conductor 1. The cone can be a circular truncated cone, and preferably, the cone angle is 40 degrees; it may also be a symmetrical trapezoid, preferably with a trapezoid angle of 40 degrees.
The coaxial resonant cavity part comprises an outer conductor 1, an inner conductor 3, a middle tube 4, an inner tube 5, a sample tube 6, a sample inlet 7, an inner layer gas inlet 8, a middle layer gas inlet 9, an outer layer gas inlet 10, a cooling ring 14 and an impedance matching cone 15. Except that the outer conductor 1 is divided into an upper part and a lower part, the rest parts of the coaxial resonant cavity are the same as the embodiment 1 of the invention, and are not described again.
The outer conductor 1 is installed perpendicular to the length direction of the standard waveguide 2 between the first port and the second port of the standard waveguide 2. The outer conductor 1 is divided into an upper part and a lower part, the upper part of the outer conductor is fastened with the outer side of the upper wall between the first port and the second port of the standard waveguide 2 in the length direction, and the lower part of the outer conductor is fastened with the outer side of the lower wall between the first port and the second port of the standard waveguide 2 in the length direction. The lower part of the outer conductor is coaxial with the upper part of the outer conductor and is tightly closed with the inner conductor 3.
Preferably, the overall depth of the upper end surface of the outer conductor and the bottom surface of the outer conductor is (2n +1)/4 times (n is 1, 2, 3) the wavelength of the microwave used, and the symmetrical center line of the double-sided cone in the height direction of the standard waveguide 2 is located at a distance of 1/4 times the wavelength of the microwave used from the bottom surface of the outer conductor. For example, when n is 1, the upper end surface of the outer conductor is about 90-100 mm away from the bottom surface of the cavity. And the symmetrical center lines of the two side cones in the height direction of the standard waveguide 2 are located at the positions which are about 30-31 mm away from the bottom surface of the outer conductor.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims (3)
1. A waveguide feed-in type microwave coupling plasma generating device is composed of a waveguide part and a coaxial resonant cavity part; the waveguide part comprises a standard waveguide (2), a waveguide-coaxial conversion cone (11), a short-circuit piston (12) and an adjusting rod (13); the coaxial resonant cavity part comprises an outer conductor (1), an inner conductor (3), a middle pipe (4), an inner pipe (5), a sample pipe (6), a sample inlet (7), an inner layer gas inlet (8), a middle layer gas inlet (9), an outer layer gas inlet (10), a cooling ring (14) and an impedance matching cone (15);
the first port of the standard waveguide (2) is connected with a microwave generation system, an outer conductor (1) and a waveguide-coaxial conversion cone (11) of a coaxial resonant cavity are vertically arranged in the length direction between the first port and the second port of the standard waveguide (2), the central axis of the cone is superposed with the central axis of the outer conductor (1), and the waveguide-coaxial conversion cone (11) is a hollow circular truncated cone or a hollow trapezoid; the second port of the standard waveguide (2) is closed by a short-circuit piston (12), and the short-circuit piston (12) is connected with an adjusting rod (13);
the microwave resonant cavity is characterized in that an outer conductor (1), an inner conductor (3), a middle pipe (4), an inner pipe (5) and a sample pipe (6) are sequentially nested and coaxial from outside to inside, the sample pipe (6), the inner pipe (5), the middle pipe (4) and the inner conductor (3) are flush at the outlet end face of the formed resonant cavity, the sample pipe (6), the inner pipe (5), the middle pipe (4), the inner conductor (3) and the outer conductor (1) form the microwave resonant cavity of a nested coaxial structure, and the characteristic impedance range of the resonant cavity is 50-80 ohms;
the outer conductor (1) is arranged between a first port and a second port of the standard waveguide (2) and is vertically intersected with the length direction of the standard waveguide (2), the waveguide-coaxial conversion cone (11) is a double-sided cone, the outer conductor (1) is divided into an upper part and a lower part, the bottom surface of the upper half part of the outer conductor (1) is superposed with the lower bottom surface of the upper cone of the waveguide-coaxial conversion cone (11), the top surface of the lower half part of the outer conductor (1) is superposed with the upper bottom surface of the lower cone of the waveguide-coaxial conversion cone (11), the upper cone and the lower cone of the waveguide-coaxial conversion cone (11) are two hollow round tables which are vertically symmetrical along the central axis of the standard waveguide (2), the sum of the heights is smaller than the height of the waveguide standard (2), and the distance between the lowest surface of the inner cavity of the outer conductor (1) and the central axis of the standard waveguide (2) is 1/4 times of the wavelength of the used microwave, the distance between the lowest surface of the inner cavity and the highest surface of the inner cavity of the outer conductor (1) is (2n +1)/4 times of the wavelength of the used microwave, wherein n = 1, 2 or 3, and the outer conductor (1) is a metal cylinder with a hollow inner part;
the inner conductor (3) is fastened and sealed with the bottom of the outer conductor (1); the inner conductor (3) is a metal cylinder with a hollow inner part;
the outer wall of the middle pipe (4) and the inner conductor (3) are sealed at the lower part of the inner conductor (3) to form an annular gap with a closed bottom end and an open top end face for laminar flow of outer layer gas; the middle pipe (4) is a metal cylinder with a hollow interior;
the outer wall of the inner pipe (5) and the middle pipe (4) are sealed at the lower part of the middle pipe (4) to form an annular gap with a closed bottom end and an open top end face for laminar flow of the middle layer gas; the inner pipe (5) is a metal cylinder with a hollow inner part;
the outer wall of the sample tube (6) and the inner tube (5) are closed at the lower part of the inner tube (5) to form an annular gap with closed bottom end and open top end face for laminar flow of inner layer gas; the sample tube (6) is a cylinder with a hollow inner part;
the sample inlet (7) is positioned at the bottom axial line position of the sample tube (6), and a sample enters the sample tube (6) through the sample inlet (7), flows out of the end face of the outlet side of the coaxial resonant cavity, enters plasma, and is excited and ionized by the plasma;
the inner layer gas inlet (8) is positioned at the radial position of the lower part of the inner pipe (5) close to the bottom end of the inner pipe (5) and adopts a radial gas inlet mode; the inner layer gas is introduced into an annular gap formed by the inner surface of the inner tube (5) and the outer surface of the sample tube (6), flows out at the end face of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms inner layer plasma after ionization;
the middle layer gas inlet (9) is positioned at the radial position of the lower part of the middle pipe (4) close to the bottom end of the middle pipe (4) and adopts a radial gas inlet mode; the middle layer gas is introduced into an annular gap formed by the inner surface of the middle pipe (4) and the outer surface of the inner pipe (5), flows out at the end surface of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms middle layer plasma after ionization;
the outer layer gas inlet (10) is positioned at the radial position of the lower part of the inner conductor (3) close to the bottom end of the inner conductor (3) and adopts a radial gas inlet mode; the outer layer gas is introduced into an annular gap between the inner surface of the inner conductor (3) and the outer surface of the middle pipe (4), flows out at the end surface of the outlet side of the coaxial resonant cavity in a laminar flow state, and forms outer layer plasma after ionization;
the cooling ring (14) is arranged at the interval position below the upper end surface of the outer conductor (1), and the cooling ring (14) is tightly contacted with the outer conductor (1); the cooling ring (14) cools the outer conductor (1) in a water cooling or compressed air cooling mode to reduce the temperature of a cavity body near the plasma torch and ensure that the coaxial resonant cavity can normally work for a long time;
the impedance matching cone (15) is arranged on the upper end face of the outer conductor (1) and is tightly connected with the upper end face of the outer conductor (1); the size of the lower opening of the impedance matching cone (15) is the same as the size of the inner diameter of the outer conductor (1), the inner surface of the impedance matching cone (15) is a rotating parabolic curved surface, and the height of the inner surface is greater than or equal to 1/4 times of the wavelength of the used microwave.
2. A waveguide fed microwave coupled plasma generator according to claim 1, characterized in that the outer conductor (1), the inner conductor (3), the middle tube (4) and the inner tube (5) are made of metal with resistivity less than 30n Ω -m.
3. A waveguide fed microwave coupled plasma generator according to claim 1, characterized in that the sample tube (6) is made of metal, ceramic, graphite or quartz.
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