JP4022590B2 - Microwave plasma generator - Google Patents

Description

  The present invention relates to a microwave plasma generator for generating a thermal plasma gas by converting a gas at atmospheric pressure into a plasma gas by microwave excitation.

  Thermal plasma is almost synonymous with atmospheric pressure plasma. In the 1970s, development for industrial applications became active. Applications include industrial materials melting, fusing, joining, refining, metallurgy, spraying, and other industrial materials processing, lighting fields such as light sources for displays that use plasma-generated light, fine particle generation, induction This is a field of chemical analysis of trace sample components using plasma as a means of ionization, and a field of cleaning of surface treatment of materials such as semiconductor processes, which covers a wide range of fields.

  In the 1980s, it was noticed by using it for removing the causative substances of air pollution. Tepla RF plasma source and ARIOS atmospheric pressure plasma source have been developed and used. The former has a low plasma conversion efficiency because the high frequency for exciting the gas into the plasma state is relatively low at 13.56 MHz. In addition, the apparatus has become large due to the frequency relationship.

  The atmospheric pressure plasma source of ARIOS will be described with reference to FIG. This apparatus uses a microwave that oscillates near an excitation frequency of 2.45 GHz for this plasma source. A microwave waveguide 10 is used as means for supplying microwaves to a plasma cavity inside a microwave plasma source 1 that generates plasma gas. The impedance when the load side is viewed from the microwave oscillator 7 varies greatly before and after the plasma is lit. In order to supply appropriate power to the plasma source, a stub tuner 11 is provided in the middle of the waveguide 10, and the stub tuner 11 is automatically controlled to stably supply power. Since a waveguide is used, the size and weight of the device cannot be avoided. The diameter of the plasma cavity is relatively large at 15 cm. In order to automatically control the stub tuner 11, a pulse motor that performs mechanical control is required.

An object of the present invention is to provide a microwave plasma generator capable of stably generating low-temperature plasma operating at atmospheric pressure (or atmospheric pressure close thereto) with a small apparatus.
Still another object of the present invention is to provide a microwave plasma generator capable of moving a plasma head freely by further reducing the size of a plasma generator using a coaxial resonator.
Still another object of the present invention is to provide a microwave plasma generator that is easy to handle using a circuit that stabilizes the operation of a coaxial resonator.

In order to achieve the above object, a microwave plasma generator according to claim 1 according to the present invention comprises:
In a microwave plasma generator that generates a plasma gas by exciting a gas close to atmospheric pressure with a microwave ,
After the excitation, it is a coaxial resonance cavity where a coaxial resonance state different from that before excitation is formed,
The outer wall of the coaxial resonant cavity, a central conductor shorter than the length of the outer wall, and a plasma generation gas path are formed to discharge plasma gas from the other end of the coaxial resonant cavity, and the outer wall is excited and plasma of the internal gas is emitted. Comprising a non-metallic pipe that forms a central conductor in a coaxial resonance state in cooperation with the central conductor, and a coaxial cable connecting portion that supplies excitation power to the outer wall. A coaxial resonant cavity that is converted into a mode in which an electric field is generated from the outer wall of the resonant cavity toward the non-metallic pipe;
A microwave supply circuit for exciting the coaxial resonant cavity;
A coaxial cable connecting the microwave of the microwave supply circuit to the coaxial resonant cavity;
It is characterized by comprising.
The microwave plasma generator according to claim 2 of the present invention is the microwave plasma generator according to claim 1,
The non-metallic pipe is exposed in the cavity between the central conductors or between the central conductor and the outer wall on the plasma gas discharge side of the coaxial resonant cavity,
The coaxial resonance cavity is converted from a mode (TM) before excitation along the non-metallic pipe to a mode (TEM) after excitation.
The microwave plasma generator according to claim 3 of the present invention is the microwave plasma generator according to claim 1,
The outer conductor of the coaxial cable is connected to the outer wall of the coaxial resonance cavity.
A microwave plasma generator according to claim 4 of the present invention is the microwave plasma generator according to claim 1,
The central conductor of the coaxial cable is coupled to a space in the coaxial resonance cavity as an antenna.

The microwave plasma generation apparatus of the present invention has high conversion efficiency, no auxiliary circuit for mechanical control, small size and high output, and can be used in a wide range of fields.
A microwave plasma generator that generates a plasma gas by exciting a gas close to atmospheric pressure with a microwave, is easy to handle, and can operate stably. Excitation power can be supplied directly from the coaxial cable to the coaxial resonant cavity.
Since the length of the cavity can be an integral multiple of 1/2 of the excitation wavelength, the coaxial resonance cavity can be made smaller than the conventional one.

The coaxial resonant cavity, because it is Rukoto comprises a three-dimensional circuit which constitutes the suppressing electromagnetic radiation preventing choke electromagnetic emanations from the cavity by the plasma of the gas into a plasma gas discharge side, used in various fields it can.
The coaxial resonant cavity, the operation is stable because it constructed by selecting a three-dimensional circuit parameters as variations in the load is reduced due to a difference in the operation mode before and after plasma in the coaxial resonant cavity.

The microwave feed circuit includes a microwave generating source, said supply circuit, since the operating state of the coaxial resonant cavity can be constructed from the feedback circuit for feeding back to the microwave source, easily automated without any particular adjustment Easy to handle.
It said microwave source is a magnetron, is supplied to the coaxial resonant cavity via a circulator, a change in the operation of the coaxial resonant cavity to stabilize the operation is fed back to the excitation coil and the anode of the magnetron Since it can comprise, a large plasma output can be taken out stably.

  Since the microwave generation source can be a solid state oscillator, the apparatus can be further miniaturized and the whole can be configured to be portable.

  Embodiments of the present invention will be described below with reference to the drawings and the like. FIG. 1 is a schematic view of a microwave plasma generator of the present invention. The microwave plasma generation source 101 includes a coaxial cavity 102 and a central gas flow path quartz pipe 103. A microwave oscillator (magnetron) 107 oscillates an excitation microwave. 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 cavity excitation. The directional coupler 111 detects the traveling wave and the reflected wave, and is feedback-connected 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. Yes. Excitation microwave power is supplied from the cavity excitation antenna 105. The internal electromagnetic field is detected by the internal electromagnetic field detection loop antenna 106 and is feedback-connected to the excitation coil 117 of the microwave oscillator (magnetron) 107 via the differential amplifier 116 for excitation.

A coaxial cavity 102 is formed inside the microwave plasma generation source 101, and a thin quartz pipe 103 that forms a gas flow path is disposed at the center of the coaxial portion. A part of the coaxial part at the center of the coaxial cavity 102 is removed, and the quartz pipe 103 is exposed at the part.
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 the lower part of the gas flow path quartz pipe 103.
The microwave oscillator 107 generates a microwave that excites the coaxial cavity 102. The frequency of this microwave is 2.450 GHz in the IMS (Industrial Medical Science) frequency band recognized for industrial use.

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 the plasma state and the load immediately after it change greatly. It is not preferable that the excitation frequency change due to this change.
As a first step of this measure, the present invention uses a change in the electric field distribution in the cavity before plasma formation and the electric field distribution after plasma formation so that it operates as a resonator having the same frequency before and after plasma formation. design.
Even if such a design is used, slight fluctuations in the frequency cannot be avoided. Therefore, as a second step, the change in the frequency before and after the plasma formation is detected, and this data is used as the anode voltage of the microwave oscillator 107. And the method of controlling the exciting current and locking the oscillation frequency.

Next, the structure of the microwave plasma generation source 101 will be described in some detail. FIG. 2 is a perspective view showing the 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 central part of the cavity 102 through the quartz pipe 103 for gas flow path. The quartz pipe 103 passes through the central portion of the upper central conductor 205.
The gas flow path quartz pipe 103 also penetrates the central portion of the lower center conductor 208. Only the gas flow path 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 gas flow path quartz pipe 103 is excited and turned into plasma.

FIG. 13 is a diagram showing the plasma-like gas inside the gas flow path quartz pipe 103 of the microwave plasma generation source section, and FIG. 14 is directed in the radial direction from the center portion inside the gas flow path quartz pipe of the microwave plasma generation source section. It is a figure which shows electric field strength distribution of each position. When the gas is turned into plasma, the plasma gas 1302 inside the gas flow path quartz pipe 103 shown in FIG. 13 can be regarded as an electrical conductor. Therefore, the excitation microwave cannot enter the plasma gas 1302.
The electric field of the microwave for excitation exists on the outer periphery of the pipe as shown by a curve 1401 shown in FIG. 14, and the inside wall of the pipe 103 is attenuated as the center of the inner wall of the pipe 103 is centered only at the same potential as the external electric field. Draw. This is similar to the phenomenon of the skin effect where charges are concentrated only on the surface of a metal conductor. Thus, the electric field in the vicinity of the inner wall of the gas flow path quartz pipe 103 is strong, but decreases rapidly toward the center. The plasma gas appears as an electrical conductor when viewed from the outside. That is, since the gas is turned into plasma in the lower center conductor 208, the gas has electrical characteristics like a conductor. Therefore, this portion shows just the effect of the antenna, and microwaves may be emitted to the outside. This point will be described later.

FIG. 3 is a diagram showing the distribution of the excitation electric field of the microwave plasma generation source before plasma generation in 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 generation source immediately after plasma generation. FIG. 3 shows an excitation electric field 301 generated in the space between the upper center conductor and the lower center conductor just before the carrier gas is turned into plasma. An electric field is applied between the upper central conductor 205 and the lower central conductor 208 in the vertical direction. Distribution of the electric field is in the vibration of the reentrant mode (TM mode). FIG. 4 shows the electric field distribution after plasmatization.
The excitation electric field 401 is applied in the direction from the inner wall on the outer side of the cavity toward the central conductor, and exhibits just a coaxial mode (TEM mode) vibration.

FIG. 5 and FIG. 6 respectively show the electric field distribution and the electric equivalent circuit immediately before and after the gas is turned into plasma. Field vibration mode of FIG. 5 is Ri Do the reentrant Mode (TM mode), the electrical equivalent circuit ing the series circuit of L ₁ and C ₁ and L _2. The operation mode of FIG. 6 is a TEM mode, and the resonance frequencies are respectively expressed by the following equations.
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 )]))

As described above, a change in the resonance frequency according to the operation mode occurs. However, such a change in the resonance frequency is not preferable, and if any, it is desirable that the difference is small. Therefore, in the present invention, optimization is performed so that f ₁ and f ₂ are substantially equal by changing the structure of the cavity. This is nothing but selecting the shape of the cavity so that C ₁ (L ₁ + L ₂ ) and 2C ₂ L ₃ L ₄ / (L ₃ + L ₄ ) are equal in the above formula. In this way, the structure of the coaxial cavity 102 is optimally designed and viewed from the cavity excitation antenna at the microwave input section even if the load immediately before the carrier gas becomes plasma and the load immediately after it change greatly. Load fluctuation can be reduced. This can greatly increase the stability of the system operation.

  The second countermeasure 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 excitation magnetic field of the microwave oscillator (magnetron) 107. The output of the microwave oscillator (magnetron) 107 is supplied to the circulator 108. This circulator 108 is used for avoiding a phenomenon in which the load fluctuation before and after the plasma state affects and changing the oscillation frequency of the microwave oscillator (magnetron) 107, that is, for insulating the reflected power of the load. . Further, the signal is added to the directional coupler 111 via the coaxial connector 109, and the output from the directional coupler 111 is supplied to the cavity 102 of the microwave plasma generation source 101 via the cavity excitation antenna 105.

A traveling wave and a reflected wave are output to the b terminal of the directional coupler 11, respectively. The reflected wave is applied to the P ₂ terminal of the 3db coupler 113 through the phase shifter 112. The power of the reflected wave is set to be a minimum value at the resonance frequency by adjusting the phase shifter 112. 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 shifter 112 is set so that the phase of the reflected wave and the traveling wave is in phase during resonance.

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 is applied to the P ₁ terminal of the 3db coupler 113. The output terminals P ₃ and P ₄ of the 3db coupler 113 are supplied to the detector 114 and converted into a DC voltage. Each DC voltage is supplied to the input of the 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 a plasma state, the microwave plasma generation source 101 is set to operate at a 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 formation can be sufficiently reduced. When this load state changes, this frequency is slightly different from the natural resonance frequency of the cavity 102, but in order to further reduce this frequency difference, an electrical negative feedback is applied to the microwave oscillator 107. This control method will be described. When the microwave oscillator (magnetron) 107 supplies power at this different frequency, a reflected wave is generated from the cavity 102, and this reflected wave is generated at the b terminal of the directional coupler 111. Further, the signal passes through the phase shifter 112 and is supplied to P ₂ of the output terminal of the 3db coupler 113.

On the other hand, the traveling wave is supplied to P ₁ of the output terminal of the 3db coupler 113. As a result, the output signal of the detector 114 generates voltages having different amplitudes. This differential 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, a circuit (not shown in FIG. 1) is added to naturally supply the differential voltage of the differential amplifier 115 in synchronization with the pulse voltage of the anode. That is, it operates 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 specific resonance frequency of the cavity 102.

  Furthermore, in order to increase the frequency stability 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, so that the inherent resonance of the cavity 102 is generated. Feedback is provided so as to approach the frequency. As described above, in the circuit of FIG. 1, both the anode voltage and the excitation current can be controlled, and the stability of the frequency of the system can be achieved.

  As described above, the plasma gas appears as an electrical conductor in the microwave band when viewed from the outside. That is, since the gas is turned into plasma in the lower center conductor 208, the gas has electrical characteristics like a conductor. Therefore, this portion shows just the effect of the antenna, and microwaves may be emitted to the outside. For this purpose, a choke structure is formed particularly in the lower central conductor 208. This structure prevents radio waves from being transmitted to the outside. In order to suppress this externally emitted microwave (because it acts as a disturbing radio wave on an external device), a choke structure is provided inside the lower center conductor 208. By inserting a coaxial choke having a λ / 4 structure as this choke, the leaking microwave can be greatly reduced. As described above, the choke 302 (FIGS. 3 and 4) is provided in order to suppress microwave leaking to the outside after the gas is turned into plasma. FIG. 4 shows the electric field distribution after plasmatization. The excitation electric field 401 is applied in the direction of the center conductor from the inner wall outside the cavity, and exhibits exactly the vibration of the coaxial mode. The diameter of the gas flow path quartz pipe 103 passing through the center of the upper center conductor 205 is sufficiently smaller than the wavelength of the microwave, and the flowing gas is a gas that is not converted into plasma. There is no radiation outside.

FIG. 7 is a view showing a microwave plasma generation source having a structure different from that of the microwave plasma generation source according to the present invention. The above-described microwave plasma generation source 101 has a configuration in which the upper conductor having the structure 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. A carrier gas is led from the upper part of the cavity to the central part of the cavity through a gas inlet quartz pipe 103 provided through the central conductor 705. Between the central conductor 705 and the lower part of the cavity, only the gas flow path quartz pipe 103 is exposed. Since an electric field is applied to the exposed portion, the carrier gas in the gas flow path quartz pipe 103 is excited and turned into plasma.

The electric field distribution of the microwave plasma generation source having this structure is the distribution shown in FIG. 8 before the plasma conversion, and changes to the distribution shown in FIG. 9 immediately after the plasma conversion. FIG. 8 shows an excitation electric field 801 generated in the space between the upper center conductor and the lower 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 cavity. This distribution of an electric field is in the vibration of reentrant mode. FIG. 9 shows the electric field distribution after plasmatization. An excitation electric field 901 is applied in the direction of the pipe 103 from the inner wall outside the cavity, and exhibits just a coaxial mode vibration. Similar to the embodiment shown in FIG. 2, the circuit structure can be designed so that the resonance frequency does not change before and after.

In this embodiment, since the gas is turned into plasma at the lower part of the cavity, the gas has electrical characteristics like a conductor. Therefore, this portion shows just the effect of the antenna, and the microwave is 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.
As the choke 707, a leaking microwave can be greatly reduced by inserting a coaxial choke having a λ / 4 structure.

  As in the embodiment of FIG. 7, in the embodiment shown in FIG. 2, the gas is converted into plasma from the lower part of the cavity, so that the gas has electrical characteristics like a conductor. 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. This suppresses externally emitted microwaves.

Next, with reference to FIGS. 10-12, the Example which determined the use condition and improved the Example shown in FIG. 2 mentioned above is further demonstrated. In this embodiment as well, the length of the coaxial cavity is designed to be n (λ / 2) where λ is the wavelength of the microwave. 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 great feature that extends the application range can be obtained.
A microwave plasma generator such as a plasma torch that can be miniaturized and has good portability and operability is shown. FIG. 10 is a diagram illustrating the distribution of the excitation electric field of the microwave plasma generation source, and FIG. 11 is a diagram illustrating the electric field distribution after the plasma generation of the microwave plasma generation source immediately after plasma generation. FIG. 12 is a diagram illustrating a use state of the microwave plasma generation source.

  As shown in FIG. 10, the apparatus has a coaxial elongated structure, and uses a carrier gas 1001 flowing into the pipe 103 from above. The pipe 103 passes through the upper center conductor 107 and the lower center conductor 108 at the center of the coaxial cavity 1003. As shown in FIG. 10, immediately before the inflowing gas becomes a plasma state, the excitation electric field 1004 is applied in a coaxial long direction. Microwave power is supplied to the coaxial cavity 1003 by the coupling group. At this time, the gas is excited into a plasma state by the electric field in the cavity.

  When the gas is in a plasma state, microwaves are radiated to the outside due to the antenna effect due to the plasma gas conducting phenomenon. In order to suppress this, a λ / 4 structure choke 1006 is disposed. As shown in FIG. 11, immediately after the inflowing gas becomes a plasma state, the excitation electric field 1104 is applied in the direction of the coaxial center line from the inner wall outside the cavity. This electric field keeps the gas in a plasma state. When the gas is in a plasma state, a plasma gas conducting phenomenon occurs, and microwaves are radiated to the outside due to the antenna effect. In order to suppress this, a λ / 4 structure choke 1006 is disposed. The structure of the case covering the choke 1006 at the bottom of the coaxial cavity is shaped like a pen nib. Plasma gas 1007 converted into plasma is emitted from the tip, and this gas is widely used for various cleanings.

In the microwave plasma generator of the present invention, an example in which a magnetron is used for microwave generation has been shown. A solid-state element can also be used as the microwave generation source of the present invention, and a microwave FET can be used as the solid-state element. As the microwave FET, GaAs MESFET and HEMTFET are suitable.
FIG. 15 is a circuit diagram showing a use state of a microwave plasma generator using the solid-state device, and FIG. 16 shows an embodiment of a circuit portion of the microwave plasma generator using a solid-state device as a microwave source. It is a block diagram.
As shown in FIG. 15, microwave power is supplied from a microwave oscillation device 1508 to a plasma generation device (plasma torch) 1513 through a coaxial cable 1509. A gas to be converted into plasma is supplied from a gas cylinder 1512 to a plasma generator (plasma torch) 1513 through a gas flow path hose 1511.

  FIG. 16 shows a circuit diagram of the microwave oscillator 1508. The electromagnetic field in the cavity is detected, and the detection signal 1505 is detected by an error signal detection circuit 1506 (referring to a circuit composed of a coupler or the like shown in FIG. 1) and converted to a feedback control voltage 1507. This voltage 1507 is applied to a VCO (Voltage Controlled Oscillator) 1501 using a solid element. The output signal of the VCO 1501 passes through the circulator 1502, is amplified in power by a solid-state amplifier 1503 such as a MOSFET, and is supplied to the cavity of the plasma generator 1513 shown in FIG. Since this apparatus uses a solid element, the apparatus can be further reduced in size as compared with the apparatus using the magnetron described above.

It is a figure which shows the Example of the microwave plasma generator by this invention. It is a figure which shows the Example of the microwave plasma generation source by this invention. It is a figure which shows distribution of the excitation electric field of the microwave plasma generation source just before plasma generation by this invention. It is a figure which shows distribution of the excitation electric field of the microwave plasma generation source immediately after the plasma generation by this invention. It is a figure which shows the electrical equivalent circuit of the said microwave plasma generation source just before the plasma generation by this invention. It is a figure which shows the electrical equivalent circuit of the said microwave plasma generation source immediately after the plasma generation by this invention. It is a figure which shows the microwave plasma generation source of a structure different from the said microwave plasma generation source by this invention. It is a figure which shows distribution of the excitation electric field of an example microwave plasma generation source just before the plasma generation of the structure different from the said microwave plasma generation source by this invention. It is a figure which shows distribution of the excitation electric field of an example microwave plasma generation source immediately after the plasma generation of the structure different from the said microwave plasma generation source by this invention. It is a figure which shows the distribution of the excitation electric field of the elongate miniaturized microwave plasma generation source before the plasma generation by this invention. It is a figure which shows the electric field distribution after plasmification of the elongate miniaturized microwave plasma generation source after the plasma generation by this invention. It is a figure which shows the use condition of the elongate miniaturized microwave plasma generation source by this invention. It is a figure which shows the plasma-like gas inside the gas flow path quartz pipe of a microwave plasma generation source part. It is a figure which shows electric field strength distribution of each position which goes to a radial direction from the center part inside the gas flow path quartz pipe of a microwave plasma generation source part. It is a circuit diagram which shows the use condition of the microwave plasma generator using the said solid-state apparatus. It is a block diagram which shows the Example of the circuit part of the microwave plasma generator which used the solid-state apparatus as a microwave generation source. It is a figure which shows the example of the 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 Channel Quartz Pipe 104 Plasma Gas 105 Cavity Excitation Antenna 106 Inside Loop antenna for electromagnetic field detection 107 Microwave oscillator (magnetron)
DESCRIPTION OF SYMBOLS 108 Circulator 109 Coaxial connector 110 Coaxial cable 111 Directional coupler 112 Phaser 113 3db coupler 114 Detector 115 Differential amplifier 116 Excitation differential amplifier 205 Central conductor 208 Central conductor 302 Choke 401 Excitation electric field 705 Central conductor 706 Outer conductor 707 Choke 1001 Carrier gas 1002 Coupling group antenna 1003 Coaxial cavity 1004 Excitation electric field 1006 Choke 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 Feedback control voltage 1508 Microwave oscillation device 1509 Coaxial cable 1510 Negative feedback cable 1511 Gas flow path hose 1512 Gas cylinder 1513 Plasma generator (plasma torch) )
1514 samples

Claims (4)

In a microwave plasma generator that generates a plasma gas by exciting a gas close to atmospheric pressure with a microwave ,
After the excitation, it is a coaxial resonance cavity where a coaxial resonance state different from that before excitation is formed,
The outer wall of the coaxial resonant cavity, a central conductor shorter than the length of the outer wall, and a plasma generation gas path are formed to discharge plasma gas from the other end of the coaxial resonant cavity, and the outer wall is excited and plasma of the internal gas is emitted. Comprising a non-metallic pipe that forms a central conductor in a coaxial resonance state in cooperation with the central conductor, and a coaxial cable connecting portion that supplies excitation power to the outer wall. A coaxial resonant cavity that is converted into a mode in which an electric field is generated from the outer wall of the resonant cavity toward the non-metallic pipe;
A microwave supply circuit for exciting the coaxial resonant cavity;
A coaxial cable connecting the microwave of the microwave supply circuit to the coaxial resonant cavity;
The microwave plasma generator characterized by comprising . In the microwave plasma generator of Claim 1,
The non-metallic pipe is exposed in the cavity between the central conductors or between the central conductor and the outer wall on the plasma gas discharge side of the coaxial resonant cavity,
The coaxial resonance cavity is converted from a mode (TM) before excitation along the non-metallic pipe to a mode (TEM) after excitation. In the microwave plasma generator of Claim 1,
The microwave plasma generator according to claim 1, wherein an outer conductor of the coaxial cable is connected to an outer wall of the coaxial resonance cavity. In the microwave plasma generator of Claim 1,
The microwave plasma generator according to claim 1, wherein a central conductor of the coaxial cable is coupled to a space in the coaxial resonance cavity as an antenna.

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