Interrupted ring in an x-ray tube

Abstract

The present invention relates to an interrupt ring in an x-ray tube, wherein the x-ray tube 10 can have (a) a housing that electrically isolates a cathode 11 from an anode 12; (b) a coating ring 18 on an inner surface of the housing, the coating ring 18 encircling a longitudinal axis 16 of the housing; (c) an interrupt ring 19 located at a different location on the inner surface of the housing than the coating ring 18. The interrupt ring 19 can encircle the longitudinal axis 16 at a different location along the longitudinal axis 16 relative to the coating ring 18. The interrupt ring 19 can encircle the longitudinal axis 16 at a different radius from the longitudinal axis 16 than the coating ring 18. The coating ring 18 and the interrupt ring 19 can reduce uneven charge buildup on the inner surface of the housing and can protect a triple point.

Description

[0001] This application claims priority to U.S. Provisional Patent Application No. 63112216, filed November 11, 2020, which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates generally to x-ray tubes. BACKGROUND

[0003] An x-ray tube can produce x-rays by sending electrons to a target of an anode from a cathode by a voltage difference between the cathode and the anode. X-rays are formed when the electrons hit the target. SUMMARY

[0004] The present application provides an x-ray tube comprising: a cathode and an anode electrically insulated from each other, the cathode configured to emit electrons toward the anode, and the anode configured to emit x-rays from the x-ray tube in response to electron impingement from the cathode; an enclosure attached to the cathode and the anode and electrically insulating the cathode from the anode; a current path at an inner surface of the enclosure, the current path comprising a coating ring and a break ring in series; R I R C wherein R is an electrical resistance per unit length through the break ring, and R c is an electrical resistance per unit length through the coating ring, both measured along the current path; p C p E wherein p C is a bulk resistivity of the coating ring, and p E is a bulk resistivity of the enclosure; and the coating ring encircles a longitudinal axis of the enclosure, the coating ring is located on the inner surface, the break ring encircles the longitudinal axis, and the break ring is distinguished from the coating ring. The present application also provides a method of manufacturing an enclosure of an x-ray tube, comprising coating the inner surface of the enclosure, and then removing a ring of the coating to form the break ring. The present application also provides a method of manufacturing an enclosure for an x-ray tube, the method comprising: masking a ring at the inner surface of the enclosure; coating unmasked portions of the inner surface, forming a break ring at the masked portions of the inner surface, and forming a coating ring at the coated portions of the inner surface, wherein p I = p E and p I > p C , and p I is a bulk resistivity of the break ring. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1 is a cross-sectional side view of an x-ray tube 10 having the following components, (a) a cylinder 15 that electrically insulates a cathode 11 from an anode 12; (b) a coating ring 16 at an inner surface 15 icoating ring 18 on the inner surface 15 of the cylinder 15 i between the interrupt ring 19 and the coating ring 18.

[0006] Figure 2 is a cross-sectional side view of an x-ray tube 20 with a coated cylinder 15, similar to Figure 1 the coated cylinder 15. The interrupt ring 19 in the x-ray tube 20 is closer to the anode 12 than to the cathode 11 and is a region of thinner coating than the coating ring 18.

[0007] Figure 3 is a cross-sectional side view of an x-ray tube 30 with a coated cylinder 15, similar to Figures 1-2 the coated cylinder 15. The interrupt ring 19 in the x-ray tube 30 is closer to the cathode 11 than to the anode 12.

[0008] Figure 4 is a cross-sectional side view of an x-ray tube 40 with a coated cylinder 15, similar to Figures 1-3 the coated cylinder 15. The cylinder 15 in the x-ray tube 40 includes two interrupt rings 19.

[0009] Figure 5 is a cross-sectional side view of an x-ray tube 50 with a coated cylinder 15, similar to Figures 1-4 the coated cylinder 15. The interrupt ring 19 and the coating ring 18 in the x-ray tube 50 are adjacent helical rings on the inner surface 15 of the cylinder 15 i .

[0010] Figure 6 is a top view of a coating ring 18 and an interrupt ring 19 on the inner surface 62 of an electrically insulating disc 62. The disc 62 encircles a region 61. i The region 61 can be at least a portion of the cathode 11 or at least a portion of the anode 12.

[0011] Figure 7 is a top view of a coating ring 18 and an interrupt ring 19 on the inner surface 62 of an electrically insulating disc 62. The disc 62 encircles a region 61. i The region 61 can be at least a portion of the cathode 11 or at least a portion of the anode 12.

[0012] Figure 8 is a top view of a coating ring 18 and an interrupt ring 19 on the inner surface 62 of an electrically insulating disc 62 as adjacent helical rings. The disc 62 encircles a region 61. i The region 61 can be at least a portion of the cathode 11 or at least a portion of the anode 12.

[0013] Figure 9 is a cross-sectional perspective view of an x-ray tube 90 with a coated disc 62 encircling at least a portion of the cathode 11.

[0014] Figure 10 is a cross-sectional perspective view of an x-ray tube 100 having a coated disc 62 surrounding at least a portion of the anode 12.

[0015] Figure 11 is a partial cross-sectional side view of one half of an x-ray tube 110 plus equipotential lines 123. The one half of the x-ray tube 110 has a coating ring 18 (not shown in the figure).

[0016] Figure 12 is a partial cross-sectional side view of one half of an x-ray tube 120 plus equipotential lines 123. The one half of the x-ray tube 120 has a coating ring 18 and an interrupt ring 19 (both not shown in the figure).

[0017] Figure 13 is a cross-sectional side view of step 130 in a method of manufacturing a housing for an x-ray tube, including forming a coating ring 18 and an interrupt ring 19 by masking a ring at an inner surface of the housing and coating the unmasked portion of the inner surface.

[0018] Figure 14 is a cross-sectional side view of step 140 in a method of manufacturing a housing for an x-ray tube, including forming a coating ring 18 by coating an inner surface of the housing and then removing part or all of the ring of coating to form an interrupt ring 19.

[0019] Figure 15 is a cross-sectional side view of step 150 in a method of manufacturing a housing for an x-ray tube, including forming a coating ring 18 and an interrupt ring 19 by depositing a coating on the inner surface with a spray tool 151 and adjusting the time and / or flow rate through the spray tool 151 at different locations to provide different thicknesses of coating, or locations with and without coating.

[0020] DEFINITIONS: The following definitions, including their plural forms, apply throughout this patent application.

[0021] As used herein, the terms "on", "located on", "located", and "above" mean directly on or above, with some other solid material in between. The terms "directly on", "adjoin", "adjoins", and "adjoining" mean direct and immediate contact.

[0022] As used herein, the phrase "same material composition" means exactly the same, the same within normal manufacturing tolerances, or nearly exactly the same, such that any deviation from exactly the same would have a negligible effect on the ordinary use of the device.

[0023] As used herein, the term "tube" is not limited to a cylindrical shape. The term "x-ray tube" is used because that is the normal term for this x-ray device.

[0024] Unless otherwise expressly specified herein, all values related to temperature are values at 25 °C. DETAILED DESCRIPTION

[0025] As shown in FIGS. Figures 1-5 , Figure 9 and Figure 10 The x-ray tubes 10, 20, 30, 40, 50, 90, and 100 include an envelope attached to the cathode 11 and the anode 12 and electrically insulating the cathode 11 from the anode 12. Example materials for the envelope include glass or ceramic (e.g., alumina). A vacuum can exist inside the envelope.

[0026] The envelope, the cathode 11, and the anode 12 can define and form a housing that is hermetically sealed and capable of holding a vacuum therein. The envelope can include a cylinder 15, a disk 62, or both. A bore can extend through a core of the cylinder 15. The term “cylinder” is used because this is a common shape; however, the cylinder 15 can have other shapes. For example, the cylinder 15 can have a hollow frustoconical body shape.

[0027] Transmission-target x-ray tubes 10, 20, 30, 40, 50, 90, and 100 are shown in the figures, but the present invention is equally applicable to reflection-target or side-window x-ray tubes.

[0028] The cathode 11 can include an electron emitter 11 EE (e.g., a filament) for emitting electrons toward the anode 12. The anode 12 can include a target 14 (e.g., gold, rhodium, tungsten) for generating x-rays. Electrons that strike the target 14 can generate x-rays. The x-rays can be emitted from the x-ray tube through an x-ray window 13.

[0029] Some of the electrons will bounce and not form x-rays. These electrons can cause a charge to build up on the inner surface of the envelope, such as on the inner surface 15 i of the cylinder 15 and / or the inner surface 62 i of the disk 62. The charge build-up can cause a sharp voltage gradient to occur inside the envelope, which can cause the x-ray tube to fail in arcing. The inner surface of the envelope can be an interior surface of the envelope that faces inward toward the cavity of the x-ray tube.

[0030] The charge can build up unevenly on the inner surface of the envelope. This uneven charge can move the electron beam away from the center of the target 14. As a result of this movement, x-rays can be emitted from different locations on the target 14. It can be difficult to aim the moving, or off-center, x-ray beam.

[0031] A triple-point is formed at the junction of (a) the outer casing, (b) the internal vacuum inside the outer casing, and (c) the cathode 11 or anode 12. The triple-point can have high stress and a large electric field gradient. Arcing failure of the X-ray tube may be caused by this high stress and large electric field gradient at the triple-point.

[0032] The coating ring 18 and interruption ring 19 on the inner surface of the housing can reduce charge accumulation, prevent uneven charge accumulation, and protect the triple point. The coating ring 18 and interruption ring 19 can be applied to the inner surface 15 of the cylinder 15. i The inner surface 62 of the disk 62 of the cathode 11 i The inner surface 62 of the disk 62 of anode 12 i Above, or a combination thereof.

[0033] Part or all of the inner surface of the housing may be coated with a resistive material, which may form a coating ring 18. The coating ring 18 may have a lower bulk resistivity than the housing. The coating ring 18 may provide a path for electrons on the inner surface of the housing to flow to ground. The surface resistivity of the coating ring 18 (e.g., 10⁻⁶) 10 -10 14 The ohm / square can be selected to allow only a small current between the cathode 11 and the anode 12.

[0034] The coating ring 18 can be adjacent to the cathode 11 or the anode 12. There can be multiple coating rings 18, one adjacent to the cathode 11 and another adjacent to the anode 12.

[0035] like Figure 4 As shown, the material 45 of the coating ring 18 can also coat the exterior (partial or complete) of the cylinder 15. This material can extend between the cathode 11 and the cylinder 15, between the anode 12 and the cylinder 15, or between both. Therefore, the material 45 can be continuous from the coating ring 18 to the exterior of the cylinder 15. This material in these locations helps protect the triple point.

[0036] A coating ring 18 may surround the longitudinal axis 16 of the housing. The longitudinal axis 16 may extend between and through the cathode 11 and anode 12. The longitudinal axis 16 may be located within the electron emitter 11. EE Extending between and through the electron emitter 11 and the target 14 EE And target 14. The longitudinal axis 16 can be located at the center of the electron beam and cylinder 15.

[0037] The interruption ring 19 on the inner surface of the housing can improve the electric field lines inside the housing. The interruption ring 19, parallel to the longitudinal axis 16 and relative to the coating ring 18, can provide a ring with higher resistance per unit length. The interruption ring 19 can pull the electric field away from the triple point, thus protecting the triple point. The interruption ring 19 can be positioned and sized for electron beam shaping.

[0038] The interrupt ring 19 may differ from the coating ring 18. The interrupt ring 19 may differ from the coating ring 18 in structure and dimensions. For example, the interrupt ring 19 may have a different thickness and / or a different width than the coating ring 18. The interrupt ring 19 may differ from the coating ring 18 chemically. For example, the interrupt ring 19 may comprise a different material than the coating ring 18. The interrupt ring 19 may be located in a different position than the coating ring 18. For example, the interrupt ring 19 may be located in a different longitudinal and / or radial position than the coating ring 18.

[0039] The coating ring 18 and the interruption ring 19 can be located on the inner surface of the housing and between the anode 12 and the cathode 11, and at the electron emitter 11. EE Between target 14 and electron transmitter 11 EE A series current path 51 is formed between the cylinder 15 and the x-ray window 13, or a combination thereof. The current path 51 may extend longitudinally along the length of the cylinder 15 (see figure). Figures 1-5 The current path 51 can be between the cylinder 15 and the electron emitter 11. EE Extending radially between (see) Figure 9 The current path 51 may extend radially between the cylinder 15 and the target 14 and / or the anode 12's X-ray window 13 (see...). Figure 10 ).

[0040] The relatively high resistance per unit length of interrupt ring 19 helps to form electric field lines. An example resistance relationship between coated ring 18 and interrupt ring 19 includes R... C <R I 2*R C <R I 10*R C <R I 100*R C <R I 1000*R C <R I 10,000*R C <R I “R” C "R" represents the resistance per unit length passing through the coated ring 18. I "It is the resistance per unit length passing through interrupted ring 19."

[0041] The resistance per unit length in RC and R I A smooth, linear, or gradual transition between electric field gradients can reduce abrupt electric field gradients. This can also be achieved by adjusting R... C and R I The electric field gradient is reduced by multiple small resistance changes per unit length. For example... Figure 1 and Figure 3 As shown, a transition region 17 may be present between the interrupted ring 19 and the coated ring 18. The transition region 17 may have an intermediate thickness or material between the thickness or material of the interrupted ring 19 and the coated ring 18. Therefore, the transition region 17 can provide R... I and R C A smooth transition of resistance per unit length between them.

[0042] The coated ring 18 can have a lower bulk resistivity than the outer shell, thus providing a lower-resistivity path for electrons inside the shell to flow to ground. Therefore, ρ C <ρ E , where ρ C It is the volume resistivity of the coating ring 18, while ρ E This refers to the volume resistivity of the outer casing. The volume resistivity of the interrupted ring 19 can be higher than or equal to the volume resistivity of the coating ring 18. Therefore, ρ I ≥ρ C , where ρ I This refers to the volume resistivity of interrupt ring 19. The volume resistivity of interrupt ring 19 can be lower than or equal to the volume resistivity of the casing (ρ). I ≤ρ E ).

[0043] The coating ring 18 and the interruption ring 19 can be on the inner surface 15 of the cylinder 15. i On the inner surface 62 of the disk 62 surrounding at least a portion of the cathode 11 i At the inner surface 62 of at least a portion of the disk 62 surrounding the anode 12 i The cylinder 15 and / or the disk 62 may be oriented perpendicular to the longitudinal axis 16. The cylinder 15 and / or the disk 62 may be electrically insulating. The cylinder 15 and / or the disk 62 may form a housing and may electrically insulate the cathode 11 from the anode 12.

[0044] Figures 1-5 The coating ring 18 and interrupted ring 19 on the inner surface 15i of the cylinder 15 are shown. Figures 1-4 As shown, the interrupted ring 19 can surround the longitudinal axis 16 at different positions relative to the coating ring 18 along the longitudinal axis 16. Figure 5 As shown, the interrupted ring 19 and the coating ring 18 can be on the inner surface 15 of the cylinder 15. i The adjacent helical rings.

[0045] Figures 6-10 The inner surface 62 of the electrically insulating disk 62 is shown. i The coating ring 18 and the interrupted ring 19 are on top. For example... Figures 6-10 As shown, the interrupted ring 19 can surround the longitudinal axis 16 at the same position relative to the coating ring 18 along the longitudinal axis 16. As... Figures 6-7 and Figures 9-10 As shown, compared to the coating ring 18, the interrupted ring 19 can surround the longitudinal axis 16 with a different radius than the longitudinal axis 16. Figure 8 As shown, the interrupted ring 19 and the coated ring 18 can be the inner surface 62 of the electrically insulating disk 62. i The adjacent spiral ring.

[0046] Disk 62 can surround region 61. For example... Figure 9 As shown, region 61 may be at least a portion of cathode 11, and coating ring 18 and interruption ring 19 may be on the inner surface 62 of target material 14 facing anode 12 of disk 62. i Above. (As shown) Figure 10 As shown, region 61 may be at least a portion of anode 12, and coating ring 18 and interruption ring 19 may be on the inner surface 62 of disk 62 facing cathode 11. i superior.

[0047] like Figure 1 , Figure 2 and Figure 4 As shown, the interruption ring 19 can be closer to the anode 12 rather than closer to the cathode 11. (As...) Figures 1-2 As shown, any or all interrupted rings 19 can be closer to the anode 12 rather than closer to the cathode 11. Figures 3-4 As shown, the interruption ring 19 can be closer to the cathode 11 rather than closer to the anode 12. (As indicated...) Figure 3 As shown, any or all interruption rings 19 can be closer to the cathode 11 rather than closer to the anode 12. The location of these different interruption rings 19 can be selected based on the desired shape of the potential line.

[0048] like Figures 2-4 and Figure 6 As shown, the interrupt ring 19 can interrupt the coating ring 18, with at least two separate coating rings 18 formed on each of the two opposite sides of the interrupt ring 19. A series current path 51 can thus pass through one coating ring 18, through the interrupt ring 19, and then through the other coating ring 18.

[0049] like Figure 4 and Figure 6As shown, the coating ring 18 can be interrupted by an interruption ring 19, forming at least two separate interruption rings 19 on each of the two opposite sides of the coating ring 18. The series current path 51 can thus be through one interruption ring 19, through the coating ring 18, and then through another interruption ring 19. Also as shown, the interruption ring 19 can be interrupted by a coating ring 18, forming at least two separate coating rings 18 on each of the two opposite sides of the interruption ring 19. The series current path 51 can thus be through one coating ring 18, through the interruption ring 19, and then through another coating ring 18. Figure 4 As shown, the interruption ring 19 can be interrupted by a coating ring 18, forming at least two separate coating rings 18 on each of the two opposite sides of the interruption ring 19. The series current path 51 can thus be through one coating ring 18, through the interruption ring 19, and then through another coating ring 18. Figure 6 As shown, there can be multiple coating rings 18 and multiple interruption rings 19. As shown, the interruption ring 19 can be interrupted by a coating ring 18, forming at least two separate coating rings 18 on each of the two opposite sides of the interruption ring 19. The series current path 51 can thus be through one coating ring 18, through the interruption ring 19, and then through another coating ring 18.

[0050] As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figures 1-4 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figures 6-7 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. As shown, the coating ring 18 and the interruption ring 19 can have a circular shape.

[0051] As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figure 5 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figure 8 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. As shown, the coating ring 18 and the interruption ring 19 can have a circular shape.

[0052] As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. As shown, the coating ring 18 and the interruption ring 19 can have a circular shape.

[0053] As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figure 3 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figure 4 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figure 5 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. As shown, the coating ring 18 and the interruption ring 19 can have a circular shape.

[0054] As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. Figures 1-2 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 19 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 18 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 19 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 18 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. C As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. I As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. I As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. C As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 19 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 19 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. 18 As shown, the coating ring 18 and the interruption ring 19 can have a circular shape. As shown, the coating ring 18 and the interruption ring 19 can have a circular shape.

[0055] The ease of manufacturing the electric field lines and the desired shape can be used to determine the appropriate method. Figures 1-5 Choose between the designs.

[0056] The thickness Th of interrupted ring 19 19 and the thickness Th of the coating ring 18 18 Smooth, linear, or gradual transitions in material thickness can reduce sharp electric field gradients.

[0057] like Figure 1 and Figure 3 As shown, the transition region 17 may contain the same chemical elements as the coating ring 18 and the interrupted ring 19. The transition region 17 may have the same material composition as the coating ring 18 and the interrupted ring 19.

[0058] The transition region can have a thickness Th from the coating ring 18 18 The thickness Th to interrupt ring 19 19 Thickness Th 17 Smooth changes ( Figure 3 Th 19 =0).

[0059] Transition region 17 can be applied to any other example described here.

[0060] The coating ring 18 and the interrupted ring 19 can have the same material composition. For example, Figure 2 The interrupted ring 19 can be formed by coating the inner surface of the housing and then grinding, sandblasting, or wiping away part of the coating. The coating ring 18 and the interrupted ring 19 may include titanium oxide, chromium oxide, or both.

[0061] The coating ring 18 and the interrupted ring 19 can have different material compositions from each other. For example, Figure 3 , Figure 4 and Figure 5 The interruption ring 19 can be formed by removing all coatings, or by not depositing a coating on the inner surface of the housing at the desired location of the interruption ring 19. Thus, for example, the coating ring 18 may include titanium oxide, chromium oxide, or both; and the interruption ring 19 may not have titanium oxide, chromium oxide, or neither. As another example, the coating ring 18 and the interruption ring 19 may have different metal oxides (i.e., no common metal oxide).

[0062] The width W of the interruption ring 19 I The width W of the cylinder 15 between the cathode 11 and the anode 12 can be... C Approximately 12%. For example, 0.01 ≤ W I / W C 0.05≤W I / W Cor 0.10 < W I / W C ; and W I / W C ≤ 0.15, W I / W C ≤ 0.20, W I / W C ≤ 0.40, W I / W C ≤ 0.60, W I / W C ≤ 0.90. W I is the width of the interrupt ring 19, and W C is the width of the cylinder 15 between the cathode 11 and the anode 12, each measured parallel to the longitudinal axis 16 (see Figure 2 and Figure 4 ). If there are multiple interrupt rings 19, each interrupt ring can have a width W I within the bounds described in this paragraph.

[0063] The width W1, thickness Th 19 , location, and material of the interrupt ring 19 can be adjusted for a desired resistivity to control the high voltage field and the flow of electrons along the inner surface of the envelope.

[0064] Representations of the half x-ray tubes 110 and 120, plus equipotential lines 123, are shown in Figures 11-12 . The half x-ray tube 110 has the coating ring 18 but no interrupt ring 19. The half x-ray tube 120 has the coating ring 18 and the interrupt ring 19. The interrupt ring 19 of the half x-ray tube 120 is close to the anode 12, like the x-ray tube 20.

[0065] The equipotential lines 123 near the triple point 121 of the half x-ray tube 110 are closer to each other than the equipotential lines of the half x-ray tube 120. Thus, the interrupt ring 19 of the half x-ray tube 120 protects the triple point 121 by spacing the equipotential lines 123 near the triple point 121.

[0066] The equipotential lines 123 in the half x-ray tube 120 converge due to the interrupt ring 19 at the location 122. This convergence of the equipotential lines 123 can be moved to different locations to shape or direct the electron beam. Thus, the location, size, and resistance of the interrupt ring 19 are tools for improving x-ray tube design.

[0067] Method

[0068] A method of manufacturing an envelope to insulate a cathode 11 from an anode 12 in an x-ray tube, such as the envelope described above, can include some or all of the following steps. The envelope, coating ring 18, and interrupt ring 19 can have the properties described above. The cylinder 15 is in Figures 13-15As shown, it can be replaced by disk 62.

[0069] The method may include: (a) forming a coating ring 18 and an interruption ring 19 on the inner surface of the housing (see Figures 13-15 (b) Generate a current path 51 through the series-connected coated ring 18 and interrupted ring 19 (see Figures 1-8 ).

[0070] The coating ring 18 and the interrupted ring 19 may each surround the longitudinal axis 16 of the housing (e.g., cylinder 15) at different positions relative to each other along the longitudinal axis 16, such as... Figures 1-5 As shown. The coating ring 18 and the interrupted ring 19 may each surround the longitudinal axis 16 of the housing (e.g., disk 62) with different radii relative to each other from the longitudinal axis 16 outwards, as... Figures 6-10 As shown.

[0071] Forming the coating ring 18 and the interruption ring 19 may include a masking ring on the inner surface of the housing and coating the unmasked portion of the inner surface. For example... Figure 13 As shown, mask 139 prevents deposition tool 131 from coating the area covered by mask 139. After forming a coating ring 18 in the unmasked area by depositing material from deposition tool 131, mask 139 can be removed to expose interrupted ring 19. Therefore, interrupted ring 19 can be below the masked portion of the inner surface and can be uncoated. Therefore, interrupted ring 19 can have (a) a higher bulk resistivity (ρ) than coating ring 18. I >ρ C (b) The resistance per unit length is higher than that of the coating ring by 18 (R). I >R C (c) The volume resistivity is equal to the shell resistivity (ρ). I =ρ E ).

[0072] Forming the coating ring 18 and the interrupted ring 19 may involve coating the inner surface of the housing, and then removing part or all of the coating ring to form the interrupted ring 19. For example... Figure 14 As shown, removal tool 141 (e.g., brush, rag, sandblaster, grinder, or chemical sprayer) can remove material to form interrupted rings 19. Example methods of this removal include grinding, sandblasting, wiping off the coating, and chemical removal. The coating may be easier to remove before baking it in an oven. See Figures 1-10 .

[0073] If a portion of the thickness of the coating ring is removed by the removal tool 141 to form an interrupted ring 19, then (a) the interrupted ring 19 can have a volume resistivity (ρ) equal to that of the coating ring 18. I =ρ C (b) The resistance per unit length of the interrupted ring 19 is higher than that of the coated ring 18 (R).I >R C (c) Both the coating ring 18 and the interrupted ring 19 have a volume resistivity (ρ) less than that of the shell. I <ρ E and ρ C <ρ E ).See Figure 2 .

[0074] If the entire ring of the coating is removed by removal tool 141 to form an interrupted ring 19, the interrupted ring 19 may have (a) a higher volume resistivity (ρ) than the coated ring 18. I >ρ C (b) The resistance per unit length is higher than that of the coating ring by 18 (R). I >R C (c) The volume resistivity is equal to the shell resistivity (ρ). I =ρ E ).

[0075] Forming the coating ring 18 and the interrupted ring 19 may include depositing a coating with a tapered thickness on the inner surface. This can be accomplished by masking, adjusting the deposition time, or modifying other coating distribution characteristics of the coating tool.

[0076] like Figure 15 As shown, the spraying tool 151 can deposit a coating ring 18, and may also deposit thinner areas for interrupting the ring 19. The spraying tool 151 can form a helical or spiral coating, such as... Figure 5 and Figure 8 As shown. By adjusting the time or volumetric flow rate of the spraying tool 151 in different areas, a transition zone 17 can be formed, such as... Figure 1 and Figure 3 As shown.

Claims

1. An x-ray tube, comprising: a cathode and an anode electrically insulated from each other, the cathode configured to emit electrons toward the anode, and the anode configured to emit x-rays from the x-ray tube in response to electron impact from the cathode; a housing attached to the cathode and the anode and electrically insulating the cathode from the anode; a current path at an inner surface of the housing, the current path comprising a coating ring and an interrupt ring in series; R I >R C where R I is the resistance per unit length of the interrupt ring, and R C is the resistance per unit length of the coating ring, both measured along the current path; p C <ρ E where p C is the bulk resistivity of the coating ring, and p E is the bulk resistivity of the outer shell; and the coating ring encircling a longitudinal axis of the housing, the coating ring being on the inner surface, the interrupt ring encircling the longitudinal axis, and the interrupt ring being distinct from the coating ring, wherein the interrupt ring contains the same chemical element as the coating ring, but the thickness of the interrupt ring is less than the thickness of the coating ring.

2. The x-ray tube of claim 1, wherein, the coating ring is adjacent to the cathode.

3. The x-ray tube of claim 1, further comprising a transition region between the interrupt ring and the coating ring, the transition region providing a smooth transition of electrical resistance per unit length between R I and R C .

4. The x-ray tube of claim 1, wherein, the interrupt ring is on an inner surface of an electrically insulating disc, and the disc encircles at least part of the cathode or at least part of the anode; and the interrupt ring encircles the longitudinal axis at a different radius than the coating ring.

5. The x-ray tube of claim 1, wherein, the interrupt ring encircles the longitudinal axis at a different position along the longitudinal axis than the coating ring.

6. The x-ray tube of claim 1, wherein, 0.05 < W I / W C < 0.90, where W I is the width of the interrupt ring, and W C is the width of the cylinder of the outer shell between the cathode and the anode, each measured parallel to the longitudinal axis.

7. The x-ray tube of claim 1, wherein, the material of the coating ring is coated on the outside of a cylinder of the housing.

8. A method of manufacturing the x-ray tube of claim 1, the method comprising coating the inner surface of the housing, and then removing a ring of the coating to form the interrupt ring.

9. A method of manufacturing a housing for an x-ray tube, the method comprising: masking a ring at an inner surface of the housing; coating the unmasked portion of the inner surface, forming an interrupted ring at the masked portion of the inner surface, forming a coated ring at the coated portion of the inner surface, wherein p I = p E and p I > p C and p I is the bulk resistivity of the interrupted ring, p E is the bulk resistivity of the outer shell, and p C is the bulk resistivity of the coated ring, wherein the interrupt ring contains the same chemical element as the coating ring, but the thickness of the interrupt ring is less than the thickness of the coating ring.

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