X-ray tube with improved cooling of the anode head

Abstract

An X-ray tube (1) comprising a source (4) for the release of electrons and an anode head (6) with a central axis (ZA), wherein a target (11) is formed on an end face (10) of the anode head (6), onto which the electrons in an excited region (9) impinge during operation, wherein the anode head (6) provides a flow path (16) for a cooling fluid, which leads from at least one inlet port (14a) via a radially outer section (20), further via a cooling gap (21), and further via a radially inner section (22) to at least one outlet port (15a), is characterized in that the excited region (9) of the target (11) is essentially annular, and that in a region (26) of the anode head (6) opposite the excited region (9) of the target (11) a local height (H1, H2) of the cooling gap (21) increases continuously from radially outside to radially inside. increases.The X-ray tube according to the invention can be operated with higher power and / or less wear.

Description

[0001] The invention relates to an X-ray tube, comprising a source for the release of electrons and an anode head with a central axis, wherein a target is formed on an end face of the anode head, onto which the electrons in an excited region impinge during operation, wherein the anode head provides a flow path for a cooling fluid, which leads from at least one inlet port via a radially outer section, further via a cooling gap, and further via a radially inner section to at least one outlet port.

[0002] Such an X-ray tube became known through EP 4 141 905 A1.

[0003] X-rays are used in a variety of ways to investigate the chemical and physical properties of samples and objects of all kinds. For example, X-ray fluorescence can be used to determine the atomic composition of samples both qualitatively and quantitatively. X-rays are also able to penetrate and pass through the interior of a body without damaging it. This allows for the determination of internal compositions.

[0004] In many cases, it is desirable to use high-intensity X-ray radiation to enable more accurate and / or faster X-ray measurements.

[0005] X-rays are typically generated using an X-ray tube. An electron source, such as a filament, is located in an evacuated section of the X-ray tube. This source is configured as the cathode. A target, configured as the anode, is also located in the evacuated section. The target can be made of materials such as copper, rhodium, chromium, molybdenum, or silver. Electrons from the source are accelerated by an electric field and strike the target. The impacting electrons are decelerated, producing bremsstrahlung. Furthermore, the impacting electrons knock other electrons out of the atoms of the target material; when the empty electron shells are refilled, characteristic X-rays are emitted. The electrons striking the target heat it considerably, so it usually requires active cooling.If the target gets too hot, it can melt, which would destroy the X-ray tube. In practice, therefore, cooling the target often limits the power of the X-ray tube.

[0006] From EP 4 141 905 A1, an X-ray tube is known in which a substantially cylindrical anode head forms a target at its end face within a cathode housing. Electrons released from a heated cathode in the cathode housing are accelerated onto the target. A coolant supply line is connected to a first channel in the anode head, which comprises an inclined section and then a section running along a central axis of the anode head. The first channel leads into a cooling gap below the target, which is perpendicular to the central axis of the anode head and has a uniform height. The cooling gap transitions into an annular channel located radially outside the anode head. A second coolant channel leads away from this annular channel, to which a return line is connected.A flow of coolant (water) centrally and axially through the first channel, across the cooling gap from radially inside to outside, and axially back into the second channel in the annular gap cools the target or the anode head as a whole. Alternatively, the water flow can also be reversed.

[0007] This setup allows an X-ray tube to be provided with sufficient X-ray power for many purposes.

[0008] Depending on the heating power of the electrons striking the target, the water in the cooling gap below the target can partially evaporate, forming boiling bubbles. It's important to note that while the boiling bubbles (i.e., the water vapor) can absorb a significant amount of heat during their formation through the phase transition of evaporation, the water vapor in the boiling bubbles can then absorb and dissipate considerably less heat than liquid water. If the boiling bubbles are not removed quickly enough, the cooling capacity in the anode head drops sharply, and the target can melt.

[0009] Furthermore, boiling bubbles that form can collapse shortly after their formation (so-called cavitation), leading to mechanical stress on the surrounding material. While cavitation does not impair cooling performance, it does increase wear on the anode head.

[0010] The power of the X-ray tube known from EP 4 141 905 A1 is selected in such a way as to avoid melting of the target, and also to keep wear due to cavitation within an acceptably low range.

[0011] From DE 10 2017 216 059 A1, an X-ray tube has become known in which the target is arranged on a massive, bump-shaped base body.

[0012] US 2021 / 0249214 A1 describes an X-ray tube cooled by a cooling fluid which, in a specific design, flows from a central feed chamber through a curved gap below the target into an annular, radially outer return chamber. The curved gap has a constant width.

[0013] From DE 10 2016 000 033 B4, an X-ray tube is known which has a target at a tapered end of a carrier body. The carrier body is coupled via a connecting body, a heat dissipation body and an area of ​​insulating material to a radially external cooling unit, which may be water-cooled.

[0014] German patent DE 10 2017 217 181 B3 describes a vertical anode for an X-ray tube, comprising an anode base and a nozzle projecting into the anode base. A cooling channel for supplying cooling fluid runs axially through the center of the nozzle, transitioning into a funnel-shaped outlet at its end. The anode base forms a conical heat exchange surface opposite the target and the nozzle outlet. A gap of uniform height exists between the heat exchange surface and the nozzle outlet. The cooling fluid can flow out at a radial outer surface of the nozzle.

[0015] US Patent 6,580,780 B1 discloses a cooling system for X-ray tubes with a stationary anode, wherein a coolant injection arrangement is located in a stationary anode. An aeration for the incoming coolant runs axially centrally in the injection arrangement, narrowing towards an aperture to accelerate the coolant. Downstream of the aperture are a surface enhancement structure with radially outward-facing flow channels and a flow deflection device. The flow deflection device is corrugated and located on the inside of the stationary anode opposite the target surface. The coolant flows back radially on the outside of the coolant injection arrangement.

[0016] From JP 2021 044 155 A, an X-ray tube is known in which an anode is formed with an inner tube and an outer tube. The outer tube is closed at one end by an end wall on which a target surface is formed. Coolant flows into the inner tube, strikes the back of the end wall, is deflected radially outwards, and flows back between the outer and inner tubes. The inner tube is thickened at its target-side end, with a channel of constant height for the coolant formed between the end of the inner tube and the back of the end wall. Aufgabe der Erfindung

[0017] The object of the present invention is to provide an X-ray tube that can be operated with higher power and / or less wear. Beschreibung der Erfindung

[0018] This problem is solved according to the invention by an X-ray tube of the type mentioned above, which is characterized in that that the excited area of ​​the target is essentially ring-shaped, and that in an area of ​​the anode head opposite the excited area of ​​the target, the local height of the cooling gap increases steadily from radially outside to radially inside.

[0019] The X-ray tube according to the invention enables improved cooling. Due to the improved cooling, the X-ray tube can be operated at a higher X-ray power, or, at the same X-ray power, with less wear and thus a longer service life.

[0020] In the X-ray tube according to the invention, the cooling fluid flows from radially outside to radially inside the cooling gap via the provided connections (inlet and outlet). During operation, boiling bubbles form in the cooling gap. Through their formation (more precisely, through the phase change of liquid water to water vapor, or correspondingly for other cooling fluids), the boiling bubbles achieve a noticeable cooling effect. The increasing height of the cooling gap in the direction of fluid flow improves the removal of boiling bubbles from the cooling gap. Even large quantities of boiling bubbles can then be reliably and rapidly flushed out with the cooling water. Accordingly, good heat dissipation can be ensured even at higher X-ray power (and thus a higher heat load on the target). This allows the X-ray tube according to the invention to be operated at a higher power than conventional X-ray tubes.

[0021] Because the cooling fluid flows from the outside in, the cross-sectional area of ​​the flow path can be kept relatively small along the flow direction, despite the increasing height of the cooling gap. In contrast, with an inside-to-outside flow direction, the cross-sectional area would inevitably increase significantly as the height of the flow path increases in the flow direction. Because the cross-sectional area can be kept relatively small along the flow direction, the coolant pressure can be maintained at a high level, especially since the coolant pressure in the cooling gap remains constant or even increases along the flow direction. This prevents the collapse of boiling bubbles (or cavitation) in or near the cooling gap. Consequently, low wear in the anode head is achieved.

[0022] The excited region of the target is essentially ring-shaped. In the corresponding, opposite region of the anode head (i.e., below or behind the excited region), the cooling gap can then be positioned with an increasing height in the flow direction, from which the boiling bubbles can be efficiently carried away. A center of the anode head's face remains free of direct electron impact, so it does not heat up as much, and no or only a few boiling bubbles are generated in adjacent parts of the flow path. Typically, a pin is located opposite the center of the face (see below).

[0023] The local height of the cooling gap can be measured in a direction perpendicular to the target-facing wall of the cooling gap (any micro-ripples in the target-facing wall are neglected). This direction usually corresponds essentially to the axial direction (direction of the central axis of the anode head).

[0024] The end face is typically oriented at least substantially perpendicular to the central axis of the anode head. The central axis and the annular excited region are typically concentric. Typically, the external shape of the anode head is rotationally symmetrical about the central axis, at least in the area of ​​the end face and a circumferential side wall. The anode head can, in particular, have a substantially circular cylindrical shape.

[0025] The area in which the local height of the cooling gap increases from radially outside to radially inside typically comprises at least 15% of the radius of the anode head, preferably at least 20%, and particularly preferably at least 25%. Bevorzugte Ausführungsformen der Erfindung

[0026] A preferred embodiment of the X-ray tube according to the invention features a local cross-sectional area of ​​the cooling gap in the region of the anode head opposite the excited area of ​​the target that decreases continuously from the radial outside to the radial inside, remains constant, or increases continuously by a maximum of 15%. A decreasing cross-sectional area in the cooling gap along the flow direction allows the pressure in the cooling fluid to be maintained or increased, particularly in the radially inner region of the cooling gap. The average flow velocity of the cooling fluid then remains constant or increases radially inward in the cooling gap. This counteracts cavitation and reduces macroscopic recirculation. Typically, the overall decrease in cross-sectional area is approximately 5–20%.Since the volume of the cooling fluid increases along the flow path in the direction of flow (i.e., radially inward within the cooling gap) due to boiling bubbles and thermal expansion, a constant cross-sectional area or even a slight increase in cross-sectional area can be acceptable without increasing cavitation. Reduced cavitation improves the lifespan of the X-ray tube. Lower recirculation improves cooling performance. The local cross-sectional area can be measured as a portion of a conical or cylindrical shell, with this shell oriented along a direction perpendicular to the target-facing wall of the cooling gap (any micro-ripples in the target-facing wall are neglected). This direction usually corresponds essentially to the axial direction.

[0027] An advantageous embodiment is one in which the local cross-sectional area of ​​the cooling gap in the region of the anode head opposite the excited area of ​​the target decreases continuously from radially outside to radially inside, in particular by a maximum of 20%. This decreasing cross-sectional area ensures that the pressure in the cooling fluid along the flow path in the cooling gap region always increases from outside to inside (even if no or only a few boiling bubbles have yet formed and / or thermal expansion effects are minimal), thus minimizing cavitation. If the decrease in cross-sectional area is 20% or less, and the flow velocity of the cooling fluid does not increase excessively, mechanical erosion of material from the anode head is prevented.

[0028] A preferred embodiment is one in which the flow path in the anode head is at least substantially rotationally symmetrical with respect to the central axis. This allows for particularly uniform cooling of the excited area of ​​the target. Note that the flow path is typically not completely rotationally symmetrical. In particular, a deviation may occur in the outer section of the flow path due to distribution structures in an otherwise rotationally symmetrical, circumferential radial gap, or at the transitions to the inlet or outlet. In the area of ​​rectifying elements, there is typically a rotational symmetry with respect to the central axis with a count (usually a high count, e.g., 8 or higher), and in the area of ​​swirl elements, for example, a rotation-translational symmetry (e.g.,A helical flow path (with the central axis as the screw axis) or, conversely, a rotational symmetry with a number of turns (usually a high number, e.g., 8 or higher) with respect to the central axis may be present. Such deviations are still considered consistent with an essentially rotationally symmetrical flow path.

[0029] An advantageous embodiment is one in which the radially outer section of the flow path extends at least substantially around the entire circumference of the anode head. This contributes to particularly uniform cooling of the excited area of ​​the target. Preferably, the flow path in the radially outer section extends completely around the entire circumference of the anode head.

[0030] A particularly preferred embodiment includes distribution structures in the radially outer section of the flow path, which distribute and homogenize the cooling fluid flow from the at least one inlet port to the cooling gap around the circumference of the anode head. This results in particularly uniform and efficient cooling of the excited area of ​​the target. The distribution structures can be formed, in particular, by a plurality of axially and azimuthally spaced fins or guide vanes.

[0031] An advantageous further development of this embodiment provides that the distribution structures in a target-adjacent section of the radially outer section around the circumference of the anode head comprise a set of rectifying elements for the cooling fluid, distributed across the circumference. These elements extend between an inlet-side annular gap and an outlet-side annular gap or the cooling gap, and allow for the establishment and separation of at least substantially parallel partial flows of the cooling fluid. The rectifying elements ensure that a fluid flow inflowing locally around the circumference is distributed circumferentially into axial partial flows, preventing it from continuing axially at its original location in the circumferential direction without deflection. In particular, any swirl introduced upstream in the fluid flow can be eliminated or at least minimized in the resulting fluid flow.The annular gap located upstream of the set of straightening elements ("inlet-side") and, if present, the annular gap following the set of straightening elements in the flow direction ("outlet-side") each form a smoothing zone. The cooling gap typically adjoins the outlet-side annular gap. The subflows, which are at least substantially parallel, typically have an angle between them of 20° or less, usually 10° or less (relative to the mean flow direction in the respective subflow).

[0032] Another advantageous embodiment of the above provides that the distribution structures, in a section of the radially outer part of the flow path farther from the target and distributed around the circumference of the anode head, comprise a set of straightening elements for the cooling fluid flow. These elements extend between an inlet-side annular gap and an outlet-side annular gap and allow for the establishment and separation of at least substantially parallel partial flows of the cooling fluid. The straightening elements ensure that a fluid flow entering locally at the circumference is distributed circumferentially into axial partial flows and cannot continue to flow axially at its original location in the circumferential direction without deflection. In particular, any swirl introduced upstream in the fluid flow can be eliminated or at least minimized in the resulting fluid flow.The inlet-side annular gap leading to the rectifying elements of the section furthest from the target typically contains at least one inlet connection; alternatively, a swirling cooling fluid flow from upstream swirl elements can also flow into the inlet-side annular gap. The at least substantially parallel partial flows typically have an intermediate angle of 20° or less, usually 10° or less (relative to a mean flow direction in the respective partial flow).

[0033] A further advantage is a sub-variant in which sets of rectification elements are provided both in a target-adjacent sub-section and in a target-distant (or more distant) sub-section of the radially outer section of the flow path, wherein it is provided that that the outlet-side annular gap to the rectifying elements of the target-distant section is simultaneously the inlet-side annular gap to the rectifying elements of the target-adjacent section, and that the set of rectifying elements of the target-adjacent section is offset from the set of rectifying elements of the target-distant section relative to the central axis of the anode head in the azimuthal direction. This introduces a minimum deflection into the coolant flow in the central annular gap, and achieves particularly good uniformity of the cooling performance in the azimuthal direction.

[0034] A preferred sub-variant is one in which the rectifying elements are aligned at least substantially in the axial direction, and correspondingly, the partial flows of the cooling fluid are also aligned at least substantially in the axial direction. This design is structurally simple and reliably minimizes swirl in the cooling fluid. Typically, the deviation from a perfectly axial alignment is a maximum of 10°, usually a maximum of 5°, or even 0°.

[0035] A preferred sub-variant provides that the rectifying elements are at least partially formed by parallel lamellae, in particular straight parallel lamellae, and / or trapezoidal or triangular lamellae, and / or teardrop-shaped or diamond-shaped lamellae, The lamellae are formed on a radially outward-facing wall side and / or a radially inward-facing wall side of the anode head, with the radially outward-facing wall side and the radially inward-facing wall side defining the radially outer section of the flow path. These designs have proven effective in practice and are relatively easy to manufacture.

[0036] A further advantage is a sub-variant in which the rectifying elements are at least partially formed by a multitude of parallel hollow structures arranged in the radially outer section of the flow path, particularly where the multitude of parallel hollow structures forms a honeycomb structure. The hollow structures are easy to construct. A honeycomb structure allows the hollow structures to be packed particularly densely, thus providing a particularly large cross-sectional area for the partial flows.

[0037] In an advantageous embodiment, the distribution structures in a section of the flow path furthest from the target comprise one or more swirl elements arranged between the at least one inlet port and an outlet-side annular gap. These elements introduce a swirl about the central axis into the cooling fluid flow. The swirl of the cooling fluid ensures a uniform distribution of the cooling fluid (and the cooling fluid flow) over the circumference of the radially outer part of the flow path. The swirl imparts a velocity component to the cooling fluid in the circumferential direction of the anode head, causing the cooling fluid to rotate around the anode axis. Typically, the section furthest from the target, in which the swirl elements are arranged, is also the section of the flow path furthest from the target.

[0038] A preferred embodiment features at least one helical element arranged helically around the central axis of the anode head, thereby creating at least one helical channel for the coolant flow. This design has proven effective in practice and is also suitable for use with high coolant flow rates to reliably introduce swirl into the coolant flow. A helical helical element preferably rotates at least 0.8 times, more preferably at least 1.0 times, and most preferably at least 2.0 times, around the central axis.

[0039] In a preferred embodiment, several helical elements are arranged helically around the central axis of the anode head, thereby creating multiple helical channels, offset azimuthally and / or axially from one another, for partial flows of the cooling fluid. These multiple helical channels allow the coolant flow to be divided along the circumference and each channel to be imparted with a helical motion, thus contributing to a uniform distribution of the cooling capacity.

[0040] A preferred embodiment features distribution structures in the radially outer section of the flow path, wherein a homogenization zone for the cooling fluid flow is provided between distribution structures of a target-remote subsection of the radially outer section and distribution structures of a target-closer subsection of the radially outer section, particularly wherein the homogenization zone is configured as an annular gap. Within a homogenization zone between two (adjacent) subsections, the flow velocity of the cooling fluid can be homogenized. In particular, the axial flow velocity (with respect to the flow direction of the cooling fluid) behind the homogenization zone can exhibit less dispersion around the circumference than in front of the homogenization zone.Furthermore, equalization zones can be provided upstream of distribution structures of a subsection furthest from the target and / or downstream of distribution structures of a subsection closest to the target in the radially outer section of the flow path.

[0041] In a preferred embodiment, the anode head is designed with a first flow element and a second flow element that are nested inside each other, and which form at least part of the flow path between them. This is structurally simple and has proven effective in practice.

[0042] A particularly preferred embodiment is one in which at least the radially inner section of the flow path, and optionally also the cooling gap, is partially delimited by a pin that projects from the end face of the anode head into the interior of the anode head. In other words, the pin projects from a target-facing wall of the flow path into the radially inner section of the flow path inside the anode head. The pin is typically located on the central axis. The pin prevents direct contact (in the radial flow direction) of the converging cooling fluid from different radial directions in the transition region between the cooling gap and the radially inner section of the flow path. The pin allows the cooling fluid to be deflected, particularly in the axial direction, and the flow of the cooling fluid can be approximately parallelized.Furthermore, the pressure profile and flow rate in the cooling fluid can be maintained or moderated using the nozzle.

[0043] The present invention also includes an X-ray tube arrangement, The device comprises an X-ray tube according to the invention, as described above, and a supply device for a cooling fluid, wherein the supply device provides fresh cooling fluid at a delivery outlet and the delivery outlet is connected to the at least one inlet port, and in particular wherein the supply device further receives heated cooling fluid at a return inlet and the outlet port is connected to the return inlet. The supply device provides and typically also delivers (e.g., pumps) the cooling fluid, and the cooling fluid flow in the anode head is adjusted from radially outside to radially inside. The X-ray tube achieves particularly good cooling.

[0044] Also within the scope of the present invention is the use of an X-ray tube or an X-ray tube arrangement according to the invention and described above, wherein during operation of the X-ray tube Electrons from the source strike a ring-shaped, excited region of the target, generating X-rays. Cooling fluid flows radially outward to radially inward in the cooling gap opposite the excited region. Cooling by the fluid in the cooling gap is highly efficient. Boiling bubbles can contribute to heat absorption and are effectively dissipated by the cooling gap, which increases in height in the flow direction. Simultaneously, cavitation is minimized.

[0045] In a preferred embodiment of the invention, the mean flow velocity of the cooling fluid in the cooling gap remains constant or increases from the radial outside to the radial inside relative to the excited area, in particular by a maximum of 25%. This increasing flow velocity ensures that the pressure in the cooling fluid does not decrease, and cavitation remains particularly low. Accordingly, wear on the anode head is also low.

[0046] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those described in more detail below can each be used individually or in any combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention. Detaillierte Beschreibung der Erfindung und Zeichnung

[0047] Fig. 1 shows a schematic longitudinal section through an exemplary embodiment of an X-ray tube according to the invention; Fig. 2a shows a schematic longitudinal section through an exemplary anode head according to a first design for the invention, with swirl elements in a lower, target-distant section and rectification elements in an upper, target-closer section of a radially outer section of the flow path; Fig. 2b shows a schematic cross-section through the anode head of Fig. 2a , at level BB of Fig. 2a Fig. 2c shows a schematic cross-section through the anode head of Fig. 2a , at the CC level of Fig. 2a Fig. 2d shows a schematic top view of the anode head of Fig. 2a Fig. 2e shows a schematic, semi-open perspective view of the anode head of Fig. 2a , with internal flow element; Fig. 2f shows a schematic, semi-open perspective view of the anode head of Fig. 2a , without an internal flow element; Fig. 2g shows a magnification of the anode head of Fig. 2a in the area near the front face; Fig. 3a shows a schematic longitudinal section through an exemplary anode head according to a second design for the invention, with rectification elements in a lower, target-distant section and rectification elements in an upper, target-closer section of a radially outer section of the flow path; Fig. 3b shows a schematic cross-section through the anode head of Fig. 3a , at level BB of Fig. 3a Fig. 3c shows a schematic cross-section through the anode head of Fig. 3a , at the CC level of Fig. 3a Fig. 3d shows a schematic cross-section through the anode head of Fig. 3a , at the DD level of Fig. 3a Fig. 3e shows a schematic, semi-open perspective view of the anode head of Fig. 3a , with internal flow element; Fig. 3f shows a schematic, semi-open perspective view of the anode head of Fig. 3a , without an internal flow element; Fig. 3g shows a magnification of the anode head of Fig. 3a in the area near the front face; Fig. 4a shows a schematic longitudinal section through an exemplary anode head according to a third design for the invention, with swirl elements in a lower, target-distant section, rectification elements in a centrally located, target-distant section, and rectification elements in an upper, target-closer section of a radially outer section of the flow path; Fig. 4b shows a schematic cross-section through the anode head of Fig. 4a , at level BB of Fig. 4a Fig. 4c shows a schematic cross-section through the anode head of Fig. 4a , at the CC level of Fig. 4a Fig. 4d shows a schematic cross-section through the anode head of Fig. 4a , at the DD level of Fig. 4a Fig. 4e shows a schematic, semi-open perspective view of the anode head of Fig. 4a , with internal flow element; Fig. 4f shows a schematic, semi-open perspective view of the anode head of Fig. 4a , without an internal flow element; Fig. 4g shows a magnification of the anode head of Fig. 4a in the area near the front face; Fig. 5 shows a schematic, semi-open side view of an anode head for the invention in the area of ​​the radially outer section of the flow path, with helical swirl elements and teardrop-shaped rectifying elements; Fig. 6 shows a schematic, semi-open side view of an anode head for the invention in the area of ​​the radially outer section of the flow path, with swirl elements designed as obliquely extending lamellae and trapezoidal rectifying elements; Fig. 7 shows a schematic, semi-open side view of an anode head for the invention in the area of ​​the radially outer section of the flow path, with hollow structures as rectifying elements and trapezoidal rectifying elements.

[0048] The Fig. 1 Figure 1 shows a schematic longitudinal section illustrating an exemplary embodiment of an X-ray tube according to the invention.

[0049] In their Fig. 1 The upper part of the housing 2 (also called the cathode housing) encloses an evacuated space 3. An electron source 4, formed here by a ring-shaped filament, is located in the evacuated space 3. The filament can be heated with an electric current via the terminals 5. An anode head 6 also projects into the evacuated space 3.

[0050] The source 4 is brought to a negative electrical potential (relative to the anode head 6) via terminals 5, thus acting as the cathode. The anode head 6 is brought to a positive electrical potential (relative to the source 4) via an electrical terminal 7, thus acting as the anode. Electrons released at the source 4 are then accelerated by the potential difference between the source 4 and the anode head 6 through the evacuated space 3 towards the anode head 6. Typically, the potential difference (also called accelerating voltage) is between 1 kV and 100 kV.

[0051] By means of suitably configured deflection electrodes 8 at a suitable potential, the trajectory of the electrons is adjusted so that the electrons are in a ring-shaped region 9 (indicated by dots in the diagram). Fig. 1 , see also Fig. 2d (for this purpose) strike the front face 10 of the anode head 6. A target 11 is formed on the front face 10 of the anode head 6. The target 11 consists of a rhodium disc (or alternatively, for example, copper, molybdenum, chromium, or silver, depending on the desired characteristic X-ray radiation), which extends over the entire surface of the flat front face 10.

[0052] The electrons striking the target 11 in the ring-shaped, excited region 9 penetrate the material of the target 11 and are thereby decelerated. This produces X-rays in the form of bremsstrahlung. Additionally, electrons are ejected from the electron shells of the atoms in the target 11's material. When these electron shells are refilled with electrons from higher shells, characteristic X-rays are produced. The X-rays generated in this way at the target 11 largely exit through an X-ray window 12 in the housing 2 and are then used for an application, for example, an X-ray fluorescence experiment (application not shown in detail). The X-ray window 12 is formed by a beryllium disk.

[0053] The housing 2 and the anode head 6 are arranged here on an insulating body 13. The insulating body 13 can be designed, for example, as in EP 4 141 905 A1.

[0054] The electrons striking the target 11 during operation cause the anode head 6 to heat up considerably. Therefore, the anode head 6 is actively cooled with a cooling fluid. This cooling fluid can be, for example, water.

[0055] A supply line 14 for fresh (cool) cooling fluid leads through the insulation body 13 to an inlet port 14a of the anode head 6. Furthermore, a drain line 15 for used (heated) cooling fluid runs from an outlet port 15a of the anode head 6 through the insulation body 13. Within the anode head 6, a flow path 16 for the cooling fluid leads from the inlet port 14a to the outlet port 15a (for the flow path 16, see in particular...). Figuren 2a-2g below).

[0056] The X-ray tube 1 is connected to a cooling fluid supply unit 17. Fresh cooling fluid is pumped from the supply unit 17 at a delivery outlet 14b and fed into the anode head 6 via the inlet line 14. Heated cooling fluid flows from the anode head 6 via the outlet line 15 to the return inlet 15b of the supply unit 17. The supply unit 17 may include a cooling unit and a pump for the cooling fluid (not shown in detail). The entire assembly consisting of the X-ray tube 1 and the connected cooling fluid supply unit 17 is also referred to as the X-ray tube assembly 40.

[0057] The Figuren 2a bis 2g Illustrate an exemplary anode head 6 in a first design form for the invention. Fig. 2a shows a longitudinal section, and Fig. 2b und 2c show cross-sections at levels BB and CC. Fig. 2d shows a top view of the anode head 6 on its front face 10. Figuren 2e und 2f show semi-open perspective views of the anode head 6, with internal flow element 18 ( Fig. 2e ) and without an internal flow element ( Fig. 2f). Fig. 2g Finally, an enlargement from the longitudinal section of Fig. 2a in the area near the front face 10 of the anode head 6.

[0058] The anode head 6 of the Figuren 2a-2g corresponds to the anode head of Fig. 1 (see also there). Additionally, parts of the inlet line 14 and the outlet line 15 for the coolant are illustrated, cf. Fig. 2a , 2e, 2f Regarding this: The coolant flows along the flow direction FR. From above... Fig. 2d The excited, ring-shaped area 9 (boundary shown with a dashed line) of the target 11 is also clearly visible. The target 11 lies perpendicular to the central axis ZA of the anode head 6. The anode head 6 is essentially cylindrical overall, with two small, circumferential shoulders.

[0059] In the illustrated embodiment, the anode head 6 is formed by a first, inner flow element (or component) 18 and a second, outer flow element (or component) 19. The flow elements 18 and 19 are nested one inside the other along a central axis ZA of the anode head 6. The second, outer flow element 19 comprises a cap 19a, which rests on a base 19b and is soldered or welded to it. The flow path 16 for the cooling fluid is formed within the inner flow element 18 and between the flow elements 18 and 19. The flow path 16 runs from the inlet connection 14a via an inlet channel 14c (here axially but off-center), a radially outer section 20, a cooling gap 21, a radially inner section 22 (here axially and centrally located) and an outlet channel 15c (here inclined to the central axis) to the outlet connection 15a.

[0060] The radially outer section 20 runs between the radial outer side of the inner flow element 18 and the radial inner side of the outer flow element 19. The cooling gap 21 lies behind the target 11, opposite the annular, excited region 9 of the target 11 (well in Fig. 2g (recognizable). The cooling gap 21 is bounded above by the outer flow element 19 and below by the inner flow element 18. The cooling gap 21 runs essentially transversely to the central axis ZA. A pin 23 of the outer flow element 19 projects into the radially inner section 22 in an upper part, so that in this upper part the radially inner section 22 is bounded by the outer flow element 19 and the inner flow element 18. In a lower part of the radially inner section 22 of the flow path 16, only the radially inner flow element 18 binds the radially inner section 22. The axial, radially inner section 22 transitions into the inclined drain channel 15c.

[0061] The cooling fluid flows axially upwards in the flow path 16 along the radially outer section, from radially outside to radially inside in the area of ​​the cooling gap 21, and axially downwards in the area of ​​the radially inner section 22.

[0062] How good in Fig. 2g As can be seen, in the depicted design, the upper, target-facing wall 24 of the cooling gap 21 is perpendicular to the central axis ZA. The lower, target-away wall 25 of the cooling gap 21 is straight, but with a slight inclination perpendicular to the central axis, sloping downwards radially inwards. In a region 26 opposite the annular, excited region 9 of the target 11, the height of the cooling gap 21 (measured in a direction perpendicular to the target-facing wall 24, i.e., measured axially) increases continuously from radially outwards to radially inwards (i.e., along the flow direction FR in the cooling gap 21). For illustrative purposes, a first height H1 further radially outwards and a second height H2 further radially inwards are shown, each at the edge of region 26.The increasing height of the cooling gap 21 along the flow direction FR facilitates the removal of boiling bubbles from the cooling gap 21 into the radially inner section 22 (and thus also from the anode head 6 as a whole). The area 26, in which the height of the cooling channel 21 steadily increases, extends over approximately 30% of the radius of the anode head 6 (at the axial position of the cooling gap 21).

[0063] Furthermore, in region 26, the cross-sectional area available to the cooling fluid in the cooling gap 21 also changes along the flow direction FR, i.e., from radially outside to radially inside. Here, the cross-sectional area corresponds to a cylindrical surface area in the cooling gap 21, which at the respective radial position lies perpendicular to the upper, target-facing wall 24. For example, a first area F1 further radially outside and a second area F2 further radially inside, each at the edge of region 26, are marked with dotted lines. Note that the cross-sectional area is calculated as the product of the circumference and the height of the cooling gap at the corresponding radial position. In the embodiment shown, the cross-sectional area decreases slightly from radially outside to radially inside, where approximately F2 = 0.8 * F1 (note that in the Fig. 2g The radius decreases more rapidly inwards than the height of the cooling gap increases; therefore, the cross-sectional area decreases radially inwards, even though the height increases. The decreasing cross-sectional area in the cooling gap 21 in the flow direction FR ensures that the pressure in the cooling fluid in the cooling gap 21 increases slightly radially inwards; this prevents the boiling bubbles from collapsing (cavitation).

[0064] The flow of the cooling fluid, which flows radially inwards from the cooling gap 21, is deflected axially downwards by means of the pin 23. The partial flows of the cooling fluid, originating from different azimuthal positions, flow essentially parallel to each other along the axial direction after being deflected by the pin 23, until they finally merge at the lower end of the pin with respect to the radial direction. This ensures an efficient flow of the cooling fluid.

[0065] In the illustrated design, the radially outer section 20 comprises two subsections 27a, 27b, each containing distribution structures 28 for the cooling fluid. In the flow direction FR, annular gaps 29a, 29b, 29c (also referred to as annular channels) are arranged upstream, between, and downstream of subsections 27a, 27b. The cooling fluid can spread across the entire circumference of the annular gaps; no distribution structures are arranged within the annular gaps. With the distribution structures 28 in the subsections 27a, 27b and the annular gaps 29a-29c acting as equalization zones 32, the cooling fluid, which here flows into the anode head 6 via a single inlet connection 14a and inlet channel 14c, is distributed over the circumference of the anode head 6, so that an essentially uniform coolant flow in the axial direction is achieved immediately in front of the cooling gap 21 at all circumferential positions.

[0066] The inlet channel 14c, which is in Fig. 2a The anode head 6, which is formed near the right edge in the lower part, opens into the lower annular gap 29a. This gap runs around the entire circumference of the anode head 6. The lower annular gap 29a acts as a homogenization zone 32 and contains no distribution structures.

[0067] The lower annular gap 29a is adjoined by the target-distant subsection 27a. In this embodiment, a helical swirl element 30 is provided as the first target-distant distribution structure 28, which here is formed on the radially outer side of the inner flow element 18, as shown in Fig. 2e This is clearly visible. The helical swirl element 30 winds approximately twice around the central axis ZA. The helical swirl element 30 extends to the radially inner side of the outer flow element 19, so that a helical channel 31 is formed in the section 27a furthest from the target (in the radial gap between the flow elements 18, 19). As the cooling fluid flows through the helical channel 31, it acquires a velocity component in the circumferential direction around the central axis ZA.

[0068] The helical channel 31 opens into the central annular gap 29b. The annular gap 29b also runs around the entire circumference of the anode head 6. The central annular gap 29b also acts as a homogenization zone 32 and contains no distribution structures. The swirl introduced into the cooling fluid distributes the cooling fluid flow very evenly in the annular gap 29b over the entire circumference of the anode head 6.

[0069] The target-adjacent section 27b adjoins the central annular gap 29b. In the target-adjacent section 27b (in the radial gap between the flow elements 18, 19), a set 33 of rectifying elements 34 is provided. The rectifying elements 34 are designed here as straight lamellae 34a running parallel to the central axis ZA. The straight lamellae 34a are designed here as radially inwardly directed projections on the radially inner side of the outer flow element 19, as shown in Fig. 2f This is clearly visible. The rectifying elements 34 remove the swirl from the cooling fluid. In the section 27 near the target, the coolant flows axially upwards in the spaces 35 between the fins 34a.

[0070] The upper annular gap 29c adjoins the target-adjacent section 27b. The spaces 35 open into this annular gap 29c. The annular gap 29c also runs around the entire circumference of the anode head 6. This annular gap 29c also acts as a homogenization zone 32 and contains no distribution structures.

[0071] The upper annular gap 29c transitions into the cooling gap 21 at its upper end. The distribution structures 28 in sections 27a and 27b, in conjunction with the homogenization zones 32 (annular gaps 29a, 29b, and 29c), ensure that cooling fluid flows radially inward into and through the cooling gap 21 at approximately the same rate from all locations along the circumference of the anode head 6. This results in uniform cooling of the anode head 6, particularly in the (radial) region 26, which is located opposite and close to the excited region 9 of the target 11.

[0072] The Figuren 3a bis 3g Illustrate an exemplary anode head 6 in a second design for the invention. Fig. 3a shows a longitudinal section, and Fig. 3b, 3c und 3d Cross-sections at levels BB, CC and DD. The Figuren 3e und 3f show semi-open perspective views of the anode head 6, each with and without internal flow element 18. Fig. 3g Finally, an enlargement from the longitudinal section of Fig. 3a in the area near the front face 10 of the anode head 6. The second design is largely similar to the first design of Fig. 2a-2g (especially with regard to the cooling channel 21 and the radially inner section 22 of the flow path 16), so that only the essential differences (especially in the area of ​​the radially outer section 20 of the flow path 16) will be explained below.

[0073] The lower annular gap 29a adjoins the section 27a furthest from the target. Within this section, a first set 33a of rectifying elements 34 is provided. The rectifying elements 34 are designed as straight lamellae 34a running parallel to the central axis ZA. These straight lamellae 34a are formed as radially inwardly directed projections on the radial inner surface of the outer flow element 19. In the section 27b closest to the target, the cooling fluid flows axially upwards in the spaces 35 between the lamellae 34a.

[0074] The lower, target-distant section 27a is adjoined by the middle annular gap 29b. The annular gap 29b also runs around the entire circumference of the anode head 6. The middle annular gap 29b acts as a homogenization zone 32.

[0075] The central annular gap 29b is adjoined by the target-adjacent subsection 27b. A second set 33b of rectifying elements 34 is provided in this section. Here, the rectifying elements 34 are also designed as straight lamellae 34a running parallel to the central axis ZA. The straight lamellae 34a are designed as radially inwardly directed projections on the radial inner surface of the outer flow element 19, as shown in Fig. 3f This is clearly visible. The cooling fluid flows axially upwards in the target-adjacent section 27b in the spaces 35 between the fins 34a.

[0076] The second set 33b of rectifying elements 34 is arranged here offset in the azimuthal direction relative to the first set 33a of rectifying elements 34, as in Fig. 3c und Fig. 3d This is clearly visible. At the azimuthal position of each lamella 34a in the first set 33a, there is an aligning gap 35 in the second set 33b, and vice versa. This ensures that a partial flow of cooling fluid from a gap 35 in the first set 33a cannot continue in a straight (axial) direction into a gap 35 of the second set 33b, but must be deflected transversely. This transverse deflection is further conveyed by the central annular gap 29b.

[0077] The upper annular gap 29c adjoins the target-adjacent section 27b. The spaces 35 of the second set 33b open into this annular gap 29c. The annular gap 29c also runs around the entire circumference of the anode head 6. This annular gap 29c also acts as a homogenization zone 32.

[0078] The Figuren 4a bis 4g Illustrate an exemplary anode head 6 in a third design for the invention. Fig. 4a shows a longitudinal section, and Fig. 4b, 4c und 4d Cross-sections at levels BB, CC and DD. The Figuren 4e und 4f show semi-open perspective views of the anode head 6, each with and without internal flow element 18. Fig. 4g Finally, an enlargement from the longitudinal section of Fig. 4a in the area near the front face 10 of the anode head 6. The third design is largely similar to the first design of Fig. 2a-2g , so that only the essential differences will be explained below.

[0079] In the design of Fig. 4a-4f The radially outer section 20 of the flow path 16 comprises three subsections: the lower, target-distant (and most distant) subsection 27a, a middle, also target-distant subsection 27c, and an upper, target-close subsection 27b. Annular gaps 29a, 29b, 29c, and 29d, each representing homogenization zones 32, are located upstream of subsection 27a, downstream of subsection 27b, and between subsections 27a, 27c, and 27b.

[0080] The formation of the lower annular gap 29a, the lower target-distant subsection 27a with a helical twisting element 30 as a distribution structure 28 and the subsequent middle annular gap 29b correspond to the design of Fig. 2a-2g .

[0081] The middle subsection 27c adjoins the middle annular gap 29b. Since this middle subsection 27c is not the subsection that is closest to the target 11 in the axial direction, it is also considered to be furthest from the target.

[0082] In the central subsection 27c, a first set 33a of rectifying elements 34 is provided. The rectifying elements 34 are designed here as straight lamellae 34a running parallel to the central axis ZA. The straight lamellae 34a are designed here as radially inwardly directed projections on the radial inner side of the outer flow element 19, as shown in Fig. 4f Clearly visible. The coolant flows axially upwards in the central section 27c in the spaces 35 between the fins 34a.

[0083] The middle section 27c is followed by the further, middle annular gap 29d. The annular gap 29d also runs around the entire circumference of the anode head 6. The annular gap 29d acts as a homogenization zone 32.

[0084] The target-adjacent section 27b adjoins the central annular gap 29d. A second set 33b of rectifying elements 34 is provided in this section. Here, the rectifying elements 34 are also designed as straight lamellae 34a running parallel to the central axis ZA. The straight lamellae 34a are designed here as radially inwardly directed projections on the radially inner side of the outer flow element 19, as shown in Fig. 4f This is clearly visible. The cooling fluid flows axially upwards in the target-adjacent section 27b in the spaces 35 between the fins 34a.

[0085] The second set 33b of rectifying elements 34 is again arranged in an azimuthal direction relative to the first set 33a of rectifying elements 34, as shown in Fig. 4c und Fig. 4d This is clearly visible. At the azimuthal position of each lamella 34a in the first set 33a, there is an aligning gap 35 in the second set 33b, and vice versa. This ensures that a partial flow from a gap 35 in the first set 33a cannot continue in a straight (axial) direction into a gap 35 of the second set 33b, but must be deflected transversely. This transverse deflection is further conveyed by the central annular gap 29d. Note that the lamellae 34a and the gaps 35 can have different widths in the azimuthal direction.

[0086] The upper annular gap 29c adjoins the target-adjacent section 27b. The spaces 35 of the second set 33b open into this annular gap 29c. The annular gap 29c also runs around the entire circumference of the anode head 6. This annular gap 29c also acts as a homogenization zone 32.

[0087] How good in Fig. 4g As can be seen, in the illustrated embodiment, the upper, target-facing wall 24 of the cooling gap 21 is oriented with a slight inclination in a direction perpendicular to the central axis ZA, with the target-facing wall 24 sloping downwards radially inwards. The lower, target-away wall 25 of the cooling gap 21 runs approximately straight with a somewhat steeper inclination in the direction perpendicular to the central axis ZA, with the target-away wall 25 also sloping downwards radially inwards. In a region 26 opposite the annular, excited region 9 of the target 11, the height of the cooling gap 21 (measured in a direction perpendicular to the target-facing wall 24, i.e., in a direction slightly oblique to the central axis ZA) increases from radially outwards to radially inwards (i.e., along the flow direction FR in the cooling gap 21).For illustrative purposes, a first height H1 further radially outward and a second height H2 further radially inward are shown, each at the edge of the area 26. This facilitates the removal of boiling bubbles from the cooling gap 21 into the radially inner section 22.

[0088] Furthermore, in region 26, the cross-sectional area available to the coolant in the cooling gap 21 also changes along the flow direction FR, i.e., from radially outside to radially inside. Here, the cross-sectional area corresponds to a conical surface in the cooling gap 21, which at the respective radial position is perpendicular to the upper, target-facing wall 24. For example, a first surface F1 further radially outside and a second surface F2 further radially inside, each at the edge of region 26, are marked with dotted lines. In this configuration as well, the cross-sectional area decreases from radially outside to inside, i.e., F2. <F1. Durch die im Kühlspalt 21 in Fließrichtung FR abnehmende Querschnittsfläche wird sichergestellt, dass der Druck im Kühlfluid nach radial innen hin etwas zunimmt; dies verhindert ein Kollabieren der Siedeblasen (Kavitation).

[0089] The Fig. 5 Figure 1 illustrates another exemplary design of an anode head 6 for the invention. Only a portion of the anode head 6 is shown in a highly schematic side view, encompassing the radially outer section of the flow path 16. The radially outer flow element 19 is cut open and removed on the side facing the viewer, allowing the viewer to see the inner flow element 18 and the distribution structures 28 in the radially outer section 20 of the flow path 16 ("semi-open" anode head 6). The essential deviations from the design of [reference missing] are shown. Fig. 2a-2g explained.

[0090] In the lower, target-distant section 27a, a total of four helical swirl elements 30 are provided (helical swirl elements 30 on the rear side of the radially inner flow element 18 are shown as dashed lines), through which a total of four helical channels 31 are provided.

[0091] In the upper, target-adjacent section 27b, the straightening elements 34 are provided here as teardrop-shaped lamellae 34b. These are all axially aligned (along the central axis ZA). The lamellae 34b are formed here on the radially outward-facing wall side 38 of the inner flow element 18 and project into the radial gap 37 between this wall side 38 and the radially inward-facing wall side 39 of the radially outer flow element 19. Alternatively, the lamellae 34b can also be formed on the wall side 39 (not shown in detail, but see, for example, [reference]). Fig. 2f (for this purpose). The radial gap 37 essentially forms the radially outer section 20 of the flow path 16.

[0092] The Fig. 6 shows another exemplary design of an anode head 6 for the invention, again in a semi-open view as in Figure 1. Fig. 5 The main differences compared to the design of [previous design] are explained. Fig. 2a-2g explained.

[0093] In the lower, target-remote section 27a, a multitude of swirl elements 36 are provided, each designed as an individual lamella inclined to the central axis ZA. All swirl elements 36 exhibit the same inclination ("pitch") to the central axis ZA and are distributed circumferentially and axially within section 27a on the outer surface of the radially inner flow element 18. Note that in other designs, subsets of the swirl elements may also be inclined differently (not shown in detail). Each individual lamella covers only a small portion of the circumference (e.g., 1 / 10 or less). The individual lamellae are spaced radially and axially apart.

[0094] In the upper, target-adjacent section 27b, the straightening elements 34 are provided here as trapezoidal lamellae 34c. The trapezoidal lamellae 34c are all axially aligned (along the central axis ZA). However, the orientation of the trapezoidal lamellae 34c alternates here, so that the thin end is alternately positioned at the top and bottom. As a result, the spaces 35 between the lamellae each have a slight inclination relative to the central axis ZA, with this inclination also alternating along the circumferential direction. Accordingly, the partial flows of the cooling fluid in adjacent spaces 35 are also slightly inclined to each other (with respect to their mean flow direction; see also the flow directions FR). This can contribute to a better homogenization of the partial flows of the cooling fluid.

[0095] The Fig. 7 shows another exemplary design of an anode head 6, again in a semi-open representation as in the Fig. 5 The main differences compared to the design of [previous design] are explained. Fig. 3a-3g explained.

[0096] In the lower, target-distant section 27a, a multitude of rectification elements 34 are provided, which are designed as hollow structures 34d in the form of round tubes. The tubes are all aligned parallel to the central axis ZA. The tubes completely fill the radial gap 37 between the inner flow element 18 and the outer flow element 19, here with a single layer of the round tubes or hollow structures 34d; residual spaces ("wedges") are filled with a resin (not shown in detail). Alternatively, the hollow structures 34d can also be honeycomb-shaped, for example, and typically fill the gap 37 with several layers of honeycomb (not shown in detail).

[0097] In the upper, target-adjacent section 27b, the rectifying elements 34 are designed as triangular lamellae 34e. The triangular lamellae 34e are all axially aligned (along the central axis ZA), with their points facing upwards. Accordingly, the gaps 35 are narrower at the bottom than at the top. This allows the pressure in the annular gap 29b in front of it to be maintained at a high level, which improves the uniformity of the cooling fluid flow. Bezugszeichenliste

[0098] 1 X-ray tube 2 Housing 3 Evacuated space 4 Electron release source, here filament 5 Electrical connections (of the cathode) 6 Anode head 7 Electrical connection (of the anode) 8 Deflection electrodes 9 (Annular) excited area 10 Anode head end face 11 Target 12 X-ray window, here beryllium disk 13 Insulator 14 Coolant inlet 14a Anode head inlet 14b Flow outlet 14c Inlet channel 15 Coolant outlet 15a Anode head drain 15b Return inlet 15c Drain channel 16 Flow path 17 Coolant supply device 18 Inner (first) flow element 19 Outer (second) flow element 19a Cap of the outer Flow element 19b Foot of the outer flow element 20 Radial outer section of the flow path 21 Cooling gap 22 Radial inner section of the flow path 23 Pin 24 Target-facing wall of the cooling gap 25 Target-away wall of the cooling gap 26 Area of ​​the anode head,which lies opposite the excited area of ​​the target 27a (lower) target-distant subsection 27b (upper) target-adjacent subsection 27c (middle) target-distant subsection 28 Distribution structures (general) 29a-d Annular gap 30 Helix-like swirl element 31 Helical channel 32 Smoothing zone 33 Set of rectifying elements 33a First set of rectifying elements 33b Second set of rectifying elements 34 Rectifying elements (general) 34a Straight lamellae 34b Droplet-shaped lamellae 34c Trapezoidal lamellae 34d Hollow structures (here round tubes) 34e Triangular lamellae 35 Intervals 36 Swirl element (inclined single lamella) 37 Radial gap 38 Radially outward-facing wall side (on the inner flow element) 39 Radially to inward-facing wall side (at the outer flow element) 40 X-ray tube arrangement FRF flow direction ZA central axis,

Claims

1. X-ray tube (1) comprising a source (4) for the release of electrons and an anode head (6) with a central axis (ZA), wherein a target (11) is formed on an end face (10) of the anode head (6), onto which the electrons in an excited region (9) strike during operation, wherein the anode head (6) provides a flow path (16) for a cooling fluid, which leads from at least one inlet port (14a) via a radially outer section (20), further via a cooling gap (21), and further via a radially inner section (22) to at least one outlet port (15a), characterized by that the excited area (9) of the target (11) is essentially ring-shaped, and that in a region (26) of the anode head (6) opposite the excited region (9) of the target (11) a local height (H1, H2) of the cooling gap (21) increases steadily from radial outside to radial inside.

2. X-ray tube (1) according to claim 1, characterized by the fact that a local cross-sectional area (F1, F2) of the cooling gap (21) in the area (26) of the anode head (6) opposite the excited area (9) of the target (11) decreases continuously from radial outside to radial inside, remains constant or increases continuously by a maximum of 15%.

3. X-ray tube (1) according to claim 1 or 2, characterized by the fact that a local cross-sectional area (F1, F2) of the cooling gap (21) in the area (26) of the anode head (6) opposite the excited area (9) of the target (11) decreases continuously from radial outside to radial inside, in particular by a maximum of 20% continuously.

4. X-ray tube (1) according to one of the preceding claims, characterized by the fact that the flow path (16) in the anode head (6) is at least essentially rotationally symmetric with respect to the central axis (ZA).

5. X-ray tube (1) according to one of the preceding claims, characterized by the fact thatthe radially outer section (20) of the flow path (16) is formed at least substantially around the entire circumference of the anode head (6).

6. X-ray tube (1) according to one of the preceding claims, characterized by the fact that In the radially outer section (20) of the flow path (16) distribution structures (28) are formed with which a cooling fluid flow from the at least one inlet connection (14a) to the cooling gap (21) can be distributed and homogenized over the circumference of the anode head (6).

7. X-ray tube (1) according to claim 6, characterized by the fact thatThe distribution structures (28) in a target-adjacent subsection (27b) of the radially outer section (20) around the circumference of the anode head (6) comprise a set (33; 33b) of rectification elements (34) for the cooling fluid, which run between an inlet-side annular gap (29b; 29d) and an outlet-side annular gap (29c) or the cooling gap (21), and with which at least substantially parallel partial flows of the cooling fluid can be established and separated from each other.

8. X-ray tube (1) according to one of claims 6 or 7, characterized by the fact thatThe distribution structures (28) in a target-remote subsection (27a; 27c) of the radially outer section (20) of the flow path (16) around the circumference of the anode head (6) comprise a set (33a) of rectifying elements (34) for the cooling fluid flow, which run between an inlet-side annular gap (29a; 29b) and an outlet-side annular gap (29b; 29d), and with which at least substantially parallel partial flows of the cooling fluid can be established and separated from each other.

9. X-ray tube (1) according to claims 7 and 8, characterized by the fact thatthe outlet-side annular gap (29b; 29d) to the rectification elements (34) of the target-distant subsection (27a; 27c) is at the same time the inlet-side annular gap (29b; 29d) to the rectification elements (34) of the target-near subsection (27b), and that the set (33b) of rectification elements (34) of the target-near subsection (27b) is offset from each other in an azimuthal direction with respect to the central axis (ZA) compared to the set (33a) of rectification elements (34) of the target-distant subsection (33a).

10. X-ray tube (1) according to one of claims 7 to 9, characterized by the fact that the rectifying elements (34) are aligned at least substantially in the axial direction, and accordingly the partial flows of the cooling fluid are aligned at least substantially in the axial direction.

11. X-ray tube (1) according to one of claims 7 to 10, characterized by the fact thatthe rectifying elements (34) are formed at least in part by - parallel lamellae (34a; 34b; 34e), in particular straight parallel lamellae (34a), and / or - trapezoidal (34c) or triangular lamellae (34e), and / or - teardrop-shaped (34b) or rhomboid-shaped lamellae, wherein the lamellae (34a; 34b; 34c; 34e) are formed on a radially outwardly directed wall side (38) and / or a radially inwardly directed wall side (39) of the anode head (6), wherein the radially outwardly directed wall side (38) and the radially inwardly directed wall side (39) define the radially outer section (20) of the flow path (16).

12. X-ray tube (1) according to one of claims 7 to 11, characterized by the fact thatthe rectifying elements (34) are at least partially formed by a plurality of parallel hollow structures (34d) arranged in the radially outer section (20) of the flow path (16), in particular wherein the plurality of parallel hollow structures (34d) forms a honeycomb structure.

13. X-ray tube (1) according to one of claims 6 to 12, characterized by the fact that the distribution structures (28) in a target-remote subsection (27a) of the radially outer section (20) of the flow path (16) comprise one or more swirl elements (30; 36) which are arranged between the at least one inlet connection (14a) and an outlet-side annular gap (29b), and with which a swirl with respect to the central axis (ZA) can be introduced into the cooling fluid flow.

14. X-ray tube (1) according to claim 13, characterized by the fact thatthat at least one spiral element (30) runs helically around the central axis (ZA) of the anode head (6), thereby providing at least one helical channel (31) for the cooling fluid flow.

15. X-ray tube (1) according to claim 13 or 14, characterized by the fact that Several spiral elements (30) run helically around the central axis (ZA) of the anode head (6), thereby creating several helical channels (31) offset azimuthally and / or axially to each other for partial flows of the cooling fluid.

16. X-ray tube (1) according to one of claims 6 to 15, characterized by the fact that a homogenization zone (32) for the cooling fluid flow is provided between distribution structures (28) of a target-distant subsection (27a; 27c) of the radially outer section (20) and distribution structures (28) of a target-adjacent subsection (27b) of the radially outer section (20), in particular wherein the homogenization zone (32) is provided as an annular gap (29b; 29d).

17. X-ray tube (1) according to one of the preceding claims, characterized by the fact that the anode head (6) is formed with a first flow element (18) and a second flow element (19) which are inserted into each other and which form at least part of the flow path (16) between them.

18. X-ray tube (1) according to one of the preceding claims, characterized by the fact that at least the radially inner section (22) of the flow path (16), and possibly also the cooling gap (21), are partially limited by a pin (23) that projects from the front face (10) of the anode head (6) into the interior of the anode head (6).

19. X-ray tube arrangement (40) comprising an X-ray tube (1) according to one of the preceding claims and a supply device (17) for a cooling fluid, wherein the supply device (17) provides fresh cooling fluid at a delivery outlet (14b) and the delivery outlet (14b) is connected to the at least one inlet port (14a), in particular wherein the supply device (17) further receives heated cooling fluid at a return inlet (15b) and the outlet port (15a) is connected to the return inlet (15b).

20. Use of an X-ray tube (1) according to one of claims 1 to 18 or an X-ray tube arrangement (40) according to claim 19, wherein in the operation of the X-ray tube (1) - electrons from the source (4) strike an annular, excited region (9) of the target (11) to release electrons and thereby generate X-ray radiation, and - cooling fluid flows in the cooling gap (21) opposite the excited region (9) from radially outside to radially inside.

21. Use according to claim 20, characterized by the fact that a mean flow velocity of the cooling fluid in the cooling gap (21) relative to the excited area (9) remains the same or increases from radial outside to radial inside, in particular by a maximum of 25%.

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