Cathode structure, method for designing a cathode structure, and X-ray tube

Abstract

The present invention provides a cathode structure that can suppress the generation of secondary focal points and obtain a focal point of desired dimensions, a method for designing such a cathode structure, and an X-ray tube. [Solution] The cathode structure of the X-ray tube comprises an electron emission source that emits an electron beam, and a focusing body that has a groove in which the electron emission source is housed and focuses the electron beam emitted from the electron emission source. The groove has a first groove in which the electron emission source is housed, a second groove in which the first groove is housed, and a projection that forms part of the inner wall surface of the first groove and narrows the distance between the inner wall surface of the first groove and the electron emission source. The first groove has an opening at a depth H1 from the opening of the second groove, and at least a part of its inner wall surface overlaps with a part of the inner wall surface of the second groove. The projection is located in the region where the inner wall surfaces of the first groove and the inner wall surfaces of the second groove overlap. The electron emission source is FH

Description

Technical Field

[0004]

[0001] The present disclosure relates to a cathode structure, a method for designing the cathode structure, and an X-ray tube.

Background Art

[0002] An X-ray tube is an electron tube that generates X-rays and is used in medical diagnostic devices, industrial non-destructive inspection devices, and the like.

[0003] The X-ray tube causes an electron beam generated by a cathode structure to collide with an anode target to generate X-rays. The cathode structure includes an electron emission source that emits an electron beam, a focusing body that focuses the electron beam emitted from the electron emission source, and the like.

[0004] The electron beam emitted from the cathode structure is focused by the focusing body to form a focal point on the anode target, but the electron density distribution is not uniform, resulting in a main focal point and a sub-focal point. The main focal point is the focal point formed by electrons emitted from the front surface of the electron emission source (the surface facing the anode target), and the sub-focal point is the focal point formed by electrons emitted from the sides and rear of the electron emission source.

[0005] In Patent Documents 1 and 2, it is proposed to suppress the generation of the sub-focal point by providing a groove portion with a predetermined shape in the focusing body (focusing electrode) and disposing the electron emission source in the groove portion.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] One embodiment of the technology disclosed herein provides a cathode structure, a method for designing the cathode structure, and an X-ray tube that can suppress the generation of a sub-focus and obtain a focus with a desired size. **Means for Solving the Problem**

[0008] [1] A cathode structure of an X-ray tube including an electron emission source that emits an electron beam and a focusing body that has a groove portion for accommodating the electron emission source and focuses the electron beam emitted from the electron emission source, wherein the groove portion includes a first groove portion for accommodating the electron emission source, a second groove portion for accommodating the first groove portion, and a protrusion portion that forms a part of the inner wall surface of the first groove portion and narrows the distance between the inner wall surface of the first groove portion and the electron emission source. The first groove portion has an opening at a position of depth H1 from the opening of the second groove portion, and at least a part of the inner wall surface is arranged to overlap a part of the inner wall surface of the second groove portion. The protrusion portion is arranged in a region where the inner wall surface of the first groove portion and the inner wall surface of the second groove portion overlap. When FH < H, the electron emission source is arranged to protrude by an amount FH from the opening of the first groove portion.

[0009] [2] The cathode structure according to [1], wherein the protrusion portion is provided at the opening of the first groove portion.

[0010] [3] The cathode structure according to [1] or [2], wherein the protrusion portion is detachable.

[0011] [4] The groove portion further has a frame body detachably attached to the opening of the first groove portion. The frame body has an opening smaller than the opening of the first groove portion. When the frame body is attached to the opening of the first groove portion, the portion protruding inside the opening of the first groove portion constitutes the protrusion portion. The cathode structure according to [3].

[0012] [5] The cathode structure according to any one of [1] to [4], wherein the surface of the protrusion portion facing the electron emission source is formed as an inclined surface.

[0013] [6] The cathode structure according to [5], wherein the protrusion portion has a triangular cross-section.

[0014] [7] The cathode structure according to any one of [1] to [6], wherein the distance Wα between the protrusion and the electron emission source and the protrusion amount FH of the electron emission source satisfy the relationship Wα / FH < 1.2.

[0015] [8] The cathode structure according to any one of [1] to [7], wherein the protrusion is made of tungsten.

[0016] [9] The cathode structure according to any one of [1] to [8], having a convex portion at the bottom of the second groove portion and provided with a first groove portion in the convex portion.

[0017]

[10] The cathode structure according to any one of [1] to [9], wherein the electron emission source is a coiled filament.

[0018]

[11] An X-ray tube comprising the cathode structure according to any one of [1] to

[10] , an anode structure that emits X-rays when collided with an electron beam emitted from the cathode structure, and an outer container that houses the cathode structure and the anode structure.

[0019]

[12] A method for designing a cathode structure of an X-ray tube, comprising an electron emission source that emits an electron beam and a focusing body that has a groove portion in which the electron emission source is accommodated and focuses the electron beam emitted from the electron emission source. The groove portion is provided with a first groove portion in which the electron emission source is accommodated, a second groove portion in which the first groove portion is accommodated, and a protrusion portion that constitutes a part of the inner wall surface of the first groove portion and narrows the interval between the inner wall surface of the first groove portion and the electron emission source. The first groove portion is provided with an opening at a position of a depth H1 from the opening of the second groove portion, and at least a part of the inner wall surface is arranged to overlap with a part of the inner wall surface of the second groove portion. The protrusion portion is arranged in a region where the inner wall surface of the first groove portion and the inner wall surface of the second groove portion overlap. When FH < H1, the electron emission source is arranged to protrude by a protrusion amount FH from the opening of the first groove portion. The relationship between the distance Wα between the protrusion portion and the electron emission source and the protrusion amount FH of the electron emission source is adjusted to adjust the focal width of the electron beam focused by the focusing body.

[0020]

[13] Adjust the ratio of the protrusion amount FH to the distance Wα to adjust the focal width of the electron beam focused by the focusing body, the cathode structure design method according to

[12] .

[0021]

[14] Adjust the focal width of the electron beam focused by the focusing body within the allowable range with respect to the focal designation, the cathode structure design method according to

[12] or

[13] .

Effect of the Invention

[0022] According to the present invention, the generation of the sub-focus can be suppressed, and a focus of a desired size can be obtained.

Brief Description of the Drawings

[0023] [Figure 1] A diagram showing the overall schematic configuration of the X-ray tube device [Figure 2] A plan view of the cathode structure as viewed from the target side [Figure 3] A cross-sectional view taken along line 3-3 of FIG. 2 [Figure 4] A cross-sectional view showing the configuration of the focusing groove [Figure 5] A graph showing the relationship between the ratio of the protrusion amount FH to the distance Wα and the focal width [Figure 6] A diagram comparing the ease of penetration of the electric field depending on the presence or absence of the overlapping region [Figure 7] A diagram explaining the difference in the action effect due to the difference in the cross-sectional shape of the protrusion [Figure 8] A diagram showing an example of a focusing groove having a detachable protrusion [Figure 9] A cross-sectional view taken along line 9-9 of FIG. 8 [Figure 10] A cross-sectional view taken along line 10-10 of FIG. 8

Modes for Carrying Out the Invention

[0024] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] FIG. 1 is a diagram showing the overall schematic configuration of the X-ray tube device.

[0026] As shown in Figure 1, the X-ray tube apparatus 1 comprises an X-ray tube 10 that generates X-rays, and a container 20 that houses the X-ray tube 10.

[0027] The X-ray tube 10 comprises a cathode structure 100 that generates an electron beam, an anode structure 12 to which a positive potential is applied to the cathode structure 100, and an enclosure 13 that holds the cathode structure 100 and the anode structure 12 in a vacuum atmosphere.

[0028] The cathode structure 100 comprises an electron emission source (cathode) that emits an electron beam, and a focusing electrode that acts as a focusing cap. The focusing electrode functions as an electron lens, focusing the electron beam emitted from the electron emission source toward the X-ray focal point on the anode structure 12. The electron emission source and the focusing electrode are at the same potential. Details of the cathode structure 100 will be described later.

[0029] The anode structure 12 comprises a target and an anode matrix, and has an overall disc shape. The target is made of a material with a high melting point and a large atomic number, such as tungsten. When an electron beam emitted from the cathode structure 100 collides with the X-ray focal spot on the target, X-rays are emitted from the X-ray focal spot. The anode matrix is ​​made of a material with high thermal conductivity, such as copper, and holds the target. The target and the anode matrix are at the same potential.

[0030] The enclosure 13 holds the cathode structure 100 and the anode structure 12 in a vacuum atmosphere, electrically insulating them from each other. The potential of the enclosure 13 is the ground potential. The cathode structure 100 is supported by the cathode structure support 14 and positioned in a predetermined location within the enclosure 13. The anode structure 12 is supported by the rotation support 15 and positioned in a predetermined location within the enclosure 13, and is held so as to be rotatable around its axis.

[0031] Electrons emitted from the cathode structure 100 are accelerated by the voltage applied between the cathode structure 100 and the anode structure 12 to form an electron beam 17. The electron beam 17 is focused by the focusing electric field formed by the focusing electrode and collides with the X-ray focal point on the target. When the electron beam 17 collides with the X-ray focal point on the target, X-rays 18 are generated from the X-ray focal point. The energy of the generated X-rays 18 is determined by the voltage (tube voltage) applied between the cathode structure 100 and the anode structure 12. The dose of the generated X-rays 18 is determined by the amount of electrons emitted from the cathode structure 100 (tube current) and the tube voltage.

[0032] Only about 1% of the energy of the electron beam 17 is converted into X-rays; most of the energy is converted into heat. The tube voltage of the X-ray tube 10 installed in medical equipment such as X-ray CT (Computed Tomography) devices is several hundred kV, and the tube current is several hundred mA. Therefore, the anode structure 12 is heated with a heat energy of several tens of kilowatts. To prevent overheating and melting due to such heating, the anode structure 12 is driven to rotate. The rotating support part 15 that holds the anode structure 12 is driven to rotate using the magnetic field generated by the excitation coil (stator) 16 as power. The excitation coil 16 is arranged on the outer circumference of the enclosure 13, surrounding the rotating support part 15. By rotating the anode structure 12, the position where the electron beam 17 collides changes continuously, and overheating and melting of the anode structure 12 is suppressed.

[0033] The X-ray tube 10 and excitation coil 16 are housed in a container 20. The container 20 is filled with insulating oil to insulate and cool the X-ray tube 10 and other components. The container 20 is also equipped with a radiation window 21. X-rays 18 generated from the X-ray focal spot are emitted outside the container 20 through the radiation window 21. The radiation window 21 is made of a material with a low atomic number, such as beryllium, which has high X-ray transmittance.

[0034] [Cathode structure] [Configuration and its design method] As described above, the cathode structure 100 is supported by the cathode structure support portion 14 and positioned in a predetermined location within the enclosure 13. The cathode structure support portion 14 has a cylindrical connecting portion 14a that is connected to the enclosure 13 and a holding portion 14b that holds the cathode structure 100, and provides insulating support for the cathode structure 100.

[0035] Figure 2 is a plan view of the cathode structure as seen from the target side. Figure 3 is a cross-sectional view of line 3-3 in Figure 2 (a cross-sectional view perpendicular to the longitudinal direction of the electron emission source). In Figures 2 and 3, the α-axis, β-axis, and γ-axis are three mutually orthogonal axes. The depth direction of the cathode structure 100 is the α-axis direction, the width direction is the β-axis direction, and the height direction is the γ-axis direction.

[0036] The cathode structure 100 includes an electron emission source that emits an electron beam and a focusing electrode 120 that acts as a focusing body.

[0037] At least one electron emission source is provided in the cathode structure 100. As an example, this embodiment will describe a case in which three electron emission sources are provided.

[0038] For example, a coiled filament, an oxide cathode, or an impregnated cathode can be used as the electron emission source. As an example, this embodiment will describe the case in which a directly heated coiled filament is used. The directly heated coiled filament (hereinafter referred to as "filament") is heated by passing an electric current through it and emits an electron beam.

[0039] The three filaments 110A, 110B, and 110C are each positioned along the α-axis. That is, the longitudinal direction (axial direction) of the coil is positioned parallel to the α-axis. In addition, the three filaments 110A, 110B, and 110C are positioned with spacing in the rotational direction R of the target.

[0040] In this embodiment, the three filaments 110A, 110B, and 110C are used such that, for example, filaments 110B and 110C are used as filaments for high focal length, and filament 110A is used as a filament for low focal length. For example, in this embodiment, the filaments 110B and 110C for high focal length are arranged symmetrically with the filament 110A for low focal length in between. That is, the filament 110A for low focal length is placed in the center, and the filaments 110B and 110C for high focal length are placed on either side of it. For example, the filaments 110B and 110C for high focal length are composed of filaments with more coil turns and / or a thicker wire diameter than the filament 110A for low focal length.

[0041] The focusing electrode 120 forms a focusing electric field to focus the electron beams emitted from the filaments 110A, 110B, and 110C onto the X-ray focus on the target. The focusing electrode 120 has focusing grooves 130A, 130B, and 130C on the surface facing the target, which accommodate the filaments 110A, 110B, and 110C. In this embodiment, the focusing grooves 130A, 130B, and 130C are examples of grooves.

[0042] The focusing grooves 130A, 130B, and 130C are provided for each filament 110A, 110B, and 110C. The focusing groove 130A, which accommodates the filament 110A, is positioned directly facing the target surface S (the surface of the target that constitutes the anode structure 12). The focusing grooves 130B and 130C, which accommodate the filaments 110B and 110C, are positioned symmetrically across the focusing groove 130A and are inclined with respect to the target surface S.

[0043] Figure 4 is a cross-sectional view showing the configuration of the focusing groove.

[0044] The basic configuration of the three focusing grooves 130A, 130B, and 130C is the same. Therefore, here we will describe the configuration of focusing groove 130. The filament housed in focusing groove 130 will be referred to as filament 110.

[0045] In Figure 4, the x, y, and z axes are three orthogonal axes. The longitudinal direction of the focusing groove 130 is the z-axis direction, the width direction is the x-axis direction, and the depth direction is the y-axis direction. The z-axis direction is the same as the arrangement direction of the filament 110 (α-axis direction). Therefore, the z-axis direction and the α-axis direction coincide.

[0046] As shown in Figure 4, the focusing groove 130 has a double groove structure consisting of a first groove 131 and a second groove 132. That is, it has a structure in which a groove is further arranged inside a groove. The first groove 131 is provided at the bottom of the second groove 132, and the second groove 132 is positioned to accommodate the first groove 131. The focusing groove 130 has a symmetrical shape in a cross section perpendicular to the longitudinal direction (z-axis direction). Therefore, the first groove 131 is positioned along the second groove 132 and is located in the center of the second groove 132 in the width direction (x-axis direction).

[0047] In this embodiment, both the first groove 131 and the second groove 132 are composed of straight grooves with a rectangular cross-section. That is, they are composed of straight grooves with opposing inner wall surfaces parallel and perpendicular to the bottom surface. Therefore, the first groove 131 is composed of straight grooves with opposing inner wall surfaces 131s parallel and perpendicular to the bottom surface 131b. Similarly, the second groove 132 is composed of straight grooves with opposing inner wall surfaces 132s parallel and perpendicular to the bottom surface 132b. In this embodiment, the first groove 131 is an example of the first groove section, and the second groove 132 is an example of the second groove section.

[0048] In the following, the inner wall surface 131s of the first groove 131 will be referred to as the first inner wall surface 131s, and the inner wall surface 132s of the second groove 132 will be referred to as the second inner wall surface 132s, distinguishing between the two (the inner wall surfaces of each groove). Similarly, the bottom surface 131b of the first groove 131 will be referred to as the first bottom surface 131b, and the bottom surface 132b of the second groove 132 will be referred to as the second bottom surface 132b, distinguishing between the two (the bottom surfaces of each groove).

[0049] The second groove 132 has a convex portion 133 at the bottom, and the first groove 131 is provided in the convex portion 133. In the present embodiment, the convex portion 133 has a trapezoidal cross-sectional shape and is arranged at the center in the width direction of the converging groove 130 with a width W3 (width on the bottom side of the groove). The width W3 of the convex portion 133 is set to be narrower than the width W2 of the second groove 132 (W3 < W2).

[0050] The convex portion 133 is arranged at a predetermined height H3 from the second bottom surface 132b. The convex portion 133 is provided inside the second groove 132, and further, the first groove 131 is provided in the convex portion 133. As a result, the first groove 131 and the second groove 132 are arranged with a partial overlap. That is, at least a part of the first inner wall surface 131s overlaps with a part of the second inner wall surface 132s. In the converging groove 130 of the present embodiment, the first inner wall surface 131s and the second inner wall surface 132s overlap by the height H3 of the convex portion 133.

[0051] The first groove 131 is provided to open at the end face of the convex portion 133. Therefore, the first groove 131 is provided to open at a position at a height H3 from the second bottom surface 132b.

[0052] The convex portion 133 is provided at a height H3 lower than the depth H2 of the second groove 132 (H3 < H2). That is, it is provided at a height that does not protrude from the opening 132o of the second groove 132 (hereinafter referred to as the "second opening 132o"). Therefore, the opening 131o of the first groove 131 (hereinafter referred to as the "first opening 131o") is also provided at a position that does not protrude from the second opening 132o, that is, at a position retracted inward from the second opening 132o. Specifically, the first opening 131o is provided at a position with a depth H1 from the second opening 132o (H1 = H2 - H3).

[0053] The filament 110 is housed in the first groove 131 and arranged at a predetermined position in the converging groove 130. Therefore, the first groove 131 has a width W1 capable of housing the filament 110. Specifically, the first groove 131 has a width W1 larger than the outer diameter Fd of the filament 110 (Fd < W1).

[0054] On the other hand, to suppress secondary focal points, it is effective to narrow the width W1 of the first groove 131. That is, it is effective to narrow the opening of the first groove 131 and reduce the distance (gap width) Wβ between the first inner wall surface 131s and the filament 110.

[0055] Therefore, in this embodiment, a projection 134 is provided on the first inner wall surface 131s, and the distance Wβ between the first inner wall surface 131s and the filament 110 is narrowed. The projection 134 constitutes a part of the first inner wall surface 131s and has the effect of substantially narrowing the width W1 of the first groove 131 (the width of the area excluding the projection 134).

[0056] The projection 134 is positioned in the region where the first inner wall surface 131s overlaps with the second inner wall surface 132s (the region with a height H3 of the protrusion 133). As an example, in this embodiment, the projection 134 is positioned at the location of the first opening 131o. That is, the first opening 131o is directly narrowed by the projection 134.

[0057] The first opening 131o, narrowed by the projection 134, has a width W4 (distance between opposing projections 134) that is narrower than the width W1 (distance between opposing first inner wall surfaces 131s) of the first groove 131 (W4 <W1)。

[0058] As shown in Figure 4, in this embodiment, the projection 134 has a triangular cross-sectional shape with a length Py in the depth direction (y-axis direction) of the groove and a length Px in the width direction (x-axis direction) of the groove, and the surface facing the filament 110 (the surface constituting the first inner wall surface 131s) is composed of an inclined surface 134s. The inclined surface 134s is composed of a surface that slopes inward from the first bottom surface 131b toward the first opening 131o. As a result, the first groove 131 is configured such that, in the vicinity of the first opening 131o, the width gradually narrows toward the first opening 131o, and becomes narrowest at the position of the first opening 131o.

[0059] As shown in Figure 4, a portion of the filament 110 protrudes from the first opening 131o and is positioned within the first groove 131.

[0060] The inventors of this application have found that secondary focal points can be suppressed more effectively by adjusting the amount FH of the filament 110 protruding from the first aperture 131o and the distance (gap width) Wα between the filament 110 and the projection 134. Specifically, they found that the focal width changes by changing the ratio of the protrusion amount FH to the distance Wα (Wα / FH).

[0061] Figure 5 is a graph showing the relationship between the ratio of the protrusion amount FH to the distance Wα and the focal width.

[0062] The graph in Figure 5 shows the test results from an experiment investigating how the focal width changes when the protrusion amount FH and distance Wα are varied in the focusing groove 130 with the configuration shown in Figure 4. In particular, Figure 5 shows an example when the nominal focal length is f1.2. In Figure 5, the horizontal axis is the ratio Wα / FH of the protrusion amount FH and distance Wα, and the vertical axis is the focal width [mm].

[0063] As shown in Figure 5, it can be confirmed that the focal width changes when the ratio Wα / FH, which is the ratio of the protrusion amount FH to the distance Wα, changes. Therefore, by adjusting the relationship between the protrusion amount FH and the distance Wα (Wα / FH), the occurrence of secondary focal points can be suppressed, and a focal point of the desired dimensions can be obtained.

[0064] For a focal spot nominal f1.2, the tolerance range is 1.20 to 1.70 mm (Japanese Industrial Standards, Medical X-ray Tube Equipment, JIS Z 4704). As can be seen from the graph in Figure 5, when the ratio of protrusion amount FH to distance Wα, Wα / FH, exceeds 1.2, it is confirmed that the upper limit of the tolerance range for the focal spot width (1.70 mm) is exceeded. Therefore, by setting the protrusion amount FH and distance Wα so that Wα / FH < 1.2, the width of the focused focal spot (focal spot width) can be kept within the tolerance range, and a focal spot of the desired dimensions can be obtained.

[0065] In this way, the relationship between the protrusion amount FH and the distance Wα is adjusted to control the width of the focal point. That is, the width of the focal point is adjusted so that it falls within the specified tolerance range for the nominal focal point being set. For example, if the nominal focal point is f2.0, the focal width is adjusted to fall within the range of 2.00 to 2.60 [mm]. If the nominal focal point is f1.50, the focal width is adjusted to fall within the range of 1.50 to 2.00 [mm]. If the nominal focal point is f1.0, the focal width is adjusted to fall within the range of 1.00 to 1.40 [mm]. If the nominal focal point is f0.8, the focal width is adjusted to fall within the range of 0.80 to 1.20 [mm]. If the nominal focal point is f0.6, the focal width is adjusted to fall within the range of 0.60 to 0.90 [mm].

[0066] Furthermore, if the distance Wα between the filament 110 and the projection 134 (the width of the gap) is set too narrow, the filament 110 is more likely to come into contact with the projection when it deforms due to heat (so-called filament touch). Therefore, it is preferable to set the projection amount FH that satisfies the conditions while ensuring the distance Wα.

[0067] [Effects and Effects] (1) Double groove structure As described above, in this embodiment, the cathode structure 100 has a double groove structure in the focusing groove 130 (130A, 130B, 130C) of the focusing electrode 120, consisting of a first groove 131 and a second groove 132, and the filament 110 (110A, 110B, 110C) is housed and arranged in the inner first groove 131.

[0068] The first groove 131 and the second groove 132 are arranged with some overlap. That is, at least a portion of the first inner wall surface 131s overlaps with a portion of the second inner wall surface 132s. This makes it easier for an electric field to enter the focusing groove 130. Therefore, the electron beam can be focused more easily.

[0069] Figure 6 is a diagram comparing the ease with which an electric field penetrates depending on the presence or absence of overlapping regions. Figure 6(A) shows an example of equipotential lines in a focusing groove where the first groove 131 and the second groove 132 are arranged in a partially overlapping manner (an embodiment of the present invention). Figure 6(B) shows an example of equipotential lines in a focusing groove where the first groove 131 and the second groove 132 are arranged without overlapping manner (a comparative example). In Figures 6(A) and (B), dashed lines represent equipotential lines.

[0070] As shown in Figure 6, the arrangement of the first groove 131 and the second groove 132 with some overlap allows the electric field to easily enter the focusing groove 130. Therefore, the electron beam can be focused more easily.

[0071] (2) Protrusions on the first inner wall surface Furthermore, in this embodiment, the focusing groove 130 is provided with a projection 134 on the inner wall surface (first inner wall surface) 131s of the first groove 131, thereby narrowing the distance (gap width) between the filament 110 housed in the first groove 131 and the first inner wall surface 131s. In particular, in this embodiment, the projection 134 is provided at the opening (first opening) 131o of the first groove 131, thereby narrowing the width W4 of the first opening 131o. That is, the first opening 131o is constricted. This makes it possible to suppress the occurrence of secondary focal points.

[0072] Furthermore, instead of simply narrowing the first aperture 131o, the amount of protrusion FH of the filament 110 and the distance Wα between the filament 110 and the projection 134 are adjusted so that the electron beam is focused to a predetermined focal width. In other words, the focal width is adjusted to fall within a defined tolerance range for the nominal focal width (if the nominal focal width is f1.2, the tolerance range is 1.20 to 1.70 [mm]). This allows a focal width of the desired dimensions to be obtained, that is, a focal width within the tolerance range is obtained.

[0073] (3) Shape of the protrusion Furthermore, in this embodiment, the projection 134 has a triangular cross-section, and the surface facing the filament 110 is composed of a slope 134s. This suppresses filament contact.

[0074] Figure 7 illustrates the differences in effects due to differences in the cross-sectional shape of the protrusions. Figure 7(A) shows an example of the arrangement relationship between the protrusion 134 and the filament 110 when the cross-sectional shape of the protrusion 134 is triangular (an embodiment of the present invention). Figure 7(B) shows an example of the arrangement relationship between the protrusion 134x and the filament 110 when the cross-sectional shape of the protrusion is rectangular (a comparative example).

[0075] Figures 7(A) and 7(B) both show examples where projections 134 and 134x are provided in the first opening 131o to narrow the width of the first opening 131o.

[0076] When a projection is provided in the first opening 131o to narrow the width of the first opening 131o to the same width W4, as shown in Figure 7(B), with a rectangular cross-section projection 134x, the distance between the projection 134x and the filament 110 decreases as you move towards the bottom of the first groove 131. That is, the gap with the filament 110 narrows. On the other hand, as shown in Figure 7(A), in the case of a triangular cross-section projection 134 (where the surface facing the filament 110 is composed of a slope 134s), the distance between the projection 134x and the filament 110 increases as you move towards the bottom of the first groove 131. That is, the gap with the filament 110 widens. Therefore, even if the filament 110 deforms or vibrates due to heat, for example, contact with the filament 110 can be suppressed.

[0077] [Differentiation] [Protrusion] The projection 134 may be provided as an integral part of the first groove 131, or it may be provided as a separate part of the first groove 131. If it is a separate part, it is preferable that the projection 134 be detachable (removable).

[0078] Figure 8 shows an example of a convergence groove having a detachable projection. Figure 8 is a plan view of the convergence groove as seen from the opening side. Figure 9 is a cross-sectional view of line 9-9 in Figure 8. Figure 10 is a cross-sectional view of line 10-10 in Figure 8.

[0079] As shown in Figures 8 to 10, in this example, the convergence groove 130 has a frame 135 attached to the tip of the protrusion 133 that narrows the opening of the first groove 131.

[0080] The frame 135 has a rectangular flat plate shape and is fixed to the tip surface of the protrusion 133 using screws 136. The protrusion 133 is provided with multiple screw holes 133h (two in this example) for fixing the frame 135. By fixing it with screws 136, the frame 135 has a configuration that allows it to be attached to and detached from the protrusion 133.

[0081] The frame 135 has a rectangular opening 135o. The opening 135o of the frame 135 has a width narrower than the groove width of the first groove 131. Therefore, when the frame 135 is attached to the protrusion 133, the opening of the first groove 131 is narrowed in the width direction.

[0082] When the frame 135 is attached to the protrusion 133, the opening 135o of the frame 135 forms the opening of the first groove 131.

[0083] Furthermore, the frame 135 is attached to the protrusion 133, and the portion that extends from the inner wall surface 131s of the first groove 131 constitutes the projection 134. The portion constituting the projection 134 is preferably triangular in cross-section.

[0084] Thus, the projection 134 can be made detachable. Making the projection 134 detachable makes assembly easier.

[0085] If the projection 134 is made of a separate part, it is preferable to make the material constituting the projection 134 from a material with a low coefficient of thermal expansion, such as tungsten. This suppresses changes in the groove width, and more specifically the width of the first opening, due to thermal expansion. Alternatively, the entire convergence groove 130, including the projection 134, may be molded from a material with a low coefficient of thermal expansion.

[0086] [Other variations] In the above embodiment, an example was described in which a single cathode structure is equipped with multiple electron emission sources, but it is sufficient to have at least one electron emission source. The focusing electrode is equipped with the same number of focusing grooves as the electron emission sources. Therefore, if there is one electron emission source, there is also one focusing groove.

[0087] Furthermore, the type of electron emission source used is not particularly limited, and an electron emission source with a configuration other than a coiled filament may be used.

[0088] Furthermore, although the above embodiment described the case in which the present invention is applied to an X-ray tube in which the anode rotates (rotating anode X-ray tube), the present invention can be similarly applied to an X-ray tube in which the anode is fixed (fixed anode X-ray tube).

[0089] Furthermore, in this specification, the terms “same” and “identical” include not only the meaning of completely identical, but also the meaning of “approximately identical,” which includes tolerances in design and manufacturing. Furthermore, in this specification, the term “orthogonal” includes not only the meaning of completely orthogonal, but also the meaning of “approximately orthogonal,” which includes tolerances in design and manufacturing. Furthermore, in this specification, the term “parallel” includes not only the meaning of completely parallel, but also the meaning of “approximately parallel,” which includes tolerances in design and manufacturing. Furthermore, in this specification, the term “perpendicular” includes not only the meaning of completely perpendicular, but also the meaning of “approximately perpendicular,” which includes tolerances in design and manufacturing. [Explanation of Symbols]

[0090] 1...X-ray tube device 10...X-ray tube 12… Anode structure 13...Envelope 14...Cathode structure support part 14a...Connection part 14b...Holding part 15... Rotating support part 16…Excitation coil 17… Electron beam 18...X-ray 20…Container 21... Radiation window 100... Cathode structure 110…Filament 110A…Filament 110B…Filament 110C…Filament 120…Focusing electrode 130…Focusing groove 130A…Focusing groove 130B…Focusing groove 130C…Focusing groove 131…1st groove 131b...First bottom surface (bottom surface of the first groove) 131o...First opening (opening of the first groove) 131s...First inner wall surface (inner wall surface of the first groove) 132…Second groove 132b...Second base (bottom surface of the second groove) 132o...Second opening (opening of the second groove) 132s... Second inner wall surface (inner wall surface of the second groove) 133... protruding part 133h... Screw hole 134...Protrusion 134s... Inclined surface (the surface facing the filament of the protrusion) 134x…Protrusion 135...Frame body 135o...Opening of the frame 136... Screw FH...Filament protrusion from the first opening Fd... outer diameter of the filament H1... Depth from the second opening H2…Depth of the second groove H3... Height of the protrusion R...Target rotation direction S...Target surface W1...Width of the first groove W2…Width of the second groove W3...Width of the protruding part W4…Width of the first opening (distance between opposing protrusions) Wα… The distance between the filament and the projection (the width of the gap). Wβ… Distance between the first inner wall surface and the filament (width of the gap)

Claims

1. A cathode structure for an X-ray tube comprising an electron emission source that emits an electron beam, and a focusing body having a groove in which the electron emission source is housed and which focuses the electron beam emitted from the electron emission source, The groove portion is The first groove portion in which the electron emission source is housed, The second groove portion in which the first groove portion is housed, A projection that forms part of the inner wall surface of the first groove and narrows the gap between the inner wall surface of the first groove and the electron emission source, It has, The first groove has an opening at a depth H1 from the opening of the second groove, and at least a portion of its inner wall surface overlaps with a portion of the inner wall surface of the second groove. The projection is positioned in the region where the inner wall surface of the first groove and the inner wall surface of the second groove overlap. When FH < H1, the electron emission source is positioned so that a portion of it protrudes from the opening of the first groove by an amount FH. Cathode structure.

2. The projection is provided in the opening of the first groove. The cathode structure according to claim 1.

3. The aforementioned projection is detachable. The cathode structure according to claim 2.

4. The groove portion further comprises a frame that is detachably attached to the opening of the first groove portion. The frame has an opening smaller than the opening of the first groove, and when the frame is attached to the opening of the first groove, the portion that protrudes inward from the opening of the first groove constitutes the projection. The cathode structure according to claim 3.

5. The projection has a surface facing the electron emission source that is sloped. The cathode structure according to any one of claims 1 to 4.

6. The aforementioned projection has a triangular cross-section. The cathode structure according to claim 5.

7. The distance Wα between the projection and the electron emission source and the amount of protrusion FH of the electron emission source are such that Wα / FH < 1.

2. The cathode structure according to any one of claims 1 to 4.

8. The aforementioned protrusion is made of tungsten. The cathode structure according to any one of claims 1 to 4.

9. The bottom of the second groove has a protrusion, The protrusion is provided with the first groove. The cathode structure according to any one of claims 1 to 4.

10. The electron emission source is a coiled filament. The cathode structure according to any one of claims 1 to 4.

11. A cathode structure according to any one of claims 1 to 4, An anode structure that emits X-rays upon collision with an electron beam emitted from the cathode structure, An enclosure housing the cathode structure and the anode structure, An X-ray tube equipped with [a specific feature / equipment].

12. A method for designing a cathode structure for an X-ray tube, comprising an electron emission source that emits an electron beam, and a focusing body having a groove in which the electron emission source is housed and which focuses the electron beam emitted from the electron emission source, The groove portion includes a first groove portion in which the electron emission source is housed, a second groove portion in which the first groove portion is housed, and a projection portion which forms part of the inner wall surface of the first groove portion and narrows the distance between the inner wall surface of the first groove portion and the electron emission source. The first groove has an opening at a depth H1 from the opening of the second groove, and at least a portion of its inner wall surface overlaps with a portion of the inner wall surface of the second groove. The projection is positioned in the region where the inner wall surface of the first groove and the inner wall surface of the second groove overlap. The electron emission source is positioned such that, when FH < H1, a portion of it protrudes from the opening of the first groove by a protrusion amount FH. The relationship between the distance Wα between the projection and the electron emission source and the protrusion amount FH of the electron emission source is adjusted to adjust the focal width of the electron beam focused by the focusing body. Cathode structure design method.

13. The ratio of the protrusion amount FH to the distance Wα is adjusted to adjust the focal width of the electron beam focused by the focusing device. A method for designing a cathode structure according to claim 12.

14. The focal width of the electron beam focused by the aforementioned focusing device is adjusted to within the acceptable range for the nominal focal point. A method for designing a cathode structure according to claim 12 or 13.

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