JP2004172044A - Microwave plasma generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave plasma generating device capable of generating low-temperature plasma operating at atmospheric pressure (or pressure close to it) by using a small device. <P>SOLUTION: The microwave plasma generating device generates plasma gas by exciting gas close to the atmospheric pressure by using a microwave. The length of a coaxial resonance cavity 102 is an integral multiple of a half of an excitation wavelength, and central conductors 205, 208 are made shorter arranged with a non-metal pipe 103 for a gas flow channel set along the center of the central conductors 205, 208. Gas injected from one end is excited by the microwave at a gap where the non-metal pipe is not covered with the central conductors and discharged from the other end forming plasma. The cavity is excited by a microwave supply circuit. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a microwave plasma generator that converts a gas at atmospheric pressure into a plasma gas by microwave excitation and generates a thermal plasma gas.
[0002]
[Prior art]
Thermal plasma is substantially synonymous with atmospheric pressure plasma. In the 1970's, development for industrial applications flourished. Application fields include industrial materials such as melting, fusing, joining, refining, metallurgy, spraying, etc., lighting fields such as light sources for displays using plasma-generated light, fine particle generation, and induction. It is an analysis field for chemical analysis of trace sample components using plasma as an ionization means, and a cleaning field for surface treatment of materials such as a semiconductor process, which covers a wide field.
[0003]
In the 1980s, attention was paid to its use in removing substances causing air pollution. An RF plasma source from TePLA and an atmospheric pressure plasma source from ARIOS have been developed and used. In the former, the high frequency for exciting the gas into the plasma state is relatively low at 13.56 MHz, so that the plasma conversion efficiency is low. Also, the size of the device is large because of the frequency.
[0004]
An atmospheric pressure plasma source manufactured by Arios will be described with reference to FIG. This apparatus uses a microwave oscillating at an excitation frequency near 2.45 GHz as the plasma source. A microwave waveguide 10 is used as a means for supplying a microwave to a plasma cavity inside a microwave plasma source 1 for generating a plasma gas. The impedance when the load side is viewed from the microwave oscillator 7 changes greatly before and after the plasma is turned on. A stub tuner 11 is provided in the middle of the waveguide 10 to supply appropriate power to the plasma source, and the stub tuner 11 is automatically controlled to stably supply power. The use of a waveguide inevitably increases the size and weight of the device. The diameter of the plasma cavity is relatively large at 15 cm. In order to automatically control the stub tuner 11, a pulse motor for performing mechanical control is required.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a microwave plasma generator capable of stably generating a low-temperature plasma operating at an atmospheric pressure (or a pressure close thereto) with a small-sized device.
Still another object of the present invention is to provide a microwave plasma generator capable of freely moving a plasma head by making a plasma generator smaller using a coaxial resonator.
Still another object of the present invention is to provide a microwave plasma generator which is easy to handle by using a circuit for stabilizing the operation of the coaxial resonator.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a microwave plasma generator according to claim 1 according to the present invention,
A microwave plasma generator that generates a plasma gas by exciting a gas near atmospheric pressure with a microwave,
The length of the cavity is an integral multiple of 1/2 of the excitation wavelength, the center conductor is shorter than the length, a non-metallic pipe for gas flow is arranged along the center of the center conductor, and injected from one end. A coaxial resonance cavity in which the non-metallic pipe is excited by microwaves and is emitted as plasma from the other end in the gap G where the non-metallic pipe is not covered with the center conductor; and
And a microwave supply circuit for exciting the cavity.
[0007]
According to a second aspect of the present invention, there is provided a microwave plasma generator according to the first aspect, wherein the pipe is formed of a quartz pipe.
A microwave plasma generator according to a third aspect of the present invention is the microwave plasma generator according to the first aspect,
The center conductor is formed of a first center conductor on the excitation side and a second center conductor on the plasma generation side, and is configured such that gas is excited between the first center conductor and the second center conductor on the plasma generation side. ing.
A microwave plasma generator according to a fourth aspect of the present invention is the microwave plasma generator according to the first aspect, wherein the central conductor has a length having a gap between the emission-side walls of the coaxial resonance cavity. The gas is excited between the central conductor and the wall surface on the emission side.
According to a fifth aspect of the present invention, there is provided a microwave plasma generating apparatus according to the first to fourth aspects, wherein the coaxial resonance cavity suppresses radiation of electromagnetic waves from the cavity due to gasification of gas. A three-dimensional circuit constituting a choke for preventing electromagnetic wave radiation is provided on the plasma gas discharge side.
[0008]
A microwave plasma generator according to claim 6 of the present invention is the microwave plasma generator according to claims 1 to 4, wherein the coaxial resonance cavity is initially excited in the TM010 mode to generate a high electric field in the gap. When the gas is turned into plasma, the circuit is configured to operate in the TEM mode, and the three-dimensional circuit is designed and configured so that the resonance frequency in the state where the gas is turned into plasma does not change from the resonance frequency before the plasma is turned. Have been.
According to a seventh aspect of the present invention, there is provided the microwave plasma generating apparatus according to the first to sixth aspects, wherein an equivalent circuit when the inflowing gas is turned into plasma in the coaxial resonance cavity is configured such that the gap is made conductive. It is configured so that the operation can be regarded as a coaxial cavity.
According to the microwave plasma generator according to claim 8 of the present invention, in the microwave plasma generator according to claim 6 or 7, the fluctuation of the load due to the difference in the operation mode before and after the formation of plasma in the coaxial resonance cavity is reduced. Is configured by selecting three-dimensional circuit parameters.
[0009]
According to a ninth aspect of the present invention, there is provided the microwave plasma generating apparatus according to the first aspect, wherein the microwave supply circuit includes a microwave source, the supply circuit, and an operation of the coaxial resonance cavity. It is composed of a feedback circuit that returns the state to the microwave generation source.
[0010]
The microwave plasma generator according to claim 10 of the present invention is the microwave plasma generator according to claim 9, wherein the micro source is a magnetron, supplied to the coaxial resonance cavity via a circulator, and The change in the operation of the resonance cavity is fed back to the excitation coil and the anode of the magnetron to stabilize the operation.
A microwave plasma generator according to claim 11 of the present invention is the microwave plasma generator according to claim 9, wherein the micro source is a solid-state oscillator.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. FIG. 1 is a schematic diagram of a microwave plasma generator of the present invention. The microwave plasma source 101 includes a coaxial cavity 102 and a central gas passage quartz pipe 103. A microwave oscillator (magnetron) 107 oscillates a microwave for excitation. The output is connected to the coaxial cavity 102 via a circulator 108, a coaxial connector 109, a coaxial cable 110, a directional coupler 111, and an antenna 105 for exciting the cavity. The directional coupler 111 detects the traveling wave and the reflected wave, and is connected back to the anode of the microwave oscillator (magnetron) 107 via the phase shifter 112, the 3db coupler 113, the detector 114, and the differential amplifier 115. I have. Microwave power for excitation is supplied from the cavity excitation antenna 105. The internal electromagnetic field is detected by the loop antenna 106 for detecting the internal electromagnetic field, and is fed back to the exciting coil 117 of the microwave oscillator (magnetron) 107 via the differential amplifier 116 for exciting.
[0012]
The inside of the microwave plasma generation source 101 forms a coaxial cavity 102, and a thin quartz pipe 103 forming a gas flow path is disposed at the center of the coaxial portion. A part of the coaxial portion at the center of the coaxial cavity 102 is partially removed, and the quartz pipe 103 is exposed at that portion.
The carrier gas is sent from the upper end of the quartz pipe 103 to the coaxial cavity 102. This carrier gas is excited by an electric field inside the coaxial cavity 102 at the center of the coaxial cavity 102 to be in a plasma state, and is discharged as a plasma gas 104 from a lower portion of the gas flow channel quartz pipe 103.
The microwave oscillator 107 generates a microwave for exciting the coaxial cavity 102. The frequency of this microwave is 2.450 GHz in the IMS (Industrial Medical Science) frequency band which is recognized for industrial use.
[0013]
When the carrier gas changes to the plasma state at the center of the coaxial cavity 102, the state inside the cavity changes suddenly, so that the load before and immediately after the plasma state changes greatly. It is not preferable that the excitation frequency changes due to this change.
As a first step of this measure, the present invention utilizes a change in the electric field distribution in the cavity before plasma formation and the change in the electric field distribution after plasma formation to operate as a resonator having the same frequency before and after plasma formation. design.
Even with such a design, a slight change in the frequency cannot be avoided. As a second step, the above-mentioned change in the frequency before and after the formation of plasma is detected, and this data is used as the anode voltage of the microwave oscillator 107. And the excitation current is controlled to lock the oscillation frequency.
[0014]
Next, the structure of the microwave plasma source 101 will be described in some detail. FIG. 2 is a perspective view showing a cavity structure. The cavity 102 is covered with a copper body. A carrier gas is guided from the upper part of the cavity 102 to the center of the cavity 102 through a quartz pipe 103 for a gas passage. The quartz pipe 103 passes through the center of the upper center conductor 205.
The gas flow passage quartz pipe 103 also penetrates the center of the lower center conductor 208. Only the gas flow passage quartz pipe 103 is exposed between the upper center conductor 205 and the lower center conductor 208. Since an electric field is applied to the exposed portion, the carrier gas in the quartz pipe 103 for the gas flow path is excited and turned into plasma.
[0015]
FIG. 13 is a diagram showing a plasma-like gas inside the gas flow passage quartz pipe 103 of the microwave plasma generation source portion, and FIG. 14 is directed radially from a center portion inside the gas flow passage quartz pipe of the microwave plasma generation source portion. It is a figure which shows the electric field intensity distribution of each position. When the gas is turned into plasma, the plasma-like gas 1302 inside the gas flow channel quartz pipe 103 shown in FIG. 13 can be electrically regarded as a conductor. Therefore, the microwave for excitation cannot enter the plasma-like gas 1302.
The electric field of the microwave for excitation is present on the outer periphery of the pipe as shown by a curve 1401 shown in FIG. 14, and in the pipe 103, the inner wall surface of the pipe 103 is attenuated only at the same potential as the external electric field. Draw. This is similar to the skin effect phenomenon in which charges are concentrated only on the surface of a metal conductor. As described above, the electric field near the inner wall of the gas passage quartz pipe 103 is strong, but decreases sharply toward the center. The plasma gas looks electrically conductive when viewed from the outside. That is, since the gas is turned into plasma in the lower central conductor 208, the gas has electric characteristics like a conductor, and thus the effect of the antenna is exactly exhibited at this portion, and microwaves may be emitted to the outside. This will be described later.
[0016]
FIG. 3 is a diagram showing the distribution of the excitation electric field of the microwave plasma source before the plasma is generated by the apparatus according to the present invention, and FIG. 4 is a diagram showing the distribution of the excitation electric field of the microwave plasma source immediately after the plasma is generated. FIG. 3 shows an excitation electric field 301 generated in the space between the upper center conductor and the lower center conductor immediately before the carrier gas is turned into plasma. An electric field is applied vertically between the upper center conductor 205 and the lower center conductor 208. The distribution of the electric field is a vibration in a reentrant run mode (TM mode). FIG. 4 shows the electric field distribution after the formation of plasma.
The excitation electric field 401 is applied from the inner wall outside the cavity in the direction of the center conductor, and shows just coaxial mode (TEM mode) vibration.
[0017]
FIG. 5 shows the distribution of the electric field immediately before the gas is turned into plasma and the electrical equivalent circuit. The vibration mode of this electric field is a reentrant run mode (TM mode). The electrical equivalent circuit is L ₁ And C ₁ And L ₂ And the resonance frequency is expressed by the following equation.
f ₁ = 1 / (2π (ROOT [C ₁ * (L ₁ + L ₂ )]))
f ₂ = 1 / (2π (ROOT [C ₂ * L ₃ * L ₄ / (L ₃ + L ₄ )]))
[0018]
As described above, the change in the resonance frequency accompanying the operation mode occurs, but it is not preferable that such a change in the resonance frequency occurs, and it is desirable that the difference be small, if any. Therefore, in the present invention, by changing the structure inside the cavity, f ₁ And f ₂ Is optimized so that is approximately equal to This is because C ₁ (L ₁ + L ₂ ) And 2C ₂ L ₃ L ₄ / (L ₃ + L ₄ ) Is nothing but the choice of cavity shape. In this way, the structure of the coaxial cavity 102 is optimally designed, and even if the load immediately before and immediately after the carrier gas enters the plasma state greatly changes, the structure is viewed from the cavity excitation antenna at the microwave input portion. Load fluctuation can be reduced. Thereby, the stabilization of the operation of the system can be greatly improved.
[0019]
The second measure will be described together with the operation of the circuit with reference to FIG. The second countermeasure is performed by controlling the anode voltage and the excitation magnetic field of the microwave oscillator (magnetron) 107. The output of the microwave oscillator (magnetron) 107 is supplied to a circulator. The circulator 108 is used to avoid a phenomenon in which load fluctuations before and after the plasma state affect and change the oscillation frequency of the microwave oscillator (magnetron) 107, that is, to insulate the reflected power of the load. . Further, it is applied to the directional coupler 111 via the coaxial connector 109, and is supplied from the output of the directional coupler 111 to the cavity 102 of the microwave plasma source 101 via the cavity excitation antenna 105.
[0020]
A traveling wave and a reflected wave are output to the terminal b of the directional coupler 11, respectively. The reflected wave is passed through the phase shifter 112 to the P ₂ Added to terminal. By adjusting the phase shifter 112, the power of the reflected wave is set to be a minimum value at the resonance frequency. Since the phase shifter 112 can freely set the phase of the reflected wave with respect to the phase of the traveling wave, the phase of the reflected wave and the traveling wave is set to be the same at the time of resonance.
[0021]
The phase difference between the reflected wave and the traveling wave with respect to the oscillation frequency becomes zero at the resonance frequency. On the other hand, the traveling wave ₁ Add to terminal. P of the output terminal of the 3db coupler 113 ₃ And P ₄ Is supplied to the detector 114 and converted into a DC voltage. Each DC voltage is supplied to an input of a differential amplifier 115. The output voltage of the differential amplifier 115 is adjusted so that the output becomes zero when the two DC voltages are equal. When the gas in the center of the cavity 102 of the microwave plasma generation source 101 does not enter the plasma state, it is set to operate at the resonance frequency. When oscillation starts and the gas changes to a plasma state, the electric field distribution in the cavity 102 changes. As described in detail above, by optimizing the dimensional design of the cavity, the frequency change before and after the plasma can be sufficiently reduced. If this load condition changes, this frequency will be a little different from the natural resonance frequency of the cavity 102, but in order to further reduce this frequency difference, a negative feedback is applied to the microwave oscillator 107 electrically. The control method will be described. When the microwave oscillator (magnetron) 107 supplies power at these different frequencies, a reflected wave is generated from the cavity 102, and this reflected wave is generated at the terminal b of the directional coupler 111. Further, the signal passes through the phase shifter 112 and the P terminal of the output terminal of the 3 db coupler 113 ₂ Supplied to
[0022]
On the other hand, the traveling wave ₁ Supplied to As a result, the output signal of the detector 114 generates voltages having different amplitudes. This difference voltage is generated at the output of the differential amplifier 115. This voltage is superimposed on the anode voltage of the microwave oscillator (magnetron) 107 and applied. Since the anode voltage is supplied in pulses,
Naturally, a circuit (not shown in FIG. 1) in which the differential voltage of the differential amplifier 115 is supplied in synchronization with the pulse voltage of the anode is added. That is, the operation is performed so as to approach the resonance frequency of the cavity 102. By this feedback operation, the oscillation frequency of the microwave oscillator (magnetron) 107 is phase-locked to the unique resonance frequency of the cavity 102.
[0023]
Further, in order to increase the stability of the frequency of the system, the current of the exciting coil of the microwave oscillator (magnetron) 107 is also controlled. That is, the error signal detected from the internal electromagnetic field detection loop antenna 106 generates a current corresponding to the error signal in the excitation differential amplifier 116, and the current of the excitation coil is changed by this current. Feedback is made to approach the frequency. As described above, in the circuit of FIG. 1, both the anode voltage and the exciting current are controlled, and the frequency of the system can be stabilized.
[0024]
As described above, the plasma gas looks electrically conductive in the microwave band when viewed from the outside. That is, since the gas is turned into plasma in the lower central conductor 208, the gas has electric characteristics like a conductor, and thus the effect of the antenna is exactly exhibited at this portion, and microwaves may be emitted to the outside. For this purpose, a choke structure is formed particularly inside the lower center conductor 208. This structure prevents the transmission of radio waves to the outside. A choke structure is provided inside the lower center conductor 208 in order to suppress the externally emitted microwave (because it acts as an interference wave to an external device). By inserting a coaxial choke having a λ / 4 structure as the choke, the leaking microwave can be significantly reduced. As described above, the choke 302 (FIGS. 3 and 4) is provided to suppress microwaves leaking to the outside after the gas is turned into plasma. FIG. 4 shows the electric field distribution after the formation of plasma. The excitation electric field 401 is constricted from the inner wall outside the cavity toward the center conductor, and shows just coaxial mode vibration. Note that the diameter of the gas flow passage quartz pipe 103 passing through the center of the upper central conductor 205 is sufficiently smaller than the wavelength of the microwave, and the flowing gas is a gas that is not converted into plasma. It does not radiate outside.
[0025]
FIG. 7 is a view showing a microwave plasma source having a structure different from that of the microwave plasma source according to the present invention. The above-described microwave plasma generation source 101 has a configuration in which the upper conductor having the configuration shown in FIG. 2 is extended by a cavity having a different structure, and the lower conductor is omitted. The basic operating principle is not different. The same functions or shapes as those shown in FIG. 2 are denoted by the same reference numerals.
The cavity is covered with a copper body. Carrier gas is led from the upper part of the cavity to the center of the cavity through a gas inflow quartz pipe 103 provided through the central conductor 705. Between the center conductor 705 and the lower part of the cavity, only the gas flow passage quartz pipe 103 is exposed. Since an electric field is applied to this exposed portion, the carrier gas in the gas flow channel quartz pipe 103 is excited and turned into plasma.
[0026]
The electric field distribution of the microwave plasma generation source having this structure becomes the distribution shown in FIG. 8 before the formation of the plasma, and changes to the distribution shown in FIG. 9 immediately after the formation of the plasma. FIG. 8 shows an excitation electric field 801 generated in the space between the upper center conductor and the lower part of the cavity immediately before the carrier gas is turned into plasma. An electric field is applied vertically between the upper central conductor 705 and the lower part of the cavity. This means that the distribution of the electric field becomes reentrant run mode oscillation. FIG. 9 shows the electric field distribution after the formation of plasma. The excitation electric field 901 is applied in the direction of the pipe 103 from the inner wall outside the cavity, and shows just coaxial mode vibration. As in the embodiment shown in FIG. 2, the circuit structure can be designed so that the resonance frequency does not change before and after.
[0027]
In this embodiment, when the gas is turned into plasma at the lower portion of the cavity, the gas has electrical characteristics like a conductor, so that this portion exhibits the effect of the antenna, and microwaves are emitted to the outside. A choke 707 (see FIGS. 8 and 9) is disposed in the outer conductor 706 to suppress this externally emitted microwave.
By inserting a coaxial choke having a λ / 4 structure as the choke 707, the leaked microwave can be significantly reduced.
[0028]
Similar to the embodiment of FIG. 7, in the embodiment shown in FIG. 2, since the gas is turned into plasma from the lower portion of the cavity, the gas has electric characteristics like a conductor, and the effect of the antenna is shown in this portion. Then, microwaves are emitted to the outside. For this purpose, a similar choke 302 (see FIGS. 3 and 4) is used in the cavity shown in FIG. Thereby, the external emission microwave is suppressed.
[0029]
Next, an embodiment in which the use state is determined and the embodiment is improved from the embodiment shown in FIG. 2 will be further described with reference to FIGS. In this embodiment, the length of the coaxial cavity is designed to be n (λ / 2), where λ is the wavelength of the microwave, as described above. The diameter of the coaxial cavity is about 2 cm at a frequency of 2.450 GHz.
In particular, since the device is excellent in miniaturization and portability, a large feature that can be applied to a wide range can be obtained.
1 shows a microwave plasma generator such as a plasma torch that can be miniaturized and has good portability and operability. FIG. 10 is a diagram showing the distribution of the excitation electric field of the microwave plasma source, and FIG. 11 is a diagram showing the electric field distribution after the microwave plasma source is turned into plasma immediately after the plasma generation. FIG. 12 is a diagram illustrating a usage state of the microwave plasma generation source.
[0030]
As shown in FIG. 10, the device has a coaxial elongated structure, and a carrier gas 1001 is used by flowing a carrier gas 1001 into a pipe 103 from above. The pipe 103 passes through the upper central conductor 107 and the lower central conductor 108 at the center of the coaxial cavity 1003. Immediately before the inflowing gas enters the plasma state as shown in FIG. 10, the excitation electric field 1004 is applied in a coaxial long direction. Microwave power is supplied to the coaxial cavity 1003 by a coupling loop. At this time, the gas is excited into a plasma state by the electric field in the cavity.
[0031]
When the gas is in a plasma state, microwaves are radiated to the outside by an antenna effect due to the plasma gas becoming conductive. In order to suppress this, a choke 1006 having a λ / 4 structure is arranged. As shown in FIG. 11, immediately after the inflowing gas enters the plasma state, the excitation electric field 1104 is applied from the inner wall outside the cavity to the direction of the coaxial center line. This electric field keeps the gas in a plasma state. When the gas is in a plasma state, the plasma gas becomes conductive, and microwaves are radiated to the outside due to an antenna effect. In order to suppress this, a choke 1006 having a λ / 4 structure is arranged. The structure of the case covering the choke 1006 below the coaxial cavity is shaped like a pen tip. Plasma gas 1007, which has been turned into plasma, is released from the tip, and this gas is widely used for various cleanings and the like.
[0032]
In the microwave plasma generator of the present invention, an example in which a magnetron is used for microwave generation has been described. A solid-state device can be used as the microwave generation source of the present invention, and a microwave FET can be used as the solid-state device. GaAs MESFETs and HEMTFETs are suitable as microwave FETs.
FIG. 15 is a circuit diagram showing a usage state of a microwave plasma generator using the solid-state device. FIG. 16 shows an embodiment of a circuit portion of the microwave plasma generator using a solid-state device as a microwave generation source. It is a block diagram.
As shown in FIG. 15, microwave power is supplied from a microwave oscillator 1508 to a plasma generator (plasma torch) 1513 through a coaxial cable 1509. The gas to be turned into plasma is supplied from a gas cylinder 1512 to a plasma generator (plasma torch) 1513 through a gas passage hose 1511.
[0033]
FIG. 16 is a circuit diagram of the microwave oscillator 1508. An electromagnetic field in the cavity is detected, and a detection signal 1505 is detected by an error signal detection circuit 1506 (which is a circuit composed of a coupler or the like shown in FIG. 1) and converted into a feedback control voltage 1507. This voltage 1507 is applied to a VCO (Voltage Controlled Oscillator) 1501 using a solid-state device. An output signal of the VCO 1501 passes through a circulator 1502, is power-amplified by a solid-state amplifier 1503 such as a MOSFET, and is supplied to a cavity of a plasma generator 1513 shown in FIG. Since this device uses a solid-state device, the device can be made more compact as compared with the above-described device using a magnetron.
[0034]
【The invention's effect】
As described above, the microwave plasma generator of the present invention has a high conversion efficiency, has no auxiliary circuit for mechanical control, is small in size and has a high output, and can be used in a wide range of fields.
A microwave plasma generator for generating a plasma gas by exciting a gas near atmospheric pressure with a microwave, which is easy to handle and can operate stably.
Since the coaxial resonance cavity has a cavity length that is an integral multiple of 1/2 the excitation wavelength, the coaxial resonance cavity can be made smaller than conventional ones.
[0035]
The coaxial resonance cavity is provided with a three-dimensional circuit on the plasma gas emission side that constitutes an electromagnetic wave emission preventing choke that suppresses electromagnetic wave emission from the cavity due to gasification of gas, and thus can be used in various fields.
The operation of the coaxial resonance cavity is stable because the three-dimensional circuit parameters are selected so that the fluctuation of the load due to the difference between the operation modes before and after the plasma conversion in the coaxial resonance cavity is reduced.
[0036]
Since the microwave supply circuit includes a micro-source, the supply circuit, and a feedback circuit that returns the operating state of the coaxial resonance cavity to the microwave source, automation is easy without any particular adjustment. Easy to handle.
The micro-source is a magnetron, which is supplied to the coaxial resonance cavity via a circulator, and a change in the operation of the coaxial resonance cavity is fed back to an excitation coil and an anode of the magnetron to stabilize the operation. Therefore, a large plasma output can be taken out stably.
[0037]
Since the micro-source can be a solid-state oscillator, the device can be made smaller and the whole can be made portable.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a microwave plasma generator according to the present invention.
FIG. 2 is a diagram showing an embodiment of a microwave plasma generation source according to the present invention.
FIG. 3 is a diagram showing a distribution of an excitation electric field of a microwave plasma source immediately before plasma generation according to the present invention.
FIG. 4 is a diagram showing a distribution of an excitation electric field of a microwave plasma source immediately after plasma generation according to the present invention.
FIG. 5 is a diagram showing an electrical equivalent circuit of the microwave plasma source immediately before plasma generation according to the present invention.
FIG. 6 is a diagram showing an electrical equivalent circuit of the microwave plasma source immediately after plasma generation according to the present invention.
FIG. 7 is a view showing a microwave plasma source having a structure different from that of the microwave plasma source according to the present invention;
FIG. 8 is a diagram showing a distribution of an excitation electric field of an example of a microwave plasma source immediately before generation of plasma having a structure different from that of the microwave plasma source according to the present invention.
FIG. 9 is a diagram showing a distribution of an excitation electric field of an example of a microwave plasma source immediately after generation of plasma having a structure different from that of the microwave plasma source according to the present invention.
FIG. 10 is a diagram showing a distribution of an excitation electric field of a small and elongated microwave plasma generation source before plasma generation according to the present invention.
FIG. 11 is a diagram showing an electric field distribution after the plasma of the elongated and miniaturized microwave plasma source after the plasma is generated according to the present invention.
FIG. 12 is a view showing a use state of an elongated miniaturized microwave plasma source according to the present invention.
FIG. 13 is a view showing a plasma-like gas in a quartz pipe in a gas flow path of a microwave plasma generation source unit.
FIG. 14 is a diagram showing electric field intensity distributions at respective positions in a radial direction from a central portion inside the gas flow channel quartz pipe of the microwave plasma generating source portion.
FIG. 15 is a circuit diagram showing a state of use of a microwave plasma generator using the solid-state device.
FIG. 16 is a block diagram showing an embodiment of a circuit portion of a microwave plasma generator using a solid-state device as a microwave source.
FIG. 17 is a diagram showing an example of a conventional microwave plasma generator.
[Explanation of symbols]
1 Microwave plasma source
7 Microwave oscillator
8 circulator
10 Microwave waveguide
11 Pulse motor control 3 stub tuner
101 Microwave Plasma Source
102 Coaxial cavity
103 Gas flow channel quartz pipe
104 plasma gas
105 Cavity Excitation Antenna
106 Loop antenna for detecting internal electromagnetic field
107 Microwave oscillator (magnetron)
108 circulator
109 coaxial connector
110 coaxial cable
111 directional coupler
112 phase shifter
113 3db coupler
114 detector
115 differential amplifier
116 Differential amplifier for excitation
205 center conductor
208 center conductor
302 chalk
401 excitation electric field
705 center conductor
706 outer conductor
707 Chalk
1001 carrier gas
1002 Coupling loop antenna
1003 Coaxial cavity
1004 Excitation electric field
1006 chalk
1302 Plasma-like gas
1501 Microwave solid-state oscillator (VCO)
1502 circulator
1503 Solid-state amplifier
1504 Microwave power signal
1505 Detection signal
1506 Error signal detection circuit
1507 Voltage for feedback control
1508 Microwave oscillator
1509 Coaxial cable
1510 Negative feedback cable
1511 Gas flow hose
1512 Gas cylinder
1513 Plasma generator (plasma torch)
1514 samples

Claims (11)

A microwave plasma generator that generates a plasma gas by exciting a gas near atmospheric pressure with a microwave,
The length of the cavity is an integral multiple of one half of the excitation wavelength, the center conductor is shorter than the length, a non-metallic pipe for a gas flow path is arranged along the center of the center conductor, and injected from one end. A coaxial resonance cavity in which the non-metallic pipe is excited by microwaves and is emitted as plasma from the other end in the gap G where the non-metallic pipe is not covered with the central conductor, and the cavity is excited. A microwave supply circuit,
A microwave plasma generator composed of: The microwave plasma generator according to claim 1, wherein the pipe is a quartz pipe. The center conductor is formed of a first center conductor on the excitation side and a second center conductor on the plasma generation side, and is configured such that gas is excited between the first center conductor and the second center conductor on the plasma generation side. The microwave plasma generator according to claim 1, wherein: 2. The center conductor having a length having a gap between the emission-side wall surfaces of the coaxial resonance cavity, and configured to excite gas between the center conductor and the emission-side wall surface. 3. Microwave plasma generator. The microwave plasma according to any one of claims 1 to 4, wherein the coaxial resonance cavity includes a three-dimensional circuit on a plasma gas emission side, which forms a choke for preventing electromagnetic wave radiation that suppresses electromagnetic wave radiation from the cavity due to gasification of gas. Generator. The coaxial resonance cavity is initially excited in the TM010 mode, is configured to operate in the TEM mode when the gas is turned into plasma by generating a high electric field in the gap, and the resonance frequency when the gas is turned into plasma is reduced. 5. The microwave plasma generator according to claim 1, wherein a three-dimensional circuit is designed so as not to be different from the resonance frequency before the plasma conversion. 7. The microwave plasma generator according to claim 1, wherein an equivalent circuit when the inflowing gas is turned into plasma in the coaxial resonance cavity is configured to operate such that the gap can be regarded as a conductive coaxial cavity. 8. The microwave plasma generating apparatus according to claim 6, wherein a three-dimensional circuit parameter is selected so as to reduce a change in load due to a difference in an operation mode between before and after plasma formation in the coaxial resonance cavity. The microwave plasma generator according to claim 1, wherein the microwave supply circuit includes a microwave generation source, the supply circuit, and a feedback circuit that returns an operation state of the coaxial resonance cavity to the microwave generation source. The micro source is a magnetron, which is supplied to the coaxial resonance cavity via a circulator, and a change in the operation of the coaxial resonance cavity is fed back to an excitation coil and an anode of the magnetron to stabilize the operation. Item 10. A microwave plasma generator according to item 9. The microwave plasma generator according to claim 9, wherein the micro source is a solid-state oscillator.

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