Emitter structure and electron gun

Abstract

Provided are an emitter structure and an electron gun that are capable of suppressing occurrence of distortion in an emitter.　An emitter structure (81) comprises an emitter (84), a pair of support rod members (85, 86), a first insulator (87), a second insulator (88), and a thermal expansion member (89). The thermal expansion member has an opposite surface (89a) that is opposite to a heat release surface (84b) of the emitter across a gap therebetween and that receives radiant heat from the heat release surface. The thermal expansion member is electrically insulated from the pair of support rod members by the first insulator and the second insulator. When the temperature of the opposite surface has risen upon receiving radiant heat from the heat release surface, the thermal expansion member expands in the extension direction (X) thereof and thereby causes a force to act on the pair of support rod members.

Description

Emitter structure and electron gun

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention relate to an emitter structure and an electron gun.

[0002] X-ray tubes are used for X-ray imaging diagnostics and non-destructive testing. X-ray tubes are classified as fixed anode X-ray tubes or rotating anode X-ray tubes, with the type used being appropriate for the application. For example, rotating anode X-ray tubes are commonly used for medical diagnostics. An X-ray tube includes an anode target, a cathode electron gun, and an envelope. An electron beam is incident on the anode target, forming a focal spot that emits X-rays. The cathode electron gun includes an emitter that emits electrons and a focusing electrode (electron focusing cup). The emitter is heated by the supply of current, emitting electrons. It is known that the emitter deforms due to thermal expansion during this process.

[0003] JP 2017-111854 A

[0004] The present embodiment provides an emitter structure and an electron gun that can suppress distortion of the emitter.

[0005] An emitter structure according to one embodiment comprises an emitter extending in a plate-like shape and having an electron emission surface that emits electrons, and a heat emission surface located opposite the electron emission surface and generating thermal radiation; a pair of support rods positioned on either side of the electron emission surface and the heat emission surface in the extension direction of the emitter, electrically connected to the emitter and fixing the emitter; a first insulator attached to one of the pair of support rods; a second insulator attached to the other of the pair of support rods; and a thermal expansion member extending in the extension direction, wherein the thermal expansion member faces the heat emission surface with a gap between them and has an opposing surface that receives radiant heat from the heat emission surface, and is electrically insulated from the pair of support rods by the first insulator and the second insulator; and when the temperature of the opposing surface rises due to radiant heat from the heat emission surface, the thermal expansion member expands in the extension direction and exerts a force on the pair of support rods.

[0006] In addition, an emitter structure according to one embodiment comprises an emitter extending in a plate-like shape and having an electron emission surface that emits electrons, and a heat emission surface located opposite the electron emission surface and generating thermal radiation; a pair of support rods positioned on either side of the electron emission surface and the heat emission surface in the extension direction of the emitter, electrically connected to the emitter and fixing the emitter; a first insulator attached to one of the pair of support rods; and a thermal expansion member extending in the extension direction, wherein the thermal expansion member faces the heat emission surface with a gap between them and has an opposing surface that receives radiant heat from the heat emission surface, and is electrically insulated from one of the pair of support rods by the first insulator, and when the temperature of the opposing surface rises due to radiant heat from the heat emission surface, it expands in the extension direction and exerts a force on the pair of support rods.

[0007] An electron gun according to one embodiment includes an emitter structure including: an emitter extending in a plate shape and having an electron emission surface that emits electrons and a heat emission surface that is located on the opposite side of the electron emission surface and generates thermal radiation; a pair of support rods that are located on either side of the electron emission surface and the heat emission surface in the extension direction of the emitter and are electrically connected to the emitter to fix it; a first insulator attached to one of the pair of support rods; a second insulator attached to the other of the pair of support rods; and a thermal expansion member extending in the extension direction; The device comprises a support member that supports the pair of support rods via the second insulator and is electrically insulated from the pair of support rods by the first insulator and the second insulator, and a focusing electrode that fixes the support member and focuses electrons from the electron emission surface, wherein the thermal expansion member faces the heat emission surface with a gap between them and has an opposing surface that receives radiant heat from the heat emission surface, is electrically insulated from the pair of support rods by the first insulator and the second insulator, and when the temperature of the opposing surface rises due to radiant heat from the heat emission surface, it expands in the extension direction and applies a force to the pair of support rods.

[0008] Fig. 1 is a cross-sectional view showing an X-ray tube assembly according to a first embodiment. Fig. 2 is a plan view of an electron gun in the direction of an arrow A in Fig. 1. Fig. 3 is a cross-sectional view of the electron gun taken along line B-B in Fig. 2. Fig. 4 is a perspective view showing the emitter structure and support member shown in Fig. 3. Fig. 5 is a cross-sectional view showing a state before the emitter is fixed to a support rod. Fig. 6 is a cross-sectional view of an electron gun according to a second embodiment.

[0009] Each embodiment of the present invention will be described below with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily make while maintaining the spirit of the invention are naturally included within the scope of the present invention. Furthermore, to clarify the drawings and explanations, the width, thickness, shape, etc. of each part may be shown schematically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the previous drawings may be designated by the same reference numerals, and detailed descriptions may be omitted where appropriate.

[0010] First, the basic concept of an embodiment of the present invention will be described. An X-ray tube includes an anode target, a cathode electron gun, an envelope, etc. The cathode electron gun includes an emitter and a focusing electrode, etc. When a high voltage of several tens to several hundreds of kV is applied between the anode target and the cathode electron gun, electrons emitted from the emitter are accelerated toward the anode target. At this time, the focusing electrode acts as an electron lens, focusing the electrons toward the anode target.

[0011] X-ray tubes typically have two foci: a large focus that is large and can accept a large current, and a small focus that is small and accepts less current but has high resolution. Some X-ray tubes have three foci. The size of each focus depends on the shape and positional relationship between the emitter and the focusing electrode, and is usually fixed. When using a large or small focus, the imaging conditions are determined by determining the spatial resolution and input current (which affect contrast and noise) according to the diagnostic purpose, and the large or small focus is used accordingly.

[0012] However, with only two foci, the imaging conditions are discontinuous, and it may not be possible to obtain the images necessary for X-ray imaging diagnosis. In particular, when performing continuous imaging in the axial direction of the subject, such as with helical scanning in an X-ray CT scanner, the variable input due to discontinuous two foci may not maintain continuity in image quality, making accurate image diagnosis impossible. Furthermore, the amount of X-rays emitted must be adjusted to suit each individual patient; for example, the amount of X-rays emitted to a large patient is higher than that emitted to a small child. Because this amount of X-rays depends on the amount of current supplied to the emitter of the cathode electron gun, the structure of the cathode electron gun and the design of the emitter are important.

[0013] When conventional filament coils are used as electron emission sources, various issues arise, such as the need for large currents, current controllability, and focal spot size controllability. To address these issues, plate-shaped emitters (flat emitters) are increasingly being used as electron emission sources. Plate-shaped emitters have a flat surface from which electrons are emitted, making it easier to control the electron beam flux that forms the focal spot size. This allows for a larger electron-emitting area, which also allows for a larger current.

[0014] On the other hand, the temperature of the emitter rises when current is supplied. This causes a problem of deformation of the emitter's shape. The amount of electrons emitted from the emitter (electron quantity) depends on the distance between the emitter and the focusing electrode. In other words, if the emitter distorts due to thermal expansion, the amount of electrons emitted from the emitter changes. The amount of X-rays emitted from the focal spot changes in response to changes in the amount of emitted electrons, which changes the performance of an image evaluation device such as an X-ray CT scanner. Therefore, embodiments of the present invention address this problem by providing an emitter structure and an electron gun that can suppress distortion of the emitter when the emitter temperature rises.

[0015] 1 is a cross-sectional view showing an X-ray tube assembly according to the first embodiment. As shown in Fig. 1, the X-ray tube assembly includes a rotating anode X-ray tube (hereinafter also referred to as a "rotating anode X-ray tube") 1, a stator coil 2 as a coil for generating a magnetic field, a housing 3 that accommodates the rotating anode X-ray tube 1 and the stator coil 2, and a coolant 4 filled in the housing 3.

[0016] The rotating anode X-ray tube 1 includes a rotation mechanism 5, an anode target 50, a cathode electron gun (hereinafter also simply referred to as "electron gun") 80, and an envelope 70. The rotation mechanism 5 includes a fixed shaft 10, a rotating body 20, a bearing 30, and a rotor 40. The fixed shaft 10 is formed in a cylindrical shape and extends along a rotation axis a. The fixed shaft 10 is made of a metal such as an Fe (iron) alloy or an Mo (molybdenum) alloy. The rotating body 20 is configured to be rotatable around the fixed shaft 10. The rotating body 20 is made of a metal such as an Fe alloy or an Mo alloy.

[0017] The bearing 30 is formed between the fixed shaft 10 and the rotating body 20. The bearing 30 supports the rotating body 20 so that it can rotate around the fixed shaft 10. In one example, the bearing 30 has ball bearings 31 and 32. The ball bearings 31, 32 are fixed between the fixed shaft 10 and the rotating body 20. One method for fixing the ball bearings 31, 32 is to provide the ball bearings 31, 32 on the fixed shaft 10, heat the rotating body 20, and then press-fit the fixed shaft 10 and the ball bearings 31, 32 into the rotating body 20 by shrink fitting.

[0018] The bearing 30 is not limited to the ball bearings 31 and 32, and may be configured as, for example, a plain bearing having radial bearing surfaces on the outer peripheral surface of the fixed shaft 10 and the inner peripheral surface of the rotating body 20. In this case, liquid metal is filled as a lubricant between the fixed shaft 10 and the rotating body 20. The rotor 40 is formed in a cylindrical shape extending along the rotation axis a, and is fixed to the outer peripheral surface of the rotating body 20. The rotor 40 can be fixed to the rotating body 20 by brazing, for example.

[0019] The anode target 50 is formed in an umbrella-like, approximately disc-like shape and is disposed coaxially with the fixed shaft 10 and the rotor 20. The anode target 50 includes an anode target body 51 and a target layer 52 disposed on a portion of the outer surface of the anode target body 51. The anode target body 51 is formed of molybdenum, tungsten, or a metal containing these. The melting point of the metal forming the target layer 52 is the same as or higher than the melting point of the metal forming the anode target body 51. For example, the anode target body 51 is formed of a molybdenum alloy, and the target layer 52 is formed of a tungsten alloy. The anode target 50 is rotatable together with the rotor 20. When electrons collide with a target surface S52 of the target layer 52, a focal spot is formed on the target surface S52. As a result, the anode target 50 emits X-rays from the focal spot.

[0020] The electron gun 80 is disposed facing the target layer 52 of the anode target 50 with a gap therebetween. The electron gun 80 is supported by a cathode support 60 fixed to the envelope 70. The electron gun 80 has an emitter structure 81. When a high voltage is applied, the electron gun 80 emits electrons toward the anode target 50. The cathode support 60 has a cavity through which passes wiring 61 that connects the electron gun 80 to a power supply (not shown). Details of the electron gun 80 and the emitter structure 81 will be described later in connection with FIGS. 2, 3, and 4.

[0021] The envelope 70 is formed in a cylindrical shape. The envelope 70 is made of glass, ceramic, and metal. The outer diameter of the portion of the envelope 70 facing the anode target 50 is larger than the outer diameter of the portion facing the rotor 40. The envelope 70 has an opening 71 and an X-ray transmission window 72 that transmits X-rays. The envelope 70 is sealed, houses the anode target 50 and the electron gun 80, and fixes the fixed shaft 10. The interior of the envelope 70 is maintained in a vacuum state (reduced pressure state).

[0022] The stator coil 2 is disposed facing the outer peripheral surface of the rotor 40 and surrounding the outside of the enclosure 70. The stator coil 2 is annular in shape. The stator coil 2 generates a magnetic field that is applied to the rotor 40 (rotating body 20), causing the rotating body 20 and the anode target 50 to rotate. The housing 3 is cylindrical in shape. The housing 3 is formed of a brittle material such as aluminum casting. A lead plate that shields X-rays is attached to the inner surface of the housing 3. The coolant 4 fills the space between the rotating anode X-ray tube 1 and the housing 3. The coolant 4 can be insulating oil or a water-based coolant.

[0023] FIG. 2 is a plan view of the electron gun 80 as viewed along arrow A in FIG. 1 . FIG. 3 is a cross-sectional view of the electron gun 80 taken along line B-B in FIG. 2 . FIG. 4 is a perspective view of the emitter structure 81 and support member 82 shown in FIG. 3 . As shown in FIGS. 2 , 3 , and 4 , the electron gun 80 includes the emitter structure 81, the support member 82, and a focusing electrode 83. The emitter structure 81 includes an emitter 84, a pair of support rods 85 and 86, a first insulator 87, a second insulator 88, a thermal expansion member 89, and a sleeve 90. The emitter 84 extends in a plate shape and includes an electron emission surface 84a that emits electrons, a heat emission surface 84b located opposite the electron emission surface 84a and generating thermal radiation, and multiple slits 84c. The electron emission surface 84a faces the anode target 50. In one example, the heat emission surface 84b is a surface parallel to the electron emission surface 84a.

[0024] The multiple slits 84c penetrate from the electron emission surface 84a to the heat emission surface 84b, forming a current path for current flowing through the emitter 84. More specifically, the multiple slits 84c form a current path through the electron emission surface 84a, the heat emission surface 84b, and the region between the electron emission surface 84a and the heat emission surface 84b. The emitter 84 further has one end surface 84f parallel to the electron emission surface 84a and perpendicular to the extension direction X, and another end surface 84g opposite the one end surface 84f. In one example, the multiple slits 84c are composed of a first slit 84c1 formed by recessing the one end surface 84f and a second slit 84c2 formed by recessing the other end surface 84c2. In one example, the first slits 84c1 and the second slits 84c2 are arranged alternately along the extension direction X. This allows a continuous zigzag current path to be formed in the region of the emitter 84 having the electron emission surface 84a and heat emission surface 84b, ensuring the area of ​​the electron emission surface 84a that emits electrons. The emitter 84 is made of, for example, tungsten. The thermal expansion coefficient of tungsten is approximately 5.2×10 －６ / K. The emitter 84 further has connection portions 84d and 84e located on either side of the electron emission surface 84a and the heat emission surface 84b in the extension direction X of the emitter 84, and fitting holes H1 formed in the connection portions 84d and 84e. The fitting holes H1 are holes formed to penetrate in the orthogonal direction Y that is perpendicular to the electron emission surface 84a.

[0025] The support rod 85 is formed in a columnar shape extending in the orthogonal direction Y and has a large diameter portion 85a and a small diameter portion 85b. The support rod 86 is formed in the orthogonal direction Y and has a large diameter portion 86a and a small diameter portion 86b. The pair of support rods 85, 86 are positioned on either side of the electron emission surface 84a and the heat emission surface 84b in the extension direction X, are electrically connected to the emitter 84, and fix the emitter 84. The pair of support rods 85, 86 have a first groove G1 and a second groove G2. The first groove G1 is formed by recessing the upper surfaces of the large diameter portions 85a, 86a. The first groove G1 accommodates the connection portions 84d, 84e. The second groove G2 is formed by recessing the upper surface of the first groove G1 and is a groove extending in the extension direction X. Both ends of the second groove G2 in the extension direction X are formed in an arc shape in a plan view. Note that the second groove G2 is not limited to a groove with both ends formed in an arc shape, and may be, for example, a groove with a rectangular shape in a plan view. The second groove G2 is used when positioning the emitter 84 with respect to the support rods 85, 86.

[0026] The support rods 85, 86 fix the emitter 84 by joining the large-diameter portion 85a to the connecting portion 84d and the large-diameter portion 86a to the connecting portion 84e. The support rods 85, 86 are electrically connected to the emitter 84 by contacting the large-diameter portion 85a with the connecting portion 84d and the large-diameter portion 86a with the connecting portion 84e. The material of the pair of support rods 85, 86 is, for example, molybdenum. The emitter 84 is fixed to the pair of support rods 85, 86 under a tensile load in the extension direction X at room temperature. The procedure for fixing the emitter 84 to the pair of support rods 85, 86 will be described later with reference to FIG. 5 . The emitter 84 may also be fixed to the pair of support rods 85, 86 under a tensile load.

[0027] The first insulator 87 is composed of three insulators 87a, 87b, and 87c. The first insulator 87 is attached to one of the pair of support rods 85 and 86 (support rod 85 in FIG. 2). The first insulator 87 is made of a ceramic material such as alumina (aluminum oxide), zirconia (zirconium oxide), or silicon nitride, and has electrical insulating properties. Each of the insulators 87a, 87b, and 87c has a through-hole H2 formed therethrough in the orthogonal direction Y. The small-diameter portion 85b of the support rod 85 is inserted into the through-hole H2.

[0028] The second insulator 88 is composed of three insulators 88a, 88b, and 88c. The second insulator 88 is attached to the other of the pair of support rods 85 and 86 (support rod 86 in FIG. 2). The second insulator 88 is made of a ceramic material such as alumina, zirconia, or silicon nitride and has electrical insulating properties. Each of the insulators 88a, 88b, and 88c has a through-hole H3 formed therethrough in the orthogonal direction Y. The small-diameter portion 86b of the support rod 86 is inserted into the through-hole H3.

[0029] The thermal expansion member 89 extends in the extension direction X and has an opposing surface 89a that faces the heat dissipation surface 84b with a gap therebetween and receives radiant heat from the heat dissipation surface 84b. The opposing surface 89a is parallel to the heat dissipation surface 84b. The thermal expansion member 89 further has a connecting portion 89b, a connecting portion 89c, a through hole H4 formed in the connecting portion 89b, and a through hole H5 formed in the connecting portion 89c. The connecting portion 89b and the connecting portion 89c are located on either side of the opposing surface 89a. The through hole H4 is a hole that penetrates the connecting portion 89b in the orthogonal direction Y. The through hole H5 is a hole that penetrates the connecting portion 89c in the orthogonal direction Y.

[0030] The thermal expansion member 89 is fixed to the pair of support rods 85, 86 via a first insulator 87 and a second insulator 88. Specifically, the thermal expansion member 89 is fixed to the pair of support rods 85, 86 by sandwiching the connecting portion 89b of the thermal expansion member 89 between the insulators 87a and 87b, so that the inner circumferential surface of the through hole H4 contacts the outer circumferential surface of the insulator 87a, and by sandwiching the connecting portion 89c between the insulators 88a and 88b, so that the inner circumferential surface of the through hole H5 contacts the outer circumferential surface of the insulator 88a. Note that the thermal expansion member 89 does not necessarily have to be fixed to the support rods 85, 86. For example, the thermal expansion member 89 may be attached so as to be slightly movable relative to the support rods 85, 86. The thermal expansion member 89 is also electrically insulated from the pair of support rods 85, 86 by the first insulator 87 and the second insulator 88. The thermal expansion coefficient of the thermal expansion member 89 is larger than that of the emitter 84. The thermal expansion member 89 is made of, for example, copper (Cu) or a copper-based alloy. In this case, the thermal expansion coefficient of the thermal expansion member 89 is 15×10 －６ ~17×10 －６ / K.

[0031] One sleeve 90 is provided for each of the support rods 85 and 86. The sleeve 90 is formed in a cylindrical shape extending in the orthogonal direction Y and has a cylindrical portion 90a and a flange portion 90b formed on the outer peripheral surface of the cylindrical portion 90a. The cylindrical portion 90a of the sleeve 90 provided for the support rod 85 is positioned to surround the small diameter portion 85b and is fixed to the small diameter portion 85b. The cylindrical portion 90a of the sleeve 90 provided for the support rod 86 is positioned to surround the small diameter portion 86b and is fixed to the small diameter portion 86b. The sleeve 90 is fixed to the support rods 85 and 86 by joining the cylindrical portions 90a to the small diameter portions 85b and 86b.

[0032] The flange 90b is in contact with the insulators 87c and 88c. As a result, the sleeve 90 fixes the first insulator 87 to the support rod 85 and fixes the second insulator 88 to the support rod 86. The flange 90b may be joined to the insulators 87c and 88c. The flange 90b prevents the insulators 87c and 88c from moving in the orthogonal direction Y.

[0033] The sleeve 90 may be configured without the cylindrical portion 90a, and may be configured, for example, with only the flange portion 90b. If the sleeve 90 is configured with only the flange portion 90b, the position of the flange portion 90b will shift when the support rods 85, 86 thermally expand in the orthogonal direction Y. If the sleeve 90 has the cylindrical portion 90a, the cylindrical portion 90a expands together with the support rods 85, 86, thereby preventing the flange portion 90b from shifting in position. For this reason, it is preferable that the sleeve 90 have the cylindrical portion 90a.

[0034] The support member 82 extends in the extension direction X and has through holes H6 and H7 formed to penetrate in the perpendicular direction Y. The through hole H6 is located surrounding the first insulator 87 and the support rod 85. The through hole H7 is located surrounding the second insulator 88 and the support rod 86. The support member 82 supports the pair of support rods 85 and 86 via the first insulator 87 and the second insulator 88, and is electrically insulated from the pair of support rods 85 and 86 by the first insulator 87 and the second insulator 88. The support member 82 is made of a metal such as nickel (Ni), stainless steel (SUS), or Kovar (KOV). In this case, the thermal expansion coefficient of the support member 82 is 4×10 －６ ~14×10 －６ / K.

[0035] In one example, the support member 82 secures the first insulator 87 by contacting the inner circumferential surface of the through hole H6 with the outer circumferential surface of the insulator 87c. In other words, the support member 82 secures one of the pair of support rods 85, 86 (in one example, the support rod 85) via the first insulator 87. In the extension direction X, there is a gap between the inner circumferential surface of the through hole H7 of the support member 82 and the outer circumferential surface of the second insulator 88. In other words, the support member 82 does not contact the second insulator 88 in the extension direction X. The through hole H7 is, for example, an elongated hole extending in the extension direction X. Furthermore, the support member 82 has a movement limiting portion 82a inside the through hole H7 that faces the second insulator 88 on the opposite side of the first insulator 87 in the extension direction X.

[0036] The focus electrode 83 controls the electrons emitted from the emitter 84. More specifically, the focus electrode 83 focuses electrons from the electron emission surface 84a. For example, when a current is supplied to the focus electrode 83, the focus electrode 83 focuses the electrons emitted from the emitter 84 to a focal point on the anode target 50. In one example, the focus electrode 83 is formed in an annular shape and has an accommodation hole 83a therein that accommodates the emitter 84. A support member 82 is fixed to the inner surface of the focus electrode 83. In other words, the focus electrode 83 fixes the support member 82.

[0037] The thermal expansion coefficient of the support member 82 is equal to that of the focus electrode 83. The focus electrode 83 may be made of the same material as the support member 82, such as nickel or stainless steel. The thermal expansion coefficient of the focus electrode 83 does not have to be equal to that of the support member 82. In this case, the focus electrode 83 is made of iron, for example. The X-ray tube assembly according to the first embodiment is configured as described above.

[0038] In operation of the electron gun 80 of the X-ray tube device, when a current is supplied to the emitter 84 via the pair of support rods 85, 86, the emitter 84 emits electrons from the electron emission surface 84a toward the anode target 50. At this time, the temperature of the emitter 84 rises, and the emitter 84 expands in the extension direction X. Meanwhile, heat radiation occurs at the heat emission surface 84b, and the opposing surface 89a of the thermal expansion member 89 receives radiant heat from the heat emission surface 84b. At this time, the temperature of the thermal expansion member 89 rises, and the thermal expansion member 89 expands in the extension direction X.

[0039] As a result, the thermal expansion member 89 applies a force to the pair of support rods 85, 86 via the first insulator 87 and the second insulator 88. In other words, when the temperature of the opposing surface 89a of the thermal expansion member 89 rises due to radiant heat from the heat dissipation surface 84b, the thermal expansion member 89 expands in the extension direction X and applies a force to the pair of support rods 85, 86. As a result, the support rods 86 move in the extension direction X according to the amount of expansion of the thermal expansion member 89. Note that if the thermal expansion member 89 thermally expands excessively, the movement limiting portion 82a of the support member 82 comes into contact with the second insulator, thereby limiting the movement of the support rods 86.

[0040] Here, an example of a procedure for fixing the emitter 84 to the support rods 85, 86 will be described. FIG. 5 is a cross-sectional view showing the state before the emitter 84 is fixed to the support rods 85, 86. As shown in FIG. 5, first, the emitter 84, a pair of support rods 85, 86 to which a thermal expansion member 89 is fixed, and pins P1, P2 are prepared, and the emitter 84 is placed in the first groove G1. Next, the pin P1 is inserted into the fitting hole H1 of the connecting portion 84d and the second groove G2 of the large-diameter portion 85a, and the pin P1 is moved in the extension direction X along the second groove G2 of the large-diameter portion 85a to determine the position of the emitter 84 relative to the support rod 85. Thereafter, the connecting portion 84d and the large-diameter portion 85a are joined. Next, the pin P2 is inserted into the fitting hole H1 of the connecting portion 84e and the second groove G2 of the large diameter portion 86a, and a tensile load is applied to the emitter 84 in the extension direction X, and the pin P2 is moved along the second groove G2 of the large diameter portion 86a, thereby determining the position of the emitter 84 with respect to the pair of support rods 85, 86. Thereafter, the connecting portion 84e and the large diameter portion 86a are joined, and the pins P1 and P2 are withdrawn from the fitting hole H1 and the second groove G2, completing the fixation of the emitter 84 to the support rods 85, 86. Note that the pin P1 may be withdrawn when the connecting portion 84e and the large diameter portion 85a are joined.

[0041] The effects of the first embodiment will now be described. According to the emitter structure and electron gun of the first embodiment configured as described above, the emitter structure 81 includes an emitter 84, a pair of support rods 85 and 86, a first insulator 87, a second insulator 88, and a thermal expansion member 89. The thermal expansion member 89 has an opposing surface 89a that receives radiant heat from the heat emission surface 84b of the emitter 84. When the opposing surface 89a receives radiant heat and its temperature rises, it expands in the extension direction X and exerts a force on the pair of support rods. The electron gun 80 includes, in addition to the emitter structure 81, a support member 82 and a focus electrode 83. The support member 82 supports the pair of support rods 85 and 86, and the focus electrode 83 fixes the support member 82. The emitter 84 has a plurality of slits 84c. This makes it possible to obtain the emitter structure 81 and the electron gun 80 that can prevent distortion of the emitter 84 when the temperature of the emitter 84 rises. Furthermore, it is possible to prevent the slit 84c from shrinking in the extension direction X, and it is possible to maintain the amount of electrons emitted from the emitter 84.

[0042] The thermal expansion member 89 is fixed to a pair of support rods 85 and 86. The support member 82 fixes one of the pair of support rods 85 and 86. This makes it possible to suppress deformation and movement of the emitter 84 when the emitter structure 81 and the electron gun 80 are used in an X-ray CT device and are subjected to centrifugal acceleration.

[0043] The thermal expansion coefficient of the thermal expansion member 89 is larger than that of the emitter 84. The emitter is fixed to the pair of support rods 85, 86 in a state where a tensile load is applied in the extension direction X at room temperature. This makes it possible to alleviate stress caused by thermal expansion of the emitter 84 and suppress distortion of the emitter 84, even when the temperature of the emitter 84 is lower than the temperature of the thermal expansion member 89.

[0044] The support member 82 has a movement limiting portion 82a facing the second insulator 88 on the opposite side of the first insulator 87 in the extension direction X. This makes it possible to prevent the emitter 84 from expanding excessively in the extension direction X. The thermal expansion coefficient of the support member 82 is equal to that of the focus electrode 83. As long as the support member 82 fixes the support rod 85, the relative positional relationship between the support rod 85 and the focus electrode 83 can be maintained even if the support member 82 and the focus electrode 83 thermally expand.

[0045] Second Embodiment Next, a second embodiment will be described. FIG. 6 is a cross-sectional view of an electron gun 80 according to the second embodiment. The electron gun 80 has the same configuration as the first embodiment, except for the configuration described in the second embodiment. As shown in FIG. 6, the electron gun 80 has an emitter structure 81, a support member 82, and a focusing electrode 83. The emitter structure 81 includes an emitter 84, a pair of support rods 85 and 86, a first insulator 87, a thermal expansion member 89, and a sleeve 90. In other words, the emitter structure 81 is configured without a second insulator 88.

[0046] The connecting portion 89c of the thermal expansion member 89 is fixed to the support rod 86. Specifically, the inner peripheral surface of the through hole H5 of the thermal expansion member 89 comes into contact with the outer peripheral surface of the support rod 86, thereby fixing the thermal expansion member 89 to the support rod 86. Note that the thermal expansion member 89 may be bonded to the support rod 86. The support member 82 is fixed to the focusing electrode 83, and supports the support rod 85 via a first insulator 87. In one example, the support member 82 fixes the support rod 85 via the first insulator 87. The support member 82 is configured without the through hole H7 and the movement limiting portion 82a, and does not support the support rod 86.

[0047] The operation of the electron gun 80 will now be described. The thermal expansion member 89 is electrically insulated from one of the support rods 85. Therefore, when current is supplied to the emitter 84 via the pair of support rods 85, 86, no current flows through the thermal expansion member 89. As in the first embodiment, the temperature of the thermal expansion member 89 rises as it receives radiant heat from the emitter 84. Because the thermal expansion member 89 is fixed to the pair of support rods 85, 86, the thermal expansion member 89 applies a force to the pair of support rods 85, 86. As a result, the support rod 86 moves in the extension direction X by the amount of expansion of the thermal expansion member 89.

[0048] According to the emitter structure according to the second embodiment configured as described above, the emitter structure 81 includes the emitter 84, a pair of support rods 85 and 86, a first insulator 87, and a thermal expansion member 89. This reduces the number of parts, and an inexpensive emitter structure 81 can be obtained.

[0049] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Multiple embodiments can also be combined as necessary.

Claims

1. An emitter structure comprising: an emitter extending in a plate-like shape and having an electron emission surface that emits electrons, and a heat emission surface located opposite the electron emission surface and generating thermal radiation; a pair of support rods located on either side of the electron emission surface and the heat emission surface in the extension direction of the emitter, electrically connected to the emitter and fixing the emitter; a first insulator attached to one of the pair of support rods; a second insulator attached to the other of the pair of support rods; and a thermal expansion member extending in the extension direction, wherein the thermal expansion member faces the heat emission surface with a gap between them and has an opposing surface that receives radiated heat from the heat emission surface, is electrically insulated from the pair of support rods by the first insulator and the second insulator, and when the temperature of the opposing surface rises due to receiving radiated heat from the heat emission surface, it expands in the extension direction and exerts a force on the pair of support rods.

2. The emitter structure according to claim 1, wherein the thermal expansion member is fixed to the pair of support rods via the first insulator and the second insulator.

3. The emitter structure according to claim 2, wherein the thermal expansion coefficient of the thermal expansion member is greater than the thermal expansion coefficient of the emitter.

4. The emitter structure according to claim 2, wherein the emitter is fixed to the pair of support rods in a state where a tensile load is applied in the extension direction at room temperature.

5. The emitter structure described in claim 4, wherein the emitter has one end face in a direction parallel to the electron emission surface and perpendicular to the extension direction, another end face opposite the one end face, and a plurality of slits that penetrate from the electron emission surface to the heat emission surface and form a current path for a current flowing through the emitter, the plurality of slits being composed of a first slit formed by recessing the one end face and a second slit formed by recessing the other end face.

6. The emitter structure according to claim 1, wherein the thermal expansion coefficient of the thermal expansion member is greater than the thermal expansion coefficient of the emitter.

7. The emitter structure described in claim 1, wherein the emitter has one end face in a direction parallel to the electron emission surface and perpendicular to the extension direction, another end face opposite the one end face, and a plurality of slits that penetrate from the electron emission surface to the heat emission surface and form a current path for a current flowing through the emitter, the plurality of slits being composed of a first slit formed by recessing the one end face and a second slit formed by recessing the other end face.

8. An emitter structure comprising: an emitter extending in a plate-like shape and having an electron emission surface that emits electrons, and a heat emission surface located opposite the electron emission surface and generating thermal radiation; a pair of support rods located on either side of the electron emission surface and the heat emission surface in the extension direction of the emitter, electrically connected to the emitter and fixing the emitter; a first insulator attached to one of the pair of support rods; and a thermal expansion member extending in the extension direction, wherein the thermal expansion member faces the heat emission surface with a gap provided and has an opposing surface that receives radiated heat from the heat emission surface, is electrically insulated from one of the pair of support rods by the first insulator, and when the temperature of the opposing surface rises due to receiving radiated heat from the heat emission surface, it expands in the extension direction and exerts a force on the pair of support rods.

9. An emitter structure comprising: an emitter extending in a plate shape and having an electron emission surface that emits electrons and a heat emission surface located opposite the electron emission surface and generating thermal radiation; a pair of support rods located on either side of the electron emission surface and the heat emission surface in the extension direction of the emitter and electrically connected to the emitter to fix the emitter; a first insulator attached to one of the pair of support rods, a second insulator attached to the other of the pair of support rods, and a thermal expansion member extending in the extension direction; a support member that supports the pair of support rods via the first insulator and the second insulator and is electrically insulated from the pair of support rods by the first insulator and the second insulator; and a focusing electrode that fixes the support member and focuses electrons from the electron emission surface, wherein the thermal expansion member faces the heat emission surface with a gap provided and has an opposing surface that receives radiated heat from the heat emission surface, an electron gun, the electron gun being electrically insulated from the pair of support rods by the first insulator and the second insulator, and when the temperature of the opposing surface increases due to radiant heat from the heat dissipation surface, the opposing surface expands in the extension direction and exerts a force on the pair of support rods.

10. The electron gun according to claim 9, wherein the thermal expansion member is fixed to the pair of support rods via the first insulator and the second insulator.

11. The electron gun according to claim 10, wherein the thermal expansion coefficient of the thermal expansion member is greater than the thermal expansion coefficient of the emitter.

12. The electron gun according to claim 10, wherein the emitter is fixed to the pair of support rods in a state where a tensile load is applied in the extension direction at room temperature.

13. The electron gun described in claim 12, wherein the emitter has one end face in a direction parallel to the electron emission surface and perpendicular to the extension direction, another end face opposite to the one end face, and a plurality of slits that penetrate from the electron emission surface to the heat emission surface and form a current path for a current flowing through the emitter, the plurality of slits being composed of a first slit formed by recessing the one end face and a second slit formed by recessing the other end face.

14. The electron gun according to claim 9, wherein the thermal expansion coefficient of the thermal expansion member is greater than the thermal expansion coefficient of the emitter.

15. An electron gun as described in claim 9, wherein the emitter has one end face in a direction parallel to the electron emission surface and perpendicular to the extension direction, another end face opposite to the one end face, and a plurality of slits that penetrate from the electron emission surface to the heat emission surface and form a current path for a current flowing through the emitter, the plurality of slits being composed of a first slit formed by recessing the one end face and a second slit formed by recessing the other end face.

16. The electron gun according to claim 9, wherein the support member fixes one of the pair of support rods via the first insulator.

17. The electron gun according to claim 16, wherein the support member has a movement limiting portion facing the second insulator on a side opposite to the first insulator in the extending direction.

18. The electron gun according to claim 16, wherein the thermal expansion coefficient of the support member is equal to the thermal expansion coefficient of the focus electrode.

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