CONTROL OF THERMAL PLASMA GENERATION

Abstract

A plasma torch having an open end from which a plume of plasma or plasma effluent, for use in therapeutic treatment of tissue in vivo, preferably skin and/or wounds, is emitted in use. The plasma torch comprising: a cathode rod; and a grounded conductive tube having at least one opening and being arranged around the cathode and spaced therefrom to form a cavity in which, in use, an arc discharge between the cathode and grounded conductor ionizes a feed gas to produce a thermal plasma, the plasma or effluent being emitted in a plume from the opening of the grounded conductor. The opening of the grounded conductor tube comprises a lip, the inwardly facing surface of which defining an orifice, the orifice having a length to an opening width ratio of at least 2.5:1.

Claims

1. A plasma torch having an open end from which a plume of plasma or plasma effluent, for use in therapeutic treatment of tissue in vivo, is emitted in use, comprising: a cathode rod; a grounded conductive tube having at least one opening and being arranged around the cathode and spaced therefrom to form a cavity in which, in use, an arc discharge between the cathode and grounded conductor ionizes a feed gas to produce a thermal plasma, the plasma or effluent being emitted in a plume from the opening of the grounded conductor; wherein the opening of the grounded conductor tube comprises a lip, an inwardly facing surface of the lip defining an orifice, the orifice having a length to an opening width ratio of at least 2.5:1.

2. A plasma torch as claimed in claim 1, wherein the orifice has a length to an opening width ratio of at least 3:1, optionally at least 4:1, optionally at least 5:1.

3. A plasma torch as claimed in claim 1, wherein the orifice has a length of at least 6 mm, optionally at least 7 mm, optionally at least 8 mm, optionally at least 9 mm, optionally at least 10 mm.

4. A plasma torch as claimed in claim 1, wherein the orifice has an opening width of at most 4 mm, optionally at most 3 mm, optionally at most 2 mm.

5. A plasma torch as claimed in claim 1, wherein the cathode is recessed from the opening at the surface in the conductive tube, such that the thermal plasma is, in use, produced inside the grounded conductor tube and passes through an orifice having a length to an opening width ratio of at least 2.5:1, and at least 8 mm in length.

6. A plasma torch as claimed in claim 5, wherein the orifice is configured to wick thermal energy away from the thermal plasma or plasma effluent before it is emitted from the opening in the grounded conductive chamber.

7. A plasma torch as claimed in claim 1, wherein the cross section of the orifice varies along its length to change the surface area of the wicking region.

8. A plasma torch as claimed in claim 1, wherein the cathode has a rounded or flattened or non-pointed end, and is not tapered towards its end.

9. A plasma torch as claimed in claim 1, wherein the plasma torch is configured to, in normal use, only be usable to produce the thermal plasma.

10. A plasma torch as claimed in claim 1, wherein the plasma torch does not comprise components configured to produce, in normal use, a non-thermal plasma or dielectric barrier discharge plasma.

11. A plasma torch as claimed in claim 1, further comprising a plasma active cooling mechanism configured to, in normal use, to cause or be operable to cause a temperature of the plasma or plasma effluent emitted as a plume from the plasma torch to be cooled.

12. A plasma torch as claimed in claim 11, wherein the plasma active cooling mechanism comprises at least one of: means for pre-cooling the feed gas; means for mixing the plasma or plasma effluent with a cooler gas.

13. A plasma torch as claimed in claim 1, wherein the cathode rod further comprises a thermionically emissive material, which in use enhances the ionization of the feed gas between the cathode and grounded conductive tube.

14. A plasma torch as claimed in claim 1, wherein the cathode rod further comprises a material resilient to operation using non-inert feed gases.

15. A plasma torch as claimed in claim 1, wherein the grounded conductive tube is detachably connected to the plasma torch as a or as part of a replaceable modular assembly, and the central cathode rod is detachably connected to the torch as a or as part of a replaceable modular assembly, such that the grounded conductive tube is interchangeable and the central cathode rod is interchangeable.

16. A plasma torch as claimed in claim 1, further comprising at least one container of feed gas, wherein the feed gas is supplied to the cavity to be ionized in use.

17. A plasma torch as claimed in claim 1, further comprising a front half comprising the cathode rod and the cylindrical cavity to which the feed gas is fed for ionization and from which the thermal plasma is emitted in use; and a rear half which supports and retains the components of the front half and provides at least one coupling to at least one container of feed gas.

18. A plasma torch as claimed in claim 1, wherein the plasma torch is configured to be operated with an arc current of 2A-5A between the central cathode rod and grounded conductive tube, the arc current preferably being fixed during plasma production.

19. A plasma torch as claimed in claim 1, wherein the plasma torch is configured such that the feed gas delivered to the first cylindrical cavity is at a flow rate of 1 Ln/min-10 Ln/min.

20. A plasma torch as claimed in claim 1, wherein the plasma torch is configured such that the operation and configuration of the plasma torch is arranged to produce, in normal use, a total plasma plume fluence of at most 30 W, or a total energy of 120 J over a 4-5 second dose.

21. A plasma torch as claimed in claim 20, wherein the plasma plume intensity produced will be at most 120 W/cm2.

22. A plasma torch as claimed in claim 1, wherein the opening in the grounded conductor tube is configured to direct the plasma or plasma effluent emitted therefrom in a direction away from directly towards the treatment direction in normal use.

23. An apparatus for generating a plasma plume comprising an electrical power generator unit coupled with the plasma torch as claimed in claim 1, for use in therapeutic treatment of tissue in vivo, the electrical power generator providing power to a plasma torch when in use, the electrical power generator unit comprising: means configured to provide to the central cathode rod in use a constant direct current (DC) electrical power supply plus a high voltage pulsed electrical power supply to initiate the arc discharge in the first cylindrical cavity; and means configured to control the rate of flow of the feed gas into the first cylindrical cavity which, in use, indirectly controls the fluence of the central thermal plasma emitted from the open end of the first cavity.

24. A method of generating a plasma plume from an open end of the plasma torch using the apparatus as claimed in claim 23, comprising: producing the arc discharge in the cavity between the central cathode rod and grounded conductive tube by providing to the cathode rod a constant direct current (DC) electrical power plus a high voltage pulsed electrical power to initiate the arc discharge between the tapered end of the central cathode rod and the grounded conductive tube; and ionizing the feed gas using the arc discharge in the cylindrical cavity in the plasma torch to produce the central thermal plasma emitted at the open end of the first cylindrical cavity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Aspects of the invention may best be understood by reference to the following description of certain exemplary embodiments together with the accompanying drawings in which:

[0066] FIG. 1 shows a view of an apparatus for generating a plasma plume for cosmetic treatment of skin according to an embodiment of aspects of the invention;

[0067] FIG. 2a is a cutaway view of the FIG. 1 apparatus;

[0068] FIG. 2b is a cutaway view of a further embodiment the apparatus;

[0069] FIG. 3a shows a view of an apparatus for generating a plasma plume for cosmetic treatment of skin according to another embodiment of aspects of the invention;

[0070] FIG. 3b is a cutaway view of the FIG. 3a apparatus;

[0071] FIG. 4 is a diagram illustrating the shape and geometry of the part of the apparatus for generating the hot stage of the plasma torches shown in FIGS. 1-3b to generate an arc discharge and thermal plasma;

[0072] FIG. 5 is a diagram illustrating the operation of the cold stage of the plasma torches shown in FIGS. 1-3b to generate an dielectric barrier discharge and non-thermal plasma;

[0073] FIG. 6 illustrates the two stages of the plasma generated by the plasma torch and the cooperative effect to generate a collimated, focused plasma plume;

[0074] FIG. 7 shows the voltage and current vs time waveform provided by the DC power supply to generate the hot stage of the plasma;

[0075] FIG. 8 shows the voltage vs time waveform provided by the high-voltage pulse width modulated power supply to generate the cold stage of the plasma;

[0076] FIG. 9 shows the end portion of the plasma device featuring an endpiece of the grounded tube and lip portion;

[0077] FIG. 10 shows the end portion of the plasma device featuring the endpiece of the grounded tube, the grounded tube and cathode; and

[0078] FIG. 11 shows a cross section of a thermal plasma-only plasma torch having a grounded conduction tube having an orifice having a length to an opening width ratio of significantly greater than 2.5:1.

DETAILED DESCRIPTION

[0079] The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practised. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention. Furthermore, terms comprises, comprising, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that apparatuses and method steps that comprises a list of elements or steps does not include only those elements but may include other elements or steps not expressly listed or inherent. An element or step proceeded by comprises . . . a does not, without more constraints, preclude the existence of additional identical elements or steps that comprises the element or step

[0080] Referring now to FIG. 1, an apparatus 100 for generating a plasma plume in accordance with an embodiment of aspects of the invention includes a plasma torch 101. As will be explained in further detail below, by operating a system control unit (not shown) by means of controls, a controller (not shown) can be caused to release one or more feed gases from a gas supply (not shown) where they are stored under pressure to ionization cavities inside the plasma torch 101 via feed gas connectors 102 and 108.

[0081] Once the gas is flowing into the plasma torch 101 through the feed gas connectors 102 and 108, the controller causes a power supply (not shown) to generate one or more different electrical power signals that are provided via power supply cabling (not shown) to one or more electrodes in the plasma torch 101 to cause electrical discharge inside the plasma torch 101. A grounded rod 104 is also provided to act as the ground reference for the grounded components of the plasma torch 101. The feed gas inside the plasma torch 101 is then ionised by the discharge and is emitted from an open end 109 of the plasma torch 101 in the form of a two-stage plasma plume: a higher energy central focused thermal plasma emitted from opening 105, and a surrounding lower energy non-thermal plasma halo emitted from opening 106, as will be described in more detail below. The plasma plume may be generated for a sustained period of time or may be caused to be emitted in pulses. The outer, non-thermal plasma halo may be ignited alone or in addition to, the central, thermal plasma.

[0082] According to some of the example embodiments, the apparatus is typically supplied a current fixed during plasma generation (by control) to be in the range of 2A to no more than 5A. Specifically, a current of at most 5A, at most 4.8A, at most 4.6A, at most 4.4A, at most 4.2A, at most 4A, at most 3.8A, at most 3.6A, at most 3.4A, at most 3.2A, at most 3A, at most 2.8A, at most 2.6A, at most 2.4A, at most 2.2A, or at most 2A may be used. According to some of the embodiments, the current is an arc current between the central cathode rod and grounded conductive tube, where the arc current preferably being fixed during plasma production. Such a current range may be beneficial in producing the hot arc plasma to have a temperature and energy at a level at which the plasma is suitable for therapeutic treatment of tissue in vivo. In particular, the temperature of the plasma which will be placed on the treatment surface will be suitable for exposure to live tissue without irreparable thermal damage.

[0083] According to some of the example embodiments, a gas flow of 1-10 Ln/min is employed. Specifically, it should be appreciated that a flow rate of at most 10 Ln/min, at most 9 Ln/min, at most 8 Ln/min, at most 7 Ln/min, at most 6 Ln/min, at most 5 Ln/min, at most 4 Ln/min, at most 3 Ln/min, at most 2 Ln/min, or at most 1 Ln/min may be used. According to some of the embodiments, the feed gas delivered to the first cylindrical cavity comprising a flow rate as discussed above. Such a range of flow rates may be beneficial in stabilizing the generation of the relatively low energy hot plasma generated at a fixed plasma current in the range of at most 5A. Specifically, the flow rate of 1-10 Ln/min stabilizes the plasma such that the plasma does not prolapse out of the cavity, thus significantly reducing the occurrence of oxidation and corrosion of the electrodes, which would otherwise inhibit the formation of the arc, preventing the device from being turned off and on, and shortening the useful life of the torch components.

[0084] One reason for operating at such low flow rates and currents, as compared to industrial plasma based devices, is to ensure the amount of heat imparted to the gas is suitable for use on skin or a wound. Such operating conditions also ensure the plasma is stable and forms with the electrode arrangement, thereby creating a consistent spot size and energy profile. The operating conditions further aid in reducing the amount of oxygen that gets into the plasma. Too high a flow rate and/or too high a current increases the potential of plasma instability and oxidation of the electrodes which may prevent the ability to turn the apparatus on and off with any reliability, compared to low plasma currents and flow rates.

[0085] According to some of the example embodiments, operating parameters comprising an upper threshold of at most 5A and a flow rate of at most 10 Ln/min may produce, at a distance of around 25 mm from the open end 109, a plasma plume with an energy distribution giving a spot size of approximately 0.5 cm across, or spread over 0.25 cm.sup.2. Generally, the operation and configuration of the plasma torch in accordance with embodiments will be arranged to produce a total plasma plume fluence of at most 30W, or a total energy of 120J over a 4-5 second dose.

[0086] Generally, the plasma plume intensity produced will be at most 120 W/cm.sup.2. It should be appreciated that the energy level may be determined with the use of a calorimeter, such as a solid state uncooled calorimeter.

[0087] An operator of the apparatus 100 can manipulate the plasma torch 101 to direct the plasma plume emitted from opening 109 onto tissue to carry out cosmetic or surgical procedures. For example, the plume may be used for the cosmetic treatment of deep wrinkles such as crow's feet and other, significant skin irregularities.

[0088] FIGS. 2a and 2b are cutaway views of the plasma torch 101 showing the electrode structure which gives rise to the creation of the two-stage cooperative plasma in use. FIG. 2b is the same embodiment as FIG. 2a but viewed from a different angle. The plasma torch 101 can be conceptually divided into two halves. The front half, indicated by the arrow F in FIGS. 1, 2a and 2b, contains the electrodes and cavities to which gas is fed for ionisation and from which the two-stage plasma is emitted in use. The front half of the plasma torch 101 is constructed by two user-replaceable modular components, facilitating servicing of the plasma torch 101 when the electrodes therein become worn. The rear half of the plasma torch 101, indicated by the arrow R in FIGS. 1, 2a and 2b, acts to support and retain the components of the front half and to provide a coupling to the feed gas supply to enable sealed fluid communication of the feed gas from the feed gas supply to the cavities 33, 34 in the front halfand to electrically couple the electrodes 2, 6 in the front half F to an electrical power source.

[0089] The components of the plasma torch 101 in the front half F are encased in a grounded stainless steel casing 1. The casing 1 is tubular and tapered in form, with the front end of the casing 1, comprising the opening 109, having a smaller diameter than the rear end of the casing 1. The tapered shape of the casing 1 gives the operator an increased field of vision, such that the operator has improved visibility of the area requiring treatment. This has particular benefit in treatments requiring a higher level of precision, where the operator requires a clear view of where the plasma plume is contacting the surface requiring treatment.

[0090] A grounded stainless steel body 31 forms the rear end R of plasma torch 101. Threaded portions (not shown) may be provided on casing 1 and stainless steel body 31 to allow the front F and rear R parts of the torch to be mated. The body 31 has towards its front end a solid block machined into a perforated bulkhead 32 that acts to retain certain other components of the plasma torch 101 and to admit feed gas and electrical coupling wires from the rear to the front of the plasma torch 101. A grounded rod 104 is provided in the rear part of the plasma torch 101. A bore 20 in the bulkhead 32 forms a cavity sized to receive the grounded rod 104, which acts as the ground reference for the grounded components of the plasma torch 101.

[0091] A cathode rod 2, formed of either tungsten, lanthanated tungsten, ceriated tungsten or thoriated tungsten, is provided in the front half of the plasma torch 101 to extend along the central axis thereof. Arranged coaxially around the cathode rod 2 and spaced apart therefrom, there is provided a grounded stainless steel arc tube 3. A cylindrical annular cavity 33 formed between the rod 2 and the grounded tube 3 is open at its front end 105 but it is sealed at its back end, except for feed gas inlets. As will be explained in greater detail below, in use, the cathode rod 2 is provided with an electrical power signal sufficient to create an arc between the cathode rod 2 and the grounded tube 3 which is used to generate a hot thermal plasma in the cylindrical annular cavity 33 that is then emitted from the open front end 105 of the cavity 33.

[0092] It should be noted that the axial extent of the cathode rod 2 at the front end thereof is recessed relative to the open end of the front of the grounded tube 3. This relative positioning causes a force to be generated by the fluid dynamics of the flowing feed gas in use, which causes the central thermal plasma to be accelerated towards the central axis of the plasma torch 101 causing the hot stage of the plasma plume to become focused. As will be discussed in more detail later, the grounded tube 3 comprises a lip 9, which acts to restrict the opening 105, and in use helps to control the fluence of the thermal plasma, to collimate and focus the thermal plasma onto the treatment surface, and also to control the angular distribution of the thermal plasma emitted from the open end 105 of the plasma torch 101.

[0093] The cathode rod 2 comprises an emissive material, and is tapered, or pointed, in form at the front end nearest the opening 105, thus allowing the location of the arc discharge on the cathode rod 2 to be, in use, fixed at the pointed end of the cathode 2. Such a pointed end may allow repeatability of the location of the arc discharge since electric field lines are concentrated at sharp points and edges, which locally increases the likelihood of electrical breakdown. Furthermore, a sharpened emissive cathode may also benefit from a faster warm-up period, due to the concentration of heating at the pointed tip of the cathode rod.

[0094] Arranged coaxially around the grounded tube 3 and spaced apart therefrom is a Borosilicate glass or ceramic (Boron Nitride/Alumina) tube 5 that has a dielectric constant of around 4.6 and that acts as a dielectric barrier to a high-voltage copper electrode 6 arranged radially outwardly thereof. A second cylindrical cavity 34 is formed between the grounded tube 3 and the dielectric barrier tube 5 that is open at its front end but is sealed at its back end by bulkhead 32, except for inlets formed by bores 20 in the bulkhead 32 that enable the passage of feed gas, and a coaxial power supply cable 8 from the rear R to the front F of the plasma torch 101. In use, the high-voltage electrode 6 is provided with an electrical power signal sufficient to create a dielectric barrier discharge between the dielectric barrier tube 5 and the grounded tube 3 which is used to generate a cold non-thermal plasma in the cylindrical annular cavity 34 that is then emitted from the open front end 106 of the cavity 34. The high-voltage electrode 6 is connected to a brass threaded rod 7 acting as a high voltage connector and having a conductive core of a coaxial cable 8 soldered to it. In use, the coaxial cable 8 conducts the high-voltage electric power signal generated by a power supply to the high-voltage electrode 6.

[0095] A ceramic (Boron Nitride/Alumina) block 12 is arranged to extend around the high-voltage electrode 6 to electrically and thermally insulate the high-voltage electrode 6 from all other grounded metal surfaces. A bore is formed on the block 12 to receive the coaxial cable core 8 for connection to the high-voltage electrode 6 via the high-voltage connector 7. A further bore (not shown) is formed in the block 12 to receive a thermocouple (not shown) arranged to monitor temperature of the high-voltage electrode 6 in use to ensure that it does not overheat. Holes are provided through the bulkhead 32 registered to the bores provided in the block 12 for passing the thermocouple and coaxial cable from the rear to the front of the plasma torch 101.

[0096] To the rear of the bulkhead 32, there is provided a large central bore that contains a brass cathode connector 16. A bore in the brass cathode connector 16 forms a cavity sized to receive a stainless steel cathode base 15 with an interference fit therein. The cathode 2 is supported by and extends from the cathode base 15 to the front of the plasma torch 101, via a bore in the bulkhead 32.

[0097] The grounded tube 3 has on its radially outward facing surface a screw thread 14 that mutually co-operates with a screw thread 14 provided on a radially inner surface of a central bore of the bulkhead 32, such that the grounded tube 3 is releasably engageable with the grounded steel body 31 and is grounded thereby in use.

[0098] In the embodiment, a replaceable cold tip module is provided by the grounded casing 1 and comprises at least the dielectric tube 5 and high-voltage electrode 6. These components are provided together in a single assembly that is releasably engageable with the body of the plasma torch 101. A replaceable hot tip module is provided by the cathode 2, grounded tube 3, and cathode base 15. These components are provided together in a single assembly that is releasably engageable with the body of the plasma torch 101.

[0099] The cold tip and hot tip modules can be easily replaced by the user to service the plasma torch 101 when the electrodes thereof become worn. In other embodiments, the cold tip, which includes the high-voltage electrode 6 at least, and the hot tip, which includes the cathode 2 at least, may be constructed differently and have different components in the assembly to that shown for the embodiment described in detail in FIG. 2a. For example, as is shown in FIG. 3b, a fastening mechanism other than a screw thread may be usable to connect the hot tip and cold tip modules to the body of the plasma torch 101.

[0100] To the rear of the rear end R of the plasma torch 101, the plasma torch 101 is sealed by a radially extending feed through plate 24 having holes therethrough and connectors for interfacing with a power supply and a gas supply. Both feed gas connectors 102, 108 extend through the holes provided in the feed through plate 24.

[0101] To the rear of the bulkhead 32, a chamber 23 is provided which is closed at the rear end by the cathode base 15, except for an outlet from feed gas connector 108. The gas supplied to ionisation cavity 33 for production of the hot thermal plasma is fed from the feed gas supply to cavity 33 via feed gas connector 108, which mates with the cathode base 15. In use, the feed gas supply for the central, thermal plasma to be ionised in cavity 33 is connected to feed gas connector 108. A fluid communication channel is thereby provided between the feed gas connector 108 and the cavity 33 via grooves provided through the stainless steel cathode base 15 that allow the feed gas to pass from cathode base 15 into chamber 23 and then from chamber 23 through into the cavity 33 formed in the space between the cathode rod 2 and the grounded tube 3.

[0102] The gas supplied to ionisation cavity 34 for production of the cold non-thermal plasma is fed from the feed gas supply to cavity 34 via feed gas connector 102. The cold feed gas connector 102 extends through a hole in the feed through plate 24, and through a hole, or bore, in the bulkhead 32. In use, the cold feed gas supply for the non-thermal plasma to be ionised in cavity 34 is connected to the feed gas connector 102. Nitrile O-rings (not shown) arranged between the feed through plate 24 and the body 31 provide a seal between the external atmosphere and the interior of the device when under compression. A bore (not shown) in the bulkhead 32 provided between feed gas connector 102 and cavity 34 provides a fluid communication path for the cold feed gas from feed gas connector 102 at the rear R of the plasma torch 101 to the front of the plasma torch 101.

[0103] The bore accommodating the cold feed gas connector 102 also performs the function of providing a passageway for the high-voltage coaxial cable 8 that extends from a hole in the feed through plate 24 at the rear of the plasma torch 101, through feed gas connector 102, through the bore 20 in the bulkhead 32, and through a bore in the ceramic insulator 12. At the front of the bore in the ceramic insulator 12 the conductive core of the coaxial cable 8 is connected to the high-voltage electrode 6 by a high-voltage connector 7. In this way, a conductive connection is formed between the high-voltage electrode 6 and a power supply via electrical power cabling (not shown).

[0104] To connect a power supply (not shown) to the cathode 2, single core wires extending into the plasma torch 101 via holes in the feed through plate 24 are soldered to the cathode connector 16. In this way, a conductive connection is formed between the cathode 2 and a power supply via electrical power cabling.

[0105] In the embodiment shown in FIG. 2a, the first cavity 33 and second cavity 34 are sealed from each other such that they are not in fluid communication (except via the open front ends) and separate gas supplies are connected to feed the first 33 and second 34 cavities separately. Noble gases such as nitrogen or argon or mixtures thereof may be used as feed gases and different types or compositions of these gases may be fed separately to the first 33 and second 34 cavities. Alternatively, the same type or composition of gases may be fed separately to both the first 33 and second 34 cavities. Alternatively, in other embodiments, the fluid passages for communicating feed gas from the rear R to the front F of the plasma torch 101 may be unified/in fluid communication such that a single gas supply may be used to feed gas of the same type to the first 33 and second 34 cavities.

[0106] Screw 107 is engaged with the bulkhead 32 in the rear end R of the plasma torch 101. Threaded portions (not shown) are provided in a bore in the bulkhead 32, the bore extending through the body 31 and connecting a radially outward facing surface of the body 31 to a radially outward facing surface of the grounded tube 3. The bolt also comprises a threaded portion which allows the bolt 107 to mate with the bore in the bulkhead 32 in use. When fully mated, the bolt 107 extends from the radially outward facing surface of the body 31 to the radially outward facing surface of the grounded tube 3, and makes contact with the grounded tube 3. In use, the screw 107 provides a ground connection to the body 31.

[0107] FIGS. 3a and 3b show another embodiment of the apparatus 200 for generating a plasma plume in accordance with an embodiment of aspects of the invention which includes a plasma torch 201. Plasma torch 201 functions in the same way as the embodiment shown in FIGS. 1, 2a and 2b. In contrast to FIGS. 1, 2a and 2b, the embodiment shown in FIGS. 3a and 3b comprises a cathode rod 241 and grounded tube 203 which extend outwith a casing 201, such that an open front end 205 from where a hot thermal plasma is emitted extends further along a main axis of the plasma torch 201 than an open front end 206 from where a cold non-thermal plasma is emitted. Such a configuration provides improved visibility of the plasma plume emitted from the open end of the plasma torch and also improved visibility of the tissue being treated. This allows a more precise application of the plasma to the tissue requiring treatment.

[0108] A replaceable hot tip module 242 is provided by the cathode rod 241, grounded tube 203, and cathode base 215. These components are provided together in a single assembly that is releasably engageable with the body of the plasma torch 201 by means of a spring-loaded bayonet mechanism.

[0109] The spring-loaded bayonet mechanism comprises a threaded retainer 240 for attaching the mechanism to the plasma torch 201, spring 244 and retaining bayonet pins 246. In use, the hot tip module 242 is inserted into the plasma torch 201 and passes the bayonet pins 246 due to appropriately shaped channels 245 (such as V-shaped channels) in grounded tube 203. The module 242 is then pushed against the spring 244 and the channels 245 engage with the bayonet pins 246. Whilst pushing, the hot tip module 242 is then turned clockwise to lock the module 242 in place. When in the locked position, an electrical connection is made between the cathode base 215 and a high voltage cable 248 supplying power to the cathode rod 241 in use.

[0110] To remove the hot tip module 242, the module 242 is pushed against the spring 244 and turned in an anti-clockwise direction to disengage the module 242 from the bayonet pins 246, and thus releasing the module 242 from the plasma torch 201.

[0111] In some embodiments, each bayonet pin 246 has identical dimensions, that is each bayonet pin 246 is the same size. In some embodiments, each bayonet pin 246 has different dimensions, that is a different size, such that the hot tip module 242 can only be inserted in one orientation.

[0112] Operation of the apparatus 100 to generate the two-stage cooperative plasma plume will now be described with reference to FIGS. 4 and 5.

[0113] In order to begin production of the two-stage plasma, the gas supply in the system control unit is caused by the controller in response to user operation of the controls to begin releasing feed gas under pressure to the first 33 and second 34 cavities via a gas supply conduit (not shown). Then the controller causes the power supply to generate electrical power signals which are provided to the cathode 2 and high-voltage electrode 6 via the electrical power cabling.

[0114] FIG. 4 shows the pointed tip of the cathode rod 2, the grounded tube 3 with lip 9, and the cavity 33 therebetween. The cathode 2 is connected to a DC power supply provided by the power supply. The DC power supply consists of a constant supply at 25V, 4.2A DC plus a ballast/ignitor high-voltage pulse circuit to initiate the arc discharge. This DC power supply generates and sustains a voltage and current vs time waveform as shown in FIG. 7 in which an initial voltage pulse of 100-200V is applied by the ballast/igniter circuit which, as the electrical field breaks down and an electrical arc is initiated between the cathode 2 and the grounded tube 3 through the feed gas then settles down to around 20-60V DC steady state. The electrical arc provides the heating and ionisation mechanism for generating from the feed gas the highly ionised, high-energy thermal plasma that provides the hot component of the device's plasma plume. Once the feed gas flows into the cavity 33 as described above, the electrical power signal provided to the cathode rod 2 causes an electrical discharge inside the cavity 33 creating an arc discharge 41 between the cathode rod 2 and the grounded tube 3. The arc discharge 41 ionises the feed gas, creating a thermal plasma. The thermal plasma is propagated in use towards the open end 105 of the plasma torch 101 by the dynamics of the flowing feed gas where it is then emitted.

[0115] The thermal plasma then concentrates at a concentration point P in front of the plasma torch 101. The concentration point P is located on the tissue requiring treatment 50, such as skin. As a result, the apparatus 100 achieves a significantly improved tissue resurfacing, regenerating and rejuvenating effect compared to known plasma tissue resurfacing devices, improving patient outcomes in both cosmetic and surgical tissue treatments. Indeed, the patient outcomes achieved by the apparatus 100 are comparable in order to the known laser systems, described above, without any of the attendant disadvantages like the pin-prick patterning on the skin. Instead, the finish on skin for cosmetic treatments using the two-stage plasma is smoother and more easily blended such that cosmetic treatment of smaller zones of the skin is enabled while still providing a homogeneous surface finish.

[0116] The plasma generation system 100 may be configured such that, in use, the spot size and shape of the plume may be adjustable. Characteristics of the plasma 601 such as the fluence and the spot size at the concentration point P, can be altered depending on the characteristics and dimensions of the lip 9, and resulting size and dimensions of the open end 105. The fluence may also be manipulated by varying the distance, or recess, between the pointed tip of the cathode rod 2 and the lip 9.

[0117] Depending on the distribution of energy required to treat the tissue 50, it is desirable that the operator of the plasma torch 101 can vary the geometry of the cathode rod 2 and the lip 9. A metric useful for assessing the energy of the plasma 601 is fluence, defined as the energy of the plasma 601 (Joules, J) divided by the area of the incident spot on the treatment surface 50 (in cm.sup.2). The area of the incident spot on the treatment surface 50 is related to the area of opening 105. Generally, the greater the fluence of the plasma 601, the greater the depth of penetration and rejuvenation of the dermis.

[0118] One way to manipulate the fluence, and thus the spatial distribution of the energy delivered to the treatment surface 50, is by varying the location and dimensions of the arc discharge 41. This can be achieved by altering the recess 43 between the pointed tip of the cathode rod 2 and the lip 9, and the separation 42 between the tip of the cathode rod 2 and the grounded tube 3. Adjusting and fine tuning the relative axial positioning of the front ends of the cathode 2 and grounded tube 3 alters the directionality of the forces that act on the thermal plasma, and consequently alters the fluence of the plasma 601, as well as altering the concentration distance P and spot size on the treatment surface 50. The axial positioning can be manipulated by, for example, providing a user-controllable electrode geometry alteration mechanism in the plasma torch, such as a mechanical scroll wheel, or by means of controls.

[0119] The fluence, spot size, and other characteristics of the plasma 601 may also be manipulated by varying the geometry of the lip 9, for example the width 45 of the resulting opening 105 and the depth 44. A larger lip depth 44 can help to collimate and focus the plasma 601 on the treatment surface 50.

[0120] The radial extent of the lip 9 from the grounded tube 3 towards the central axis of the plasma torch 101 determines the width 45 of the resulting opening 105. Furthermore, the end of the lip 9 defining the opening 105 may be flat, or in some embodiments it may be angled, thus allowing the angular distribution of the plasma 601 to be manipulated. An angled lip 9 results in a plasma 601 which is emitted from the plasma torch 101 towards a concentration point located at a distance away from the central axis of the plasma torch 101. This may provide some benefit because it may provide an operator with improved visibility of the plasma 601 and the tissue being treated which could be useful where a higher level of precision is required when treating the surface 50.

[0121] Since fluence is determined by the energy of the plasma divided by the area of the opening 105, a smaller width 45 will result in a higher fluence whereas a larger width 45 will result in a smaller fluence, for the same plasma energy. Therefore, a smaller width 45 allows a more highly focused, higher-energy plasma 601, with a much smaller, more centralised, spot size which is particularly suited in treatments requiring a high level of precision, such as where the treatment area is very small, for example deep laughter line wrinkles formed around the mouth. Furthermore, a high fluence enables a more penetrative effect on the tissue 50, thus allowing deeper layers of tissue, such as skin, to be treated.

[0122] On the other hand, a larger width 45 results in a less focused, lower-energy, plasma 601, with a much larger, less centralised, spot size. The larger spot size may be around 1-2 mm away from the concentration point P, which lies on the central axis of the plasma torch 101. It is more difficult to precisely target specific areas for treatment using a larger spot size, instead they are more suited to treating larger areas of tissue with little precision, such as blending treated laughter lines and to treat wider areas of fine wrinkles, such as crow's feet around the eyes.

[0123] It is conceivable that the user could select from a range of detachable and interchangeable tubes when deciding on the most suitable distribution of energy for a treatment, and install these tubes with bespoke tooling before a procedure. For example, there are a variety of different detachable tubes with different lip widths and depths, and also different lip angles, which can be selected from when deciding on the distribution of energy required.

[0124] Further controls may be provided in the plasma control system operable, for example, from the control panel which may allow the user to adjust the spot size or plume geometry by causing the feed gas pressure to be increased or decreased or providing a power supply unit operable in use to enable increasing or decreasing or otherwise changing the power supply waveforms to the electrodes to generate the one or both of the two plasma stages. Finely adjusting these parameters individually or in combination, particularly with the electrode and lip geometries discussed above, allows a variety of spot sizes and plume geometries to be achievable, allowing the plasma generation device to provide a palette of plasma plumes usable in a variety of different ways to facilitate treatment of different wrinkles and skin irregularities, and to facilitate blending.

[0125] As shown in FIG. 5, to generate the cold stage of the plasma, the high-voltage electrode 6 is connected to a high-voltage pulse width modulated (PWM) power supply provided by power supply (in other embodiments, an AC power supply may be used rather than a PWM, but a PWM is more efficient and effective in this context). The high-voltage PWM power supply consists of a variable frequency PWM power supply providing a PWM voltage signal to high voltage electrode 6 as shown in FIG. 8 of 2-8 kV, 25 mA at a frequency of 23 kHz up to RF for the duration of the cold stage discharge (two discharge pulses are shown in FIG. 8). This powers a dielectric barrier discharge between the grounded tube 3 and the dielectric barrier layer tube 5, providing the plasma production mechanism that weekly ionises the feed gas in cavity 34 that is convected downstream under pressure to provide an emission of annular, relatively low energy, non-thermal plasma as a cold stage shaped as a halo 603 surrounding the central high-energy, thermal plasma 601 (as shown in FIG. 6). The dielectric barrier discharge produces in the cold halo plasma a relatively high proportion of free radicals, which have a sterilising effect when incident on the tissue.

[0126] As shown in FIG. 6, the high-energy central thermal plasma 601 has a collimating and focusing effect on the surrounding convected relatively low energy dielectric barrier halo plasma 603 which, due to a shear induced turbulent flux from the thermal plasma 601, becomes entrained with the thermal plasma 601 to produce a cooperative, focused plasma plume 610. The plume 610 has a high-energy central plasma spot with a relatively high degree of free radicals that is used to ablate tissue and heat subsurface dermal layers. This is surrounded by an entrained sterilizing, relatively low energy, non-thermal plasma halo, which is the source of the free radicals, which acts to sterilise the trauma induced in the tissue in situ and to promote healing thereof.

[0127] When the cooperative plasma plume 610 is used to rejuvenate skin tissue and to treat deep wrinkles and other significant skin irregularities, the ablated surface layers of the tissue are not immediately vaporised and are instead caused to disintegrate and slough off over the course of a few hours to days. In the meantime, the heating and trauma caused to the subsurface epidermal and dermal layers that encourage collagen and elastin production and rejuvenation are sterilised by the plume and protected by the remaining surface epidermal layers, thus reducing the likelihood of subsequent infection by bacteria found on the skin. In some embodiments, the traumatised subsurface layers may be provided with an in situ sterile dressing that may significantly promote healing and improve the recovery time while minimising the side-effects and downtime of the rejuvenating skin treatment.

[0128] In order to use the plasma plume 610 for cosmetic or surgical treatment, the operator would initiate the plasma plume and move the tip of the plasma torch 101 along the treatment area of the tissue at a fixed distance, in a paintbrush fashion, to achieve the desired effect and outcome. This distance is controlled using disposable patient interface tubes that allow the user to see the area and the plume of the device. For cosmetic, non-surgical use of the plasma to reduce wrinkles and rejuvenate skin, the cosmetic treatments may be performed by appropriately trained, non-medical personnel (such as a cosmetic technician) in a non-medical setting as the treatment is non-invasive and poses minimal health risks and side effects as the plasma plume itself provides a sterile dressing. For purely cosmetic treatments, the operator need not be a skilled medical professional. However, for wound debridement and for stimulating regeneration of tissue for medically curative purposes, or for cauterisation in a surgical setting or as part of a wider surgical intervention, the two-stage plasma plume will need to be operated by a medical professional.

[0129] A trigger control (not shown) may be provided on the plasma torch to initiate the release of the feed gas and the activation of the power supply by the system control unit in order to produce the co-operative plume on-demand (or just the non-thermal plasma, or just the thermal plasma) by the operator. The apparatus may be configured such that the trigger mechanism may cause the plasma plume to be constantly generated for as long as the trigger is depressed. Alternatively, the apparatus may be configured such that a short blast or pulse of plasma is generated in response to depressing of the trigger. Repeated operation of the trigger may then be necessary in order to produce plasma pulses for use in cosmetic and surgical treatments. The energy to be delivered to the surface will be controlled on the base unit.

[0130] FIG. 9 illustrates a further view of the end of an embodiment of the device. Specifically, FIG. 9 illustrates an endpiece 3a or tip for of the grounded tube 3, formed to define the lip 9, which may be inserted into an open end of a main body (not shown in FIG. 9) of the grounded tube 3 and retained therein by interference fit. Both the grounded tube 3 and the endpiece 3a may be formed of aluminium, for example. Alternatively, the grounded tube 3 may be formed to have a lip defined at its end, such that the endpiece is effectively integral therewith.

[0131] It should be appreciated that all dimensions illustrated in FIG. 9 are provided as an example. The sharp tip of the tapered cathode 2 is configured to be situated radially within the lip 9 axially proximal to the entrance of the lip 9, as illustrated in FIG. 10. Note that the lip 9 comprises a frustoconical surface 9a, which is inclined at an interior angle of 140, formed as a wall extending in from main body of the grounded tube 3 or endpiece 3a towards an inner surface 9b of the lip 9, defining an orifice having an opening width W, or inner diameter of 2 mm. The length L of the inner surface 9b of the orifice is 4 mm. The inclined angle of the frustoconical surface 9a and inner surface 9b of the lip cooperate to increase the pressure in the vented gas in that region, and also to stabilise the gas flow to enable a generation of a stable plasma output from the orifice. It should be appreciated that while FIGS. 9 and 10 feature an inclined frustoconical surface with an angle of 140, other angles which are at most 170, or at most 160 may also be utilized. Having a surface with too steep an angle, for example of 180 causes an instability in the gas flow and plasma breakdown and prolapse. In some of the embodiments, the arc is formed between the cathode 2 and grounded tube 3, being stably pinned not only at the tip 2a of the cathode 2, but at the discontinuity between the frustoconical surface 9a and inner surface 9b of the lip. This gives a stable plasma generation.

[0132] While the foregoing embodiments are example plasma torches described as having the surrounding cold stage of plasma and having orifices having aspect ratios of length to width of 1:1 or, in the case of the FIGS. 9 and 10 endpiece, 2:1, these embodiments are shown and described to facilitate understanding of the present disclosure. As shown below in relation to FIG. 11, it will be understood that the present inventors have found that, by increasing the aspect ratio of the orifice to 2.5:1 or greater such that the orifice becomes more of a tunnel, significant benefits can be realised in terms of thermal energy control, plasma generation reliability and stability, and also to the extent that a surrounding halo of cold plasma can be practically dispensed with, providing an even slimmer and more ergonomic design.

[0133] Referring now to FIG. 11, which shows a plasma torch having a grounded conductive tube 3 having a lengthened endpiece 3a arranged to provide a relatively lengthened and narrowed orifice defined by the inner surface of lip 9. Here, the orifice has a length to an opening width ratio of significantly greater than 2.5:1. The aspect ratio of the orifice is at least 5:1. By having such large aspect ratios, a tunnel is defined through which the plasma produced and mixed inside the cavity is conducted, losing sufficient thermal energy to the grounded conductive tube to give a stable, relatively low thermal energy plasma suitable for reliable and predictable treatment of a patient, requiring less expertise. The cathode is recessed from the opening at the surface in the conductive tube, such that the thermal plasma is, in use, produced inside the grounded conductor tube and passes through an orifice. The plasma generation is less likely to prolapse out of the cavity, reducing the likelihood of damage to the plasma torch by mixing with the atmosphere. Further, more reliable starts and production of the plasma can be achieved. These beneficial effects are achieved compared to lower aspect ratios, such as that shown in FIGS. 9 and 10.

[0134] The orifice is configured to wick thermal energy away from the thermal plasma or plasma effluent before it is emitted from the opening in the grounded conductive chamber. Although not shown, in other embodiments, the cross section of the orifice may vary along its length to change the surface area of the wicking region.

[0135] As a result of the lengthened and narrowed orifice, although not shown, in other embodiments the cathode may not be pointed or tapered. Indeed, the cathode may have a rounded or flattened or non-pointed end.

[0136] As can be seen, the plasma torch of FIG. 11 is enabled to be a thermal plasma-only torch. Indeed, the plasma torch does not comprise components configured to produce a non-thermal plasma or dielectric barrier discharge plasma.

[0137] As the plasma is produced inside the cavity in the FIG. 11 arrangement, in other embodiments, the opening in the grounded conductor tube may be configured to direct the plasma or plasma effluent emitted therefrom in a direction away from directly towards the treatment direction in normal use.

[0138] Although not shown, a plasma active cooling mechanism may be provided. This is to further cool the thermal plasma emitted from the torch. This may be achieved by providing a mechanism for cooling the feed, for example, to cryogenic temperatues, or by mixing the produced plasma with a cooled gas. This further facilitates the reliable application of a favourable plasma to a patient.

[0139] In some embodiments, while the cathode rod may comprise tungsten, in other embodiments, the cathode rod may further comprise a material resilient to operation using non-inert feed gases. Such a material may be Lanthanum Hexaboride.

[0140] In some of the embodiments, the second arc hot spot is created pinned on the discontinuity between the frustoconical surface 9a and inner surface 9b of the lip 9. The length of the inner surface 9b serves to collimate and obscure the hotspot from exposure to the treatment surface, which aids in reducing the radiative heat exposure therefrom and thus in keeping the temperature produced by the formation of the plasma down thereby making the in vivo treatment comfortable for a patient. The plasma is thus formed in the section of the lip forward of the entrance to the lip, where the arc occurs. The plasma plume is then passed along the inner surface 9b of the lip 9 and ejected from the orifice by gas pressure, on towards the tissue. The endpiece 3a or lip section of an integrally formed grounded tube acts as a heat sink, wicking heat away from the hot plasma by the interfacing of the plasma and the inner surface 9b of the lip. This can serve to cool the hot plasma to a temperature suitable for treatment of the tissue. The inner surface is in embodiments at least 3 mm long, in other embodiments, it is at least 4 mm long, at least 5 mm long, at least 6 mm long, at least 7 mm long, or at least 8 mm long.

[0141] According to some of the example embodiments, a spacer (not shown) may be provided on the plasma torch towards an end of the lip portion. The spacer provides a constant and minimum operational distance between the opening 105 and the treatment surface (i.e., skin or wound). By creating a constant and minimum operational distance, the spot size and energy of the plasma by be kept constant during the treatment, and also limited to prevent too high a dose at smaller spot areas that would be produced by the plume between the opening 105 and the end of the spacer. According to some of the example embodiments, the spacer may be arranged to define a minimum treatment distance of at least 10 mm, at least 15 mm, at least 20 mm or at least 30 mm from the treatment surface or at most 50 mm, at most 40 mm, or at most 30 mm from the treatment surface. It should be appreciated that the further the distance from the opening 105 and the treatment surface, the greater the spot size of the plasma due to dissipation of the plume, and so the lower the treatment dosage (or energy level) of the plasma will be per unit area of the tissue surface.

[0142] According to some of the example embodiments, the device may comprise a timer used to ensure a consistent treatment time (e.g., of approximately 4 seconds) on the treatment surface. The timer may serve to limit the maximum plasma energy dose applicable to tissue in one operation of the device, which may serve to enable an operator to meter the treatment to areas of the tissue. It should be appreciated that treatment times will vary depending on the produce, patient and specific operating parameters used by the device.

[0143] The description of the preferred embodiments of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but covers modifications within the scope of the present invention as defined by the appended claims.