JP2018160352A - Plasma generator and plasma generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma generator capable of surely generating plasma while preventing degradation of an electrode in a discharge vessel and creeping discharge.SOLUTION: Disclosed is a plasma generator having a pair of electrodes (13a and 15, 13a' and 15, and 23 and 23 or 23' and 23") which are arranged and installed opposite to each other via discharge containers (10, 20). The pair of electrodes is covered with dielectric bodies (13b, 13b' and 20a) constituting a part of the discharge vessel so as not to be exposed to discharge gas in the discharge vessel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plasma generation apparatus and a plasma generation method.

  In a conventional plasma generator, for example, plasma is generated in a discharge vessel (Patent Documents 1 and 2). There is also known an apparatus that generates a plasma between electrodes by flowing a discharge gas between a pair of electrodes facing each other with a dielectric material interposed therebetween (Patent Document 3).

JP 2014-212839 A JP 2007-207475 A JP 2009-187862 A

  However, in the apparatus of Patent Document 1, since one inner electrode of the pair of electrodes is directly arranged in the discharge space, the gas for discharge flowing in the discharge space reacts with the electrode (for example, oxygen or fluorine). If the discharge gas contains a highly reactive discharge gas (hereinafter simply referred to as a discharge gas), electrode deterioration (for example, oxidation) occurs. As a result, there is a possibility that plasma is hardly generated. In the device described in Patent Document 2, a dielectric is disposed between the discharge space and the inner electrode, but the inner electrode is covered with the dielectric in a region where the discharge gas other than the discharge space flows. Is exposed. For this reason, similarly to Patent Document 1, there is a possibility that the inner electrode deteriorates and plasma is hardly generated. Moreover, in the apparatus of Patent Document 2, the state (for example, pressure, concentration, flow rate) of the discharge gas in the discharge space is likely to be non-uniform. As a result, the voltage required for dielectric breakdown, that is, the plasma generation start voltage (discharge start voltage) becomes unstable, and the plasma generation itself may become unstable. Furthermore, the dielectric material (glass body) of Patent Document 3 is cylindrical, and a pair of opposed outer electrodes are arranged on the outer surface of the cylindrical glass body, so that a high frequency voltage is applied between the pair of electrodes. When this occurs, creeping discharge (plasma on the outer surface of the discharge vessel) may occur along the outer surface of the cylindrical glass body. As a result, the electric field strength in the discharge space is reduced, and plasma may not be generated.

  An object of the present invention is to provide a plasma generation apparatus and a plasma generation method capable of reliably generating plasma while preventing electrode deterioration and creeping discharge in the discharge vessel based on the above problem awareness.

  The plasma generator of the present invention is a plasma generator having a pair of electrodes arranged opposite to each other with a discharge vessel interposed therebetween, so that the pair of electrodes are not exposed to the discharge gas in the discharge vessel. It is characterized by being covered with a dielectric that constitutes a part of the discharge vessel.

  In one embodiment of the plasma generator, the discharge vessel has a discharge gas inlet and a plasma outlet generated by the discharge gas.

  One electrode of the pair of electrodes may be an inner electrode disposed inside the discharge vessel, and the inner electrode may be embedded in the dielectric.

  The dielectric may constitute a part of the discharge vessel.

  The electric field strength between the pair of electrodes may be non-uniform along the circumferential direction of the discharge vessel.

  The radial thickness of the dielectric may be non-uniform along the circumferential direction.

  The inner electrode may be a strip electrode, and the dielectric may be thinnest on the outer side in the width direction of the strip electrode.

  In the strip electrode, the thickness of at least one of both edges in the width direction may be smaller than the thickness of the central portion of the strip electrode.

  The strip electrode may have a knife edge shape at both edges in the width direction of the strip electrode.

  In one embodiment of the plasma generator of the present invention, at least one of the pair of electrodes may be embedded in the tube wall of the discharge vessel.

  The plasma generation method of the present invention uses the plasma generation apparatus described above, introduces a discharge gas into the discharge vessel, generates plasma between the pair of electrodes, and discharges the plasma out of the discharge vessel. It is characterized by doing.

  In the plasma generator of the present invention, the electrode in the discharge vessel is covered with a dielectric in the discharge vessel in which the discharge gas flows. This eliminates the reaction between the discharge gas and the electrode even if the discharge gas contains a highly reactive gas with the electrode, and reliably generates plasma over a long period of time regardless of the type of discharge gas. it can. Further, by making the electric field strength in the discharge space nonuniform along the discharge vessel circumferential direction, the discharge space has a portion where the electric field strength is locally high, and discharge (plasma) can be generated even at a low voltage. . For this reason, plasma can be reliably generated, and startability of plasma generation can be improved. Moreover, creeping discharge does not occur on the outer surface of the discharge vessel by providing at least one electrode in the discharge vessel or being covered with a dielectric.

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 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 VV line of FIG. It is sectional drawing corresponding to FIG. 5 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 vessel (discharge tube) 10. The discharge vessel 10 is made of a dielectric material (for example, quartz), and is formed in a cylindrical shape having a perfect cross section in the illustrated example. At one end of the discharge vessel 10 in the axial direction, an inlet 11 for a reactive discharge gas (hereinafter simply referred to as discharge gas) is formed in the radial direction of the discharge vessel 10, and at the other end of the discharge vessel 10. An outlet 12 is formed through which discharge gas and plasma (radical) flow out in the axial direction. The inflow port 11 is formed in the tube wall 10 a of the discharge vessel 10 and communicates with a connection tube 11 a extending in the radial direction of the discharge vessel 10. One end of the tube wall 10a is closed by an end wall 10b integral with the tube wall 10a. Note that the inflow port and the outflow port may be exchanged with the same configuration to cause the discharge gas to flow in the reverse direction in the discharge vessel (the direction of the arrow in the figure is reversed).

  On the other hand, inside the discharge vessel 10, an inner electrode 13 a that is one of a pair of electrodes and an inner tube 13 b in which the inner electrode 13 a is embedded (covered) are disposed along the axial center of the discharge vessel 10. Has been. 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) in a state where the inner electrode 13a is inserted into a tubular dielectric. The Further, the inner tube 13 b is integrated with the discharge vessel 10 by heat welding (heat forming) on the end wall 10 b on the inlet 11 side of the discharge vessel 10 and constitutes a part of the discharge vessel 10. A cylindrical space between the inner tube 13b and the discharge vessel 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 vessel 10, the flow direction of the discharge gas in the discharge vessel) 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). Its thickness is thinner 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 vessel 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 vessel 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 via the inner tube 13b, the discharge space 14, and the tube wall 10a of the discharge vessel 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 plasma (radical) using the atmospheric pressure plasma generator 100 having the above-described configuration, a discharge gas or the like is caused to flow into the discharge vessel 10 from the inlet 11 of the discharge vessel 10 and flow in the discharge space 14. Then, it is discharged from the outlet 12 of the discharge vessel 10 to the outside which is the atmosphere. The discharge gas is not limited to a highly reactive gas such as oxygen, but may be an inert gas such as helium, argon, or nitrogen, or a mixed gas of a highly reactive gas and an inert gas.

  As described above, the discharge gas is supplied (inflowed) into the discharge space 14 of the discharge vessel 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 vessel 10, the dielectric breakdown from the vicinity of both edges 13 a 2 where the electric field strength is high between the inner electrode 13 a and the outer electrode 15 starts, and the discharge space 14 Plasma (discharge) is generated throughout. The fact that the electric field intensity in the vicinity of both edge portions 13a2 is locally 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 the thickness is minimized at both edges 13a2 (knife edge-shaped tips) of the inner electrode 13a. ing. It is known that the electric field strength becomes higher as the thickness of the dielectric becomes thinner. Therefore, in the discharge space 14, the plasma (in the at least one of the two spaces X in the width direction of the inner electrode 13 a is surely plasma ( Discharge) 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 vessel (discharge tube), either one of the two edge portions 13a2 of the inner electrode 13a is made larger than the thickness of the central portion. By making it thinner (knife edge shape), the width of the inner electrode 13a is made nonuniform along the circumferential direction of the discharge vessel, or the thickness of the dielectric between the pair of electrodes is taken along the circumferential direction of the discharge vessel. From the viewpoint of making the inner tube 13b uneven, by providing the inner tube 13b with a thin portion (thin wall portion), the inner tube thickness (outer diameter) is made uneven along the circumferential direction of the discharge tube. As a result, the electric field strength in the discharge vessel can be locally increased, and the electric field strength becomes non-uniform along the circumferential direction of the discharge vessel (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 vessel 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 vessel 10 flows in the discharge space 14 along the axial direction. It becomes plasma (radical).

  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. That is, the inner electrode 13a in the discharge vessel 10 is covered with the inner tube (dielectric) 13b, so that the discharge gas (the highly reactive gas contained in the discharge gas) and the inner electrode 13a are not in contact with each other. Since the inner electrode 13a is not deteriorated by the discharge gas, plasma can be reliably generated over a long period of time. Furthermore, since the inner tube (dielectric) 13b covering the inner electrode 13a and the discharge vessel 10 are integrally configured, deterioration of the entire electrode can be prevented more reliably. 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. 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 uneven along the circumferential direction of the discharge vessel 10, and the portion of the discharge space 14 where the thickness of the inner tube 13b ′ is the thinnest. 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 and plasma can be reliably generated over a long period of time.

  4 and 5 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 vessel 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 vessel 20, and a tube wall 20a at the approximate center of the end wall 20b. A discharge gas inlet 21 is formed coaxially, and an outlet 22 is formed coaxially with the tube wall 20a at the other end of the tube wall 20a. A connecting tube 21 a communicating with the inflow port 21 is integrally formed on the outer surface of the end wall 20 b to constitute a part of the discharge vessel 20. The cylindrical space in the tube wall 20a constitutes a discharge space (plasma generation space) 24.

  In this embodiment, as shown in FIG. 5, 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 vessel 20, and the tube wall 20a and the discharge electrode It is embed | buried in the tube wall 20a of the discharge vessel 20 so that it may oppose through the space 24. FIG. The pair of electrodes 23 are symmetrical with respect to an axis of symmetry passing through the central axis of the discharge vessel 20, and are bent with a curvature corresponding to the curvature of the tube wall 20a of the discharge vessel 20, 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 of embedding the pair of electrodes 23 in the tube wall 20a of the discharge vessel 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.

  In the atmospheric pressure plasma generator 100 described above, both edges 232 of the pair of electrodes 23 of the discharge vessel 20 have a sharp knife-edge shape, and the discharge space 24 and the cylindrical wall surface (dielectric) of the discharge vessel 20. Are opposed to each other in the diameter direction. For this reason, in the radial cross section of the discharge vessel 20, the distance between the pair of electrodes 23 and the thickness of the dielectric become nonuniform 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 nonuniform along the circumferential direction of the discharge vessel 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 vessel 20 is caused. As a starting point, plasma (discharge) is generated in the entire discharge space 24.

  In the present embodiment, the strip-shaped electrode 23 is embedded in the tube wall 20a and is not exposed on the outer surface of the tube wall 20a. Therefore, since the discharge gas in the discharge vessel 20 does not contact the electrode 23, the electrode 23 is not deteriorated by the discharge gas, and plasma can be reliably generated over a long period of time. Further, since creeping discharge does not occur on the outer surface of the tube wall 20a of the discharge vessel 20, 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 provided. A safe plasma generator that is not exposed on the outer surface of the discharge vessel 20 can be provided.

  FIG. 6 shows a modification of the second embodiment. In this modification, of the pair of electrodes of the second embodiment, the electrode 23 ″ is embedded in the tube wall 20a of the discharge vessel 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 vessel 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 ″. The electric field strength between the pair of electrodes 23 ′ and 23 ″ locally increases in the vicinity of both edge portions 232 ′ and 232 ″, and the discharge vessel becomes uneven. 20 becomes non-uniform along the 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 vessel 20 and Plasma is generated in the entire discharge space 24 starting from dielectric breakdown in the vicinity of 232 ″.

  Also in this modified example, the entire region of the discharge space 24 is covered with the tube wall 20 a made of a dielectric without exposing the pair of electrodes 23 ′ and 23 ″ to the discharge space 24. Therefore, the discharge gas in the discharge vessel 20 does not come into contact with the pair of electrodes 23 ′ and 23 ″, so that the pair of electrodes 23 ′ and 23 ″ is not deteriorated by the discharge gas and can be reliably obtained over a long period of time. Plasma can be generated. In this modification, one electrode 23 ″ is embedded in the tube wall 20 a of the discharge vessel 20 and is not exposed on the outer surface of the tube wall 20 a. For this reason, creeping discharge does not occur on the outer surface of the tube wall 20a. Therefore, 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 in the discharge vessel 20. It is possible to provide a safe plasma generator that is not exposed to the outer surface of the plasma.

10 Discharge vessel (discharge tube)
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 15 outer electrode (the other electrode, strip electrode)
20 Discharge vessel (discharge tube)
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)
24 discharge space 100 atmospheric pressure plasma generator

Claims (11)

In the plasma generator having a pair of electrodes disposed opposite to each other with a discharge vessel interposed therebetween,
The pair of electrodes are covered with a dielectric that constitutes a part of the discharge vessel so as not to be exposed to the discharge gas in the discharge vessel;
A plasma generator characterized by the above.   2. The plasma generator according to claim 1, wherein the discharge vessel has a discharge gas inlet and a plasma outlet generated by the discharge gas.   3. The plasma generator according to claim 1, wherein one electrode of the pair of electrodes is an inner electrode disposed inside the discharge vessel, and the inner electrode is embedded in the dielectric. Plasma generator.   4. The plasma generating apparatus according to claim 3, wherein the dielectric is formed by integrating a part of the discharge vessel.   The plasma generator according to any one of claims 1 to 4, wherein the electric field strength between the pair of electrodes is non-uniform along the circumferential direction of the discharge vessel.   The plasma generator according to any one of claims 3 to 5, wherein a radial thickness of the dielectric is non-uniform along a circumferential direction.   7. The plasma generator according to claim 6, wherein the inner electrode is a strip electrode, and the thickness of the dielectric is the smallest on the outer side in the width direction of the strip electrode.   8. The plasma generator according to claim 7, wherein the thickness of at least one of both edges in the width direction of the strip electrode is thinner than the thickness of the central portion of the strip electrode.   9. The plasma generator according to claim 7, wherein both edges in the width direction of the belt-like electrode have a knife edge shape.   3. The plasma generator according to claim 1, wherein at least one of the pair of electrodes is embedded in a tube wall of the discharge vessel.   A plasma generator according to any one of claims 1 to 10, wherein a discharge gas is introduced into the discharge vessel, plasma is generated between the pair of electrodes, and the plasma is discharged from the discharge vessel. Method of generating plasma to be released.

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