JP2011064173A - High voltage plasma generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high voltage plasma generator of which NO<SB>x</SB>processing efficiency is high. <P>SOLUTION: The high voltage plasma generator for generating plasma by applying high voltage 10<SP>2</SP>-10<SP>5</SP>V for a gas supplied as a gas flow under an atmospheric pressure includes a first electrode to which an electric power for generating the plasma is supplied, a metallic casing covering around the first electrode, a second electrode arranged apart from the first electrode to generate plasma between the first electrode and it and grounded, and an electric power supply device for intermittently supplying an AC current of the same frequency as a resonance frequency when the first electrode radiates an electromagnetic wave to the first electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a high voltage plasma generator for generating plasma using a high voltage of 10 ² to 10 ⁵ V in a high frequency band, for example, a frequency band of 100 MHz to 10 GHz, for example, from a diesel engine used in a ship or an automobile. The present invention relates to an apparatus that can be suitably used in a field such as a processing apparatus for NOx (nitrogen oxidizing gas) in exhaust gas exhausted.

  Today, in order to oxidize NO in exhaust gas exhausted from a diesel engine or the like, a processing apparatus using plasma generated in atmospheric pressure has been proposed.

  Conventionally, a plasma reactor has been proposed in which a high voltage of several kV is applied between electrodes to generate plasma, and this plasma is used to oxidize supplied NO (Non-patent Document 1). FIG. 7 shows the apparatus configuration of this plasma reactor. As shown in FIG. 7, the plasma reactor 10 includes a cylindrical dielectric glass tube 12, an electrode 16 wound around the outer peripheral surface of the dielectric glass tube 12, and a porous dielectric in the dielectric glass tube 12. A spherical pellet 22 made of a dielectric crystal disposed in a space where both sides are separated by body plates 18 and 20, and an AC power source 24 that applies an AC voltage of 60 Hz between the discharge electrode 14 and the electrode 16. .

  By applying a voltage between the discharge electrode 14 and the electrode 16, a high electric field is formed between the spherical pellets 22, and a micro discharge having a short period of nanosecond order is generated to generate non-equilibrium plasma. On the other hand, a nitrogen oxidizing gas containing NO flows through the gap between the spherical pellets 22 as a gas fluid in the dielectric glass tube 12. Therefore, the nitrogen oxidizing gas containing NO is oxidized using the plasma generated in the narrow gap between the spherical pellets 22 and is discharged from the dielectric glass tube 12. Thereby, it is supposed that the oxidation process of NO can be performed efficiently.

"Non-equilibrium plasma and chemical reaction process combined removal technology of nitrogen oxide gas (performance comparison between conventional and barrier plasma reactors), Toshiaki Yamamoto et al., Transactions of the Japan Society of Mechanical Engineers, 66-646B (2000), 1501- 1506

In the plasma reactor 10 described above, since the spherical pellets 22 are disposed in the flow path through which the gas flows, it is difficult to ensure a sufficient flow rate due to flow path resistance or the like. In addition, since the micro discharge having a short period of nanosecond order is used, the efficiency of the oxidation treatment of NO is low. Further, in the plasma reactor 10 described above, it is impossible to decompose NO _2.
It is known that NO ₂ in the exhaust gas becomes nitric acid by reacting with water in the atmosphere, which causes acid rain. Therefore, a plasma generator capable of decomposing NO ₂ is desired.

  Accordingly, an object of the present invention is to provide a high voltage plasma generator having high NOx treatment efficiency.

In order to solve the above problems, a high voltage plasma generator of the present invention is a high voltage plasma that generates plasma by applying a high voltage of 10 ² to 10 ⁵ V to a gas supplied as a gas flow at atmospheric pressure. A generator, which generates plasma between a first electrode to which power for generating plasma is supplied, a metal casing that covers the periphery of the first electrode, and the first electrode Therefore, the second electrode, which is provided apart from the first electrode and is grounded, and the AC signal having the same frequency as the resonance frequency when the first electrode emits electromagnetic waves are intermittently supplied to the first electrode. And a power supply device for supplying power to the electrode.

  The high-voltage plasma generator of the present invention includes a supply pipe that supplies gas to the inside of the casing, a discharge pipe that discharges gas inside the casing, and one of the gases discharged to the discharge pipe. It is preferable to include a branch pipe that branches the section and supplies the branched pipe to the supply pipe.

  The first electrode is a long electrode that generates a high voltage by generating resonance by feeding the AC signal, and the AC signal is provided at a substantially middle portion in the longitudinal direction of the first electrode. It is preferable that a feeding point is provided.

  Further, it is preferable that the casing is grounded, and the second electrode is a mesh electrode provided at a supply port through which gas is supplied to the casing and electrically connected to the casing.

  Further, it is preferable that the supply pipe supplies a gas containing a nitrogen oxidizing gas into the housing, and the generated plasma decomposes the nitrogen dioxide gas in the nitrogen oxidizing gas.

  According to the high voltage plasma generator of the present invention, NOx can be processed with high efficiency.

It is a figure which shows the structure of the plasma reactor which is one Embodiment of the high voltage plasma generator of this invention. It is a figure which shows the structure of the electric power supply unit of the plasma reactor shown in FIG. (A) is a figure which shows RF signal which a CW oscillator produces | generates, (b) is a figure which shows the rectangular pulse signal which a modulation | alteration oscillator produces | generates, (c) is a signal which an RF burst generator outputs FIG. It is a figure which shows the resonance state of the plasma reactor shown in FIG. (A) is a figure which shows the area | region of the plasma generate | occur | produced in the state without gas supply, (b) is a figure which shows the area | region of the plasma generated in the state supplied with gas. It is a figure which shows the structure of the plasma reactor which is one Embodiment of the high voltage plasma generator of this invention. It is a figure which shows the structure of the conventional plasma reactor.

<First Embodiment>
Hereinafter, the plasma reactor which is one embodiment of the high voltage plasma generator of the present invention will be described.
FIG. 1 is a schematic configuration diagram of the plasma reactor of the present embodiment. The plasma reactor introduces nitrogen oxidizing gas (NOx) into the plasma reactor, continuously generates plasma in the vicinity of the gas supply port in the plasma reactor, and processes and discharges NOx using this plasma.
Specifically, the plasma reactor mainly includes a rod-shaped electrode 100, a housing 110, a mesh electrode 112, and a power supply unit 140.

  The rod-shaped electrode 100 (corresponding to “first electrode”) is an electrode having a long rod shape. The rod-shaped electrode 100 is fed with a high-frequency signal, and generates a high voltage when resonance occurs in the rod-shaped electrode 100. The rod-like electrode 100 of this embodiment is made of copper, but silver, aluminum, etc. are also preferably used.

A feeding point 102 for high-frequency signals is provided at an intermediate portion in the longitudinal direction of the rod-shaped electrode 100. A high frequency signal is applied as power from the feeder 118 to the feeding point 102. Assuming that the length of the rod-shaped electrode 100 in the longitudinal direction is 21, the feeding point 102 is located at a position slightly shifted from the center position of the rod-shaped electrode 100 in the longitudinal direction. When the distance from the longitudinal center position of the rod-shaped electrode 100 to a position where the feeding point 102 is provided to x _0, x ₀ satisfies the relation represented by the following formula (1).

Here, Z ₀₀ is the characteristic impedance of the feeder line that feeds the feeding point, and Z _C is the characteristic impedance when the linear electrode 100 is used as the transmission line. Further, when the coefficient indicating the energy loss of the equivalent capacitance C at the time of plasma generation in the high voltage plasma generator is χ, Q = 1 / χ.

The reason why the feeding point 102 is provided at a position slightly deviated from the center position in the longitudinal direction of the rod-shaped electrode 100 is to obtain impedance matching when feeding power to the plasma reactor. As in the case of the AC dipole antenna, when the half length of the wavelength λ of the transmission signal transmitted through the rod-shaped electrode 100 becomes the length 2l of the rod-shaped electrode 100, resonance of the lowest mode occurs in the rod-shaped electrode 100, and it is efficient. A high voltage is generated. Therefore, the length 21 of the rod-shaped electrode 100 is an important factor for determining the resonance frequency in the plasma reactor.
In this embodiment, the length 2l of the rod-shaped electrode 100 is set so that a high voltage is effectively generated in a frequency band of 100 MHz to 10 GHz.

  A dielectric barrier 104 is provided at the end of the rod-like electrode 100 on the mesh electrode 112 side (left end in FIG. 1). A dielectric barrier 104 is provided to maintain the generated plasma. The dielectric barrier 104 is made of alumina having a thickness of about several mm.

The casing 110 is provided so as to cover the periphery of the rod-shaped electrode 100. A supply port 114 for supplying a gas is formed in the housing 110 at a position spaced from at least one end (the left end in FIG. 1) of the rod-shaped electrode 100 toward the extended upper side of the rod-shaped electrode 100. Further, the casing 110 is formed with a discharge port 116 for discharging gas from the other end (the right end in FIG. 1) of the rod electrode 100 at a position spaced apart from the extension of the rod electrode 100. That is, the supply port 114 and the discharge port 116 are positioned on the extension of the rod-shaped electrode 100, and gas is supplied and discharged in parallel with the longitudinal direction of the rod-shaped electrode 100. The housing 110 is made of a metal member that confines electromagnetic waves radiated from the rod-shaped electrode 100 in the internal space. The housing 110 is grounded.
In addition, the housing 110 is provided with an observation window 124 made of an acrylic plate so that the generated plasma can be observed.

  The mesh electrode 112 (corresponding to the “second electrode”) is provided in the vicinity of one end (the left end in FIG. 1) of the rod-like electrode 100 and spaced from this end. The mesh electrode 112 is provided so as to cover the supply port 114 which is an opening provided at an end of the metal casing 110. Further, the mesh electrode 112 is electrically connected to the housing 110. As described above, since the casing 110 is grounded, the potential of the mesh electrode 112 is zero. For the mesh electrode 112, a conductive material having high conductivity, for example, silver, copper, aluminum, or the like is preferably used.

  A supply pipe 130 for supplying nitrogen oxidizing gas (NOx) is connected to the supply port 114 of the housing 110. For example, the supply pipe 130 is connected to an exhaust port such as a diesel engine. A discharge pipe 132 for discharging gas is connected to the discharge port 116 of the housing 110. A blower (not shown) is connected to the discharge pipe 132, and the gas inside the housing 110 is discharged to the atmosphere.

  The power supply unit 140 supplies power to the feeding point 102 intermittently with an AC signal having the same frequency as the resonance frequency of the rod-shaped electrode 100. In the approximate frequency range of the signal supplied by the power supply unit 140, the length of half of the wavelength λ of the transmission signal transmitted through the rod-shaped electrode 100 is the length 2l of the rod-shaped electrode 100, and resonance in the lowest order mode occurs. It is prescribed as follows. The power supply unit 140 supplies a signal having a frequency corresponding to the resonance frequency while adjusting the frequency of the high-frequency signal using the measurement signal obtained from the electric field probe 122 provided in the housing 110.

Here, a schematic configuration of the power supply unit 140 will be described with reference to FIG. As shown in FIG. 2, the power supply unit 140 includes a CW oscillator 142, a modulation oscillator 144, an RF burst generator 146, and an amplifier 148.
The CW oscillator 142 oscillates a continuous wave having a frequency of 100 MHz to 10 GHz and generates an RF signal. In the following description, the frequency at which the CW oscillator 142 oscillates is assumed to be f ₁ [Hz]. The frequency f ₁ oscillated by the CW oscillator 142 is adjusted based on the measurement result of the electric field probe 122. The RF signal generated by the CW oscillator 142 is output to the RF burst generator 146.
Note that the power supply unit 140 can also supply a signal having a frequency corresponding to the resonance frequency based on the intensity of the signal reflected by the connection terminal 120.

The modulation oscillator 144 generates a rectangular pulse signal at a predetermined frequency. In the following description, the pulse width of the rectangular pulse signal generated by the modulation oscillator 144 is W [s], and the frequency for generating the rectangular pulse signal is f ₂ [Hz]. Here, 1 / f ₁ <W <1 / f ₂ . The pulse width W of the rectangular pulse signal generated by the modulation oscillator 144 is such that when the high frequency signal having the same frequency as the resonance frequency of the rod electrode 100 is fed to the feeding point 102, the voltage of the rod electrode 100 that is increased by the feeding becomes the insulation voltage. It is set to be longer than the period until the plasma is generated.
Generally, if the pulse width W is too long, thermal plasma described later may be generated. When the thermal plasma is generated, heat is generated in the rod-shaped electrode 100, and NO or NO ₂ may be generated due to this. Therefore, the pulse width W is preferably set to a length that does not generate thermal plasma.
The rectangular pulse signal generated by the modulation oscillator 144 is output to the RF burst generator 146.

The RF burst generator 146 receives the RF signal generated by the CW oscillator 142. The RF burst generator 146 receives the input of the rectangular pulse signal generated by the modulation oscillator 144. The RF burst generator 146 outputs the RF signal generated by the CW oscillator 142 only during the period of W [s] receiving the input of the rectangular pulse signal. That is, the RF burst generator 146 intermittently outputs an AC signal having a frequency of f ₁ [Hz] during W [s] with a period of 1 / f ₂ [s].
The amplifier 148 amplifies the signal output from the RF burst generator 146. The signal amplified by the amplifier 148 is output to the connection terminal 120.

Here, an example of a signal generated by the power supply unit 140 will be described with reference to FIG. FIG. 3A is a diagram illustrating an example of an RF signal generated by the CW oscillator 142. FIG. 3B is a diagram illustrating an example of a rectangular pulse signal generated by the modulation oscillator 144. FIG. 3C is a diagram illustrating an example of a signal output from the RF burst generator 146.
The power supply unit 140 of the present embodiment intermittently feeds an AC signal having the same frequency as the resonance frequency when the rod-shaped electrode 100 radiates electromagnetic waves to the feeding point 102. Thereby, NOx can be processed efficiently. That is, by outputting an RF signal to the rod-shaped electrode 100 during W [s], the plasma reactor can process NOx without shifting to thermal plasma. In particular, the power supply unit 140 of the present embodiment can be decomposed conventionally by intermittently feeding an AC signal having the same frequency as the resonance frequency when the rod-shaped electrode 100 emits electromagnetic waves to the feeding point 102. It was possible to decompose NO ₂ which was difficult.

Next, a resonance state when a high frequency signal having the same frequency as the resonance frequency of the rod-shaped electrode 100 is fed to the feeding point 102 will be described with reference to FIG. FIG. 4 is a diagram showing a resonance state of the plasma reactor shown in FIG. As shown in FIG. 4, when a high-frequency signal having the same frequency as the resonance frequency is fed to the feeding point 102, resonance that maximizes the voltage occurs at both ends of the rod-shaped electrode 100. A voltage _{Vout of} several kV is generated at both ends of the rod electrode 100.
As described above, the feeding point 102 is displaced by a distance x ₀ of the formula (1) with respect to the center position of the rod-shaped electrode 100. The ratio of the voltage V _out at both ends of the rod-shaped electrode 100 to the voltage V _{in at the} feeding point 102 is expressed as 1 / sin {x ₀ / (2l)} using x ₀ / (2l) determined by the equation (1). Is done.

  Next, plasma generated in the plasma reactor will be described with reference to FIG. FIG. 5A shows the plasma P generated by air at atmospheric pressure in a state where a gas such as nitrogen oxidizing gas is not supplied. As shown in FIG. 5A, when a gas such as a nitrogen oxidizing gas is not supplied, plasma P is generated in a region between the mesh electrode 112 and the end of the rod electrode 100. FIG. 5B shows the plasma P generated by air at atmospheric pressure in a state where a gas such as nitrogen oxidizing gas is supplied. As shown in FIG. 5B, when a gas such as a nitrogen oxidizing gas is supplied, the supplied gas flows separately above and below the rod-like electrode 100. Thereby, the generated plasma P spreads up and down the rod-shaped electrode 100 along the gas flow. Thus, by supplying gas to the plasma reactor, the region where the plasma P is generated becomes wider. As a result, the processing efficiency of the nitrogen oxidizing gas is improved.

  In general, when a continuous wave having the same frequency as the resonance frequency when the rod-shaped electrode 100 emits electromagnetic waves is fed to the feeding point 102, the continuous wave power fed to the feeding point 102 after plasma is generated exceeding the insulation voltage. Does not contribute to the generation of plasma to treat NOx. In contrast, the plasma reactor according to the present embodiment intermittently supplies power to the power supply point 102 so that the power supply to the power supply point 102 is stopped after the plasma is generated exceeding the insulation voltage, so that the power efficiency is improved. be able to. For this reason, the processing efficiency of NOx with respect to the input power is improved.

Further, in the plasma reactor of the present embodiment, the power supply unit 140 intermittently feeds an AC signal having the same frequency as the resonance frequency when the rod-shaped electrode 100 radiates electromagnetic waves to the feeding point 102, so that NO ₂ Can be disassembled.

<Second Embodiment>
Next, the plasma reactor according to the second embodiment will be described.
FIG. 6 is a schematic configuration diagram of the plasma reactor of the present embodiment. The basic configuration of the plasma reactor of the present embodiment is the same as that of the plasma reactor of the first embodiment described above. The plasma reactor of the present embodiment is the same as the plasma reactor of the first embodiment, and further includes a branch pipe 134 and a blower 136.

  As shown in FIG. 6, the branch pipe 134 has one end connected to the discharge pipe 134 and the other end connected to the supply pipe 130. A blower 136 is connected to the branch pipe 134. The gas discharged to the discharge pipe 132 through the discharge port 116 is sucked into the branch pipe 134 by the blower 136 and supplied to the supply pipe 130.

  According to the plasma reactor of the present embodiment, the nitrogen oxidizing gas supplied from the supply pipe 130 is processed by plasma and then supplied again to the supply pipe 130 through the branch pipe 134. As a result, even if the nitrogen oxidizing gas is not sufficiently processed only by flowing once through the casing 110, the processing efficiency of the nitrogen oxidizing gas can be increased by flowing the nitrogen oxidizing gas repeatedly through the casing 110.

  Further, the branch pipe 134 circulates the gas discharged to the discharge pipe 132, whereby the flow rate of the gas flowing through the supply port 114 can be increased. Therefore, as described with reference to FIG. 5, the region where the plasma P is generated is widened, and the processing efficiency of NOx is improved.

  In general, when plasma is generated, the generated ions have a lower speed than electrons, so that ion gas tends to remain in a region where plasma is generated. On the other hand, according to the present embodiment, the branch pipe 134 circulates the gas discharged to the discharge pipe 132, whereby the flow rate of the gas flowing through the supply port 114 can be increased, and the plasma is generated. It is possible to diffuse ion gas that tends to remain in the gas. As a result, the stability of the plasma reactor is increased.

Example 1
Hereinafter, Example 1 performed in order to confirm the effect of this invention is demonstrated.
In this example, it was confirmed that NO ₂ was decomposed using the plasma reactor of the first embodiment described with reference to FIG. The dimensions of the rod-shaped electrode 100 were 344 mm in length in the longitudinal direction, 4 mm in height (length in the vertical direction in FIG. 1), and 6 mm in depth (length in the direction perpendicular to the paper in FIG. 1). In addition, the dimensions of the casing 110 were 428 mm in length in the longitudinal direction, 72 mm in height, and 60 mm in depth. The thickness of the dielectric barrier 104 was 3 mm. The distance between the mesh electrode 114 and the dielectric barrier 104 was 3 mm.

As a result of performing impedance matching by sweeping the resonance frequency in the range of 380 to 420 MHz by the measurement signal of the electric field probe 122, the resonance frequency was 396.1 MHz. Further, the Q value was approximately 3000, and the voltage _Vout at both ends of the rod-shaped electrode 100 was approximately 30 kV.
Therefore, the frequency f ₁ oscillated by the CW oscillator 142 is set to 396.1 MHz. The pulse width W of the rectangular pulse signal generated by the modulation oscillator 144 is set to 0.7 μs. Further, a frequency _{f 2} which modulation oscillator 144 generates a rectangular pulse signal is a 2.5 kHz.

NO ₂ gas was diluted with nitrogen gas (N ₂ gas) to 202.8 ppm and supplied to the supply pipe 130. The oxygen concentration of the gas supplied to the supply pipe 130 was 10.72%. The flow rate of the gas supplied to the supply pipe 130 is 2.0 liters per minute. At this time, when the concentration of NO ₂ contained in the gas discharged from the discharge pipe 132 was measured, it was 70.2 ppm.
From this, it was confirmed that according to the plasma reactor of this example, NO ₂ supplied from the supply pipe 130 is decomposed.

In this embodiment, the gas obtained by diluting NO ₂ gas with nitrogen gas is supplied to the supply pipe 130 and it is confirmed that NO ₂ is decomposed. However, the gas obtained by diluting NO gas with nitrogen gas is supplied. In the same manner, NO ₂ generated during the process is also decomposed. That is, when a gas obtained by diluting NO gas with nitrogen gas is supplied to the supply pipe 130, the NO gas is first oxidized by plasma to become NO ₂ gas. Thereafter, the NO ₂ gas is decomposed as described above.

(Example 2)
Next, Example 2 performed for confirming the effect of the present invention will be described.
In this example, it was confirmed that NO ₂ was decomposed using the plasma reactor of the second embodiment described with reference to FIG. The dimensions of the rod-shaped electrode 100 were 344 mm in length in the longitudinal direction, 4 mm in height (length in the vertical direction in FIG. 1), and 6 mm in depth (length in the direction perpendicular to the paper in FIG. 1). In addition, the dimensions of the casing 110 were 428 mm in length in the longitudinal direction, 72 mm in height, and 60 mm in depth. The thickness of the dielectric barrier 104 was 3 mm. The distance between the mesh electrode 114 and the dielectric barrier 104 was 3 mm.

As a result of searching for the resonance frequency in the range of 380 to 420 MHz by impedance measurement using the measurement signal of the electric field probe 122, the resonance frequency was 395.3 MHz. Further, the Q value was approximately 3000, and the voltage _Vout at both ends of the rod-shaped electrode 100 was approximately 30 kV.
Therefore, the frequency f ₁ oscillated by the CW oscillator 142 is set to 395.3 MHz. The pulse width W of the rectangular pulse signal generated by the modulation oscillator 144 is set to 0.7 μs. Further, a frequency _{f 2} which modulation oscillator 144 generates a rectangular pulse signal is a 2.5 kHz.

NO ₂ gas was diluted with nitrogen gas (N ₂ gas) to 202.8 ppm and supplied to the supply pipe 130. The oxygen concentration of the gas supplied to the supply pipe 130 was 10.72%. The flow rate of the gas supplied to the supply pipe 130 is 2.0 liters per minute. The flow rate of the gas sucked into the branch pipe 134 by the blower 136 and circulated through the supply pipe 130 is 20 liters per minute.
When the gas supplied to the supply pipe 130 and the gas circulated to the supply pipe 130 by the branch pipe 134 reach an equilibrium state, the concentration of NO ₂ contained in the gas discharged from the discharge pipe 132 is measured to be 40 ppm or less. Met.
Thus, according to the plasma reactor of the present embodiment, since the gas is circulated by the branch pipe 134, the more efficiently NO ₂ is decomposed was confirmed.

  As mentioned above, although the high voltage plasma generator of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, various improvements and changes may be made. Of course.

DESCRIPTION OF SYMBOLS 100 Rod-shaped electrode 102 Feeding point 104 Dielectric barrier 110 Case 112 Reticulated electrode 114 Supply port 116 Discharge port 118 Feed line 120 Connection terminal 122 Electric field probe 124 Observation window 130 Supply pipe 132 Discharge pipe 134 Branch pipe 136 Blower 140 Power supply unit 142 CW oscillator 144 Modulation oscillator 146 RF burst generator 148 Amplifier

Claims (5)

A high voltage plasma generator for generating plasma by applying a high voltage of 10 ² to 10 ⁵ V to a gas supplied as a gas flow at atmospheric pressure,
A first electrode to which power for generating plasma is supplied;
A metal casing covering the first electrode;
A second electrode that is spaced from the first electrode and grounded to generate plasma with the first electrode;
A power supply device that intermittently supplies an alternating current signal having the same frequency as the resonance frequency when the first electrode emits electromagnetic waves to the first electrode;
A high voltage plasma generator characterized by comprising: A supply pipe for supplying gas into the housing;
A discharge pipe for discharging the gas inside the housing;
A branch pipe that branches a part of the gas discharged to the discharge pipe and supplies the branched pipe to the supply pipe;
The high voltage plasma generator of Claim 1 provided with these.   The first electrode is a long electrode that generates a high voltage by generating resonance by supplying the AC signal, and the AC signal is supplied to a substantially middle portion in the longitudinal direction of the first electrode. The high-voltage plasma generator according to claim 1 or 2, wherein a point is provided. The housing is grounded;
The high-voltage plasma according to any one of claims 1 to 3, wherein the second electrode is a mesh electrode provided at a supply port through which gas is supplied to the casing and electrically connected to the casing. Generator. The supply pipe supplies a gas containing nitrogen oxidizing gas into the housing,
The high voltage plasma generator according to any one of claims 1 to 4, wherein the generated plasma decomposes nitrogen dioxide gas in the nitrogen oxidizing gas.