JP7144780B2 - Atmospheric pressure plasma generator - Google Patents

Description

The present invention relates to an atmospheric pressure plasma generation device, and more particularly to an atmospheric pressure plasma generation device capable of generating an atmospheric pressure low frequency plasma jet.

Atmospheric-pressure low-frequency plasma jets can relatively easily generate non-thermal equilibrium plasma (low-temperature plasma) under atmospheric pressure, so they are used in the medical field, materials field, and the like. For example, Patent Literature 1 discloses a plasma generator that performs preliminary discharge and main discharge in order to easily generate plasma under atmospheric pressure without using a rare gas such as helium (He). Specifically, a first gas supply head for supplying a preliminary discharge gas is provided at one end of a cell in which a gas flow path is formed, and the preliminary discharge gas is ionized or activated by a low-frequency electrode, It is supplied to the plasma generation area together with the main discharge gas supplied from the two-gas supply head, and the high-frequency electrode generates glow discharge to generate plasma.

Further, Patent Document 2 discloses a plasma generation apparatus that performs preliminary discharge and main discharge so that plasma ignition can be reliably performed and starting can be performed satisfactorily. Specifically, a preliminary discharge section is provided on the upstream side of a cylindrical reaction vessel, and an ignition means for igniting plasma is provided on the downstream side.

JP-A-11-16696 JP-A-2002-8894

However, conventional general atmospheric pressure plasma generators have a problem that the types of gases that can be used for plasma generation are limited. For example, when argon (Ar) or argon (Ar)+oxygen (O ₂ ) gas is used for plasma generation, plasma may not be generated if the input power to the discharge electrode is low. In addition, when the input power is increased, the glow discharge does not occur, but the arc discharge occurs, and the plasma cannot be generated in some cases. In the conventional plasma generators disclosed in Patent Documents 1 and 2, etc., the restrictions on the gas species are relaxed to some extent by the preliminary discharge, but all of them have a constant gas flow path from the preliminary discharge to the main discharge. There was no change in the width, and a non-uniform discharge state sometimes occurred in the preliminary discharge. Therefore, it was still difficult to obtain a stable plasma discharge.

SUMMARY OF THE INVENTION In view of such circumstances, it is an object of the present invention to provide an atmospheric pressure plasma generating apparatus capable of reliably and stably generating plasma without depending on gas species.

In order to achieve the object of the present invention described above, an atmospheric pressure plasma generation apparatus according to the present invention comprises a preionization section and a plasma generation section. The preionization unit for preionizing the working gas includes an input capillary to which the working gas is supplied, an ionization chamber connected to the input capillary and having at least parallel opposing planes, and an opposing plane sandwiching the opposing plane of the ionization chamber. Consists of parallel plates arranged in parallel and energized from a predischarge power source, having predischarge electrodes for ionizing or exciting the working gas, and an output capillary connected to the ionization chamber. Good luck. The plasma generating section, which generates plasma using the gas ionized or excited by the preionization section as seeds, includes a cylindrical tube connected to the output capillary tube of the preionization section, and a plasma for applying a high AC voltage to the cylindrical tube. and a plasma generation electrode to which a voltage is applied from a generation power source.

Here, the ionization chamber of the preliminary ionization section may have a width of the opposing flat surface larger than the diameter of the input capillary.

Also, the output capillary of the preliminary ionization section may have a diameter smaller than the width of the opposing plane of the ionization chamber.

Moreover, the voltage from the plasma generation power source applied to the plasma generation electrode of the plasma generation section may be a low frequency high voltage.

Also, the ionization chamber of the preliminary ionization section may have a shape that widens from the input capillary side.

Here, the ionization chamber of the preliminary ionization section may have an air intake hole on the side surface of the shape that spreads toward the bottom.

Further, the preliminary discharge electrode of the preliminary ionization section may be a dielectric barrier discharge electrode.

The atmospheric pressure plasma generating apparatus of the present invention has the advantage of being able to reliably and stably generate plasma without depending on gas species.

FIG. 1 is a schematic cross-sectional view for explaining the atmospheric pressure plasma generation apparatus of the present invention. FIG. 2 is a schematic enlarged cross-sectional view for explaining an example in which an air intake hole is provided in the preliminary ionization section of the atmospheric pressure plasma generating apparatus of the present invention. FIG. 3 is a graph for explaining changes in discharge start time depending on the presence or absence of preliminary discharge in the atmospheric pressure plasma generation apparatus of the present invention. FIG. 4 is a graph for explaining the amount of oxygen-based radicals generated by the plasma jet generated by the atmospheric pressure plasma generator of the present invention. FIG. 5 shows the spectroscopic analysis results of the plasma jet generated by the atmospheric pressure plasma generator of the present invention. FIG. 6 is a spectroscopic analysis result of a plasma jet generated using Ar+O ₂ as the gas species of the working gas in the atmospheric pressure plasma generating apparatus of the present invention.

Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. The atmospheric pressure plasma generation apparatus of the present invention generates plasma under atmospheric pressure. The plasma is for example an atmospheric pressure low frequency plasma jet (LF plasma jet). 1A and 1B are schematic cross-sectional views for explaining the atmospheric pressure plasma generating apparatus of the present invention, FIG. 1(a) being its front view and FIG. 1(b) being its side view. As shown in the figure, the atmospheric pressure plasma generation apparatus of the present invention is mainly composed of a preliminary ionization section 10 and a plasma generation section 20 . The preionization unit 10 preionizes the working gas. A so-called preliminary discharge is performed by the preliminary ionization section 10 . The plasma generating section 20 generates plasma using the gas ionized or excited by the preliminary ionization section 10 as a seed. A so-called main discharge is performed by the plasma generator 20 .

The preliminary ionization section 10 is mainly composed of an input capillary 11 , an ionization chamber 12 , a preliminary discharge electrode 13 and an output capillary 15 . A preliminary discharge power supply 14 is connected to the preliminary discharge electrode 13 .

A working gas is supplied to the input capillary tube 11 . The input thin tube 11 may be, for example, a dielectric cylindrical thin tube. Specifically, for example, a glass tube such as quartz glass may be used. Here, the working gas is not limited to helium (He), but may be argon (Ar) or argon (Ar)+oxygen (O ₂ ) gas.

The ionization chamber 12 is connected to the input tubule 11 . The ionization chamber 12 has at least parallel opposing planes. For example, an approximately rectangular parallelepiped shape made of a dielectric may be used. In the illustrated example, the opposing plane of the ionization chamber 12 has a width larger than the diameter of the input capillary tube 11 . However, the present invention is not limited to this, and the ionization chamber 12 may have the same diameter as the input tubule 11 and may have a shape having parallel opposing planes. Also, the ionization chamber 12 may have a shape that widens from the input capillary 11 side. And it is sufficient if it has a tapered shape toward the output capillary tube 15 . As shown in FIG. 1(a), the ionization chamber 12 is wider than the input capillary 11 when viewed from the front, and has the same width as the input capillary 11 when viewed from the side as shown in FIG. 1(b). Any height is fine. In the illustrated example, the input capillary tube 11 and the ionization chamber 12 are configured to have the same height when viewed from the side. may be configured to be smaller.

The preliminary discharge electrodes 13 are for ionizing or exciting the working gas, and are arranged in parallel to the plane facing the ionization chamber 12 so as to sandwich the plane facing the ionization chamber 12 . The preliminary discharge electrode 13 is formed of a parallel plate aligned with the plane facing the ionization chamber 12. The parallel plates of the preliminary discharge electrode 13 are configured to sandwich the ionization chamber 12 from above and below in parallel. One of the parallel plates serves as a ground electrode and the other serves as an application electrode, so that a voltage is applied from the preliminary discharge power source 14 so as to serve as a counter electrode. The preliminary discharge power supply 14 may be, for example, a high-frequency high-voltage power supply. Specifically, it is sufficient that a high frequency high voltage of about 3 kV to 12 kV can be applied. Specifically, the preliminary discharge electrode 13 may be an electrode capable of dielectric barrier discharge.

The output capillary tube 15 is connected to the ionization chamber 12 . Specifically, the output capillary tube 15 may be connected to the opposite side of the input capillary tube 11 of the ionization chamber 12 . For example, a dielectric cylindrical thin tube may be used. The output capillary tube 15 has a diameter smaller than the width of the opposing plane of the ionization chamber 12, as shown in the drawing. Note that the present invention is not limited to this, and the output capillary tube 15 may have the same diameter as the width of the opposing plane of the ionization chamber 12 . The output capillary 15 has a smaller diameter than the width of the ionization chamber 12 when viewed from the front, as shown in FIG. It is sufficient if the diameter is the same as the width (height). In the illustrated example, the output capillary tube 15 and the ionization chamber 12 are configured to have the same height when viewed from the side, but the present invention is not limited to this. It may be configured to have a smaller diameter.

Note that the preliminary ionization unit 10 may be integrally configured as shown in the drawing, or may be configured by connecting separately configured components with a connector or the like.

By configuring the preliminary ionization section 10 in this way, the working gas supplied from the input capillary tube 11 spreads in the space inside the ionization chamber 12 . When a predetermined voltage is applied to this space from a high-frequency high-voltage power supply using the preliminary discharge electrode 13, the working gas is ionized or excited in the space of the ionization chamber 12 sandwiched between the parallel plates of the preliminary discharge electrode 13. be done. This ionized or excited gas flows to the output capillary 15 side. At this time, since a voltage can be applied to the ionization chamber 12 having a facing plane by using the preliminary discharge electrode 13 having a large area, stable ionization or excitation can be achieved. Further, the flow velocity increases by passing through the output capillary 15 having a small diameter, and even if the ionization is unevenly performed in the ionization chamber 12, the density increases and the uniformity increases.

In the atmospheric pressure plasma generation apparatus of the present invention, the preliminary ionization section 10 is provided on the upstream side in this way, and the working gas is ionized or excited before reaching the plasma generation section 20 . Then, the ionized or excited gas is supplied to the plasma generating section 20 as seeds.

Specifically, a plasma generation unit 20 is connected to the preliminary ionization unit 10 . The plasma generating section 20 generates plasma using the gas ionized or excited by the preliminary ionization section 10 as a seed. The plasma generation part 20 is mainly composed of a cylindrical tube 21 and a plasma generation electrode 22 . A plasma generation power source 23 is connected to the plasma generation electrode 22 .

The cylindrical tube 21 is connected to the output capillary tube 15 of the preionization section 10 . The cylindrical tube 21 may be made of a dielectric, specifically a glass tube such as quartz glass. In the illustrated example, the diameter of the cylindrical tube 21 is the same as that of the input thin tube 11, but the present invention is not limited to this, and may have different diameters.

The plasma generating electrode 22 is used to apply AC high voltage to the cylindrical tube 21 . A plasma generation power supply 23 is connected to the plasma generation electrode 22 , and a voltage is applied from the plasma generation power supply 23 . The plasma generation power supply 23 can apply a low frequency, eg, a high voltage of about several kHz, eg, an AC high voltage of about 9 kV to 12 kV, to the plasma generation electrode 22 . The plasma generation power source 23 may be a pulse output such as a rectangular wave, for example. The plasma generation electrode 22 is composed of a pair of application electrode and ground electrode, and is a conductor arranged so as to surround the outer circumference of the cylindrical tube 21 . The application electrode and the ground electrode of the plasma generation electrode 22 are arranged with a predetermined gap therebetween, and the cylindrical tube 21 acts as a dielectric barrier to prevent short-circuiting of both electrodes. The plasma generating electrode 22 has a ground electrode on the plasma emission side and an application electrode on the preliminary ionization section 10 side.

The plasma generating electrode 22 of the atmospheric pressure plasma generating apparatus of the present invention is not limited to the illustrated example. For example, the application electrode may be provided inside the cylindrical tube 21 and the ground electrode may be arranged so as to surround the outer circumference of the cylindrical tube 21 . Furthermore, only the application electrodes may be arranged so as to surround the outer circumference of the cylindrical tube 21 .

The gas ionized or excited by the preliminary ionization section 10 flows toward the output capillary tube 15 and into the cylindrical tube 21 of the plasma generation section 20 . Then, by applying a voltage from the plasma generating electrode 22, glow discharge is generated and an atmospheric pressure low frequency plasma jet is generated. In the atmospheric pressure plasma generating apparatus of the present invention, since the primary discharge is performed after the preliminary discharge, the discharge does not transition to the arc discharge, but the glow discharge is ensured. Also, fluctuations in the ignition (discharge start) delay time are suppressed.

In the atmospheric pressure plasma generation apparatus of the present invention, the preliminary discharge power source 14 and the plasma generation power source 23 are different. voltage. Further, by increasing the length of the output capillary tube 15 and/or the cylindrical tube 21, the preionization section 10 and the plasma generation section 20 can be separated from each other. Therefore, it is possible to minimize the influence of the preionization section 10 to which a high frequency and high voltage is applied to the object to be irradiated with the atmospheric pressure plasma.

Next, an example in which an air intake hole is provided in the ionization chamber of the preliminary ionization section of the atmospheric pressure plasma generating apparatus of the present invention will be described. FIG. 2 is a schematic enlarged cross-sectional view for explaining an example in which an air intake hole is provided in the preliminary ionization section of the atmospheric pressure plasma generating apparatus of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIG. 1 represent the same parts. As described above, the ionization chamber 12 of the preliminary ionization section 10 has a shape that widens from the input capillary 11 side. Further, as shown in FIG. 2, an air intake hole 17 is provided in the side surface 16 of this widening shape. As a result, by positively taking in air from the atmosphere and increasing the amount of oxygen radicals, it is possible to further promote the oxidation reaction, for example. In addition to air in the atmosphere, other reaction gas may be added through the air intake hole 17 .

表１から分かる通り、ＡｒやＡｒ＋Ｏ_２（１％）では、予備電離部無しでは大気圧低周波プラズマジェットの生成が困難なことが分かる。そして、予備電離部を用いて予備電離を行うことで、容易に大気圧低周波プラズマジェットが生成可能となることが分かる。大気圧低周波プラズマジェットを生成可能なプラズマ生成部と比べて、予備電離部の誘電体バリア放電は、ガス種に依存せずに放電が持続できるという特徴があり、予備電離部による予備電離が有用であることが分かる。本発明の大気圧プラズマ生成装置は、Ｈｅのような高価な動作ガスだけでなく、ＡｒやＡｒ＋Ｏ_２（１％）のような安価な動作ガスでも、確実に且つ安定的にプラズマを生成可能である。 Hereinafter, the difference in whether or not plasma can be generated depending on the presence or absence of the preliminary ionization section 10 in the atmospheric pressure plasma generation apparatus of the present invention will be described with specific examples. First, dielectric barrier discharge was used as the preliminary ionization section 10 . The voltage applied to the electrodes of the power source 14 for preliminary discharge of the preliminary ionization section 10 is set to 11 kV, and the voltage applied to the electrodes of the power source 22 for plasma generation of the plasma generation section 20 is set to 11 kV. The gas flow rate of the working gas supplied to the input capillary tube 11 of the preliminary ionization section 10 is assumed to be 3.0 L/min. Under these conditions, an experiment was conducted to see if an atmospheric pressure low-frequency plasma jet was generated using three types of working gases, namely He, Ar, and Ar+O ₂ (1%). The results are shown below.

As can be seen from Table 1, with Ar or Ar+O ₂ (1%), it is difficult to generate an atmospheric pressure low-frequency plasma jet without a preionization section. It can be seen that the atmospheric pressure low frequency plasma jet can be easily generated by performing preliminary ionization using the preliminary ionization unit. Compared to the plasma generation section that can generate an atmospheric pressure low-frequency plasma jet, the dielectric barrier discharge in the preionization section has the characteristic that the discharge can be sustained without depending on the gas species. It turns out to be useful. The atmospheric pressure plasma generator of the present invention can reliably and stably generate plasma not only from expensive working gases such as He but also from inexpensive working gases such as Ar and Ar+O ₂ (1%). be.

Next, in order to verify the effect of the preliminary discharge by the preliminary ionization section, the electrode voltage applied to the plasma generation electrode was changed and the results of measuring the discharge start voltage of the atmospheric pressure low frequency plasma jet will be described. FIG. 3 is a graph for explaining changes in discharge starting voltage depending on the presence or absence of preliminary discharge in the atmospheric pressure plasma generation apparatus of the present invention. In the figure, the horizontal axis is the gas flow rate, and the vertical axis is the firing voltage of the main discharge. As the measurement conditions, the electrode voltage applied to the preliminary discharge power supply 14 of the preliminary ionization section 10 was set to 11 kV, and the electrode voltage applied to the plasma generation electrode 22 of the plasma generation section 20 was varied from 3.8 kV, which is the lower limit of the power supply, to 11 kV. rice field. The gas type of the working gas supplied to the input capillary tube 11 of the preliminary ionization unit 10 is He, and the gas flow rates are 0.5 L/min, 1.0 L/min, 2.0 L/min, and 3.0 L/min, respectively. The discharge starting voltage was measured at . FIG. 3 is the result of repeating these measurements five times. As shown in the figure, in the case of the atmospheric pressure plasma generator of the present invention with preliminary discharge, the discharge start voltage is stable at about 3.8 kV without depending on the gas flow rate, and there is no variation. It can also be seen that glow discharge can be stably generated and maintained even when the gas flow rate is extremely low. On the other hand, in the comparative example without preliminary discharge, the firing voltage was not stabilized at around 6 kV depending on the gas flow rate, and even with the same gas flow rate, the firing voltage varied widely. As described above, in the atmospheric pressure plasma generation apparatus of the present invention, by performing preliminary discharge in the preliminary ionization section, it can be seen that the condition range in which the main discharge can be stably generated can be expanded.

Next, the irradiation effect of the atmospheric pressure low frequency plasma jet generated by the atmospheric pressure plasma generating apparatus of the present invention will be described. FIG. 4 is a graph for explaining the amount of oxygen-based radicals generated by the plasma jet generated by the atmospheric pressure plasma generator of the present invention. In the figure, the horizontal axis is time, and the vertical axis is the amount of ozone. In the application of atmospheric pressure low-frequency plasma jet, the irradiation effect is considered to be due to the generated oxygen-based radicals. Therefore, the amount of oxygen-based radicals generated by the plasma jet generated by the atmospheric pressure plasma generator of the present invention was evaluated. As an evaluation of the amount of oxygen-based radicals generated, the amount of ozone, which is easy to detect, was evaluated. Specifically, the plasma generator 20 is placed in a vacuum chamber filled with air at an atmospheric pressure of about 20 liters, and changes in the amount of ozone in the space over time are monitored by an ozone monitor (APPLICS CO., LTD., OZG -EM-010K). As measurement conditions, the electrode voltage applied to the preliminary discharge power source 14 of the preliminary ionization section 10 was set to 11 kV, and the electrode voltage applied to the plasma generation electrode 22 of the plasma generation section 20 was set to 11 kV. Also, the gas species of the working gas was measured using He and Ar, respectively. The gas flow rate at that time was 3.0 L/min. These measurements are: 1. 2. no predischarge; 2. Preliminary discharge is always present during measurement; Preliminary discharge was performed only until the start of main discharge, and three patterns were used. The results are shown in FIG. The start of measurement was based on the time when the working gas started to flow, and the main discharge started at 15 seconds. As shown in the figure, it can be seen that in both patterns 2 and 3 in which preliminary discharge was performed, the amount of ozone generated per unit time increased compared to the case without preliminary discharge. Specifically, when the gas type of the working gas was He, the increase in ozone was 0.010 ppm/s in pattern 1, 0.019 ppm/s in pattern 2, and 0.019 ppm/s in pattern 3. was 0.012 ppm/s. In addition, when the gas type of the working gas is Ar, the increase in ozone in pattern 1 was 0.028 ppm/s, whereas in pattern 2 it was 0.034 ppm/s and in pattern 3 it was 0.034 ppm/s. 030 ppm/s. From this result, it is expected that not only ozone but also other radicals are generated by the preliminary discharge, and the improvement of the irradiation effect can be expected in the application of the atmospheric pressure low frequency plasma jet.

Furthermore, the amount of oxygen-based radicals generated was also evaluated by spectroscopically analyzing the plasma jet generated by the atmospheric pressure plasma generator of the present invention. FIG. 5 shows the spectroscopic analysis results of the plasma jet generated by the atmospheric pressure plasma generator of the present invention. The measurement conditions were the same as in FIG. 4, and He was used as the working gas. 5(a) and 5(b) show the region between the plasma generation electrodes 22, and FIGS. 5(c) and 5(d) show the region where the plasma extends from the end of the cylindrical tube 21. , are the results of measurement using a CCD spectrometer. 5(a) and 5(c) are the results without preliminary discharge, and FIGS. 5(b) and 5(d) are the results with preliminary discharge. As shown in the figure, when there is preliminary discharge, the emission intensity of OH decreases, and the emission intensity of OI and HI increases. This is considered to indicate that dissociation and ionization progressed in the discharge gas and atmosphere gas of the main discharge due to the preliminary discharge.

FIG. 6 shows the spectroscopic analysis results of a plasma jet generated using Ar+O ₂ as the working gas in the atmospheric pressure plasma generator of the present invention. FIG. 6(a) is a comparative example in which Ar is used as the gas type, and FIG. 6(b) is a case in which Ar+O ₂ is used as the gas type. 6(c) and 6(d) are enlarged views of FIGS. 6(a) and 6(b), respectively. As shown in the figure, when Ar+ _O2 , which enables stable discharge by preliminary discharge, is used as the gas species, the emission intensity of OI is increased compared to the case where normal Ar is used as the gas species. I understand. This is considered to indicate that the preliminary discharge increased the amount of radicals generated, and that oxygen can be mixed with the discharge gas to further increase the amount of oxygen-based radicals generated.

It should be noted that the atmospheric pressure plasma generating apparatus of the present invention is not limited to the illustrated examples described above, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

REFERENCE SIGNS LIST 10 preliminary ionization part 11 input capillary 12 ionization chamber 13 preliminary discharge electrode 14 preliminary discharge power source 15 output capillary 16 side surface of widening bottom 17 air suction hole 20 plasma generation part 21 cylindrical tube 22 plasma generation electrode 23 plasma generation power supply

Claims (7)

An atmospheric pressure plasma generation device for generating plasma under atmospheric pressure, the atmospheric pressure plasma generation device comprising:
A pre-ionization section for pre-ionizing the working gas, the pre-ionization section comprising:
an input capillary to which the working gas is supplied;
an ionization chamber connected to the input capillary and having at least parallel opposing planes forming a flat-shaped space having the same height as the diameter of the input capillary or a height smaller than the diameter of the input capillary ;
Preliminary discharge for ionizing or exciting the working gas spreading in the flat space, which is arranged parallel to the plane facing the ionization chamber so as to sandwich the plane facing the ionization chamber, and is composed of parallel plates to which a voltage is applied from a power source for preliminary discharge. an electrode for
an output capillary connected to the ionization chamber and having a diameter equal to or smaller than the flat space ;
a preionization section having
A plasma generation unit for generating plasma using the gas ionized or excited by the preliminary ionization unit as a seed, the plasma generation unit comprising:
a cylindrical tube connected to the output capillary tube of the preionization unit;
a plasma generation electrode to which a voltage is applied from a plasma generation power supply to apply a high AC voltage to the cylindrical tube;
a plasma generator having
An atmospheric pressure plasma generation device comprising: 2. The atmospheric pressure plasma generator according to claim 1, wherein the ionization chamber of said preliminary ionization section has a width of the opposing planes larger than the diameter of the input narrow tube. 3. The atmospheric pressure plasma generator according to claim 1, wherein said output capillary of said preliminary ionization section has a diameter smaller than the width of the opposing plane of said ionization chamber. 4. The atmospheric pressure plasma generation apparatus according to any one of claims 1 to 3, wherein the voltage from the plasma generation power source applied to the plasma generation electrode of the plasma generation unit is a low frequency high voltage. An atmospheric pressure plasma generator characterized by: 5. The atmospheric pressure plasma generator according to claim 1, wherein the ionization chamber of said preliminary ionization section has a shape that widens from the input capillary side. 6. The atmospheric pressure plasma generating apparatus according to claim 5, wherein the ionization chamber of said preliminary ionization section has an air intake hole on a side surface of a widening shape. 7. The atmospheric pressure plasma generator according to claim 1, wherein the preliminary discharge electrode of said preliminary ionization section is a dielectric barrier discharge electrode.

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