DEVICE AND METHOD FOR PLASMA GENERATION IN A WIDE PRESSURE RANGE AND SYSTEM AND METHOD FOR OPTICAL GAS ANALYSIS/DETECTION BY MEANS OF SUCH A DEVICE

Abstract

The present invention relates to a device for plasma generation in a wide pressure range. The device comprises a first plasma source (1) in a first discharge chamber (2) in order to generate a first plasma in a low-pressure range, a second plasma source (3) in a second discharge chamber (4) in order to generate a second plasma in a high-pressure range, a first coupling element (5) for coupling the device to a system, in order to guide gas out of the system, and a second coupling element (6) for coupling the device to an optical sensor (12). The first discharge chamber (2) has a first optical connection with at least one optical lens (7, 8) to the second coupling element (6) and the second discharge chamber (4) has a second optical connection with at least one optical lens (8) to the second coupling element (6). This invention further relates to a system for optical gas analysis or gas detection and corresponding methods for plasma generation and for operating the system.

Claims

1. Device for plasma generation in a wide pressure range comprising: a first plasma source (1), wherein the first plasma source (1) is arranged in a first discharge chamber (2) and is adapted to generate a first plasma (14) in a low-pressure range, wherein the low-pressure range extends in particular up to high vacuum, i.e. for example up to 10.sup.?8 Torr; a second plasma source (3), wherein the second plasma source (3) is arranged in a second discharge chamber (4) and is adapted to generate a second plasma (15) in a high-pressure range, wherein the high-pressure range extends in particular to above normal pressure, i.e. for example to 1500 Torr, a first coupling element (S), in particular having a flange, for coupling the device to a system, wherein the coupling element (5) is designed to lead gas out of the system; a second coupling element (6) for coupling the device to an optical sensor, such as a photodiode or spectrometer, for optical gas analysis or gas detection, wherein the first discharge chamber (2) has a first optical connection (L1) having at least one optical lens (7, 8) to the second coupling element (6), and the second discharge chamber (4) has a second optical connection (L2) having at least one optical lens (8) to the second coupling element (6).

2. Device according to claim 1, wherein the low-pressure range and the high-pressure range together extend over a pressure range of at least 10 decades, in particular over 12 decades.

3. Device according to claim 1, wherein the low-pressure range and the high-pressure range overlap, in particular over a pressure range of one decade, e.g. from 0.35 Torr to 3.5 Torr.

4. Device according to claim 1, wherein the first and second plasma sources (1, 3) are different plasma sources, e.g., one each from the group consisting of a glow discharge source, a silent discharge source, a radio frequency plasma source, a microwave plasma source, and an inductively coupled plasma source.

5. Device according to claim 1, wherein the first discharge chamber (2) is fluidically coupled to the second discharge chamber (4).

6. Device according to claim 1, wherein gas can be supplied from the first coupling element (5) into the first discharge chamber (2) and can be supplied from the first discharge chamber (2) into the second discharge chamber (4).

7. Device according to claim 1, wherein an optical lens (7), which is part of the first optical connection (L1), is arranged between the first discharge chamber (2) and the second discharge chamber (4).

8. Device according to claim 1, wherein the second coupling element (6) comprises an optical lens (8) which is part of the first and/or the second optical connection (L1, L2).

9. Device according to claim 1, wherein the second optical connection (12) is part of the first optical connection (L1).

10. Device according to claim 1, wherein the device further comprises a pressure sensor.

11. Device according to claim 10, wherein the device further comprises a controller which is designed to control the first and/or the second plasma source (1, 3), in particular to switch the first and/or the second plasma source (1, 3) on or off, as a function of the pressure determined by means of the pressure sensor.

12. Device according to claim 1, wherein the first discharge chamber (2) and the second discharge chamber (4) are of cylindrical design and are arranged coaxially one behind the other, wherein the first coupling element (5) is arranged on the first discharge chamber (2) and the second coupling element (6) is arranged on the second discharge chamber (4), wherein the first plasma source (1) is in particular a glow discharge source and wherein the second plasma source (3) is in particular a silent discharge source.

13. Device according to claim 12, wherein an anode (9) of the first plasma source (1) is glazed in a vacuum-tight manner in a feedthrough through the optical lens (8) in the second coupling element (6), and in particular also in a feedthrough through the optical lens (7), which is arranged between the first discharge chamber (2) and the second discharge chamber (4), and the two feedthroughs are arranged in particular centrally in the two optical lenses (7, 8), and the anode (9) extends coaxially through the second discharge chamber (4) into the first discharge chamber (2).

14. Device according to claim 12, wherein the second plasma source (3) has a high-voltage electrode (10) and a ground electrode (11), wherein the high-voltage electrode (10) is embedded in a dielectric which forms at least part of an inner wall of the second discharge chamber (4), and the ground electrode (11) is arranged concentrically to the high-voltage electrode (10) within the second discharge chamber (4) and along the inner wall, at a distance of less than 1 mm, in particular between 0.05 mm and 0.5 mm, from the high-voltage electrode (10), in particular on a hollow cylinder, e.g. of ceramic, wherein a gap is located between the inner wall and the ground electrode (11), in which gap a discharge zone with a plasma is formed when an alternating voltage is applied between the high-voltage electrode (10) and the ground electrode (11), e.g. with a voltage in the range from ?1 to ?10 kV and a frequency in the range from 1 to 10 KHz.

15. Device according to claim 12, wherein the high-voltage electrode (10) is connectable to ground (GND) for operation of the first plasma source (1) and is connectable to a high-voltage alternating current source for operation of the second plasma source (3), and/or wherein the anode (9) is connectable to a high-voltage direct current source for operation of the first plasma source (1) and is connectable to ground (GND) for operation of the second plasma source (3).

16. System for optical gas analysis or gas detection comprising: a device for plasma generation according to claim 1; a gas source, wherein the device for plasma generation is coupled to the gas source with a first coupling element, in particular with a flange; an optical sensor, such as a photodiode or a spectrometer for optical gas analysis or gas detection, wherein the plasma generation device is coupled to the optical sensor by a second coupling element.

17. Method for plasma generation in a wide pressure range by means of the device according to claim 1, comprising the steps of: feeding a gas from a system via a first coupling element (S) into a first discharge chamber (2) having a first plasma source (1) and/or into a second discharge chamber (4) having a second plasma source (3); generating a first plasma (14) by the first plasma source (1) in a low-pressure range in the first discharge chamber (2), wherein the low-pressure range extends in particular to high vacuum, i.e. for example to 10.sup.?8 Torr, and/or generating a second plasma (15) by the second plasma source (3) in a high-pressure range in the second discharge chamber (4), wherein the high-pressure range extends to above normal pressure, i.e., for example, to 1500 Torr; guiding light which is emitted from the first plasma (14) from the first discharge chamber (2) via a first optical connection (L1) having at least one optical lens (7, 8) and/or light emitted from the second plasma (15) from the second discharge chamber (4) via a second optical connection (L2) having at least one optical lens (8) to a second coupling element (6) for coupling the device to an optical sensor, such as a photodiode or a spectrometer; coupling out at least a portion of the light, which is emitted by the first and/or the second plasma (14, 15), by the second coupling element (6).

18. Method according to claim 17, wherein the first and/or the second plasma source (1, 3) is controlled as a function of the pressure determined with the aid of a pressure sensor, in particular the first and/or the second plasma source (1, 3) is switched on or off.

19. Method according to claim 18, wherein in a pressure range in which the low-pressure range and the high-pressure range overlap, e.g., in a pressure range of 0.35 Torr to 3.5 Torr, the first and second plasma sources (1, 3) simultaneously generate a first and a second plasma (14, 15).

20. Method for optical gas analysis or gas detection, comprising carrying out the steps according to claim 17 and further comprising the steps of: directing the decoupled light to an optical sensor, such as a photodiode or spectrometer, determining a gas or components of a gas or detecting a specific gas or specific components of a gas or determining a pressure of the gas based on the decoupled light, in particular an intensity and/or a spectral distribution of the decoupled light.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Non-limiting exemplary embodiments of the present invention are explained in further detail below with reference to figures, wherein:

[0064] FIG. 1 shows a schematic representation of an exemplary embodiment of a device according to the invention for plasma generation in a wide pressure range;

[0065] FIG. 2 shows a longitudinal section through an exemplary embodiment of a device according to the invention for plasma generation in a wide pressure range with size details;

[0066] FIG. 3 shows an alternative representation of the longitudinal section through the exemplary embodiment according to FIG. 2 with drawn-in plasma regions;

[0067] FIG. 4 shows a variant of the device; and

[0068] FIG. 5 shows another variant of the device.

[0069] In the figures, the same reference signs denote the same elements.

DETAILED DESCRIPTION OF THE INVENTION

[0070] FIG. 1 shows in a schematic representation an exemplary embodiment of a device according to the invention for plasma generation in a wide pressure range. The device comprises a first plasma source 1, e.g. a glow discharge source (GD, cold cathode source), which is arranged in a first discharge chamber 2, and a second plasma source 3, e.g. a silent discharge source (DBD source), which is arranged in a second discharge chamber 4, wherein the two discharge chambers 2, 4 are arranged one behind the other (in series), adjacent to each other. Further, the device comprises a first coupling element 5, e.g. having a flange, for coupling the device to a system (not shown) in which a gas is present. The gas is fed out of the system into the first discharge chamber 2 via the coupling element 5. From the first discharge chamber 2, the gas can flow into the second discharge chamber 4. For this purpose, there are, for example, several (e.g. 6 to 12) vent holes, each with a diameter of at least 1 mm, between the two discharge chambers 2, 4. Further, the device comprises a second coupling element 6 for coupling the device to an optical sensor, such as a photodiode or a spectrometer, for optical gas analysis or gas detection (or also for gas pressure measurement).

[0071] The first plasma source 1 is suitable for generating a plasma in a low-pressure range, e.g. from 10.sup.?8 Torr to about 3.5 Torr, and the second plasma source 2 is suitable for generating a plasma in a high-pressure range, e.g. from about 0.35 Torr to 1500 Torr. Depending on the pressure of the gas, the first (at low pressure->high vacuum) or the second (at atmospheric pressure) plasma source 1, 3 will therefore ignite the gas and thereby generate a first or second plasma 14, 15 which emits different light depending on the type or composition of the gas. In the pressure overlap range of the two plasma sources 1, 3, e.g. from 0.35 Torr to 3.5 Torr, both plasma sources 1, 3 can also be active at the same time and thus generate a first as well as a second plasma 14, 15 simultaneously. This parallel operation of both plasma sources 1, 3 is especially possible because of the low power of both discharges.

[0072] The light emitted from the first plasma 14 in the first discharge chamber 2 is guided through an optical lens 7, which is located between the two discharge chambers 2, 4. The light is then guided through the second discharge chamber 4 and passes through a second optical lens 8, which is located in the second coupling element 6, to an optical sensor 12, with the aid of which an optical gas analysis or gas detection (or also a gas pressure measurement) can be carried out. The optical sensor 12 is sensitive in the wavelength range which can be transmitted through the two optical lenses 7, 8. The optical sensor 12 can be a simple radiation sensor, e.g. a light sensor such as a photodiode, but it can also be a more complex optical sensor, e.g. a spectrometer.

[0073] The anode 9 of the first plasma source 1 is guided from the second coupling element 6 through the second optical lens 8 in the second coupling element 6 through the second discharge chamber 4 through the first optical lens 7 between the two discharge chambers 2, 4 into the first discharge chamber 2. In particular, the anode 9 is glazed in a vacuum-tight manner in a feedthrough through the optical lens 8 in the second coupling element 6. The anode 9 may also be glazed in a feedthrough through the optical lens 7 between the two discharge chambers 2, 4. The feedthrough through the optical lens 7 can also be designed to be vacuum-tight, although this is not absolutely necessary. The two feedthroughs are arranged in particular centrally in the two optical lenses 7, 8, so that the anode 9 extends coaxially through the second discharge chamber 4 into the first discharge chamber 2. The cathode of the first plasma source 1 is located at the edge of the first discharge chamber 2 spaced from the anode 9. The inner wall of the first discharge chamber 2 may in this case form the cathode. For example, the cathode is made of titanium. To generate a glow discharge of the gas, a high DC voltage (HV DC) of, for example, 3.3 kV is applied between the anode 9 and the cathode. This high voltage accelerates electrons from the cathode material towards the anode 9. By applying an external magnetic field by means of (permanent) magnets 13, the electrons are directed along circular or spiral paths. This increases the probability of collision with an atom/molecule of the gas. These collisions lead to the excitation or ionization of the atom/molecule. The ions migrate towards the cathode, generating an ion current. Photons are generated on the one hand by relaxation of the excited atoms, molecules, ions and on the other hand by recombination of these ions. The emitted photons radiate into the whole space and hit, among others, the first optical lens 7 between the two discharge chambers 2, 4. Here the incoming photons are refracted and directed to the second optical lens 8 in the second coupling element 6. The optical lenses 7, 8 can be made of one or more materials, e.g. sapphire, as well as having an aspherical shape to counteract spherical or chromatic aberration.

[0074] The optical wavelength range includes electromagnetic radiation with wavelengths from 100 nm to 1 mm, i.e. in particular the ranges of visible light, ultraviolet radiation and infrared radiation.

[0075] Details concerning the second plasma source 3, i.e. the device for generating a silent plasma discharge, can be taken from the Swiss patent application filed on the same day as the present patent application and entitled Vacuum feedthrough, electrode assembly and device for generating a silent plasma discharge by the same applicant as the present patent application. The second plasma source 3 has a high-voltage electrode 10 and a ground electrode 11, wherein the high-voltage electrode 10 is embedded in a dielectric forming at least part of an inner wall of the second discharge chamber 4. The ground electrode 11 is arranged concentrically to the high-voltage electrode 10 on the inner wall of the second discharge chamber 4, in particular on a hollow cylinder, for example made of ceramic. The ground electrode 11 is located at a distance of less than 1 mm from the high voltage electrode 10, wherein a gap is located between the inner wall and the ground electrode 11, in which a discharge zone with the (second) plasma 15 is formed when a high alternating voltage (HV AC) is applied between the high voltage electrode 10 and the ground electrode 11. The inventors have recognized that with this expansion of the gap, a dielectric barrier discharge (DBD) can be stably generated with a high AC voltage in the range ?1 to ?10 kV and a frequency in the range 1 to 10 kHz over a wide pressure range approximately from 0.35 Torr to 1500 Torr.

[0076] In FIG. 2, a longitudinal section through an exemplary embodiment of a device according to the invention for plasma generation in a wide pressure range is shown together with size details. In this embodiment variant, the first discharge chamber 2 and the second discharge chamber 4 are of cylindrical design and arranged coaxially one behind the other (connected in series, so to speak). As in FIG. 1, the first coupling element 5 is arranged on the right side of the first discharge chamber 2 and the second coupling element 6 is arranged on the left side of the second discharge chamber 4. The overall length of the device in this example is only just about 60 mm and the overall diameter in this example is only about 25 mm. As this shows, the present invention allows for a very compact design, which consequently saves a lot of space.

[0077] FIG. 3 shows an alternative representation of the longitudinal section through the exemplary embodiment according to FIG. 2. FIG. 3 also shows the plasmas 14, 15 in the two discharge chambers 2, 4 and schematically indicates the two optical connections L1, L2. The areas in which the plasmas 14, 15 are generated are outlined with dashed lines.

[0078] FIG. 4 shows a longitudinal section through an embodiment which largely corresponds to the embodiment shown in FIG. 1. In addition, this variant has at least one further electrode 16, which is guided radially outside the high-voltage electrode 10 of the second plasma source and insulated from it from the vacuum side to the outside. This further electrode is guided through, for example, between a fused glass ring and a cylinder of insulating material. The cylinder of insulating material can, for example, project beyond the fused glass ring on both sides in order to form a continuous contact surface for the electrode. A plurality of such further electrodes is possible, wherein the electrodes can, for example, be of strip-shaped design with a longitudinal direction parallel to the longitudinal axis of the device. A plurality of such further electrodes may be distributed in an azimuthal direction and arranged insulated from each other, so that most of them would not be visible or are not visible in this longitudinal sectional view. One or more such electrodes allow for the connection of additional sensors on the vacuum side, or alternative ways of connecting the anodes and cathodes of the first and second plasma sources discussed so far.

[0079] FIG. 5 shows an alternative connection 17 to the anode of the first plasma source compared with the embodiment in FIG. 4. The feedthrough from the outside to the plasma side is designed as discussed in connection with FIG. 4 for the further electrode 16 and is opposite the further electrode 16 visible in longitudinal section by 180 degrees in the case shown with respect to the longitudinal axis of the device. Through a hole, the alternative connection 17 is led into the first discharge chamber 2 and contacts the central anode pin. This means that the electrical connection led centrally through the second discharge chamber 4 in the variant according to FIG. 4 and the associated feedthrough through the first optical lens 7 and second optical lens 8 can be omitted. This has the effect that a greater proportion of the electromagnetic radiation from the first or second plasma reaches the outside. Electrodes can, for example, be covered over their entire length with an insulating layer.

[0080] This has the advantage that in electron/ion optics often undesirable open potentials, which could influence charged particles, are avoided. For this purpose, for example, a glass ring lying over the electrodes can be further extended axially or individual conductive tracks can be realized with a thin glass layer, which lies overlapping over the respective conductive track.

[0081] Advantages of the present invention include integrating multiple plasma sources together in a single device, wherein the device also has only a single connection for introducing the gas to be analyzed and only a single connection for coupling the device to an optical sensor. With the device according to the invention, a stable plasma can be generated over a pressure range of over about 12 decades (in Torr), from high vacuum (10.sup.?8 Torr) to above normal pressure (>atmospheric pressure, e.g. 1500 Torr). According to the invention, it is also provided to select and control the respective optimal plasma source depending on the pressure range by means of a device-internal pressure measurement.

LIST OF REFERENCE SIGNS

[0082] 1 First plasma source [0083] 2 First discharge chamber [0084] 3 Second plasma source [0085] 4 Second discharge chamber [0086] 5 First coupling element [0087] 6 Second coupling element [0088] 7 First optical lens (between the two discharge chambers) [0089] 8 Second optical lens (in the second coupling element) [0090] 9 Anode of the first plasma source [0091] 10 High-voltage electrode of the second plasma source [0092] 11 Mass electrode of the second plasma source [0093] 12 Optical sensor (e.g. photodiode or spectrometer) [0094] 13 (Permanent) magnet [0095] 14 First plasma [0096] 15 Second plasma [0097] 16 Further electrode [0098] 17 Alternative connection to the anode of the first plasma source [0099] L1 First optical connection [0100] L2 Second optical connection