JP2006278191A - Electrode for plasma jet generation - Google Patents

Abstract

A long-life electrode for generating a plasma jet capable of generating a low-temperature plasma jet in a pressure atmosphere near atmospheric pressure and reducing thermal damage to a substrate to be processed is provided.
A plasma jet that discharges a discharge plasma generated by supplying a discharge gas 20 between a pair of coaxially arranged electrodes 3 and 6 and applying an alternating electric field as a plasma jet under a pressure near atmospheric pressure. In the generating electrode, the metal electrodes 3 and 6 arranged along the central axis are cooled by causing the discharge gas 20 supplied therein to flow in a spiral flow along the wall surface in the internal holes. Thus, a low temperature plasma jet is generated.
[Selection] Figure 2

Description

The present invention is particularly suitable for plasma jet generation applied in the field of plasma processing, such as surface modification and adhesion improvement of substrates mainly composed of organic substances such as plastics, and removal of organic contaminants on the surface of inorganic substrates such as glass. It relates to an electrode.

Conventionally, there are many cases in which various surface treatments are performed using plasma generated in a pressure atmosphere near atmospheric pressure.

As such plasma, discharge is generated inside the electrode nozzle, and it is ejected as a plasma jet by a gas flow from an ejection hole provided in a part of the nozzle, and only a specific part of the substrate to be treated is subjected to plasma treatment, for example, Techniques for cleaning organic, inorganic base materials, surface modification, and improving adhesiveness are known.

Such a nozzle for generating a plasma jet has, for example, an electrode disposed on the central axis in the nozzle passage and a counter electrode which is rotatable about the axis, and further allows working gas to flow in the nozzle passage. A plasma nozzle having a spiral system for spirally flowing is exemplified (see Patent Document 1).
JP 2001-68298 A

Moreover, as plasma generated in a pressure atmosphere near atmospheric pressure, a plasma torch by arc discharge has been known for a long time and is used for cutting and welding of metals.

However, the known plasma torch generally uses arc discharge thermoionized plasma, and its temperature reaches several tens of thousands of degrees, so it is not suitable for surface modification of organic and inorganic substrates. Since the electrode that generates plasma is constantly exposed to high temperatures, the consumption is severe and frequent electrode member replacement or water cooling of the electrode is required. In addition, the plasma jet generated in an atmosphere near atmospheric pressure is at a lower temperature than the plasma torch, but when the substrate to be treated is exposed to the plasma jet for a long time, its shape is caused by heat, particularly in the case of an organic substrate. Has the disadvantage of deforming.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plasma jet generating electrode that can generate a low-temperature plasma jet and has a long life.

The electrode for generating a plasma jet according to claim 1 of the present invention has a structure in which a pair of electrodes each having a substantially cylindrical shape are arranged coaxially via an insulator, and a discharge gas is provided between the two electrodes. In the plasma jet generating electrode that discharges the discharge plasma generated by applying an alternating electric field through the tip opening as a plasma jet, the inner electrode of the pair of electrodes has a closed structure at the tip, A gas introduction pipe disposed along the central axis; and a gas outlet hole opened toward the discharge space sandwiched between the inner electrode and the outer electrode on the outer surface of the base portion thereof; and the inner electrode The flow of the discharge gas introduced from the root portion into the gas introduction tube is reversed at the tip portion and flows in the direction of the root portion, and is further dammed at the root portion, and is outside the inner electrode through the gas blowing hole. It is characterized in that it has a structure that can be ejected.

The electrode for plasma jet generation according to claim 2 of the present invention is the electrode for plasma jet generation according to claim 1, wherein the pair of electrodes is composed of an inner electrode and an outer electrode, and the inner electrode is coaxial double It consists of a central tube and an outer tube that form a tube structure, and has a closed structure in which both of them are fused at the tip, and has a structure that blocks the gas flow at the base, and the tip is the meat. The insulator has a hole that connects the center tube and a space sandwiched between the center tube and the outer tube, and the insulator has a cylindrical shape and is integrated with the inner electrode. The flow of the discharge gas introduced into the central tube functioning as a gas introduction tube is coaxially arranged with an interval of the above inversion in the hole at the tip of the inner electrode, and the central tube and the Spouts into the space between the outer tube and the space When flowing toward the root portion of the serial inner electrode, it is characterized in that flows along on the inner wall surface of the outer wall surface and the outer peripheral tube of the central tube.

The electrode for plasma jet generation according to claim 3 of the present invention is the electrode for plasma jet generation according to claim 2, wherein the discharge gas ejected into a space sandwiched between the central tube and the outer peripheral tube is: When flowing in the space toward the root of the inner electrode, a spiral flow is formed that swirls around the center axis of the electrode and flows along the outer wall surface of the central tube or the inner wall surface of the outer peripheral tube. It is characterized by.

A plasma jet generation electrode according to claim 4 of the present invention is the plasma jet generation electrode according to claim 3, wherein the plasma jet generation electrode is ejected from a gas blowout hole formed in an outer surface of a root portion of an outer peripheral tube of the inner electrode. The discharge gas swirls around the center axis of the electrode when flowing toward the tip of the electrode in the plasma discharge space formed between the insulator disposed in contact with the outer electrode and the inner electrode. In addition, a spiral flow that flows along the outer wall surface of the outer peripheral tube of the inner electrode and the inner wall surface of the insulator is formed.

A plasma jet generating electrode according to claim 5 of the present invention is the plasma jet generating electrode according to claim 3 or 4, characterized in that the inner electrode is provided with means for forming the spiral flow. To do.

A plasma jet generating electrode according to claim 6 of the present invention is the plasma jet generating electrode according to claim 4, wherein the means for forming the spiral flow is provided in the inner electrode and the outer electrode. It is characterized by.

A plasma jet generating electrode according to a seventh aspect of the present invention is the plasma jet generating electrode according to any one of the first to sixth aspects, wherein the discharge plasma is generated in a pressure atmosphere near atmospheric pressure. .

An electrode for generating a plasma jet according to an eighth aspect of the present invention is the electrode for generating a plasma jet according to the first to seventh aspects, wherein the inner electrode and the outer electrode are made of metal, and the insulator is a solid dielectric. It is comprised from these.

A plasma jet generation electrode according to claim 9 of the present invention is the plasma jet generation electrode according to any one of claims 1 to 8, wherein the tip of the inner electrode is any one of tungsten, molybdenum, tantalum, copper, brass, and stainless steel. It is composed of a metal selected from the above or an alloy thereof, and has a convex shape.

A plasma jet generation electrode according to claim 10 of the present invention is the plasma jet generation electrode according to any one of claims 1 to 9, wherein the discharge gas is any one of air, nitrogen, oxygen, and argon, or these. It is a mixed gas having a main component.

According to the present invention, since the plasma jet generating electrode itself is cooled by the discharge gas flowing inside, the temperature rise is suppressed, the damage caused at the time of discharge is small, and replacement is unnecessary for a long time, which is economically advantageous. Further, since the discharge gas flowing inside the electrode flows in a spiral flow along the wall surface of the cylindrical body constituting the electrode, the electrode wall surface can be efficiently cooled, and the effect of the invention is enhanced. The

In addition, according to the present invention, since the discharge gas itself also serves as a cooling medium for the electrode, it is not necessary to provide a separate electrode cooling mechanism, and the configuration of the apparatus using the electrode of the present invention is simplified, meaning But it is economically advantageous.

Furthermore, according to the present invention, since a low-temperature plasma jet can be generated, there is an industrially significant advantage particularly for applications in which a plastic substrate that is easily thermally deformed is processed at a low temperature.

The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the appearance of the plasma jet generating electrode of the present invention, and FIG. 2 shows an example of its internal structure. The plasma jet generating electrode 1 has a nozzle shape as a whole, and ejects a plasma jet 30 from a plasma jet ejection hole 12 that is opened at an arbitrary portion of the electrode end. Further, this electrode has a cylindrical inner electrode 2 arranged on the central axis thereof, a cylindrical outer electrode 3 arranged coaxially therewith, and a cylindrical shape arranged in close contact with a part of the outer electrode 3. It comprises a solid dielectric 4 and a power supply unit 15 connected to these electrodes 2 and 3.

The electrodes 2 and 3 are made of a metal material having good workability, corrosion resistance, and conductivity, such as copper, aluminum, brass, and stainless steel. The cylindrical inner electrode 2 has a coaxial double tube structure composed of a center tube 5 and an outer tube 6, and has a convex curved surface shape separable from the center tube 5 and the outer tube 6 at the tip. A metal tip 7 is provided. The convex top portion of the tip 7 is disposed so as to face the plasma jet ejection hole 12. Further, a hole hole 9 through which discharge gas flows is provided inside the tip end portion 7, and both ends of the hole hole 9 are continuous with a gas blowing hole 10 formed by drilling the flat plate portion 7A. 10 is connected to an internal space sandwiched between the central tube 5 and the outer peripheral tube 6 of the inner electrode 2. Further, on the upper side surface of the outer tube 6, a gas blowing hole 11 for blowing discharge gas from the inside of the inner electrode 2 is provided in a space sandwiched between the outer tube 6 of the inner electrode 2 and the cylindrical solid dielectric 4. Yes.

Here, the material of the cylindrical solid dielectric 4 is not particularly limited, but an insulator such as quartz, alumina, or polytetrafluoroethylene can be selected. Since the thickness of the cylindrical solid dielectric 4 is appropriately determined depending on the dimensions of the electrode nozzle and the like, it is not particularly specified but is preferably in the range of 0.5 to 3 mm. If the thickness of the cylindrical solid dielectric 4 is less than 0.5 mm, the dielectric is liable to cause dielectric breakdown. If the thickness exceeds 3 mm, a high voltage is required to generate discharge plasma, and the price of the power source becomes expensive. End up.

A method for generating a plasma jet using the electrode configured as described above will be described below. The electrode for generating a plasma jet of the present invention can be operated in a pressure atmosphere near atmospheric pressure (88.0 to 117.3 kPa (660 to 880 torr)). In that case, between the cylindrical inner electrode 2 and the cylindrical outer electrode 3, an alternating electric field generated by the power supply unit 15, for example, having a frequency of 1 to 100 kHz and a voltage peak value of 5 to 30 kVp is applied. If the frequency of the alternating electric field is less than 1 kHz, the density of the discharge plasma decreases and the surface treatment speed may be reduced. If the frequency is higher than 100 kHz, it is affected by the stray capacitance existing in the wiring and the desired power Impedance matching is necessary to put the plasma into the plasma, which complicates the apparatus. When the voltage peak value is less than 5 kVp, it tends to be difficult to generate discharge plasma, and it is difficult to create a transformer that generates high watts at a high voltage exceeding 30 kVp, which is expensive and large.

In the plasma jet generating electrode of the present invention, first, as shown in FIGS. 2 and 3, a discharge gas is introduced from a discharge gas introduction hole 8 in the upper part of the cylindrical inner electrode 2. Reference numeral 20 denotes a discharge gas flow. The discharge gas passes through the center tube 5 of the cylindrical inner electrode 2 and then circulates through the hole 9 of the tip 7, and the flat plate portion 7 </ b> A of the tip 7 has a predetermined angle with respect to the electrode center axis direction. And the gas is blown out through the gas blowing holes 10 formed obliquely so that a spiral flow is formed in the space between the center tube 5 and the outer tube 6 of the inner electrode 2 and flows.

The discharge gas that has become a spiral flow flows upward along the outer surface of the central tube 5 and the inner surface of the outer tube 6, and then is blown out on the upper side surface of the outer tube 6 of the inner electrode 2. The gas discharge hole 11 is pierced in a tangential direction with respect to the circumference of the inner electrode 2, while being ejected from the hole 11 into an annular discharge space sandwiched between the cylindrical inner electrode 2 and the cylindrical solid dielectric 4. Therefore, also in the discharge space, a spiral flow is formed again and flows in the direction of the lower electrode tip along the outer surface of the cylindrical inner electrode 2 and the inner surface of the cylindrical solid dielectric 4. . (See Figure 2)

Due to the action of the alternating electric field applied between the inner electrode 2 and the outer electrode 3 and the solid dielectric 4, a discharge is generated in an annular space sandwiched between the inner electrode 2 and the solid dielectric 4. With this pre-ionization, a discharge plasma is newly generated between the tip 7 provided at the tip of the inner electrode 2 and the outer electrode 3.

The spiral flow of the discharge gas flows while contacting the inner and outer surfaces of the cylindrical inner electrode 2, the outer electrode 3, and the inner surface of the cylindrical solid dielectric 4. The flow velocity is increased by reaching the portion and being converged by the plasma jet ejection holes 12. As a result, the spiral flow not only stabilizes the discharge plasma generated inside the electrode on the gas flow and ejects it as a plasma jet from the plasma jet orifice 12, but also extends the jet length of the jet. Has the effect of

Here, the distance between the cylindrical inner electrode 2 and the cylindrical solid dielectric 4 can be arbitrarily determined, but is preferably in the range of 0.5 to 3 mm, more preferably in the range of 1 to 2 mm. If it is less than 0.5 mm, gas circulation is hindered, and if it exceeds 3 mm, it becomes difficult to generate preliminary ionization.

Further, the discharge gas used in the present invention can be any one of air, nitrogen, oxygen, and argon, or a mixed gas containing these main components as a main component. Examples of the gas to be mixed with these include carbon tetrafluoride, tetraethoxysilane, and the like, which can be applied to a film forming process of an organic thin film, but the application is not limited thereto.

According to the embodiment of the present invention, the plasma jet generating electrode 1 can use the structure shown in FIGS. 2, 3 and 4 in order to efficiently cool the inner electrode 2 with a discharge gas. . The cylindrical inner electrode 2 is provided at the distal end portion 7 by guiding the discharge gas supplied to the central tube 5 to the distal end portion 7 and reversing the gas flow direction in the process of circulating the hole 9 inside the distal end portion 7. It has a structure in which the gas is blown out from the gas blowing hole 10 and directed toward the base of the electrode. Further, the cylindrical inner electrode 2 has a lid 6A that blocks the gas flow at the base portion, and has a gas that opens toward the space sandwiched between the inner electrode 2 and the outer electrode 3 on the outer surface of the base portion. And a blowout hole 11. For this reason, the flow path of the discharge gas flowing inside the electrode 1 is inverted twice in the vertical direction, and the probability that the gas flow contacts the wall surface is higher than that in the case of one-way passage, and the cooling of the electrode is made efficient. Can be done automatically. Since cooling is performed inside the electrode in this way, the temperature rise is suppressed even if the discharge plasma is generated for a long time. In general, when the temperature of the discharge electrode rises, it is known that the plasma is heated and easily shifts to arc discharge, and further, it causes a vicious cycle in which the electrode is heated mainly by ion bombardment in the plasma whose temperature has risen. The generated plasma jet itself is maintained at a low temperature without increasing the temperature by cooling with the discharge gas. As a result, thermal damage during surface treatment of the substrate to be treated, particularly a low melting point substrate such as plastic, can be greatly reduced.

In addition, according to the embodiment of the present invention, although not shown in detail in FIG. 2, the gas blowing hole 10 at the distal end portion 7 of the inner electrode 2 is predetermined in the flat plate portion 7A of the distal end portion 7 with respect to the electrode central axis direction. Since it is perforated at an angle, the streamlines of the discharge gas ejected from the gas ejection hole 10 are drawn while spiraling in the space between the central tube 5 and the outer peripheral tube 6 of the inner electrode 2. It flows in the direction of the root. Therefore, when the discharge gas forms a spiral flow, it flows along the electrode wall surface for a longer time than when a spiral flow such as a linear flow is not formed, so there is a probability that the gas flow contacts the wall surface. As a result, the electrode can be cooled more efficiently.

Furthermore, according to the embodiment of the present invention, the tip 7 of the inner electrode 2 is selected from a metal selected from tungsten, molybdenum, tantalum, copper, brass, and stainless steel, or an alloy thereof. If the shape is a convex curved surface, the effect of the present invention can be further improved. That is, by selecting a metal having a high melting point and good conductivity, melting and wear due to an increase in the temperature of the electrode are suppressed, and further, a shape having a convex curved surface is frequently generated in an electrode shape having an edge portion. It becomes possible to suppress sputtering of the electrode due to such charge concentration. As the convex curved surface, various convex curved surfaces including a spherical surface can be selected.

FIG. 5 shows an electrode structure of another embodiment of the inner electrode 2. The discharge gas introduced from the gas introduction hole 8 is ejected from the gas blowing hole 10 provided in the central tube 5 into the gap between the central tube 5 and the outer peripheral tube 6, and the wall surfaces of both of them are formed in the gap between the central tube 5 and the outer peripheral tube 6. The gas flows from the gas blowing hole 11 to the inner space of the outer electrode 3 through the metal spiral flow path 13 provided in close contact with the gas. The metal spiral flow path 13 is composed of a rectangular copper wire having good heat dissipation and conductivity, and contributes to further strengthening the air cooling of the electrode. Further, since the discharge gas passes through the spiral flow path 13 and a spiral gas flow is formed and the discharge gas is ejected from the gas blowout hole 11 as it is, air cooling inside the outer electrode 3 can be performed efficiently. .

There are various methods other than the above as means for forming the spiral gas flow. For example, as shown in FIG. 6, in the sectional view of the plasma jet generating electrode 1 as viewed from above, the inner periphery of the cylinder constituting the outer electrode 3 It is possible to form a spiral gas flow in the gap between the inner electrode 2 and the outer electrode 3 by introducing gas from the gas introduction hole 8 provided in the tangential direction. Although not clearly shown in FIGS. 2 and 3, as described above as the embodiment of the invention related to FIGS. 2 and 3, the circumferential tangent of the outer peripheral tube 6 at the upper portion of the outer peripheral tube 6 of the inner electrode 2. Since the gas blowout holes 11 are provided in the direction, the discharge gas is blown out from the gas blowout holes 11 so that the gap between the inner electrode 2 and the cylindrical solid dielectric 4 or between the inner electrode 2 and the outer electrode 3 is increased. A spiral gas flow can be formed in the space between them. On the other hand, as shown in FIG. 8, when gas is introduced from a gas introduction hole 8 provided in the wall surface of the outer electrode 3 so as to be orthogonal to the electrode center axis and is flowed so as to be dispersed in two directions, the inner electrode 2 It tends to be turbulent in the gap between the outer electrode 3 and the inner space of the outer electrode 3, making it difficult to control the gas flow and the shape of the ejected plasma jet.

There are various methods for confirming the formation of the spiral gas flow inside the electrode. For example, a transparent body such as a quartz tube or an acrylic pipe processed into the same dimensions as the desired electrode is used, and a powder or the like is relatively used as a supply gas. The flow of gas can be visualized by mixing a colored substance with a light specific gravity.

Examples of the present invention will be described below, but the present invention is not limited thereto.

In Example 1, plasma jet generating electrodes each having the structure shown in FIGS. 1 to 4 were used. As a substrate to be treated, a polyethylene terephthalate substrate (50 × 50 mm, thickness 1 mm) was selected, and this was subjected to surface treatment with a plasma jet generated by the electrodes.

Stainless steel pipes having an outer diameter of 10 mm, a wall thickness of 1 mm, an outer diameter of 25 mm, and a wall thickness of 1 mm are coaxially arranged as a central tube 5 and an outer tube 6, respectively, and a metal tip having a schematic shape shown in FIG. The portion 7 and the metal upper lid 6A are melt-processed and integrated to form a cylindrical inner electrode 2, and the cylindrical solid dielectric 4 is a bottle obtained by processing a quartz tube having an inner diameter of 27 mm and a wall thickness of 1.5 mm. The outer electrode 3 is obtained by processing one end of an aluminum pipe having an inner diameter of 30 mm and a wall thickness of 1.5 mm, and the inner electrode 2, the outer electrode 3, and the cylindrical solid dielectric 4. Are arranged coaxially, the cylindrical solid dielectric 4 is in close contact with the inner surface of the outer electrode 3, and the gap between the cylindrical inner electrode 2 and the cylindrical solid dielectric 4 is 1 mm, A jet generating electrode 1 was constructed. The tip 7 of the inner electrode 2 has a hemispherical shape with a radius of 10 mm, and is configured using a copper-tungsten alloy. In this example, the inner hole 9 is formed in the tip 7 so as to follow the hemispherical surface. The outer electrode 3 was provided with a plasma jet ejection hole 12 having a diameter of 3 mm at the lower center of the shaft.

Here, dry air at atmospheric pressure was supplied as a discharge gas at a flow rate of 20 L / min, and a sinusoidal voltage of 20 kHz and 15 kVp was applied as an alternating electric field at a power output of 300 W to generate an air plasma jet. The distance from the lower part of the electrode to the substrate to be treated was set to 5 mm, the electrode side was kept stationary, and the substrate to be treated was scanned at a speed of 5 m / min on an XY stage to perform surface modification treatment. The treatment effect was achieved by dropping pure water onto the substrate to be treated and measuring its contact angle.

The contact angle after the plasma treatment changed from 89 degrees in the untreated case to 7 degrees, the surface energy value of the substrate to be treated increased, and it was found that wettability was improved by surface modification. It was confirmed that the electrode of the invention functions effectively. At this time, the treated substrate surface was visually observed, but no melting or deformation was confirmed.

In Example 2, a plasma jet generating electrode having the same configuration as in Example 1 is used, dry nitrogen at atmospheric pressure is supplied at a flow rate of 30 L / min, and an alternating electric field of 10 kHz, a sine wave voltage of 15 kVp is applied at a power output of 500 W. Then, continuous operation was performed for 350 hours in a state where a plasma jet was generated, but no wear or deformation due to heat was observed at the tip 7 of the inner electrode 2 made of copper-tungsten alloy.

A plasma jet is generated under the conditions of a flow rate of dry nitrogen at atmospheric pressure of 25 L / min, a sine wave frequency of 25 kHz, a sine wave voltage of 20 kVp, and a power output of 250 W, using an electrode for plasma jet generation having the same configuration as in Examples 1 and 2. Using a polyimide film with a thickness of 50 × 50 mm and a thickness of 10 μm for the substrate to be processed, the distance from the lower part of the electrode to the substrate to be processed is 3 mm, and the substrate to be processed is stationary for 10 seconds. However, thermal deformation of the polyimide film substrate was not observed.

On the other hand, in the plasma jet generating electrode, as shown in FIGS. 7 and 8, gas is introduced from the direction orthogonal to the electrode central axis, and there is no formation of a spiral gas flow, so that the air inside the cylindrical inner electrode is cooled. Otherwise, a plasma jet generating electrode having the same structure as in Example 2 was used, and the operation was performed for 350 hours under the same gas introduction and plasma generation conditions as in Example 2. As a result, wear of about 0.5 mm was observed at a part of the tip of the inner electrode made of copper-tungsten alloy. (Comparative Example 1)

Using the plasma jet generating electrode of Comparative Example 1, the polyimide film was plasma-treated under the same conditions as in Example 3. However, the substrate was thermally deformed in a few seconds and was subjected to plasma irradiation in 10 seconds. The part was completely melted. (Comparative Example 2)

The electrode for generating a plasma jet according to the present invention can be used in the field of plasma processing such as surface modification and adhesion improvement of a base material mainly composed of an organic substance such as plastic, and surface cleaning of an inorganic base material such as glass.

It is a figure for demonstrating the structure of the electrode for plasma jet generation of the Example of this invention. It is a perspective sectional view showing the internal structure of the electrode for plasma jet generation of the example of the present invention. FIG. 3 is a perspective sectional perspective view showing a structure of an inner electrode of the electrode shown in FIG. 2. It is a perspective view which shows the structure of the front-end | tip part of the inner side electrode shown in FIG. It is a perspective perspective view which shows the structure of the inner side electrode of the electrode for plasma jet production | generation of the other Example of this invention. It is sectional drawing which shows an example of the gas introduction method to the clearance gap between the inner side electrode and outer side electrode which concerns on an Example. It is a perspective section perspective view for demonstrating the structure of the electrode for plasma jet generation which concerns on a comparative example. It is sectional drawing which shows the gas introduction method to the gap | interval of the inner side electrode and outer side electrode which concern on a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode for plasma jet generation 2 Inner electrode 3 Outer electrode cylindrical solid dielectric 4 Solid dielectric 5 Center tube 6 Outer tube 6A Upper cover body 7 End part 7A Flat plate part 8 Gas introduction hole 8A Gas introduction hole 9 Hole hole 10 Gas blowout Hole 11 Gas blowout hole 12 Plasma jet blowout hole 13 Spiral flow path 15 Power supply unit 20 Discharge gas flow 30 Plasma jet

Claims (10)

A pair of electrodes each having a substantially cylindrical shape are arranged coaxially via an insulator, and a discharge plasma generated by applying an alternating electric field by flowing a discharge gas between the two electrodes. In the plasma jet generating electrode ejected as a plasma jet from the tip opening, the inner electrode of the pair of electrodes has a closed structure at the tip, and a gas introduction pipe arranged along the central axis, and its root A gas blowing hole that opens toward the discharge space sandwiched between the inner electrode and the outer electrode on the outer surface of the portion, and is introduced into the gas introduction pipe from the root portion into the inner electrode. The structure is characterized in that the flow of the discharge gas is reversed at the tip portion and flows in the direction of the root portion, and is blocked by the root portion and can be ejected from the gas blowing hole to the outside of the inner electrode. The Zumajetto generation electrode. The pair of electrodes is composed of an inner electrode and an outer electrode, and the inner electrode is composed of a central tube and an outer tube having a coaxial double tube structure, and has a closed structure in which both of them are fused at the tip portion. It has a structure that blocks the gas flow at the base part, and the tip part is thick, and the center pipe and the space between the central pipe and the outer pipe are connected inside A flow of a discharge gas introduced into the central tube functioning as a gas introduction tube, the insulator being substantially cylindrical in shape and coaxially arranged at an integral interval with the inner electrode; Is reversed in the hole at the tip of the inner electrode and sprayed into a space sandwiched between the central tube and the outer peripheral tube and flows in the space toward the root of the inner electrode. And flow along the outer wall surface of the central tube and the inner wall surface of the outer peripheral tube. Plasma jet generation electrode according to claim 1, wherein. When the discharge gas ejected into a space sandwiched between the central tube and the outer peripheral tube flows in the space toward the root portion of the inner electrode, the discharge gas swirls around the central axis of the electrode and The electrode for generating a plasma jet according to claim 2, wherein a spiral flow that flows along an outer wall surface or an inner wall surface of the outer peripheral tube is formed. The discharge gas ejected from a gas blowout hole formed on the outer surface of the root portion of the outer peripheral tube of the inner electrode is formed between the insulator disposed in contact with the outer electrode and the inner electrode. When flowing in the plasma discharge space toward the tip of the electrode, a spiral flow swirling around the electrode central axis and flowing along the outer wall surface of the outer peripheral tube of the inner electrode and the inner wall surface of the insulator is formed. The plasma jet generating electrode according to claim 3, wherein the electrode is a plasma jet generating electrode. The electrode for generating a plasma jet according to claim 3 or 4, wherein means for forming the spiral flow is provided in the inner electrode. The electrode for generating a plasma jet according to claim 4, wherein means for forming the spiral flow is provided in the inner electrode and the outer electrode. 7. The plasma jet generation electrode according to claim 1, wherein the discharge plasma is generated in an atmosphere near atmospheric pressure. 8. The plasma jet generating electrode according to claim 1, wherein the inner electrode and the outer electrode are made of metal, and the insulator is made of a solid dielectric. The tip of the inner electrode is made of a metal selected from any one of tungsten, molybdenum, tantalum, copper, brass, and stainless steel, or an alloy thereof, and has a convex curved surface shape. The plasma jet generating electrode according to claim 1. 10. The plasma jet generating electrode according to claim 1, wherein the discharge gas is any one of air, nitrogen, oxygen, and argon, or a mixed gas containing these as a main component.

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