JP2018160354A - Atmospheric pressure plasma generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact atmospheric pressure plasma generating device, which reliably generates plasma and is improved in startability of plasma generation, without increasing a voltage applied between electrodes.SOLUTION: An atmospheric pressure plasma generating device includes a discharge tube (10, 20) where discharge gas flows in and out, and a pair of electrodes (13a and 15, 13a' and 15, 23 and 23, or 23' and 23'') disposed to face each other with the discharge tube interposed therebetween, the discharge gas flowing at the inside of the discharge tube. In the plasma generating device, the electric field intensity between the pair of electrodes is non-uniform along the circumferential direction of the discharge tube.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an atmospheric pressure plasma generator for generating plasma.

  In the conventional plasma generator, one electrode of the pair of electrodes is provided on the outer surface of the discharge tube, and the other electrode is disposed in the discharge tube. Plasma is generated by flowing a discharge gas into the discharge space of the discharge tube and applying a voltage between the pair of electrodes (Patent Document 1).

JP 2007-207475 A

  In such an apparatus in which discharge gas flowing in from the outside flows in the discharge space and flows out to the outside (atmosphere), a voltage necessary for dielectric breakdown, that is, a plasma generation start voltage (discharge start voltage) becomes high. Therefore, in order to generate plasma with such an apparatus, it is necessary to apply a very large voltage. Further, in such an apparatus, the state of the discharge gas in the discharge space (eg, pressure, concentration, flow rate) tends to be non-uniform, the plasma generation start voltage becomes unstable, and the plasma generation itself becomes unstable. There was a fear. As a result, it is necessary to increase the voltage applied between the electrodes in order to reliably generate plasma, the startability of plasma generation is poor, and the application of a high voltage between the electrodes increases the size of the power supply device. There was a problem.

  The present invention is based on the above-mentioned problem awareness of the conventional atmospheric pressure plasma generator, and can be reliably generated without increasing the applied voltage between the electrodes, and is a compact type that improves the startability of plasma generation. An object is to obtain an atmospheric pressure plasma generator.

  According to the present invention, when a high electric field strength portion and a low electric field strength portion are generated in the discharge space (nonuniform along the circumferential direction of the discharge tube), the discharge (plasma) is generated even at a low voltage in the high electric field strength portion. Since it can be generated, it is based on the viewpoint that plasma can be generated reliably.

  An atmospheric pressure plasma generator of the present invention includes a discharge tube into which discharge gas flows in and out, and a pair of electrodes arranged to face each other with the discharge tube interposed therebetween, and the discharge gas is disposed inside the discharge tube. In the atmospheric pressure plasma generating apparatus that flows, the electric field strength between the pair of electrodes is non-uniform along the circumferential direction of the discharge tube.

  By making the distance between the pair of electrodes or the thickness of the dielectric non-uniform along the circumferential direction or radial direction of the discharge tube, a region having a locally high electric field strength is formed in the discharge tube. Also good.

  At least one electrode of the pair of electrodes may be an inner electrode disposed inside the discharge tube, and the width of the inner electrode may be non-uniform along the circumferential direction of the discharge tube. That is, the inner electrode does not have to be a cylinder having a perfect cross section.

  The inner electrode is a strip electrode disposed along the axial direction of the discharge tube, and the thickness of at least one of both edge portions (along the longitudinal direction) of the strip electrode in the width direction is It may be thinner than the thickness of the central portion of the strip electrode.

  The atmospheric pressure plasma generator of the present invention may have an inner tube in which the inner electrode is embedded, and the inner tube may have the smallest thickness in the maximum width direction of the inner electrode.

  One electrode of the pair of electrodes is an inner electrode disposed on the inner side of the discharge tube, and is embedded by an inner tube disposed on the inner side of the discharge tube. The radial thickness of the tube may be non-uniform along the circumferential direction of the discharge tube.

  It is practical to heat mold the inner tube integrally with the discharge tube.

  At least one of the pair of electrodes is a strip electrode along the tube wall of the discharge tube, and may be embedded in the tube wall of the discharge tube.

  The strip electrode may be embedded by heat welding between a small diameter tube and a large diameter tube constituting the discharge tube.

  The band-shaped electrode may have a knife edge shape at both edges in the width direction (along the longitudinal direction) of the band-shaped electrode.

  The atmospheric pressure plasma generator according to the present invention makes the electric field strength between a pair of electrodes non-uniform along the circumferential direction of the discharge tube, and generates a portion in the discharge tube where the electric field strength is locally high. (Plasma) can be generated. As a result, it is possible to obtain a small apparatus that can reliably generate plasma and has good startability for generating plasma.

1 is a longitudinal sectional view showing a first embodiment of an atmospheric pressure plasma generator according to the present invention. It is sectional drawing which follows the II-II line | wire of FIG. It is sectional drawing corresponding to FIG. 2 which shows the modification of the 1st Embodiment of this invention. It is sectional drawing corresponding to FIG. 2 which shows another modification of the 1st Embodiment of this invention. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the atmospheric pressure plasma generator by this invention. It is sectional drawing which follows the VI-VI line of FIG. It is sectional drawing corresponding to FIG. 6 which shows the modification of the 2nd Embodiment of this invention.

  Hereinafter, an embodiment of an atmospheric pressure plasma generator 100 according to the present invention will be described with reference to the drawings. 1 and 2 show a first embodiment of an atmospheric pressure plasma generator according to the present invention. As shown in FIGS. 1 and 2, the atmospheric pressure plasma generator 100 includes a discharge tube 10 as a discharge vessel. The discharge tube 10 is made of a dielectric (for example, quartz), and is formed in a cylindrical shape having a perfect cross section in the illustrated example. One end of the discharge tube 10 is provided with an inlet 11 through which discharge gas flows into the discharge tube, and the other end has an outlet (atmosphere release port) 12 through which discharge gas flows out from the discharge tube to the outside (atmosphere). Prepare. The inflow port 11 is formed in the tube wall 10 a of the discharge tube 10 and communicates with a connection tube 11 a extending in the radial direction of the discharge tube 10. One end of the tube wall 10a is closed by an end wall 10b integral with the tube wall 10a. It should be noted that the inlet and outlet may be interchanged with the same configuration to cause the discharge gas to flow reversely in the discharge tube (the direction of the arrow in the figure is reversed).

  On the other hand, inside the discharge tube 10, an inner electrode 13 a that is one of a pair of electrodes along the axis of the discharge tube 10 and an inner tube (inner dielectric) in which the inner electrode 13 a is embedded (covered). 13b. The inner tube 13b in which the inner electrode 13a is embedded is made of a dielectric (for example, quartz), and is formed by melting and softening (heating welding) with the inner electrode 13a inserted in a tubular dielectric. . Further, the inner tube 13b is integrated with the discharge tube 10 by heat welding (heating molding) on the end wall 10b on the inlet 11 side of the discharge tube 10 and constitutes a part of the discharge tube (discharge vessel) 10. Yes. A cylindrical space between the inner tube 13b and the discharge tube 10 (tube wall 10a) constitutes a discharge space (plasma generation space) 14.

  In the illustrated embodiment, the inner electrode 13a has a strip shape (foil shape, plate shape) having a uniform cross section in the longitudinal direction (the axial direction of the discharge tube 10, the flow direction of the discharge gas in the discharge tube) as shown in FIG. The thickness of the central portion 13a1 in the width direction is thicker than the thickness of both edge portions 13a2, and sharpens toward both edge portions 13a2 (both end portions along the width direction). The thickness is smaller than that of the central portion 13a1, and both edge portions 13a2 have a sharp and sharp knife edge shape. The radial thickness of the discharge tube 10 of the inner tube 13b in which the inner electrode 13a is embedded is uneven along the circumferential direction, and the width direction (both edges 13a2 along the width direction of the embedded inner electrode 13a is The outer thickness d in the extended direction) is the thinnest.

  On the other hand, an outer electrode 15 serving as the other electrode of the pair of electrodes is disposed on the outer peripheral surface of the discharge tube 10 (tube wall 10a). In the illustrated embodiment, the outer electrode 15 is depicted as a metal film-like (foil-like) electrode, but may be a metal wire wound spirally. The axial length of the outer electrode 15 and the inner electrode 13a facing each other corresponds to the discharge space 14.

  The inner electrode 13a and the outer electrode 15 described above are a pair of electrodes facing each other through the inner tube 13b, the discharge space 14, and the tube wall 10a of the discharge tube 10, and are electrically connected to a power supply unit (not shown). The inner electrode 13a is a high-voltage side electrode, and the outer electrode 15 is a ground-side electrode.

  In order to generate discharge (plasma) using the atmospheric pressure plasma generator 100 having the above-described configuration, a discharge gas or the like (hereinafter simply referred to as discharge gas) flows into the discharge tube 10 from the inlet 11 of the discharge tube 10. Then, after flowing in the discharge space 14, it is discharged from the outlet 12 to the outside which is the atmosphere. The discharge gas is, for example, a known rare gas or a mixed gas of a rare gas and another gas.

  In this manner, the discharge gas is supplied (inflowed) into the discharge space 14 of the discharge tube 10 and is necessary for the start of discharge (dielectric breakdown) between the inner electrode 13a and the outer electrode 15 by the power supply unit. When a high voltage is applied, in the discharge space 14 of the discharge tube 10, the dielectric breakdown from the vicinity of both edge portions 13 a 2 where the electric field strength is high between the inner electrode 13 a and the outer electrode 15 is the starting point. Plasma (discharge) is generated throughout. The fact that the electric field intensity in the vicinity of both edge portions 13a2 is high will be described below. Since the thickness of the inner electrode 13a becomes thinner from the central portion 13a1 in the width direction toward both edge portions 13a2, and the both edge portions 13a2 have a sharp knife edge shape, for example, compared with a cylindrical electrode, Electric field concentration is likely to occur. As a result, the electric field strength in the discharge space 14 along the width direction of the inner electrode 13a (the region where the discharge distance is shortest between the both edges 13a2 and the outer electrode 15) is locally increased.

  In addition, in the illustrated embodiment, the thickness of the inner tube 13b covering the inner electrode 13a is not uniform in the circumferential direction, and both edges 13a2 of the inner electrode 13a (the tip of the knife edge shape, the maximum width direction of the inner electrode 13a) ) Has a minimum thickness. It is known that the electric field strength increases as the thickness of the dielectric decreases, so that in the discharge space 14, the electric field is reliably discharged in at least one of the two spaces X in the width direction of the inner electrode 13 a ( Plasma) can be generated.

  In other words, from the viewpoint of making the distance between the pair of electrodes non-uniform along the circumferential direction of the discharge tube, either one of both edge portions 13a2 of the inner electrode 13a is made thinner than the thickness of the central portion (knife The width of the inner electrode 13a is non-uniform along the circumferential direction of the discharge tube, or the thickness of the dielectric between the pair of electrodes is non-uniform along the circumferential direction of the discharge tube. In view of the above, any one of making the thickness (outer diameter) of the inner tube 13b non-uniform along the circumferential direction of the discharge tube by providing the inner tube 13b with a thin portion (thin wall portion). Thus, the electric field strength in the discharge tube can be locally increased, and the electric field strength becomes non-uniform along the circumferential direction of the discharge tube. By applying at least one of these methods, plasma can be generated even at a relatively low discharge start voltage, so that the state (for example, pressure, concentration, flow rate) of the discharge gas in the discharge space 14 is not uniform. Even in such a case, plasma can be reliably generated without increasing the discharge start voltage. In addition, by providing the thin wall portion of the inner tube 13b outside the both edge portions 13a2 having a knife edge shape, the electric field strength in the discharge tube can be locally increased by a synergistic effect, and the plasma can be more reliably generated. Can be generated.

  Therefore, according to the atmospheric pressure plasma generator 100 described above, the discharge gas flowing (supplied) from the inlet 11 into the discharge space 14 in the discharge tube 10 flows in the discharge space 14 along the axial direction. It becomes plasma.

  Moreover, in the above 1st Embodiment, since the inner side electrode 13a is embed | buried in the inner side pipe | tube 13b, the inner side electrode 13a is not damaged in the case of discharge. In addition, since both edge portions 13a2 in the width direction of the strip-shaped inner electrode 13a have a knife edge shape, no gap is generated between the inner tube 13b and the inner edge 13a2. Accordingly, it is possible to prevent oxygen (atmosphere) entering the gap from reacting (oxidizing) with the inner electrode 13a and deteriorating the inner electrode 13a.

  FIG. 3 shows a modification of the first embodiment. Only the inner electrode 13a in which both end portions 13a2 have a knife edge shape is formed in the discharge tube 10 without embedding the inner electrode 13a in the inner tube 13b. It is placed inside. Even in this modification, the width of the inner electrode (the width and thickness of the band-shaped inner electrode) is not uniform along the circumferential direction of the discharge tube, so that the distance between the pair of electrodes is increased in the circumferential direction of the discharge tube. The electric field strength between the inner electrode 13a and the outer electrode 15 (electric field strength in the discharge space 14) is locally increased in the vicinity of both edges 13a2 in the width direction of the inner electrode 13a. it can. In this modification, a band-shaped inner electrode is used. However, by using an inner electrode having an elliptical (oval, polygonal) cross section and making the width non-uniform in the circumferential direction, Can be made uneven along the circumferential direction of the discharge tube, and the electric field strength in the discharge tube can be locally increased.

  FIG. 4 shows still another modification of the first embodiment. The inner electrode 13a ′ has a circular cross section, and the inner tube 13b ′ has an elliptical (oval) cross section. Is uneven in the circumferential direction. Also in this modified example, the thickness of the inner tube 13b ′, which is a dielectric, becomes nonuniform along the circumferential direction of the discharge tube 10, and the thickness of the inner tube 13b ′ is the smallest in the discharge space 14. It is possible to locally increase the electric field strength in the space X in the vicinity of the inner electrode 13a ′ in contact with the electrode. Since the inner electrode 13a 'is embedded in the inner tube 13b', the inner electrode 13a 'is not damaged.

  5 and 6 show a second embodiment of the atmospheric pressure plasma generator according to the present invention. The second embodiment differs from the first embodiment in the arrangement of the pair of electrodes and the arrangement of the discharge gas inlet. The discharge tube 20 includes a cylindrical tube wall 20a made of a dielectric material (for example, quartz), an end wall 20b that closes one end of the discharge tube 20, and a tube wall 20a at the approximate center of the end wall 20b. An inflow port 21 for discharge gas or the like formed coaxially and an outflow port 22 formed coaxially with the tube wall 20 a at the other end of the discharge tube 20 are provided. A connecting tube 21 a communicating with the inflow port 21 is integrally formed on the outer surface of the end wall 20 b and constitutes a part of the discharge tube 20.

  In this embodiment, as shown in FIG. 6, the pair of electrodes 23 are band-shaped electrodes formed in a band shape (plate shape) with a uniform cross section along the axial direction of the discharge tube 10, and the tube wall 20a and the discharge electrode It is embedded in the tube wall 20a of the discharge tube 20 so as to face each other through the space 24. The pair of electrodes 23 are symmetrical with respect to an axis of symmetry passing through the central axis of the discharge tube 20, are bent at a curvature corresponding to the curvature of the tube wall 20 a of the discharge tube 20, and Along the direction, the thickness of the central portion 231 is the largest, and a knife edge shape is formed in which the thickness is gradually reduced toward both edge portions 232 and becomes thinner. The pair of electrodes 23 are electrically connected to the power supply device by a power supply member 23a connected to one end in the longitudinal direction.

  As a method for embedding the pair of electrodes 23 in the tube wall 20a of the discharge tube 20 by thermoforming, the pair of electrodes 23 is inserted between a small diameter tube (quartz tube) and a large diameter tube (quartz tube). A manufacturing method in which air between a small diameter tube and a large diameter tube is sucked and the small diameter tube and the large diameter tube are heat-welded and integrated can be applied.

  The above atmospheric pressure plasma generator 100 has a knife-edge shape in which both edges 232 of the pair of electrodes 23 of the discharge tube 20 are pointed, and the discharge wall 24 and the cylindrical wall surface (dielectric) of the discharge tube 20 are formed. Opposite across. For this reason, in the radial cross section of the discharge tube 20, the distance between the pair of electrodes 23 and the thickness of the dielectric are not uniform along the symmetry axis (the radial direction of the discharge tube) of the pair of electrodes 23. The electric field strength in the discharge space 24 increases locally in the vicinity of both edge portions 232 of the pair of electrodes 23 and becomes non-uniform along the circumferential direction of the discharge tube 20.

  Therefore, as in the first embodiment, when a high voltage necessary for the start of discharge (dielectric breakdown) is applied between the pair of electrodes 23 by the power supply unit, the dielectric breakdown in the vicinity of both edges 232 in the discharge tube 20 is caused. As a starting point, plasma (discharge) is generated in the entire discharge space 24.

  In this embodiment, the strip-shaped electrode 23 is embedded in the tube wall 20a of the discharge tube 20 and is not exposed on the outer surface of the tube wall 20a. Therefore, creeping discharge does not occur on the outer surface of the tube wall 20a of the discharge tube 20, so that the generation of plasma in the discharge space 24 is not hindered by the creeping discharge, and the electrode 23 to which a high voltage is applied is provided. A safe plasma generator that is not exposed on the outer surface of the discharge tube 20 can be provided.

  FIG. 7 shows a modification of the second embodiment. In this modified example, of the pair of electrodes of the second embodiment, the electrode 23 ″ is embedded in the tube wall 20a of the discharge tube 20, and the electrode 23 ′ is disposed along the outer surface of the tube wall 20a. It is a thing. The pair of electrodes 23 ′ and 23 ″ of this modification form a symmetrical shape with the symmetry axis as the center, and the thickness of the central portions 231 ′ and 231 ″ is the largest along the circumferential direction. It has a knife edge shape that gradually decreases in thickness toward both edges 232 ′, 232 ″ in the circumferential direction. Therefore, also in this modification, in the radial cross section of the discharge tube 20, the distance between the pair of electrodes 23 ′ and 23 ″ and the thickness of the dielectric are the symmetry axes (discharges) of the pair of electrodes 23 ′ and 23 ″. Therefore, the electric field strength between the pair of electrodes 23 ′ and 23 ″ locally increases in the vicinity of both edges 232 ′ and 232 ″, and the discharge tube It becomes non-uniform along the 20 circumferential direction. Similarly to the first embodiment, when a high voltage required for the start of discharge (dielectric breakdown) is applied between the pair of electrodes 23 ′ and 23 ″ by the power supply unit, both edges 232 ′ in the discharge tube 20 Plasma (discharge) is generated in the entire discharge space 24 starting from dielectric breakdown in the vicinity of 232 ″.

  In this modification, since one electrode 23 ″ is embedded in the tube wall 20a of the discharge tube 20 and is not exposed on the outer surface of the tube wall 20a, creeping discharge does not occur on the outer surface of the tube wall 20a. Further, it is possible to provide a safe atmospheric pressure plasma generating apparatus in which plasma generation in the discharge space 24 is not hindered by creeping discharge, and the electrode 23 ″ to which a high voltage is applied is not exposed on the outer surface of the discharge tube 20. .

10 Discharge tube (discharge vessel)
10a Tube wall 10b End wall 11 Inlet (discharge gas inlet)
11a Connection pipe 12 Outflow port 13a, 13a 'Inner electrode (one electrode, strip electrode)
13a1 center part 13a2 edge (both edges)
13b, 13b ′ inner tube 14 discharge space (plasma generation space)
15 Outer electrode (the other electrode, strip electrode)
20 Discharge tube (discharge vessel)
20a Pipe wall 20b End wall 21 Inlet 22 Outlet 23, 23 ', 23''electrode (band electrode)
231, 231 ′, 231 ″ center 232, 232 ′, 232 ″ edge (both edges)
100 atmospheric pressure plasma generator

Claims (10)

In an atmospheric pressure plasma generator comprising a discharge tube into which a discharge gas flows in and out, and a pair of electrodes arranged to face each other with the discharge tube interposed therebetween, the discharge gas flows inside the discharge tube.
The electric field strength between the pair of electrodes is non-uniform along the circumferential direction of the discharge tube;
An atmospheric pressure plasma generator characterized by.   2. The atmospheric pressure plasma generator according to claim 1, wherein the distance between the pair of electrodes or the thickness of the dielectric is not uniform along the circumferential direction or the radial direction of the discharge tube. An atmospheric pressure plasma generator in which a region where the electric field strength is locally high is formed.   3. The atmospheric pressure plasma generator according to claim 1, wherein at least one of the pair of electrodes is an inner electrode disposed inside the discharge tube, and a width of the inner electrode is the discharge. An atmospheric pressure plasma generator that is non-uniform along the circumferential direction of the tube.   4. The atmospheric pressure plasma generator according to claim 3, wherein the inner electrode is a strip electrode disposed along the axial direction of the discharge tube, and at least one of both edges in the width direction of the strip electrode. An atmospheric pressure plasma generator whose thickness is thinner than the thickness of the central portion of the strip electrode.   5. The atmospheric pressure plasma generator according to claim 3, further comprising an inner tube in which the inner electrode is embedded, wherein the inner tube has the smallest thickness in the maximum width direction of the inner electrode. .   4. The atmospheric pressure plasma generator according to claim 3, wherein one electrode of the pair of electrodes is an inner electrode disposed inside the discharge tube, and is an inner tube disposed inside the discharge tube. The atmospheric pressure plasma generator according to claim 1, wherein the radial thickness of the discharge tube of the inner tube is non-uniform along the circumferential direction of the discharge tube.   The atmospheric pressure plasma generator according to claim 5 or 6, wherein the inner tube is thermoformed integrally with the discharge tube.   3. The atmospheric pressure plasma generator according to claim 1, wherein at least one of the pair of electrodes is a strip electrode along a tube wall of the discharge tube and is embedded in the tube wall of the discharge tube. Atmospheric pressure plasma generator.   9. The atmospheric pressure plasma generator according to claim 8, wherein the strip electrode is embedded by heat welding between a small diameter tube and a large diameter tube constituting the discharge tube.   10. The atmospheric pressure plasma generator according to claim 8, wherein both edges in the width direction of the belt-like electrode have a knife edge shape. 11.

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