Electron emitter with a rotatable emission surface

Abstract

The invention relates to an electron emitter for a rotary piston X-ray tube, a cathode for a rotary piston X-ray tube, a rotary piston X-ray tube, a rotary piston X-ray source, a method for emitting electrons by means of an electron emitter, and an associated computer program. The electron emitter according to the invention for a rotary piston X-ray tube has a segmented emitter surface, wherein the segmented emitter surface has a plurality of emitter needles and is configured to activate a subset of the segments of the segmented emitter surface as an activated emission surface for the field-effect emission of electrons from the activated emission surface such that activated emission surfaces can be rotated pairwise about a pivot point by changing the subset.

Description

[0001] The invention relates to an electron emitter for a rotary X-ray tube, a cathode for a rotary X-ray tube, a rotary X-ray tube, a rotary X-ray source, a method for emitting electrons by means of an electron emitter and an associated computer program product.

[0002] A conventional rotary piston X-ray tube typically comprises a housing and a rotary piston X-ray tube, which is mounted within the housing so that it can rotate relative to the housing. For example, DE 19 741 750 A1 discloses such an X-ray tube with a forced-cooled rotating anode, with a rotary piston tube whose vacuum envelope rotates within the housing filled with a liquid coolant.

[0003] In a conventional rotary piston X-ray tube, the entire rotary piston X-ray tube typically rotates, particularly the evacuated rotary piston along with the anode. In some rotary piston X-ray tubes, a cathode with an electron emitter is also rotationally fixed to the rotary piston, so that the cathode, anode, and rotary piston have the same rotation frequency. Other rotary piston X-ray tubes have a cathode with an electron emitter that are stationary and thus do not rotate together with the anode and rotary piston, as described, for example, in DE 4 108 591 A1. In contrast, in a conventional rotating anode X-ray tube, only the rotating anode rotates relative to the evacuated tube housing.

[0004] Another difference between a conventional rotating anode X-ray tube and a conventional rotary piston X-ray tube concerns the placement of the electron emitter. In a conventional rotating anode X-ray tube, the electron emitter, which, unlike the anode, is stationary, is usually placed eccentrically outside the rotation axis directly above a circular focal path of the anode. The focal path is created in particular by the fact that the electrons arriving at a focal spot interact with the anode on a circular path due to the rotation of the anode. An electron emitter in such a rotating anode X-ray tube can, for example, have up to three different emitter elements, whose emitted electrons can be geometrically focused to different focal spot sizes. This focusing is achieved in particular by means of a deflection unit, which generates an electric or electromagnetic field for this purpose.

[0005] In a conventional rotary X-ray tube, the electron emitter is typically located centrally on the rotation axis above the anode. To keep the focal spot stationary relative to the housing, the emitted electrons are deflected away from the rotation axis toward an edge region of the anode, usually by an electromagnetic field. For this purpose, the deflection unit has, in particular, a first quadrupole magnet, which is designed to adjust the ratio of the length to width of the focal spot. If the deflection unit has a second quadrupole magnet, this can typically be used to adjust the size of the focal spot. Designing a rotary X-ray tube with at least one quadrupole magnet is comparatively complex and cost-intensive.

[0006] The invention is based on the object of specifying an electron emitter for a rotary piston X-ray tube, a cathode for a rotary piston X-ray tube, a rotary piston X-ray tube, a rotary piston X-ray source, a method for emitting electrons by means of an electron emitter and an associated computer program product, in which the electron emission by means of the electron emitter itself is more flexible in order to reduce the need for additional deflection of the electrons.

[0007] The problem is solved by the features of the independent claims. Advantageous embodiments are described in the subclaims.

[0008] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0009] The electron emitter according to the invention for a rotary piston X-ray tube has a segmented emitter surface, wherein the segmented emitter surface has a plurality of emitter needles and is designed to activate a subset of the segments of the segmented emitter surface as an activated emission surface for the field effect emission of electrons from the activated emission surface in such a way that activated emission surfaces can be rotated in pairs relative to one another about a pivot point by changing the subset.

[0010] The electron emitter is particularly advantageous because the activated emission surfaces are rotatable, making electron emission more flexible overall. Rotating the activated emission surfaces advantageously allows for the reduction and / or elimination of additional deflection processes using a deflection unit.

[0011] The electron emitter is particularly suitable for medical imaging. Alternatively or additionally, the electron emitter can be suitable for materials testing.

[0012] The segmented emitter surface is, in particular, a field-effect emitter surface. Field-effect emission occurs, in particular, by applying a gate voltage to a carrier of the emitter surface, on which the plurality of field-effect emitter needles are arranged. The applied gate voltage causes electrons to escape, particularly at the tip of the field-effect emitter needles. The field-effect emitter needles typically comprise carbon, silicon, and / or molybdenum.

[0013] In particular, in the case of a field-effect emitter surface, the emitter surface can have a multitude of segments. Activating only a portion, i.e., not all segments, of such an emitter element can be achieved, for example, by exciting only a portion of the emitter needles and thus only a portion of the segments to field-effect emission. Exciting the emitter needles to field-effect emission can be referred to as activating or switching on the respective segment with these emitter needles. The emitter surface can therefore be divided into segments that can be activated independently of one another. The field-effect emitter surface is, in particular, a so-called pixelated emitter surface. The segmentation of the field-effect emitter surface is, in particular, a Cartesian or rotationally symmetric segmentation.

[0014] The segmented emitter surface in particular has at least four segments arranged in a 2x2 matrix. Preferably, the emitter surface has at least nine or 100 segments. A number of segments greater than 256 or 1024 is also conceivable.

[0015] An external shape of the segmented emitter surface can be rectangular, in particular square, or round. In the latter case, the segmented emitter surface is, in particular, rotationally symmetrical. An external shape of the activated emitter surface can differ from the external shape of the segmented emitter surface. For example, it is conceivable that the external shape of the segmented emitter surface is square and the external shape of the activated emitter surface is round, or vice versa. Alternatively, it is conceivable that the external shape of the activated emitter surface is similar to or corresponds to the external shape of the segmented emitter surface.

[0016] A segment of the emitter surface is, in particular, designed such that electron emission can be switched on or off by the activated emission surface of this segment. In the latter case, this means that this segment does not have an activated emission surface, but rather a deactivated emission surface.

[0017] The activation or deactivation of the emission surface can be performed in a clocked manner and / or multiple times depending on an emitter switching signal. The emitter switching signal can, in particular, be provided by a control unit. The emitter switching signal can, in particular, comprise switching on or off a gate voltage with respect to the activated subset of the segments.

[0018] Configuring the segmented emitter surface to activate at least a subset of the segments means, in particular, that the segmented emitter surface is or can be at least partially or completely activated depending, for example, on the emitter switching signal. For example, the emitter switching signal can contain information about the segments to be activated or about the activated segments that form the subset and / or directly activate these segments based on an electrical and / or physical connection.

[0019] The activated emission area can comprise exclusively activated segments. Alternatively, it is conceivable that the activated emission area comprises at least one segment that is deactivated.

[0020] The fact that the activated emission surfaces can be rotated in pairs around a pivot point by changing the subset means, in particular, that during operation of the electron emitter, the activated emission surfaces can rotate and / or appear to rotate, since the emission surfaces are activated one after the other and can differ from each other in pairs. In this context, the term "rotation" particularly encompasses enclosing an angle greater than zero or being twisted or tilted.

[0021] In this context, rotation does not refer to a physical movement of the emitter surface as such in a rotational direction. The fact that activated emission surfaces are rotatable means, in particular, that those emission surfaces from which the electrons emerge are rotatable with respect to the segmented emitter surface. The fact that the activated emission surfaces are rotatable includes, in particular, activating at least one further segment and / or deactivating at least one other segment. Activation and deactivation can occur simultaneously.

[0022] According to the invention, it is therefore advantageously possible to rotate the electron emission from the segmented emitter surface over time. This means, in particular, that the segmented emitter surface can be operated in a type of propeller, screw, or pointer operation, in which the activated emitter surfaces can rotate in pairs relative to one another per unit of time. Being rotatable in pairs relative to one another about a pivot point by changing the subset means, in particular, that a first activated emitter surface can be rotated at a first point in time relative to a second activated emitter surface at a second point in time, wherein the first point in time differs from the second point in time and the first activated emitter surface differs from the wide emitter surface.An activated subset of the segments at the first activated emission area differs in particular from an activated subset of the segments at the second activated emission area.

[0023] According to the invention, the emission of electrons can be carried out using a method comprising the following steps: Receiving a rotational frequency signal, activating different subsets of the segments of the segmented emitter surface such that the activated emitting surfaces rotate about a pivot point depending on the received rotational frequency signal.

[0024] The rotational frequency signal is received, for example, by a control unit via an interface. The rotational frequency signal is transmitted, for example, to the interface. Alternatively, the signal can be received within a control unit by a sub-control unit, with another sub-control unit within the control unit transmitting the rotational frequency signal.

[0025] The rotational frequency signal describes and / or transmits, in particular, a value of a rotational frequency. The rotational frequency signal can, in particular, depend on an electron current and / or an acceleration voltage and / or a rotational frequency of a cathode. The rotational frequency signal can, in particular, correspond to the rotational frequency of the cathode.

[0026] The rotation of the activated emission surfaces can occur, in particular, as a function of the rotational frequency signal, which means, in particular, that an alternating frequency according to which the subset of segments is changed is at least influenced by the rotational frequency signal or corresponds to the rotational frequency signal. In other words, the activated emission surface advantageously changes at an alternating frequency that corresponds, in particular, to the negative magnitude of the rotational frequency signal. The switching of the activated emission surface occurs, in particular, counter to the rotational frequency.

[0027] One embodiment provides that the pivot point is a center point of the segmented emitter surface. This embodiment is particularly advantageous because it allows the proportion of usable emitter surface to be increased, especially if the respective activated emitter surfaces differ only in their angle of rotation relative to the pivot point. Advantageously, each activated emitter surface can have substantially the same shape and / or the same number of activated segments and / or the same size and / or the same electron current.

[0028] One embodiment provides that the activated emission surfaces overlap at most partially. This embodiment advantageously ensures that the same subset of segments is not reactivated in immediate succession. Typically, the activated emission surfaces overlap at the pivot point and / or around the pivot point. In this case, the activated emission surfaces particularly encompass the pivot point. In principle, it is alternatively conceivable for the activated emission surfaces not to overlap, particularly if the respective activated emission surface is arranged outside the pivot point. In other words, the respective activated emission surface does not encompass the pivot point in this case.

[0029] One embodiment provides that the activated emission surfaces form a circle when placed on top of one another. In this embodiment, a plurality of different points in time are typically considered, at which a plurality of different subsets of the segments are activated. This embodiment can typically be achieved independently of the external shape of the segmented emitter surface. The external shape of the segmented emitter surface can expressly be round or square, while the external shape of the emission surfaces placed on top of one another is round. The external shape of the emission surfaces placed on top of one another is in particular independent of the respective shape of the activated emission surfaces considered separately. Placed on top of one another means in particular added together and / or activated at least once during operation of the electron emitter.

[0030] A cathode according to the invention for a rotary piston X-ray tube has a cathode head rotatable about a rotation axis with a rotation frequency relative to a fixed bearing part and an electron emitter which is non-rotatably inserted into the cathode head, characterized by that the segmented emitter surface is configured to activate the subset of segments such that the emission surfaces activated according to a different subset of segments are rotatable counter to the rotational frequency.

[0031] The cathode head typically has a round outer shape and can be designed as a focus head. The outer shape of the cathode head can alternatively be oval or square.

[0032] The cathode head can, in particular, have a bearing means, wherein the cathode head can be mounted about the rotation axis by means of the bearing means. The cathode head can, in particular, be mounted with respect to the stationary bearing part. The stationary bearing part and, optionally, the bearing means can be part of a bearing unit. The bearing unit can, in particular, be a rotary bearing and / or part of the cathode or part of the rotary piston X-ray tube or part of the rotary piston X-ray source. The bearing means can, for example, be a rotor and / or rotating bearing part. The stationary bearing part can, in particular, be a stator. The rotary bearing can, in particular, be a ball bearing or a plain bearing, in particular a liquid metal bearing.

[0033] The fact that the cathode head is mountable applies analogously to the electron emitter. In other words, the bearing means can be part of the electron emitter, by means of which the electron emitter can be mounted so as to rotate about the rotation axis at the rotational frequency relative to the stationary bearing part. In particular, because the electron emitter is non-rotatably mounted in the cathode head, mounting the cathode head also means mounting the electron emitter, and vice versa.

[0034] The bearing unit enables, in particular, rotation of the cathode head or the electron emitter at the rotational frequency. The rotational frequency is, for example, at least 5 Hz, in particular 50 Hz, preferably 200 Hz.

[0035] The electron emitter is typically firmly connected to the cathode head. The rotationally fixed insertion particularly includes rotationally fixed fastening. The electron emitter can be inserted into the cathode head, in particular, by means of a fastening means. The fastening means can be a screw and / or a soldering point and / or a welding point.

[0036] Advantageously, the cathode can be operated in such a way that the emitting surfaces, activated according to the different subsets of the segments, rotate counter to the rotational frequency. This advantageously counteracts the rotation of the cathode relative to the stationary bearing part by changing the subset of the segments, thereby reducing the influence of the rotation.

[0037] A particularly advantageous embodiment is one in which the activated emission surfaces are rotatable counter to the rotational frequency at the magnitude of the rotational frequency, so that the activated emission surfaces are essentially stationary relative to the stationary bearing part. Advantageously, the rotation of the cathode relative to the stationary bearing part can be counteracted by changing the subset of segments in such a way that, upon rotation of the cathode, the electron emission appears essentially stationary. The active emission surface is rotatable, so to speak, counter to the rotation of the cathode head in such a way that the electron emission appears essentially stationary.The fact that the activated emission surfaces are essentially stationary relative to the stationary bearing part means, in particular, that, with respect to the coordinate system of the stationary bearing part, the extent and / or shape of the electron current from the origin in the respective activated emission surfaces is essentially the same. In this respect, "stationary" means "stationary."

[0038] In this context, "essentially" means that due to the dynamics of changing the activated emission surfaces and / or physical interactions during activation and / or deactivation of the segments and / or between the emitted electrons, marginal deviations in the extent and / or shape of the electron current can arise. Preferably, the cathode is configured such that these deviations are minimal or nonexistent.

[0039] One embodiment provides that the pivot point of the electron emitter lies on the rotation axis. This embodiment is particularly advantageous for use of the electron emitter in a rotary piston X-ray tube.

[0040] The rotary piston X-ray tube according to the invention has a cathode, an evacuated rotary piston that can be mounted around the rotation axis at the rotation frequency relative to a fixed bearing part and an anode, wherein the cathode and the anode are connected to the rotary piston in a rotationally fixed manner, wherein the cathode has a cathode head and an electron emitter which is inserted into the cathode head in a rotationally fixed manner, characterized in that the rotary piston consists of a glass in a section between the anode and the cathode.

[0041] The glass version of the rotary piston offers, among other advantages, advantages that arise directly from the external shape of the rotary piston and thus of the rotary piston X-ray tube. The rotary piston X-ray tube according to the invention is particularly suitable as a comparatively cost-effective design.

[0042] Another advantage of the rotary flask is that glass is insulating, allowing an optional deflection unit to be positioned closer to the glass flask. The insulating properties of glass are particularly advantageous because no additional material, such as conventional ceramic, is required for electrical insulation.

[0043] The rotary bulb according to the invention, in its glass version, can in particular be referred to as a glass bulb. The glass bulb advantageously enables a relatively compact design, which, unlike conventional rotary bulb X-ray tubes, does not require a waist. A minimum length of the rotary bulb is therefore determined, in particular, by the required insulation length between the anode and cathode. Deflection of the emitted electrons by means of a deflection unit can thus preferably occur directly from the cathode, whereas in a conventional rotary bulb X-ray tube, the deflection only occurs after the waist.

[0044] The anode cooling in a rotary piston X-ray tube is directly cooled, whereby heat can be dissipated from the anode directly into the cooling medium, e.g., oil, flowing around the rotary piston. This advantageously eliminates the need for intermediate heat storage in an intermediate heat accumulator, which is thermally coupled to the anode and is usually made of graphite. Thus, the maximum thermal load of the anode is preferably comparatively very large relative to the size of the anode and the heat capacity, which is somewhat related to the size.

[0045] The rotary piston X-ray tube, especially the rotary piston, is typically vacuum-capable. The rotary piston is advantageously hermetically sealed. The evacuated rotary piston, in particular, comprises a high vacuum.

[0046] The rotary piston can be mounted or supported around the rotational axis, in particular by means of a bearing. The rotary piston can rotate around the rotational axis, in particular at the rotational frequency. The stationary bearing part can, in particular, be part of a bearing unit. The stationary bearing part is, in particular, part of a rotary piston X-ray tube and not part of the rotary piston X-ray tube. In principle, it is conceivable that the entire bearing unit, and thus the stationary bearing part, are part of the rotary piston X-ray tube.

[0047] The cathode head can alternatively, in particular, comprise the bearing means, wherein the cathode head can be mounted about the rotation axis by means of the bearing means. The cathode head can, in particular, be mounted with respect to the stationary bearing part. The stationary bearing part and, optionally, the bearing means can be part of the bearing unit. The bearing unit can, in particular, be a rotary bearing and / or part of the cathode or part of the rotary piston X-ray tube or part of the rotary piston X-ray source. The bearing means can, for example, be a rotor and / or rotating bearing part. The stationary bearing part can, in particular, be a stator. The rotary bearing can, in particular, be a ball bearing or a plain bearing, in particular a liquid metal bearing.

[0048] The bearing unit enables, in particular, rotation of the cathode head or the electron emitter or the rotary piston at a rotational frequency. The rotational frequency is, for example, at least 5 Hz, in particular 50 Hz, preferably 200 Hz.

[0049] The cathode and anode are typically arranged on opposite sides within the rotary piston. A high vacuum is present between the cathode and anode. The rotationally fixed connection of the cathode and anode to the rotary piston is achieved, for example, by means of a fastening means. The fastening means can, in particular, be a soldering point and / or a welding point. The rotationally fixed connection of the cathode and anode to the rotary piston can, alternatively or additionally, be achieved by parts of the bearing unit, so that the cathode and anode are not directly coupled to the rotary piston. The anode and cathode, as well as the electron emitter and the rotary piston, rotate together around the rotation axis at the same rotational frequency.

[0050] The section between the anode and the cathode, which consists of glass, is in particular annular and / or rotationally symmetrical to the axis of rotation. The glass section extends in particular in the length direction of the rotary piston over at least half the distance between the cathode and the anode. The glass section can extend in the length direction of the rotary piston up to the height of the cathode or beyond. Alternatively or additionally, the glass section can extend in the length direction of the rotary piston up to the height in front of the focal path on the anode or behind the focal path on the anode. In the latter case, the glass section serves in particular as an X-ray exit window. The focal path comprises in particular those focal spots at which the emitted electrons strike the anode and, due to the rotation, form the annular focal path.

[0051] The cathode head typically has a round outer shape and can be designed as a focus head. The outer shape of the cathode head can alternatively be oval or square.

[0052] The fact that the cathode head is mountable applies analogously to the electron emitter. In other words, the bearing means can be part of the electron emitter, by means of which the electron emitter can be mounted so as to rotate about the rotation axis at the rotational frequency relative to the stationary bearing part. In particular, because the electron emitter is non-rotatably mounted in the cathode head, mounting the cathode head also means mounting the electron emitter, and vice versa.

[0053] The electron emitter is particularly suitable for medical imaging. Alternatively or additionally, the electron emitter can be suitable for materials testing.

[0054] The electron emitter is typically firmly connected to the cathode head and thus to the rotary piston. The rotationally fixed insertion particularly includes rotationally fixed fastening. The electron emitter can be inserted into the cathode head, in particular, by means of a fastening means. The fastening means can be a screw and / or a soldering point and / or a welding point.

[0055] One embodiment provides that the rotary piston is cylindrical and a first end face of the cylindrical rotary piston is designed to receive a cathode-side bearing part and a second end face of the cylindrical rotary piston is designed to receive an anode-side bearing part, wherein the cathode is attached to the cathode-side bearing part and the anode is attached to the anode-side bearing part, and wherein the cathode-side bearing part and the anode-side bearing part are designed to rotate the rotary piston relative to the stationary bearing part about the axis of rotation. The cylindrical shape advantageously enables a compact rotary piston X-ray tube. The first end face and the second end face close off the cylindrical rotary piston on the opposite sides along the axis of rotation. The center axis of the cylinder corresponds in particular to the axis of rotation.The cathode-side bearing part can be connected to the rotary piston in a vacuum-tight manner, particularly at the first end face. The anode-side bearing part can be connected to the rotary piston in a vacuum-tight manner, particularly at the second end face. The cathode-side bearing part and / or the anode-side bearing part are typically part of the bearing unit, particularly of the rotating bearing part and / or the rotor. The cathode-side bearing part and / or the anode-side bearing part can cooperate, in particular, with the stationary bearing part to rotate the rotary piston.

[0056] One embodiment provides for the rotary piston to be cylindrical, and for the entire outer surface of the rotary piston to be made of glass. In this case, the rotary piston can consist essentially of the outer surface and / or exclusively of glass. This embodiment is particularly advantageous in conjunction with the previous embodiment.

[0057] One embodiment provides for the rotary piston X-ray tube to be a bipolar high-voltage tube, with a negative high-voltage potential applied to the cathode and a positive high-voltage potential applied to the anode. The difference between the positive high-voltage potential and the negative high-voltage potential specifies, in particular, an acceleration voltage at which the electrons can be accelerated from the cathode toward the anode. Alternatively, it is conceivable for the cathode or the anode to be at ground potential, and only one of the two electrodes to be at high-voltage potential.

[0058] One embodiment provides for a diameter of the rotary piston perpendicular to the rotational axis to be less than 100 mm, preferably 85 mm or 65 mm. In this embodiment, the center axis of the rotary piston corresponds in particular to the rotational axis. The rotary piston is designed to be rotationally symmetrical, in particular, to the rotational axis. This design is advantageous due to its compactness.

[0059] One embodiment provides for the length of the rotary piston along the rotational axis to be less than 200 mm. In this embodiment, the center axis of the rotary piston corresponds in particular to the rotational axis. The rotary piston is designed to be rotationally symmetrical, in particular, to the rotational axis. This advantageously allows for a smaller design of the rotary piston X-ray tube.

[0060] One embodiment provides for the rotary piston to be rotatable about the rotation axis by means of a ball bearing. In this case, the bearing unit is the rotary bearing, which is designed as a ball bearing. The bearing unit can be mounted in oil or in a vacuum. The bearing means can, in particular, be the balls of the ball bearing.

[0061] The rotary piston X-ray tube according to the invention has a housing, a rotary X-ray tube and a deflection unit, wherein the rotary piston X-ray tube is mounted within the housing so as to be rotatable about a rotation axis at a rotation frequency relative to the housing, wherein the rotary piston X-ray tube has a cathode, a rotary piston and an anode, wherein the anode is connected to the rotary piston in a rotationally fixed manner within the rotary piston, wherein the cathode has a cathode head and an electron emitter inserted into the cathode head for emitting electrons and is arranged within the rotary piston on the rotation axis, characterized in that the deflection unit is set up to generate an inhomogeneous field between the cathode and the anode within the rotary piston, wherein the inhomogeneous field influences the emitted electrons on their various paths in the direction of the anode and is designed such that path length differences of the emitted electrons along the various paths within the inhomogeneous field are taken into account.

[0062] The rotary piston X-ray tube is particularly advantageous because, by using the deflection unit to generate the inhomogeneous field, the design of the rotary piston X-ray tube is significantly less complex and thus more cost-effective. The rotary piston X-ray tube preferably does not include a separate dipole / quadrupole magnet or another additional high-pole magnet. According to the invention, an inhomogeneous field is generated to deflect the electrons and simultaneously focus them appropriately, without using a dipole / quadrupole magnet or another additional high-pole magnet. Because the inhomogeneous field takes into account the path length differences of the emitted electrons, the need for complex deflection is preferably eliminated. Advantageously, the deflection unit enables uniform coverage in the electrical focal spot, which is preferably accompanied by a homogeneous temperature distribution.

[0063] The housing typically completely encloses the rotary X-ray tube and the deflection unit and / or is closed. The housing can have a cooling medium for cooling the rotary X-ray tube and / or the deflection unit. The cooling medium can be liquid and / or gaseous. The cooling medium is, in particular, air and / or oil. The housing can have a cooling device by which the cooling medium is tempered and / or exchanged and / or circulated. The cooling device can have a heat exchanger and / or a cooling medium supply and a cooling medium discharge. On an outer side of the housing, a surface of the housing can be enlarged, for example by cooling fins.

[0064] The deflection unit generates the inhomogeneous field in a manner that traditionally requires a quadrupole magnet. According to the invention, the deflection unit is simplified compared to a conventional rotary piston X-ray tube with a quadrupole magnet, allowing the deflection unit to be optimally adjusted for comparatively fewer operating points. However, the deflection unit according to the invention is technically less complex, does not require complex control, and is therefore more cost-effective.

[0065] The deflection unit preferably generates the inhomogeneous field such that the electrons can be spread out and / or deflected in the radial direction, particularly taking path length differences into account. Spreading out in the radial direction advantageously increases the length of the electrical focal spot. Deflection in the radial direction, in particular, enables the electrons to reach the predetermined focal trajectory. A further advantage of radial deflection is that the width of the focal spot can be reduced, particularly when the activated emission surface of the electron emitter is wider than the desired optical width.

[0066] The deflection unit generates, in particular, a field whose field strength depends on the location. The deflection unit generates such an inhomogeneous field, in particular, in a volume section of the rotary piston that lies between the electron emitter and the anode. The volume section lies, in particular, between the activated emission surface and a focal path on the anode. It is conceivable that the volume section does not lie on a direct line of sight between the activated emission surface and the focal path, in particular due to the forces acting on the electrons that result from the generated inhomogeneous field. The deflection unit is, in particular, arranged and aligned in such a way that forces that result from the generated inhomogeneous field act on a large proportion of the emitted electrons. The deflection and / or fanning out of the electrons in the radial direction occurs largely, in particular, by means of location-dependent forces.

[0067] The fact that the deflection unit generates an inhomogeneous field can comprise the fact that a homogeneous field is generated in another volume section by the deflection unit. In principle, it is conceivable that in the volume section with the inhomogeneous field, the field strength does not depend on the location to a small extent. This part advantageously lies outside the trajectory of the electrons and / or acts on less than 50%, preferably less than 20%, of the emitted electrons. The deflection unit is in particular aligned with the trajectories of the electrons in such a way that a large proportion, advantageously at least 80%, of the electrons are influenced by the inhomogeneous field. The deflection unit is in particular aligned with the trajectories of the electrons in such a way that a large proportion, advantageously at least 80%, of the electrons are influenced by the inhomogeneous field.

[0068] The deflection unit generates, in particular, an inhomogeneous field that is static for an emission period. The inhomogeneous field is, in particular, constant within the emission period. The emission period comprises, in particular, at least one pulse duration of an X-ray pulse.

[0069] The influence of the emitted electrons on their various trajectories means, in particular, that the inhomogeneous field exerts forces on the emitted electrons, which can lead to the deflection of at least one electron. Since the electron emitter is typically not a point-like electron source, but rather emits electrons from an activated emission surface within a specific, non-point-like area with various starting positions, the emitted electrons regularly exhibit a spatial distribution perpendicular to the rotation axis, which results in the emitted electrons propagating on different trajectories. The differences in path length are based, in particular, on the different starting positions of the respective electrons at the electron emitter or the spatial distribution.Propagation toward the anode is achieved in particular by the acceleration unit, which, in particular, provides the high voltage between the cathode and the anode. Deflecting multiple electrons in this context can, in particular, mean shifting them while maintaining their relative distances from one another and / or focusing and / or defocusing. During focusing or defocusing, the deflection of multiple electrons changes at least one distance between the electrons, in particular reducing it during focusing and increasing it during defocusing.

[0070] Due to the fanning out and / or deflection in the radial direction, the emitted electrons typically propagate along a curved trajectory. The various paths of the emitted electrons are usually curved according to the curved trajectory. The curvature of the trajectory means that the electrons can travel different path lengths along the respective paths until they interact with the anode at the focal spot. The path length differences resulting from the curvature of the trajectory along the various electron paths are advantageously taken into account by designing the location-dependent forces of the inhomogeneous field. The inhomogeneous field can, in particular, be designed such that the electrons are exposed to different location-dependent forces depending on their paths.

[0071] It is conceivable that the inhomogeneous field is generated by the deflection unit as a function of the high voltage between the cathode and the anode. The inhomogeneous field can, in particular, be generated such that a spatial distribution of the electrons on the cathode side differs from a spatial distribution of the electrons on the anode side. "Cathode side" or "anode side" refers, in particular, to the spatial distribution after electron emission at the cathode or before the electrons strike the anode, respectively. The difference in the spatial distribution between the cathode and the anode can be a different extent, in particular perpendicular to the rotation axis, preferably a different width and / or different length.

[0072] One embodiment provides that the deflection unit surrounds the rotary piston in a plane perpendicular to the rotation axis by less than 360°, in particular less than 180°. In this case, the deflection unit does not completely surround the rotary piston in the circumferential direction, in particular not largely. This embodiment therefore offers the advantage of requiring less space for the deflection unit.

[0073] One embodiment provides that the inhomogeneous field is a magnetic field and that the deflection unit in particular has a coil with a magnetic core. In principle, it is conceivable for the deflection unit to have a coil without a magnetic core. Alternatively, the deflection unit can in particular comprise exclusively a permanent magnet. The deflection unit generates in particular an inhomogeneous magnetic field by means of the coil with the magnetic core. In particular, current flows through the coil and / or has multiple windings. The multiple windings can be distributed over a single winding package or multiple winding packages. The magnetic field generated by the coil with the magnetic core is static, in particular during the emission period. This embodiment is particularly advantageous because the inhomogeneous magnetic field is particularly suitable for taking into account the path length differences of the electrons.The magnetic core typically comprises a soft magnetic material and / or ferrite or is a permanent magnet. When the coil is combined with the magnetic core, the inhomogeneous field is generated jointly, in particular by the coil and the magnetic core. If the magnetic core is a permanent magnet in this case, the coil current of the coil can advantageously be reduced, since the permanent magnet can compensate for the lower magnetic field of the coil. The magnetic core advantageously reduces the coil current required to achieve the magnetic field. Alternatively or additionally, the magnetic core can influence the field gradient of the inhomogeneous field. This can, in particular, influence the deflection in length and / or width. Ideally, higher moments of the magnetic field can be minimized using the magnetic core. From a purely physical perspective, a magnetic field typically has no effect in the direction of the (instantaneous) velocity of the electrons.Since the electrons essentially fly along the rotation axis, the magnetic field is particularly inhomogeneous in a plane perpendicular to the rotation axis.

[0074] It is conceivable for the coil to comprise multiple winding packs, wherein the multiple winding packs are attached to mutually angled sections of the magnetic core. In other words, in this embodiment, a center axis of a first winding pack is at an angle other than 180° to a center axis of a second winding pack, and the two are thus not on the same line. The number of winding packs can be two or three, in particular. The winding packs and the sections of the magnetic core can be arranged and configured symmetrically to one another.

[0075] The magnetic core can, in particular, have a curved shape. The magnetic core is, in particular, not rod-shaped. The curved shape can, in particular, be a C-shape. The ends of the magnetic core can form an angle other than zero. The angle can, in particular, be equal to or less than 180°. The angle can, in particular, be between 90° and 180°.

[0076] Alternatively or additionally, at least one end of the magnetic core or both ends of the magnetic core can be chamfered. In this case, the chamfer refers to a direction of curvature of the magnetic core. In particular, the magnetic core is not chamfered if the end surface of the magnetic core forming the end is perpendicular to the direction of curvature of the magnetic core. A chamfer is therefore present in particular if the end surface of the magnetic core forming the end is at an angle other than 90° to the direction of curvature.

[0077] The curved shape and / or the beveled ends mean, in particular, that the magnetic core is advantageously designed in such a way that the proportion of parallel magnetic field lines outside the magnetic core is reduced. This advantageously generates the inhomogeneous field.

[0078] One embodiment provides that the magnetic core is aligned such that the ends of the magnetic core lie in the same plane perpendicular to the rotation axis and are aligned equidistantly from the rotation axis. The ends of the magnetic core are, in particular, at the same height relative to the rotation axis. The equidistant alignment enables, in particular, a symmetrical alignment of the magnetic core around the rotation axis.

[0079] One embodiment provides that the magnetic core is oriented such that a plane perpendicular to the rotation axis, in which the ends of the magnetic core lie, intersects the rotation axis between the cathode and the anode. This embodiment is particularly advantageous because the deflection unit is arranged comparatively close to the electrons.

[0080] One embodiment provides that the magnetic core is oriented such that a center axis of the coil windings lies in the plane perpendicular to the rotation axis, in which the ends of the magnetic core lie. In this case, in particular, the ends of the magnetic core and the center axis of the windings are preferably at the same height relative to the rotation axis.

[0081] The computer program product can be a computer program or comprise a computer program. The computer program product, in particular, has the program code means that map the method steps according to the invention. This allows the method according to the invention to be defined and executed repeatedly, and control over the dissemination of the method according to the invention can be exercised. The computer program product is preferably configured such that the computing unit can execute the method steps according to the invention using the computer program product. The program code means can, in particular, be loaded into a memory of the computing unit and typically executed by a processor of the computing unit with access to the memory.If the computer program product, in particular the program code means, is executed in the computing unit, typically all inventive embodiments of the described method can be carried out. The computer program product is, for example, stored on a physical, computer-readable medium and / or digitally stored as a data packet in a computer network. The computer program product can represent the physical, computer-readable medium and / or the data packet in the computer network. Thus, the invention can also be based on the physical, computer-readable medium and / or the data packet in the computer network. The physical, computer-readable medium is usually directly connectable to the computing unit, for example by inserting the physical, computer-readable medium into a DVD drive or plugging it into a USB port, whereby the computing unit can access the physical, computer-readable medium, in particular for reading purposes.The data packet can preferably be retrieved from the computer network. The computer network can have the 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 digitally stored on a cloud server at a storage location of the computer network and transferred to the computing unit via the WAN over the Internet and / or via the WLAN or LAN, in particular by calling up a download link that points to the storage location of the computer program product.

[0082] Features, advantages, or alternative embodiments mentioned in the description of the device are also applicable to the method, and vice versa. In other words, claims to the method can be developed using features of the device, and vice versa. In particular, the device according to the invention can be used in the method.

[0083] The invention is described and explained in more detail below with reference to the exemplary embodiments illustrated in the figures. In the following description of the figures, essentially identical structures and units are generally designated by the same reference numerals as when the respective structure or unit first appeared.

[0084] They show: Fig. 1 an electron emitter according to the invention for a rotary piston X-ray tube, Fig. 2 the electron emitter in an alternative embodiment, Fig. 3 a cathode for a rotary piston X-ray tube, Fig. 4 the cathode in another view, Fig. 5 a method for emitting electrons using an electron emitter according to the invention, Fig. 6 a rotary piston X-ray tube according to the invention, Fig. 7 a variant of the rotary piston X-ray tube according to the invention, Fig. 8 a rotary piston X-ray tube according to the invention, Fig. 9 a variant of the deflection unit, Fig. 10 another variant of the deflection unit, Fig. 11 another variant of the deflection unit, Fig. 12 an inhomogeneous field

[0085] Fig. 1 shows an electron emitter 10 for a rotary piston X-ray tube 30 in a plan view.

[0086] The electron emitter 10 has a segmented emitter surface 11. The segmented emitter surface 11 has a plurality of emitter needles in multiple segments. Each segment typically includes at least one emitter needle.

[0087] The segmentation of the emitter surface 11 is in Fig. 1 not shown for reasons of clarity. The segmentation of the emitter surface 11 can be approximately derived from the illustrated activated emission surfaces 11.A, which are delimited along the boundaries of the segments. The representation in Fig. 1 is schematic in this regard, since a segment is usually not infinitesimally small, i.e., comprising only a point-shaped emitter needle. This means that the rod-shaped emission surfaces 11.A in practice have, for example, jagged or grooved edges. As previously explained, the number of segments can be four in an extreme case, based on the Fig. 1 In the embodiment shown, the number is, for example, 100 or more.

[0088] The segmented emitter surface 11 is configured to activate a subset of the segments of the segmented emitter surface 11 as an activated emission surface 11.A for the field-effect emission of electrons from the activated emission surface 11.A such that activated emission surfaces 11.A can be rotated in pairs relative to one another about a pivot point D by changing the subset. The direction of rotation of the activated emission surfaces 11.A is indicated by the arrow.

[0089] Furthermore, in Fig. 1 It is shown that the pivot point D is a center point of the segmented emitter surface. The activated emission surfaces 11.A overlap to a maximum extent and form a circle when placed on top of each other. Each activated emission surface 11.A in Fig. 1 has substantially the same rod-like shape, preferably the same number of activated segments, the same size and advantageously the same electron current.

[0090] Fig. 2 shows the electron emitter 10 in an alternative embodiment. Instead of the round outer shape as in Fig. 1 As shown, the segmented emitter surface 11 has a square outer shape. In this case, the segmented emitter surface 11 has segments, particularly in a region toward the corners, which typically do not emit electrons.

[0091] Fig. 3 shows a cathode 20 for a rotary piston X-ray tube 30 in a plan view.

[0092] The cathode 20 for a rotary piston X-ray tube 30 has a cathode head 21 and an electron emitter 10 which is inserted into the cathode head 21 in a rotationally fixed manner.

[0093] In this exemplary embodiment, the cathode head 21 and the electron emitter 10 have a round outer shape. It would be conceivable for the cathode head 21, in particular, to have a non-round, but rather oval outer shape. The cathode head 21 can be mounted so as to rotate about a rotation axis A at a rotation frequency relative to a stationary bearing part. The pivot point D of the electron emitter 10 lies on the rotation axis A.

[0094] The segmented emitter surface 11 is configured to activate the subset of segments such that the emission surfaces 11.A activated according to a different subset of segments are rotatable counter to the rotational frequency.

[0095] Fig. 4 shows the cathode 20 of the Fig. 3 in another view.

[0096] The cathode 20 is relative to a fixed bearing part, which is not in Fig. 4 shown, and rotates at a rotational frequency. The direction of rotation of the cathode head 21 together with the electron emitter 10 is indicated by the dashed arrow. The activated emission surfaces 11.A are rotatable counter to the rotational frequency at the magnitude of the rotational frequency, so that the activated emission surfaces 11.A are essentially stationary relative to the stationary bearing part.

[0097] According to this embodiment in Fig. 4 The activated emission surfaces 11.A appear superimposed and stationary. In other words, the rotation of the cathode head 21 together with the inserted electron emitter 21 and the rotation of the activated emission surfaces 11.A cancel each other out.

[0098] Fig. 5 shows a flowchart of a method for emitting electrons by means of an electron emitter 10 according to the invention with the steps: Method step S100 characterizes receiving a rotational frequency signal.

[0099] Method step S101 characterizes an activation of different subsets of the segments of the segmented emitter surface 11 such that the activated emission surfaces 11.A rotate about a pivot point D depending on the received rotation frequency signal.

[0100] Fig. 6 shows a rotary piston X-ray tube 30 in a longitudinal section along the rotation axis A.

[0101] The rotary piston X-ray tube 30 has a cathode 20, a rotating element 22, which is arranged around a rotation axis A at a rotation frequency relative to a non-rotating element 23. Fig. 6 The rotary piston 31, which can be mounted on the stationary bearing part shown, and an anode 32 are connected to the rotary piston 31 in a rotationally fixed manner. The cathode 20 has a cathode head 21 and an electron emitter 10, which is inserted into the cathode head 21 in a rotationally fixed manner. The rotary piston 31 consists of a glass in a section 33 between the anode 32 and the cathode 20.

[0102] Furthermore, Fig. 6 shown that the rotary piston 31 is cylindrical. A first end face of the cylindrical rotary piston 31 is designed to receive a cathode-side bearing part 34. The cathode 20 is fastened to the cathode-side bearing part 34. A second end face of the cylindrical rotary piston 31 is designed to receive an anode-side bearing part 35. The anode 32 is fastened to the anode-side bearing part 35. The cathode-side bearing part 34 and the anode-side bearing part 35 are designed to rotate the rotary piston 31 relative to the Fig. 1 shown stationary bearing part about the rotation axis A in the direction of rotation R or against the direction of rotation R. The cathode-side bearing part 34 and the anode-side bearing part 35 each have a shaft aligned with the rotation axis A. The shaft rotates, for example, in the direction of rotation R or against the direction of rotation R and the rest of the rotary piston X-ray tube 30 rotates with the shaft. The rotary piston 31 could be rotatable about the rotation axis A by means of a ball bearing, not shown.

[0103] In this design, the entire outer surface of the rotary piston 31 is made of glass. The rotary piston X-ray tube 30 is a bipolar high-voltage tube, with a negative high-voltage potential applied to the cathode 20 and a positive high-voltage potential applied to the anode 32.

[0104] In this exemplary embodiment, the diameter of the rotary piston 31 perpendicular to the rotation axis A is less than 100 mm, amounting to 85 mm. The length of the rotary piston 31 along the rotation axis A is less than 200 mm, amounting to 156 mm. Such a length is suitable for the glass piston 30 to insulate an acceleration voltage of up to 125 kV between the cathode 20 and the anode 32. For example, the negative high-voltage potential can be -62.5 kV and the positive high-voltage potential 62.5 kV. The distance between the cathode 20 and the anode 32 is, for example, 90 mm, with the anode 32 having an anode angle of, in particular, 14°.

[0105] Fig. 7 shows a variant of the rotary piston X-ray tube 30 in a longitudinal section along the rotation axis A. In this variant, the anode angle of the anode 32 is 16° and the diameter of the rotary piston 31 perpendicular to the rotation axis A is 65 mm.

[0106] Fig. 8 shows a longitudinal section through a rotary piston X-ray tube 40.

[0107] The rotary piston X-ray tube 40 comprises a housing 41, a rotary piston X-ray tube 30, and a deflection unit 42. The rotary piston X-ray tube 30 is mounted within the housing 41 for rotation about a rotation axis A at a rotation frequency relative to the housing 41. The rotary piston X-ray tube 30 comprises a cathode 20, a rotary piston 31, and an anode 32. The anode 32 is rotationally fixedly connected to the rotary piston 31. The cathode 20 comprises a cathode head 21 and an electron emitter 10 inserted into the cathode head 21 for emitting electrons, and is arranged within the rotary piston 31 on the rotation axis A.

[0108] The deflection unit 42 is configured to generate an inhomogeneous field between the cathode 20 and the anode 32 within the rotary piston 31. The inhomogeneous field influences the emitted electrons on their various paths toward the anode 32 and is configured such that path length differences of the emitted electrons along the various paths within the inhomogeneous field are taken into account. If the deflection unit 42 comprises a coil with a magnetic core, the deflection unit 42 is Fig. 8 For example, it is designed such that a plane perpendicular to the rotation axis A, in which the ends of the magnetic core lie, intersects the rotation axis A between the cathode 20 and the anode 31.

[0109] The rotary piston X-ray tube 40 further includes a stationary bearing part 43, which is rotationally fixedly connected to the housing 41. The stationary bearing part 43 cooperates in particular with the cathode-side bearing part 34 and the anode-side bearing part 35 to enable the rotation of the rotary piston X-ray tube 30 relative to the housing 41.

[0110] Fig. 9 shows three views of a variant of the deflection unit 42. The deflection unit 42 surrounds the rotary piston 31 in a plane perpendicular to the rotation axis A by less than 360°, in particular less than 180°.

[0111] The deflection unit 42 has a coil with a magnetic core. The magnetic core is oriented such that the ends of the magnetic core lie in the same plane perpendicular to the rotation axis A and are equidistant from the rotation axis A. The magnetic core is further oriented such that a center axis of the coil windings lies in the plane perpendicular to the rotation axis A, in which the ends of the magnetic core lie. The magnetic core is further configured such that the proportion of parallel magnetic field lines outside the magnetic core is reduced.

[0112] The top row shows the two views of the deflection unit 42 together with the rotary piston 31, on the left in a frontal view and on the right in a side view. The bottom row shows a perspective view of the deflection unit 42.

[0113] Fig. 10 shows a further variant of the deflection unit 42 in a detailed view. The inhomogeneous field is a magnetic field. The deflection unit 42 has a coil with a magnetic core. The magnetic core is curved, and at least one end—in this embodiment, both ends—of the magnetic core are beveled.

[0114] Fig. 11 shows three views (front, side, perspective from left to right) of another variant of the deflection unit 42. The deflection unit 42 has a coil with a magnetic core. The coil comprises several winding packages. The several winding packages are attached to mutually angled sections of the magnetic core.

[0115] Fig. 12 shows an inhomogeneous magnetic field. The deflection unit 42 has a coil with a magnetic core. The magnetic field components are shown schematically, resulting in the course of the field lines shown along the solid lines. An inhomogeneous magnetic field configured in this way is particularly advantageous because Bx has a gradient in the negative y-direction, and By has the sign of the x-axis and a gradient in the y-direction.

[0116] Furthermore, in Fig. 12 The position of the rotation axis A is shown purely as an example at the height of the x-axis. A shift of the rotation axis A upwards or downwards along the y-axis is easily conceivable.

[0117] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is nevertheless not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

1. Electron emitter (10) for a rotary piston X-ray tube (30), comprising - a segmented emitter surface (11), wherein the segmented emitter surface (11) has a plurality of emitter needles and is configured to activate a subset of the segments of the segmented emitter surface (11) as an activated emission surface (11.A) for the field effect emission of electrons from the activated emission surface (11.A) in such a way that activated emission surfaces (11.A) can be rotated in pairs relative to one another about a pivot point (D) by changing the subset.

2. Electron emitter (10) according to claim 1, wherein the pivot point (D) is a center point of the segmented emitter surface (11).

3. Electron emitter (10) according to one of the preceding claims, wherein the activated emission surfaces (11.A) overlap at most partially.

4. Electron emitter (10) according to one of the preceding claims, wherein the activated emission surfaces (11.A) superimposed form a circle.

5. Electron emitter (10) according to one of the preceding claims, wherein each activated emission surface (11.A) has substantially the same shape and / or the same number of activated segments and / or the same size and / or the same amount of electron current.

6. Cathode (20) for a rotary piston X-ray tube (30), comprising - a cathode head (21) rotatably mounted about a rotation axis (A) at a rotational frequency relative to a fixed bearing part and - an electron emitter (10) according to one of the preceding claims, which is inserted into the cathode head (21) in a rotationally fixed manner, characterized by thatthe segmented emitter surface (11.A) is configured to activate the subset of segments such that the emission surfaces (11.A) activated according to a different subset of segments are rotatable counter to the rotational frequency.

7. Cathode (20) according to claim 6, wherein the activated emission surfaces are rotatable against the rotational frequency with the magnitude of the rotational frequency, so that the activated emission surfaces are substantially stationary relative to the stationary bearing part.

8. Cathode (20) according to one of claims 6 or 7, wherein the pivot point (D) of the electron emitter (1) lies on the rotation axis (A).

9. Rotary piston X-ray tube, comprising - a cathode according to one of claims 6 to 8, - an evacuated rotary piston which can be mounted about the axis of rotation at the rotational frequency relative to the fixed bearing part and - an anode, wherein the cathode and the anode are connected to the rotary piston within the rotary piston in a rotationally fixed manner.

10. A rotary piston X-ray tube according to claim 9, wherein the rotary piston is made of glass in a section between the cathode and the anode.

11. A rotary piston X-ray tube comprising - a housing, - a stationary bearing part and - a rotary piston X-ray tube according to one of claims 9 or 10, wherein the stationary bearing part is connected to the housing in a rotationally fixed manner and the rotary piston X-ray tube is mounted within the housing by means of the stationary bearing part so as to be rotatable relative to the housing.

12. Rotary piston X-ray tube according to claim 11, wherein the rotary piston X-ray tube has a deflection unit, wherein the deflection unit is configured to generate an inhomogeneous field between the cathode and the anode within the rotary piston, wherein the inhomogeneous field influences the emitted electrons on their various paths towards the anode and is configured such that the inhomogeneous field is a magnetic field and wherein the deflection unit has a coil with a bent magnetic core such that path length differences of the emitted electrons along the various paths within the inhomogeneous field are taken into account.

13. Rotary piston X-ray tube according to claim 12, wherein the deflection unit surrounds the rotary piston in a plane perpendicular to the axis of rotation by less than 360°, in particular less than 180°.

14. A method for emitting electrons by means of an electron emitter according to one of claims 1 to 5, - receiving a rotational frequency signal, - activating different subsets of the segments of the segmented emitter surface such that the activated emission surfaces rotate about a pivot point depending on the received rotational frequency signal.

15. A computer program product which is directly loadable into a memory of a computing unit, comprising program code means for executing a method according to claim 14 when the computer program product is executed in the computing unit.

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