WO2024235719A1 - Device for generating a cold plasma - Google Patents

Abstract

The invention relates to a device (10) for generating a cold plasma, the device comprising: - an outer housing (100) forming a cavity (104) that is open at the primary end (102); - a central electrode (200) arranged in the housing (104) that extends from the outer base (101) towards one of its ends, the central electrode (200) comprising, at its free end, at least one tip, the central electrode (200) defining, together with the outer housing (100), an annular space (300); - means for injecting a primary gas into the cavity (104); - an auxiliary injection means configured to allow an auxiliary gas to be injected into the annular space (300) towards the opening (105) for the purpose of thermalising the device (10); - microwave means (600) configured to transmit a microwave field to the central electrode (200).

Description

Device for generating cold plasma FIELD OF THE INVENTION

The present invention relates to the field of plasma generators, in particular cold plasma generators. More particularly, the present invention relates to a cold plasma generator configured to enable the generation of a plasma of appreciable extent. This aspect makes it possible in particular to envisage the treatment, for example a medical treatment, of a larger surface area in reasonable durations.

The present invention also relates to a cold plasma generator whose gas consumption remains limited.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Plasma generating devices are now used in many fields, particularly in the medical field.

In this regard, document US 11,264,211 B2 discloses a device for generating a cold plasma. This device, as illustrated in of document US 11,264,211, is provided with a casing, of cylindrical shape, and forming a housing opening through an opening arranged at one end of said casing. The device also comprises a central electrode, of generally elongated shape and arranged in the housing. In particular, the electrode ends at one of its ends with a pointed conical section accessible through the opening.

The device further comprises an inlet for a gas capable of forming a cold plasma when it is subjected to an electric field greater than a so-called breakdown field. In particular, the device is configured to allow the gas to flow from the inlet to the conical section.

Finally, the device comprises activation means configured to impose a voltage, greater than a breakdown voltage, such that the electric field in the vicinity of the tip of the conical section is greater than the breakdown field.

Thus, in operation, the gas is injected into the device through the inlet and flows towards the conical section to which a voltage greater than the breakdown voltage is imposed. Upon arrival in the vicinity of the tip of the conical section, the gas ionizes under the effect of the electric field to form a plasma jet through the opening of the housing.

However, the extent of the plasma jet is relatively restricted so that its implementation remains limited to the treatment of small surfaces.

Furthermore, the implementation of such a device requires, for thermalization purposes, a relatively high gas flow rate - so that only a fraction of said gas is actually transformed, the rest of the gas escaping through the opening. However, the gases likely to be used for plasma formation have a relatively high financial cost that must be contained.

Thus, an aim of the present invention is to propose a device for generating a cold plasma and whose gas consumption is optimized.

Another aim of the present invention is to propose a device for generating a cold plasma of appreciable extent.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a device for generating a cold plasma, said device, of generally elongated shape along an elongation axis XX’, comprising:

- an external casing of cylindrical shape, which extends along the axis of elongation, between an external base and a main end, and forming a housing, said housing being open by the main end;

- a central electrode of cylindrical shape, arranged coaxially with the external housing in the housing and which extends from the external base towards one of its ends called the free end, said central electrode comprising, at its free end, at least one point, the central electrode defining with the external housing an annular space;

- means for injecting, into the housing, a main gas capable of forming a cold plasma when it is subjected to an electric field greater than a so-called breakdown field;

- an auxiliary injection means, configured to allow the injection of an auxiliary gas into the annular space towards the opening for the purposes of thermalizing the device and according to a conduit different from the main gas;

- microwave means configured to transmit a microwave field to the central electrode, and such that said microwave field propagates in the annular space in the direction XX' towards the opening, the at least one tip ensuring the focusing of said microwave field such that the field in the vicinity of the at least one tip is greater than the breakdown field.

According to one embodiment, the central electrode is hollow and forms a channel for circulation of the main gas to the free end, and so that the auxiliary gas flows into the annular space.

According to one embodiment, said device comprises a tubular jacket, made of an electrically insulating material, arranged coaxially with the central electrode, in the housing, and delimiting with the external housing the annular space, the tubular jacket being arranged to allow the circulation of the main gas between the central electrode and said tubular jacket and the circulation of the auxiliary gas between said tubular jacket and the external housing.

According to one embodiment, the end of the central electrode has a conical shape.

According to one embodiment, the at least one tip forms a plurality of tips, each tip of the plurality of tips being arranged to allow the initiation of a plasma at the end of said tip.

According to one embodiment, the central electrode comprises at its free end a conical section, said conical section comprising recesses defining the tips.

According to one embodiment, the recesses extend from the base of the conical section.

According to one embodiment, the conical section has a cone angle of between 10° and 180°, advantageously between 30° and 150°, even more advantageously between 60° and 120°.

According to one embodiment, the central electrode ends at its free end with a flat face, the tips being projected relative to said flat face.

According to one embodiment, said device comprises an insert arranged in the annular space on the passage of the auxiliary gas, and configured to impose a laminar flow on said auxiliary gas.

Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

There is a schematic representation, along a section plane comprising the elongation axis XX', of the device for generating a cold plasma according to a first example in accordance with the principles of the present invention;

There is a schematic representation, in perspective view, of a conical section carrying a plurality of tips and disposed on the free end of the central electrode;

There is a representation according to a profile view of the conic section of the ;

There is a representation of the conic section of the by its summit;

There is a representation of a tip arrangement according to another variation of the present invention;

There is a schematic representation, according to a section plane comprising the elongation axis XX', of the device for generating a cold plasma using means for injecting an auxiliary gas for thermalization purposes;

There is a schematic representation, in a perspective view, of the device for generating a cold plasma using means for injecting an auxiliary gas for thermalization purposes according to a variant of the invention;

There is a schematic representation of a central electrode on which a cylindrical sleeve is fitted;

There is a schematic representation of a central electrode on which another type of cylindrical sleeve is fitted;

There is a schematic representation of the device according to the present invention and provided with a microwave generator.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a device for generating a cold plasma. In particular, the present invention relates to a device, of generally elongated shape along an elongation axis XX’, which comprises:

- an external casing of cylindrical shape, which extends along the axis of elongation, between an external base and a main end, and forming a housing, said housing being open by the main end;

- a central electrode of cylindrical shape, arranged coaxially with the external housing in the housing and which extends from the external base towards one of its ends called the free end, said central electrode comprising, at its free end, a plurality of points, the central electrode delimiting with the external housing an annular space;

- means for injecting, into the housing, a main gas capable of forming a cold plasma when it is subjected to an electric field greater than a so-called breakdown field;

- microwave means configured to transmit a microwave field to the central electrode, and such that said microwave field propagates along the central electrode to the free end, the tips ensuring the focusing of said microwave field such that the field near the tips is greater than the breakdown field.

There is a schematic representation in perspective view of a first example of a cold plasma generation device 10 in accordance with the principles of the present invention.

In particular, the device 10 comprises an external housing 100 which extends along an elongation axis XX'. The external housing 100 is cylindrical in shape and extends from a base, called the external base 101, towards an end, called the main end 102. In general, the external housing 100 is delimited laterally by a lateral envelope 103, giving said external housing its cylindrical shape, and such that the latter forms a housing 104. The external housing 100 also comprises, at its main end 102, an opening 105.

It is understood that the housing 104, insofar as it is delimited by the external base 101 and the lateral envelope 103, is also of cylindrical shape and extends along the elongation axis XX' of the external base towards the opening 105.

The device 10 also comprises a central electrode 200 which is cylindrical in shape and which extends along the elongation axis XX'. In particular, the central electrode 200 is arranged coaxially with the external housing 100 in the housing 104 and so as to provide an annular space 300 between the central electrode 200 and the external housing 100. More particularly, the central electrode 200 extends, along the elongation axis, from the external base towards one of its ends called the free end 201.

It is understood, without needing to be specified, that the free end 201 is accessible through the opening 105.

The central electrode 200 comprising, at its free end 201, at least one tip.

Advantageously, and according to a first aspect of this first example, the free end may comprise only a single point. For example, the free end may be conical in shape.

According to a second aspect of this first example, the free end may comprise a plurality of tips 203. This second aspect will be described in more detail in the remainder of the statement of the present invention.

Furthermore, according to the present invention, the electrode 200 may be hollow, and be configured to allow the flow of a gas and its evacuation through the free end 201.

The device 10 further comprises means for injecting, into the housing, a main gas capable of forming a cold plasma when it is subjected to an electric field greater than a so-called breakdown field. This gas may comprise argon or a mixture comprising argon. However, the present invention should not be limited to this aspect alone and a person skilled in the art may consider any other main gas capable of fulfilling the desired function. In particular, the main gas may comprise helium, nitrogen, or even dioxygen.

These injection means comprise in particular an inlet, called the main inlet 106, through which the main gas is capable of being injected. According to the variants considered, the main inlet 106 can be arranged to allow the injection of the main gas into the annular space 300 or into the central electrode 200.

The device also comprises microwave transmission means 600 associated with a microwave generator (not shown). The microwave transmission means comprise a cylindrical section 610 and secured by one of its ends to the central electrode 200. In particular, the cylindrical section 610 is configured to allow the microwaves coming from the microwave generator to be generated in the external housing housing 100. Those skilled in the art will find the elements necessary for dimensioning the external housing, the central electrode and the microwave transmission means in document US 11,264,211 B2. The frequency of the microwaves can be between 800 MHz and 50 GHz.

Furthermore, it is understood that the cylindrical section 610 comprises a dielectric material, in particular an electrical insulator, in order to maintain the confinement of the microwaves in a cable running through the cylindrical section and conveying said microwaves into the housing.

According to the present invention, both the outer casing 100 and the central electrode 200 may comprise a highly electrically conductive material such as copper, brass or silver. This latter aspect allows the elements considered to have a very low skin thickness.

Thus, the microwave transmission means 600 are configured to transmit a microwave field in the annular space and so that said field propagates within said annular space and in the direction of the free end. The tip(s) arranged at the free end of the central electrode 200, by their shape, focus the microwave field so that the electric field in the vicinity of said tips increases substantially and in particular beyond the breakdown field.

The main gas, injected into the device through the main inlet 106, flowing in the vicinity of said points is then subjected to this electric field and then forms a plasma jet through the opening of the housing.

Furthermore, the distance between the tips is adapted so that the plasma jet is generated at each of said tips.

It is understood that such an effect can be obtained for different configurations or arrangements of the tips. More particularly, the person skilled in the art will be able to consider any arrangement of tips, in particular in terms of geometry and/or distance, capable of generating, concomitantly, the plasma jet at each tip.

Considering a plurality of tips makes it possible to form a plasma jet of greater extent than plasma jets formed by devices in which the central electrode is provided with only one tip.

According to a variant illustrated in the , to the and to the , the central electrode comprises, at its free end 201, a conical section 202, said conical section comprising recesses 204 defining the tips 203. In particular, the recesses 204 can form passages through which the main gas is likely to flow.

More particularly, the recesses 204 extend, parallel to the axis of revolution of the conical section 202, for example from the base of said conical section and perpendicular to the latter.

Advantageously, the intersection of a plane perpendicular to the axis of revolution of the conic section and each recess can take the form of a chevron, a “V”, or even a parabola.

Still advantageously, the conical section has a cone angle of between 10° and 180°, advantageously between 30° and 150°, even more advantageously between 60° and 120°.

According to another variant illustrated in the , the central electrode ends at its free end with a flat face, the points being projected relative to said flat face.

According to a second example, taken alone or in combination with either of the first aspect and the second aspect of the first example, illustrated in , the device 10 may comprise an auxiliary injection means, configured to allow the injection of an auxiliary gas into the annular space towards the opening for the purposes of thermalizing the device. It is understood that the auxiliary injection means is configured to allow the circulation of the auxiliary gas from an inlet, called auxiliary inlet 107, and towards the opening. It is also understood that the device is configured so that the auxiliary gas flows along a fluid path specific to it.

Thus, and as an example, the device of the is configured so that the auxiliary gas flows into the annular space 300, and the main gas flows into the central electrode 200 which is hollow and open at its free end. According to this configuration, the flow of each of these two gases takes place in a space specific to it. In particular, the implementation of the auxiliary gas, for example air, makes it possible to limit the consumption of main gas, and to ensure thermalization (limit heating) of the device 10.

There is an illustration of a variant of this embodiment. In particular, according to this variant, the device comprises a tubular jacket 400, made of an electrically insulating material, coaxial with the central electrode and interposed between said central electrode 200 and the external housing 100. According to this variant, the annular space 300 is delimited by the lateral envelope 103 and the tubular jacket. Still according to this variant, the tubular jacket 400 has an internal diameter greater than the diameter of the central electrode 200, thus providing an internal annular space 401 in which the main gas can flow from the main inlet to the free end.

There is an illustration of another variant of this embodiment. In particular according to this other variant, the device comprises a cylindrical sleeve 410 in place of the tubular jacket. In particular, the tubular sleeve, made of an electrically insulating material, can extend the central electrode beyond its free end.

It is understood that the consideration of the cylindrical sleeve requires the central electrode to be hollow in order to allow the circulation of the main gas within it.

In the example shown in the , the internal diameter of the cylindrical sleeve is substantially equal to the external diameter of the central electrode. The cylindrical sleeve can be held on the central electrode by a press-fitted tightening.

However, it is possible to consider a cylindrical sleeve whose internal diameter is greater than the external diameter of the central electrode. According to this aspect, and as illustrated in the , the cylindrical sleeve may comprise a holding section 420, also cylindrical and whose internal diameter is substantially equal to the external diameter of the central electrode.

According to the third example taken alone or in combination with one or the other of the first aspect and the second aspect of the first example and/or in combination with the second example, the device 10 comprises an insert arranged in the annular space on the passage of the auxiliary gas, and configured to impose a laminar flow on said auxiliary gas.

In particular, and as illustrated in the , the insert 500, generally of cylindrical shape, extends along the elongation axis XX'. More particularly, the insert 500 comprises passages, crossing it over its entire length, and allowing the circulation of a gas, and in particular of an auxiliary gas. These crossing passages are configured to impose a laminar flow on the gases considered and thus limit the noise likely to be generated in the event of turbulent flow.

Alternatively, the insert 500 may comprise an open porosity foam.

Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims (10)

Device (10) for generating a cold plasma, said device (10), of generally elongated shape along an elongation axis XX', comprising:
- an external housing (100) of cylindrical shape, which extends along the elongation axis, between an external base (101) and a main end (102), and forming a housing (104), said housing (104) being open by the main end (102);
- a central electrode (200) of cylindrical shape, arranged coaxially with the external housing (100) in the housing (104) and which extends from the external base (101) towards one of its ends called the free end (201), said central electrode (200) comprising, at its free end (201), at least one tip (203), the central electrode (200) defining with the external housing (100) an annular space (300);
- means for injecting, into the housing (104), a main gas capable of forming a cold plasma when it is subjected to an electric field greater than a so-called breakdown field;
- an auxiliary injection means, configured to allow the injection of an auxiliary gas into the annular space (300) towards the opening (105) for the purposes of thermalizing the device (10) and according to a conduit different from the main gas;
- microwave means (600) configured to transmit a microwave field to the central electrode (200), and such that said microwave field propagates in the annular space (300) in the direction XX' towards the opening (105), the at least one tip (203) ensuring the focusing of said microwave field such that the field in the vicinity of the at least one tip is greater than the breakdown field. Device (10) according to claim 1, in which the central electrode (200) is hollow and forms a channel for circulation of the main gas to the free end (201), and so that the auxiliary gas flows into the annular space (300). Device (10) according to claim 1 or 2, wherein said device (10) comprises a tubular jacket (400), made of an electrically insulating material, arranged coaxially with the central electrode (200), in the housing (104), and delimiting with the external housing (100) the annular space (300), the tubular jacket (400) being arranged to allow the circulation of the main gas between the central electrode (200) and said tubular jacket (400) and the circulation of the auxiliary gas between said tubular jacket (400) and the external housing (100). Device (10) according to one of claims 1 to 3, in which the end of the central electrode (200) has a conical shape. Device (10) according to one of claims 1 to 3, in which the at least one tip forms a plurality of tips, each tip of the plurality of tips being arranged to allow the initiation of a plasma at the end of said tip. Device (10) according to claim 5, in which the central electrode (200) comprises at its free end (201) a conical section (202), said conical section (202) comprising recesses defining the tips. A device (10) according to claim 6, wherein the recesses extend from the base of the conical section (202). Device (10) according to claim 6 or 7, in which the conical section (202) has a cone angle of between 10° and 180°, advantageously of between 30° and 150°, even more advantageously of between 60° and 120°. Device (10) according to claim 5, in which the central electrode (200) ends at its free end (201) with a flat face, the points being projecting relative to said flat face. Device (10) according to one of claims 1 to 9, in which said device (10) comprises an insert (500) arranged in the annular space (300) on the passage of the auxiliary gas, and configured to impose a laminar flow on said auxiliary gas.