Cathode device with improved electron emitter contacting

Abstract

The invention relates to a cathode device and an X-ray source. The cathode device according to the invention for an X-ray source has - an electron emitter and - an emitter seat, where the electron emitter - a plurality of parallel aligned field effect emitter elements to form an emission surface, - a gate electrode arranged above the emission surface, - and has a plurality of first contact elements, characterized by - that the emitter seat has a plurality of second contact elements which can be connected to the plurality of first contact elements at the end of the current paths, - that the plurality of first contact elements are arranged on a side of the plurality of parallel aligned field effect emitter elements facing away from the emission surface.

Description

This invention relates to a cathode device and an X-ray source.X-ray sources typically generate x-rays by means of electrons, which are generated by an electron emitter in a vacuum and, after acceleration thereof by means of high voltage, are decelerated during an interaction with an anode. The electron emitters regularly used for this purpose can be distinguished in particular into so-called thermionic electron emitters and cold electron emitters. Thermionic electron emitters generate the electrons in particular according to the Edison-Richardson effect with heating of the emitter elements. Cold electron emitters emit the electrons in particular without a comparable heating, but for example according to the field effect by means of field effect emitter elements configured accordingly thereto.Conventional electron emitters with field effect emitter elements are known in particular from U.S. Pat. No. 9,748,071 B2 or EP 3 933 881 A1. The former describes in particular a construction of the field effect emitter elements from emitter needles comprising transistor structures, in order to preferably enable switching of independent groups of the field effect emitter elements. The latter, on the other hand, relates to protective devices for preventing charged particles from being deposited in the field effect emitter elements during operation of such electron emitters.U.S. Pat. No. 5,075,595 also discloses a field effect emitter. EP 3 075 000 B1 is concerned with protecting a cold cathode against ion impacts.DE 10 2009 011 642 A1 relates to an improved X-ray tube with a plurality of cathodes in an evacuated region. Furthermore, a plurality of wirelessly controllable elements are arranged in the evacuated region, which elements are each assigned to a cathode or a group of cathodes and which, upon receiving a control signal from outside the evacuated region, produce an electrically conductive connection of this cathode or group of cathodes to a cathode control voltage line.WO 2013 / 136 299 A1 relates to an image capturing device comprising an electron receiving construct and an electron emitting construct and further comprising an inner gap providing an unobstructed space between the electron emitting construct and the electron receiving construct. The image sensing device further comprises a resistive layer disposed between the field emission type electron-emitting construct and the emitter seat.Electron emitters with field effect emitter elements are usually more susceptible to damage or even destruction due to electrical discharge processes, in particular high-voltage sparkovers between the cathode device and the anode, within the X-ray source, in comparison with thermionic emitter elements. Such high voltage breakdowns can cause, for example, a short circuit between the field effect emitter elements and the gate electrode of the electron emitter. See, for example, R. F. Asadi, T. Zheng, J. Da Silva, G. Rughoobur, A. I. Akinwande and B. Gnade, "Failure Mode of Si Field Emission Arrays based on Emission Pattern Analysis," 2021 34th International Vacuum Nanoelectronics Conference (IVNC), Lyon, France, 2021, pp. 1-2, doi: 10.1109 / IVNC52431.2021.9600740 with respect to the related effects.It is an object of the invention to provide a cathode device and an X-ray source in which the damage to potentially destructive discharge processes can be reduced.The object is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.Regardless of the grammatical sex of a certain term, individuals with male, female or other sex identity are included.The cathode device for an X-ray source according to the invention comprisesan electron emitter; andan emitter seat,wherein the electron emittera plurality of parallel-oriented field effect emitter elements for forming an emission surface on the upper side of the plurality of parallel-oriented field effect emitter elements,a gate electrode which is arranged above the emission surface,and a plurality of first contact elements for at least two current-carrying current paths of the electron emitter independently of one another,wherein, depending on an emission voltage between the gate electrode and the emission surface, electrons can be emitted from at least one of the current paths by means of the field effect emitter elements, characterized in that,the emitter seat has a plurality of second contact elements which can be connected to the plurality of first contact elements at the end of the current paths,the plurality of first contact elements are arranged on a side of the plurality of parallel-oriented field effect emitter elements facing away from the emission surface.The cathode device according to the invention is particularly advantageous since the electron emitters known from the prior art are regularly contacted via structures which are integrated into the emission surface of the electron emitter and / or project. The cathode device according to the invention overcomes this disadvantage by switching from the front-side contacting to a non-front-side contacting. Destructive discharge processes are preferably reduced, since fewer, to no, such contact structures are present in the emission surface.The cathode device according to the invention therefore has in particular no structures which project in the emission direction. The emission direction of the electron emitter is therefore not restricted for further attachments. In particular, a focusing unit for the emitted electrons and / or a protection device against discharging processes can be provided above the electron emitter in the emission direction.A further advantage of the cathode device according to the invention relates to the possibility that the electron emitter can be aligned and / or inserted relative to the plurality of second contact elements of the emitter seat, in particular during the production of the cathode device, on account of the plurality of first contact elements.The X-ray source according to the invention comprisesthe cathode device,an anode andan evacuated housing,wherein the cathode means and the anode are disposed within the evacuated housing.The anode can be, in particular, a rotating anode or a standing anode. In principle, it is conceivable for the anode to rotate together with the evacuated housing.The electrons generated by means of the cathode device are accelerated in particular by the cathode device in the direction of the anode by means of an acceleration unit. The acceleration unit comprises in particular a high-voltage source or a high-frequency source. Depending on the type of acceleration unit, the X-ray source is typically an X-ray emitter, in particular for imaging applications in the keV range, or a linear accelerator, in particular for imaging or therapeutic applications in the MeV range.The cathode device forms in particular a cathode for the X-ray source. The electrical potential of the cathode is typically more negative compared to the electrical potential of the anode.The electron emitter is configured in particular to generate the electrons by means of the field effect emitter elements. The electron emitter is in particular a closed component, for example an electron emitter chip. The electron emitter can consist, for example, of the multiplicity of parallel-oriented field effect emitter elements, the gate electrode and the plurality of first contact elements.The term plurality of field effect emitter elements means in particular that so many field effect emitter elements are part of the emission surface that the emission surface has an electron current density of at least 0.1 A / cm^2, preferably at least 3 A / cm^2, particularly advantageously at least 10 A / cm^2. The number of field effect emitter elements required for this is typically at least 1000, regularly more than 10000. Advantageously, the emission surface has dimensions of at least 0.1 to 0.1 cm^2 and / or at most 10 to 10 cm^2.The field effect emitter elements can be embedded in an insulating matrix. The insulating matrix preferably holds the plurality of field effect emitter elements together.The field effect emitter elements are aligned in particular parallel and / or flush with respect to the emission surface. In this case, the emission surface is advantageously as planar as possible. The emission surface can basically be finished in order to be planar.The field effect emitter elements typically have an emission point or an emission section at one end of the respective field effect emitter elements. The emission surface consists in particular of the emission points or the emission sections of the field effect emitter elements. The emission point is, for example, the tip of a field effect emitter element designed as a field effect emitter needle. The emission section comprises, for example, the emission point and an adjacent region lying around the emission point.The emission surface forms in particular the upper side of the plurality of field effect emitter elements. An upper side of the electron emitter can correspond to the upper side of the plurality of field effect emitter elements, in particular when the gate electrode is not viewed and / or when the gate electrode is fully integrated into the volume of the field effect emitter elements.The sides of the plurality of field effect emitter elements define in particular the surfaces of the plurality of field effect emitter elements and are fundamentally synonymous in the present description. The sides of the plurality of field effect emitter elements comprise in particular an upper side, an underside and a cladding side. The surfaces of the plurality of field effect emitter elements accordingly comprise in particular a surface which typically corresponds to the emission surface, a lower surface and a lateral surface which typically corresponds to the lateral surfaces.The upper side and the lower side of the field effect emitter elements typically have the same dimensions and / or the same geometric shape. The geometric shape can be angular, in particular quadrangular, preferably rectangular, or round.The side surfaces of the plurality of parallel-oriented field effect emitter elements connect in particular the upper side and the lower side. The side surfaces of the plurality of parallel-oriented field effect emitter elements are formed in particular by the longitudinal sides of the outermost field effect emitter elements and / or by the matrix surrounding the outermost field effect emitter elements.The side surfaces cover in particular the circumference of the field effect emitter elements completely, i.e. by 360°. If the geometric shape of the upper side of the field effect emitter elements is round, a side surface is, by definition, a lateral surface with a maximum of 90° of the circumference. If the geometric shape of the upper side of the field effect emitter elements is angular, a side surface spans a lateral surface from one edge to an adjacent edge, wherein the edges respectively connect the respective corners of the upper side and lower side.It is conceivable for the field effect emitter elements to be grown on a substrate. The substrate can in principle have been removed, for example ground, after the growth of the field effect emitter elements. The substrate is typically arranged on a bottom side of the field effect emitter elements.The field effect emitter elements are designed, for example, as field effect emitter needles, the tips of which form the emission points and thus the emission surface. The field effect emitter needles are in particular nanotubes. Alternatively, it is conceivable for the field effect emitter elements to form at least one spindt cathode.It is regularly possible to integrate transistor structures, for example, into the field effect emitter needles, in particular if the field effect emitter needles consist of a semiconductor such as silicon, carbon or molybdenum, for example.The field effect emitter elements can be switched in particular individually, in groups or all together. Electron emitters which comprise field effect emitter elements that can be switched individually or in groups are typically so-called pixelated or segmented emitters. The segmentation of the circuit of the field effect emitter elements and thus of the electron emitter can be effected by means of different first or second contact elements and / or a segmentation of the gate electrode.In the present application, current paths are defined in such a way that all field effect emitter elements, which can only be turned on or off together, form their own current-carrying current path. Depending on the interconnection, the plurality of field effect emitter elements can therefore comprise a plurality of current paths for the individual field effect emitter elements, some current paths for field effect emitter elements switchable into groups or a single current path if all field effect emitter elements can only be connected together. A separately switchable current path, i.e. one which can be connected or disconnected by means of a contact element, is typically a current path which conducts current independently of other current paths.Typically, each current path is assigned exactly one segment of the electron emitter. Such a segment of the electron emitter forms in particular a pixel.The gate electrode can be designed in particular as a grid. The gate electrode is arranged in particular above the emission surface in such a way as to cause electron emission in the respective field effect emitter elements by means of the emission voltage between the gate electrode and the emission surface in accordance with the field effect. In this context, the term above includes the fact that the gate electrode extends as close as possible to the respective field effect emitter elements, for example is arranged directly at the height of the ends of the field effect emitter elements forming the emission surface and / or surrounds these ends of the field effect emitter elements.The gate electrode is advantageously arranged in such a way as to minimize e.g. an electron emission in or on the gate electrode and / or thermal effects. Alternatively or additionally, the gate electrode is advantageously arranged in such a way as to maximize, for example, the electron emission in or onto the anode and / or a mechanical stability and / or a robustness with respect to a high-voltage breakdown.The emission voltage is present in particular between the emission point or the emission section of the respective field effect elements and the gate electrode. For electron emission, the current path from which the electrons for electron emission originate is typically closed.The potential of the gate electrode is usually more positive than the potential of the field effect emitter elements. For example, the gate electrode can be at constant ground potential and the field effect emitter elements can be at negative potential. Alternatively, the field effect emitter elements can be at constant ground potential.It is conceivable that the gate electrode can provide different emission voltages to the emission surface, in particular if the gate electrode is designed as a grid. In this case, in particular the gate electrode can be segmented, so that the electron emitter is a segmented electron emitter. For example, the emission voltage between groups of field effect emitter elements can be varied by means of the segmented gate electrode, for example in that the electrical potential of the segments of the gate electrode differs.The plurality of first contact elements and the plurality of second contact elements are in particular designed to establish a reliable electrical connection by means of mutual contacting. In particular, an electrical connection can be made by a first contact element and a second contact element. This electrical connection typically connects the current path at this point. The plurality of second contact elements are in particular configured as part of the emitter seat in such a way that they can be connected to the plurality of first contact elements.The contact elements may comprise contact points or contact surfaces. The contact points typically have a contact surface which is as small as possible and is still electrically secure. It is conceivable that a first contact element has a contact point and a second contact element has a contact surface, wherein the contact point of the first contact element and the contact surface of the second contact element can be connected to one another, or vice versa. A contact surface typically has dimensions greater than a contact point, so that these two contact elements have a certain play relative to one another in one plane.The field effect emitter elements can connect directly to the plurality of first contact elements. The connection between the plurality of first contact elements and the field effect emitter elements can be effected through the substrate.The field effect emitter elements are connected to a current source in particular by means of electrically connected contact elements. In this case, a current path extends in particular from the current source via a second contact element, a first contact element connected thereto, as far as the field effect emitter element.It is conceivable that a first contact element is connected to one or more field effect emitter elements. A second contact element may be connectable to one or more first contact elements. The number of the first contact elements and the second contact elements may be identical or may vary.A plurality of contact elements means in particular that typically at least one order of magnitude fewer first contact elements or second contact elements are present than field effect emitter needles. In principle, it is conceivable that the number of first contact elements corresponds to the number of field effect emitter needles.Typically, the number of first contact elements correlates with the number of current paths. The plurality of first contact elements for the at least two current-carrying current paths of the electron emitter independently of one another are electrically conductively connected in particular to the at least two current paths. The at least two current paths of the electron emitter can comprise exclusively current paths of the field effect emitter elements or, in addition to the current paths of the field effect emitter elements, further current paths, for example a further current path of the gate electrode, of the electron emitter.Connectable means in particular electrically connectable, i.e. establishing an electrical connection. Electrically connectable means in particular electrically contactable. Electrically connected means in particular electrically contacted.Depending on the configuration of the cathode device, the connectable contact elements can already be electrically connected. Non-connected contact elements have in particular not closed an associated current path, but rather the latter is open. In principle, the first contact elements and the second contact elements can be connected equally or mutually exchanged.The emitter seat typically has fastening means for fastening and / or aligning the electron emitter on the emitter seat by means of the fastening means. The emitter seat has, in particular, a carrier body to which the second contact elements are fastened. The carrier body and the second contact elements are usually galvanically separated. The second contact elements are arranged in particular on a side of the emitter seat facing the electron emitter, in particular of the carrier body.The emitter seat, in particular the carrier body, can be designed as a focus head for the emitted electrons. The emitter seat, in particular the carrier body, can be configured to be metallic, in particular additionally electrically conductive, for example to be at a negative high-voltage potential or ground potential. The emitter seat can be configured in such a way as to lengthen the current paths of the field effect emitter elements as far as the current source in order to enable connection of the field effect emitter elements to the current source. For this purpose, the emitter seat can have, for example, at least one line which connects a field effect emitter element to the current source.The side facing away from the emission surface is in particular not the surface or top side. The side facing away from the emission surface can be, in particular, the underside and / or a jacket side. In particular, the plurality of second contact elements does not face the emission surface, but rather the plurality of first contact elements. When the plurality of first contact elements face the plurality of second contact elements, the first contact elements and the second contact elements are typically connectable.One embodiment provides that the plurality of first contact elements are arranged exclusively on the remote side. This embodiment is particularly advantageous because of its compactness.One embodiment provides that the side facing away from the emission surface is the underside of the plurality of parallel-oriented field effect emitter elements opposite the emission surface and facing the emitter seat. This embodiment is particularly advantageous due to the contacting of the plurality of parallel-oriented field effect emitter elements from below.One embodiment provides that the first contact elements are arranged exclusively in a first plane. In particular, contacting of the field effect emitter elements is thereby simplified. Exclusively means that no first contact elements are arranged outside the first plane.One embodiment provides that the plurality of second contact elements are arranged exclusively in a second plane. In particular, this simplifies the provision of the contacting of the field effect emitter elements. Exclusively means that no second contact elements are arranged outside the second plane.One embodiment provides that the first plane and the second plane are oriented parallel to one another. This embodiment advantageously makes comparatively simple contacting possible.One embodiment provides that for the connection the plurality of second contact elements and / or the plurality of first contact elements are configured to be movable. This embodiment is particularly advantageous since the contacting can take place by means of the movable contact elements and can be canceled again. In other words, the movable configuration advantageously enables the connection of connectable contact elements, in particular without changing the orientation of the electron emitter relative to the emitter seat. In particular, the plurality of second contact elements are configured to be movable relative to the emitter seat for the connection to the plurality of first contact elements and / or the plurality of first contact elements are configured to be movable relative to the electron emitter for the connection to the plurality of second contact elements. The movable configuration can be carried out separately for individual or grouped contact elements or for all first contact elements and / or all second contact elements together.One embodiment provides that the movable configuration is realized by means of an elastic connecting element. This embodiment is particularly advantageous for producing an electrically secure, equally flexible connection. In particular, the at least one elastic connecting element has a mechanical force transmitter, which is a pressing pin or a spring pin. A plurality of pressing pins and / or spring pins can be part of the movable configuration of the contact elements. Depending on the type of movable configuration, a plurality of elastic connecting elements can be provided, in particular also separately for individual or grouped contact elements.One embodiment provides that the plurality of second contact elements are connected to the plurality of first contact elements exclusively in a force-fitting and / or form-fitting manner. The plurality of second contact elements are connected to the plurality of first contact elements in particular in a non-materially bonded manner, that is to say in particular not soldered. This embodiment offers in particular the advantage of a reversible contacting, which enables an electron emitter to be exchanged without removing the emitter seat from the cathode device or X-ray source.One embodiment provides that the plurality of first contact elements are arranged according to a BGA ball grid arrangement. In this case, the plurality of second contact elements are also regularly arranged according to the BGA ball grid arrangement. This embodiment is particularly advantageous due to the use of a standardized arrangement of the plurality of first and / or second contact elements.One embodiment provides that a contact surface of one of the plurality of first contact elements and a contact surface of one of the plurality of second contact elements have a different surface area. In other words, the surface area of the one of the plurality of first contact elements and the one of the plurality of second contact elements differ. For example, it is conceivable that one of the contact surfaces is a contact point and thus the smaller of the two surface areas approximately only has the surface area necessary for a secure, electrical connection.Features, advantages or alternative embodiments mentioned in the description of the device are likewise to be transferred to the method and vice versa. In other words, claims can be further developed on the method with features of the device and vice versa. In particular, the device according to the invention can be used in the method.The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. In principle, structures and units that remain substantially the same are denoted by the same reference sign as when the respective structure or unit occurs for the first time in the following description of the figures.The following are shown: FIG. 1 shows a cathode device according to the invention, FIG. 2 shows a cathode device in a first exemplary embodiment, FIG. 3 shows an X-ray source.FIG. 1 shows a cathode device 30 according to the invention in a schematic sectional view. The cathode device 30 comprises an electron emitter 10 and an emitter seat 20.The electron emitter 10 has a plurality of parallel-aligned field effect emitter elements 11 for forming an emission surface 12 on the upper side of the plurality of parallel-aligned field effect emitter elements 11. The field effect emitter elements 11 are arranged on an optional substrate. The emission surface 12 is perpendicular to the image plane of FIG. 1 and is indicated by a dashed line.The electron emitter 10 further comprises a gate electrode 13 which is arranged above the emission surface 12. The gate electrode 13 is formed as a grid. The grating is arranged as close as possible to the ends of the field effect emitter elements 11.In addition, the electron emitter 10 has a plurality of first contact elements 14 for at least two current-carrying current paths of the electron emitter 10 which are independent of one another. The plurality of first contact elements 14 are configured to be stationary in FIG. 1.A first current path in FIG. 1 comprises four field effect emitter elements 11 and a second current path comprises four further field effect emitter elements 11, which can each be connected to a separate second contact element 21 via a separate first contact element 14. The electron emitter 10 of FIG. 1 is thus a so-called segmented or pixelated emitter.The emitter seat 20 has a plurality of second contact elements 21, which can be connected to the plurality of first contact elements 14 at the end of the current paths and are electrically connected in FIG. 1. Depending on an emission voltage between the gate electrode 13 and the emission surface 12, in particular also on the electrical connection between the contact elements 14, 21, electrons can be emitted from at least one of the current paths by means of the field effect emitter elements 11.The plurality of first contact elements 14 are arranged on a side of the plurality of parallel-oriented field effect emitter elements 12 facing away from the emission surface 12. In the cathode device 30 of FIG. 1, the plurality of first contact elements 14 are arranged exclusively on the side facing away from the emission surface 12, wherein the side facing away from the emission surface 12 is the underside of the plurality of parallel-oriented field effect emitter elements 11 opposite the emission surface 12 and facing the emitter seat 20.The first contact elements 14 are arranged exclusively in a first plane. The plurality of second contact elements 21 are arranged exclusively in a second plane. The first plane and the second plane are oriented parallel to each other. The plurality of first contact elements 14 are advantageously arranged according to a BGA ball grid arrangement.A contact surface of one of the plurality of first contact elements 14 and a contact surface of one of the plurality of second contact elements 21 have different surface areas. The plurality of second contact elements 21 each have a contact point, so that its surface area is smaller than the surface area of the associated plurality of first contact elements 14.FIG. 2 shows a first exemplary embodiment of the cathode device 30 in a schematic sectional view.The emitter seat 20 has a carrier body 22, and for the connection, the plurality of second contact elements 21 are configured to be movable relative to the carrier body 22. Alternatively or additionally, the plurality of first contact elements 14 can be configured to be movable relative to the field effect emitter elements 11.A further current path of the at least two current-carrying current paths independently of one another has the gate electrode 13 and one of the plurality of second contact elements 21. This current path additionally has a further first contact element 14. A portion of the gate electrode 13 may form the further first contact element 14.The movable configuration takes place by means of an elastic connecting element, wherein the at least one elastic connecting element has a mechanical force transmitter which is a press pin or a spring pin. The plurality of second contact elements 21 are exclusively connected in a force-fit manner to the plurality of first contact elements 14. Alternatively or additionally, a form-fit connection would be conceivable.FIG. 3 shows an X-ray source 40 in a schematic longitudinal section.The X-ray source 40 includes a cathode device 30, an anode 41 and an evacuated housing 42. The cathode assembly 30 and the anode 41 are disposed within the evacuated housing 42.Although the invention has been illustrated and described in more detail by the preferred exemplary embodiments, the invention is nevertheless not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

Claims

Cathode device (30) for an X-ray source (40), having - an electron emitter (10) and - an emitter seat (20), wherein the electron emitter (10) has - a multiplicity of field effect emitter elements (11) aligned in parallel for forming an emission surface (12) on the upper side of the multiplicity of field effect emitter elements (11) aligned in parallel, - a gate electrode (13) which is arranged above the emission surface (12), - and a plurality of first contact elements (14) for at least two current-carrying current paths of the electron emitter (10) independently of one another, - wherein electrons can be emitted from at least one of the current paths by means of the field effect emitter elements (11) as a function of an emission voltage between the gate electrode (13) and the emission surface (12), characterized - in that the emitter seat (20) has a plurality of second contact elements (21), which can be connected to the plurality of first contact elements (14) at the end of the current paths, - in that the plurality of first contact elements (14) are arranged on a side of the plurality of field effect emitter elements (11) which are oriented parallel and which faces away from the emission surface (12).The cathode device (30) according to claim 1, wherein the plurality of first contact elements (14) are arranged exclusively on the opposite side.Cathode device (30) according to one of the preceding claims, wherein the side facing away from the emission surface (12) is the underside of the plurality of parallel-oriented field effect emitter elements (11) opposite the emission surface (12) and facing the emitter seat (20).Cathode device (30) according to one of the preceding claims, wherein the first contact elements (14) are arranged exclusively in a first plane.Cathode device (30) according to one of the preceding claims, wherein the plurality of second contact elements (21) are arranged exclusively in a second plane.Cathode device (30) according to claims 4 and 5, wherein the first plane and the second plane are oriented parallel to each other.Cathode device (30) according to one of the preceding claims, wherein the plurality of second contact elements and / or the plurality of first contact elements are configured to be movable for the connection.Cathode device (30) according to claim 7, wherein the movable configuration takes place by means of an elastic connecting element.Cathode device (30) according to Claim 8, wherein the at least one elastic connecting element has a mechanical force transmission.The cathode device (30) according to claim 9, wherein the mechanical force transmitter is a pressing pin or a spring pin.Cathode device (30) according to one of the preceding claims, wherein the plurality of second contact elements (21) are connected to the plurality of first contact elements (14) exclusively in a force-fitting and / or form-fitting manner.The cathode device (30) according to any of the preceding claims, wherein the plurality of first contact elements (14) are arranged according to a BGA ball grid arrangement.Cathode device (30) according to one of the preceding claims, wherein a further current path of the at least two current-carrying current paths independently of one another has the gate electrode (13) and one of the plurality of second contact elements (21).Cathode device (30) according to one of the preceding claims, wherein a contact surface of one of the plurality of first contact elements (14) and a contact surface of one of the plurality of second contact elements (21) have a different surface area.An X-ray source (40) comprising - a cathode device (30) according to any of the preceding claims, - an anode (41) and - an evacuated housing (42), wherein the cathode device (30) and the anode (41) are arranged within the evacuated housing (42).

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