Coaxial microwave plasma torch

Abstract

Included are a body 1 having a coaxial structure consisting of a discharge antenna 2 situated inside and a counter electrode 3 situated outside, a microwave input portion 4 provided near a base end of the discharge antenna in the body, a plasma generation portion 6 provided near a tip end 2a of the discharge antenna in the body and communicating with a plasma outlet 5, and a gas supply portion 7 configured to supply the plasma generation portion with gas. The tip end of the discharge antenna is formed in a hemispherical shape, and the counter electrode is formed with a portion that faces the tip end of the discharge antenna tapering toward the plasma outlet.

Description

TECHNICAL FIELD

[0001] The present invention relates to a microwave plasma torch capable of generating plasma under atmospheric pressure, specifically a coaxial microwave plasma torch.BACKGROUND ART

[0002] Conventional coaxial microwave plasma torches are described in, for example, Patent Documents 1 and 2. These coaxial microwave plasma torches have a coaxial structure consisting of a discharge antenna situated inside and a counter electrode situated outside, and include a microwave input portion and a plasma generation portion, which are provided near a base end and a tip end, respectively, of the discharge antenna in the coaxial structure.

[0003] The coaxial microwave plasma torches further include a gas supply portion for supplying the plasma generation portion with gas through an internal space of the coaxial structure.

[0004] When the plasma generation portion is supplied with gas by the gas supply portion through the internal space of the coaxial structure in this manner, and the microwave input portion is supplied with microwaves, the electric field of the microwaves concentrates at the tip end of the discharge antenna, creating a high electric field that induces plasma generation at the tip end of the discharge antenna.

[0005] However, in such conventional coaxial microwave plasma torches, the tip end of the discharge antenna either has a pointed shape or has a shape formed by cutting the discharge antenna along a plane perpendicular to the center axis thereof, with the result that, in the former case, the electric field locally concentrates at the pointed tip end of the discharge antenna, and in the latter case, at the edge of the tip end of the discharge antenna.

[0006] As a result, the tip end or the edge portion of the tip end of the discharge antenna might be eroded by sputtering or melted due to heating, leading to destabilization of the generated plasma or a shortened lifetime of the discharge antenna.Prior Art Documents Patent Documents

[0007] Patent Document 1: Japanese Laid-Open Patent Publication No. H6-188094 Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-293955 SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0008] Therefore, the present invention aims to solve the problem of enhancing the stability of plasma in the coaxial microwave plasma torch and extending the lifetime of the discharge antenna.MEANS FOR SOLVING THE PROBLEM

[0009] To solve the above problem, the present invention provides a coaxial microwave plasma torch including a body having a coaxial structure consisting of a discharge antenna situated inside and a counter electrode situated outside, a microwave input portion provided near a base end of the discharge antenna in the body, a plasma generation portion provided near a tip end of the discharge antenna in the body and communicating with a plasma outlet, and a gas supply portion configured to supply the plasma generation portion with gas, the tip end of the discharge antenna is formed in a hemispherical shape, and the counter electrode is formed with a portion that faces the tip end of the discharge antenna tapering toward the plasma outlet.

[0010] In a preferred embodiment of the present invention, the tip end of the discharge antenna is dielectric-coated.

[0011] In another preferred embodiment of the present invention, the counter electrode is dielectric-coated on a surface that faces the discharge antenna.EFFECT OF THE INVENTION

[0012] In the present invention, the tip end of the discharge antenna is formed in a hemispherical shape, and the counter electrode is formed with the portion that faces the tip end of the discharge antenna tapering toward the plasma outlet, whereby an electric field is irradiated uniformly and stably from the tip end of the discharge antenna into a localized area between the tip end and the counter electrode, enabling stable generation of uniform and high-density plasma.

[0013] Furthermore, the tip end of the discharge antenna and the surface of the counter electrode that faces the discharge antenna are dielectric-coated, whereby the discharge antenna and the counter electrode become less susceptible to damage caused by plasma gas, thereby extending their lifetime.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a longitudinal cross-sectional view of a coaxial microwave plasma torch according to an embodiment of the present invention. FIG. 2 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to another embodiment of the present invention. FIG. 3 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. FIG. 4 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. MODES FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, the configuration of the present invention will be described with reference to the accompanying drawings, based on preferred embodiments. FIG. 1 is a longitudinal cross-sectional view of a coaxial microwave plasma torch according to an embodiment of the present invention.

[0016] Referring to FIG. 1, the coaxial microwave plasma torch of the present invention includes a body 1 having a coaxial structure consisting of a discharge antenna 2 situated inside and a counter electrode 3 situated outside, a microwave input portion 4 provided near a base end of the discharge antenna 2 in the body 1, a plasma generation portion 6 provided near a tip end of the discharge antenna 2 in the body 1 and communicating with a plasma outlet 5, and a gas supply portion 7 configured to supply the plasma generation portion 6 with (plasma-generation) gas.

[0017] It should be noted that in FIG. 1, the microwave input portion 4 is a coaxial microwave transmission cable, of which only a connecting portion 8 for connecting with each of the discharge antenna 2 and the counter electrode 3 is representatively depicted, and as the gas supply portion 7, only a gas conduit 10 is representatively depicted, with one end 10a connected to the body 1 as an opening into an internal space 9 of the coaxial structure and the other end 10b connected to a gas supply source (not shown). Moreover, in FIG. 1, reference numeral 18 denotes a dielectric retaining member for retaining the discharge antenna 2 coaxially with the counter electrode 3 within an internal space of the counter electrode 3.

[0018] The tip end 2a of the discharge antenna 2 is formed in a hemispherical shape and dielectric-coated. Moreover, the counter electrode 3 is formed with a portion that faces the tip end 2a of the discharge antenna 2 tapering toward the plasma outlet 5 and the surface of that portion being dielectric-coated.

[0019] The coaxial microwave plasma torch of the present invention further includes an ignition mechanism 11 configured to ignite plasma in the plasma generation portion 6. The ignition mechanism 11 is a plasma generation device provided upstream in the plasma-generation gas flow relative to the plasma generation portion 6 and configured to supply the plasma generation portion 6 with ignition plasma using dielectric barrier discharge.

[0020] The plasma generation device includes an ignition gas tube 12, which is a cylindrical dielectric with one end 12a connected to the body 1 as an opening into the internal space 9 of the coaxial structure and directed toward the tip end 2a of the discharge antenna 2, an ignition gas supply portion 13 connected to the other end 12b of the ignition gas tube 12, a pair of electrodes 14a and 14b provided on the outside of the ignition gas tube 12, and a power supply portion 15 configured to apply a high alternating-current voltage to the pair of electrodes 14a and 14b.

[0021] In this embodiment, the pair of electrodes 14a and 14b consist of two parallel leads 16 and 17, each covered with an insulator and wound around the outside of the ignition gas tube 12. Further, of the two leads 16 and 17, the power supply portion 15 is connected between one end 16a of the lead 16 and the end 17a of the other lead 17 that is farther from the end 16a of the lead 16. Note that the other ends 16b and 17b of the leads 16 and 17 are open.

[0022] Next, the operation of the coaxial microwave plasma torch will be described. Initially, (plasma-generation) gas is supplied into the internal space 9 of the coaxial structure through the gas conduit 10 of the gas supply portion 7, while microwaves are supplied to the discharge antenna 2 and the counter electrode 3 from the microwave input portion 4.

[0023] Then, ignition gas is supplied from the ignition gas supply portion 13 to the ignition gas tube 12 in the ignition mechanism 11, and a high alternating-current voltage is applied to the pair of electrodes 14a and 14b (i.e., the two coiled leads 16 and 17) in the ignition mechanism 11.

[0024] In this manner, the two coiled leads 16 and 17 constitute a cathode and an anode, and ignition plasma is generated in an area inside the ignition gas tube 12 corresponding to a gap between the adjacent leads 16 and 17.

[0025] The generated ignition plasma enters the internal space 9 of the body 1 through the end 12a of the ignition gas tube 12 and reaches the tip end 2a of the discharge antenna 2 to ignite atmospheric-pressure plasma in the plasma generation portion 6 provided with the microwaves.

[0026] After plasma ignition, the operation of the ignition mechanism is stopped. The generated atmospheric-pressure plasma is irradiated externally through the plasma outlet 5.

[0027] In the present invention, the tip end 2a of the discharge antenna 2 is formed in a hemispherical shape, and the counter electrode 3 is formed with the portion that faces the tip end 2a of the discharge antenna 2 tapering toward the plasma outlet 5, whereby an electric field is irradiated uniformly and stably from the tip end 2a of the discharge antenna 2 into a localized area between the tip end 2a and the counter electrode 5, enabling stable generation of uniform and high-density plasma.

[0028] Furthermore, the tip end 2a of the discharge antenna 2 and the surface of the counter electrode 3 that faces the discharge antenna 2 are dielectric-coated, whereby the discharge antenna 2 and the counter electrode 3 become less susceptible to damage (such as oxidization and etching) caused by plasma gas, thereby extending their service lives.

[0029] Furthermore, in the present invention, the ignition mechanism 11 is a plasma generation device provided upstream in the plasma-generation gas flow relative to the plasma generation portion 6 and using dielectric barrier discharge, and plasma ignition is performed by supplying ignition plasma generated by the plasma generation device to the plasma generation portion 6 within the body 1 of the coaxial microwave plasma torch, thereby enabling the realization of a compact ignition mechanism 11 and preventing the occurrence of contamination.

[0030] FIG. 2 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to another embodiment of the present invention. The embodiment in FIG. 2 differs from the embodiment in FIG. 1 only in the configuration of the pair of electrodes in the ignition mechanism. Therefore, in FIG. 2, the same elements as those shown in FIG. 1 are denoted by the same numerals and will not be elaborated upon below.

[0031] In this embodiment, the pair of electrodes 14a and 14b are a pair of semicylindrical electrodes 19a and 19b disposed on opposite sides of the ignition gas tube 12. In addition, the pair of semicylindrical electrodes 19a and 19b are connected to the power supply portion 15, with a gap between opposing side edges of the semicylindrical electrodes 19a and 19b.

[0032] In this embodiment, when ignition gas is supplied from the ignition gas supply portion 13 to the ignition gas tube 12 in the ignition mechanism 11, and a high alternating-current voltage is applied to the pair of electrodes 14a and 14b (i.e., the pair of semicylindrical electrodes 19a and 19b) in the ignition mechanism 11, ignition plasma is generated in an area inside the ignition gas tube 12 corresponding to the gap between the opposing side edges of the pair of semicylindrical electrodes 19a and 19b.

[0033] FIG. 3 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. The embodiment in FIG. 3 differs from the embodiment in FIG. 1 only in the configuration of the pair of electrodes in the ignition mechanism. Therefore, in FIG. 3, the same elements as those shown in FIG. 1 are denoted by the same numerals and will not be elaborated upon below.

[0034] In this embodiment, the pair of electrodes 14a and 14b are a pair of cylindrical electrodes 20a and 20b fitted around the outside of the ignition gas tube 12 and disposed on opposite sides in an axial direction of the ignition gas tube 12, with an insulator 21 interposed between opposing end edges of the pair of cylindrical electrodes 20a and 20b, and the pair of cylindrical electrodes 20a and 20b are connected to the power supply portion 15.

[0035] In this embodiment, when ignition gas is supplied from the ignition gas supply portion 13 to the ignition gas tube 12 in the ignition mechanism 11, and a high alternating-current voltage is applied to the pair of electrodes 14a and 14b (i.e., the pair of cylindrical electrodes 20a and 20b) in the ignition mechanism 11, ignition plasma is generated in an area inside the ignition gas tube 12 corresponding to the gap between the opposing end edges of the pair of cylindrical electrodes 20a and 20b.

[0036] FIG. 4 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. In this embodiment, as shown in FIG. 4, the ignition mechanism 1 is integrated with the gas conduit 10 of the gas supply portion 7, so that the gas conduit 10 constitutes a part of the ignition mechanism 11 (as an ignition gas tube).

[0037] In this case, the gas conduit 10 is formed of a dielectric at least in the part that constitutes the ignition mechanism 1, and the pair of electrodes 14a and 14b are provided on the outside of the dielectric gas conduit 10 and connected to the power supply portion 15 for applying a high alternating-current voltage. In this embodiment, the configurations of the pair of electrodes 14a and 14b and the power supply portion 15 are the same as those of the embodiment in FIG. 1.

[0038] This embodiment is effective when the (plasma-generation) gas and the ignition gas are of the same type, eliminating the need to separately connect the ignition gas tube to the body 2 and resulting in a more compact overall coaxial microwave plasma torch.

[0039] While the configuration of the present invention has been described above based on the preferred embodiments, the configuration of the present invention is not limited to those embodiments, and it will be understood that those skilled in the art can devise various modifications within the scope of the features as set forth in the accompanying claims.

[0040] For example, the configuration of the ignition mechanism for ignition plasma generation is not limited to the above embodiments, and any configuration can be employed so long as the ignition mechanism is a plasma generation device provided upstream in the plasma-generation gas flow relative to the plasma generation portion and using dielectric barrier discharge; more preferably, the plasma generation device includes an ignition gas tube in the form of a cylindrical dielectric with one end connected to the body as an opening into the internal space of the coaxial structure and directed toward the tip end of the discharge antenna, an ignition gas supply portion connected to the other end of the ignition gas tube, a pair of electrodes provided on the outside of the ignition gas tube, and a power supply portion configured to apply a high alternating-current voltage to the pair of electrodes.INDUSTRIAL APPLICABILITY

[0041] The coaxial microwave plasma torch according to the present invention can be utilized not only to irradiate processing targets with plasma and thereby perform plasma processing such as etching, CVD, ashing, and surface modification on the targets, but also to treat infectious diseases on external surfaces of human bodies, for example, the skin, preferably for the treatment and management of microbial infections, such as bacterial infections.

[0042] In the latter case, plasma generated by the plasma torch is irradiated onto a patient's wound, ulcer, or lesion to destroy bacteria in the wound, ulcer, or lesion and reduce the bacterial load. Normally, the infected surfaces are repeatedly exposed to the plasma until infection is eliminated.DESCRIPTION OF THE REFERENCE CHARACTERS

[0043] 1 body 2 discharge antenna 2a tip end 3 counter electrode 4 microwave input portion 5 plasma outlet 6 plasma generation portion 7 gas supply portion 8 coaxial cable connecting portion 9 internal space 10 gas conduit 10a one end 10b other end 11 ignition mechanism 12 ignition gas tube 12a one end 12b other end 13 ignition gas supply portion 14a, 14b pair of electrodes 15 power supply portion 16 lead 16a one end 16b other end 17 lead 17a, 17b end 18 retaining member 19a, 19b semicylindrical electrode 20a, 20b cylindrical electrode 21 insulator

Examples

Embodiment Construction

[0015]Hereinafter, the configuration of the present invention will be described with reference to the accompanying drawings, based on preferred embodiments. FIG. 1 is a longitudinal cross-sectional view of a coaxial microwave plasma torch according to an embodiment of the present invention.

[0016]Referring to FIG. 1, the coaxial microwave plasma torch of the present invention includes a body 1 having a coaxial structure consisting of a discharge antenna 2 situated inside and a counter electrode 3 situated outside, a microwave input portion 4 provided near a base end of the discharge antenna 2 in the body 1, a plasma generation portion 6 provided near a tip end of the discharge antenna 2 in the body 1 and communicating with a plasma outlet 5, and a gas supply portion 7 configured to supply the plasma generation portion 6 with (plasma-generation) gas.

[0017]It should be noted that in FIG. 1, the microwave input portion 4 is a coaxial microwave transmission cable, of which only a connect...

TECHNICAL FIELD

[0001] The present invention relates to a microwave plasma torch capable of generating plasma under atmospheric pressure, specifically a coaxial microwave plasma torch.BACKGROUND ART

[0002] Conventional coaxial microwave plasma torches are described in, for example, Patent Documents 1 and 2. These coaxial microwave plasma torches have a coaxial structure consisting of a discharge antenna situated inside and a counter electrode situated outside, and include a microwave input portion and a plasma generation portion, which are provided near a base end and a tip end, respectively, of the discharge antenna in the coaxial structure.

[0003] The coaxial microwave plasma torches further include a gas supply portion for supplying the plasma generation portion with gas through an internal space of the coaxial structure.

[0004] When the plasma generation portion is supplied with gas by the gas supply portion through the internal space of the coaxial structure in this manner, and the microwave input portion is supplied with microwaves, the electric field of the microwaves concentrates at the tip end of the discharge antenna, creating a high electric field that induces plasma generation at the tip end of the discharge antenna.

[0005] However, in such conventional coaxial microwave plasma torches, the tip end of the discharge antenna either has a pointed shape or has a shape formed by cutting the discharge antenna along a plane perpendicular to the center axis thereof, with the result that, in the former case, the electric field locally concentrates at the pointed tip end of the discharge antenna, and in the latter case, at the edge of the tip end of the discharge antenna.

[0006] As a result, the tip end or the edge portion of the tip end of the discharge antenna might be eroded by sputtering or melted due to heating, leading to destabilization of the generated plasma or a shortened lifetime of the discharge antenna.Prior Art Documents Patent Documents

[0007] Patent Document 1: Japanese Laid-Open Patent Publication No. H6-188094 Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-293955 SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0008] Therefore, the present invention aims to solve the problem of enhancing the stability of plasma in the coaxial microwave plasma torch and extending the lifetime of the discharge antenna.MEANS FOR SOLVING THE PROBLEM

[0009] To solve the above problem, the present invention provides a coaxial microwave plasma torch including a body having a coaxial structure consisting of a discharge antenna situated inside and a counter electrode situated outside, a microwave input portion provided near a base end of the discharge antenna in the body, a plasma generation portion provided near a tip end of the discharge antenna in the body and communicating with a plasma outlet, and a gas supply portion configured to supply the plasma generation portion with gas, the tip end of the discharge antenna is formed in a hemispherical shape, and the counter electrode is formed with a portion that faces the tip end of the discharge antenna tapering toward the plasma outlet.

[0010] In a preferred embodiment of the present invention, the tip end of the discharge antenna is dielectric-coated.

[0011] In another preferred embodiment of the present invention, the counter electrode is dielectric-coated on a surface that faces the discharge antenna.EFFECT OF THE INVENTION

[0012] In the present invention, the tip end of the discharge antenna is formed in a hemispherical shape, and the counter electrode is formed with the portion that faces the tip end of the discharge antenna tapering toward the plasma outlet, whereby an electric field is irradiated uniformly and stably from the tip end of the discharge antenna into a localized area between the tip end and the counter electrode, enabling stable generation of uniform and high-density plasma.

[0013] Furthermore, the tip end of the discharge antenna and the surface of the counter electrode that faces the discharge antenna are dielectric-coated, whereby the discharge antenna and the counter electrode become less susceptible to damage caused by plasma gas, thereby extending their lifetime.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a longitudinal cross-sectional view of a coaxial microwave plasma torch according to an embodiment of the present invention. FIG. 2 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to another embodiment of the present invention. FIG. 3 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. FIG. 4 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. MODES FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, the configuration of the present invention will be described with reference to the accompanying drawings, based on preferred embodiments. FIG. 1 is a longitudinal cross-sectional view of a coaxial microwave plasma torch according to an embodiment of the present invention.

[0016] Referring to FIG. 1, the coaxial microwave plasma torch of the present invention includes a body 1 having a coaxial structure consisting of a discharge antenna 2 situated inside and a counter electrode 3 situated outside, a microwave input portion 4 provided near a base end of the discharge antenna 2 in the body 1, a plasma generation portion 6 provided near a tip end of the discharge antenna 2 in the body 1 and communicating with a plasma outlet 5, and a gas supply portion 7 configured to supply the plasma generation portion 6 with (plasma-generation) gas.

[0017] It should be noted that in FIG. 1, the microwave input portion 4 is a coaxial microwave transmission cable, of which only a connecting portion 8 for connecting with each of the discharge antenna 2 and the counter electrode 3 is representatively depicted, and as the gas supply portion 7, only a gas conduit 10 is representatively depicted, with one end 10a connected to the body 1 as an opening into an internal space 9 of the coaxial structure and the other end 10b connected to a gas supply source (not shown). Moreover, in FIG. 1, reference numeral 18 denotes a dielectric retaining member for retaining the discharge antenna 2 coaxially with the counter electrode 3 within an internal space of the counter electrode 3.

[0018] The tip end 2a of the discharge antenna 2 is formed in a hemispherical shape and dielectric-coated. Moreover, the counter electrode 3 is formed with a portion that faces the tip end 2a of the discharge antenna 2 tapering toward the plasma outlet 5 and the surface of that portion being dielectric-coated.

[0019] The coaxial microwave plasma torch of the present invention further includes an ignition mechanism 11 configured to ignite plasma in the plasma generation portion 6. The ignition mechanism 11 is a plasma generation device provided upstream in the plasma-generation gas flow relative to the plasma generation portion 6 and configured to supply the plasma generation portion 6 with ignition plasma using dielectric barrier discharge.

[0020] The plasma generation device includes an ignition gas tube 12, which is a cylindrical dielectric with one end 12a connected to the body 1 as an opening into the internal space 9 of the coaxial structure and directed toward the tip end 2a of the discharge antenna 2, an ignition gas supply portion 13 connected to the other end 12b of the ignition gas tube 12, a pair of electrodes 14a and 14b provided on the outside of the ignition gas tube 12, and a power supply portion 15 configured to apply a high alternating-current voltage to the pair of electrodes 14a and 14b.

[0021] In this embodiment, the pair of electrodes 14a and 14b consist of two parallel leads 16 and 17, each covered with an insulator and wound around the outside of the ignition gas tube 12. Further, of the two leads 16 and 17, the power supply portion 15 is connected between one end 16a of the lead 16 and the end 17a of the other lead 17 that is farther from the end 16a of the lead 16. Note that the other ends 16b and 17b of the leads 16 and 17 are open.

[0022] Next, the operation of the coaxial microwave plasma torch will be described. Initially, (plasma-generation) gas is supplied into the internal space 9 of the coaxial structure through the gas conduit 10 of the gas supply portion 7, while microwaves are supplied to the discharge antenna 2 and the counter electrode 3 from the microwave input portion 4.

[0023] Then, ignition gas is supplied from the ignition gas supply portion 13 to the ignition gas tube 12 in the ignition mechanism 11, and a high alternating-current voltage is applied to the pair of electrodes 14a and 14b (i.e., the two coiled leads 16 and 17) in the ignition mechanism 11.

[0024] In this manner, the two coiled leads 16 and 17 constitute a cathode and an anode, and ignition plasma is generated in an area inside the ignition gas tube 12 corresponding to a gap between the adjacent leads 16 and 17.

[0025] The generated ignition plasma enters the internal space 9 of the body 1 through the end 12a of the ignition gas tube 12 and reaches the tip end 2a of the discharge antenna 2 to ignite atmospheric-pressure plasma in the plasma generation portion 6 provided with the microwaves.

[0026] After plasma ignition, the operation of the ignition mechanism is stopped. The generated atmospheric-pressure plasma is irradiated externally through the plasma outlet 5.

[0027] In the present invention, the tip end 2a of the discharge antenna 2 is formed in a hemispherical shape, and the counter electrode 3 is formed with the portion that faces the tip end 2a of the discharge antenna 2 tapering toward the plasma outlet 5, whereby an electric field is irradiated uniformly and stably from the tip end 2a of the discharge antenna 2 into a localized area between the tip end 2a and the counter electrode 5, enabling stable generation of uniform and high-density plasma.

[0028] Furthermore, the tip end 2a of the discharge antenna 2 and the surface of the counter electrode 3 that faces the discharge antenna 2 are dielectric-coated, whereby the discharge antenna 2 and the counter electrode 3 become less susceptible to damage (such as oxidization and etching) caused by plasma gas, thereby extending their service lives.

[0029] Furthermore, in the present invention, the ignition mechanism 11 is a plasma generation device provided upstream in the plasma-generation gas flow relative to the plasma generation portion 6 and using dielectric barrier discharge, and plasma ignition is performed by supplying ignition plasma generated by the plasma generation device to the plasma generation portion 6 within the body 1 of the coaxial microwave plasma torch, thereby enabling the realization of a compact ignition mechanism 11 and preventing the occurrence of contamination.

[0030] FIG. 2 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to another embodiment of the present invention. The embodiment in FIG. 2 differs from the embodiment in FIG. 1 only in the configuration of the pair of electrodes in the ignition mechanism. Therefore, in FIG. 2, the same elements as those shown in FIG. 1 are denoted by the same numerals and will not be elaborated upon below.

[0031] In this embodiment, the pair of electrodes 14a and 14b are a pair of semicylindrical electrodes 19a and 19b disposed on opposite sides of the ignition gas tube 12. In addition, the pair of semicylindrical electrodes 19a and 19b are connected to the power supply portion 15, with a gap between opposing side edges of the semicylindrical electrodes 19a and 19b.

[0032] In this embodiment, when ignition gas is supplied from the ignition gas supply portion 13 to the ignition gas tube 12 in the ignition mechanism 11, and a high alternating-current voltage is applied to the pair of electrodes 14a and 14b (i.e., the pair of semicylindrical electrodes 19a and 19b) in the ignition mechanism 11, ignition plasma is generated in an area inside the ignition gas tube 12 corresponding to the gap between the opposing side edges of the pair of semicylindrical electrodes 19a and 19b.

[0033] FIG. 3 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. The embodiment in FIG. 3 differs from the embodiment in FIG. 1 only in the configuration of the pair of electrodes in the ignition mechanism. Therefore, in FIG. 3, the same elements as those shown in FIG. 1 are denoted by the same numerals and will not be elaborated upon below.

[0034] In this embodiment, the pair of electrodes 14a and 14b are a pair of cylindrical electrodes 20a and 20b fitted around the outside of the ignition gas tube 12 and disposed on opposite sides in an axial direction of the ignition gas tube 12, with an insulator 21 interposed between opposing end edges of the pair of cylindrical electrodes 20a and 20b, and the pair of cylindrical electrodes 20a and 20b are connected to the power supply portion 15.

[0035] In this embodiment, when ignition gas is supplied from the ignition gas supply portion 13 to the ignition gas tube 12 in the ignition mechanism 11, and a high alternating-current voltage is applied to the pair of electrodes 14a and 14b (i.e., the pair of cylindrical electrodes 20a and 20b) in the ignition mechanism 11, ignition plasma is generated in an area inside the ignition gas tube 12 corresponding to the gap between the opposing end edges of the pair of cylindrical electrodes 20a and 20b.

[0036] FIG. 4 is a view similar to FIG. 1 of a coaxial microwave plasma torch according to still another embodiment of the present invention. In this embodiment, as shown in FIG. 4, the ignition mechanism 1 is integrated with the gas conduit 10 of the gas supply portion 7, so that the gas conduit 10 constitutes a part of the ignition mechanism 11 (as an ignition gas tube).

[0037] In this case, the gas conduit 10 is formed of a dielectric at least in the part that constitutes the ignition mechanism 1, and the pair of electrodes 14a and 14b are provided on the outside of the dielectric gas conduit 10 and connected to the power supply portion 15 for applying a high alternating-current voltage. In this embodiment, the configurations of the pair of electrodes 14a and 14b and the power supply portion 15 are the same as those of the embodiment in FIG. 1.

[0038] This embodiment is effective when the (plasma-generation) gas and the ignition gas are of the same type, eliminating the need to separately connect the ignition gas tube to the body 2 and resulting in a more compact overall coaxial microwave plasma torch.

[0039] While the configuration of the present invention has been described above based on the preferred embodiments, the configuration of the present invention is not limited to those embodiments, and it will be understood that those skilled in the art can devise various modifications within the scope of the features as set forth in the accompanying claims.

[0040] For example, the configuration of the ignition mechanism for ignition plasma generation is not limited to the above embodiments, and any configuration can be employed so long as the ignition mechanism is a plasma generation device provided upstream in the plasma-generation gas flow relative to the plasma generation portion and using dielectric barrier discharge; more preferably, the plasma generation device includes an ignition gas tube in the form of a cylindrical dielectric with one end connected to the body as an opening into the internal space of the coaxial structure and directed toward the tip end of the discharge antenna, an ignition gas supply portion connected to the other end of the ignition gas tube, a pair of electrodes provided on the outside of the ignition gas tube, and a power supply portion configured to apply a high alternating-current voltage to the pair of electrodes.INDUSTRIAL APPLICABILITY

[0041] The coaxial microwave plasma torch according to the present invention can be utilized not only to irradiate processing targets with plasma and thereby perform plasma processing such as etching, CVD, ashing, and surface modification on the targets, but also to treat infectious diseases on external surfaces of human bodies, for example, the skin, preferably for the treatment and management of microbial infections, such as bacterial infections.

[0042] In the latter case, plasma generated by the plasma torch is irradiated onto a patient's wound, ulcer, or lesion to destroy bacteria in the wound, ulcer, or lesion and reduce the bacterial load. Normally, the infected surfaces are repeatedly exposed to the plasma until infection is eliminated.DESCRIPTION OF THE REFERENCE CHARACTERS

[0043] 1 body 2 discharge antenna 2a tip end 3 counter electrode 4 microwave input portion 5 plasma outlet 6 plasma generation portion 7 gas supply portion 8 coaxial cable connecting portion 9 internal space 10 gas conduit 10a one end 10b other end 11 ignition mechanism 12 ignition gas tube 12a one end 12b other end 13 ignition gas supply portion 14a, 14b pair of electrodes 15 power supply portion 16 lead 16a one end 16b other end 17 lead 17a, 17b end 18 retaining member 19a, 19b semicylindrical electrode 20a, 20b cylindrical electrode 21 insulator

Examples

Embodiment Construction

[0015]Hereinafter, the configuration of the present invention will be described with reference to the accompanying drawings, based on preferred embodiments. FIG. 1 is a longitudinal cross-sectional view of a coaxial microwave plasma torch according to an embodiment of the present invention.

[0016]Referring to FIG. 1, the coaxial microwave plasma torch of the present invention includes a body 1 having a coaxial structure consisting of a discharge antenna 2 situated inside and a counter electrode 3 situated outside, a microwave input portion 4 provided near a base end of the discharge antenna 2 in the body 1, a plasma generation portion 6 provided near a tip end of the discharge antenna 2 in the body 1 and communicating with a plasma outlet 5, and a gas supply portion 7 configured to supply the plasma generation portion 6 with (plasma-generation) gas.

[0017]It should be noted that in FIG. 1, the microwave input portion 4 is a coaxial microwave transmission cable, of which only a connect...

Claims

1. A coaxial microwave plasma torch comprising: a body having a coaxial structure consisting of a discharge antenna situated inside and a counter electrode situated outside; a microwave input portion provided near a base end of the discharge antenna in the body; a plasma generation portion provided near a tip end of the discharge antenna in the body and communicating with a plasma outlet; and a gas supply portion configured to supply the plasma generation portion with gas, wherein, the tip end of the discharge antenna is formed in a hemispherical shape, and the counter electrode is formed with a portion that faces the tip end of the discharge antenna tapering toward the plasma outlet.

2. The coaxial microwave plasma torch according to claim 1, wherein the tip end of the discharge antenna is dielectric-coated.

3. The coaxial microwave plasma torch according to claim 2, wherein the counter electrode is dielectric-coated on a surface that faces the discharge antenna.

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