Elementary device for producing a plasma, having a coaxial applicator

Abstract

The present disclosure relates to an elementary device for producing a plasma. The elementary device includes a coaxial applicator of microwave power that includes a conductive central core, a conductive external shield surrounding the central core, a medium located between the central core and the shield to propagate microwave energy, and an insulating body. The elementary device further includes a system to couple to a microwave generator and is disposed at the shield. The shield has a proximal end plugged with the insulating body made of dielectric material that is transparent to the microwave energy. The insulating body has an external surface configured to contact and excite a gas located in the interior of a chamber. The insulating body extends exterior wise from the shield and its external surface is nonplanar and protrudes from the shield. The outside diameter of the body decreases from the shield to its tip.

Claims

1. An elementary device for an installation for producing a plasma, the elementary device comprising: a coaxial applicator of microwave power, the coaxial applicator comprises: a conductive central core extending along a main axis; a conductive outer shield surrounding the conductive central core; a medium located between the conductive central core and the conductive outer shield to propagate a microwave energy, wherein the medium is air; and an insulating body made of dielectric material transparent to the microwave energy and having an outer surface that is configured to be in contact with a gas to be energized localized inside a chamber in which the plasma is produced; and a coupling system configured to couple to a microwave energy generator, wherein the coupling system includes an outer conductor in contact with the conductive outer shield, wherein: the coupling system is disposed at the conductive outer shield, the conductive outer shield has a proximal end occluded by the insulating body and has a symmetry of revolution about the main axis, the insulating body protrudes outwardly of the conductive outer shield according to the main axis, the outer surface is non-planar and projects outside of the conductive outer shield with a decreasing outer diameter along the main axis starting from the conductive outer shield up to its tip, the insulating body has an inner surface in contact with the medium and crossed by the conductive central core, the inner surface being non-planar and non-orthogonal to the main axis, the conductive central core has a proximal end embedded inside the insulating body, without passing completely through the insulating body, all of the outer surface including an end face of the proximal end of the conductive central core is directly in contact with the insulating body, and the insulating body protrudes outwardly of the conductive outer shield according to the main axis by a distance which is smaller than or equal to an inner diameter of the conductive outer shield at its proximal end.

2. The elementary device according to claim 1, wherein the outer diameter of the outer surface decreases continuously along the main axis starting from the conductive outer shield up to its tip.

3. The elementary device according to claim 2, wherein the outer surface of the insulating body has a substantially truncated-cone or hemispherical shape.

4. The elementary device according to claim 3, wherein the outer surface of the insulating body has one of a substantially truncated-cone shape truncated at its end with a flat or rounded tip, or a substantially truncated-cone shape not truncated at its end with a sharp tip.

5. The elementary device according to claim 1, wherein the outer surface of the insulating body has no right-angled edges.

6. The elementary device according to claim 1, wherein the proximal end of the conductive central core protrudes from the conductive outer shield according to the main axis.

7. The elementary device according to claim 1, wherein the inner surface has an increasing outer diameter along the main axis in a direction of displacement from a distal end of the coaxial applicator towards a proximal end occluded by the insulating body.

8. The elementary device according to claim 1, wherein the inner surface of the insulating body has a generally truncated-cone shape.

9. An installation for producing a plasma comprising: a chamber within which the plasma is produced and confined, the chamber being delimited by a partition; at least one microwave energy generator; and at least one elementary device in accordance with claim 1, wherein the coupling system of the at least one elementary device is coupled with the microwave energy generator and the outer surface of the insulating body penetrates inside the chamber beyond its partition.

10. The installation according to claim 9, wherein the conductive outer shield of the coaxial applicator is either constituted by a part attached to the chamber and crossing its partition in a sealed manner, or is integrally formed at least partially with the partition.

Description

DRAWINGS

(1) In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIGS. 1(a) and 1(b are axial sectional views of two conventional elementary devices for producing a plasma;

(3) FIG. 2 is a schematic axial sectional view of a first elementary device in accordance with the present disclosure;

(4) FIG. 3 is a schematic axial sectional view of a second elementary device in accordance with the present disclosure;

(5) FIG. 4 is a schematic axial sectional view of a third elementary device in accordance with the present disclosure;

(6) FIG. 5 is a schematic perspective view of the first elementary device of FIG. 2;

(7) FIG. 6 is a schematic view of the inside of a plasma chamber in which the first elementary device of FIGS. 2 and 5 is placed; and

(8) FIG. 7 is a schematic view of the inside of a plasma chamber in which several first elementary devices of FIGS. 2 and 5 are placed.

(9) The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

(10) The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

(11) FIGS. 2 to 5 illustrate three forms of an elementary device 1 for producing a plasma, with a first form illustrated in FIGS. 2 and 5, a second form illustrated in FIG. 3 and a third form illustrated in FIG. 4, and unless otherwise explicitly or implicitly stated, members, parts, devices or elements that are structurally or functionally identical or similar will be designated by identical references in these figures.

(12) The elementary device 1 comprises a microwave power coaxial applicator 2, provided to ensure the transmission of a microwave energy between a microwave energy generator (not illustrated), in particular of the solid-state generator type, and the inside of a plasma chamber 4 (shown in FIGS. 6 and 7).

(13) This coaxial applicator 2 is made in a filiform shape, that is to say an elongated along a main axis AP, and it has: a distal end 21; and an opposite proximal end 22 intended to open into the chamber 4.

(14) The coaxial applicator 2 comprises:

(15) a conductive central core 23 extending along the main axis AP, and being in the form of a rod, and in particular a rod with a constant cross-section;

(16) a conductive outer shield 24 surrounding the central core 23, this outer shield 24 being in the form of a hollow sleeve comprising a peripheral wall having a cylindrical inner face centered on the main axis AP, and a bottom wall closing the distal end 21 of the coaxial applicator 2;

(17) a medium 25 for propagating the microwave energy located between the central core 23 and the shield 24, this propagation medium 25 being for example composed of air; and

(18) an insulating body 26 made of dielectric material transparent to microwave energy, this insulating body 26 being disposed on the proximal end 22 of the coaxial applicator 2.

(19) At the proximal end 22, the shield 24 has an open proximal end occluded by the insulating body 26 which guarantees the sealing between the propagation medium 25 and the inside of the chamber 4.

(20) The coaxial applicator 2 further comprises a coupling system 3 for coupling to the microwave energy generator. This coupling system 3 is constituted by any appropriate means ensuring the connection with a coaxial cable or a waveguide (not illustrated) connecting the generator to the coupling system 3.

(21) In the example of FIGS. 2 to 4, the coupling system 3 is designed for coupling with a coaxial cable and, for this purpose, has a structure of the coaxial structure type; such a coaxial structure comprising an outer conductor in contact with the shield 24 (described below) of the coaxial applicator 2 and surrounding an inner conductor that comes into contact with the central core 23 (described below) of the coaxial applicator 2.

(22) This coupling system 3 may be positioned on the bottom wall of the shield 24, or on its peripheral wall.

(23) The insulating body 26 occludes completely the proximal end 22 of the coaxial applicator 2, thereby separating the inside of the chamber 4, which is often maintained at low pressure, from the propagation medium 25, which is at ambient atmospheric pressure.

(24) The insulating body 26 is a part of revolution about the main axis AP, and has an outer surface 27 intended to be in contact with the inside of the chamber 4, and more precisely with a gas to be energized localized inside the chamber 4.

(25) Furthermore, this insulating body 26 protrudes outwardly of the shield 24 according to the main axis AP by a distance DC, and its outer surface 27 is non-planar and projects outside of the shield 24 by this distance DC.

(26) This distance DC is smaller than or equal to the inner diameter of the shield 24 at its proximal end; the inner diameter of the proximal end of the shield 24 meaning the diameter of its peripheral or cylindrical inner face that is in contact with the insulating body 26. Thus, this distance DC is smaller than or equal to the outer diameter of the insulating body 26 considered at the proximal end of the shield 24.

(27) This outer surface 27 is thus curved outwardly of the shield 24, without a right-angled edge, and it has a symmetry of revolution about the main axis AP.

(28) In general, the diameter of this outer surface 27 decreases continuously (that is to say without any step, notch or stage) along the main axis AP starting from the shield 24 up to its tip.

(29) This outer surface 27 has for example a generally truncated-cone shape truncated at its end and having a flat tip (as shown in FIGS. 2, 3 and 5), or a generally truncated-cone shape not truncated at its end and presenting a sharp tip (as shown in FIG. 4).

(30) It should be noted that the outer surface 27 has a generally right (with a rectilinear generatrix, as illustrated in FIGS. 2 to 7), or concave or convex (with a curved generatrix) truncated-cone shape.

(31) In non-illustrated variants, the outer surface 27 has a generally truncated-cone shape truncated at its end and having a rounded tip, or has a generally hemispherical shape.

(32) In general, the outer surface 27 has a decreasing outer diameter along the main axis AP starting from the shield 24 up to its tip (or to its free end). Thus, as it gets away from the shield 24 (and thus by plunging inside the chamber 4), the outer diameter of the outer surface 27 decreases, for example regularly (truncated-cone surface) or irregularly.

(33) In addition, the insulating body 26 also has an inner surface 28 in contact with the propagation medium 25, completely surrounded by the shield 24 and crossed by the central core 23; this inner surface 28 being the transverse surface which is in contact with the propagation medium 25.

(34) This inner surface 28 may be planar and perpendicular to the main axis AP, as shown in the forms of FIGS. 3 and 4.

(35) As shown in the form of FIG. 2, this inner surface 28 may be non-planar. This inner surface 28 is non-planar for the same reasons as those mentioned for the outer surface 27, that is to say for promoting the penetration of the waves of the propagation medium 25 to the gas to be energized through the insulating body 26, and avoiding abrupt impedance interruptions and avoiding useless generation of reflected power.

(36) In general, the inner surface 28 is not orthogonal to the main axis AP and has an increasing outer diameter along the main axis AP in a direction of displacement starting from the distal end 21 towards the proximal end 22 occluded by the insulating body 26.

(37) This inner surface 28 has for example a generally truncated-cone shape, and more precisely a generally right (with a rectilinear generatrix, as illustrated in FIG. 2), or concave or convex (with a curved generatrix) truncated-cone shape.

(38) In the forms illustrated in FIGS. 2 to 4, the central core 23 has a proximal end embedded inside the insulating body 26, without passing completely through this insulating body 26.

(39) In the examples of FIGS. 2 and 3, the proximal end of the central core 23 protrudes from the shield 24 according to the main axis AP by a distance DA smaller than the distance DC.

(40) In the example of FIG. 4, the proximal end of the central core 23 is located in alignment with the proximal end of the shield 24, and therefore does not protrude from the shield 24.

(41) In the examples of FIGS. 2 and 4, the maximum outer diameter of the insulating body 26 is substantially equivalent to the inner diameter of the shield 24. In the example of FIG. 3, the maximum outer diameter of the insulating body 26 is substantially equivalent to the outer diameter of the shield 24, so that the insulating body 26 has a shoulder extended by a section of a reduced diameter substantially equivalent to the inner diameter of the shield 24, this section being pushed into the shield 24.

(42) In non-illustrated variants, the proximal end of the central core 23 is set back (on the inside of the shield 24) with respect to the proximal end of the shield 24.

(43) In non-illustrated variants, the maximum outer diameter of the insulating body 26 is larger than the outer diameter of the shield 24. In the case where the maximum outer diameter of the insulating body 26 is equivalent to or larger than the outer diameter of the shield 24, it is also conceivable that the insulating body 26 is partly in contact with the partition 40 of the chamber 4.

(44) Such an elementary device 1 is used in an installation for producing a plasma comprising:

(45) the chamber 4 within which the plasma is produced and confined, this chamber being delimited by a partition 40;

(46) at least one microwave energy generator (not illustrated), in particular of the solid-state generator type;

(47) at least one coaxial cable or waveguide (not illustrated) connected on the one hand to the generator and on the other hand to the coupling system 3 of an elementary device 1; and

(48) at least one elementary device 1 whose outer surface 27 of the insulating body 26 penetrates inside the chamber beyond its partition 40, as shown in FIGS. 6 and 7.

(49) It should be noted that the shield 24 of the coaxial applicator 2 is either: constituted by a part attached onto the chamber 4 and crossing its partition 40 in a sealed manner; or is integrally formed at least partially with the partition 40. In other words, the shield 24 is formed partially or totally by the partition 40 itself.

(50) The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.