Patent Publication Number: US-2023156899-A1

Title: Irradiator and plasma apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an irradiator and a plasma apparatus. 
     BACKGROUND ART 
     A technique of using a plasma for wound cure, etc. has been proposed (see JP2017-508485A). A tool for curing wound disclosed in JP2017-508485A directs a plasma flow to a wound part to be cured to cure the wound with the plasma. The tool for curing wound of JP2017-508485A comprises a housing, and a piezoelectric transformer accommodated in the housing. In the tool for curing wound of JP2017-508485A, the piezoelectric transformer uses a high voltage generated a high voltage end to generate a plasma. 
     DISCLOSURE OF THE INVENTION 
     When a plasma is generated at the high voltage end of the piezoelectric transformer, a distal end portion of the tool, which generates a plasma for irradiation, has a large thickness in accordance with a thickness of the piezoelectric transformer. This makes it difficult to apply the tool to an application in which the distal end portion is inserted into a narrow space, e.g., dental treatment where the distal end portion of the tool is inserted into a mouth of a person or animal. 
     The object of the present invention is to provide an irradiator and a plasma apparatus capable of effectively solving such a problem. 
     An irradiator according to the present invention comprises: a piezoelectric transformer accommodated in a housing; a first electrode connected to the piezoelectric transformer, to which a voltage is applied from the piezoelectric transformer; and an irradiation opening that ejects at least one of a plasma generated by the first electrode and an active gas generated by the plasma; wherein at least a part of the first electrode is located between the piezoelectric transformer and the irradiation opening. 
     The irradiator according to the present invention may comprise a second electrode opposed to at least a part of the first electrode. 
     In the irradiator according to the present invention, the second electrode may surround the first electrode from a circumference about an axis of the first electrode. 
     In the irradiator according to the present invention, the first electrode may have a first end portion positioned oppositely to an end portion connected to the piezoelectric transformer, in a direction in which the axis of the first electrode extends; and the second electrode may surround the first end portion from the circumference about the axis of the first electrode. 
     In the irradiator according to the present invention, the second electrode may have a dimension larger than a dimension of the first electrode, in a direction in which an axis of the first electrode extends. 
     In the irradiator according to the present invention, the second electrode may have a dimension smaller than a dimension of the piezoelectric transformer, in a radial direction perpendicular to an axis of the first electrode. 
     In the irradiator according to the present invention, the first electrode may have a dimension smaller than a dimension of the piezoelectric transformer, in a radial direction perpendicular to an axis of the first electrode. 
     A plasma apparatus according to the present invention comprises: the aforementioned irradiator; a power source that applies a voltage to the piezoelectric transformer; and a voltage supply line connecting the piezoelectric transformer and the power source. 
     The irradiator and the plasma apparatus of the present invention can make smaller a thickness of the distal end portion of the irradiator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view showing a plasma apparatus according to one embodiment of the present invention. 
         FIG.  2    is a block diagram showing a schematic structure of the plasma apparatus according to one embodiment of the present invention. 
         FIG.  3    is a sectional view of an irradiator according to one embodiment of the present invention. 
         FIG.  4    is a perspective view of the irradiator of  FIG.  3   . 
         FIG.  5    is a sectional view of the irradiator of  FIG.  3   , taken along a V-V line. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention will be described herebelow with reference to the drawings. In the drawings attached to the specification, a scale dimension, an aspect ratio and so on are changed and exaggerated from the actual ones, for the convenience of easiness in illustration and understanding. 
     Further, terms specifying shapes, geometric conditions and their degrees, e.g., “parallel”, “perpendicular”, “same”, etc., and values of a length and an angle are not limited to their strict definitions, but construed to include a range capable of exerting a similar function, unless otherwise specified. 
     A plasma apparatus of the present invention is a plasma jet irradiation apparatus or an active gas irradiation apparatus. Both the plasma jet irradiation apparatus and the active gas irradiation apparatus generate a plasma. The plasma jet irradiation apparatus directly applies the generated plasma and an active species directly to an irradiation target. The active species is generated by reaction between a gas in the plasma or a gas around the plasma and the plasma. The active species is, for example, active oxygen species or active nitrogen species. The active oxygen species is, for example, hydroxyl radical, singlet oxygen, ozone, hydrogen peroxide, superoxide anion radical, etc. The active nitrogen species is, for example, nitrogen monoxide, nitrogen dioxide, peroxynitrite, dinitrogen trioxide, etc. The active gas irradiation apparatus applies an active gas containing an active species to an irradiation target. The active species is generated by reaction between a gas in the plasma or a gas around the plasma and the plasma. 
     An embodiment of the irradiator and the plasma apparatus is described herebelow. The plasma apparatus in this embodiment is an active gas irradiation apparatus, for example. As shown in  FIGS.  1  and  2   , the active gas irradiation apparatus  100  in this embodiment comprises an irradiator  10 , a supply unit  20 , a gas pipeline  30 , a voltage supply line  40 , a supply source  70 , a notification unit  80 , and a control unit  90  (operation unit). 
     The irradiator  10  ejects an active gas generated in the irradiator  10 . The irradiator  10  is operated by a doctor or the like, and has a shape, a size, and a weight that are easy to operate by human hands. The irradiator  10  is connected to the supply unit  20  through the gas pipeline  30 , a ground wire  31 , and the voltage supply line  40 . In the example shown in  FIG.  1   , the irradiator  10  comprises an outer cylinder member  8 , and a nozzle  9  forming a distal end of the irradiator  10 . The nozzle  9  is attached to a distal end of a second electrode  5  described later. The nozzle  9  has therein a flow channel through which an active gas flows. The active-gas flow channel in the nozzle  9  is in communication with a flow channel for a plasma generation gas inside the irradiator  10 . When the irradiator  10  has the nozzle  9 , the active gas passes through between a first electrode  4  described later and the second electrode  5 , and the flow channel inside the nozzle  9  to be ejected from a nozzle irradiation opening  9   a  positioned at a distal end of the nozzle  9 . 
     The gas pipeline  30  and the voltage supply line  40  are accommodated in a single cable  32 . In particular, the voltage supply line  40  connects a piezoelectric transformer  2  described later and an external power source. The power source applies voltage to the piezoelectric transformer  2 . The supply unit  20  supplies the irradiator  10  with power and a plasma generation gas. The supply unit  20  accommodates the supply source  70 . The supply source  70  accommodates the plasma generation gas. The supply unit  20  is powered by a power source such as a 100-V household power supply. In this case, since the voltage supply line  40  connects the piezoelectric transformer  2  and the supply unit  20 , the voltage supply line  40  connects the piezoelectric transformer  2  and the power source through the supply unit  20 . Alternatively, the supply unit  20  may incorporate a rechargeable battery as a power source. In this case, the voltage supply line  40  connects the piezoelectric transformer  2  and the power source inside the supply unit  20 . 
       FIG.  3    is a view showing the irradiator  10 , which is a sectional view (longitudinal sectional view) of a plane along a direction in which the irradiator  10  extends,  FIG.  4    is a perspective view showing the irradiator of  FIG.  3   .  FIG.  5    is a sectional view showing a section of the irradiator  10  of  FIG.  3    taken along a line V-V. In  FIGS.  3  to  5   , illustration of the outer cylinder member  8  and the nozzle  9  is omitted. As shown in  FIG.  3   , the irradiator  10  comprises the first electrode  4 , and the second electrode  5  opposed at least a part of the first electrode  4 . The first electrode  4  has an axis O 1 . The axis O 1  of the first electrode  4  is, for example, a virtual line segment which extends in a direction d 1  along which the first electrode  4  extends, and is located within a range where the first electrode  4  is located in the direction d 1 . Herebelow, the direction d 1  along which the axis O 1  extends is also referred to as axial direction d 1 . 
     In the example shown in  FIG.  3   , the irradiator  10  further comprises a housing  1 , the piezoelectric transformer  2 , a tubular dielectric  3 , O-rings  6   a,    6   b,  a piezoelectric transformer casing  7 , and buffers  7   b,    7   c.    
     The piezoelectric transformer  2  boosts a voltage applied thereto. A plasma can be generated by boosting a voltage applied to the piezoelectric transformer  2  from the power source using the piezoelectric transformer  2  to obtain a high voltage, and using the high voltage. In the example shown in  FIG.  3   , the piezoelectric transformer  2  has an input area  2   a  that converts the applied voltage to mechanical vibrations, and an output area  2   b  that convers the vibrations of the input area  2   a  to a voltage. As shown in  FIG.  3   , the voltage supply line  40  is connected to the input area  2   a.  In the example shown in  FIG.  3   , the voltage supply line  40  extends through a hole  7   a   1  provided in the piezoelectric transformer casing  7  accommodating the piezoelectric transformer  2 . The first electrode  4  described later is connected to the output area  2   b.  A voltage applied from the external power source through the voltage supply line  40  is converted by the input area  2   a  to mechanical vibrations. The vibrations of the input area  2   a  are converted by the output area  2   a  to a voltage, which is then applied to the first electrode  4 . Since the voltage is once converted to the mechanical vibrations and the mechanical vibrations are again converted to the voltage by the piezoelectric transformer  2 , the voltage applied from the power source can be boosted, and and the boosted voltage can then be applied to the first electrode  4 . 
     In this embodiment, the piezoelectric transformer  2  is accommodated in the housing  1  described later. In the example shown in  FIG.  3   , the piezoelectric transformer  2  is accommodated in the piezoelectric transformer casing  7   a,  and the piezoelectric transformer casing  7   a  is accommodated in the housing  1 . 
     The piezoelectric transformer  2  has a parallelepiped shape extending in the axial direction d 1 , for example. A dimension w 1  of the piezoelectric transformer  2  in a direction d 2  (referred to also as radial direction d 2  herebelow) perpendicular to the axis O 1  is between 3 cm or more and 20 cm or less, for example. 
     In the example shown in  FIG.  3   , the first buffer  7   b  is provided between the piezoelectric transformer  2  and the piezoelectric transformer casing  7   a.  The first buffer  7   b  allows mechanical vibrations of the piezoelectric transformer  2 , while defining a positional relationship between the piezoelectric transformer  2  and the piezoelectric transformer casing  7   a.  A material of the first buffer  7   b  is not specifically limited, as long as it does not significantly dampen the mechanical vibrations of the piezoelectric transformer  2 . The material of the first buffer  7   b  is an elastically deformable material such as rubber. In addition, in the example shown in  FIG.  3   , the second buffer  7   c  is provided between the piezoelectric transformer casing  7   a  and the housing  1 . A material of the second buffer  7   c  is similar to the material of the first buffer  7   b.  Although not shown, the irradiator  10  may be free of the second buffer  7   c.    
     The piezoelectric transformer  2  can have a size smaller than another transformer such as a winding trans. Thus, the use of the piezoelectric transformer  2  as a transformer makes it possible that the transformer is accommodated in the housing  1  grasped by a user so that the transformer constitutes a part of the irradiator  10 , and at the same time makes it possible that irradiator  10  has a small size. 
     The first electrode  4  is an electrode that is connected to the piezoelectric transformer  2 , to which a voltage for generating a plasma is applied from the piezoelectric transformer  2 . When a voltage is applied, the first electrode  4  generates a plasma. At least a part of the first electrode  4  is located between the piezoelectric transformer  2  and an irradiation opening  5   a  described later of the irradiator  10 . In the example shown in  FIG.  3   , the electrode  4  is entirely located between the piezoelectric transformer  2  and the irradiation opening  5   a  of the irradiator  10 . Thus, when a voltage is applied to the first electrode  4 , a plasma is generated between the piezoelectric transformer  2  and the irradiation opening  5   a.  The first electrode  4  according to this embodiment has a columnar shape extending in the axial direction d 1 . The first electrode  4  has a first end portion  4   a  and a second end portion  4   b  positioned at both ends in the axial direction d 1 . In the example shown in  FIG.  3   , the irradiator  10  further comprises a conductive wire  50  connected to the output area  2   b  of the piezoelectric transformer  2  and the second end portion  4   b  of the first electrode  4 . The first electrode is connected to the output area  2   b  of the piezoelectric transformer  2  through the conductive wire  50 . In the example shown in  FIG.  3   , the conductive wire  50  extends through a hole  7   a   2  provided in the piezoelectric transformer casing  7   a.    
     A material of the first electrode  4  is not specifically limited as long as it is an electrically conductive material, and a metal used for an electrode of a known plasma apparatus can be used. The material of the first electrode  4  may be, for example, a metal such as stainless steel, copper, tungsten, or carbon, etc. A material of the conductive wire  50  is not specifically limited, as long as it is an electrically conductive and is sufficiently soft so as not to suppress transmission of mechanical vibrations of the piezoelectric transformer  2  to the first electrode  4 . 
     A voltage applied from the piezoelectric transformer  2  to the first electrode  4  is not specifically limited, as long as it enables generation of a plasma between the first electrode  4  and the second electrode  5 . When a plasma is generated by using a gas containing nitrogen as a main component described later, a voltage applied to the first electrode  4  is, for example, between 0.5 kVpp or more and 20 kVpp or less. The voltage applied to the first electrode  4  is more preferably between 2 kVpp or more and 18 kVpp or less, and furthermore preferably between 5 kVpp or more and 15 kVpp or less. Note that “pp” in “kVpp” is an abbreviation for “peak to peak”. 
     The second electrode  5  is an electrode that is opposed to at least a part of the first electrode  4 . In the example shown in  FIGS.  3  and  5   , the second electrode  5  is opposed to a part of the first electrode  4 . As an example, the second electrode  5  surrounds the first electrode  4  from a circumference about the axis line O 1 . In the example shown in  FIG.  3   , from among the first end portion  4   a  and the second end portion  4   b  of the first electrode  4 , the second electrode  5  surrounds the first end portion  4   a  which is positioned oppositely to the end portion  4   b  in the axial direction d 1 , the end portion  4   b  being connected to the piezoelectric transformer  2 . In the example shown in  FIGS.  3  and  5   , the second electrode  5  surrounds a part of the first electrode  4  including the first end portion  4   a  from a circumference about the axis O 1 . In this embodiment, the second electrode  5  is a substantially cylindrical electrode that surrounds a part of the circumference of the first electrode  4 . In this embodiment, the second electrode  5  is electrically grounded. Although not shown, the second electrode  5  is connected to a grounding wire so as to be electrically grounded. 
     Since the irradiator  10  comprises the grounded second electrode  5  as well as the first electrode  4  to which a voltage is applied, an electric field for generating a plasma can be more reinforced when a plasma is generated by the first electrode  4 . By supplying a plasma generation gas to a space between the first electrode and the second electrode  5  and by applying a voltage to the first electrode  4  opposed to the second electrode  5 , electricity is discharged to a space between the first electrode  4  and the second electrode  5  so that the plasma generation gas is ionized to generate a plasma. In this case, it can be said that the first electrode  4  and the second electrode  5  generate a plasma. The plasma is generated between the first electrode  4  and the second electrode  5  opposed to each other. 
     Since the grounded second electrode  5  is opposed to at least a part of the first electrode  4 , in particular, the second electrode  5  surrounds the first electrode  4  from a circumference about the axis O 1 , an electric field generated by the first electrode  4  can be reduced by the second electrode  5 . Thus, electric shock to a user grasping the irradiator  10  can be suppressed. From the viewpoint of suppressing electric shock to a user, a dimension w 3  of the second electrode  5  in the axial direction d 1  shown in  FIG.  3    is preferably larger than a dimension w 2  of the first electrode  4  in the axial direction d 1 . Since a large area of the first electrode  4  is covered with the second electrode  5 , the electric shock to a user can be more effectively suppressed. When the electric shock to a user is sufficiently suppressed by the second electrode  5 , it is not necessary for the irradiator  10  to have another member having a protective function for suppressing the electric shock to a user, such as the outer cylinder member  8 , the nozzle  9 , etc. In this case, since another member having a protective function can be omitted, a thickness of the distal end portion positioned on the distal end side of the irradiator  10  can be made thinner. 
     A material of the second electrode  5  is not specifically limited as long as it is an electrically conductive material, and a metal used for an electrode of a known plasma apparatus can be used. The material of the second electrode  5  may be, for example, a metal such as stainless steel, copper, tungsten, or carbon, etc. 
     The irradiator  10  further comprises the irradiation opening  5   a  that ejects at least one of a generated plasma and an active gas generated by the plasma. In  FIG.  3   , the irradiation opening  5   a  is provided on an end portion of the second electrode  5  on the distal end side (left side in  FIG.  3   ) of the irradiator  10 . The irradiation opening  5   a  communicates an inner hollow  3   a  of the tubular dielectric  3  described later with the outside of the irradiator  10 . 
     The tubular dielectric  3  is a member having the inner hollow  3   a.  In the example shown in  FIGS.  3  to  5   , the tubular dielectric is a cylindrical member extending in the axial direction d 1 . As shown in  FIGS.  3  and  5   , the first electrode  4  is located in the inner hollow  3   a  of the tubular dielectric  3 . 
     In the example shown in  FIGS.  3  and  5   , the first electrode  4  is located to be apart from an inner surface of the tubular dielectric  3 . The second electrode  5  is located to be in contact with an outer surface of the tubular dielectric  3 . 
     A dielectric material used for a known plasma apparatus can be used as a material of the tubular dielectric  3 . The material of the dielectric material  3  is, for example, glass, ceramic, synthetic resin, etc. The lower the dielectric constant of the tubular dielectric  3 , the better. 
     An internal diameter R of the tubular dielectric  3  can be suitably determined in consideration of a dimension w 4  of the first electrode  4  in the radial direction d 2 . The internal diameter R is determined such that a distance s described later is within a desired range. 
     In a case where the first electrode  4  and the tubular dielectric  3  are spaced apart from each other, the distance s between the outer surface of the first electrode  4  and the inner surface of the tubular dielectric  3  is preferably between 0.05 mm and 5 mm, more preferably between 0.1 mm and 1 mm. When the distance s is equal to or more than the above lower limit value, it is easy for a plasma generation gas of a desired volume to flow therethrough, when the inner hollow  3   a  of the tubular dielectric  3  is used as a flow channel of the plasma generation gas as described later. When the distance s is equal to or less than the above upper limit value, a plasma can be more efficiently generated so that a temperature of an active gas can be lowered. 
     The housing  1  is a member grasped by a user and accommodating the piezoelectric transformer  2 . In the example shown in  FIG.  3   , the housing  1  accommodates the piezoelectric transformer casing  7   a  so as to accommodate the piezoelectric transformer  2 . In the example shown in  FIGS.  3  to  5   , the housing  1  is a substantially cylindrical member extending in the axial direction d 1 . As an example, the housing  1  has a first portion  1   a  accommodating the piezoelectric transformer  2 , and a second portion  1   b  accommodating at least a part of the first electrode  4 . In the example shown in  FIGS.  3  to  5   , the first portion  1   a  and the second potion  1   b  both have a substantially cylindrical shape extending in the axial direction d 1 . Although not shown, the first portion  1   a  and the second portion  1   b  may have a polygonal cylindrical shape, such as a quadrangular cylindrical shape, a hexagonal cylindrical shape, an octagonal cylindrical shape, etc. 
     In the example shown in  FIG.  3   , the first portion  1   a  has inside thereof an inclination surface  1   e  that is inclined with respect to the radial direction d 2 . The piezoelectric transformer casing  7   a  has a casing inclination surface  7   a   3  that is inclined with respect to the radial direction d 2  to be in contact with the inclination surface  1   e.  The piezoelectric transformer casing  7   a  is inserted into the first portion is of the housing  1  from the side of the first portion  1   a  (left side in  FIG.  3   ) such that the casing inclination surface  7   a   3  comes into contact with the inclination surface  1   e,  so that the piezoelectric transformer casing  7   a  is fixed to the housing  1 . 
     In the example shown in  FIG.  3   , a part of the second electrode  5  is inserted in the second portion  1   b  of the housing  1  so that the second portion  1   b  and the first electrode  5  are in contact with each other. As an example, the housing  1  and the second electrode  5  are fixed to each other by a fixing means, not shown. For example, the housing  1  and the second electrode  5  have screw holes, not shown, and the second electrode  5  is screwed to the housing  1 . 
     In addition, a part of the tubular dielectric  3  is inserted in the second portion  1   b  of the housing  1  so that the second portion  1   b  and the tubular dielectric  3  are in contact with each other. In the example shown in  FIG.  3   , the second electrode  5  is in contact with the tubular dielectric  3  through the O-ring  6   a  from one side along the axis O 1  to restrict movement of the tubular dielectric  3  to the one side along the axis O 1  of the tubular dielectric  3 . In addition, the housing  1  is in contact with the tubular dielectric  3  through the O-ring  6   b  from the other side along the axis O 1  to restrict movement of the tubular dielectric  3  to the other side long the axis O 1 . The O-ring  6   a,    6   b  is a member made of a resilient resin, and has an internal diameter in tight contact with an outer circumferential surface of the tubular dielectric  3 . Thus, the tubular dielectric  3  is held with its movement along the axial direction d 1  being restricted. 
     The housing  1  may have a part in contact with the first electrode  4 , so that t movement of the first electrode  4  may be restricted by the housing  1  in contact with the first electrode  4 . In addition, movement of the first electrode  4  may be restricted by the piezoelectric transformer casing  7   a  in contact with the first electrode  4 . In the example shown in  FIG.  3   , the piezoelectric transformer casing  7   a  is in contact with the second end portion  4   b  of the first electrode  4  to restrict movement of the first electrode  4  along the axial direction d 1 . The first electrode  4  has a larger diameter portion  4   c  near the first end portion  4   b,  the larger diameter portion  4   c  having a largest outward projecting length in the radial direction d 2 . The housing  1  is in contact with the larger diameter portion  4   c  to restrict movement of the first electrode  4  along the radial direction d 2 . 
     A material of the housing  1  is not specifically limited, but an insulating material is preferred. The insulating material is, for example, a thermoplastic resin, a thermosetting resin, etc. The thermoplastic resin is, for example, polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene resin (ABS resin), polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethyleneimine (PEI), polyacetal (POM), modified polyphenylene ether (mPPE), etc. The thermosetting resin is, for example, phenol resin, melamine resin, urea resin, epoxy resin, unsaturated polyester resin, silicone resin, etc. In addition, an insulating material made by filling polyethylene terephthalate (PET) as a main component with short glass fibers and/or inorganic fillers may be used. Such a material may be Unilate (registered trademark) manufactured by Unitika, Ltd. PEEK or mPPE is more preferable as a material of the housing  1 , because of their resin properties suitable for the housing  1 . 
     In the example shown in  FIG.  1   , the irradiator  10  comprises the electrically grounded outer cylinder member  8 . For example, the outer cylinder member  8  is an electrically conductive member having a substantially cylindrical shape, and accommodating the first electrode  4  and the second electrode  5  entirely. Due to the outer cylinder member  8  of the irradiator  10 , an electric field generated by the irradiator  10  can be suppressed to effectively prevent electric shock to a user handling the irradiator  10 . Although not shown, the irradiator  10  may be free of the outer cylinder member  8 . 
     In the example shown in  FIG.  1   , the irradiator  10  comprises the nozzle  9 . The nozzle  9  may be an electrically conductive member or a resin member not having electrical conductivity. When the nozzle  9  has electrical conductivity, the nozzle  9  can suppress electric field generated by the irradiator  10  to effectively prevent electric shock to a user handling the irradiator  10 . Although not shown, the irradiator may be free of the nozzle  9 . When the irradiator  10  is free of the nozzle  9 , the irradiator  10  ejects an active gas from the irradiation opening  5   a  of the second electrode  5 . 
     In the irradiator  10 , a plasma generation gas is supplied from the supply unit  20  to a space between the first electrode  4  and the second electrode  5 . In the example shown in  FIGS.  3  and  5   , the first electrode  4  and the tubular dielectric  3  are spaced apart from each other. In this case, the inner hollow  3   a  of the tubular dielectric  3  may be used as a flow channel for the plasma generation gas to supply the plasma generation gas to a space between the first electrode  4  and the second electrode  5 . Although not shown, when the second electrode  5  is spaced apart from the tubular dielectric  3 , a space between the second electrode  5  and the tubular dielectric  3  may be used as a flow channel for the plasma generation gas to supply the plasma generation gas to a space between the first electrode  4  and the second electrode  5 . 
     A method of supplying the plasma generation gas to a space between the first electrode  4  and the second electrode  5  is not specifically limited. Although not shown, a through hole may be provided in the housing  1 . In this case, the plasma generation gas supplied to the irradiator  10  through the gas pipeline  30  is supplied to a space between the first electrode  40  and the second electrode  50  through the through hole of the housing  1 . 
     In the invention according to this embodiment, an effect obtained by the fact that the piezoelectric transformer  2 , which is a transformer that boosts a voltage applied thereto, is accommodated in the housing to constitute a part of the irradiator  10  is described. Suppose that the transformer is located outside the hosing  1 , instead of being accommodated in the housing  1 . In this case, the transformer and the first electrode  4  of the irradiator  10  are connected to each other by a wire, so that a high voltage can be applied to the first electrode  4  by using the transformer. 
     However, in this case, since the transformer is located outside the housing  1 , the transformer and the first electrode  4  have to be connected to each other by a sufficiently long wire. The wire connecting the transformer and the first electrode  4  has to be thick to withstand a high voltage boosted by the transformer. Namely, a sufficiently long and thick wire has to be used. A thick wire extending from the irradiator  10  may disturb an operation of the irradiator  10 , resulting in impairment of operability of the irradiator  10 . 
     When a high voltage is applied to the wire, the wire functions as a capacitor to accumulate therein energy. In this case, in order to apply a voltage to the first electrode  4 , the power source needs to supply excessive power corresponding to the energy accumulated in the wire. When the transformer is located outside the housing  1 , the transformer outside the housing  1  and the first electrode  4  have to be connected to each other by a wire, which elongates the length of the wire to which a high voltage boosted by the transformer is applied. When the wire to which a high voltage is applied is long, a significantly large amount energy is accumulated in the wire, whereby the power source needs to supply a significantly large amount of power. 
     On the other hand, in the invention according to this embodiment, the piezoelectric transformer  2  as a transformer is accommodated in the housing  1  to constitute a part of the irradiator  10 . Thus, the length of the conductive wire  50  connecting to the piezoelectric transformer  2  and the first electrode  4  can be shortened. In addition, a voltage which is a low voltage before boosted by the piezoelectric transformer  2  is applied to the voltage supply line  40 , which is a long wire extending from the irradiator  10  to the outside of the irradiator  10 . Thus, the voltage supply line  40  can be made thinner, which less disturbs an operation of the irradiator  10 , thereby improving operability of the irradiator. In addition, since a high voltage is not applied to the voltage supply line  40 , accumulation of large amount of energy therein can be suppressed. Thus, power to be supplied by the power source can be lessened. 
     In the invention according to this embodiment, since the piezoelectric transformer  2  constitutes a part of the irradiator  10 , a low voltage before boosted by the piezoelectric transformer  2  is applied to a part of the irradiator  10 , the part connecting the piezoelectric transformer  2  and the external power source. Thus, as compared with a case in which the transformer is located outside the irradiator  10 , a ratio of a part inside the irradiator  10 , to which part a high voltage is applied, can be made smaller. Thus, a protective member, which is provided on the irradiator for preventing electric shock to a user, can be omitted. 
     Next, an effect of the first electrode  4  connected to the piezoelectric transformer  2  and the second electrode  5  opposed to the first electrode  4  is described. Suppose that the irradiator  10  does not have the first electrode  4  so that a plasma is generated at an end portion of the piezoelectric transformer  2  adjacent to the output area  2   b.  In this case, the distal end portion of the irradiator  10  positioned on the distal end side has a large thickness in accordance with the thickness of the end portion of the piezoelectric transformer  2  adjacent to the output area  2   b.  In the example shown in  FIG.  3   , the thickness of the distal end portion of the irradiator  10  and the thickness of the end portion of the piezoelectric transformer  2  are a dimension of the distal end portion of the irradiator  10  and a dimension of the end portion of the piezoelectric transformer  2  in the radial direction d 2 . Since the dimension of the piezoelectric transformer  2  has to be determined based on performance required for the piezoelectric transformer  2  as a transformer, it is difficult to make thin the end portion of the piezoelectric transformer  2  so as to make thin the distal end portion of the irradiator  10 . The thick distal end portion of the irradiator  10  makes it difficult to use the irradiator  10  in an application that requires the distal end portion of the irradiator  10  be inserted to a narrow space. 
     In addition, it is required for the irradiator  10  not to damage an irradiation target to be irradiated with an active gas by electric field action of the piezoelectric transformer  2 . In particular, when the irradiation target is a person, animal, etc., the irradiation target must not be electrified. In order to suppress damage caused by the electric field action to the irradiation target, it can be considered that an active gas is applied to the irradiation target, with a sufficient distance between the end portion of the piezoelectric transformer  2  and the irradiation target. However, in this case, since a distance between a plasma generation portion and the irradiation target is long, a ratio of the active gas that is deactivated before reaching the irradiation target increases. Alternatively, in order to suppress damage caused by the electric field action to the irradiation target while reducing a distance between the end portion of the piezoelectric transformer  2  and the irradiation target, it can be considered that a grounded electrode is provided around the end portion of the piezoelectric transformer  2 . However, in this case, the distal end portion of the irradiator  10  becomes thicker because of the grounded electrode. 
     On the other hand, the irradiator according to this embodiment comprises the first electrode  4  which is connected to the piezoelectric transformer  2  and to which a voltage is applied from the piezoelectric transformer  2 . The thickness of the first electrode  4  can be determined irrespective of the dimension of the piezoelectric transformer  2 . Thus, by making thin the first electrode  4  to sufficiently make thin the distal end portion of the irradiator  10 , the irradiator  10  can be used in an application which requires the thin distal end portion of the irradiator  10 , e.g., an application which requires that the distal end portion of the irradiator be inserted to a narrow space. In addition, since the grounded second electrode  5  is opposed to at least a part of the first electrode  4 , damage caused by the electric field action to the irradiation target can be suppressed, and the distal end portion of the irradiator  10  can be made thinner as compared with a case in which a grounded electrode is provided around the end portion of the piezoelectric transformer  2 . Since the irradiator  10  has the sufficiently thin distal end portion, the irradiator  10  can be used as an intraoral treatment tool or a dental treatment tool, for example. When the second electrode  5  surrounds the first end portion  4   a  from a circumference about the axis O 1 , the second electrode  5  can particularly effectively suppress damage caused by the electric field action to the irradiation target. 
     The dimension w 4  of the first electrode  4  in the radial direction d 2  can be suitably determined in consideration of intended use of the active gas irradiation apparatus  100  (namely, a size of the irradiator  10 ). When the active gas irradiation apparatus  100  is an intraoral treatment tool, the dimension w 4  is preferably between 0.5 mm or more and 20 mm or less, more preferably between 1 mm or more and 10 mm or less. When the dimension w 4  is equal to or more than the above lower limit value, the first electrode  4  is easy to manufacture. In addition, when the dimension w 4  is equal to or more than the above lower limit value, the irradiator  10  can have a sufficiently thin distal end portion. When the dimension w 4  is equal to or less than the above upper limit value, a surface area of the first electrode  4  increases so that a plasma can be more efficiently generated to promote cure, When the dimension w 4  is equal to or less than the above upper limit value, a plasma can be more efficiently generated to further promote cure, without making excessively larger the irradiator  10 . 
     In the example shown in  FIG.  3   , the dimension w 4  of the first electrode  4  in the radial direction d 2  is smaller than the dimension w 1  of the piezoelectric transformer  2  in the radial direction d 2 . This can make thinner the distal end portion of the irradiator  10 , as compared with a case in which the irradiator  10  does not have the first electrode  4  so that to plasma is generated at the end portion of the piezoelectric transformer  2 . 
     When the active gas irradiation apparatus  100  is an intraoral treatment tool, a dimension w 5  of the second electrode  5  in the radial direction d 2  is preferably between 1 mm or more and 15 mm or less, more preferably between 3 mm or more and 6 mm or less. 
     In the example shown in  FIG.  3   , the dimension w 5  of the second electrode  5  in the radial direction d 2  is smaller than the dimension w 1  of the piezoelectric transformer  2  in the radial direction d 2 . This can make thinner the distal end portion of the irradiator  10 , while the second electrode  5  is provided, as compared with a case in which the irradiator  10  generates a plasma at the end portion of the piezoelectric transformer  2 . 
     In the example shown in  FIG.  3   , a dimension w 7  of the second portion  1   b  of the housing  1  in the radial direction d 2  is smaller than a dimension w 6  of the first portion  1   a  of the housing  1  in the radial direction d 2 . When the active gas irradiation apparatus  100  is an intraoral treatment tool, the dimension w 7  of the second portion  1   b  in the radial direction d 2  is preferably between 3 mm or more and 20 mm or less, more preferably between 5 mm or more and 10 mm or less. This can make sufficiently thinner the thickness of a part of the irradiator  10  where the second portion  1   b  is positioned in the axial direction d 1 . 
     Next, details of parts of the active gas irradiation apparatus  100  in this embodiment, which are other than the irradiator  10 , are described with reference to  FIG.  1   . The supply unit  20  as shown in  FIG.  1    supplies the irradiator  10  with electricity and a plasma generation gas. The supply unit  20  can regulates a voltage and a frequency to be applied to the first electrode  4  through the piezoelectric transformer  2 . The supply unit  20  comprises a supply unit housing  21  accommodating the supply source  70 . Thus, when the supply source  70  accommodated in the supply unit housing  21  runs out of a gas, the supply source  70  for a plasma generation gas can be replaced with another one. 
     The supply source  70  supplies a plasma generation gas to a space between the first electrode  4  and the second electrode  5 . The supply source  70  is a pressure-resistant container that contains the plasma generation gas. As shown in  FIG.  2   , the supply source  70  is detachably mounted on a pipe  75  located in the supply unit housing  21 . The pipe  75  connects the supply source  70  and the gas pipeline  30 . A solenoid valve  71 , a pressure regulator  73 , a flowrate controller  74 , and a pressure sensor  72  (remaining volume sensor) are attached to the pipe  75 . 
     When the solenoid valve  71  is opened, the plasma generation gas is supplied from the supply source  70  to the irradiator  10  through the pipe  75  and the gas pipeline  30 . In the illustrated example, an opening degree of the solenoid valve  71  cannot be adjusted, and the solenoid valve  71  is merely turned on or off. However, an opening degree of the solenoid valve  71  may be adjusted. The pressure regulator  73  is located between the solenoid valve  71  and the supply source  70 . The present regulator  73  reduces a pressure of the plasma generation gas (depressurizes the plasma generation gas) moving from the supply source  70  toward the solenoid valve  71 . 
     The flowrate controller  74  is located between the solenoid valve  71  and the gas pipeline  30 . The flowrate controller  74  regulates a flowrate (supply volume per unit time) of the plasma generation gas having passed through the solenoid valve  71 . The flowrate controller  74  regulates a flowrate of the plasma generation gas to 3 L/min, for example. 
     The pressure sensor  72  detects a remaining volume V1 of the plasma generation gas in the supply source  70 . The pressure sensor  72  measures a pressure (remaining pressure) in the supply source  70  as a remaining volume V1. The pressure sensor  72  measures, as a pressure of the supply source  70 , a pressure (primary pressure) of the plasma generation gas passing through between the pressure regulator  73  and the supply source  70  (closer to the primary side than the pressure regulator  73 ). AP-V80 series of KEYENCE Co. (specifically, AP-15S) can be employed as the pressure sensor  72 , for example. 
     An actual remaining volume V1 (cubage) in the supply source  70  is calculated from a remaining pressure measured by the pressure sensor  72  and a capacity (internal volume) of the supply source  70 . When a supply source  70  of various capacities are used, a capacity for calculation may be set by selecting an actual capacity of the supply source  70  on a system screen of an input unit, not shown. Alternatively, when a supply source  70  of a constant capacity is used, the control unit  90  may store its capacity in advance. 
     A joint  76  is provided on an end of the pipe  75 , which end is on a side of the supply source  70 . The supply source  70  is detachably mounted on the joint  76 . By detaching and attaching the joint  76  from and to the supply source  70 , the supply source  70  of the plasma generation gas can be replaced with another one, while the solenoid valve  71 , the pressure regulator  73 , the flowrate controller  74 , and the pressure sensor  72  (referred to as “solenoid valve  71  and so on” herebelow) remain fixed in the housing  21 . In this case, the solenoid valve  71  and so on can be shared between the current supply source  70  and the replaced supply source  70 . The solenoid valve  71  and so on may be fixed to the supply source  70  so as to be detached from the supply unit housing  21  together with the supply source  70 . 
     As shown in  FIG.  1   , the gas pipeline  30  is a channel through which the plasma generation gas is supplied from the supply unit  20  to the irradiator  10 . The gas pipeline  30  is connected to a rear end of the tubular dielectric  3  of the irradiator  10 . A material of the gas pipeline  30  is not specifically limited, and a material used for a known gas pipe can be used. The gas pipeline  30  may be a resin pipe or a rubber tube, for example. A flexible material is preferred as a material of the gas pipeline  30 . 
     The voltage supply line  40  is a line that supplies a voltage from the supply unit  20  to the irradiator  10 . The voltage supply line  40  is connected to the piezoelectric transformer  2 , as described above, and is connected to a foot switch, not shown. A material of the voltage supply line  40  is not specifically limited, and a material used for a known voltage supply line can be used. The voltage supply line  40  may be a metal conducive wire covered with an insulating material. 
     The control unit  90  as shown in  FIG.  2    is formed of an information processing device. Namely, the control unit  90  comprises a CPU (Central Processer Unit), a memory, and an auxiliary storage device connected by a bus. The control unit  90  is operated by executing a program. The control unit  90  may be incorporated in the supply unit  20 , for example. The control unit  90  controls the irradiator  10 , the supply unit  20 , and the notification unit  80 . 
     A foot switch, not shown, is electrically connected to the control unit  90 . When a user of the irradiator  10  operates the foot switch, an electric signal is transmitted from the foot switch to the control unit  90 . When the control unit  90  receives the electric signal, the control unit  90  activates the solenoid valve  71  and the flowrate controller  74 , and applies a voltage to the first electrode  4 . 
     In this embodiment, every time a user presses the foot switch, the control unit  90  receives the electric signal. Then, the control unit  90  opens the solenoid valve  71  for a predetermined period of time, causes the flowrate controller  74  to regulate a flowrate of the plasma generation gas which has passed through the solenoid valve  71 , and applies a voltage to the first electrode  4  for a predetermined period of time. As a result, a certain volume of the plasma generation gas is supplied from the supply source  70  to a space between the first electrode  4  and the second electrode  5 , and an active gas is continuously ejected from the nozzle irradiation opening  9   a  for a certain period of time (e.g., from several seconds to several tens of seconds, 30 seconds in this embodiment). 
     Namely, in this embodiment, an ejection volume of the active gas per one press of the foot switch by a user is fixed. Such an operation for ejecting the active gas of the predetermined ejection volume is referred to as a unit operation. In this embodiment, the unit operation is one pressing of foot switch by a user. An ejection volume of the active gas per unit operation (a supply volume of the plasma generation gas from the supply source  70  to a space between the first electrode  4  and the second electrode  5  per unit operation) may be a fixed value that is previously set or a variable value that can be set by operating an operation panel, not shown. 
     The control unit  90  computes as remaining information at least one of a remaining number of times N and a remaining time T of the plasma generation gas. In this embodiment, the control unit  90  computes as the remaining information only the remaining number of times N among the remaining number of times N and the remaining time T. The remaining number of times N is a number of times of the unit operations to be left during which the plasma generation gas can be supplied from the supply source  70  to a space between the first electrode  4  and the second electrode  5 . The remaining time T is a time to be left during which the plasma generation gas can be supplied from the supply source  70  to a space between the first electrode  4  and the second electrode  5 . 
     Both the remaining time N and the remaining time T can be calculated from the remaining volume V1 of the plasma generation gas in the supply source. The remaining number of times N can be calculated (N=V1/V2) based on the remaining volume V1 and a supply volume V2 of the plasma generation gas per unit operation of the foot switch. Alternatively, the remaining number of times N is calculated by computing an average value V2 (average value) of usages (supplies) of the plasma generation gas over the last several times, and by dividing the remaining volume V1 of the plasma generation gas by the average value V2 (average value). The remaining time T can be calculated (T=V1/V3) based on the remaining volume V1, and a supply volume V3 of the plasma generation gas supplied from the supply source  70  to a space between the first electrode  4  and the second electrode  5  per unit time. 
     The notification unit  80  gives a notice of at least one of the remaining number of times N and the remaining time T. In this embodiment, the notification unit  80  displays the number of times N. The notification unit  80  displays the remaining number of times N calculated by the control unit  90  by a numeric character. A display unit capable of displaying a numeric character or a mechanical counter may be employed as the notification unit  80 . 
     In the illustrated example, the notification unit  80  is integrated in the supply unit housing  21  on an outer surface thereof. However, the notification unit  80  may be independent from the supply unit  20 . The notification unit  80  may display the remaining number of times N by a way different from a numerical character. For example, an analogue display structure formed of a dial and a needle may be employed as the notification unit  80 . Further, the notification unit  80  may give a notice of the remaining number of times N by displaying a color or by turning on/off light. 
     Further, the notification unit  80  may give a notice of the remaining number of times N by sound. In this case, a speaker can be employed as the notification unit  80 , for example. 
     As in this embodiment, when a certain volume of the plasma generation gas is supplied from the supply source  70  to a space between the first electrode  4  and the second electrode  5  upon pressing of the foot switch by a user, to give a notice of the remaining number of times N is more convenient for a user than to give a notice of the remaining time T. 
     Next, a method of using the active gas irradiation apparatus  100  is described. A user such as a doctor moves the irradiator  10  by hand and directs the nozzle irradiation opening  9   a  toward an irradiation target described later. Under this state, the user presses the foot switch to supply electricity and a plasma generation gas from the supply source  70  to the irradiator  10 . The plasma generation gas supplied to the irradiator  10  flows from the rear end of the tubular dielectric  3  into the inner hollow  3   a  of the tubular dielectric  3 . The plasma generation gas is ionized at a position where the first electrode  4  and the second electrode  5  are opposed to each other to become a plasma. 
     In this embodiment, the first electrode  4  and the second electrode  5  are opposed to each other in a direction orthogonal to the direction along which the plasma generation gas flows. The plasma, which was generated at the position where outer circumferential surface of the first electrode  4  and the inner circumferential surface of the second electrode  5  are opposed to each other, changes the composition of the gas to become an active gas containing active species such as radical, while flowing through the inner hollow  3   a  of the tubular dielectric  3 . 
     The active gas thus generated is ejected from the nozzle irradiation opening  9   a.  The ejected active gas further activates a part of the gas near the nozzle irradiation opening  9   a  to generate active species. The active gas containing these active species is applied to the irradiation target. 
     The irradiation target may include, for example, cells, living tissues, biological individuals, etc. The living tissues may include, for example, respective organs such as viscera, epithelial tissues covering body surfaces and inner surfaces of body cavities, periodontal tissues such as gingiva, alveolar bone, periodontal ligament and cementum, teeth, bones, etc. The biological individuals may be any mammals such as humans, dogs, cats, pigs, etc.; birds; fish, etc. 
     The plasma generation gas may be, for example, rare gases such as helium, neon, argon, krypton, etc.; nitrogen, etc. One of these gases may be used solely or two or more gases may be used in combination. The plasma generation gas preferably contains nitrogen as a main component. Herein, a gas containing nitrogen as a main component means that a nitrogen content in the plasma generation gas is more than 50% by volume. Namely, the nitrogen content in the plasma generation gas is preferably more than 50% by volume, more preferably 70% by volume, and particularly preferably between 90% by volume and 100% by volume. A gas component in the plasma generation gas, other than nitrogen, is not specifically limited, and may be, for example, oxygen, rare gas, etc. 
     When the active gas irradiation apparatus  100  is an intraoral treatment tool, an oxygen concentration of the plasma generation gas to be introduced to the tubular dielectric  3  is preferably 1% by volume or less. When the oxygen concentration is equal to or less than the upper limit value, generation of ozone can be reduced. 
     A flowrate of the plasma generation gas to be introduced to the tubular dielectric  3  is preferably between 1 L/ruin and 10 L/min. When the flowrate of the plasma generation gas to be introduced to the tubular dielectric  3  is equal to or more than the lower limit value, increase in temperature of an irradiation surface of the irradiation target can be easily suppressed. When the flowrate of the plasma generation gas is equal to or less than the upper limit value, purification, activation or cure of the the irradiation target can be further promoted. 
     A temperature of the active gas applied from the nozzle irradiation opening  9   a  is preferably 50° C. or less, more preferably 45° C. or less, further preferably 40° C. or less. When the temperature of the active gas applied from the nozzle irradiation opening  9   a  is equal to or less than the upper limit value, it is easy for the irradiation surface to have a temperature of 40° C. or less. When the irradiation surface has a temperature of 40° C. or less, stimulus to an affected area as the irradiation part can be reduced. A lower limit value of the temperature of the active gas applied from the nozzle irradiation opening  9   a  is not specifically limited, and is 10° C. or more, for example. The temperature of the active gas is a value of the temperature of the active gas, which is measured at the nozzle irradiation opening  9   a  by a thermocouple. 
     A distance (irradiation distance) from the nozzle irradiation opening  9   a  to the irradiation surface is preferably between 0.01 mm and 10 mm, for example. When the irradiation distance is equal to or more than the above lower limit value, the temperature of the irradiation surface can be lowered to further mitigate stimulus to the irradiation surface. When the irradiation distance is equal to or less than the above upper limit value, an effect such as cure can be further enhanced. 
     A temperature of the irradiation surface at a position distant from the nozzle irradiation opening  9   a  by between 1 mm or more and 10 mm or less is preferably 40° C. or less. When the irradiation surface has a temperature of 40° C. or less, stimulus to the irradiation surface can be reduced. A lower limit value of the temperature of the irradiation surface is not specifically limited, and is 10° C. or more, for example. The temperature of the irradiation surface can be adjusted by controlling an alternating voltage applied to a space between the first electrode  4  and the second electrode  5 , an ejection volume of the active gas to be applied, a way from the distal end  4   d  of the first electrode  4  to the nozzle irradiation opening  9   a,  etc. in combination. The temperature of the irradiation surface can be measured by using a thermocouple. 
     Active species (radical, etc.) contained in the active gas may include, for example, hydroxyl radical, singlet oxygen, ozone, hydrogen peroxide, superoxide anion radical, nitrogen monoxide, nitrogen dioxide, peroxynitrite, nitrous peroxide, dinitrogen trioxide, etc. A type of active species contained in the active gas can further adjusted to a type of the plasma generation gas. 
     A hydroxyl radical density (radical density) in the active gas in the active gas is preferably between 0.1 μmol/L and 300 μmol/L. When the radical density is equal to or more than the lower limit value, purification, activation, or cure of the irradiation target selected from cells, living tissues and biological individuals, can be further promoted. When the radical density is equal to or less than the upper limit value, stimulus to the irradiation surface can be reduced. 
     The radical density can be measured by the following method, for example. 0.2 mL of DMPO (5,5-dimethyl-1-pyrroline-N-oxide) 0.2 mol/L solution is irradiated with the active gas for 30 seconds. At this time, a distance from the nozzle irradiation opening  9   a  to a liquid level is 5.0 mm. A hydroxyl radical concentration of the solution irradiated with the active gas is measured using an electron spin resonance (ESR) method. The obtained value is the radial density. 
     A singlet oxygen density in the active gas is preferably between 0.1 μmol/L and 300 μmol/L. When the singlet oxygen density is equal to or more than the lower limit value, purification, activation and cure of the irradiation target such as cells, living tissues, biological individuals, etc. can be easily promoted. When the singlet oxygen is equal to or less than the upper limit value, stimulus to the irradiation surface can be reduced. 
     The singlet oxygen density can be measured by the following method, for example. 0.4 mL of TPC (2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide) 0.1 mol/L solution is irradiated with the active gas for 30 seconds. At this time, a distance from the nozzle irradiation opening  9   a  to a liquid level is 5.0 mm. A singlet oxygen concentration of the solution irradiated with the active gas is measured using an electron spin resonance (ESR) method. The obtained value is the singlet oxygen density. 
     A flowrate of the active gas applied from the nozzle irradiation opening  9   a  is preferably between 1 L/min and 10 L/min. When the flowrate of the active gas applied from the nozzle irradiation opening  9   a  is equal to or more than the lower limit value, an effect of the active gas acting on the irradiation surface can be sufficiently increased. When the flowrate of the active gas applied from the nozzle irradiation opening  9   a  is less than the upper limit value, a temperature of the irradiation surface irradiated with the active gas can be prevented from excessively increasing. In addition, when the irradiation surface is wet, rapid dry of the irradiation surface can be prevented. Further, when the irradiation surface is an affected area, stimulus to a patient can be suppressed. In the active gas irradiation apparatus  100 , a flowrate of the active gas applied from the nozzle irradiation opening  9   a  can be adjusted by a volume of the plasma generation gas supplied to the tubular dielectric  3 . 
     The active gas generated by the active gas irradiation apparatus  100  has an effect of promoting cure of traumatic injuries and abnormalities. By applying the active gas to cells, living tissues, or biological individuals, purification and/or activation of the irradiated portion, or cure of the irradiated portion can be promoted. 
     When the active gas is applied in order to promote cure of traumatic injuries and/or abnormalities, there is no particular limitation on a frequency of irradiation, a number of times of irradiation, and a period of irradiation. For example, when an affected area is irradiated with the active gas with an irradiation volume between 1 L/min and 5.0 L/min, irradiation conditions of once to five times a day, for 10 seconds to 10 minutes each time, over a day to 30 days, etc. are preferred from the viewpoint of promoting cure. 
     The active gas irradiation apparatus  100  in this embodiment is particularly useful as an intraoral treatment tool and dental treatment tool. In addition, the active gas irradiation apparatus  100  in this embodiment is suitable as an animal treatment tool. 
     In the above, one embodiment has been described with reference to the specific example, but the above specific example does not intend to limit the embodiment. The aforementioned one embodiment can be carried out in various other specific examples, and can be variously omitted, replaced and modified without departing from its scope. 
     Modification examples are described herehelow with reference to the drawings. In the below description and the drawings used for the below description, the same reference numerals as those used for the corresponding parts in the specific example described above are used for parts that can be configured in the same way as in the specific examples described above, and redundant description is omitted. 
     In the aforementioned embodiment, the example in which the first electrode  4  has a columnar shape is described. However, the shape of the first electrode  4  is not limited thereto. As an example, the first electrode  4  has a prismatic shape, in particular, a rectangular columnar shape. In this case, a plasma can be generated by the first electrode  4  near the first end portion  4   a  of the first electrode  4 , which is as follows. When a voltage is applied to the first electrode  4 , a particularly high voltage is generated at a corner of the first electrode  4 , which corner is positioned near the first end portion  4   a.  Thus, a gas around the corner can be ionized to generate a plasma. As another example, the first electrode  4  may have a needle-like shape with the first end portion  4   a  being pointed. In this case, since a particularly high voltage is locally generated at the pointed first end portion  4   a  of the first electrode  4 , a plasma can be generated around the first end portion  4   a.  Depending on conditions of a shape of the first electrode  4  or a voltage to be applied to the first electrode  4 , a plasma can be generated around the first end portion  4   a  of the first electrode  4 . When the first electrode  4  can generate a plasma near the first end portion  4   a,  the irradiator  10  may be free of the second electrode  5 . 
     In the aforementioned embodiment, the example in which the irradiator  10  comprises the first buffer  7   b  provided between the piezoelectric transformer  2  and the piezoelectric transformer casing  7   a  is described. However, although not shown, the irradiator  10  may be free of the first buffer  7   b.    
     In the aforementioned embodiment, the example in which the irradiator  10  comprises the conductive wire  50 , and the first electrode  4  is connected to the output area  2   b  of the piezoelectric transformer  2  through the conductive wire  50  is described. However, the method of connecting the first electrode  4  to the output area  2   b  of the piezoelectric transformer  2  is not limited thereto. As another example, the first electrode  4  is connected to the output area  2   b  of the piezoelectric transformer  2  by soldering. 
     The irradiator  10  may comprise one piezoelectric transformer  2  or may comprise a plurality of piezoelectric transformers  2 . When the irradiator  10  comprises a plurality of piezoelectric transformers  2 , the plurality of piezoelectric transformers  2  may be accommodated in one housing  1 . When the irradiator  10  comprises a plurality of piezoelectric transformers  2 , each of the piezoelectric transformers  2  are connected to the first electrode  4 , and a voltage is applied thereto from the plurality of piezoelectric transformers  2 . 
     The following effect can be obtained by applying voltages from the plurality of piezoelectric transformers  2  to the first electrode  4 . Even when a capacity of each of the plurality of piezoelectric transformers  2  is small, a sufficient amount of plasma can be generated between the first electrode  4  and the second electrode  5 . In addition, as compared with a case in which a voltage is applied to the first electrode  4  from one piezoelectric transformer  2  with a large capacity, a current flowing through each of the plurality of piezoelectric transformers  2  can be made smaller. In other words, a current can be distributed to the respective piezoelectric transformers  2 . 
     In the irradiator  10 , a dimension w 8  of a part in the axial direction d 1  where the first electrode  4  and the second electrode  5  are opposed to each other may be, in particular, between more than 3 mm and less than 20 mm. When the dimension w 8  is less than 20 mm, increase in a current of electric discharge generated between the first electrode  4  and the second electrode  5  can be suppressed. Thus, mechanical damage of the piezoelectric transformer  2  caused by a large current can be more effectively suppressed. In addition, when the dimension w 8  is more than 3 mm, a plasma can be generated sufficiently efficiently between the first electrode  4  and the second electrode  5  so that a sufficient amount of active species can be generated. Thus, a sufficient amount of active species can be applied to an irradiation target by using the irradiator  10 . As a result, when the irradiator  10  is used as a treatment tool, a particularly sufficient treatment effect can be obtained. From the viewpoint of further improving the above effect, the dimension w 8  is further preferably between more than 5 mm and less than 15 mm. 
     In the irradiator  10 , a distance w 9  in the axial direction d 1  between the part of the first electrode  4 , which part is opposed to the second electrode  5 , and the output area  2   b  of the piezoelectric transformer  2  may be, in particular, between more than 1 mm and less than 100 mm. An effect obtained by the distance w 9  less than 100 mm is described. Between the part of the first electrode  4 , which part is opposed to the second electrode  5 , and the output area  2   b  of the piezoelectric transformer  2 , a transmission portion is positioned, the transmission portion transmitting a voltage from the output area  2   b  of the piezoelectric transformer  2  to the part of the first electrode  4 , which part is opposed to the second electrode  5 . For example, in the example shown in  FIG.  3   , a part of the first electrode  4 , which part is closer to the part opposed to the second electrode  5  to the piezoelectric transformer  2 , and the conductive wire  50  correspond to the transmission portion. When a voltage is applied from the piezoelectric transformer  2  to the part of the first electrode  4 , which part is opposed to the second electrode  5 , the voltage is also applied to the transmission portion. In this case, the transmission portion functions as a capacitor to accumulate therein energy. Thus, it is necessary to supply excessive power corresponding to the energy accumulated in the transmission portion, in order to apply a voltage to the part of the first electrode  4 , which part is opposed to the second electrode  5 . In other words, it is necessary to supply larger power by a stray capacitance of the transmission portion. In this case, it may be necessary to increase a current flowing through the piezoelectric transformer  2 . On the other hand, when the distance w 9  is less than 100 mm, the length of the transmission portion in the axial direction d 1  can be reduced. Thus, a stray capacitance of the transmission portion can be reduced, and a sufficient voltage can be applied to the part of the first electrode  4 , which part is opposed to the second electrode  5 , without increasing a current flowing through the piezoelectric transformer  2 . From the viewpoint of further improving the above effect, the distance w 9  is further preferably between 1 mm or more and 40 mm or less. 
     A distance w 10  in the axial direction d 1  between the end of the second electrode  5 , which is provided with the irradiation opening  5   a  and the first portion  1   a  of the housing  1 , which accommodates the piezoelectric transformer  2 , may be, in particular, more than 10 mm and less than 150 mm. An effect of w 10  which is between more than 10 mm and less than 150 mm is described. The irradiator  10  is supposed to be used as an intraoral treatment tool or a dental treatment tool. The distance w 10  corresponds to a length of a part which is close to the irradiation opening  5   a  to the first portion  1   a  accommodating the piezoelectric transformer  2  of the irradiator  10 , the part being designed as being thin irrespective of the dimension of the piezoelectric transformer  2 . When the length of the part is between more than 10 mm and less than 150 mm, it is sufficiently easy to insert the distal end portion of the irradiator  10  into a mouth and to operate the irradiator  10 . From the viewpoint of improving the above effect, the distance w 10  is further preferably between more than 30 mm and less than 50 mm. 
     The aspect of the present invention is not limited to the aforementioned respective embodiments, and includes various modifications conceivable to those skilled in the art. The effect of the present invention is also not limited to the aforementioned contents. Namely, various additions, modifications and partial deletions are possible without departing from the conceptual idea and purpose of the invention derived from the content defined in the claims and their equivalents.