Ionization chamber for leak detector with inlet-sided ion repelling unit for inhibiting ion back flow

Abstract

A leak detector 104 is disclosed for detecting leakage of a tracer gas 102, e.g. helium, from vacuum equipment 140. The leak detector includes an ionization chamber 100 comprising: at least one inlet opening 108 for inletting said gas to be ionized into an interior of an ionisation housing 106; and an ion repelling unit 110 arranged outside the housing, or at the at least one inlet opening, for inhibiting a back flow of generated ions 112 through the at least one gas inlet opening. The ion repelling unit may comprise an electrically, e.g. positively, charged metallic grid 116 or plate disposed outside the ionisation housing so as not to influence the process of ionisation therein. Alternatively, the repelling unit may comprise a large plurality (110, Fig. 5) of small gas inlet openings (108) that provide a mechanical barrier function for preventing the excessive loss of ions from within housing (106).

Description

BACKGROUND ART [0001 ] The present invention relates to an ionization chamber, a leak detector, and a method.

[0002] A leak detector may implement a mass spectrometer used to detect separated charged ions. Ions are generated based on tracer atoms or molecules in an ionization chamber. The ions may move from the ionization chamber up to a detector by striking on it. Such a detector may detect a current signal generated from the incident ions. A detector output may be displayed.

[0003] However, accuracy of conventional leak detectors may be limited due to a limited efficiency of the ionization chamber. DISCLOSURE

[0004] It is an object of the present invention to provide an ionization chamber for a leak detector with high efficiency. This object is solved by the subject matter according to the independent claims. Further embodiments are shown in the dependent claims.

[0005] According to an exemplary embodiment of the invention, an ionization chamber for ionizing gas for a leak detector is provided, wherein the ionization chamber comprises an ionization housing having at least one gas inlet opening for inletting gas to be ionized into an interior of the ionization housing, and an ion repelling unit arranged outside of the ionization housing or at the at least one gas inlet opening for repelling ions ionized inside the ionization housing to inhibit a back flow of the ions through the at least one gas inlet opening out of the ionization housing.

[0006] According to another exemplary embodiment of the invention, a leak detector for detecting leakage of gas in a vacuum equipment is provided, wherein the leak detector comprises an ionization chamber having the above-mentioned features for ionizing gas leaking at the vacuum equipment.

[0007] According to still another exemplary embodiment of the invention, a method is provided which comprises inletting gas to be ionized into an interior of an ionization housing of an ionization chamber via at least one gas inlet opening of the ionization housing, at least partially ionizing the inlet gas inside the ionization housing to thereby generate ions, and repelling at least part of the ions ionized in the ionization housing by an ion repelling unit arranged outside of the ionization housing or at the at least one gas inlet opening to inhibit a back flow of the ions through the at least one gas inlet opening out of the ionization housing.

[0008] In the context of the present application, the term “ionization chamber” may particularly denote a device configured for generating ions, i.e. charged particles, based on electrically neutral gas, such as atoms and / or molecules in the gas phase.

[0009] In the context of the present application, the term “leak detector” may particularly denote an apparatus configured for being brought in gas communication with a vacuum equipment to be tested with respect to leakage and configured for determining information indicative of the leakage characteristics of such a vacuum equipment.

[0010] In the context of the present application, the term “ionization housing” may particularly denote an exterior casing of the ionization chamber inside of which ionization of gas occurs. For example, the ionization housing may surround an ionizing volume therein but may have one or more openings, such as at least one gas inlet opening for inletting gas and at least one ion outlet opening for outletting ions. Optionally, the ionization housing may comprise one or more further openings, for instance an opening for an electron beam which may be used for ionizing gas.

[0011] In the context of the present application, the term “gas inlet opening” may particularly denote one or more holes formed in an ionization housing configured for allowing or promoting inlet of gas into an interior of the ionization housing.

[0012] In the context of the present application, the term “ion repelling unit” may particularly denote any device, arrangement or mechanism configured for inhibiting ions from leaving the ionization housing via the at least one gas inlet opening. This may be accomplished by an electric force, for instance by an electric repelling force exerted by a correspondingly electrically charged ion repelling unit to the ions. Additionally or alternatively, this may be accomplished by a mechanical force, for instance by a dedicated wall section preventing ions from leaving the ionization housing via the at least one gas inlet opening.

[0013] In the context of the present application, the term “ion repelling unit arranged outside of the ionization housing or at the at least one gas inlet opening” may particularly denote that the complete ion repelling unit is entirely arranged outside of an interior ionizing volume delimited by the ionization housing. The ion repelling unit may be arranged completely outside of the ionization housing, for instance mounted from an exterior side on the exterior side of the ionization housing. The ion repelling unit may also be arranged at the at least one gas inlet opening without extending into an interior of the ionization chamber. Generally, the ion repelling unit may be arranged so that no part or portion thereof extends up to an interior of the ionization housing. In particular, the ion repelling unit may be arranged upstream of the ionization housing or at, but not inside, of the ionization housing.

[0014] In the context of the present application, the term “inhibiting a back flow of ions” may particularly denote partially reducing or completely eliminating a flow of ions created in the ionization chamber, based on gas entering the ionization chamber through the at least one gas inlet opening, back through the at least one gas inlet opening and out of the ionization chamber. Said at least partial reduction of the back flow is to be understood in comparison with a configuration without ion repelling unit.

[0015] In the context of the present application, the term “vacuum equipment” may particularly denote any apparatus usable for a vacuum application, for instance providing a vacuum in a vacuum room. For instance, such a vacuum equipment may be a vacuum pump, a vacuum container, a cryostate, vacuum tubing, etc. Generally, vacuum equipment can be any equipment for which leakage is testable by a leakage detector.

[0016] According to an exemplary embodiment of the invention, an ionization chamber is provided, which can be used as a constituent of a leak detector. In such an ionization chamber, neutral gas (for instance a tracer gas such as helium) can be converted into electrically charged ions (for instance by collision with an electron beam). Such neutral gas from a connectable vacuum equipment may be an indicator for the leakage characteristic of said vacuum equipment, for instance when supplying -3- said gas at an exterior of the vacuum equipment and detecting whether and / or which amount of the gas has reached the interior thereof. The afore-mentioned ionization chamber may be delimited spatially by an ionization housing inside of which ionization of the gas may be triggered for forming ions. At least one gas inlet opening in the ionization housing may be arranged for inletting gas (for instance tracer gas from a connected vacuum equipment) to be ionized into an interior of the ionization housing. Advantageously, an ion repelling unit may be arranged outside of the ionization housing or at the at least one gas inlet opening and may serve for repelling ions ionized inside the ionization housing. Beneficially, such an ion repelling unit may act to hinder ions from leaving the ionization housing in a backward direction through the at least one gas inlet opening. This may inhibit a back flow of the ions through the at least one gas inlet opening out of the ionization housing and may increase the percentage of generated ions which can be detected downstream of the ionization chamber, for instance after the generated ions have left the ionization chamber via at least one ion outlet opening in the ionization housing. Advantageously, the increased ion yield to be detected may improve the accuracy of the leak detection. Simulations executed by the present inventors have surprisingly shown that the accuracy of leak detection is conventionally significantly caused by back flow of ions. Exactly such a backflow can be efficiently suppressed by providing the ion repelling unit. Beneficially, the ion repelling unit may be arranged upstream of the at least one gas inlet opening or at the position of the at least one gas inlet opening rather than extending spatially into an interior of the ionization housing. This may have the advantage that the interior construction of the ionization housing for ionizing gas is not disturbed or influenced by the ion repelling unit. Furthermore, the arrangement of the ion repelling unit outside of the ionization casing or at the ionization casing may lead to a simplified construction of the ionization chamber. An easy assembly of the ion repelling unit and reduced outgassing may allow to detect a pure signal and to improve the vacuum. Furthermore, arranging the ion repelling unit outside the ionization housing may suppress artificial field components inside the ionization chamber which may have an undesired impact on electron trajectories in the ionization housing. This may increase the ionization efficiency.

[0017] In the following, further exemplary embodiments of the ionization chamber, the leak detector, and the method will be explained.

[0018] In an embodiment, the ion repelling unit is configured for electrically repelling -4- the ions. For this purpose, the ion repelling unit may be brought to an electric potential (preferably to a positive electric potential) for generating a repelling electric force repelling the (in particular positively charged) ions in the ionization chamber.

[0019] In an embodiment, the ion repelling unit comprises an electrically conductive body (such as a grid or a plate) biased with a positive voltage. A biasing unit, such as a voltage source, of the ionization chamber may be provided and configured for biasing the electrically conductive body with the positive voltage. This may create an electric force repelling positively charged ions, so that the ions may be prevented from approaching the at least one gas inlet opening. This may strongly suppress ion loss through the at least one gas inlet opening.

[0020] In an embodiment, the ion repelling unit comprises a grid, in particular an electrically conductive (for instance metallic) grid. For example, such a grid may comprise a plurality of metallic elements (such as metallic beams or webs). For example, a first group of metallic elements may extend along a first direction and a second group of metallic elements may extend along a second direction which may for instance be perpendicular to the first direction. This may create a plurality of openings in the grid through which gas can enter the ionization chamber. When appropriately electrically charging the grid, an electrically repelling force may be exerted to the ions in the ionization chamber preventing them from flowing in a backward direction through the at least one gas inlet opening.

[0021] In an embodiment, the ion repelling unit comprises a perforated plate, in particular an electrically conductive (for instance metallic) perforated plate. For example, a plurality of holes may be formed in a metal plate which may be subjected to an electric voltage. When appropriately electrically charging the perforated plate, an electrically repelling force may be exerted to the ions in the ionization chamber preventing them from flowing in a backward direction through the at least one gas inlet opening.

[0022] In an embodiment, the ion repelling unit comprises a continuous plate. For instance, such a continuous plate may be arranged in front of the at least one gas inlet opening with an open space relative to the ionization housing so that gas can flow between the continuous plate and the ionization housing into the ionization housing via the open space. The continuous plate may then suppress an undesired back flow of - 5 - ions out of the ionization housing, in particular when the continuous plate is electrically charged so as to repel the ions due to a repelling electric force.

[0023] In an embodiment, the ion repelling unit comprises a plurality of gas inlet openings, for instance at least four gas inlet openings, preferably at least eight gas inlet openings. By constituting the gas inlet by a plurality of smaller gas inlet openings rather than a single larger gas inlet opening, flow of gas into an interior of the ionization housing is enabled through the gas inlet openings, while at the same time an undesired back flow of ions from the ionization housing through the small gas inlet openings may be strongly limited. A body in which the plurality of gas inlet openings is formed may be optionally but advantageously be electrically charged, so as to add an electrically repelling force to the mechanically repelling effect of the tiny openings.

[0024] In an embodiment, the ionization chamber comprises an electron source configured for emitting an electron beam into an interior of the ionizing housing for ionizing the gas. Electrons may be emitted by the electron source and may be preferably accelerated in an interior of the ionization housing. Such an electron beam may then interact with the gas in the ionization chamber and may ionize the gas by electron-gas-collisions.

[0025] In an embodiment, the electron source comprises at least one heated filament cathode for emitting the electron beam. When heating an electrically conductive filament, for instance by a sufficiently high electric power applied to said filament, said filament may emit electrons. In embodiments, the electron source may comprise two heated filaments. One of the heated filaments may be active at a time so that when one of said filaments fails, the other filament is still available for emitting electrons. Optionally, the other filament may also act as an electrode.

[0026] In an embodiment, with respect to an electron source configured as cathode, the ionizing housing is configured as an anode. In another embodiment, with respect to an electron source configured as cathode, the ionization chamber comprises an anode in an interior of the ionizing housing. The respective anode may be configured for attracting electrons emitted by the electron source and used for ionizing the gas. In one embodiment, the ionizing housing itself may be brought to an electric potential (in particular to a positive electric potential) so as to act as an anode to accelerate electrons emitted by an electron source, such as a heated filament. In another -6- embodiment, a separate anode may be arranged inside of the ionizing housing and may be brought to an electric potential (in particular to a positive electric potential) so as to accelerate electrons emitted by an electron source. Accelerating the emitted electrons inside of the ionization housing may enhance the interaction with the gas and may therefore improve the ion generation efficiency.

[0027] In an embodiment, the ionization chamber comprises a magnetic collimator for collimating an electron beam in the ionizing housing for ionizing the gas. When taking this measure, interaction between an electron beam and gas inside of the ionizing chamber may be further enhanced so that the amount of ions created inside of the ionization chamber may be further increased. This may improve the accuracy of the leak detector.

[0028] In an embodiment, the ion repelling unit is configured for preventing at least 50%, in particular at least 60%, preferably at least 80%, of the ionized ions from flowing back through the at least one gas inlet opening out of the ionization housing. Consequently, at least 50%, in particular at least 60%, preferably at least 80% and most preferably at least 90% of the ions may exit the ionization chamber via at least one ion outlet opening of the ionization housing, rather than through the at least one gas inlet opening. This may efficiently suppress losses.

[0029] In an embodiment, the ion repelling unit is affixed to an exterior of the ionizing housing at the at least one gas inlet opening and / or forms part of the ionizing housing at the at least one gas inlet opening. For instance, the ion repelling unit (such as a grid or a plate, preferably bringable to a positive electrical potential) may be attached or mounted from an exterior side to the at least one gas inlet opening of the ionizing housing. This may lead to a simple assembly, maintenance and repair. Even more important, this may prevent any undesired impact of the provision of the ion repelling unit on the physical conditions and phenomena inside of the ionization housing, in particular may avoid any undesired impact on an ionizing electron beam inside the ionization housing. It is also possible that the ion repelling unit is integrally formed with the ionizing housing or is inserted in a mounting recess of the ionizing housing, for instance in flush with the ionizing housing.

[0030] In an embodiment, an interior of the ionizing housing is free of the entire ion repelling unit. In such a configuration, the interaction between the gas and the electron -7- beam in terms of ion generation in an interior of the ionization chamber can occur substantially independently from the ion repelling unit. Hence, excellent results in terms of ion generation efficiency may be achieved, and artefacts may be reliably prevented.

[0031] In an embodiment, the leak detector comprises a mass spectrometer downstream of the ionization chamber and configured for detecting the ionized gas (i.e. ions generated based on an initially electrically neutral gas), in particular for detecting the ionized gas based on an electric current caused by the ionized gas. The leak detector may detect a current signal generated from the incident ions representing an absolute or a relative concentration of the gas and may thus be indicative of the leakage characteristic of a connectable vacuum equipment. In the context of the present application, the term “mass spectrometer” may particularly denote a device for measuring the mass of a tracer gas, in particular for measuring the mass of atoms or molecules. The gas (for instance a tracer gas such as helium) to be analyzed can be transferred into the ionization chamber and may be ionized here. The ions can be subsequently accelerated by an electric field created by the mass spectrometer, and may be supplied to an analysis unit in which the ions can be sorted for instance according to their mass-to-charge ratio. This may be accomplished by a magnetic field separating an ion beam into different sub-beams of different types of ions. An ion subbeam of interest (for instance a helium ion beam) may then be detected by an electric current detection thereof. The electric current value may be an indication for the amount of gas entering the ionization chamber at an inlet side of the mass spectrometer.

[0032] In an embodiment, the leak detector comprises a magnetic field deflector downstream of the ionization chamber and configured for deflecting different kinds of ionized gas into different spatial regions. When ions exiting the ionization chamber are accelerated by an electric field and are subjected to a magnetic field, the ions may be separated into separate sub-beams in accordance with their mass and their electric charge. This may be accomplished by a magnetic field deflector, so that a sub-beam of interest may be selected.

[0033] In an embodiment, the leak detector comprises a separation body with an aperture (such as a slit) configured for passing selectively one kind of deflected ionized gas through the aperture. After having separated an ion beam comprising different kinds of ions into multiple ion sub-beams, each comprising a respective kind of ions (for instance helium ions), a sub-beam of interest may be selected by passing only this subbeam through the aperture while the other sub-beams may be stopped by the separation body.

[0034] In an embodiment, the leak detector comprises at least one vacuum pump upstream of the ionization chamber and configured for being brought in gas communication with the vacuum equipment. For instance, the at least one vacuum pump may comprise a forepump or rough pump (such as a rotary valve pump) followed by a further pump (such as a turbo pump) starting from the pre-vacuum provided by the forepump or rough pump and further improving the vacuum. The at least one vacuum pump may pump gas out of the vacuum equipment for which a leak detection shall be executed. Said gas may then be supplied to the ionization chamber and a mass spectrometer downstream thereof for detection.

[0035] In an embodiment, the method comprises receiving said gas from a vacuum equipment, and processing the ions for deriving leak detection information concerning said vacuum equipment. For example, a tracer gas (such as helium) may be provided, for instance by a gas dispenser, to a vacuum equipment under investigation, for instance may be supplied to a suspicious part of the vacuum equipment at which a leak is presumed. If there is a leak, the tracer gas may enter into the vacuum equipment. Gas inside of the vacuum equipment may be supplied to the ionization chamber, as described above, for converting at least part of the gas into ions, and for forwarding at least part of the ions through an ion outlet opening of the ionization chamber towards a mass spectrometer, while suppressing or eliminating undesired ion back flow through at least one gas inlet opening of the ionizing chamber thanks to the ion repelling unit. The forwardly flowing ion stream may then be analyzed for qualitative or quantitative leak detection of the vacuum equipment. BRIEF DESCRIPTION OF DRAWINGS

[0036] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to by the same reference signs. -9-

[0037] Figure 1 illustrates a leak detector with an ionization chamber according to an exemplary embodiment of the invention.

[0038] Figure 2 illustrates a conventional leak detector with an ionization chamber.

[0039] Figure 3 illustrates a leak detector with an ionization chamber according to an exemplary embodiment of the invention.

[0040] Figure 4 illustrates a three-dimensional view of an ionization chamber according to an exemplary embodiment of the invention.

[0041] Figure 5 illustrates a three-dimensional view of an ionization chamber according to another exemplary embodiment of the invention.

[0042] Figure 6 illustrates a cross-sectional view of an ionization chamber according to still another exemplary embodiment of the invention.

[0043] Figure 7 illustrates a leak detection arrangement having a leak detector with an ionization chamber according to an exemplary embodiment of the invention.

[0044] Figure 8 illustrates a leak detector with an ionization chamber according to an exemplary embodiment of the invention.

[0045] Figure 9 illustrates a leak detection arrangement having a leak detector with an ionization chamber according to an exemplary embodiment of the invention.

[0046] Figure 10 illustrates a leak detection arrangement having a leak detector with an ionization chamber according to another exemplary embodiment of the invention.

[0047] The illustration in the drawing is schematically.

[0048] Before describing the figures in further detail, some basic considerations of the present invention will be summarized based on which exemplary embodiments have been developed.

[0049] An ion source used in a leak detector may present a central hole as inlet source for the gas molecules (such as helium). The working principle of such a leak detector comprises ion acceleration towards a mass spectrometer. The present inventors have found that, with existing ion sources, a significant amount of ions escapes via the central hole, causing a huge loss of signal.

[0050] According to an exemplary embodiment, an ionization chamber for a leak detector is provided to achieve a high efficiency. In an interior of said ionization chamber, gas atoms or molecules (for instance originating from a vacuum equipment to be tested concerning leakage) can be transferred into (in particular the positively) charged ions, which may for instance be accomplished by an electron beam interacting with said gas. Said ionization chamber may comprise an ionization housing through which one or more gas inlet openings extend for inletting gas for ionization inside the ionization housing. An ion repelling unit upstream of or at the entrance into the ionization housing may repel ions which are ionized inside the ionization housing and may thus suppress their back flow. By reducing or eliminating a back flow of the ions through the at least one gas inlet opening away from a detector downstream of the ionization chamber may improve the efficiency according to which generated ions can be detected. Beneficially, the improved percentage of ions being detected after leaving the ionization chamber through at least one ion outlet opening thereof may enhance the precision of the leak detection. Simulations show that loss of ions by back flow are a main loss mechanism for an ionization chamber of a leak detector. By the ion repelling unit arranged in front of or at the at least one gas inlet opening of the ionization housing, ion backflow may be efficiently decreased without a negative impact on the interior construction of the ionization chamber. Apart from the simple construction of such an exterior ion repelling unit or an ion repelling unit arranged at the at least one gas inlet unit, an efficient reduction of outgassing phenomena may improve signal integrity and may lead to a proper vacuum. Moreover, artefacts in terms of field components inside the ionization chamber due to the implementation of an ion repelling unit may be avoided so as to obtain a high ionization efficiency.

[0051] Regarding an achievable signal gain due to the use of the repeller, simulations show an enhancement of the signal from the source to the collector, increasing from 25-30% (without the repeller) to over 80% (with the repeller) of the total generated ions. Therefore, the ion repelling unit or repeller may enable a gain of approximately 50% or more of the signal.

[0052] Thus, an exemplary embodiment of the invention may provide an ionization chamber as an improved ion source for a leak detector. Such an improved ion source for a leak detector may have an inlet shape which ensures the same conductance as prior solution but a modified electric field for repelling positive ions, thus preventing them from escaping through the wrong path. More specifically, forward rather than backward motion of the generated ions may be promoted by the inlet-sided ion repelling unit. With the adapted ion source geometry, as described, a large portion of the generated ions are accelerated through a mass spectrometer downstream of the ionization chamber, thereby efficiently reducing or even eliminating the conventional loss of ions due to back flow.

[0053] An ionization chamber according to an exemplary embodiment of the invention may therefore improve the performance of a leak detector device in terms of signal to noise ratio. Furthermore, this may enable detection of even very low leak rates. Apart from this, response speed of the leak detector may be improved.

[0054] An ionization chamber according to exemplary embodiments may be realized in particular in the following two ways:

[0055] In one embodiment, it may be possible to add a grid in front of a central hole (as an embodiment of the at least one gas inlet opening), biased with positive voltage. Such a grid may allow the gas to enter into an interior of the ionization chamber. When such a grid is biased with a positive electric voltage, back flow of the positively charged ions created by a collision between the gas and an electron beam in an interior of the ionization chamber may be suppressed by a resulting repelling electric force. To put it shortly, a positively charged grid may repel positively charged ions and may therefore keep the letter away from the at least one gas inlet opening.

[0056] Additionally or alternatively, it may be possible to replace a single central hole by a plurality of smaller holes (as an embodiment of the at least one gas inlet opening). This may limit the electric field component responsible for ion escape while maintaining the same or a similar conductance. The repelling of the ions may result from the reduced probability of a flow of ions through the small holes as compared to a single large hole. A physical structure (such as a plate or housing section) in which the plurality of holes are formed may be optionally positively charged to further enhance the repelling effect.

[0057] The present inventors have found that a conventional ionization chamber may suffer from the phenomenon that ionized molecules may disappear through the inlet (for the incoming molecules or atoms). The inventors had never before considered the inlet path (i.e. upstream of the inlet of the ion source) for the simulation of the ionized particles, but when they made such a simulation, as shown in Figure 2, it has been surprisingly found that back flow of ions is a pronounced phenomenon. In view of this, an ion repelling unit is provided by exemplary embodiments, to reduce exiting of ionized particles back through the gas inlet. Such an ion repelling function may be provided by adding an electrically charged grid, replacing a single large central inlet hole by a plurality of smaller inlet holes, and / or any other repelling measures.

[0058] Hence, a gist of an exemplary embodiments is to add - in a leak detector - a charged grid or similar to the at least one gas inlet opening, thus avoiding that ionized molecules or atoms (such as He+) may leak out strongly through the at least one gas inlet opening rather than moving forward towards a mass spectrometer or another ion detecting element of a leak detector. Taking such a measure is based on a simulation of the ion paths, indicating that conventionally ion back flow is a significant loss mechanism. In the past, only the path between ionization chamber and mass spectrometer had been considered as relevant, but the inlet part had been disregarded. By adding an ion repelling unit in front of or at at least one gas inlet opening of an ionization chamber, leak detection may be rendered much more efficient due to an achievable inhibition or even avoidance of leakage of ionized particles through the gas inlet from the ionization chamber.

[0059] Advantageously, the ion repelling unit may be located in or before the inlet of the ionization chamber, in particular so that there is no gas channel between the at least one gas inlet opening and the ion repelling unit. The ion repelling unit of an exemplary embodiment may have openings or holes, for example a grid, so that the incoming gas can flow through the ion repelling unit, while ions created inside of the ionization housing may be reflected or repelled in another way by the ion repelling unit.

[0060] This has advantages: On the one hand, this may lead to an easier assembly of the grid (or another kind of ion repelling unit) in comparison with a scenario in which the ion repelling unit is arranged in an interior of the ionization housing. Furthermore, this may bring the advantage of a reduction of outgassing inside the ionization chamber. This may make it possible to collect a cleaner signal and to improve the vacuum. Moreover, arranging the ion repelling unit outside of the ionization chamber may avoid the creation of field components inside the chamber which may unintentionally deviate the electron trajectories decreasing their ionization efficiency.

[0061] For example, the ion repelling unit of an exemplary embodiment may be a grid (or similar) with one or more gas openings but may also be a closed plate. When the ion repelling unit is located outside of the ionization chamber it may allow the entrance of the gas and may provide a high conductance by suppressing undesired backflow of ions without having an impact on the interior construction of the ionization chamber. Hence, locating the ion repelling unit at the entrance or outside of the ionization housing does not disturb an interaction between the gas and an electron beam in an interior of the ionization housing.

[0062] Beneficially, the ion repelling unit may be located at or outside the ionization housing containing the ionization facilities of the ionization chamber. An advantage of having the ion repelling unit at or outside the ionization housing is that there are less components inside the ionization housing which may otherwise lead to outgassing and may thus affect the vacuum. Further, this may allow to easily electrically couple the ion repelling unit with the ionization housing, for example for bringing the ion repelling unit and the ionization housing to the same electrical potential. Even more importantly, this positioning of the ion repelling unit may simplify the manufacturing, because the ion repelling unit just needs to be affixed to the gas entry of the ionization housing in contrast to a more difficult adjustment inside the housing.

[0063] Figure 1 illustrates a leak detector 104 with an ionization chamber 100 according to an exemplary embodiment of the invention.

[0064] The shown leak detector 104 is configured for detecting leakage of a tracer gas 102 (such as helium gas or hydrogen gas) in a vacuum equipment 140, such as a vacuum container (not shown in detail in Figure 1). For example, the vacuum equipment 140 may be connected to the leak detector 104 by a valve (not shown). Such a vacuum equipment 140 may be treated at an external side thereof with the tracer gas 102. In the event of a leakage of the vacuum equipment 140, a certain amount of the tracer gas 102 can enter into an inside of the vacuum equipment 140. This tracer gas 102 can then be detected in the leak detector 104, so that information about leakage characteristics of the vacuum equipment 140 can be obtained.

[0065] For this purpose, the leak detector 104 comprises an ionization chamber 100 for ionizing the above-mentioned tracer gas 102 from the vacuum equipment 140. Said ionization chamber 100 comprises an ionization housing 106 having a gas inlet opening 108 for inletting the tracer gas 102 to be ionized into an interior of the ionization housing 106. In an interior of the ionization chamber 100 (see for instance Figure 6) a construction (preferably involving an ionizing electron beam) may be foreseen which generates electrically charged ions 112 (in the present embodiment positively charged helium ions) from the electrically neutral tracer gas 102. As an electron source, a heated filament cathode 124 may be implemented for emitting the electron beam for collision with the tracer gas 102 in an interior of the ionization housing 106. The heated filament cathode 124 may be located outside or inside of the ionization housing 106. The generated ions 112 may leave the ionization housing 106 through an ion outlet opening 150 of the ionization housing 106, wherein the ion outlet opening 150 may be arranged to oppose the gas inlet opening 108.

[0066] An undesired phenomenon is an unintentional loss of ions 112 through the gas inlet opening 112, because such back flowing ions 112 are lost for detection downstream of the ionization chamber 100, artificially reduce the detection signal and limit accuracy of the leak detection. In order to mitigate this artifact and improve leak detection precision, the ionization chamber 100 comprises an ion repelling unit 110 arranged outside of the ionization housing 106 and being, in the shown embodiment, mounted on an exterior side of the gas inlet opening 108. Thus, in the embodiment of Figure 1, the ion repelling unit 110 is affixed to an exterior of the ionization housing 106 at the at least one gas inlet opening 108. Advantageously, the ion repelling unit 110 is configured for repelling ions 112 ionized inside the ionization housing 106 to inhibit a back flow of the ions 112 through the gas inlet opening 108 out of the ionization housing 106. As indicated schematically in Figure 1, the ion repelling unit 110 may be for example an electrically positively charged metallic grid attached to an exterior side of the ionization housing 106. Through such a positively charged grid, neutral gas 102 may efficiently flow into an interior of the ionization housing 106. However, the positively charged grid may generate a repelling electric force repelling positively charged ions 112 away from the ion repelling unit 110 and thereby keeping them away from gas inlet opening 108. By arranging the ion repelling unit 110 outside of an interior of the ionization housing 106, assembly, maintenance and repair of the ion repelling unit 110 is simplified while at the same time preventing any undesired impact of the ion repelling unit 110 on the physical conditions in an interior of the ionization housing 106. In particular, the process of ionization inside the ionization housing 106 is not influenced by such an exterior repelling unit 110 at all. Thus, a high ionization efficiency and thereby a high accuracy of the leak detection may be combined with a high user convenience.

[0067] The ions 112 leaving the ionization housing 106 predominantly through ion outlet opening 150 can then be detected by a mass spectrometer 130. The mass spectrometer 130 is arranged downstream of the ionization chamber 100. Furthermore, the mass spectrometer 130 is capable of detecting the ionized gas 102, i.e. the ions 112, based on an electric current caused by the electrically charged ions 112.

[0068] For example, the ions 112 leaving the ionization chamber 106 through ion outlet opening 150 can be accelerated by an electric field (which may be created for instance by one or more electrodes, a capacitor, etc. (not shown). Furthermore, the mass spectrometer 130 may comprise a schematically illustrated magnetic field deflector 132 arranged downstream of the ionization chamber 100 and configured for deflecting different kinds 141,142,144 of ionized gas 102 into different spatial regions. The magnetic field deflector 132 may force the different kinds 141,142,144 of ionized gas 102 on different curved paths by deflecting the ions. The different curved paths may be defined by properties such as mass and electric charge of the ions of the different kinds 141, 142, 144. In particular, ions 112 of kind 141 may be the ions of interest (such as positively charged helium ions) which have been created in the ionization chamber 100 by ionizing the tracer gas 102. Lighter ions of kind 142 and heavy ions of kind 144 can be separated from the ions of kind 141 of interest by the magnetic field deflector 132, as shown in Figure 1.

[0069] A separation body 136 with an aperture 134 (such as a slit) is arranged in a region of the magnetic field deflector 132 and is configured for passing selectively the one kind 141 of deflected ionized gas 102 of interest through the aperture 134. The separation body 136 may be placed in the magnetic field region, as a braking electrode and a target. To put it shortly, the separation body 136 with the aperture 134 is arranged so that only the ions 112 of kind 141 being of interest can pass the aperture 134, whereas the lighter and heavier ions of kinds 142,144 abut against the separation body 136 and cannot pass the aperture 134 for subsequent detection.

[0070] The ions 112 of kind 141 being of interest and having passed the collector in form of separation body 136 with the aperture 134 can then be forwarded to a preamplifier (not shown), and a corresponding electric current can be detected which is indicative of the amount of tracer gas 102, and therefore is indicative of a potential leak in the vacuum equipment 140. [0071 ] The illustrated mass spectrometer leak detector 104 is configured for locating and / or measuring the size of leaks into or out of the connected vacuum equipment 140. This method of leak detection is initiated when tracer gas 102, such as helium, is introduced to a test part in form of vacuum equipment 140 that is connected to the leak detector 104. The helium leaking from the test part diffuses through the system, its partial pressure is measured, and results are displayed. The described operating principle of the leak detector 104 comprises ionization of the gas 102 in a vacuum and its acceleration across a voltage drop and a magnetic field. The helium ions 112 are separated and collected, and the resulting ion current is amplified and may be indicated on a display. Thanks to the housing-external provision of an ion repelling unit 110, as described, an excellent accuracy of leak detection may be achieved.

[0072] The illustrated mass spectrometer leak detector 104 comprises the mass spectrometer 130 tuned to detect a specific tracer gas 102 of kind 141, such as helium. A vacuum system may be provided to maintain adequately low pressure in the mass spectrometer 130. Primary pumps may be provided to evacuate the vacuum equipment 140 as the part to be tested. Valves may be provided to enable the various stages of the leak detection cycle, from evacuation, to test, to venting. Amplifier and readout instrumentation may be provided for monitoring a spectrometer output signal. Electrical power supplies and controls are provided as well. Fixturing can be foreseen for attaching the vacuum equipment 140 to the leak detector 104.

[0073] Figure 2 illustrates a conventional leak detector 104’ with an ionization chamber 100’. It is intended that tracer gas enters via a gas inlet opening 108’ into an ionization housing 106’ of the ionization chamber 100’ in which ions are created which shall exit through an ion outlet opening 150’.

[0074] Figure 2 shows visually a result of simulations carried out by the present inventors. Surprisingly, a considerable amount of ions unintentionally leaves the ionization chamber 100’ through gas inlet opening 108’ rather than through ion outlet opening 150’. A corresponding loss of ions is indicated in Figure 2 with reference sign 152. Only a significantly reduced amount of ions, indicated in Figure 2 with reference sign 154, moves intentionally forwardly and can thus be used for detection purposes. Undesired backflow of ions through the gas inlet opening 108’ is however significant and reduces the precision of leak detection. Hence, a significant loss of signal occurs in the conventional approach of Figure 2.

[0075] Figure 3 illustrates a leak detector 104 with an ionization chamber 100 according to an exemplary embodiment of the invention.

[0076] More specifically, Figure 3 illustrates a simulation result corresponding to the one described above referring to Figure 2, but with an ion repelling unit 110 (such as an electrically conductive body 114 biased with a positive voltage, for instance a positively charged grid) attached to an exterior of the ionization housing 106 so as to at least partially cover gas inlet opening 108 according to an exemplary embodiment of the invention. Highly advantageously, the simulation result of Figure 3 indicates that the described provision of an ion repelling unit 110 significantly increases the amount of generated ions moving forwardly through ion outlet opening 150, see reference sign 154. No unintentional backflow of ions through gas inlet opening 108 is visible in Figure 3 (compare reference sign 152 in Figure 2). Thus, a significant improvement of leak detection accuracy can be achieved by exemplary embodiments.

[0077] Depending on the configuration of different embodiments, the provision of an ion repelling unit 110 at or upstream of the gas inlet opening 108 may prevent back flow of at least 50%, in particular at least 60%, preferably at least 80% or even at least 90%, of the ionized ions 112 through the gas inlet opening 108 out of the ionization housing 106.

[0078] Figure 4 illustrates a three-dimensional view of an ionization chamber 100 according to an exemplary embodiment of the invention.

[0079] The illustrated configuration of ion repelling unit 110 is capable of electrically repelling the ions 112. For this purpose, the shown ion repelling unit 110 comprises an electrically conductive body 114 biased with a positive voltage or electric potential. More specifically, the ion repelling unit 110 may comprise a metallic grid 116 to which a positive voltage may be applied. The illustrated grid 116 is composed of a first set of metallic web members 158 extending in parallel to each other along a first direction and being connected with a second set of metallic web members 160 extending in parallel to each other along a second direction being perpendicular to the first direction. As a result, a positively charged grid 116 is provided which electrically repels positively charged ions112 in an interior of the ionization housing 106 for reliably inhibiting backflow of tracer ions 112. Grid 116 has a plurality of through holes 162 through which neutral gas 102 can efficiently flow in a forward direction into the ionization housing 106. In other words, the grid 116 provides a large space for neutral tracer atoms or molecules to enter the ionization chamber 100, while simultaneously bouncing back ions 112 in an interior of the ionization housing 106 for efficiently suppressing backflow.

[0080] Figure 5 illustrates a three-dimensional view of an ionization chamber 100 according to another exemplary embodiment of the invention.

[0081] The embodiment of Figure 5 differs from the embodiment of Figure 4 in particular in that, according to Figure 5, the ion repelling unit 110 comprises a plurality of gas inlet openings 108, in the illustrated embodiment eight gas inlet openings 108. Rather than providing one large gas inlet opening, the embodiment of Figure 5 provides a large plurality of small gas inlet openings 108. The large number of gas inlet openings 108 ensures a reliable entry of gas 102 into the ionization housing 106. At the same time, the tiny gas inlet openings 108 provide a mechanical barrier function for preventing excessive backflow of ions from an interior of the ionization housing 106 through the gas inlet openings 108. In the shown embodiment, the plurality of gas inlet openings 108 are embodied as through holes in a plate section forming an integral part of the ionization housing 106. Optionally, a positive electric potential may be applied to said plate section or to the entire ionization housing 106 for further enhancing the ion repelling function of the ion repelling unit 110 by exerting a repelling electric force to the ions 112.

[0082] Figure 6 illustrates a cross-sectional view 164 of an ionization chamber 100 with an ion repelling unit 110 according to still another exemplary embodiment of the invention. Reference sign 166 shows an alternative configuration of an ion repelling unit 110.

[0083] The illustrated ionization chamber 100 according to reference sign 164 serves for ionizing gas 102 for use in a leak detector (see reference sign 104 in Figure 1, Figure 3 or Figure 7 to Figure 10). In this embodiment, the ionization chamber 100 comprises ionization housing 106 having a gas inlet opening 108 for inletting gas 102 to be ionized into an interior of the ionization housing 106. Ion repelling unit 110 is arranged outside of the ionization housing 106 or at the gas inlet opening 108 for repelling ions 112 ionized inside the ionization housing 106 to inhibit a back flow of the ions 112 through the gas inlet opening 108 out of the ionization housing 106.

[0084] In the embodiment according to reference sign 164, the ion repelling unit 110 comprises a perforated plate 117 with a plurality of perforation holes 119 through which neutral gas 102 may enter into the interior volume 168 delimited by the ionization housing 106. In the embodiment according to reference sign 166, the ion repelling unit 110 comprises a continuous plate 118 (i.e. not having perforation holes) spaced with respect to the ionization housing 106 to thereby form one or more lateral access openings 170 through which gas 102 may enter into the interior volume 168 delimited by the ionization housing 106. As shown, metallic plates 117, 118 may be positively charged for generating a repelling electric force to the positively charged ions 112 in the interior volume 168 delimited by the ionization housing 106. Due to the illustrated configurations of the ion repelling units 110, an interior of the ionizing housing 106 may remain entirely free of all constituents of the ion repelling unit 110. Thus, the process of ion generation, as described below, will advantageously not be influenced at all by the presence of the ion repelling units 110 according to Figure 6.

[0085] Moreover, the ionization chamber 100 comprises an electron source 120 configured for emitting an electron beam 122 in an interior of the ionizing housing 106 for ionizing the gas 102 by collisions. As shown in Figure 6, the electron source 120 comprises a heated filament cathode 124 for emitting the electron beam 122. Such at least one heated filament cathode 124 may be located inside the ionization housing 106 or outside thereof. It is also possible that more than one heated filament cathode 124 (for instance two) are foreseen for one ionization chamber 100. For example, one filament may emit electrons while the other one functions as electrode which may be brought to an electric potential for extending the path length of the electrons within the ionization housing 106. Furthermore, such a two-filament configuration may extend the lifetime of the ionization chamber 100, since one filament may still function when the -20- other one is already finished.

[0086] Furthermore, the ionization chamber 100 may comprise an anode 126 in an interior of the ionizing housing 106 for attracting electrons emitted by the electron source 120 and used for ionizing the gas 102. Alternatively, it may also be possible that the ionizing housing 106 itself is configured as an anode with respect to the electron source 120 functioning as cathode.

[0087] Moreover, a magnetic collimator 128 may be provided for collimating the electron beam 122 in the ionizing housing 106 for enhancing the ionization of the gas 102.

[0088] Figure 7 illustrates a leak detection arrangement having a leak detector 104 with an ionization chamber 100 according to an exemplary embodiment of the invention.

[0089] The schematic illustration of Figure 7 shows a tracer gas source 172, such as a gas bottle, comprising a tracer gas 102 like helium. By a valve 174, the tracer gas source 172 may be brought in gas communication with a gas dispenser 176 for dispensing tracer gas 102 when operating a trigger 178, such as a lever. As a consequence, tracer gas 102 may be applied to an exterior of a vacuum equipment 140, for instance a vacuum container, for which a leakage test shall be carried out. In case of a leakage, some particles of the tracer gas 102 may enter into the vacuum equipment 140. By operating a further valve 176, the interior of the vacuum equipment 140 may be brought in gas communication with leak detector 104. More precisely, leak detector 104 may comprise one or more vacuum pumps 138 upstream of an ionization chamber 100 and configured for being brought in gas communication with the vacuum equipment 140. In the presence of tracer gas 102 inside the vacuum equipment 140, said tracer gas 102 may be introduced via ion repelling unit 110 into ionization chamber 100 for creating ions 112 based on the tracer gas 102 by ionization. Said ions 112 may be prevented from unintentionally flowing back by ion repelling unit 110 and may be forwarded to a very large extent into mass spectrometer 130. A current output of mass spectrometer 130 being indicative of leakage of vacuum equipment 140 may be output by a user interface 180, such as a display.

[0090] Figure 8 illustrates a leak detector 104 with an ionization chamber 100 according to an exemplary embodiment of the invention. Also referring to the description of Figure 1 and Figure 6, a detailed construction of a leak detector 104 with magnetic mass spectrometer 130 is shown in Figure 8.

[0091] Tracer gas 102 from a vacuum equipment 140 under investigation enters via an ion repelling unit 110 (not shown) into ionization housing 106 of ionization chamber 100. An electron beam 122 created by a heated filament 124 (for instance made of tungsten) of an electron source 120 enters into ionization housing 106 of ionization chamber 100 for collision with the tracer gas 102 to thereby create ions 112. In addition to heated filament 124, a standby filament 124’ is provided which may also be operated for emitting an electron beam 122 (not shown). A (preferably stabilized) power supply unit 182 powers the filament 124 and / or the standby filament 124’ and may also bring the ionization housing 106 to a predefined or adjustable electric potential, for instance positive electric potential.

[0092] The ions 112 of different kinds 141, 142, 144 leave the ionization housing 106 by ion outlet opening 150. The ions 112 may pass through an aperture 184 (such as a slit) of a braking electrode 186 and may then be magnetically deflected for separating the ions 112 of different kinds 141, 142, 144. Only ions 112 of interest according to kind 141 are enabled to pass aperture 134 of separation body 136 of a diaphragm 186. A triode electrode 188 may contribute to this ion separation. After separation, only ions 112 of kind 141 pass through braking electrode 186 and are then detected at a target 189 outputting a leak signal 190 to an amplifier 192.

[0093] Figure 9 illustrates a leak detection arrangement having a leak detector 104 with an ionization chamber 100 according to an exemplary embodiment of the invention.

[0094] As indicated schematically in Figure 9, a vacuum equipment 140 subjected to a leak test can be connected to a test port 194. A rough pump 138A (for instance a rotary valve pump) followed by a high-pressure pump 138B (for instance a turbo pump) may pump tracer gas 102 towards leak detector 104. More precisely, the tracer gas 102 from the vacuum equipment 140 may be converted into ions 112 in ionization chamber 100 before being analyzed spectroscopically by mass spectrometer 130, as described above. The leak detection arrangement of Figure 9 also comprises a vent 196 and a gauge 198.

[0095] The embodiment of Figure 9 functions in accordance with a contraflow operation with tracer gas 102 from turbo pump foreline.

[0096] Figure 10 illustrates a leak detection arrangement having a leak detector 104 with an ionization chamber 100 according to another exemplary embodiment of the 5 invention.

[0097] The embodiment of Figure 10 differs from the embodiment of Figure 9 in particular in that, according to Figure 10, the leak detection arrangement functions in accordance with a midstage operation with tracer gas 102 from a turbo pump side port.

[0098] It should be noted that the term “comprising” does not exclude other 10 elements or features and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. Ionization chamber (100) for ionizing gas (102) for a leak detector (104), wherein the ionization chamber (100) comprises:an ionization housing (106) having at least one gas inlet opening (108) for inletting gas (102) to be ionized into an interior of the ionization housing (106); andan ion repelling unit (110) arranged outside of the ionization housing (106) or at the at least one gas inlet opening (108) for repelling ions (112) ionized inside the ionization housing (106) to inhibit a back flow of the ions (112) through the at least one gas inlet opening (108) out of the ionization housing (106).

2. Ionization chamber (100) according to claim 1, wherein the ion repelling unit (110) is configured for electrically repelling the ions (112).

3. Ionization chamber (100) according to claim 1 or 2, wherein the ion repelling unit (110) comprises an electrically conductive body (114) biased with a positive voltage.

4. Ionization chamber (100) according to any of claims 1 to 3, wherein the ion repelling unit (110) comprises a grid (116), in particular an electrically conductive grid (116), or a perforated plate (117), in particular an electrically conductive perforated plate (117).

5. Ionization chamber (100) according to any of claims 1 to 4, wherein the ion repelling unit (110) comprises a continuous plate (118).

6. Ionization chamber (100) according to any of claims 1 to 5, wherein the ion repelling unit (110) comprises a plurality of gas inlet openings (108), for instance at least four gas inlet openings (108), preferably at least eight gas inlet openings (108).

7. Ionization chamber (100) according to any of claims 1 to 6, comprising an electron source (120) configured for emitting an electron beam (122) into an interior of the ionizing housing (106) for ionizing the gas (102).

8. Ionization chamber (100) according to claim 7, wherein the electron source (120) comprises at least one heated filament cathode (124) for emitting the electron beam (122).

9. Ionization chamber (100) according to any of claims 1 to 8, wherein, with respect to an electron source (120) configured as cathode, the ionizing housing (106) is configured as an anode and / or the ionization chamber (100) comprises an anode (126) in an interior of the ionizing housing (106), the respective anode being configured for attracting electrons emitted by the electron source (120) and used for ionizing the gas (102).

10. Ionization chamber (100) according to any of claims 1 to 9, comprising a magnetic collimator (128) for collimating an electron beam (122) in the ionizing housing (106) for ionizing the gas (102).

11. Ionization chamber (100) according to any of claims 1 to 10, wherein the ion repelling unit (110) is configured for preventing at least 50%, in particular at least 60%, preferably at least 80%, of the ionized ions (112) from flowing back through the at least one gas inlet opening (108) out of the ionization housing (106).

12. Ionization chamber (100) according to any of claims 1 to 11, wherein the ion repelling unit (110) is affixed to an exterior of the ionizing housing (106) at the at least one gas inlet opening (108) and / or forms part of the ionizing housing (106) at the at least one gas inlet opening (108).

13. Ionization chamber (100) according to any of claims 1 to 12, wherein an interior of the ionizing housing (106) is free of the entire ion repelling unit (110).

14. A leak detector (104) for detecting leakage of gas (102) in a vacuum equipment (140), wherein the leak detector (104) comprises an ionization chamber (100) according to any of claims 1 to 13 for ionizing gas (102) leaking at the vacuum equipment (140).

15. Leak detector (104) according to claim 14, comprising a mass spectrometer(130) downstream of the ionization chamber (100) and configured for detecting the ionized gas (102), in particular for detecting the ionized gas (102) based on an electric current caused by the ionized gas (102).

16. Leak detector (104) according to claim 14 or 15, comprising a magnetic field deflector (132) downstream of the ionization chamber (100) and configured for deflecting different kinds (141, 142, 144) of ionized gas (102) into different spatial regions.

17. Leak detector (104) according to claim 16, comprising a separation body (136) with an aperture (134) configured for passing selectively one kind (141) of deflected ionized gas (102) through the aperture (134).

18. Leak detector (104) according to any of claims 14 to 17, comprising at least one vacuum pump (138) upstream of the ionization chamber (100) and configured for being brought in gas communication with the vacuum equipment (140).

19. A method, which comprises:inletting gas (102) to be ionized into an interior of an ionization housing (106) of an ionization chamber (100) via at least one gas inlet opening (108) of the ionization housing (106);at least partially ionizing the inlet gas (102) inside the ionization housing (106) to thereby generate ions (112); andrepelling at least part of the ions (112) ionized in the ionization housing (106) by an ion repelling unit (110) arranged outside of the ionization housing (106) or at the at least one gas inlet opening (108) to inhibit a back flow of the ions (112) through the at least one gas inlet opening (108) out of the ionization housing (106).

20. The method according to claim 19, wherein the method comprises receiving said gas (102) from a vacuum equipment (140), and processing the ions (112) for deriving leak detection information concerning said vacuum equipment (140).27

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