KR200493866Y1 - thermal plasma torch - Google Patents

Abstract

A thermal plasma torch and method are disclosed. A plasma torch abatement apparatus for treating an effluent stream from a processing tool comprises, in a plasma discharge region, an anode and a cathode arranged to generate a plasma stream from a plasma gas and an effluent stream arranged to flow the effluent stream coaxially with the plasma stream. Includes conduit. In this way, rather than intersect with the effluent stream, the plasma stream rather flows with the effluent stream. This helps to extend the reaction time of the effluent stream in the plasma stage and reduces the risk of any effluent stream completely bypassing the plasma stream. This significantly improves the abatement effect of the plasma torch.

Description

thermal plasma torch

The present invention relates to a thermal plasma torch. An embodiment relates to a thermal plasma torch abatement apparatus for treating an effluent stream from a processing tool.

Thermal plasma torches are known and are typically used to treat effluent gas streams from fabrication process tools used, for example, in the semiconductor or flat panel display fabrication industries. During such fabrication, residual fluorinated or perfluorinated compounds (PFCs) and other compounds are present in the effluent gas stream pumped from the process tool. These compounds are difficult to remove from the effluent gas stream and the release of these compounds into the environment is undesirable as they are known to have relatively high greenhouse activity.

One approach to removing PFCs and other compounds from the effluent gas stream is to use radiant burners, for example as described in EP 1 773 474. However, it is also known to use plasma torch abatement devices when fuel gases commonly used for abatement by combustion are undesirable or not readily available.

The plasma for the abatement device can be formed in a variety of ways. The microwave plasma abatement apparatus may be connected to the exhaust ports of various process chambers. Each device requires its own microwave generator, which can add significant cost to the system. Plasma torch abatement devices have advantages over microwave plasma abatement devices in terms of scalability and handling of powders (either present in the effluent stream or produced by an abatement reaction). Indeed, the presence of powder in the microwave plasma can modify the dielectric properties of the reaction tube and make microwave implantation ineffective to sustain discharge. The plasma generated by the plasma abatement device is used to destroy or reduce unwanted compounds in the effluent gas stream.

Although these devices exist for treating the effluent gas stream, each of these devices has their own drawbacks. Accordingly, it would be desirable to provide improved techniques for treatment and effluent gas streams.

According to a first aspect, there is provided a plasma torch abatement apparatus for treating an effluent stream from a processing tool, the plasma torch abatement apparatus comprising: an anode and a cathode arranged to generate a plasma stream from a plasma gas in a plasma discharge region; and an effluent stream conduit arranged to convey the effluent stream in coaxial flow with the plasma stream.

The first aspect is to recognize the suboptimal responsibility of the reduction efficiency of the existing plasma torch apparatus. In particular, the existing arrangement produces a plasma stream that is emitted by the plasma torch apparatus and this plasma stream intersects with an effluent stream to be treated later. For example, an effluent stream may flow through a conduit, and a conventional plasma torch apparatus may be circumferentially disposed on the conduit such that the plasma stream from the plasma torch apparatus radially traverses the flow of the effluent stream to exit. intersect with the flow of the stream. However, a first aspect is the recognition that the effluent stream provides a relatively short reaction time when intersecting the plasma stream and that some of the effluent stream can even completely bypass the plasma stream.

Accordingly, a plasma torch may be provided. The plasma torch may be for an abatement apparatus treating an effluent stream from a processing tool. The plasma torch may include an anode and a cathode. The anode and cathode may generate a plasma stream from the plasma gas. The plasma stream may be generated inside or inside the plasma discharge region. The plasma torch may also include an effluent stream conduit. The effluent stream conduit may be arranged, configured or directed to convey the effluent stream in coaxial flow with the plasma stream. In this way, the plasma stream rather than intersect with the effluent stream flows with the effluent stream. This helps to extend the reaction time of the effluent stream in the plasma stage and reduces the risk of any effluent stream completely bypassing the plasma stream. This significantly improves the abatement effect of the plasma torch.

In one embodiment, the effluent stream comprises an abatement reagent introduced therein. Accordingly, _{suitable abatement reagents such as H 2} O, air, O ₂ , H _{2 ,} etc. may be introduced into the effluent stream to aid the abatement reaction.

In one embodiment, the anode, cathode and effluent stream conduit are arranged to produce a plasma stream in a flow direction and convey the effluent stream to flow in the flow direction with the plasma stream. Thus, both the plasma stream and the effluent stream may be directed such that they both flow in the same direction.

In one embodiment, the effluent stream conduit is arranged to convey the effluent stream to flow coaxially within the plasma stream. Accordingly, the effluent stream may be directed inside or into the plasma stream. It also helps to avoid any effluent stream bypassing the plasma stream.

In one embodiment, the anode, cathode and effluent stream conduit are arranged to position the plasma stream as a boundary layer between at least one of the anode and cathode and the effluent stream. By providing a boundary layer, degradation of the plasma torch by the highly active compound is reduced.

In one embodiment, the anode and cathode are configured to generate the plasma stream in the shape of a cone, and the effluent stream conduit is arranged to convey the effluent stream flowably within the plasma stream along the axis of the cone.

In one embodiment, the anode and cathode are configured to produce the plasma stream in a double cone shape, and the effluent stream conduit is arranged to convey the effluent stream flowably within the plasma stream along the axis of the double cone.

In one embodiment, the anode and cathode are configured to produce a plasma stream in the shape of a double cone, each face of the double cone being joined by a throat and an outlet stream conduit within the plasma stream along the axis of the double cone and throat. arranged to flow the effluent stream in the

In one embodiment, the anode and cathode are configured to impart a rotating component to the plasma gas flow to rotate the plasma about the flow direction. To improve the stability of the plasma stream or flare, the plasma gas is stabilized by creating a spiral flow or vortex.

In one embodiment, one of the anode and cathode includes a vortex structure positioned within the gap between the anode and cathode and configured to impart a rotational component to the plasma gas flow. The vortex structure may form part of the anode and cathode or may be separate articles.

In one embodiment, the cathode comprises a generally cylindrical body housed within an anode separated by a gap through which the plasma gas flows.

In one embodiment, the conduit includes a bore in the cathode. Accordingly, the effluent stream may be arranged to flow through a bore in a cathode through which the plasma gas flows to coaxially position the effluent stream within the plasma stream.

In one embodiment, the conduit is coaxially aligned with an axis extending along the cathode. It will be appreciated that the conduit need not extend along the entire length of the cathode, nor need the conduit be located at the center of the cathode.

In one embodiment, the conduit is configured to impart a rotating component to the effluent stream to rotate the effluent stream about a direction of flow. Thus, the effluent stream can also be stabilized by creating a spiral flow or vortex. Typically, the effluent stream may be rotated in a direction consistent with the rotation of the plasma stream.

In one embodiment, the conduit includes a liner that terminates before the plasma discharge region of the cathode. Providing a liner helps to reduce degradation of the cathode by the effluent stream.

In one embodiment, the cathode comprises a high work function material proximate the plasma discharge region. Providing a high work function material helps to improve plasma ignition and generation.

In one embodiment, the cathode comprises a frusto-conical annular ring proximate the plasma discharge region.

In one embodiment, a plasma torch abatement apparatus includes a power supply unit operable to breakdown and sustain a plasma discharge.

In one embodiment, the plasma torch abatement apparatus includes a reaction zone _{proximate to the anode and operable to receive reagents that promote abatement (eg, H 2} O, air, O ₂ , H _{2 , etc.).} In one embodiment, the reaction zone may be downstream of the anode.

According to a second aspect, there is provided a method of treating an effluent stream from a processing tool, the method comprising: generating a plasma stream from a plasma gas using an anode and a cathode within a plasma discharge region; and conveying the effluent stream in coaxial flow with the plasma stream.

In one embodiment, the effluent strip includes an abatement reagent introduced therein.

In one embodiment, the method includes generating a plasma stream in a flow direction and conveying an effluent stream to flow in a flow direction with the plasma stream.

In one embodiment, the method comprises conveying the effluent stream to flow coaxially within the plasma stream.

In one embodiment, the method includes positioning the plasma stream as a boundary layer between at least one of an anode and a cathode and an effluent stream.

In one embodiment, the method comprises generating a plasma stream as a cone and conveying the effluent stream to flow in the plasma stream along an axis of the cone.

In one embodiment, the method comprises generating the plasma stream as a double cone and conveying the effluent stream to flow in the plasma stream along the axis of the double cone.

In one embodiment, the method comprises generating a plasma stream as a double cone in which each face of the double cone is joined by a neck and conveying the effluent stream flowably in the plasma stream along the axis of the double cone and the neck. include

In one embodiment, the method includes imparting a rotating component to the plasma gas to rotate the plasma about a direction of flow.

In one embodiment, the method includes positioning a vortex structure within a gap between an anode and a cathode to impart a rotating component to the plasma gas.

In one embodiment, the cathode comprises a generally cylindrical body housed within the anode separated by a gap through which the plasma gas flows.

In one embodiment, the conduit includes a bore in the cathode.

In one embodiment, the conduit is coaxially aligned with an axis extending along the cathode.

In one embodiment, the method comprises imparting a rotating component to the effluent stream to rotate the effluent stream about a direction of flow.

In one embodiment, the conduit includes a liner that terminates before the plasma discharge region of the cathode.

In one embodiment, the cathode comprises a high work function material proximate the plasma discharge region.

In one embodiment, the cathode comprises a frusto-conical annular ring proximate the plasma discharge region.

In one embodiment, the method includes generating a disruption and continuation of a plasma discharge by a power supply unit.

_{In one embodiment, the method comprises receiving a reagent (eg, H 2} O, air, O ₂ , H _{2 ,} etc.) to promote abatement in a reaction zone proximate to the anode. In one embodiment, the reaction zone may be downstream of the anode.

Further particular and preferred embodiments are set forth in the accompanying independent and dependent claims. Features of the dependent claims may, where appropriate, be combined with those of the independent claims, and other combinations thereof are expressly recited in the claims.

Where a device feature is described as being operable to provide a function, it will be understood to include a device that provides the function, or is adapted or configured to provide the function.

Now, embodiments of the present invention will be further described with reference to the accompanying drawings.
1 shows a plasma torch according to an embodiment;
FIG. 2 shows the eddy current element shown in FIG. 1 in more detail.

Before discussing the embodiments in any further detail, an overview will first be provided. Embodiments provide an arrangement in which the effluent stream is mixed with the plasma stream by a plasma torch such that the effluent stream flows together in the same direction, rather than simply passing the effluent stream through the plasma stream in a downstream reaction chamber. In particular, the plasma torch has a conduit for introducing an effluent stream to create a plasma stream and flow therewith. Allowing the effluent stream and the plasma stream to flow together, rather than allowing the effluent stream to intersect the plasma stream in the reaction chamber, extends the reaction time and allows the plasma apparatus to apply more energy to the effluent stream to improve abatement.

Typically, the effluent stream is introduced into the plasma stream so that the plasma stream surrounds the effluent stream and also reduces the likelihood that the effluent stream will bypass the plasma stream. The plasma gas used to generate the plasma stream also helps to cool the torch cathode and provides a boundary layer that stays close to the surface of the plasma torch components to reduce the extent to which reaction byproducts corrode these components.

plasma torch

1 shows a plasma torch, generally denoted by reference numeral 10 in a cross-sectional view; Plasma torch 10 includes a generally tubular cathode 12 situated within an opening upstream of a generally tubular anode 14 . The tubular anode 14 is generally kept cool by moving a liquid coolant around its surface. An annular space 16 is provided between the cathode 12 and the anode 14, through which a plasma source gas such as argon or nitrogen can flow.

Cathode 12 and optionally anode 14 are a power source that can be configured to apply direct current between cathode 12 and anode 14 or alternating current to one or both of cathode 12 and anode 14 not shown) is electrically connected. The magnitude and frequency of the required current is generally determined and selected with reference to the effluent stream or plasma source gas species and other process parameters such as flow rate, cathode-anode spacing, gas temperature, and the like. The voltage magnitude of the plasma discharge is directly affected by these parameters. In any case, a suitable initial high voltage regime causes the plasma source gas to ionize to form a plasma (in a process known as decay).

double cone construction

The internal geometry of the anode 14 includes a first inwardly tapering frusto-conical portion 18 (running from the upstream end A to the downstream end B) leading to the neck portion 20 on the substantially parallel side. wherein the neck portion leads to an outwardly tapering frusto-conical portion 22 . The effect of this geometry is to accelerate and compress the incoming gas to create a region 24 of relatively high velocity relatively compressed gas in the region immediately downstream of the cathode 12 .

The frusto-conical portion 22 may adjoin the reaction zone containing (additional) reagents necessary to cope with the abatement reaction or to treat by-products; For example, these reagents may be water supplied by a water wall along a reaction tube or by a spray nozzle.

annular ring

Cathode 12 includes a generally cylindrical body portion followed by a chamfered free end, the outer geometry of which substantially matches the inner geometry of inwardly tapering frusto-conical portion 18 of anode 14 . The cylindrical body portion of the cathode 12 is made of a highly conductive metal such as copper. The chamfered free end of the cathode 12 is formed by an annular ring 32 . An annular ring 32 is positioned coaxially on the cathode 12 . The annular ring 32 provides a preferential discharge site. This is accomplished by selecting a different material for the annular ring 32 than the main body of the cathode such that the cathode body is formed of a conductive material having a higher thermal conductivity than that of the thermionic material of the annular ring 32 . For example, it would be typical to use a copper cathode body and a hafnium or thorium tungsten annular ring 32 . The anode 14 may be formed of a material similar to the main body of the cathode 12 , for example copper.

The annular ring 32 is positioned in a region 24 of relatively high velocity, relatively compressed gas. The effect of such an arrangement is to create a preferential discharge region for the plasma source gas and the arc is supplied by the source gas in a relatively compressed high-speed state. The plasma discharge thus condenses in a small area 24 just below the cathode 12 , is guided by the frusto-conical portion 18 of the anode 14 and exits as a jet through the neck portion 20 , and thereafter the anode It expands and decelerates at the outwardly tapering frusto-conical portion 22 of (14).

To create a plasma, a plasma source gas (typically a suitably inert ionizable gas such as nitrogen or argon) is delivered to the annular space 16 through an inlet manifold (not shown). In order to start or start the plasma torch 10 , a collapse must first be created between the annular ring 32 and the anode 14 . This is typically accomplished by a high frequency, high voltage signal that may be provided by a generator associated with a power source (not shown) for the plasma torch 10 . The difference in thermal conductivity between the body of cathode 12 and the annular ring 32 means that the cathode temperature will be higher and electrons are preferentially emitted from the annular ring 32 . Therefore, when a signal is provided between the cathode 12 and the anode 14 , an arc discharge is induced in the plasma source gas flowing into the region 24 . The arc forms a current path between the anode 14 and the cathode 12 , after which the plasma is maintained by a controlled direct current between the anode 14 and the cathode 12 . The plasma source gas passing through the neck 20 creates a high momentum plasma flare of the ionized plasma source gas.

vortex element

In most cases, plasma flares are unstable and can cause anode corrosion. Thus, it needs to be stabilized by creating a spiral flow or vortex of plasma source gas between the anode 14 and cathode 12 . This spiral flow, or vortex, causes the arc to rotate to change its point of attachment, thereby avoiding anode corrosion. One way to create a vortex or gas vortex is to use a vortex element 40 on the surface of the cathode 12 .

As shown in more detail in FIG. 2 , the vortex element 40 comprises a plurality of non-linear (eg, partially-helical) grooves 44 or a conduit 46 . The effect of the conduits 46 or grooves 44 is to cause discrete sub-streams of the plasma source gas to flow along a helical trajectory, thereby creating a vortex in the region 24 where the individual sub-streams of gas converge. The rotating component of the momentum of the gas as it exits through the throat 20 causes the plasma jet to self-stabilize.

The vortex element 40 is formed of an electrically conductive metal or alloy that can withstand temperatures in excess of 200° C., such as copper, stainless steel or tungsten. In this example, the vortex element 40 is integral and is formed of the same material as the cathode 12 . However, the vortex element 40 may be a separate element that is rigidly coupled to and electrically connected to the cathode body.

insulation liner

For torch 10 to function, cathode 12 and anode 40 must be electrically isolated from each other. For that reason, any element interposed between and in contact with both cathode 12 and anode 14 must be electrically insulated.

Thus, the outer surface of the vortex element 40 cooperates with the inner surface of the annular ceramic liner 50 coaxially interposed between the outer surface of the vortex element 40 and the inner surface of the anode 14 to form a ceramic electrical insulator. is formed to provide a break). The downstream end of the ceramic liner 50 has an inner chamfered portion that matches the outer geometry of the annular ring 32 . The ceramic liner 50 is a continuation of and coplanar with the tapered surface 18 of the anode 14 and the radially outermost surface 56 consistent with the geometry of the annular recess 54 . It has a radially innermost surface 58 . Ceramic liner 50 is positioned to cooperate with vortex element 40 to form a stabilizing plasma source gas vortex. The ceramic liner 50 may extend toward each axial side of the vortex element 40 , or at least toward the downstream axial direction to ensure that no arcing occurs between the vortex element 40 and the anode 14 .

When assembled, the cathode 12 is concentrically positioned within a ceramic liner 50 that is positioned concentrically within the copper anode 14 . Accordingly, the anode 14 and the cathode 12 are spaced apart from each other to provide a conduit 16 therebetween. It will be appreciated that rather than forming helical channels or grooves in the vortex element 40 , they may rather be formed in the ceramic liner 50 .

Ceramic liner 50 is made of a dielectric material that functions as an electrical insulator between cathode 12 and anode 14 and is also somewhat resistant to chemical erosion by highly reactive plasma ions. The ceramic liner 50 is manufactured by high temperature resin, mica, glass and borosilicate (eg MACOR ^® manufactured by Corning International or DOTHERM GmbH & Co. KG, all of which have high heat resistance and electrical insulation properties). DOTEC ^® or DOTHERM ^® ) made by commercially available, inexpensive and easily machinable ceramics such as materials formed by boron nitride, silicon nitride or alumina.

outflow conduit

The cathode 12 is provided with a bore 60 extending therethrough. In this example, the bores 60 are arranged coaxially and concentrically. The bore 60 is lined with a ceramic liner 62 through which the effluent stream passes. The effluent stream is introduced through an inlet (not shown) and flows in a direction (A to B). Additional reagents required for the abatement reaction (eg, H ₂ O, air, O ₂ , H _{2 ,} etc.) may be mixed with the effluent stream in bore 60 created by ceramic liner 62 . The ceramic liner 62 has a tapered portion at its downstream end, which reduces the thickness of the ceramic liner 62 in the vicinity of the annular ring 32 . Ceramic liner 62 may be made of a material similar to ceramic liner 50 . It will also be appreciated that, although in this embodiment the ceramic liner 62 is aligned concentrically and coaxially within the cathode 12, this is not necessarily the case and multiple conduits may be provided.

In operation, once a plasma vortex is created, the effluent stream is directed through ceramic liner 62 and introduced into region 24 . The effluent gas stream is surrounded by the plasma vortex and during the entire period that the plasma vortex and the effluent stream pass from the first inwardly tapered truncated-conical portion 18 through the neck portion 20 and outwardly tapered truncated-conical portion 22 . reduction occurs. This helps to improve the abatement by extending the reaction time. Also, since the effluent stream is introduced into the plasma vortex, the likelihood that the effluent stream will bypass the plasma stream is minimized. This significantly improves the effectiveness of the abatement. The provision of the rotating plasma source gas also provides a boundary layer that serves as a barrier to prevent the effluent stream and abatement by-products from contacting the anode 14 or cathode 12 .

As noted above, the key to efficient plasma abatement of an effluent stream, such as a process gas flow, is to ensure rapid and complete mixing of the effluent stream with the thermal (hot) plasma while preventing corrosion and clogging of the apparatus. An embodiment provides an effluent gas stream to be mixed with the plasma in the plasma torch, thereby providing little opportunity for the effluent stream to bypass the plasma. Embodiments use plasma as a barrier to protect the components of the plasma torch from reaction byproducts. In particular, the cold boundary layer of the plasma source gas stays close to the surface of the components of the plasma torch, thus reducing the extent to which reaction byproducts corrode them.

An embodiment provides a vortex stabilized DC arc plasma torch having a tubular cathode 12 into which an effluent stream is injected. The use of vortex stabilization prevents the effluent stream and effluent stream abatement by-products from contacting the anode 14 and cathode 12, while also trapping the effluent stream flow so that the plasma rotating arc (which is the hottest and most reactive portion of the plasma) create a nitrogen plasma cone that acts as a barrier forcing it through the central core of This can dramatically improve the reduction _{of CF 4} , which is a compound that requires a particularly high temperature for its decay.

In an embodiment, the cathode 12 is (used in the prior art) allowing a higher operating temperature of the cathode 12 which reduces deposition and prevents corrosion due to effluent stream by-products from poly and metal etching processes. It is cooled by nitrogen gas instead of water. In addition, this nitrogen stream preheated by cathode 12 is later used as a plasma source to effectively transfer heat lost from cathode 12 back to the plasma torch. This typically helps to save about 5% of power loss. Due to the shape and characteristics of the anode 14 and cathode 12, the operating voltage will be higher, which also improves efficiency by reducing the current. Reducing the current also helps to reduce the corrosion rate of both the cathode 12 and the anode 14 because the arc corrosion rate depends primarily on the arc current.

The thorium tungsten annular ring 32 provides a substantial surface for seeding the plasma arc during ignition and is exceptionally heat resistant. The size and shape of the vortex element 40 helps to sufficiently cool the cathode 12 relative to the material of construction, but maintains a temperature of about 200[deg.] C. to prevent condensation of metal etch process gases and by-products.

Although exemplary embodiments of the present invention have been disclosed in detail herein with reference to the accompanying drawings, the present invention is not limited to the precise embodiments, and various changes and modifications are made to the present invention as defined by the appended claims and their equivalents. It is understood that the present invention may be practiced by those skilled in the art without departing from the scope of the invention.

Claims (16)

A plasma torch abatement apparatus for treating an effluent stream from a processing tool, comprising:
in the plasma discharge region, an anode and a cathode arranged to generate a plasma stream from a plasma gas; and
an effluent stream conduit arranged to convey the effluent stream in coaxial flow with the plasma stream;
wherein the effluent stream conduit includes a liner terminating before the plasma discharge region of the cathode.
Plasma torch abatement device. The method of claim 1,
wherein the anode, the cathode and the effluent stream conduit are arranged to produce the plasma stream in a flow direction and convey the effluent stream to flow in the flow direction with the plasma stream.
Plasma torch abatement device. The method of claim 1,
wherein the effluent stream conduit is arranged to convey the effluent stream in a coaxial flow with the plasma stream within the plasma stream.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
wherein the anode, the cathode and the effluent stream conduit are arranged to position the plasma stream as a boundary layer between the effluent stream and at least one of the anode and the cathode.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
wherein the anode and the cathode are configured to produce the plasma stream in a cone shape and wherein the effluent stream conduit is arranged to transport the effluent stream to flow along the cone and within the plasma stream.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
wherein the anode and the cathode are configured to produce the plasma stream in the shape of a double cone and wherein the effluent stream conduit is arranged to transport the effluent stream to flow in the plasma stream along the double cone.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
The anode and the cathode are configured to produce the plasma stream in the shape of a double cone, wherein each face of the double cone is joined by a neck portion and the outlet stream conduit is configured to generate the plasma stream along the axis of the double cone and the neck portion. arranged to convey the effluent stream to flow within the plasma stream.
Plasma torch abatement device. 3. The method of claim 2,
wherein the anode and the cathode are configured to impart a rotating component to the plasma gas to rotate the plasma about the flow direction.
Plasma torch abatement device. 9. The method of claim 8,
wherein one of the anode and the cathode comprises a vortex structure positioned within a gap between the anode and the cathode and configured to impart the rotating component to the plasma gas.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
The cathode includes a cylindrical body accommodated in the anode separated by a gap through which the plasma gas flows.
Plasma torch abatement device. 11. The method of claim 10,
wherein the effluent stream conduit includes a bore in the cathode.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
wherein the effluent stream conduit is coaxially aligned with an axis extending along the cathode.
Plasma torch abatement device. 3. The method of claim 2,
wherein the effluent stream conduit is configured to impart a rotating component to the effluent stream to rotate the effluent stream about the direction of flow.
Plasma torch abatement device. delete 4. The method according to any one of claims 1 to 3,
one end of the cathode adjacent the plasma discharge region comprises a material having a lower thermal conductivity than the opposite end of the cathode.
Plasma torch abatement device. 4. The method according to any one of claims 1 to 3,
wherein the cathode comprises a truncated-conical annular ring proximate to the plasma discharge region.
Plasma torch abatement device.

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