METHOD FOR GENERATING A PLASMA FLAME AND PLASMA GENERATING DEVICE

Description

[0001] The invention relates to a method for generating a plasma flame with a plasma fuel gas which is blown out of a plasma combustion chamber through a plasma flame opening in a plasma flame direction, wherein the plasma combustion chamber is arranged at least partially in a cavity resonator and microwave energy is supplied to the cavity resonator via a waveguide in order to generate a plasma in the plasma combustion chamber, and wherein a swirl gas is blown into the plasma combustion chamber with a swirl generating device in order to generate a swirl gas jacket surrounding the plasma flame in the plasma combustion chamber, which swirl gas jacket shields a plasma combustion chamber wall made of a dielectric solid material from the plasma flame.

[0002] Such plasma flames have a very high energy density and are used in many different applications to generate a very high process temperature in a process chamber or in the vicinity of the plasma flame opening, for example, to coat, machine, or weld workpieces. A plasma is generated in a plasma combustion chamber for plasma-chemical processes. This plasma is blown out of the plasma combustion chamber with a plasma gas supplied to the plasma combustion chamber, forming a plasma flame that can be used in plasma treatment processes. The direction of the plasma flame is determined by the flow direction of the plasma gas blown out of the plasma combustion chamber through the plasma flame opening.

[0003] It is known from practice that the energy required to generate the plasma can be supplied as microwave energy via a waveguide to a cavity resonator, in which the plasma combustion chamber is arranged such that an economically viable proportion of the microwave energy in the plasma combustion chamber can be used to generate the plasma. In many cases, the direction of the plasma flame is oriented perpendicular to a propagation direction of the microwaves from the waveguide into the cavity resonator. The plasma combustion chamber can traverse the cavity resonator, and the plasma flame opening of the plasma combustion chamber can be arranged such that the plasma flame blown out of the plasma combustion chamber through the plasma flame opening also leaves the cavity resonator and can be used for its intended purpose outside the cavity resonator.

[0004] The cavity walls of the cavity resonator are typically made of an electrically conductive material to specify or fulfill the resonance conditions for the microwave energy supplied via a waveguide in the cavity resonator. In contrast, a plasma combustion chamber wall is made of a dielectric solid material and creates the microwave-transparent, spatial separation of the plasma combustion chamber and the metallic cavity resonator by a dielectric, necessary for the operation of the plasma generation device. This prevents the plasma from leaving the plasma combustion chamber or the cavity resonator, potentially spreading through the waveguide toward the generator and causing destructive effects.

[0005] The plasma generated in the plasma combustion chamber significantly heats the interior of the plasma combustion chamber and the plasma combustion chamber wall. In many cases, the maximum possible heat output of the plasma flame during operation is limited by excessive heat transfer from the plasma flame to the surrounding plasma combustion chamber wall, which can cause damage to the plasma combustion chamber wall. To avoid damage to the plasma combustion chamber wall, it is therefore necessary to prevent excessive heating of the plasma combustion chamber wall.

[0006] It is known from practice that a portion of the plasma fuel gas flowing into the plasma combustion chamber, or a separate gas, is blown into the plasma combustion chamber as a swirl gas using a swirl generation device transversely to the plasma flame direction in order to create a swirl gas jacket surrounding the plasma flame in the plasma combustion chamber, which shields the plasma combustion chamber wall from the plasma flame and thereby reduces heat transfer from the plasma flame to the surrounding plasma combustion chamber wall. The orientation of the swirl gas transversely to the plasma flame direction is preferably specified approximately tangential to the plasma combustion chamber wall, but an orientation at an angle between 0 and 90 degrees, preferably between 0 and 15 degrees, between the plasma combustion chamber wall can also be specified in order to create a swirl gas jacket flowing predominantly along the plasma combustion chamber wall.

[0007] However, it has been shown that despite such measures, the thermal output of the plasma flame that can be achieved permanently during operation is limited, with the thermal output being unevenly distributed along the direction of the plasma flame, thus regularly causing inhomogeneous heating of the plasma combustion chamber wall along the plasma flame opening, which in many cases leads to locally excessive thermal stress on the plasma combustion chamber wall and thus to damage to the plasma combustion chamber wall.

[0008] CA 3 131 641 A1 discloses a method for generating a plasma flame using a plasma fuel gas, which is blown out of a plasma combustion chamber through a plasma flame opening in a plasma flame device. CA 3 131 641 A1 discloses the features of the preambles of claims 1 and 6.

[0009] It is therefore considered an object of the present invention to design a method for generating a plasma flame as mentioned above in such a way that the plasma flame can be generated with the highest possible heat output and can be blown out of the plasma combustion chamber in a process-reliable manner.

[0010] This object is achieved according to the invention by a method according to claim 1.

[0011] The plasma combustion chamber wall projects beyond the cavity resonator in both directions along the direction of the plasma flame and is secured in a plasma combustion chamber wall holder at a distance from the cavity resonator, wherein the plasma combustion chamber wall holder has at least one holder cooling cavity through which a coolant flows. It has been shown that, particularly in an area around the plasma combustion chamber wall holder, large gradients can arise during the heating of the plasma combustion chamber wall. In order to reduce these gradients and to enable the most homogeneous heating of the plasma combustion chamber wall possible, the invention therefore provides that the plasma combustion chamber wall is secured outside the cavity resonator, not inside the cavity resonator, and furthermore, at a distance from the cavity resonator, in a plasma combustion chamber wall holder.Due to the additional distance between the plasma combustion chamber wall holder and the cavity resonator, the distance of the direct material contact between the plasma combustion chamber wall holder on the one hand and the plasma combustion chamber wall on the other hand is arranged at a distance from the cavity resonator and the energy transfer caused therein from the radiated microwave into the plasma combustion chamber.

[0012] Since the distance between the plasma combustion chamber wall mount, on the one hand, and the cavity resonator, on the other hand, cannot or should not be specified to be large in practice, the invention also provides that each plasma combustion chamber wall mount has at least one mount cooling chamber through which a coolant flows. This allows the plasma combustion chamber wall mount to be cooled, particularly in a contact area with the plasma combustion chamber wall, and unwanted heating of the plasma combustion chamber wall in the area of the plasma combustion chamber wall mounts can be reduced or avoided. In addition, the plasma combustion chamber wall in direct contact with the plasma combustion chamber wall mount can be cooled by the coolant.

[0013] According to an advantageous embodiment of the inventive concept, a coolant is conveyed along the direction of the plasma flame in a cooling section at least on one side of the cavity resonator between the plasma combustion chamber wall and a surrounding cooling section wall, with the coolant contacting the plasma combustion chamber wall. The coolant flowing around and directly contacting the plasma combustion chamber wall additionally cools the plasma combustion chamber wall in a region between the plasma combustion chamber wall mount on the one hand and the cavity resonator on the other. In this way, it is possible to generate the plasma flame with a higher heat output and to expel it from the plasma combustion chamber without having to fear undesirable damage to the plasma combustion chamber during operation.

[0014] Optionally, it can be provided that, in the direction of the plasma flame, in a post-cooling section adjoining the plasma combustion chamber wall holder, a coolant flows through at least one post-cooling channel of a post-cooling wall of the post-cooling section. With the help of such a post-cooling section, a transition of the plasma flame from the plasma combustion chamber to the environment can be controlled and a temperature gradient that might otherwise be too large in a transition region from the plasma combustion chamber to the environment can be reduced. The coolant flows through a continuous post-cooling channel or several post-cooling channels that are arranged in the post-cooling wall of the post-cooling section. The coolant does not come into direct contact with the plasma combustion chamber wall. The post-cooling wall can be made of a suitable material with high thermal conductivity, such as metal.In addition to a suitable cooling gas, a coolant liquid can also be used as a coolant. The aftercooling channel is fluid-tightly separated from the cooling section between the plasma combustion chamber wall support and the cavity resonator, so that the coolant flowing through the at least one aftercooling channel of the aftercooling wall cannot enter the cooling sections and the cavity resonator. This allows for the use of an optimally suited coolant for each of the cooling sections, the plasma combustion chamber wall support, and the aftercooling section.

[0015] In order to increase the maximum heat output achievable with the plasma flame in continuous operation, the invention optionally provides for a second plasma combustion chamber to be arranged downstream of a first plasma combustion chamber in the plasma flame direction, with a second cavity resonator associated with the second plasma combustion chamber and a swirl generation device associated with the second plasma combustion chamber. The plasma flame is blown out of the first plasma combustion chamber in the plasma flame direction through the second plasma combustion chamber and out of the second plasma combustion chamber. It is also conceivable for one or more further plasma combustion chambers to be arranged downstream of the first plasma combustion chamber.In this way, separate plasma combustion chamber wall supports, separate cooling sections, and separate swirl generation devices can be provided for each plasma combustion chamber in order to coordinate the cooling effect and the plasma combustion gas flow, as well as the swirl gas envelope surrounding the plasma flame. Since two or more separate plasma combustion chambers are operated, each with cooling devices assigned to the respective plasma combustion chamber, a complex plasma process can be carried out in cascade with different process gases, process gas flows, or power levels, etc. The second plasma combustion chamber downstream of the first plasma combustion chamber can be operated with process parameters that differ from those of the first plasma combustion chamber, for example, at higher temperatures.The respective cooling devices and coolants, as well as the operation of the cooling devices, can be adapted to the respective process parameters in each plasma combustion chamber, for example, to different process gases or different temperatures. This makes it possible for the two plasma combustion chambers to be operated autonomously and independently of each other, and the respective cooling system can be adjusted to the individual radiation behavior of the plasma flame. This allows a significantly hotter plasma flame to be generated with a significantly higher heat output, even in continuous operation, than is currently possible with a conventional plasma generation device.

[0016] Advantageously, a preferred embodiment of the inventive concept provides that a coolant flow through the support cooling cavity and a coolant flow through the cooling section, and optionally a coolant flow through the post-cooling section, are coordinated in such a way that the most uniform temperature distribution possible is achieved in the plasma combustion chamber wall in the direction of the plasma flame. It has been shown that in many cases, damage to the plasma combustion chamber wall is primarily caused by a very uneven temperature distribution in the plasma combustion chamber wall, whereas with a uniform temperature distribution, the same plasma combustion chamber wall could also withstand comparatively high temperatures.To avoid uneven temperature distribution, the invention can provide for the operation of the individual cooling devices to be coordinated in such a way that the temperature distribution in the plasma combustion chamber wall is as uniform as possible along the direction of the plasma flame. This can lead, among other things, to an individual cooling device not necessarily being operated at its maximum possible cooling capacity. Furthermore, it can be provided that the operation of the individual cooling devices, and thus the respective coolant flow through the support cooling cavity, through the cooling section, and optionally through the post-cooling section, is also adapted to the respective current operation of the plasma generation device and the plasma flame generated thereby and its thermal output.

[0017] It can also be provided that the cooling capacities of the individual cooling devices are regulated during operation in such a way that the temperature distribution in the plasma combustion chamber wall is as uniform as possible. For this purpose, temperature parameters can be recorded along the direction of the plasma flame and evaluated using a control device to coordinate the cooling capacities of the individual cooling devices and achieve a uniform temperature distribution.

[0018] The invention also relates to a plasma generation device with a plasma combustion chamber through which a plasma fuel gas can flow and exit from a plasma flame opening, wherein the plasma combustion chamber is arranged at least partially in a cavity resonator with electrically conductive cavity walls, so that microwave energy, which is supplied into the cavity resonator via a waveguide, is used to generate a plasma in the plasma combustion chamber, and the plasma with the plasma fuel gas can be blown out of the plasma combustion chamber as a plasma flame in a plasma flame direction through the plasma flame opening, wherein the plasma combustion chamber has a plasma combustion chamber wall made of a dielectric solid material in order to effect a microwave-transparent, spatial separation between the plasma combustion chamber and the electrically conductive cavity walls of the cavity resonator, and wherein a swirl generation device is arranged on the plasma combustion chamber,with which a swirl gas can be blown into the plasma combustion chamber transversely to the direction of the plasma flame.

[0019] Various plasma generation devices are known in practice with which a plasma flame can be generated that can be blown out of a plasma combustion chamber. Such plasma generation devices are used, for example, as plasma cutting devices with a plasma flame that escapes into the environment. Plasma generation devices are also known in which the plasma flame generated is directed into a process chamber and used to treat workpieces or process materials. Experience has shown that generating the plasma with microwave energy is comparatively efficient and enables precise control of the generated plasma flame. Compared to other plasma generation devices, this heat output can be extracted and utilized with the plasma flame from the plasma combustion chamber.

[0020] It is already known from practice that, to prevent excessive heating of the plasma combustion chamber wall, a swirl gas is injected into the plasma combustion chamber perpendicular to the direction of the plasma flame. This creates a swirl gas jacket surrounding the plasma flame, shielding the plasma combustion chamber wall from the plasma flame. This can reduce heat transfer from the plasma in the plasma combustion chamber to the surrounding plasma combustion chamber wall, and thus reduce thermal stress on the plasma combustion chamber wall.However, it has been shown that, particularly during long-term operation of such a plasma generation device and a hot plasma flame with a high heat output generated thereby, the thermal loads and in particular an uneven temperature distribution in the plasma combustion chamber wall can lead to the plasma combustion chamber wall being subjected to excessive loads and thus being damaged prematurely and having to be replaced, which impairs the economically viable operation of such a plasma generation device at high heat outputs.

[0021] It is therefore considered a further aspect of the invention to further develop and design such a plasma generation device in such a way that the most continuous operation possible with a high heat output of the plasma flame generated in the plasma combustion chamber is possible.

[0022] This object is achieved according to the invention in that the plasma generation device has two plasma combustion chamber wall holders, each arranged at a distance from the cavity resonator, to which the plasma combustion chamber wall is fixed, wherein the plasma combustion chamber wall holders each have at least one holder cooling cavity through which a coolant can flow in order to be able to cool a region of the plasma combustion chamber wall holder in contact with the plasma combustion chamber wall. It has been shown that, particularly in a region of the plasma combustion chamber wall in which the plasma combustion chamber wall is in heat-transferring contact with a holder or with the surrounding cavity resonator, an uneven temperature distribution in the plasma combustion chamber wall occurs particularly frequently during operation of the plasma generation device.The distance between the plasma combustion chamber wall holder and the cavity resonator specified according to the invention also specifies a distance between the area within the plasma combustion chamber in which the plasma is generated by the microwave energy introduced into the cavity resonator and the thermal bridge between the plasma combustion chamber wall and the plasma combustion chamber wall holder, and distributes an unavoidable temperature gradient along the plasma flame direction over a larger area of the plasma combustion chamber wall.In addition, the inventive design of the plasma combustion chamber wall holders, each of which has a holder cooling cavity through which a coolant can flow, allows the heat transfer from the plasma combustion chamber through the plasma combustion chamber wall into the plasma combustion chamber wall holders to be controlled and specified in such a way that an uneven temperature distribution within the plasma combustion chamber wall in the region of the plasma combustion chamber wall holders that directly touch the plasma combustion chamber wall can be controlled.

[0023] According to an advantageous embodiment of the inventive concept, the plasma generation device comprises, at least on one side of the cavity resonator, a cooling section with a cooling section wall arranged at a distance from the plasma combustion chamber wall, between the associated plasma combustion chamber wall mount and the cavity resonator. A coolant can be conveyed through the cooling section between the cooling section wall and the plasma combustion chamber wall. The coolant conveyed through the cooling section between the cooling section wall and the plasma combustion chamber wall comes into direct contact with the plasma combustion chamber wall and can efficiently absorb and dissipate thermal energy transferred to the plasma combustion chamber wall by the plasma generated in the plasma combustion chamber.Since direct contact between the plasma combustion chamber wall on the one hand and the cooling section wall on the other hand is avoided, a comparatively uniform temperature distribution in the plasma combustion chamber wall around which the coolant flows is promoted. A length of the cooling section extending in the direction of the plasma flame can be adapted to the intended operation of the plasma generation device and the heat output generated by the plasma generated in the plasma combustion chamber and the plasma flame blown out of the plasma combustion chamber. It has proven advantageous for the cooling section to have a length in the direction of the plasma flame that is greater than a corresponding dimension of the cavity resonator in the direction of the plasma flame.

[0024] A suitable gas or a coolant liquid can be used as the coolant. When using a cooling gas, the coolant conveyed through the cooling section can also flow into the cavity resonator and be discharged from the cavity resonator at a distance from the plasma combustion chamber wall.

[0025] To promote the greatest possible heat dissipation away from the plasma combustion chamber wall in the cooling section, the invention optionally provides for the cooling section wall to be surrounded by a cooling section cavity and for the cooling section wall to have a plurality of cooling fins. The cooling fins significantly increase the surface area of the cooling section wall usable for heat transfer, allowing more thermal energy to be absorbed and dissipated by the coolant conveyed through the cooling section. The number, orientation, and dimensions of the individual cooling fins can advantageously be adapted to the cooling capacity envisaged during intended use of the plasma generation device.

[0026] Preferably, the plurality of cooling fins are arranged circumferentially around the plasma flame direction and oriented away from the plasma combustion chamber wall. The cooling fins thus do not impair the coolant flow surrounding the plasma combustion chamber wall in a jacket-like manner, thus promoting a uniform temperature distribution in the plasma combustion chamber wall within the cooling section. On a side of the cooling section wall facing away from the plasma combustion chamber wall, the plurality of cooling fins can significantly increase the surface area of the coolant wall usable for heat dissipation, without thereby impairing the most uniform temperature distribution possible in the plasma combustion chamber wall.

[0027] The cooling section wall is expediently surrounded by a cooling section housing which also surrounds the plasma combustion chamber wall, so that a coolant space is formed between the cooling section wall with the radially outwardly projecting cooling fins and the cooling section housing, through which a coolant can also flow and thereby absorb and dissipate heat.

[0028] In order to avoid an excessive temperature gradient of the plasma combustion chamber wall in an exit region of the plasma flame from the plasma generation device, it is optionally provided that the plasma generation device has an aftercooling device in a aftercooling section adjoining the plasma combustion chamber wall holder in the direction of the plasma flame, wherein the aftercooling device has at least one aftercooling channel in an aftercooling wall through which a coolant can flow. With the aftercooling device, a cooling power can be generated in an end region of the plasma combustion chamber wall by the aftercooling device arranged there, which cooling power can be predetermined independently of the cooling in the plasma combustion chamber wall holder and independently of the cooling in a cooling section between the plasma combustion chamber wall holder and the cavity resonator and can be effected during operation of the plasma generation device.In this way, it is possible to individually address the varying heat load on the plasma combustion chamber wall during operation of the plasma generation device along the direction of the plasma flame. The different cooling devices allow the cooling performance achieved in the respective sections to be adapted to the heat input from the plasma flame, so that the plasma combustion chamber wall is heated as evenly as possible along the direction of the plasma flame, or a temperature distribution as uniform as possible is achieved in the plasma combustion chamber wall during operation. The same coolant, for example, a gaseous coolant, can be used in each of the individual cooling devices.It is also conceivable that a different coolant, for example a liquid coolant, is used, particularly in the plasma combustion chamber wall supports or in the after-cooling device in which the coolant flows through after-cooling channels provided for this purpose.

[0029] The swirl generation device is typically located in an area where the plasma fuel gas is injected into the plasma combustion chamber. In many plasma combustion chambers, this area is located opposite the plasma flame opening in the plasma combustion chamber. The plasma combustion chamber is preferably tubular and defined by a hollow cylindrical plasma combustion chamber wall.

[0030] For various applications, it may be expedient, according to one embodiment of the inventive concept, for the swirl-generating device to be arranged between the cavity resonator and the plasma flame opening of the plasma combustion chamber, or adjacent to the plasma flame opening of the plasma combustion chamber. According to such a configuration of the plasma-generating device, the swirl-generating device generates a swirl gas envelope surrounding the plasma flame, which is drawn into the plasma combustion chamber or cavity resonator in a direction opposite to the plasma flame direction, and is subsequently blown out through the plasma flame opening together with the plasma fuel gas and the plasma flame in the direction of the plasma flame.It has been shown that even with a flow direction opposite to the plasma flame direction, a corresponding swirl gas jacket can significantly reduce the heat transfer from the plasma flame to the surrounding plasma combustion chamber wall.

[0031] To achieve the highest possible thermal output of the plasma flame generated by the plasma generation device, the plasma generation device can optionally be provided with a first plasma combustion chamber with an associated first cavity resonator and with an associated first swirl generation device, as well as a second plasma combustion chamber arranged downstream in the direction of the plasma flame with an associated second cavity resonator. Optionally, further plasma combustion chambers with corresponding components can also be arranged one behind the other. The plasma flame generated in the first plasma combustion chamber can be further heated in the second downstream plasma combustion chamber in order to increase the thermal output of the plasma flame then emerging from the second plasma combustion chamber.Since the plasma combustion chamber walls of the individual plasma combustion chambers can be thermally separated and insulated from each other, the individual plasma combustion chambers can be operated with different process parameters during operation. This allows, for example, different process gases, optionally additional solids or liquids, volume flows and process gas flows, or power levels to be specified in each plasma combustion chamber. The individual plasma combustion chamber walls can be cooled with significantly less effort using the respective cooling devices, ensuring the most uniform temperature distribution possible within the individual plasma combustion chamber walls.

[0032] It can further be provided that, for example, a swirl-generating device is arranged between the first plasma combustion chamber and the second plasma combustion chamber, which generates a swirl gas jacket in the first plasma combustion chamber, counter to the direction of the plasma flame, and also generates a swirl gas jacket extending into the second plasma combustion chamber in the direction of the plasma flame. This can reduce the design effort required to manufacture such a plasma generation device with multiple plasma combustion chambers.

[0033] According to a particularly advantageous embodiment of the inventive concept, the plasma generation device has, for the first plasma combustion chamber and for the second plasma combustion chamber, respectively associated first and second plasma combustion chamber wall mounts, and respectively associated first and second plasma combustion chamber wall mounts, and each associated first and at least one second cooling section with a cooling section wall. The additional cooling devices enable a significant increase in the performance of the plasma generation device, which more than offsets the additional design effort required for the manufacture and operation of such a plasma generation device.

[0034] The following are examples of the inventive concept that are illustrated in the drawing. It shows: Figure 1a schematic sectional view through a plasma generation device according to the invention along a plasma flame direction, Figure 2 a schematic perspective side view of a plasma generation device with two plasma combustion chambers arranged one behind the other and two cavity resonators, and Figure 3 a schematic sectional view through a plasma generation device according to the invention, wherein a swirl generation device is arranged adjacent to a plasma flame opening on the plasma combustion chamber.

[0035] In Figure 1A sectional view shows a schematic representation of a plasma generation device 1 according to the invention. The plasma generation device 1 has a tubular plasma combustion chamber 2, which is surrounded by a hollow-cylindrical plasma combustion chamber wall 3 made of a dielectric material, for example quartz glass. The plasma combustion chamber 2 passes through a cavity resonator 4 of a microwave device (not shown in detail), with which microwave energy is supplied to the cavity resonator 4 and the plasma combustion chamber 2 arranged therein via a waveguide 5. During operation of the plasma generation device 1, a plasma is generated by the microwave energy supplied to the plasma combustion chamber 2.

[0036] At an end of the plasma combustion chamber 2 opposite a plasma flame opening 6, a plasma fuel gas supply device 7 is arranged, with which a plasma fuel gas is blown into the plasma combustion chamber 2. The plasma fuel gas blown into the plasma combustion chamber 2 by the plasma fuel gas supply device 7 flows through the plasma combustion chamber 2 along a plasma flame direction 8 running from the plasma fuel gas supply device 7 to the oppositely arranged plasma flame opening 6 and is blown out of the plasma combustion chamber 2 through the plasma flame opening 6 in this plasma flame direction 8.

[0037] With a swirl generating device 9 arranged between the plasma fuel gas supply device 7 and the plasma combustion chamber wall 3, a swirl gas is blown in transversely to the plasma flame direction 8 tangentially to the adjacent plasma combustion chamber wall 3 and forms a swirl gas jacket which surrounds the plasma fuel gas blown through the plasma combustion chamber 2 in the plasma flame direction 8 in a tubular manner and thereby forms a shield of the plasma fuel gas from the surrounding plasma combustion chamber wall 3.

[0038] The plasma combustion chamber wall 3 is secured in a plasma combustion chamber wall mount 10 at a distance from the cavity resonator 4. A mount cooling cavity 11 is formed in each plasma combustion chamber wall mount 10, through which a coolant can flow. This coolant can be supplied and removed via a coolant supply line indicated only schematically. The supplied coolant cools the plasma combustion chamber wall mount 10 and dissipates heat from the plasma combustion chamber wall 3.Due to the respective distance between the cavity resonator 4 and the two plasma combustion chamber wall holders 10, a temperature difference between the cooled plasma combustion chamber wall holders 10 and the cavity resonator 4, in which the microwave energy is converted into plasma energy, is distributed over a larger distance along the plasma flame direction 8 and a temperature gradient within the plasma combustion chamber wall 3 is reduced.

[0039] Between each of the two plasma combustion chamber wall mounts 10 and the cavity resonator, a cooling section 12 is arranged with a cooling section wall 13, which surrounds the plasma combustion chamber wall 3 at a small radial distance, but does not touch the plasma combustion chamber wall 3. A coolant flows between the cooling section wall 13 and the plasma combustion chamber wall 3, with which the plasma combustion chamber wall 3 is cooled in the respective cooling section 12. This avoids direct contact between the cooling section wall 13 and the plasma combustion chamber wall 3 and the resulting thermal bridge. In addition to the cooling effect of the coolant flowing around the plasma combustion chamber wall 3, this also promotes the most uniform temperature distribution possible in the plasma combustion chamber wall 3 between the cavity resonator 4 and the plasma combustion chamber wall mounts 10, which are arranged at a distance on opposite sides.The coolant flowing in from an end 14 of the cooling section wall 13 facing away from the cavity resonator 4 can flow into the cavity resonator 4 and be discharged from the cavity resonator via outflow openings 15 arranged at a distance from the plasma combustion chamber wall 3.

[0040] Each cooling section wall 13 has cooling fins 16 extending circumferentially and radially outward on an outer side opposite the plasma combustion chamber wall 3. A coolant flows between the outer sides of the cooling section walls 13 with the respective cooling fins 16 and a surrounding cooling section housing 15 and can absorb and dissipate thermal energy from the cooling fins 16.

[0041] In the plasma flame direction 8, on a side opposite the cavity resonator 4, between the associated plasma combustion chamber wall mount 10 and the plasma flame opening 6, a post-cooling device 17 with a post-cooling channel 18 helically surrounding the plasma combustion chamber wall 3 is arranged in a post-cooling wall. During operation of the plasma generation device 1, a coolant, for example a cooling liquid, can flow through the post-cooling channel 18, and heat can be dissipated from the plasma combustion chamber wall 3 via the post-cooling wall 19 directly adjacent to the plasma combustion chamber wall 3.

[0042] At the start of operation of the plasma generation device 1, an ignition tip 20 can be inserted into the plasma combustion chamber 2 in an axial direction, and the resulting field increase in the cavity resonator 4 ignites a plasma in the plasma combustion chamber 2. The plasma generates a plasma flame 21 in the plasma fuel gas, which is blown out of the plasma combustion chamber 2 through the plasma flame opening 6 by the plasma fuel gas flowing through the plasma combustion chamber 2 in the plasma flame direction 8.

[0043] The various cooling devices, namely the plasma combustion chamber wall mounts 10, the cooling sections 12, and the aftercooling device 17, can each generate a cooling effect on the plasma combustion chamber wall 3. Through suitable and coordinated control of the individual cooling devices, the most uniform temperature distribution possible can be specified within the plasma combustion chamber wall 3 along the plasma flame direction 8. This reduces thermal stress on the plasma combustion chamber wall 3 and prevents premature damage to the plasma combustion chamber wall 3 due to large temperature gradients. Advantageously, the respective heating of the plasma combustion chamber wall 3 is detected with the aid of temperature sensors, and controlled operation of the individual cooling devices is carried out.

[0044] In Figure 2A variant of the plasma generation device 1 is shown only schematically, in which a second plasma combustion chamber 22 with a second cavity resonator 23 is arranged after a first plasma combustion chamber 2, which passes through a cavity resonator 4. Each plasma combustion chamber 2 is assigned separate plasma combustion chamber wall supports 10, cooling sections 12 and swirl generation devices 9, which, however, are arranged in Figure 2 are not shown in detail. In the second plasma combustion chamber 22, the plasma flame 21 generated in the first plasma combustion chamber 2 and blown into the second plasma combustion chamber 22 can be supplied with additional microwave energy, so that an additionally heated plasma flame 21 with a significantly higher heat output is blown out of the plasma flame opening 6 of the second plasma combustion chamber 2.

[0045] In Figure 3A possible arrangement of the swirl generation device 9 in the region of the plasma flame opening 6 is schematically shown according to the invention. The swirl gas blown into the plasma combustion chamber 2 through swirl gas openings 23 tangentially to the plasma combustion chamber wall 3 forms a tubular swirl gas jacket, which flows along the plasma combustion chamber wall 3 into the plasma combustion chamber 2 and is deflected at an opposite end. Together with the plasma fuel gas, it is blown through the plasma combustion chamber 2 in the plasma flame direction 8 and out of the plasma combustion chamber 2 through the plasma flame opening 6. In this embodiment, too, the swirl gas jacket forms a thermal shield between the hot plasma flame 21 and the surrounding plasma combustion chamber wall 3.

Claims

1. Method for generating a plasma flame (21) with a plasma combustion gas blown out in a plasma flame direction (8) through a plasma flame opening (6) from a plasma combustion chamber (2), wherein the plasma combustion chamber (2) is at least partially arranged in a cavity resonator (4) and microwave energy is supplied to the cavity resonator (4) via a waveguide (5) to generate a plasma in the plasma combustion chamber (2), and wherein a swirl generating device (9) is used to inject a swirl gas into the plasma combustion chamber (2) in order to generate a swirl gas jacket surrounding the plasma flame (21) in the plasma combustion chamber (2), which jacket shields a plasma combustion chamber wall (3) made of a dielectric solid material from the plasma flame (21), wherein the plasma combustion chamber wall (3) protrudes in both directions along the plasma flame direction (8) beyond the cavity resonator (4) and is fixed in each case at a distance from the cavity resonator (4) in a plasma combustion chamber wall support (10), characterized in that each plasma combustion chamber wall support (10) comprises at least one support cooling cavity (11) through which a coolant flows.

2. Method according to claim 1, characterised in that a coolant is conveyed along the plasma flame direction (8) at least on one side of the cavity resonator (4) in a cooling section (12) between the plasma combustion chamber wall (3) and a surrounding cooling section wall (13) and the coolant contacts the plasma combustion chamber wall (3) in the process.

3. Method according to claim 1 or claim 2, characterised in that a coolant flows through at least one after-cooling channel (18) in an after-cooling wall (19) of the after-cooling device (17) in the plasma flame direction (8) in an after-cooling device (17) adjoining the plasma combustion chamber wall support (10).

4. Method according to claim 2 or 3, characterised in that a coolant flow through the support cooling cavity (11) and a coolant flow through the cooling section (12) and, if appropriate, a coolant flow through the after-cooling device (17) are coordinated with one another in such a way that the most uniform possible temperature distribution possible is specified in the plasma flame direction (8) in the plasma combustion chamber wall (3).

5. Method according to any of the foregoing claims, characterised in that a second plasma combustion chamber (22) with a second cavity resonator associated with the second plasma combustion chamber (22) is arranged downstream of a first plasma combustion 20 chamber (2) in the plasma flame direction (8), and in that the plasma flame (21) is blown out of the first plasma combustion chamber (2) in the plasma flame direction (8) through the second plasma combustion chamber (22) and out of the second plasma combustion chamber (22).

6. Plasma generating apparatus (1) with a plasma combustion chamber (2) through which a plasma combustion gas can flow and emerge from a plasma flame opening (6), wherein the plasma combustion chamber (2) is at least partially arranged in a cavity resonator (4) with electrically conductive cavity walls, so that microwave energy supplied into the cavity resonator (4) via a waveguide (5) can be used to generate a plasma in the plasma combustion chamber (2) and the plasma can be blown out of the plasma combustion chamber (2) with the plasma combustion gas as a plasma flame (21) in a plasma flame direction (8) through the plasma flame opening (6), wherein the plasma combustion chamber (2) comprises a plasma combustion chamber wall (3) made of a dielectric solid material to effect a microwave-transparent spatial separation of the plasma combustion chamber (2) and the electrically conductive cavity walls of the cavity resonator (4), and wherein a swirl generating device (9) is arranged on the plasma combustion chamber (2), with which a swirl gas can be injected into the plasma combustion chamber (2) transversely to the plasma flame direction (8), characterised in that the plasma generating apparatus (1) comprises two plasma combustion chamber wall supports (10), which are each arranged at a distance from the cavity resonator (4) and to which the plasma combustion chamber wall (3) is fixed, wherein the plasma combustion chamber wall supports (10) each have at least one support cooling cavity (11) through which a coolant can flow in order to be able to cool an area of the plasma combustion chamber wall support (10) that is in contact with the plasma combustion chamber wall (3).

7. Plasma generating apparatus (1) according to claim 6, characterised in that the plasma generating apparatus (1) comprises, at least on one side of the cavity resonator (4) between the associated plasma combustion chamber wall support (3) and the cavity resonator (4), a cooling section (12) with a cooling section wall (13) arranged at a distance from the plasma combustion chamber wall (3), wherein a coolant can be conveyed through the cooling section (12) between the cooling section wall (13) and the plasma combustion chamber wall (3).

8. Plasma generating apparatus (1) according to claim 7, characterised in that in the cooling section (12) the cooling section wall (13) is surrounded by a cooling section cavity and the cooling section wall (13) comprises a plurality of cooling fins (16).

9. Plasma generating apparatus (1) according to claim 8, characterised in that the plurality of cooling fins (16) are arranged in the circumferential direction around the plasma flame direction (8) and directed away from the plasma combustion chamber wall (3).

10. Plasma generating apparatus (1) according to any one of claims 6 to 9, characterised in that the plasma generating apparatus (1) comprises an after-cooling device (17) in an after-cooling section adjoining the plasma combustion chamber wall support (10) in the plasma flame direction (8), wherein the after-cooling device (17) comprises at least one aftercooling channel (18) in an after-cooling wall (19), through which a coolant can flow.

11. Plasma generating apparatus (1) according to any one of claims 6 to 9, characterised in that the swirl generating device (9) is arranged between the cavity resonator (4) and the plasma flame opening (6) of the plasma combustion chamber (2) or adjacent to the plasma flame opening (6) of the plasma combustion chamber (2).

12. Plasma generating apparatus (1) according to any one of claims 6 to 11, characterised in that the plasma generating apparatus (1) comprises a first plasma combustion chamber (2) with an associated first cavity resonator (4) and with an associated first swirl generating device (9), as well as a second plasma combustion chamber (22) arranged downstream in the plasma flame direction (8) with an associated second cavity resonator (4).

13. Plasma generating apparatus (1) according to claim 12, characterised in that the plasma generating apparatus (1) comprises for the first plasma combustion chamber (2) and for the second plasma combustion chamber (22), respectively associated first and second plasma combustion chamber wall supports (10) and, respectively associated, at least one first and at least one second cooling section (12) with a cooling section wall (13).