Chamber for ionization vacuum gauge

Abstract

To provide a device that generates plasma in a vacuum pressure sensor, and minimizes the above described adverse effect.SOLUTION: Provided is a chamber for bounding a plasma generation region in a vacuum pressure sensor, where the chamber is equipped with a conductive casing element (1) which is arranged outside in a radial direction to a center shaft, the chamber is arranged substantially perpendicular to the center shaft, and is equipped with conductive wall elements (2, 2', 2") connected to the casing element, at least one of the wall elements has a first opening (3) through which the center shaft extends, the casing element is equipped with at least a first region (B1) and a second region (B2), and the first region is positioned closer to the center shaft than the second region. Further, provided is a vacuum pressure sensor equipped with the chamber.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum pressure sensors. In particular, the present invention relates to a chamber for a vacuum pressure sensor in the form of an ionization gauge, and a vacuum pressure sensor comprising a chamber according to the present invention.

Background Art

[0002] Vacuum pressure sensors or gauges that can determine pressures far below atmospheric pressure are known. Among the known vacuum pressure sensors, so-called ionization gauges have a particularly wide measurement range. In an ionization gauge, residual gas is ionized to generate a plasma. The electrons required to ionize the gas are generated either by a hot cathode (hot cathode ionization gauge) or a self-sustaining gas discharge between cold electrodes (cold cathode gauge). For example, the current from the anode to the cathode is measured as a parameter for determining the pressure. The anode and cathode are in contact with the generated plasma. By appropriately combining an electric field and a magnetic field, the trajectory of electrons in the vacuum pressure sensor can be extended, and thus the ion yield can be increased. The generated plasma emits radiation, which can be analyzed in addition to the measured current and used to determine the pressure or the composition of the residual gas. As an example, International Publication No. 2021 / 052599 discloses a method for determining the pressure in a vacuum system and a vacuum pressure sensor designed to evaluate the radiation emitted by a plasma.

[0003] In such a vacuum pressure sensor, the electromagnetic radiation to be analyzed reaches a detector arranged separately from the zone where the plasma is generated through a window or lens that is at least transmissive within the range of the electromagnetic spectrum. Due to the plasma, and in some cases due to the plasma-related sputtering effect on the cathode, the plasma side of the window or lens may become less and less transmissive to radiation over a longer operating time, for example due to a thin metal layer accumulating on the window or lens. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The object of the present invention was to provide components for an alternative device for generating plasma within a vacuum pressure sensor. In particular, the object of the present invention was to provide a device that minimizes the aforementioned side effects of generating plasma within a vacuum pressure sensor. [Means for solving the problem]

[0005] This objective is achieved by the chamber described in claim 1, according to the present invention. The chamber according to the present invention is designed to define a plasma generation region within a vacuum pressure sensor. The chamber comprises a conductive casing element positioned radially outward with respect to the central axis. The chamber further comprises a conductive wall element positioned substantially perpendicular to the central axis and connected to the casing element. At least one of the wall elements has a first opening through which the central axis extends. The casing element comprises at least first and second regions, the first region being located closer to the central axis than the second region.

[0006] Due to the opening in the wall element, the chamber is suitable for receiving the anode rod of the ionization vacuum gauge along the central axis of the chamber. The chamber can also act as the cathode.

[0007] Because the first and second regions of the casing element are at different distances from the axis, the casing element The element is not cylindrical. For example, the first and second regions may be positioned at different axial positions, or at different azimuthal positions relative to the axis. When a voltage is applied between the central anode and the casing element, a higher electric field is generated between the central axis of the casing element and the first region than between the second region of the casing element and the central anode. As the inventors have recognized, this difference may be advantageous for the service life of optical elements positioned in close proximity to the chamber.

[0008] The casing element may be formed as a single unit or may be composed of multiple parts.

[0009] The wall elements may include, for example, ferromagnetic materials. The ferromagnetic wall elements can interact with, for example, the permanent magnets of an ionization vacuum gauge placed outside the chamber, thereby influencing the magnetic field pattern inside the chamber.

[0010] Exemplary embodiments of the chamber according to the present invention will become apparent from the features of dependent claims 2 to 7.

[0011] In one embodiment, the cross-section passing through the casing element has a polygonal shape in a plane perpendicular to the central axis.

[0012] The polygon may be, for example, a hexagon or a dodecagon. Such polygonal cross-sections fit well in substantially cylindrical environments, but ensure the existence of regions located at smaller and larger distances from the central axis. Thus, the distance between the central axis and the casing element varies depending on the azimuth direction.

[0013] In one embodiment, the casing element is at least partially conical. The casing element may, for example, have the shape of the side surface of a frustum of a cone. In this case, the first region closer to the central axis is located at the end of the frustum of a cone having a smaller radius.

[0014] In one embodiment, the first region of the casing element is located in the center of the chamber with respect to the axial direction of the central axis.

[0015] For example, the casing element may be formed from two parts, each having the shape of a frustoconical side, with the side with the smaller radius either touching each other in the center of the chamber or being fixed to a central wall element.

[0016] In one embodiment, the chamber comprises three parallel wall elements, all of which have a central opening through which a central axis extends.

[0017] This embodiment is suitable for accommodating the anode rod of an ionization vacuum gauge that protrudes through all wall elements.

[0018] In one embodiment, at least one of the wall elements has a second opening. A second or further opening can contribute to a better hydrodynamic connection to the space where the pressure is measured. The second or further opening can also provide multiple continuous radiation paths for electromagnetic radiation generated within the plasma. The second or further opening is an opening positioned radially offset from the central axis.

[0019] In a further embodiment, the first opening is located by the inner edge of at least one wall element. It is enclosed. The inner edge has at least a first section projecting toward the central axis. The inner edge has a second section that is further away from the central axis than the first section.

[0020] The inventors have recognized that when a chamber is used to demarcate a plasma generation region within a vacuum pressure sensor, a change in the distance between the inner edge of a wall element and the central axis, which results in a change in the distance between the inner edge of the wall element and the anode, helps to ignite the plasma under unfavorable conditions, such as pressure in the lower operating range of the vacuum pressure sensor.

[0021] Such ignition assistance can be achieved, for example, by the smooth change in the azimuthal direction of the inner edge contour, caused by one or more small spikes projecting inward from the circular inner edge. When radiation emitted from the plasma is analyzed, sections that are further from the central axis block less radiation. This embodiment is particularly useful in a vacuum pressure gauge to which a spectrometer is attached. Alternatively, or in combination with the above, the inner edge surface may be oriented obliquely to the central axis, so that sections projecting toward the central axis are in different axial positions than sections further from the central axis. As an example, a tapered rim can be formed around the first opening by drilling the opening with a conical drill. In this way, a relatively sharp edge can be produced around the first opening. In embodiments having a wall element containing a ferromagnetic material, the change in distance between the inner edges of the first opening not only results in shaping of the electric field but also helps to concentrate the magnetic field in a particular region or at a particular azimuthal position along the central axis.

[0022] The present invention also relates to a vacuum pressure sensor as described in claim 8. The vacuum pressure sensor according to the present invention comprises a chamber according to the present invention. The vacuum pressure sensor further comprises an anode positioned along the central axis of the chamber and means positioned radially outward of the chamber to generate a magnetic field inside the chamber.

[0023] The chamber is suitable for functioning as the cathode or as part of the cathode of a vacuum pressure sensor in the form of an ionization vacuum gauge. Specifically, the vacuum pressure sensor described above is an inverse magnetron type ionization vacuum gauge.

[0024] In an alternative configuration of the inverted magnetron type, the present invention further relates to the vacuum pressure sensor described in claim 9.

[0025] This vacuum pressure sensor according to the invention comprises a chamber according to the invention which serves as an anode. The vacuum pressure sensor further comprises a cathode which is at least partially arranged along the central axis of the chamber, and means arranged radially outside the chamber for generating a magnetic field inside the chamber.

[0026] The chamber is suitable for functioning as the anode or part of the anode of a vacuum pressure sensor in the form of an ionization gauge. Since the roles of the anode and the cathode are reversed with respect to the aforementioned vacuum pressure sensor of the inverse magnetron type, this alternative vacuum pressure sensor is a magnetron-type ionization gauge.

[0027] Embodiments of the vacuum pressure sensor will become apparent from the features of claims 10 and 11.

[0028] One embodiment of the vacuum pressure sensor further comprises a housing. The housing has a flange surrounding an opening for establishing a fluid connection between the plasma generation region inside the vacuum pressure sensor and the measurement space outside the vacuum pressure sensor. A radiation-transmissive element is arranged on the wall of the housing so that electromagnetic radiation emitted from the plasma generation region can reach the outside of the housing through the radiation-transmissive element. The chamber according to the invention is arranged inside the housing. A first region of the casing element of the chamber is arranged on a first side of the chamber, and the first side is directed towards the flange. A second region of the casing element of the chamber is arranged on a second side of the chamber, and the second side is directed towards the radiation-transmissive element. For this to be possible, it is arranged on the wall of the housing. The chamber according to the invention is arranged inside the housing. A first region of the casing element of the chamber is arranged on a first side of the chamber, and the first side is directed towards the flange. A second region of the casing element of the chamber is arranged on a second side of the chamber, and the second side is directed towards the radiation-transmissive element.

[0029] In a particular implementation of this embodiment, the conductive casing element of the chamber has a frustoconical shape that tapers towards the flange.

[0030] Surprisingly, a relatively slight taper corresponding to an angle of approximately 3° between the central axis and the surface line on the conical casing element results in an increase in the output of radiation emitted from the plasma in a low-pressure environment. This is surprising, and as with this configuration, the plasma generation region is expected to be located further away from the radiotransmissive element, which at first glance might be expected to result in lower radiation intensity outside the housing.

[0031] In a further embodiment of the vacuum pressure sensor, an optical element, such as a lens or mirror, and a spectrometer are located outside the housing. The radiotransmissive element and the optical element work together to collect electromagnetic radiation emitted from the region around the anode and focus it onto the optically sensitive element of the spectrometer.

[0032] This type of vacuum pressure sensor benefits from both increased radiation intensity reaching the optically sensitive element of the spectrometer and increased operating time.

[0033] In certain modifications of the embodiment, the optical element can be adapted to compensate for axial displacement of the radiation emission region. This modification may be particularly combined with the above-described embodiment having a frustoconical shape in which the conductive casing element of the chamber tapers toward the flange. In this embodiment, the center and axial extension of the plasma region with the highest radiation emission may vary in response to pressure. Adaptable optical elements, such as lenses movable in the direction of the central axis, help to adjust the focus of the overall configuration formed by the spectrometer, optical elements, and radiotransmissive elements within the housing wall. A control loop can be used to continuously adjust the position of the optical element for the maximum radiation intensity acceptable to the spectrometer. In particular, the radiotransmissive element may itself be molded in the form of a lens.

[0034] Exemplary embodiments of the present invention are described in further detail below with reference to the figures. [Brief explanation of the drawing]

[0035] [Figure 1]Different diagrams of the first embodiment of the chamber are shown in subfigures 1.a) to 1.c). [Figure 2] Different diagrams of the second embodiment of the chamber are shown in subfigures 2.a) to 2.d). [Figure 3] Different diagrams of the third embodiment of the chamber are shown in subfigures 3.a) to 3.d). [Figure 4] This is a longitudinal cross-sectional view of a vacuum pressure sensor having a chamber, shown schematically. [Figure 5] This is a longitudinal cross-sectional view of one embodiment of a vacuum pressure sensor. [Figure 6] Subfigures 6.a) to 6.c) show axial cross-sectional views of modified versions of the first opening, and subfigure 6.d) shows longitudinal cross-sectional views of modified versions of the first opening. [Figure 7] Subfigures 7.a) to 7.e) show modified examples of the contour of the first opening having specific dimensions. [Figure 8] In subfigures 8.a) to 8.d), a wall element having a modified example of the first opening is shown in a perspective view. [Modes for carrying out the invention]

[0036] Figures 1.a) and 1.b) show two perspective views of the first embodiment 11 of the chamber from two viewing directions. In this embodiment, the chamber has a casing element 1 shaped like the side of a prism with a dodecagonal base. Three wall elements 2, 2', and 2'' form closures at both ends of the chamber (2, 2'') and at the intermediate wall 2', respectively. Six projections on the outer circumference of the intermediate wall 2' protrude beyond the outer surface of the casing element through rectangular slots in the casing element. A first opening 3 is located in the center of wall 2'', and as a result, the central axis A of the chamber extends through this opening. Here, the central openings of two walls 2 and 2' are not visible, so that the central anode rod of the ionization vacuum gauge can pass through all three central openings.

[0037] Figure 1.c) shows a plan view of the wall element 2. Apart from the first centrally located opening 3, the wall element has a total of six further openings 4 with a larger radius. Fastening regions 5 are located between the outwardly projecting portions on the outer circumference of the wall element, where the wall element is connected to the casing element, for example, by spot welding.

[0038] Figures 2.a) and 2.b) show two perspective views of the second embodiment 12 of the chamber from two viewing directions. In this embodiment, the casing element 1 has a frustoconical shape.

[0039] Figure 2.c) shows a plan view of the same second embodiment 12. Figure 2.d) shows a side view of the same second embodiment 12. As an example, the half-opening angle of the frustum may be 3°, as shown in this side view. As an example, the length L of the chamber may be in the range of 20 mm to 30 mm. This embodiment of the chamber also has three wall elements 2, 2', and 2''.

[0040] Figures 3.a) and 3.b) show two perspective views of the third embodiment 13 of the chamber from two viewing directions. In this embodiment, the casing element is formed from two parts, and each part 1' and 1'' of the casing element has the shape of a frustoconical side, in either case the frustoconical side having the smaller radius is fastened to the intermediate wall element 2'. In this way, the first region of the casing element is the region that is more radially closer to the central axis and is located in the center of the chamber.

[0041] Figure 3.c) shows a plan view of the same third embodiment 13. Figure 3.d) shows a side view of the same third embodiment 13. Two frustums of cones, each with a half-opening angle of 3°, are clearly visible in this figure.

[0042] Figure 4 shows a longitudinal cross-section extending along the central axis A through a vacuum pressure sensor 40 in the form of an ionization vacuum gauge having a chamber according to the present invention as an anode 41 and cathode. The chamber has wall elements 2, 2', and 2''. The shape and position of the casing element 1 are schematically shown here by a region enclosed by dashed lines as a placeholder. Various shapes of the casing element 1 are conceivable here, i.e., any one of the casing elements of the above embodiments 11, 12, and 13 of the chamber is a possible choice here. In any of these embodiments of the chamber, the chamber is a kind of push-in chamber that can be pushed from the flange side 45 of the vacuum pressure sensor into the illustrated position of the chamber. Radially outward of the chamber, a magnetic field is present inside the chamber. A permanent magnet device 44 is arranged, which functions as a means for generating a field. The permanent magnet device extends in an annular manner around an axis. According to one possible embodiment, this permanent magnet device interacts advantageously with a wall element made of a ferromagnetic material. During the operation of the vacuum pressure sensor, i.e., when a high voltage is applied between the anode and cathode and there is pressure in the chamber within the measurement range of the pressure sensor, plasma is generated in the plasma generation region 42 around the anode. The plasma emits electromagnetic radiation 43, which is transmitted through a radioactive element 46, as indicated by the corresponding arrows, for example. It can be accessed from the outside through a window or lens.

[0043] Figure 5 shows a longitudinal cross-section of one embodiment of a vacuum pressure sensor, partially generalized from the embodiment shown in Figure 4, with partially specific details. The vacuum pressure sensor 50 shown here has a housing 51 having a flange 45 connected to the measurement space. At the opposite end, a radiolucent element 46, formed in this case as a lens, allows electromagnetic radiation emitted from the radiolucent region 55 to be transmitted to the outside of the housing. The radiation path can lead to a spectrometer 54, for example, across an optional optical element 53. Although these features are not part of the vacuum pressure sensor 50, the radiolucent region 55, the indicating radiation path, the optical element 53 in the form of a lens, and the spectrometer 54, indicated by a symbol, are shown with dashed lines to show that they are useful for understanding its function and for illustrating a more specific embodiment. The chamber located inside the housing has a frustoconical casing element 1 that tapers toward the flange 45. In this way, the first region B1, which is closer to the central axis than the second region B2, is on the side closer to the flange, and the second region B2 is on the side closer to the radiolucent element 46. The anode rod 41 is positioned on a common central axis between the housing and the chamber. The electrical contacts indicated by "+" and "-" indicate how the vacuum pressure sensor operates. The modification shown here has a central anode rod 41 conductively connected to the "+" contact, as the resulting inverted magnetron vacuum pressure gauge. As described above, by switching the roles of anode and cathode, i.e., mainly by swapping "+" and "-", a magnetron-type instrument can be implemented with only slight modifications to the pressure sensor, as shown in Figure 5. The housing 51 and the inserted chamber together form the cathode of the sensor. On the radially outer side of the housing are means 52 for generating a magnetic field inside the housing. The chamber has three wall elements indicated by 2, 2', and 2'', each having an opening through which the central axis extends. The optical element 53 may be optionally axially movable, as indicated by the double-headed arrows, to adjust the focus when the radiation emission region 55 moves along the anode, or when it stretches or contracts in its axial extension in response to pressure.

[0044] Figure 6 shows variations in the shape of the first opening at the center of the wall element. Only a small portion of each wall element is shown. All the variations shown here have in common that the first opening 3 is enclosed by the inner edge of the wall element, and the inner edge has at least a first section S1 (not shown in Figures 6.a to 6.c) projecting toward the central axis A' and a second section S2 that is further away from the central axis than the first section. Multiple projecting sections S1 are possible; for example, Figures 6.a) and 6.b) have three first sections S1, and Figure 6.c) has six first sections S1. Figure 6.d) shows a projecting region S1 formed by the conical surface of the inner edge. All the variations shown here can act as ignition aids, i.e., to help the plasma be ignited and maintained at a relatively low pressure relative to the measurement range of a vacuum pressure gauge. The protruding sections may be formed as sharp spikes, as shown in Figures 6.b) and 6.d), or they may be formed with a large radius (Figure 6.a) or flat, if corresponding recesses of section S2 are formed in their vicinity (Figure 6.d).

[0045] Figures 7.a) to 7.e) show variations of the contour of the first opening in the wall element, all variations based on an approximate opening diameter of 5 mm. The protruding section (S1) and recessed section (S2) are repeated 3 times (Figures 7.a and 7.b), 6 times (Figure 7.c), 4 times (Figure 7.d), or 8 times (Figure 7.e), respectively, along the circumference of the opening. The protruding section may be limited to a small portion of the circumference (Figure 7.a) or may cover a large portion of the circumference (Figures 7.b, 7.c, 7.d), separated by a more limited recess between them.

[0046] Figures 8.a) to 8.d) show one of the wall elements 2, 2', or 2'' in the above diagram. Figure 8 shows a perspective view of a complete wall element having a first opening 3 that can serve one purpose and has a contour as shown in the corresponding subfigure of Figure 7. That is, the contour of the first opening in Figure 8.a) has, as an example, the shape shown in Figure 7.a). The thickness of the wall element shown in Figure 8 may be about 1.5 mm to match the dimensions shown in the corresponding subfigure of Figure 7. These wall elements may be made of, for example, a ferromagnetic material. In addition to the first opening 3 shown herein, the wall element can be further modified to have additional openings at other radial positions, for example, as shown in Figure 1.c). The configuration of the first opening of all wall elements shown in Figure 8 can be used as an ignition aid so that the plasma is ignited at a relatively low pressure.

[0047] Returning to the technical effects of all embodiments of the present invention, the inventors have recognized that the present invention makes it possible to achieve a geometric change in electric field strength instead of setting the voltage between electrodes to an appropriate value. Instead, it becomes possible to find an appropriate spatial position. As an example, in an embodiment having a polygonal cross-section along a circle around the anode, the position with maximum light can be found and used for optical evaluation. If process conditions change, this geometric position can be tracked.

[0048] Conical and polygonal cone-type embodiments allow for variation of plasma density along the axis. This has the advantage that it is possible to specify the emission volume and, when combined with the discovery of the minimum sputtering value, i.e., a long service life for the radioactive element is possible. [Explanation of Symbols]

[0049] List of reference symbols 1 Casing element 1',1" Part of the multiple casing element 2,2',2" wall element 3. First opening (within the wall element) 4. Second / further opening (within wall element) 5 Fastening area on wall element 6. Markings on wall elements 11,12,13 Chamber Embodiments 40 Vacuum pressure sensor 41 Anode, for example, an anode rod 42 Plasma generation region 43. Radiation 44 Permanent magnet device 45 Flange 46 Radiolucent elements 50 Vacuum pressure sensor 51 Housing 52 Means for generating a magnetic field 53 Optical elements 54 Spectrometer 55 Radiation emission area A center axis B1 First area (closer to the central axis) B2 Second region (further from the central axis) L (chamber length) S1 First section of the inner edge of the wall element S2 Second section of the inner edge of the wall element

Claims

1. A chamber for defining a plasma generation region (42) within a vacuum pressure sensor (40), wherein the chamber is A conductive casing element (1, 1', 1") is positioned radially outward with respect to the central axis (A), It comprises three parallel conductive wall elements (2, 2', 2") arranged substantially perpendicular to the central axis (A) and connected to the conductive casing element (1, 1', 1"), The three mutually parallel conductive wall elements (2, 2', 2") all have a first opening (3) through which the central axis (A) extends. The conductive casing element (1, 1', 1") comprises at least a first region (B1) and a second region (B2), wherein the first region (B1) is located closer to the central axis (A) than the second region (B2), The conductive casing element (1, 1', 1") is at least partially conical, allowing for geometrically controlled changes in electric field strength, in the chamber.

2. The chamber according to claim 1, wherein the first region (B1) of the conductive casing element (1, 1', 1") is located in the center of the chamber with respect to the axial direction of the central axis (A).

3. The chamber according to claim 1 or 2, wherein at least one of the conductive wall elements (2, 2', 2") has a second opening.

4. The chamber according to claim 1 or 2, wherein the first opening (3) is surrounded by the inner edge of at least one conductive wall element (2, 2', 2"), the inner edge having at least a first section (S1) projecting toward the central axis (A) and a second section (S2) further away from the central axis (A) than the first section (S1).

5. A vacuum pressure sensor comprising: a chamber as described in claim 1 or 2 as a cathode; an anode (41) arranged along the central axis (A) of the chamber; and means (44) arranged radially outward of the chamber to generate a magnetic field inside the chamber.

6. A vacuum pressure sensor comprising: a chamber according to claim 1 or 2 as an anode or part of an anode; a cathode at least partially disposed along the central axis (A) of the chamber; and means disposed radially outward of the chamber to generate a magnetic field inside the chamber.

7. The vacuum pressure sensor according to claim 5, further comprising a housing having a flange (45) surrounding an opening for establishing a fluid connection between the plasma generation region (42) inside the vacuum pressure sensor and the measurement space outside the vacuum pressure sensor, wherein the radioactive element (46) is positioned within the wall of the housing so that electromagnetic radiation emitted from the plasma generation region (42) can reach the outside of the housing via the radioactive element (46), the chamber is positioned inside the housing, the first region (B1) is positioned on the first side of the chamber oriented toward the flange (45), and the second region (B2) is positioned on the second side of the chamber oriented toward the radioactive element (46), in particular the conductive casing elements (1, 1', 1") of the chamber have a frustoconical shape tapering toward the flange (45).

8. The vacuum pressure sensor according to claim 7, wherein the optical element (53) and the spectrometer (54) are located outside the housing, and the radiotransmissive element (46) and the optical element (53) work together to collect electromagnetic radiation emitted from a region (55) around the anode and focus it onto the optically sensitive element of the spectrometer, and in particular the optical element (53) is adaptable to compensate for axial displacement of the radiation emission region (55).

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