Electronic emitter device

Abstract

The present invention relates to an electron emitter device, a method for generating an electron flow, an X-ray source, and a computer program product. The electron emitter device according to the present invention has: - field effect emitter pins of a first ring, the field effect emitter pins of the first ring forming a first emitter surface on the inner side of the first ring, and - field effect emitter pins of a second ring, the field effect emitter pins of the second ring forming a second emitter surface on the inner side of the second ring, wherein the first ring and the second ring are arranged such that the first emitter surface and the second emitter surface form a substantially continuous three-dimensional total emitter surface, the total emitter surface being hollow along a longitudinal axis.

Description

Field of the Invention

[0001] The present invention relates to an electron emitter device, a method for generating an electron flow, an X-ray source, and a computer program product. Background Art

[0002] Conventional electron emitter devices can include different types of electron emitters, such as thermionic emitters or field effect emitters with field effect emitter needles. Some electron emitter devices can be heated directly or indirectly. Examples of thermionic emitters are filament emitters or flat emitters. A flat emitter is disclosed in DE 10 2006 018 633 B4, which has a smaller electron density in the central region of the emitter plate during operation compared to the region adjacent to the central region.

[0003] During the operation of a conventional X-ray source having an electron emitter device, it occurs that ions from the anode of the conventional X-ray source are thrown back towards the direction of the electron emitter device. Ions are regularly generated when the electrons generated by the electron emitter device interact with the anode.

[0004] In particular, due to the relatively macroscopic structure, conventional thermionic emitters are more resistant compared to conventional field effect emitters with field effect emitter needles. And the field effect emitter needles can be damaged by the impinging ions and eventually destroyed. Summary of the Invention

[0005] The object underlying the present invention is to provide an electron emitter device, a method for generating an electron flow, an X-ray source, and a computer program product having improved robustness and service life.

[0006] This object is achieved by the features of the present invention. Advantageous designs are described in the following description.

[0007] The electron emitter device according to the present invention has:

[0008] - field effect emitter needles of a first ring, which form a first emitter surface on the inner side of the first ring, and

[0009] - field effect emitter needles of a second ring, which form a second emitter surface on the inner side of the second ring,

[0010] wherein the first ring and the second ring are arranged such that the first emitter surface and the second emitter surface form a substantially continuous three-dimensional total emitter surface, which is hollow along the longitudinal axis.

[0011] The three-dimensional total emitter surface is annular and hollow along the longitudinal axis, preferably resulting in: the three-dimensional total emitter surface having a central opening. Thus, the number of charged particles reaching the three-dimensional total emitter surface from the anode is reduced, especially the number of ions and / or charged clusters composed of multiple atoms. Because the charged particles pass through the hollow three-dimensional total emitter surface at least partially centrally. That is, the three-dimensional, especially spatial, design of the total emitter surface enables at least a part of the charged particles to pass centrally through the central opening.

[0012] The first ring and the second ring also provide the following advantages: the number of field effect emitter pins, especially the corresponding emitter surfaces, can be increased because the structural space along the longitudinal axis of the electron emitter device is advantageously utilized better. The electron emitter device especially has multiple rows of emitter surfaces arranged in a structurally space-optimized manner. The alternative traditional magnification perpendicular to the longitudinal axis is disadvantageous because widening the emitter surface also widens the focal spot, which in turn increases the blur of the X-ray radiation. Therefore, conversely, additional focusing that would be costly is required, while the present invention does not require such additional focusing. Thus, the three-dimensional total emitter surface can advantageously enhance the electron flow.

[0013] Another advantage of the three-dimensional total emitter surface is that the electron flow can be increased because a larger emitter surface reduces the influence of the effects that occur during emission, which can cause blooming and / or defocusing of the electron flow due to the space charge density, and thus can also cause widening of the focal spot.

[0014] Advantageously, field effect emitter pins are arranged on the inner side of the first ring or the second ring, which has a basic focusing effect on the electron flow, while for example, a traditional filament emitter has a defocusing effect due to its external shape.

[0015] The field effect emitter pins can be constructed in different types, for example, as carbon-field effect emitter pins, metal-field effect emitter pins, or silicon-field effect emitter pins. Typically, the electron emitter device has only one type of field effect emitter pin. The metal-field effect emitter pin is also known as a Spindt field effect emitter. Field effect emitter pins made of other materials, such as molybdenum, are also feasible. The silicon-field effect emitter pins are arranged on a silicon substrate, for example, which can be advantageously manufactured in a planar manner with respect to production techniques known in the semiconductor industry, such as silicon wafers used for computer chip production, with a diameter greater than several centimeters. In particular, the emitted electrons form an electron flow. The electron current density of the field effect emitter pins is, for example, in the range greater than 0.1 A / cm² and / or less than 200 A / cm², preferably between 1 A / cm² and 50 A / cm², and particularly advantageously between 5 A / cm² and 15 A / cm².

[0016] The difference between the field-effect emitter pins of the first ring and the field-effect emitter pins of the second ring can be based on: a row of field-effect emitter pins having a different spacing from a point on the anode than another row of field-effect emitter pins. The first ring in particular includes a first group of field-effect emitter pins at a first spacing from a point on the anode, while the second ring in particular includes a second group of field-effect emitter pins at a second spacing from a point on the anode, where the second spacing is different from the first spacing. In principle, it is conceivable that the spacing of the field-effect emitter pins of the first ring or the second ring changes, especially when the first ring or the second ring is arranged inclined relative to the anode. The first ring can in particular include field-effect emitter pins that are remote from the anode, while the second ring can in particular include field-effect emitter pins that are close to the anode.

[0017] In practice, the first emitter surface and / or the second emitter surface are often observed three-dimensionally. The first emitter surface and the second emitter surface can in particular be pixelated. The first emitter surface and the second emitter surface can be part of the same substrate and / or the same printed circuit board.

[0018] The first emitter surface and / or the second emitter surface can be segmented and / or separated pixel by pixel. It is conceivable that the first ring or the second ring consists of one piece and the first emitter surface and / or the second emitter surface are segmented and / or separated pixel by pixel. Alternatively, the first ring and / or the second ring can consist of a plurality of sub-rings and / or sub-blocks. If the first emitter surface and / or the second emitter surface are segmented and / or separated pixel by pixel, the three-dimensional total emitter surface is generally segmented and / or separated pixel by pixel.

[0019] The three-dimensional total emitter surface can essentially be referred to as an annular emitter surface-cascade. In addition to the first emitter surface and the second emitter surface, the three-dimensional total emitter surface can include other emitter surfaces, especially emitter surfaces on a third ring. In principle, more than three rings are also conceivable.

[0020] The first emitter surface and the second emitter surface are in particular arranged successively when observed along the longitudinal axis. Substantially continuous in particular means: the first emitter surface and the second emitter surface are preferably arranged relative to each other such that the spacing between the two emitter surfaces is minimized. In principle, it is conceivable that the spacing between the two emitter surfaces can be greater than zero, where nevertheless a substantially continuous three-dimensional total emitter surface is still formed. Thus, substantially continuous means: the first emitter surface and the second emitter surface are not distributed along the focal path of the anode or arranged side by side. Substantially continuous in particular means: the electron flow generated by the first emitter surface and the electron flow generated by the second emitter surface generally at least partially overlap and / or are oriented parallel. Substantially continuous can also mean: the electron flow generated by the first emitter surface can pass through the second ring during operation of the electron emitter device.

[0021] The electron emitter device in particular has a first ring, which includes field effect emitter needles of a first emitter surface. The electron emitter device in particular has a second ring, which includes field effect emitter needles of a second emitter surface.

[0022] In principle, it is conceivable that at least a part of the field effect emitter needles is arranged on the outside of the first ring and / or on the outside of the second ring. Most of the field effect emitter needles are typically arranged on the inside. The main part of the electron flow can preferably be generated by the emitter surfaces located on the inside of the first ring and / or the second ring. Depending on the cross-section of the first ring and / or the second ring, the inside in particular also includes the surface of the first ring and / or the second ring, for example, on the side facing the anode. The inside is in particular the side facing the longitudinal axis of the three-dimensional total emitter surface. The inside is at least partially located within the volume including the three-dimensional total emitter surface. The first emitter surface has at least one first emitter surface normal, which is perpendicular to the first emitter surface. The second emitter surface has at least one second emitter surface normal, which is perpendicular to the first emitter surface. Due to the geometric design of the first ring and / or the second ring, the emitter surface can have approximately infinitely many emitter surface normals.

[0023] At least one first emitter surface normal and / or the second emitter surface normal is not parallel to the longitudinal axis and / or can intersect the longitudinal axis at a finite number of points when observed mathematically.

[0024] In this context, the term "ring" in particular represents a geometric shape similar to a conventional ring, for example, a polygon with N>2 corners, which has a central opening. In other words, the first ring and / or the second ring is not necessarily circular or oval, but at least one of the two rings can be, for example, triangular, while the other ring is circular or square. In principle, it is conceivable that the ring is approximately a polygon with multiple corners. In addition, it is feasible that the first ring and / or the second ring is symmetric or asymmetric with respect to each other or with respect to itself.

[0025] One embodiment proposes that the three-dimensional total emitter surface is tubular. Tubular in particular means that the inner diameter of the three-dimensional total emitter surface is substantially constant. This embodiment is particularly advantageous because as many charged particles as possible from the anode can pass through.

[0026] An alternative embodiment to the aforementioned embodiment proposes that the three-dimensional total emitter surface tapers along the longitudinal axis. The three-dimensional total emitter surface tapering in particular means that the inner diameter of the three-dimensional total emitter surface is at least partially narrower in one section than in another section. Usually, the change in the inner diameter is smooth. Preferably, the narrower the inner diameter, the farther the section is from the anode. This embodiment is particularly advantageous because the emitter surface facing the anode becomes larger.

[0027] One embodiment proposes that the minimum inner radius of the first ring is different from the minimum inner radius of the second ring. This embodiment enables the flexible setting of the first ring and the second ring.

[0028] One embodiment proposes that the first emitter surface forms a frustoconical side surface and / or the second emitter surface forms a frustoconical side surface. The advantage of this embodiment is that, due to the design of the frustoconical side surface, the share of field emitter needles directly facing the anode can be increased.

[0029] One embodiment proposes that the first frustoconical emitter surface and the second frustoconical emitter surface are oriented in the same direction along the longitudinal axis. If the emitter surfaces are configured as frustoconical, then the emitter surfaces and thus the electron flow are oriented in the same direction, and this design is particularly advantageous.

[0030] One embodiment proposes that the cone angle of the first frustoconical emitter surface is different from the cone angle of the second frustoconical emitter surface. The cone angle particularly includes the angle between the longitudinal axis and the perpendicular to the normal of the emitter surface. This embodiment can therefore be particularly advantageous because, depending on the inner radius of the first ring or the second ring, for example, the diameter of the central opening can be optimized. The cone angle is typically between 0° and 90°, regardless of the direction of the longitudinal axis. In principle, it can be envisaged that both cone angles are 0°. In addition, it can be envisaged that one of the two cone angles is up to 90°, including 90°.

[0031] One embodiment proposes that the first emitter surface forms a cylindrical side surface and / or the second emitter surface forms a cylindrical side surface. Preferably, while ensuring sufficient electron flow, this embodiment optimizes the share of field emitter needles that are protected from charged particles with respect to the anode.

[0032] One embodiment proposes that a first electron flow for a first focal spot can be generated by means of the first emitter surface, a second electron flow for a second focal spot can be generated by means of the second emitter surface, and the first focal spot and the second focal spot are different in terms of position and / or size. The features of this embodiment can particularly lie in changing the design of the ring, such as a cylindrical or frustoconical side surface, and / or, particularly, in setting the corresponding cone angles and / or in adjusting the minimum inner radius accordingly. In principle, this embodiment enables the first ring and the second ring to operate alternately, but also simultaneously, for example, where the electron flows of the two emitter surfaces are supplemented or superimposed. Thus, for example, a higher electron flow is feasible because the emitter surfaces can be cooled in the off state during pulsed operation to reduce the thermal load. The first emitter surface and the second emitter surface can particularly be controlled to generate electron flow in such a way that a jumping focal spot or a so-called jumping focus is achieved on the anode.

[0033] One embodiment provides that the electron emitter device further has an emitter pin verification unit and a control unit, the emitter pin verification unit being configured to determine the degree of functionality of at least one field effect emitter pin on the first ring and / or the second ring, and the control unit being configured to switch on or off the first emitter surface or the second emitter surface according to the degree of functionality of at least one field effect emitter pin. This embodiment is particularly advantageous because the electron emitter device is constructed redundantly, such that a defect within the first ring or the second ring does not necessarily cause the failure of the entire electron emitter device. Because due to the three-dimensional internal total emitter surface, the function of the first ring or the second ring can be replaced by the function of the other ring without having to replace the electron emitter device.

[0034] An X-ray source according to the invention has:

[0035] - an evacuated X-ray tube housing,

[0036] - an electron emitter device arranged in the evacuated X-ray tube housing, and

[0037] - an anode arranged in the evacuated X-ray tube housing for generating X-rays according to electrons incident from the electron emitter device.

[0038] Typically, the electron emitter device is arranged opposite the focal path of the anode. Depending on the design of the X-ray source, a focusing head (Fokuskopf) can be provided, which deflects the electron beam from the electron emitter device in the direction of the anode. Alternatively or additionally, an electrostatic or electromagnetic deflection system between the electron emitter device and the anode, which is part of the X-ray source, can deflect the electron beam onto the anode. The deflection can in principle include the focusing and / or shaping and / or positioning of the electron beam.

[0039] The anode typically has a conductive material, such as molybdenum, graphite and / or tungsten. Thus, the anode typically has a single potential evenly distributed over the anode. In principle, it is conceivable that the anode consists of a conductive material.

[0040] A method according to the invention for generating an electron beam has the following steps:

[0041] - providing an electron emitter device,

[0042] - determining, by means of the emitter pin verification unit, the degree of functionality of at least one field effect emitter pin on the first ring and / or the second ring, and

[0043] - switching on the first emitter surface or the second emitter surface by means of the control unit according to the degree of functionality of at least one field effect emitter pin, wherein an electron beam is generated.

[0044] One embodiment proposes to alternately operate the first emitter face or the second emitter face.

[0045] A computer program product that can be directly loaded into the memory of a computing unit according to the present invention has program code means for performing a method for generating an electron flow when the computer program product is run on the computing unit. In particular, the computing unit can be configured as part of a control unit.

[0046] The computer program product can be a computer program or can include a computer program. The computer program product particularly has program code means that depict the method steps according to the present invention. Thereby, the method according to the present invention can be performed in a defined and repeatable manner, and control over the propagation of the method according to the present invention can be implemented. The computer program product is preferably configured such that the computing unit can perform the method steps according to the present invention with the aid of the computer program product. The program code means can in particular be loaded into the memory of the computing unit and typically run by means of the processor of the computing unit accessing the memory. If the computer program product, in particular the program code means, is run on the computing unit, typically all embodiments according to the present invention of the described method can be performed. The computer program product is, for example, stored on a physical, computer-readable medium and / or stored digitally as a data packet in a computer network. The computer program product can be a physical, computer-readable medium and / or a data packet in a computer network. Thus, the present invention can also be based on a physical, computer-readable medium and / or a data packet in a computer network. The physical, computer-readable medium can generally be directly connected to the computing unit, for example by placing the physical, computer-readable medium in a DVD disk drive or inserting it into a USB port, whereby the computing unit can in particular access the physical, computer-readable medium in a read manner. The data packet can preferably be retrieved from a computer network. The computer network can have a computing unit or be indirectly connected to the computing unit via a wide area network (WAN) or a (wireless) local area network connection (WLAN or LAN). For example, the computer program product can be stored digitally at a storage location in a computer network on a cloud server and transmitted to the computing unit via the WAN via the Internet and / or via the WLAN or LAN, in particular by invoking a download link pointing to the storage location of the computer program product.

[0047] The features, advantages or alternative embodiments mentioned when describing the device can equally be transferred to the method, and vice versa. In other words, embodiments for the method can be improved with the aid of the features of the device, and vice versa. In particular, the device according to the present invention can be used in the method. Description of the Drawings

[0048] The present invention will be described and explained in detail below based on the embodiments shown in the accompanying drawings. In principle, in the following description of the drawings, substantially the same structures and units are named with the same reference numerals as when they first appear in the corresponding structure or unit.

[0049] The accompanying drawings show:

[0050] Figures 1 to 6 showing different design schemes of an electron emitter device according to the present invention,

[0051] Figure 7 showing another electron emitter device,

[0052] Figure 8 showing an X-ray source, and

[0053] Figure 9 showing a method for generating an electron flow. Detailed Description of the Embodiment

[0054] Figures 1 to 6 showing different cross-sections of the electron emitter device 10. The electron emitter device 10 has field-effect emitter pins of a first ring 11, and the field-effect emitter pins of the first ring form a first emitter surface 11.F on the inner side 11.I of the first ring 11. The electron emitter device 10 has field-effect emitter pins of a second ring 12, and the field-effect emitter pins of the second ring form a second emitter surface 12.F on the inner side 12.I of the second ring 12. The first ring 11 and the second ring 12 are arranged such that the first emitter surface 11.F and the second emitter surface 12.F form a substantially continuous three-dimensional total emitter surface 13, and the total emitter surface is hollow along the longitudinal axis L.

[0055] Charged particles from the anode can preferably pass through the electron emitter device 10 along the longitudinal axis L without interacting with one of the emitter surfaces 11.F, 12.F.

[0056] A first electron flow can be generated by means of the first emitter surface 11.F, typically for a first focal spot. A second electron flow can be generated by means of the second emitter surface 12.F, for example for a first focal spot or a second focal spot. Figures 1 to 6 The electron emitter device 10 can be improved such that the first focal spot and the second focal spot are different in terms of position and / or size.

[0057] Figure 1 showing a first embodiment of the electron emitter device 10. The three-dimensional total emitter surface 13 is tubular. The first emitter surface 11.F forms a cylindrical side surface. The second emitter surface 12.F forms a cylindrical side surface.

[0058] Figure 2Shows a second embodiment of the electron emitter device 10. The three-dimensional total emitter surface 13 is tubular. The first emitter surface 11.F forms a frustoconical side surface, and the second emitter surface 12.F forms a frustoconical side surface. The frustoconical first emitter surface 11.F and the frustoconical second emitter surface 12.F are oriented in the same direction along the longitudinal axis L.

[0059] In contrast to Figure 1 and Figure 2 On the contrary, in Figures 3 to 6 the embodiment of, the three-dimensional total emitter surface 13 tapers. In addition, the minimum inner radius of the first ring 11 is different from the minimum inner radius of the second ring 12. In this embodiment, the anode, not shown, is typically disposed closer to the first ring 11 than to the second ring 12.

[0060] Figure 3 Shows a third embodiment of the electron emitter device 10. The first emitter surface 11.F forms a cylindrical side surface. The second emitter surface 12.F forms a cylindrical side surface.

[0061] Figure 4 Shows a fourth embodiment of the electron emitter device 10. The first emitter surface 11.F forms a frustoconical side surface, and the second emitter surface 12.F forms a frustoconical side surface. The frustoconical first emitter surface 11.F and the frustoconical second emitter surface 12.F are oriented in the same direction along the longitudinal axis L.

[0062] In this embodiment, the cone angle of the frustoconical first emitter surface 11.F and the cone angle

[0063] Figure 5 of the frustoconical second emitter surface 12.F

[0064] are equal. The cone angle of the frustoconical first emitter surface 11.F

[0065] Figure 6 Shows a sixth embodiment alternative to the embodiment shown in Figure 5 in which mainly the cone angle varies.

[0066] The sixth embodiment can in principle be converted into an embodiment (not shown) having a rectangular total emitter surface 13, where the cone angle is 90°, and the cone angle is 0°.

[0067] Figure 7 Another design of the electron emitter device 10 is shown. For reasons of overview, mainly two rings 11, 12 of the electron emitter device 10 are shown without the implementation details shown previously.

[0068] The electron emitter device 10 also has an emitter pin verification unit 14, which is configured to determine the degree of functionality of at least one field-effect emitter pin on the first ring 11 and / or the second ring 12. The degree of functionality can be, for example, "operable" and "defective" in a binary manner. In addition, intermediate stages according to the remaining performance and / or remaining electron current capacity can also be envisaged. The emitter pin verification unit 14 can have an optical sensor or an infrared sensor to detect, for example, the first emitter surface 11.F and / or the second emitter surface 12.F in the form of an image. By means of an image algorithm program code mechanism, the computing unit can preferably determine the degree of functionality of the field-effect emitter pins in the detected image. Alternatively or additionally, the emitter pin verification unit 14 can have an ammeter and / or a voltmeter, which provide the degree of functionality by supplying current to the field-effect emitter pins and / or via the voltage drop across the field-effect emitter pins. The emitter pin verification unit 14 can include an interface that can output a signal according to the degree of functionality. It can be envisaged that the emitter pin verification unit 14 continuously monitors and accordingly verifies the field-effect emitter pins during operation.

[0069] The electron emitter device 10 additionally has a control unit 15, which is configured to switch on or off the first emitter surface 11.F or the second emitter surface 12.F according to the degree of functionality of at least one field-effect emitter pin. The control unit 15 can, for example, have an interface for receiving the signal of the emitter pin verification unit 14. In particular, the control unit recognizes based on a comparison with a threshold when, for example, the degree of functionality of at least one field-effect emitter pin is already insufficient or will soon be insufficient. In this case, the control unit in particular switches off the emitter surfaces 11.F, 12.F having this field-effect emitter pin and switches on the respective other emitter surface 12.F, 11.F. It can be envisaged that the control unit 15 additionally controls a steering system so that, for example, the focal spot parameters can be adjusted according to the switched-on field-effect emitter surfaces 11.F, 12.F.

[0070] Figure 8The X-ray source 20 is shown. The X-ray source 20 has an evacuated X-ray tube housing 21. The X-ray tube housing 21 typically includes a metal and / or glass housing enclosed in a vacuum-sealed manner. An electron emitter device 10 and an anode 22 are provided in the evacuated X-ray tube housing 21. The anode 22 is configured to generate X-rays according to the electrons incident from the electron emitter device 10. The electrons are typically accelerated from the electron emitter device 10 towards the anode 22 by means of an acceleration voltage unit. The acceleration voltage is particularly between 10 kV and 150 kV. The anode can be a rotatably supported anode or a fixed anode. The incident electrons interact with the anode, most of which generate heat, while a small part generates X-rays. The X-ray source 20 can have a cooling unit for heat dissipation. The X-ray radiation is particularly suitable for computed tomography, angiography, radiography, and / or mammography.

[0071] Figure 9 A method for generating an electron flow is shown in a flowchart, the method having the following steps:

[0072] S100 represents providing the electron emitter device 10.

[0073] S101 represents determining the degree of functionality of at least one field-effect emitter pin on the first ring 11 and / or the second ring 12 by means of the emitter pin verification unit 14.

[0074] S102 represents turning on the first emitter surface 11.F or the second emitter surface 12.F by means of the control unit 15 according to the degree of functionality of at least one field-effect emitter pin, wherein an electron flow is generated.

[0075] In principle, it is conceivable that the first emitter surface 11.F or the second emitter surface 12.F operates alternately.

[0076] Although the details of the present invention have been described and illustrated in detail by the preferred embodiments, the present invention is not limited by the disclosed examples, and other variants can be derived therefrom by those skilled in the art without departing from the scope of protection of the present invention.

Claims

1. An electron emitter device (10), the electron emitter device (10) having: - Field - effect emitter pins of a first ring (11), the field - effect emitter pins of the first ring (11) forming a first emitter surface (11.F) on the inner side (11.I) of the first ring (11), - Field - effect emitter pins of a second ring (12), the field - effect emitter pins of the second ring (12) forming a second emitter surface (12.F) on the inner side (12.I) of the second ring (12), wherein the first ring (11) and the second ring (12) are arranged such that the first emitter surface (11.F) and the second emitter surface (12.F) form a substantially continuous three - dimensional total emitter surface (13), the three - dimensional total emitter surface (13) being hollow along a longitudinal axis (L), and wherein the electron emitter device is configured to emit electrons towards an anode outside the hollow three - dimensional total emitter surface (13), - An emitter pin verification unit (14), the emitter pin verification unit (14) being configured to determine the degree of functionality of at least one field - effect emitter pin on the first ring (11) and / or the second ring (12), and - A control unit (15), the control unit (15) being configured to turn on or off the first emitter surface (11.F) or the second emitter surface (12.F) according to the degree of functionality of the at least one field - effect emitter pin.

2. The electron emitter device (10) according to claim 1, wherein the three - dimensional total emitter surface (13) is tubular.

3. The electron emitter device (10) according to claim 1, wherein the three - dimensional total emitter surface (13) tapers along the longitudinal axis (L).

4. The electron emitter device (10) according to any one of the above claims, wherein the minimum inner radius of the first ring (11) is different from the minimum inner radius of the second ring (12).

5. The electron emitter device (10) according to any one of claims 1 to 3 above, wherein the first emitter surface (11.F) forms a frustoconical side surface and / or the second emitter surface (12.F) forms a frustoconical side surface.

6. The electron emitter device (10) according to claim 5, wherein the frustoconical first emitter surface (11.F) and the frustoconical second emitter surface (12.F) are oriented in the same direction along the longitudinal axis (L).

7. The electron emitter device (10) according to claim 5 or 6, wherein the cone angle (φ1) of the frustoconical first emitter surface (11.F) is different from the cone angle (φ2) of the frustoconical second emitter surface (12.F).

8. The electron emitter device (10) according to any one of claims 1 to 4 above, wherein the first emitter surface (11.F) forms a cylindrical side surface and / or the second emitter surface (12.F) forms a cylindrical side surface.

9. The electron emitter device (10) according to any one of the preceding claims, wherein a first electron current for a first focal spot can be generated by means of the first emitter surface (11.F), a second electron current for a second focal spot can be generated by means of the second emitter surface (12.F), and wherein the first focal spot and the second focal spot differ in terms of position and / or size.

10. A method for generating an electron current, the method having the following steps: - providing an electron emitter device (10) according to any one of the preceding claims, - determining, by means of an emitter pin verification unit (14), the degree of functionality of at least one field-effect emitter pin on the first ring (11) and / or the second ring (12), and - switching on the first emitter surface (11.F) or the second emitter surface (12.F) by means of a control unit (15) as a function of the degree of functionality of the at least one field-effect emitter pin, wherein an electron current is generated.

11. The method according to claim 10, wherein the first emitter surface (11.F) or the second emitter surface (12.F) is operated alternately.

12. An X-ray source (20), the X-ray source (20) having: - an evacuated X-ray tube housing (21), - an electron emitter device (10) according to any one of claims 1 to 9 arranged in the evacuated X-ray tube housing (21), and - an anode (22) arranged in the evacuated X-ray tube housing (21) for generating X-rays from the electrons incident from the electron emitter device (10).

13. A computer program product which can be directly loaded into the memory of a computing unit, the computer program product having program code means for performing the method according to claim 10 or 11 when the computer program product is run on the computing unit.

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