JP2008204870A - Atmospheric pressure plasma generator and ignition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atmospheric pressure plasma generator which has a simple and compact structure and is capable of igniting plasma stably without damaging a plasma generating circuit such as a matching circuit whether there is a single reaction tube or there are a plurality of them arranged parallel. <P>SOLUTION: The atmospheric pressure plasma generator is provided with a reaction tube 1 whose one end is open as a diffuser 5, an antenna 2 or an electrode disposed around the circumference or in the vicinity of the reaction tube 1, a gas supply means which introduces a gas 7 into the reaction tube 1 from the other end, a high frequency power supply 4 which applies high frequency voltage to the antenna 2 or the electrode. A pair of ignition electrodes 12 and 13 are disposed on one end side and the other end side of the reactor tube 1 with the antenna 2 or the electrode inserted in-between, one of the ignition electrode 12 is electrically grounded, and the other ignition electrode 13 is connected to an ignition device 14 which generates high voltage for predetermined time, so that ignition discharge occurs and vertically penetrates the plasma generating part corresponding to the antenna 2 in the reaction tube 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an atmospheric pressure plasma generation apparatus and an ignition method capable of stably igniting atmospheric pressure plasma with a simple configuration in an atmospheric pressure plasma generation apparatus.

  An atmospheric pressure plasma generator introduces a gas from one end of a reaction tube and applies a high frequency voltage to an antenna or an electrode disposed around or in the vicinity of the reaction tube to generate plasma in the reaction tube. The plasma is blown out from the other end. In such an atmospheric pressure plasma apparatus, a predetermined high-frequency voltage necessary for continuously generating plasma in a state where the atmospheric pressure plasma is ignited is applied to an antenna or an electrode, and gas is introduced into a reaction tube. Alone, the atmospheric pressure plasma is not ignited first, and in order to ignite, it is necessary to apply a high voltage to the antenna and the electrode. Therefore, it is conceivable to apply a high voltage necessary for ignition from a high-frequency power source that applies a high-frequency voltage to the antenna or electrode, but the matching circuit that can withstand high output has a high withstand voltage and current, and the parts used are large. And the device is not compact. Therefore, an ignition device is provided that uses a low-output high-frequency power source and applies a high voltage in or near the reaction tube to ignite plasma.

  As an atmospheric pressure plasma generator having an ignition device, as shown in FIG. 7, a pair of plasma generating electrodes 22, 23 are arranged on the outer periphery of the reaction tube 21 at an appropriate interval in the axial direction. While supplying gas, a high-frequency voltage is applied between the plasma generation electrodes 22 and 23 from the high-frequency power source 24 via the matching circuit 25, thereby generating plasma at the plasma generation unit 26 between the plasma generation electrodes 22 and 23. In the atmospheric pressure plasma generator that is blown out from the outlet 27, the ignition electrode 28 connected to the high-voltage pulse generator 29 is positioned in the vicinity of the outlet 27 of the reaction tube 21 at the downstream of the plasma ignition. By applying a high voltage pulse voltage, discharge between the ignition electrode 28 and the grounded plasma generation electrode 23 causes preionized plasma to be discharged. Raised, that so as to ignite a plasma in the plasma generating section 26 is known in the pre-ionized plasma (for example, see Patent Document 1).

  Further, as shown in FIG. 8, a pair of plasma generating electrodes 32 and 33 are arranged on the outer periphery of the reaction tube 31 at an appropriate interval in the axial direction, and a high frequency power supply 34 is provided between the plasma generating electrodes 32 and 33. A high-frequency voltage is applied via the matching circuit 35, the plasma generating electrodes 32 and 33 are used as a plasma generating unit 36, and the other end of the reaction tube 31 is used as a plasma blowing outlet 37. , A gas introduction pipe 39 is connected between the first gas introduction port 38 at one end of the reaction tube 31 and the plasma generating electrode 32, and a range between the first gas introduction port 38 and the gas introduction pipe 39 is set. A pair of preliminary discharge electrodes 40, 41 are arranged opposite to each other in contact with the outer surface of the reaction tube 31, and a high voltage is applied between the preliminary discharge electrodes 40, 41 from the preliminary discharge power source 42 to generate plasma in the reaction tube 31. Also known as having a pre-discharge space 43 on the upstream side of the 36 (for example, see Patent Document 2).

In the configuration of FIG. 8, at the time of plasma ignition, a gas 44 that is easily ionized into the reaction tube 31 from the first gas introduction port 38 is introduced, and a high-frequency voltage is applied between the plasma generating electrodes 32 and 33. By applying a high voltage between the preliminary discharge electrodes 40 and 41 in the applied state, a preliminary discharge plasma 45 is generated in the preliminary discharge space 43, and the generated charged particles are generated along the gas flow in the plasma generating section. The plasma is ignited by the plasma generator 36 by being introduced into 36. Thereafter, by introducing another gas 47 such as a reactive gas into the reaction tube 31 from the second gas introduction port 46 of the gas introduction tube 39, a required plasma is generated in the plasma generation unit 36, and is emitted from the blowout port 37. Blown out.
JP 2001-126898 A JP 2002-008894 A

  However, in the configuration of Patent Document 1 shown in FIG. 7, it is necessary to retract the ignition device from the vicinity of the outlet 27 after plasma ignition, and a moving mechanism of the ignition device is required, which makes the device configuration complicated. There is a problem that a compact and inexpensive configuration cannot be realized, and ignition is performed by applying a high voltage in the vicinity of the air outlet 27. Therefore, an atmospheric pressure plasma generator having a plurality of reaction tubes 21 arranged in parallel However, when plasma is generated in one reaction tube 21 first, a high voltage cannot be appropriately applied to other adjacent reaction tubes 21 due to the influence, and ignition is impossible.

  Further, in the configuration of Patent Document 2 shown in FIG. 8, it is necessary to introduce a gas 44 that is easily ignited from the first gas inlet 38, and the first gas inlet 38 and the second gas inlet are used for plasma processing. 46, different types of gas need to be supplied from different supply systems, and since a plurality of gas supply systems are required, the configuration is complicated, and a compact and inexpensive configuration cannot be realized. In addition, since the preliminary discharge plasma 45 is generated and ignited on the upstream side of the plasma generator 36, in the atmospheric pressure plasma generator in which the plurality of reaction tubes 31 are arranged in parallel, all the reaction tubes 31 are stable. Therefore, there is a problem that it is difficult to ignite the plasma.

  In view of the above-described conventional problems, the present invention has a simple and compact configuration without damaging a plasma generation circuit such as a matching circuit even when a single reaction tube or a plurality of reaction tubes are arranged in parallel. It is an object of the present invention to provide an atmospheric pressure plasma generator and an ignition method capable of stably igniting a plasma.

  The atmospheric pressure plasma generator of the present invention includes a reaction tube having one end opened as a blow-out port, an antenna or an electrode disposed around or in the vicinity of the reaction tube, and a gas supply for introducing gas from the other end into the reaction tube In an atmospheric pressure plasma generator comprising a means and a high-frequency power source for applying a high-frequency voltage to the antenna or electrode, a pair of ignition electrodes are arranged on one end side and the other end side of the reaction tube with the antenna or electrode in between Then, one ignition electrode is electrically grounded, and the other ignition electrode is connected to an ignition device that generates a high voltage for a predetermined time.

  According to this configuration, one of a pair of ignition electrodes arranged on both sides of the antenna or electrode is grounded, and a high voltage is applied between the ignition electrodes from the ignition device, so that the inside of the reaction tube Since a discharge for ignition occurs through the plasma generation area corresponding to the antenna or electrode, it is possible to ignite surely and stably without being affected by the outside of the reaction tube, and one of the ignition electrodes is grounded. Therefore, there is no risk of discharge power being accidentally input to a circuit for generating plasma such as a matching circuit and causing damage, and the power supply for ignition is connected to a pair of ignition electrodes provided in the reaction tube. Therefore, it can be configured simply and compactly.

  If the one ignition electrode is disposed on one end of the reaction tube and the other ignition electrode is disposed on the other end of the reaction tube, the ignition electrode on the outlet side of the reaction tube is grounded. It is preferable that an abnormal discharge can be prevented from occurring between various members arranged in the vicinity of the air outlet at the time of ignition when a high voltage is applied. Conventionally, it has been assumed that if the vicinity of the outlet of the reaction tube is set to the ground potential, the plasma cannot be properly blown out from the outlet, but in the course of the present inventor's research, the plasma blowing is completely affected. The present invention has been invented based on the finding that it is not given.

  In addition, it is preferable that the ignition device generates an alternating current or pulsed high voltage because it can be ignited effectively and stably by an alternating electric field. The high voltage output from the ignition device is preferably at least three times the output voltage of the high-frequency power source for generating plasma, for example, about several kV to 30 kV.

  In addition, when a plurality of reaction tubes are arranged, an ignition device is provided for each of the other ignition electrodes provided in each reaction tube, and each other ignition electrode and the corresponding ignition device are connected to each other, Each tube can be ignited reliably and stably as described above, and all reaction tubes can be ignited reliably and stably even when multiple reaction tubes are arranged in parallel. Can do.

  In addition, when the one ignition electrode is connected to a case that covers the reaction tube and is electrically grounded, the one ignition electrode can be grounded with a simple configuration, which is simpler and more compact. It can be set as a simple structure.

  Further, the atmospheric pressure plasma ignition method of the present invention introduces a gas from the other end of the reaction tube whose one end is opened as an outlet, and applies a high-frequency voltage to an antenna or an electrode disposed around or in the vicinity of the reaction tube. In an applied state, one ignition electrode of a pair of ignition electrodes disposed on one end side and the other end side of the reaction tube with the antenna or electrode interposed therebetween is electrically grounded, and the other ignition electrode is connected to the other ignition electrode. A high voltage is applied for a predetermined time to ignite plasma.

  According to this configuration, as described above, an ignition discharge is generated through the plasma generation region corresponding to the antenna or electrode in the reaction tube, so that the ignition is reliably and stably performed without being affected by the outside of the reaction tube. Since one of the ignition electrodes is grounded, there is no risk of discharge power being accidentally input to a plasma generation circuit such as a matching circuit, causing damage, and a pair of ignitions provided in the reaction tube Since only a high voltage is applied to the electrode for a predetermined time, it can be configured simply and compactly.

  In addition, when a plurality of reaction tubes are arranged, if a plasma is ignited by applying a high voltage for a predetermined time independently for each reaction tube, all the reaction tubes are arranged in parallel as described above. The reaction tube can be reliably and stably ignited.

  According to the atmospheric pressure plasma generator and ignition method of the present invention, one of a pair of ignition electrodes arranged on both sides of an antenna or an electrode is grounded, and a high voltage is applied from the ignition device between both ignition electrodes. Is applied to cause a discharge for ignition through the plasma generation region corresponding to the antenna or electrode in the reaction tube, and can be ignited reliably and stably without being affected by the outside of the reaction tube, In addition, since one of the ignition electrodes is grounded, there is no risk of the discharge power being accidentally input to a plasma generation circuit such as a matching circuit to cause damage, and the pair of ignition electrodes provided in the reaction tube Since it is the structure which connected the ignition device, it can comprise simply and compactly.

  Hereinafter, each embodiment of the atmospheric pressure plasma generator of the present invention will be described with reference to FIGS.

(First embodiment)
First, a first embodiment of an atmospheric pressure plasma generator of the present invention will be described with reference to FIGS.

  In FIG. 1, reference numeral 1 denotes a reaction tube made of a dielectric, and a coiled antenna 2 is wound around the outer periphery thereof. Both ends of the antenna 2 are connected to a high frequency power source 4 via a matching circuit 3. As the high-frequency power source 4, an RF frequency band typified by 13.56 MHz or a VHF frequency band typified by 100 MHz is preferably used. In this case, the matching circuit 3 is indispensable for suppressing reflected waves. It is.

  One end opening of the reaction tube 1 is a plasma outlet 5, and a gas 7 is supplied to the other end opening 6 from a gas supply unit 8 through a flow rate control unit 9 as shown in FIG. 2. It is configured. The atmospheric pressure plasma generator 10 in FIG. 2 is a unit in which the reaction tube 1, the coil 2, and the matching circuit 3 are housed in a shielding housing (not shown).

  The gas 7 is a mixed gas of an inert gas and a reactive gas, and the gas supplied from the gas supply unit 8 is controlled by the flow rate control means 9 so that the composition and flow rate are accurately the same, and the reaction tube 1 It is comprised so that it may supply. As the inert gas, a single gas or a mixed gas selected from argon, neon, xenon, helium, and nitrogen is applied. As the reactive gas, oxygen, air, an oxidizing gas such as CO 2 or N 2 O, a reducing gas such as hydrogen or ammonia, a chlorofluorocarbon gas such as CF 4, or the like is applied depending on the type of plasma treatment.

  On the outer surface of the reaction tube 1, ignition electrodes 12 and 13 are disposed on one end side and the other end side with the antenna 2 interposed therebetween. The ignition electrode 12 at one end near the outlet 5 of the reaction tube 1 is electrically grounded, and the ignition electrode 13 at the other end is connected to an ignition device 14 that generates a high voltage for a predetermined time. It is preferable that the ignition electrode 13 is formed to be tapered and have a pointed tip so that the electric charge supplied from the ignition device 14 is concentrated on the tip and discharge is likely to occur. The ignition device 14 only needs to generate an alternating current or pulsed high voltage of several kV to 30 kV. In addition, the ignition electrode 12 is grounded by connecting it to a shielding housing (not shown) that covers the reaction tube 1 and the coil 2, and a reference side terminal (0 V shown) of the output voltage of the ignition device 14. Also, it is preferable to connect to the casing, and it is more preferable to ground the casing.

  As shown in FIG. 2, the high-frequency power source 4, the flow rate control unit 9, and the ignition device 14 are controlled by the control unit 15 to perform the following operations.

  According to the above configuration, the ignition device 14 is operated in a state where a high frequency voltage is applied to the antenna 2 via the matching circuit 3 while supplying the gas 7 from the other end opening 6 into the reaction tube 1. When operated and an AC or pulsed high voltage is applied to the ignition electrode 13 for a predetermined time, the reaction tube 1 is connected between the ignition electrode 13 and the grounded ignition electrode 12 as shown in FIG. A discharge 16 is generated through the inside, and the gas 7 in the plasma generation region to which the induction electric field is applied from the antenna 2 is excited at once, and the plasma 11 is ignited. Once the plasma 11 is ignited, the plasma 11 is continuously generated by the induction electric field from the antenna 2, and the generated plasma 11 blows out from the outlet 5 at one end of the reaction tube 1 to an open space in the atmosphere. Plasma treatment can be performed by irradiating the surface of the object with the plasma 11.

  At this time, even if the ignition electrodes 12 and 13 are arranged on both sides of the antenna 2, the ignition electrode 12 to which a high voltage is applied and the pair of ignition electrodes 12 are grounded. , 13, the discharge 16 is surely generated, and there is no fear that the discharge power is input to the matching circuit 3. Therefore, the discharge 16 is generated through the plasma generation region in the reaction tube 1, and the plasma of the matching circuit 3 or the like is generated. There is no risk of damaging the generating circuit. In addition, since the ignition electrode 12 in the vicinity of the outlet 5 of the reaction tube 1 is grounded, a high voltage is applied in the vicinity of the outlet 5 at the time of ignition to apply a high voltage, and various kinds of electrodes arranged in the vicinity thereof. Abnormal discharge does not occur between the members.

  Note that the application time of the high voltage to the ignition electrode 13 by the ignition device 14 does not necessarily have to be a predetermined time, and is applied to a sensor (not shown) in which the plasma 11 blown out from the blowout port 5 is arranged in the vicinity thereof. The controller 15 may stop the operation of the ignition device 14 based on the detection signal.

(Second Embodiment)
Next, a second embodiment of the atmospheric pressure plasma generator of the present invention will be described with reference to FIGS. In the following description of the embodiment, the same components as those in the preceding embodiment are denoted by the same reference numerals, description thereof is omitted, and only differences will be mainly described.

  In the first embodiment, the example in which the single reaction tube 1 is provided in the atmospheric pressure plasma generation unit 10 has been described. However, in this embodiment, the atmospheric pressure is set so that a wide range can be subjected to plasma processing at a time. A pair of reaction tubes 1a and 1b are arranged in parallel in the plasma generation unit 10, and antennas 2a and 2b are wound around the plasma generation unit 10, respectively. These antennas 2a and 2b are configured so that the winding directions are opposite to each other, and high-frequency noise generated in the plasma 11 blown out from the reaction tubes 1a and 1b cancels each other between the reaction tubes 1a and 1b. The high-frequency noise leaking to the screen is reduced. In the illustrated example, the antennas 2a and 2b are connected in parallel and connected to the matching circuit 3. However, the antennas 2a and 2b may be connected in series and connected to the matching circuit 3.

  The ignition electrodes 12a and 12b provided on one end side of the reaction tubes 1a and 1b are connected to each other and grounded, and the ignition electrodes 13a and 13b provided on the other end side are individually provided ignition devices. 14a and 14b, and is configured to apply a high voltage independently to each other.

  The reaction tubes 1a and 1b, the antennas 2a and 2b, and the matching circuit 3 are accommodated and disposed in a shielding casing 17 in order to prevent the generated high-frequency noise from leaking outside. The blow-out port 5 at one end of the reaction tubes 1a and 1b is opened to the outside through an opening provided in the housing 17, and the plasma 11 blown out from the blow-out port 5 is blown into an external open space to irradiate the surface of the object. And it is comprised so that plasma processing may be carried out.

  According to the present embodiment, since the plurality of reaction tubes 1a and 1b are arranged in parallel, a wide region can be plasma-treated at once with the plasma 11 blown out from the reaction tubes 1a and 1b. Moreover, conventionally, when a plurality of reaction tubes are arranged in parallel, if one reaction tube ignites, the other reaction tubes cannot be ignited or the ignition becomes unstable. In the present invention, as described above, During the ignition, a discharge 16 penetrating the plasma generation region in the reaction tube 1 can be generated without being influenced by the outside, and ignition can be performed reliably. In this embodiment, the ignition electrodes 13a of the reaction tubes 1a and 1b are provided. , 13b are provided with igniters 14a, 14b, respectively, so that each reaction tube 1a, 1b is ignited independently. Therefore, even if a plurality of reaction tubes 1a, 1b are arranged in parallel, It is possible to reliably and stably ignite both reaction tubes 1a and 1b.

  Referring to FIG. 5, the ignition electrodes 14a and 14b are operated by applying a high-frequency voltage from the high-frequency power source 4 to the antennas 2a and 2b and supplying the gas 7 to the reaction tubes 1a and 1b. When a pulsed high voltage is applied between the electrodes 12a and 12b and the ignition electrodes 13a and 13b, the plasma is ignited independently in the reaction tubes 1a and 1b within the operation time of the ignition devices 14a and 14b, respectively. While the application and the supply of the gas 7 are continued, the plasma 11 is continuously blown out from both reaction tubes 1a and 1b.

(Third embodiment)
Next, a third embodiment of the atmospheric pressure plasma generator of the present invention will be described with reference to FIG.

  In the above embodiment, a configuration example in which a pair of reaction tubes 1a and 1b are arranged in parallel is shown. However, in this embodiment, four reaction tubes 1a to 1d are arranged in parallel, and antennas 2a to 2d are arranged on the outer circumferences. It is wound and arranged. The antennas 2a to 2d are configured so that the winding directions of adjacent ones are opposite to each other, are sequentially connected in series, and one end thereof is connected to one terminal of the matching circuit 3 and the high-frequency power source 4, and is connected in series. The other ends of the antennas 2 a to 2 d and the other terminals of the matching circuit 3 and the high-frequency power source 4 are connected to the housing 17. The casing 17 is connected to the ground by arranging a copper plate on the surface to reduce resistance. The ignition electrodes 12a to 12d disposed on one end side of the reaction tubes 1a to 1d are connected to the casing 17, and the ignition electrodes 13a to 13d disposed on the other end side of the reaction tubes 1a to 1d are Each is connected to an ignition device 14a-14d provided separately. In the present embodiment, the reaction tubes 1 a to 1 d and the antennas 2 a to 2 d are covered with the casing 17, and the matching circuit 3 is disposed outside the casing 17.

  Even when four reaction tubes 1a to 1d are arranged in parallel as in the present embodiment or a plurality of reaction tubes of more than one are arranged in parallel, the reaction tubes 1a to 1d are all arranged in the same manner as in the above embodiment. Thus, stable ignition can be performed reliably, and plasma processing for a large area can be performed efficiently. Further, since the other ends of the antennas 2a to 2d connected in series and the ignition electrodes 12a to 12d on the ground side are connected to the grounded casing 17, the connection configuration with respect to the ground becomes simple, and the simpler and more compact. It can be set as a simple structure.

  If the ignition timings in the reaction tubes 1a to 1d may be slightly shifted, the ignition electrodes 13a to 13d are connected to a single ignition device 14 via a switching device so that the ignition is performed sequentially. good.

  In the above embodiment, the example in which the coiled antenna 2 (2a to 2d) is wound around the outer periphery of the reaction tube 1 (1a to 1d) has been shown, but in the vicinity of the outer periphery of the reaction tube 1 (1a to 1d). Whether it is a configuration in which a wave-shaped antenna is arranged or a configuration in which various types of electrodes are arranged, the ignition electrodes 12 (12a to 12d) and 13 (13a to 13d) and the ignition device 14 (14a to 14d) of the present invention are used. The same effect can be achieved by applying.

  According to the atmospheric pressure plasma generation apparatus and the ignition method of the present invention, it is possible to generate a discharge for ignition through the plasma generation region corresponding to the antenna or the electrode in the reaction tube, and to be affected by the influence outside the reaction tube. Therefore, it can be ignited reliably and stably, and there is no risk of damage caused by accidental input of discharge power to a plasma generation circuit such as a matching circuit, and it can be configured simply and compactly. It can be effectively used in an atmospheric pressure plasma processing apparatus.

The block diagram of the atmospheric pressure plasma generator of the 1st Embodiment of this invention. The block diagram which shows the control structure of the embodiment. Sectional drawing which shows the ignition effect | action in the same embodiment. The block diagram of the atmospheric pressure plasma generator of the 2nd Embodiment of this invention. The operation | movement timing diagram of the embodiment. The block diagram of the atmospheric pressure plasma generator of the 3rd Embodiment of this invention. The block diagram of the atmospheric pressure plasma generator of a prior art example. Sectional drawing which shows the structure of the atmospheric pressure plasma generator of another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a, 1b, 1a-1d Reaction tube 2, 2a, 2b, 2a-2d Antenna 4 High frequency power supply 5 Outlet 6 Other end opening 7 Gas 8 Gas supply part 11 Plasma 12, 12a, 12b, 12a-12d Ignition electrode 13, 13a, 13b, 13a-13d The other ignition electrode 14, 14a, 14b, 14a-14d Ignition device 17 Housing

Claims (7)

  A reaction tube having one end opened as an outlet, an antenna or electrode arranged around or in the vicinity of the reaction tube, a gas supply means for introducing gas from the other end into the reaction tube, and a high-frequency voltage applied to the antenna or electrode In an atmospheric pressure plasma generator having a high-frequency power source to be applied, a pair of ignition electrodes are arranged on one end side and the other end side of a reaction tube with an antenna or an electrode interposed therebetween, and one of the ignition electrodes is electrically connected An atmospheric pressure plasma generator characterized in that the other ignition electrode is connected to an ignition device that generates a high voltage for a predetermined time.   2. The atmospheric pressure plasma generator according to claim 1, wherein the one ignition electrode is disposed on one end side of the reaction tube, and the other ignition electrode is disposed on the other end side of the reaction tube.   The atmospheric pressure plasma generator according to claim 1 or 2, wherein the ignition device generates an alternating current or a pulsed high voltage.   A plurality of reaction tubes are arranged, an ignition device is provided for each of the other ignition electrodes provided in each reaction tube, and each of the other ignition electrodes is connected to the corresponding ignition device. The atmospheric pressure plasma generator in any one of Claims 1-3.   5. The atmospheric pressure plasma generator according to claim 1, wherein the one ignition electrode is connected to a casing that covers the reaction tube and is electrically grounded.   Gas is introduced from the other end of the reaction tube, one end of which is opened as a blowout port, and the antenna or electrode is sandwiched between the antenna or electrode disposed around or near the reaction tube. Then, one ignition electrode of a pair of ignition electrodes disposed on one end side and the other end side of the reaction tube is electrically grounded, and a high voltage is applied to the other ignition electrode for a predetermined time to ignite plasma. An atmospheric pressure plasma ignition method.   7. The atmospheric pressure plasma ignition method according to claim 6, wherein when a plurality of reaction tubes are arranged, the plasma is ignited by applying a high voltage for a predetermined time independently for each reaction tube.

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