Electron gun and method for manufacturing electron gun

Abstract

The present invention relates to an electron gun and a method for manufacturing the same, the electron gun comprising: a cathode which has an electron emission surface, has a circular planar shape, and emits electrons; a heater for raising the temperature of the cathode; and an anode for applying a positive potential to the cathode and leading out electrons in a certain direction. The cathode has a through-hole in the center portion thereof along the center axis of the cathode, and has a non-emission layer on at least one of the opening edge portion of the through-hole on the electron emission surface side and the inner surface of the through-hole, or the opening edge portion of the through-hole on the electron emission surface side is a chamfered C-surface or a chamfered R-surface.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202011165465.4, filed on October 27, 2020, entitled "Electron Gun and Method of Manufacturing an Electron Gun". Technical Field

[0002] This disclosure relates to electron guns, and more particularly to electron guns that supply electrons for the operation of electron beam generating devices, Linac (linear accelerators), TWT (traveling wave tubes), klystrons, etc., and methods for manufacturing electron guns. Background Technology

[0003] In electron beam generating devices, Linac, TWT, klystrons, etc., which are used in applications utilizing electron beams, such as Figure 18 As shown, an electron gun 101 is provided, which uses a heater 105 to heat a cathode 102 that is sprayed, coated, or impregnated with a thermionic emission material on a metal substrate, thereby causing thermionic emission. Conventional electron guns 101 are used to apply a positive potential to the cathode 102 at the anode 103 and Wiener 104 in order to move electrons in a certain direction and focus the electron beam. Besides... Figure 18 In addition to the binary structure shown, such as Figure 19 As shown, there is also a method that configures the gate 106 to form a triode and applies a positive control voltage to the cathode 102 to control the electron flow. Furthermore, by applying a negative potential to the gate 106 relative to the cathode 102, thereby using an electric field to block the electron flow and controlling the cutoff state, the electron flow can be controlled more easily compared to controlling a high voltage between the cathode 102 and the anode 103.

[0004] exist Figure 18 and Figure 19 In any case, electrons are emitted from the electron gun 101, and the emitted electron beam is focused in a certain direction using an electric field or magnetic field. For example, it is used in applications such as directly using electrons or indirectly using the energy of electrons when they collide with a target to generate X-rays. In addition, in order to obtain higher electron energy, electrons are accelerated by a high-frequency electric field, such as in Linac, to increase their energy, or the electron flow, travel / delay is modulated by a high-frequency electric field, such as in TWT and klystron.

[0005] Even in any of the above applications, not all emitted electron beams are delivered to the next part (e.g., Linac, TWT, etc.), but reflection will always occur, and a portion will return to the electron gun 101 side (see Patent Document 1). Furthermore, secondary electrons are generated due to electron collisions, and sometimes these secondary electrons travel towards the electron gun 101 side. Additionally, ions that have received energy from electrons sometimes flow back to the electron gun 101 side. In any case, when the energy possessed by electrons, secondary electrons, or ions collides with the grid 106 and cathode 102, damage to the grid 106 and cathode 102 is usually caused by impact or overheating. Therefore, to avoid the cathode heating caused by a portion of electrons emitted from the cathode, secondary electrons generated by electron collisions, and ions returning to the cathode, the following method is known: A structure forming a through-hole in the center of the cathode, called a hollow cathode or annular cathode, is used to prevent back-bombardment (the phenomenon where a portion of electrons emitted from the cathode, electrons in the accelerating phase, receive energy from the high-frequency electric field and return to the cathode, colliding with it) (see Patent Document 2).

[0006] Existing technical documents Patent documents Patent Document 1: International Publication 2016 / 029065A1 Patent Document 2: CN202633200U Summary of the Invention The problem the invention aims to solve However, even with the method in Patent Document 2, in hollow / ring cathodes, the following problems exist: electrons emitted from the inner surface of the through-holes formed in the cathode disrupt the electron orbits, or hinder electron beam formation, or generate an unnecessary leakage current called dark current flowing from the cathode to the anode. Furthermore, when emitter material scattered due to evaporation or sputtering adheres to the through-holes formed in the cathode, electron emission occurs from this emitter material, similarly disrupting electron orbits, hindering electron beam formation, or generating dark current.

[0007] Therefore, the object of this disclosure is to provide an electron gun and a method for manufacturing an electron gun, the electron gun being able to suppress the emission of electrons from the edges formed in the through-hole formed in the cathode and when the through-hole is opened in the cathode electron emitting surface.

[0008] Methods for solving problems To achieve the above objectives, in one embodiment, this disclosure relates to an electron gun comprising: a cathode having an electron emitting surface and a circular planar shape; a heater; and an anode disposed opposite to the cathode, wherein a through hole is provided at the center of the cathode along the central axis of the cathode, and at least one of the opening edge of the through hole on the electron emitting surface side and the inner surface of the through hole has a non-emission layer.

[0009] According to this embodiment of the present disclosure, a non-emission layer is provided, thus preventing the electron-emitting material from being present at the opening edge of the cathode's through-hole or on the inner surface of the through-hole, thereby eliminating the emission of electrons from the cathode's through-hole. As a result, interference with electron beam formation or the generation of dark current can be prevented.

[0010] In other embodiments, this disclosure relates to an electron gun comprising: a cathode having an electron emitting surface and a circular planar shape; a heater; and an anode disposed opposite to the cathode, wherein a through hole is provided at the center of the cathode along the central axis of the cathode, and the opening edge of the through hole on the electron emitting surface side is a chamfered C-surface or a chamfered R-surface.

[0011] Invention Effects According to another embodiment of this disclosure, the opening edge of the cathode via is chamfered on the C-plane or R-plane, thereby eliminating electron emission from the opening edge of the via and preventing the generation of dark current. Attached Figure Description

[0012] Figure 1 This is a cross-sectional view showing a schematic structure of the base of the electron gun of this disclosure.

[0013] Figure 2 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 1 of this disclosure, showing a configuration in which a cylindrical metal layer is formed in the through-hole of the cathode as a non-emission layer.

[0014] Figure 3 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 1 of this disclosure. It shows a configuration in which an annular metal layer is formed as a non-emission layer at the opening edge of the cathode via on the electron emission surface side.

[0015] Figure 4 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 1 of this disclosure. It shows a configuration in which a metal tube and a cylindrical metal layer serve as a non-emission layer within the cathode's through-hole.

[0016] Figure 5This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 2 of this disclosure. It shows a method in which a cylindrical metal layer formed in the through-hole of the cathode after the metal substrate has melted and solidified serves as a non-emission layer.

[0017] Figure 6 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 2 of this disclosure. It shows a non-emission layer formed at the opening edge of the cathode's through-hole on the electron emission surface side, where a metal substrate melts and solidifies.

[0018] Figure 7 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 3 of this disclosure. It shows a non-emission layer formed in the through-hole of the cathode, consisting only of a cylindrical layer made of a porous metal substrate.

[0019] Figure 8 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 3 of this disclosure. It shows a non-emission layer formed at the opening edge of the cathode's through-hole on the electron emission surface side, consisting only of a porous metal substrate.

[0020] Figure 9 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 4 of this disclosure. It shows a non-emission layer formed in the through-hole of the cathode, in which a cylindrical layer of ceramic impregnated in the fine pores of a porous metal substrate is formed.

[0021] Figure 10 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 4 of this disclosure. It shows a non-emission layer formed at the opening edge of the electron emission surface side of the cathode aperture, where a ring-shaped portion of ceramic impregnated in the fine pores of a porous metal substrate is formed.

[0022] Figure 11 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 5 of this disclosure. It shows that the opening edge of the electron emission surface side of the cathode's through-hole is a chamfered C-surface.

[0023] Figure 12 This is an enlarged cross-sectional view of the electron gun, particularly the cathode, according to Embodiment 5 of this disclosure. It shows that the opening edge of the electron emission surface side of the cathode's through-hole is a chamfered R-surface.

[0024] Figure 13 This is a cross-sectional view showing a schematic construction of another structure that serves as the base of the electron gun of this disclosure.

[0025] Figure 14This is a graph showing the relationship between the ratio of the diameter of the aperture of the gate of the electron gun of the present disclosure to the diameter of the through-hole of the cathode and the cathode leakage current.

[0026] Figure 15 This is a graph showing the relationship between the ratio of the diameter of the aperture of the gate of the electron gun of the present disclosure to the diameter of the through-hole of the cathode and the difference between the diameter of the aperture of the gate and the diameter of the electron beam.

[0027] Figure 16 This is a cross-sectional view showing a schematic construction of another structure that serves as the base of the electron gun of this disclosure.

[0028] Figure 17 It means Figure 16 A three-dimensional view of the heat-resistant components of the electron gun.

[0029] Figure 18 This is a cross-sectional view showing a schematic structure of an existing diode electron gun.

[0030] Figure 19 This is a cross-sectional view showing a schematic structure of an existing triode electron gun. Detailed Implementation

[0031] Below, based on Figures 1-17 The embodiments shown illustrate this disclosure. It should be noted that each figure is merely a schematic diagram illustrating the structure of the electron gun 1 of the present invention, and does not strictly represent the detailed construction of each part or the dimensional relationships between them.

[0032] (Common approach) Figure 1 This is a cross-sectional view showing a schematic structure of the base of the electron gun 1 of the present invention. It should be noted that... Figure 1 The electron gun 1 shown is a diode electron gun. The main difference between this electron gun 1 and existing electron guns lies in the fact that after forming a through-hole 2a in the cathode 2, measures such as sealing the inner surface of the through-hole 2a and its surrounding area are implemented to suppress electron emission. Regarding this measure, in... Figure 1 It is not explicitly stated in the text that... Figures 2-12 In this specification, "non-emission layer" refers to the non-emission layer 11, or the chamfered C-face or R-face. In this specification, the term "non-emission layer" means a layer that prevents the exposure of electron-emitting material from the cathode and thus does not emit electrons. Detailed descriptions of structures equivalent to those in the past are omitted, but... Figure 1 The electron gun 1 shown is roughly configured as follows.

[0033] The electron gun 1 has a cathode 2, a heater 3, an anode 4, and a Wehnelt 5, and emits electrons mainly in the direction of arrow A from the opening 4a formed in the anode 4. The electron gun 1 is housed in a frame (not shown) formed of insulating material and operates in a state of being connected to a vacuum device and having its interior maintained under vacuum.

[0034] Electron gun 1 is used in conjunction with an application that utilizes an electron beam (e.g., an electron beam generator, Linac, TWT, klystron, etc.). In this case, reflection occurs on the application side, and some electrons return to the electron gun 1 side, or secondary electrons generated by electron impacts flow back to the electron gun 1 side, or ions that receive energy from the electric field of the application travel to the electron gun 1 side. In this specification, such electrons, secondary electrons, and ions are referred to as "returning electrons, etc."

[0035] The electron gun 1 has a through-hole 2a formed in the cathode 2 and has a structure referred to as a hollow cathode or annular cathode. With such an electron gun 1, even when return electrons flowing back from the next part (e.g., Linac, TWT, etc.) reach the cathode 2, they pass through the through-hole 2a located at the center of the cathode 2, thus preventing localized heating at the center of the cathode 2. Therefore, even in an electron gun designed with a very high electron beam current density, damage to the cathode 2 can be prevented, thereby reducing the temperature rise and deterioration of the heater 3 and the insulating material 8.

[0036] The cathode 2 is supported by the conductive sleeve 7. In addition, the anode 4 and the Vinal 5 are each supported by a separate conductive component to fix their relative positions within the frame.

[0037] The cathode 2 has an electron emitting surface, which is circular in shape and heated by the heater 3 to emit electrons. The cathode 2 is an electron beam focusing type cathode, and while some cathodes have a planar electron emitting surface, it is primarily concave to focus the electron beam. The cathode 2 is formed, for example, by spraying, coating, or impregnating a thermionic electron emitting material onto a metal substrate. Regarding the metal substrate constituting the cathode 2, materials with excellent heat resistance, low gas generation, and low work function, such as tungsten, are used. In the case of a metal substrate constituting an impregnated cathode, raw materials capable of further impregnating an emitter material are used, such as porous metals, specifically porous tungsten, porous tungsten compounds, or raw materials doped with other elements in porous tungsten. As the impregnating electron emitting material (emitter material), examples include barium, calcium, rhenium, strontium, or compounds containing them, and alumina is mixed in during impregnation. The thermal conductivity of the metal substrate is preferably high; for example, tungsten has a thermal conductivity of 173 W / m². m -1 k-1 At cathode 2, a predetermined negative potential is applied to anode 4 and Vinal 5 through a power source (not shown).

[0038] In cathode 2, a through-hole 2a is formed at its center along the central axis of the cathode (along a direction perpendicular to the circular shape of the cathode 2's planar shape). The through-hole 2a prevents deformation of the cathode 2 due to the energy of backfire from returning electrons traveling towards electron gun 1, or deterioration of the electron emitting material and the metal substrate itself. The through-hole 2a is formed as a hole at the center of cathode 2, and its cross-section orthogonal to the central axis of cathode 2 (in the direction of arrow A) is circular, penetrating the cathode 2 along its central axis (along arrow A (the direction of electron travel)). The diameter of the circular cross-section of the through-hole 2a orthogonal to the central axis of cathode 2 is typically set to about 1 to 3 mm, but this must be determined considering the electron beam diameter and focusing electric field. In this case, the outer diameter of the cathode is about 3 to 15 mm. Furthermore, the cross-sectional shape of the through-hole 2a does not need to be circular; any uniform size is acceptable.

[0039] Heater 3 is used to heat cathode 2. Heater 3 is surrounded and held by insulating material 8. Insulating material 8 is formed of a material that is both insulating and heat-resistant, specifically, for example, aluminum oxide.

[0040] The anode 4 is positioned opposite the cathode 2 to allow electrons emitted from the cathode 2 to travel through the opening 4a. A predetermined potential is applied to the anode 4 by a power source (not shown).

[0041] Wiener 5 is an electrode used to focus an electron beam by creating an electric field distribution with the anode 4, causing the electrons emitted from the cathode 2 to bend their orbits. A predetermined potential is applied to Wiener 5 by a power source (not shown).

[0042] According to the electron gun 1 with this structure, the cathode 2 is heated by the heater 3, thereby generating thermionic emission. The directionality of electron movement is determined by the electric field between the cathode 2 and the anode 4, and the electron beam is focused under the influence of the electric field generated by the Wiener 5. That is, the electrons emitted from the cathode 2 are focused towards the opening 4a of the anode 4 by the voltage difference between the potential applied to the anode 4 and the potential applied to the cathode 2, and travel simultaneously.

[0043] It should be noted that the structure / construction of the base of the electron gun 1 disclosed herein is not limited to the manner shown in each figure. Specifically, for example, the arrangement of the heater 3 and the insulating material 8 is not limited to the manner shown in each figure. That is, a portion of the electrons emitted from the cathode 2 travels further mainly in the direction of arrow A through the opening 4a of the anode 4 and proceeds to the next part utilizing the electron beam (e.g., Linac, TWT, etc.). Then, in the next part, the electrons collide with a small amount of gas or ions present in the tube sphere, which should ideally be a vacuum, or are partially reflected by the electric field, or return electrons such as secondary electrons generated by the impact of the electron beam, and flow back to the cathode 2. Therefore, if the heating wire of the heater 3 and the insulating material 8 are arranged on the same axis as the through hole 2a of the cathode 2, they will be affected by back-bombardment, so the heater 3 and the insulating material 8 may not be arranged on the same axis as the through hole 2a of the cathode 2.

[0044] (Implementation Method 1) Optionally, in embodiment 1, a metal layer 11a is provided as a non-emission layer 11 on the opening edge of the electron emission surface side of the through hole 2a of the cathode 2 or on the inner surface of the through hole 2a. Figures 2-4 This is an enlarged cross-sectional view of the electron gun 1 of Embodiment 1, particularly the cathode 2. In other words, the metal layer 11a, which is a non-emission layer 11, fills or covers the opening edge of the electron emission surface side of the through hole 2a of the cathode 2 and the fine holes and irregularities on the inner surface of the through hole 2a, thereby preventing the electron emission material from being exposed on the surface and preventing electrons from being emitted from the surface.

[0045] Optionally, Figure 2 The electron gun 1 shown includes: a cathode 2 having an electron emitting surface and a circular planar shape; a heater 3 that heats the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and draws electrons out in a certain direction (see reference). Figure 1 In the center of the cathode 2, a through hole 2a is provided along the central axis (arrow A) of the cathode 2, and a metal layer 11a is provided on the inner surface of the through hole 2a as a non-emission layer.

[0046] The metal layer 11a is formed, for example, by attaching powdered or thin-film metal to the inner surface of the through-hole 2a, for example, by melting it through heating in a furnace and then solidifying it through cooling. The metal layer 11a is applied or attached in such a way that it covers the entire circumference of the inner surface of the through-hole 2a, and the metal melts and solidifies to form a cylinder. Alternatively, while the metal substrate is coated or attached to the inner surface of the through-hole 2a of the cathode 2, the outer surface can be melted, for example, by laser irradiation, to completely cover the entire inner surface of the through-hole 2a. The thickness of the metal layer 11a is not limited to a specific size; for example, it can be appropriately adjusted to a suitable size, taking into account its potential use as a seal for the inner surface of the through-hole 2a. Specifically, the thickness of the metal layer 11a is adjusted to approximately 0.3 to 2 mm.

[0047] Figure 3 The electron gun 1 shown, in addition to having a metal layer 11a, which serves as a non-emission layer 11, arranged in a ring at the opening edge of the through-hole 2a on the electron emission surface side, also has the same characteristics as described above. Figure 2 The electron gun 1 shown has the same structure. It should be noted that... Figure 3 The text describes a metal layer 11a, which is a non-emission layer 11, formed within the outer shape of the cathode 2 (the interior of the cathode 2). However, the metal layer 11a can be provided in such a way that it covers the opening edge of the electron emission surface side of the through hole 2a of the cathode 2. Alternatively, the metal layer 11a can be provided further throughout the interior of the cathode 2 to cover the opening edge of the electron emission surface side of the through hole 2a of the cathode 2.

[0048] The metal layer 11a is formed, for example, by attaching powdered or thin-film metal to the opening edge of the electron-emitting surface side of the through-hole 2a, for example, by melting it through furnace heating or laser irradiation and then solidifying it (therefore, as...). Figure 3 As shown, a metal layer 11a is formed inside the cathode 2. The metal layer 11a is coated with metal in such a way that it covers the opening edge of the through hole 2a on the entire circumference. The metal melts, solidifies, and forms a ring. The cross-sectional dimensions of the metal layer 11a (the thickness of the ring) are not limited to a specific value, but are specifically adjusted to approximately 0.3 to 1 mm.

[0049] Figure 4 The electron gun 1 shown, in addition to having a non-emission layer 11 that is a metal tube 11e fixed to the through hole 2a, also has the same characteristics as described above. Figure 2 The electron gun 1 shown has the same structure. The metal tube 11e is fixed to the through hole 2a by a metal layer 11a that is molten and solidified between the metal tube 11e and the inner surface of the through hole 2a, for example by heating in a furnace. The metal tube 11e and the metal layer 11a form a non-emission layer 11.

[0050] The metal tube 11e is formed as a tubular (cylindrical) metal component, and its length is adjusted to be the same as that of the through hole 2a in the axial direction. The wall thickness of the metal tube 11e is not limited to a specific size, but is specifically adjusted to approximately 0.3 to 2 mm. The outer diameter of the metal tube 11e is adjusted by forming a metal layer 11a between the outer circumferential surface of the metal tube 11e and the inner circumferential surface of the through hole 2a when the metal tube 11e is inserted into the through hole 2a. The metal tube 11e is fixed to the through hole 2a by the metal layer 11a formed by the solidification of metal between the metal tube 11e and the inner circumferential surface of the through hole 2a. It should be noted that the metal tube 11e does not have to be formed as a cylinder, and can also be a tubular metal foil, without the need for self-support like a cylinder.

[0051] The metal tube 11e is made of a material with high heat resistance, preferably a material that can be used stably even at the assumed temperature of the metal tube 11e when using the electron gun 1 without causing thermal deformation or gas release. The metal tube 11e is also preferably made of a metal with a high work function and a low secondary electron multiplication factor. This suppresses the generation of secondary and tertiary electrons when returning electrons traveling to the electron gun 1 collide with the metal tube 11e, and prevents the electron beam emitted from the electron gun 1 from being affected. Specifically, the metal tube 11e is formed of, for example, a high heat-resistant component such as molybdenum, tungsten, tantalum, or hafnium, or an alloy containing said substances, or a compound or mixture of said substances.

[0052] In this method, the metal layer 11a is formed by: attaching powdered or thin-film metal to the outer peripheral surface of the metal tube 11e inserted into the through-hole 2a and melting it by heating in a furnace, then cooling and solidifying it; or attaching powdered or thin-film metal to at least one of the outer peripheral surface of the metal tube 11e and the inner peripheral surface of the through-hole 2a, melting it by heating in a furnace or laser irradiation, inserting the metal tube 11e into the through-hole 2a, and then solidifying the molten metal by cooling. The metal layer 11a is formed by arranging the metal in such a way that it fills the space between the outer peripheral surface of the metal tube 11e and the inner peripheral surface of the through-hole 2a over the entire circumference, and the metal solidifies and covers the inner peripheral surface of the through-hole 2a. The thickness of the metal layer 11a is not limited to a specific size, but is appropriately adjusted to a suitable size, for example, taking into account the overall size with the wall thickness of the metal tube 11e. Specifically, the thickness of the metal layer 11a is adjusted to approximately 0.3 to 2 mm.

[0053] The metal used to form the metal layer 11a in Embodiment 1 is preferably a material with high heat resistance, and is preferably a material that can be used stably even at the assumed temperature of the cathode 2 when using the electron gun 1 without causing thermal deformation or gas release. Specifically, molybdenum, a molybdenum-containing alloy, or a molybdenum compound is used as the metal for forming the metal layer 11a. By using molybdenum, a molybdenum-containing alloy, or a molybdenum compound, the opening edge of the electron emission surface side of the through-hole 2a or the inner surface of the through-hole 2a can be well sealed, and a metal layer for eliminating electron emission can be formed. Alternatively, an alloy containing tungsten, tantalum, or hafnium, or a compound or mixture of these substances, can also be used as the metal for forming the metal layer 11a.

[0054] It should be noted that, for the cathode 2, in addition to having a cylindrical metal layer 11a or a metal tube 11e fixed to the through hole 2a, it may also have an annular metal layer 11a.

[0055] (Implementation Method 2) Optionally, in embodiment 2, a non-emission layer 11 is provided on the opening edge of the electron emission surface side of the through hole 2a of the cathode 2, or on the inner surface of the through hole 2a. The metal layer 11b formed by melting and solidifying the metal substrate constituting the cathode 2 is provided as a non-emission layer 11. Figure 5 , Figure 6 This is an enlarged cross-sectional view of the electron gun 1 of Embodiment 2, particularly the cathode 2. In other words, the metal layer 11b, which is a non-emission layer 11, after melting and solidifying, blocks the opening edge of the through hole 2a on the electron emission surface side of the cathode 2 or the fine pores on the inner surface of the through hole 2a, thereby preventing the electron emission material from being exposed to the surface and preventing electrons from being emitted from the surface.

[0056] Figure 5 The electron gun 1 shown includes: a cathode 2 having an electron emitting surface, a circular planar shape, and comprising a metal substrate and an electron emitting material; a heater 3 that heats the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and draws electrons out in a certain direction (see reference). Figure 1 In the center of the cathode 2, a through hole 2a is provided along the central axis (arrow A) of the cathode 2. On the inner surface of the through hole 2a, there is a metal layer 11b after the metal substrate has been melted and solidified as a non-emissive layer 11.

[0057] The metal layer 11b, formed by the melting and solidification of the metal substrate, is formed as follows: the surface portion of the inner surface of the through-hole 2a in the metal substrate constituting the cathode 2 is melted to generate molten metal, and this molten metal is then solidified. The metal layer 11b, formed by the melting and solidification of the metal substrate, is formed by the melting of the surface portion of the metal substrate on the entire circumference of the inner surface of the through-hole 2a to generate molten metal, which then solidifies to form a cylinder. The thickness of the metal layer 11b (the wall thickness of the cylinder) is not limited to a specific size; for example, it can be appropriately adjusted to a suitable size, taking into account its potential use as a seal for the inner circumferential surface of the through-hole 2a. Specifically, the thickness of the metal layer 11b (the wall thickness of the cylinder) is adjusted to, for example, approximately 0.3 to 2 mm.

[0058] Figure 6 The electron gun 1 shown, except that the metal layer 11b, which is formed by melting and solidifying the non-emission layer 11 metal substrate, is arranged in a ring at the opening edge of the through hole 2a on the electron emission surface side, has the same characteristics as described above. Figure 5 The electron gun 1 shown has the same structure.

[0059] The metal layer 11b, formed after the metal substrate has melted and solidified, is formed by melting the edge portion of the opening on the electron emission surface side of the through-hole 2a in the metal substrate constituting the cathode 2 to generate molten metal, and then solidifying the molten metal. The metal layer 11b, formed after the metal substrate has melted and solidified, is formed by melting the edge portion of the metal substrate surrounding the entire circumference of the opening of the through-hole 2a to generate molten metal, which then solidifies to form a ring. The cross-sectional dimensions (ring size) of the metal layer 11b after the metal substrate has melted and solidified are not limited to a specific value, but are specifically adjusted, for example, to approximately 0.3 to 2 mm.

[0060] The method for melting the metal substrate to generate molten metal in Embodiment 2 is not limited to a specific method; for example, a suitable method can be appropriately selected based on considerations such as the material of the metal substrate. Specifically, for example, a method of generating molten metal by melting the metal substrate using a laser can be cited. In the method of melting and solidifying powdered or thin-film metal that has adhered to the through-hole 2a by heating in a furnace, as in Embodiment 1, the molten metal enters the cathode 2. In contrast, according to the method of directly melting the metal substrate using a laser, only the surface layer of the metal substrate can be melted to generate molten metal without impregnating excess metal into the metal substrate. Therefore, the volume of the cathode 2 that can be impregnated is larger than that in Embodiment 1, and the lifespan is longer. Furthermore, by using a laser, the time and effort required to generate molten metal from the metal substrate can be reduced.

[0061] It should be noted that, for cathode 2, in addition to having a cylindrical metal substrate melted and solidified metal layer 11b, it can also have an annular metal substrate melted and solidified metal layer 11b.

[0062] (Implementation Method 3) Optionally, in embodiment 3, a non-emission layer 11 is provided on the opening edge of the electron emission surface side of the through hole 2a of the cathode 2, or on the inner surface of the through hole 2a. This layer is made only of the metal substrate constituting the cathode 2. Figure 7 , Figure 8 This is an enlarged cross-sectional view of the electron gun 1 of Embodiment 3, particularly the cathode 2.

[0063] Figure 7 The electron gun 1 shown includes: a cathode 2 having an electron emitting surface, a circular planar shape, and a porous metal substrate and an electron emitting material impregnated in the pores of the porous metal substrate; a heater 3 that heats the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and draws electrons out in a certain direction (see reference). Figure 1 In the center of the cathode 2, a through hole 2a is provided along the central axis (arrow A) of the cathode 2. On the inner surface of the through hole 2a, there is a layer 11c made of only a porous metal substrate as a non-emission layer 11.

[0064] The layer 11c, consisting solely of a porous metal substrate, is formed by removing electron-emitting material from the surface portion of the inner surface of the through-hole 2a in the metal substrate constituting the cathode 2. The layer 11c, consisting solely of a porous metal substrate, is formed into a cylinder by removing electron-emitting material from the surface portion of the metal substrate along the entire circumference of the inner surface of the through-hole 2a. The thickness of the layer 11c (the wall thickness of the cylinder) is not limited to a specific size, but is specifically adjusted, for example, to approximately 0.3 to 2 mm. As a result, the electric field generated between the layer and the anode 4 does not penetrate into the interior of the cathode 2, thus preventing electric field emission of electrons from electron-emitting material located at deeper positions, and suppressing leakage current (dark current).

[0065] Figure 8 The electron gun 1 shown, in addition to having a layer 11c consisting only of a porous metal substrate serving as a non-emission layer 11 arranged in a ring at the opening edge of the through-hole 2a on the electron emission surface side, also has the same characteristics as described above. Figure 7 The electron gun 1 shown has the same structure.

[0066] The layer 11c, consisting solely of a porous metal substrate, is formed by removing electron-emitting material from the opening edge portion of the through-hole 2a on the electron-emitting surface side of the metal substrate constituting the cathode 2. The layer 11c, consisting solely of a porous metal substrate, removes electron-emitting material from the metal substrate at the edge portion surrounding the entire circumference of the opening of the through-hole 2a to form a ring. The cross-sectional dimensions (ring thickness) of the layer 11c, consisting solely of a porous metal substrate, are not limited to specific values, but are specifically adjusted, for example, to approximately 0.3 to 2 mm.

[0067] The method for removing electron-emitting material from the metal substrate in Embodiment 3 is not limited to a specific method. For example, a suitable method can be appropriately selected based on considerations such as the material of the metal substrate. Specifically, for example, the method can be as follows: after impregnating the electron-emitting material into the metal substrate, pure water, ethanol, or a mixture of pure water and ethanol are impregnated onto the surface of a porous metal substrate at a predetermined location of the cathode 2 (specifically, the inner surface portion of the through-hole 2a, or the opening edge portion of the through-hole 2a on the anode 4 side), thereby removing the electron-emitting material impregnated in the metal substrate from the metal substrate. In this way, by using a specific substance, the electron-emitting material can be removed more appropriately from the predetermined portion of the cathode.

[0068] It should be noted that, for the cathode 2, in addition to having a cylindrical layer 11c consisting only of a porous metal substrate, it may also have an annular layer 11c consisting only of a porous metal substrate.

[0069] (Implementation Method 4) Optionally, in embodiment 4, a non-emission layer 11 is provided at the opening edge of the electron emission surface side of the through hole 2a of the cathode 2, or on the inner surface of the through hole 2a, a layer 11d in which ceramic is impregnated in the fine pores of the porous metal substrate constituting the cathode 2 is provided. Figure 9 , Figure 10 This is an enlarged cross-sectional view, particularly of the cathode 2, showing the specific configuration of the electron gun 1 according to Embodiment 4. In other words, a ceramic layer 11d, impregnated within the pores of the porous metal substrate serving as the non-electron emission layer 11, fills or covers the pores and irregularities of the opening edge on the electron emission surface side of the through-hole 2a of the cathode 2 and the inner surface of the through-hole 2a. This prevents the electron-emitting material from being exposed to the surface and prevents electrons from being emitted from that surface. The ceramic is preferably a material that does not produce gas even under high-temperature vacuum conditions; for example, alumina (Al2O3) can be used.

[0070] Figure 9 The electron gun 1 shown includes: a cathode 2 having an electron emitting surface, a circular planar shape, and a porous metal substrate and an electron emitting material impregnated in the pores of the porous metal substrate; a heater 3 that heats the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and draws electrons out in a certain direction (see reference). Figure 1 In the center of the cathode 2, a through hole 2a is provided along the central axis (arrow A) of the cathode 2. On the inner surface of the through hole 2a, there is a layer 11d in which ceramic is impregnated in the fine pores of the porous metal substrate as a non-emissive layer 11.

[0071] The ceramic layer 11d impregnated within the pores of a porous metal substrate is formed by impregnating the ceramic onto the surface portion of the inner surface of a through-hole 2a in the metal substrate constituting the cathode 2. The ceramic layer 11d impregnated within the pores of the porous metal substrate forms a cylindrical shape by impregnating the ceramic onto the surface portion of the entire circumference of the inner surface of the through-hole 2a. The thickness (wall thickness of the cylinder) of the ceramic layer 11d impregnated within the pores of the porous metal substrate is not limited to a specific dimension, but is specifically adjusted, for example, to approximately 0.3 to 2 mm.

[0072] Figure 10 The electron gun 1 shown, in addition to having a ceramic layer 11d impregnated in the fine pores of the porous metal substrate serving as the non-emission layer 11 and arranged in a ring at the opening edge of the through-hole 2a on the electron emission surface side, also has the same characteristics as described above. Figure 9 The electron gun 1 shown has the same structure.

[0073] The ceramic layer 11d impregnated within the pores of a porous metal substrate is formed by impregnating the ceramic with the opening edge of the through-hole 2a on the electron emission surface side of the metal substrate constituting the cathode 2. The ceramic layer 11d is impregnated with the metal substrate along the edge portion of the entire circumference surrounding the opening of the through-hole 2a to form a ring. The cross-sectional dimensions (ring thickness) of the ceramic layer 11d impregnated within the pores of the porous metal substrate are not limited to specific values, but are specifically adjusted, for example, to approximately 0.3 to 2 mm.

[0074] It should be noted that, for cathode 2, in addition to having a cylindrical layer 11d in which ceramic is impregnated in the fine pores of a porous metal substrate, it can also have an annular layer 11d in which ceramic is impregnated in the fine pores of a porous metal substrate.

[0075] (Implementation Method 5) Figure 11 as well as Figure 12 This is an enlarged cross-sectional view of the electron gun 1 of Embodiment 5, particularly the cathode 2. Optionally, the electron gun 1 of Embodiment 5 includes: a cathode 2 having an electron emitting surface and a circular planar shape; a heater 3 that heats the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and draws electrons out in a certain direction (see reference). Figure 1 ); wherein, at the center of the cathode 2, a through hole 2a is provided along the central axis of the cathode 2 (arrow A), and the opening edge of the through hole 2a on the electron emission surface side is a chamfered C-surface (in Figure 11 The middle part is symbol 22) or the chamfered R-face (in Figure 12 The symbol in the middle is 23).

[0076] The chamfering process used to form a C-face or R-face is performed in such a way that it surrounds the opening edge of the through hole 2a of the cathode 2 around the entire circumference. The size and extent of the C-face or R-face are not limited to specific values, but are appropriately adjusted to suitable values ​​based on considerations such as the range in which electrons emitted from the opening edge of the through hole 2a are less likely to be affected by the electric field between the cathode and anode.

[0077] It should be noted that, for the cathode 2, in addition to having the cylindrical metal layer 11a described in Embodiment 1, the metal tube 11e fixed to the through hole 2a, the metal layer 11b after melting and solidification of the cylindrical metal substrate described in Embodiment 2, the cylindrical non-emissive layer 11c composed only of a porous metal substrate described in Embodiment 3, or the cylindrical layer 11d in which ceramics are impregnated in the fine pores of the porous metal substrate described in Embodiment 4, the opening edge of the through hole 2a can also be chamfered into a C-shape or a R-shape.

[0078] (Implementation Method 6) Figure 13 This is a cross-sectional view showing a schematic construction of another structure that forms the base of the electron gun 1 of this disclosure. Figure 13 In the electron gun 1 shown, besides... Figure 1 In addition to the equivalent structure of the electron gun 1 shown, the Wiener 5 is also connected to a gate 6. That is, Figure 13 The electron gun 1 shown is a tripolar electron gun. It should be noted that, regarding... Figure 1 The electron gun 1 shown is equivalent in structure, and its description is omitted by adding the same symbols.

[0079] A gate 6, used to control the cathode current, is mounted on the cathode 2 side of the Wiener 5. The gate 6 is driven by a potential applied to the Wiener 5. The gate 6 is formed, for example, from a conductive material into a mesh or perforated shape with an aperture ratio. By applying a negative voltage to the anode 4 at the gate 6 (thereby applying a positive control voltage to the cathode 2 to the gate 6 to control the electron flow), the cathode current can be controlled by applying an electric field that draws more electrons from the cathode 2.

[0080] The electron gun 1 can improve its operability by controlling the flow rate of electrons from the cathode 2 through the gate 6 and traveling in the direction of arrow A by using the potential applied to the Wiener 5 by the gate 6.

[0081] Furthermore, optionally, the electron gun 1 of embodiment 6 has a gate 6 for controlling the flow of electrons between the cathode 2 and the anode 4, and a hole 6a is provided on the same axis as the through hole 2a of the cathode 2 in the gate 6.

[0082] The hole 6a is used to prevent the grid 6 from being thermally deformed or degraded by the energy of back-bombardment due to the passage of return electrons flowing back to the electron gun 1 side. The hole 6a is formed in the center of the grid 6 as a circular hole that passes through the grid 6 along the central axis of the cathode 2. The hole 6a of the grid 6 and the through hole 2a of the cathode 2 are respectively formed at a position coaxial with each other in the electron emission direction A.

[0083] The diameter of the circular cross-section of the hole 6a orthogonal to the central axis of the cathode 2 is preferably set to 75-97% relative to the diameter of the circular cross-section of the through hole 2a of the cathode 2 orthogonal to the central axis of the cathode 2. Figure 14 This graph shows the relationship between the diameter of the hole 6a of the gate 6 relative to the diameter of the through hole 2a of the cathode 2 and the cathode leakage current when a constant negative potential is applied to the cathode 2 by the gate 6. If the diameter of the hole 6a of the gate 6 relative to the diameter of the through hole 2a of the cathode 2 is 97% or more, the cathode leakage current increases, making it impossible to cut off the cathode current. Similarly, when a positive potential is applied to the cathode 2 by the gate 6 to control the cathode current, i.e., the electron flow rate, the same applies: if the diameter of the hole 6a of the gate 6 relative to the diameter of the through hole 2a of the cathode 2 is 97% or more, control is impossible unless the gate control voltage is set to a very high value. Figure 15 This diagram illustrates the relationship between the ratio of the diameter of the hole 6a in the gate 6 to the diameter of the through-hole 2a in the cathode 2 and the difference between the diameter of the hole 6a in the gate 6 and the diameter of the electron beam. If the ratio of the diameter of the hole 6a in the gate 6 to the diameter of the through-hole 2a in the cathode 2 is 75% or less, the limit of the difference between the diameter of the hole 6a in the gate 6 and the diameter of the electron beam is 0.5 mm or less, and the position is difficult to adjust. Therefore, the ratio of the diameter of the hole 6a in the gate 6 to the diameter of the through-hole 2a in the cathode 2 is preferably 75% to 97%. This prevents electrons emitted near the center of the cathode from leaking through the hole formed in the gate, prevents the generation of dark current, and also prevents damage to the gate caused by back-bombardment, which is intended for this purpose. When the through-hole 2a in the cathode 2 and the hole 6a in the gate 6 are not circular, the average diameter can be used.

[0084] The electron gun 1 includes a gate 6, and an aperture 6a is formed in the gate 6 so that return electrons flowing back to the electron gun 1 pass through the aperture 6a of the gate 6. With this electron gun 1, by providing the aperture 6a in the gate 6, the flow rate of electrons traveling parallel to the cathode 2 through the gate 6, i.e., the cathode current, can be controlled. Furthermore, the operability of the electron gun 1 can be improved, localized heating at the center of the gate 6 can be prevented, and damage to the gate 6 can be prevented.

[0085] (Implementation Method 7) Figure 16 This is a cross-sectional view illustrating a schematic construction of another structure serving as the base of the electron gun 1 of the present invention. Figure 16 In the electron gun 1 shown, besides... Figure 1 In addition to having the same structure as the electron gun 1 shown, a heat-resistant component 9 is also provided at the through hole 2a of the cathode 2. It should be noted that, regarding the... Figure 1 The electron gun 1 shown is equivalent in structure, and its description is omitted by adding the same symbols.

[0086] Figure 16 The electron gun 1 shown is configured to be equipped with a heat-resistant member 9, which has a first part (a protrusion 92 in this embodiment 7) that blocks the through hole 2a of the cathode 2 and a second part (a flat plate 91 in this embodiment 7) located between the cathode 2 and the heater 3.

[0087] The heat-resistant member 9 is used to prevent the dissipation of heat generated by impact while preventing the return of electrons flowing back through the through-hole 2a provided in the cathode 2 and preventing damage to the article. The heat-resistant member 9 is preferably formed as a member that seamlessly covers and blocks the through-hole 2a provided in the cathode 2, is installed on the bottom surface of the cathode 2 (the end face on the heater 3 side), and engages with the bottom surface of the cathode 2. Furthermore, the heat-resistant member 9 is preferably configured to partially contact the sleeve 7. The heat-resistant member 9 contacts the bottom surface of the cathode 2 or the sleeve 7, thereby conducting heat from the heat-resistant member 9 to the cathode 2. In addition, the heat-resistant member 9 blocks the cathode 2 from the heater 3 side containing the insulating material 8, thereby preventing poor insulation due to the inflow of electron-emitting substances such as barium ions contained in the cathode 2 into the heater 3 side.

[0088] The heat-resistant component 9 is formed of a material with high heat resistance, preferably a material that can be used stably even at the assumed temperature of the heat-resistant component 9 when using the electron gun 1 without causing thermal deformation or gas release. The heat-resistant component 9 is also preferably formed of a metal with a high work function and a low secondary electron multiplication factor. This suppresses the generation of secondary and tertiary electrons when return electrons flowing back to the electron gun 1 collide with the heat-resistant component 9, and prevents the electron beam emitted from the electron gun 1 from being affected. The heat-resistant component 9 preferably has a higher thermal conductivity than the cathode 2. This is because it is preferable to avoid localized heating that would allow the heat generated by back-bombardment to diffuse across the entire cathode 2. However, even if the thermal conductivity of the heat-resistant component 9 is the same as that of the cathode 2, it is still effective in preventing impacts from return electrons on the surface of the cathode 2. Specifically, the heat-resistant component 9 is, for example, made of molybdenum (thermal conductivity 138 W / m²). m -1 k -1The heat-resistant component 9 may be formed from high heat-resistant materials such as tungsten, tantalum, or hafnium, or compounds or mixtures of these materials, or alloys containing them. Alternatively, the heat-resistant component 9 may also be formed from ceramic or SiC (silicon carbide).

[0089] By forming a heat-resistant member 9 from metal and electrically connecting it to a portion that should be at the same potential as the cathode 2 (or by mounting the heat-resistant member 9 onto the cathode 2), the heat-resistant member 9 and the cathode 2 can be made to be at the same potential. Therefore, the function of electrons emitted from the cathode 2, which is the voltage difference between the potential applied to the anode 4 and the potential applied to the cathode 2, is not hindered. In other words, the heat-resistant member 9 can be provided without hindering the function of the electron gun 1.

[0090] Here, the insulating material 8 is made of a heat-resistant material, so the heating of the cathode 2 does not come from direct radiation from the heater 3, but mostly from heat conduction or thermal radiation through the insulating material 8 and the sleeve 7. According to the inventors' research, it has been confirmed that by appropriately adjusting the thickness of the heat-resistant member 9, the heating efficiency of the heater 3 on the cathode 2 will not be significantly reduced. In other words, the heat-resistant member 9 is configured in a way that allows returning electrons to collide with the surface of the cathode 2 for appropriate heat diffusion, without significantly reducing the heating efficiency of the heater 3 on the cathode 2.

[0091] While it also depends on the physical properties of the heat-resistant member 9, the inventors' research has confirmed that setting the thickness of the portion of the heat-resistant member 9 existing between the heater 3 and the cathode 2 (the thickness of the flat plate portion) to, for example, 1 mm or less will not significantly reduce the heating efficiency of the heater 3 on the cathode 2. It should be noted that, in this case, the thickness of the protrusion (the thickness of the portion protruding from the flat plate portion) can be set to 0.3 to 2.5 mm.

[0092] The heat-resistant component 9 can also be formed into a simple flat plate with both the surface and the interior being planar (in other words, it can also be formed into a plate with a constant thickness in the electron emission direction A). However, in order to effectively prevent mechanical deterioration such as deformation or changes in surface condition of the heat-resistant component 9 caused by the energy of the back bombardment of returning electrons, etc., and without significantly reducing the heating efficiency of the heater 3 on the cathode 2, the part that is impacted by returning electrons, etc. through the through hole 2a of the cathode 2 (the part opposite to the through hole 2a) can be thickened, while the other parts (the parts not opposite to the through hole 2a) can be thinned.

[0093] Specifically, heat-resistant component 9 can also be formed, for example, as shown in the figure. Figure 17 The shape shown. Figure 17The heat-resistant member 9 shown is only thickened in the portion impacted by returning electrons through the through-hole 2a of the cathode 2 (the portion opposite to the through-hole 2a), and has a flat plate portion 91 and a protrusion 92 formed on one surface of the flat plate portion 91. The flat plate portion 91 engages with the end face (bottom surface of the cathode 2) on the heater 3 side of the cathode 2, thereby mounting the heat-resistant member 9 to the cathode 2. In this state, the protrusion 92 is embedded into the through-hole 2a of the cathode 2. Figure 17 In the example shown, the flat plate portion 91 is formed into a circle, becoming a circular flat plate portion 91. The shape of the protrusion 92 is not limited to that shown. Figure 17 The coin shape shown can also be a mountain shape with a gentle slope.

[0094] Optionally, the peripheral end 93 of the circular flat plate portion 91 of the heat-resistant member 9 contacts the sleeve 7 over the entire circumference. This effectively ensures the heat of the heat-resistant member 9 is conducted to the sleeve 7.

[0095] One or more holes may also be formed in the flat plate portion 91 of the heat-resistant member 9. By forming holes in the flat plate portion 91, it is possible to ensure that the heat of the heat-resistant member 9 is conducted to the sleeve 7 while the radiant heat from the heater 3 (heat via the insulating material 8 and the sleeve 7) is effectively conducted to the cathode 2, and the heating efficiency of the cathode 2 is ensured.

[0096] The heat-resistant component 9 is only affected by the portion (opposite to the through-hole 2a) where return electrons or other particles impact the heat-resistant component 9 through the through-hole 2a of the cathode 2. Figure 17 In the example shown, the part (opposite to the through hole 2a including the protrusion 92) is made of a heat-resistant material, and the whole can be formed as one piece (one part), or it can be combined to form multiple parts.

[0097] Here, a portion of the electrons emitted from the cathode 2 travels further in the direction of arrow A through the opening 4a of the anode 4, heading towards the next part of the electron beam (e.g., Linac, TWT, etc.). Then, in the next part, the electrons collide with small amounts of gas or ions present in the tube, which should ideally be a vacuum; some electrons are reflected by the electric field; or return electrons, such as secondary electrons generated by the electron beam impact, flow back to the cathode 2. However, in the case of the electron gun 1 of embodiment 7, the return electrons flowing back to the cathode 2 collide with the heat-resistant member 9 through the through-hole 2a. The heat generated by the back-bombardment of these return electrons is diffused by the heat-resistant member 9 and mainly transferred to the bottom surface of the cathode 2 and the sleeve 7 side. Some of the heat contributes to the heating of the cathode 2, but the heat transferred from the bottom surface of the cathode 2 or the inner surface of the through-hole 2a, although smaller than the heating heat from the heater 3, still contributes to the overall heating of the cathode 2. Therefore, localized heating will not occur at the center of cathode 2 as in the past, and abnormal evaporation of thermionic emission material immersed in the surface of cathode 2 and the space (pores and air holes) of the porous metal substrate can be prevented.

[0098] According to the electron gun 1 of embodiment 7, even when return electrons (e.g., Linac, TWT, etc.) flowing back from the next part of the electron beam emitted from the electron gun 1 reach the cathode 2, they pass through the through-hole 2a provided at the center of the cathode 2. Therefore, local impact and heat generation at the center of the cathode 2 can be suppressed. At the same time, the return electrons passing through the through-hole 2a collide with the heat-resistant member 9, so the heat generation caused by the back-bombardment of the return electrons is diffused by the heat-resistant member 9. Therefore, even in an electron gun designed with a very high electron beam current density, damage to the cathode 2 can be prevented, thereby reducing the temperature rise and deterioration of the heater 3 and the insulating material 8. As a result, changes in the characteristics of the electron gun 1 can be prevented, insulation failure can be prevented, and stable thermionic emission can be ensured for a long time.

[0099] Here, since the heat generated by backflow of electrons returning to the electron gun 1 cannot be ignored, the overheating of the cathode 2 caused by the heating of the heat-resistant member 9 can be suppressed by pre-reducing the heat of the heater 3. That is, according to the electron gun 1 of this embodiment 7, by arranging the heat-resistant member 9 near the cathode 2 and between it and the heater 3, the design freedom of the heater 3 can be improved. In other words, in the existing hollow cathode, if the heating wire of the heater 3 and the insulating material 8 are arranged on the same axis as the through hole 2a of the cathode 2, they are affected by backflow, and thus the design constraints of the electron gun become stricter. In contrast, the electron gun 1 of this embodiment 7 makes it easier to arrange the heater 3 and the insulating material 8 on the same axis as the through hole 2a of the cathode 2.

[0100] In addition, in heat-resistant components 9, such as Figure 17 When the structure shown has a flat plate portion 91 and a protrusion 92, the return electrons and the like that reaching the heat-resistant member 9 through the through hole 2a of the cathode 2 collide with the thickened protrusion 92 of the heat-resistant member 9. Therefore, the heat generated by the back-bombardment of the return electrons and the like can be fully diffused. Furthermore, the heat-resistant member 9, which exists between the cathode 2 and the heater 3, becomes a flat plate portion 91, so as to ensure the heating efficiency of the cathode 2 by the heat from the heater 3 (the heat from the insulating material 8 and the sleeve 7).

[0101] It should be noted that Embodiment 7 can also be used in combination with any one of Embodiments 1 to 5 and / or Embodiment 6. For example, Embodiment 1 and Embodiment 7 can be combined, and the cathode 2, in addition to having at least one of a cylindrical metal layer 11a, an annular metal layer 11a, or a metal tube 11e fixed to a through hole through a metal layer 11a as a non-emission layer 11, can also have a heat-resistant member 9. Alternatively, Embodiments 1, 7, and 6 can be combined, and the cathode 2, in addition to having at least one of a cylindrical metal layer 11a, an annular metal layer 11a, or a metal tube 11e fixed to a through hole through a metal layer 11a as a non-emission layer 11 and having a heat-resistant member 9, can also have a gate 6.

[0102] The embodiments 1 to 7 of this disclosure have been described above, but the specific structure is not limited to the above embodiments 1 to 7. Even design changes that do not depart from the scope of this disclosure are included in this disclosure. For example, in the above embodiment 7, the heat-resistant member 9 is mounted on the cathode 2 via the plate-shaped portion 91, but as long as it is disposed between the cathode 2 and the heater 3, the mounting method of the heat-resistant member 9 is not limited to a specific method.

[0103] According to the disclosure of embodiments 1 to 5 above, a non-emission layer is provided at least one of the opening edge on the electron emission surface side of the cathode via or the inner surface of the via. Since there is no electron-emitting material in this non-emission layer, the emission of unexpected electrons from the cathode via can be suppressed. As a result, interference with electron beam formation or the generation of dark current can be prevented.

[0104] Furthermore, according to the disclosures of embodiments 1 and 2 above, optionally, a cylindrical metal layer or a metal layer formed by melting and solidifying a metal substrate, or a metal tube, is provided on the inner surface of the cathode through-hole; or an annular metal layer or a metal layer formed by melting and solidifying a metal substrate is provided at the opening edge on the electron emission surface side of the through-hole. Therefore, the inner circumferential surface and opening edge of the cathode through-hole can be sealed, preventing electrons from being emitted from the cathode through-hole and the opening edge, and ensuring that no electrons exist within the range of the applied electric field. Additionally, interference from unnecessary electrons in electron beam formation or the generation of dark current caused by leakage current can be prevented, and an electron beam with an ideally designed electron trajectory can be ensured.

[0105] Symbol Explanation 1 Electron Gun 2 cathodes 2a Through Hole 3 heaters 4 anodes 4a opening 5 Vinal 6 gates 6a hole 7 sleeves 8 Insulation materials 9 heat-resistant components 91 Flat plate portion 92 convex part 93 Zhou Duan 11 Non-emissive layer 11a metal layer 11b Metal layer after melting and solidification of the metal matrix 11c is a layer consisting only of a porous metal matrix. 11d contains a ceramic layer impregnated within the pores of a porous metal substrate. 11e metal tube 22. C-surface with beveled edges 23. Beveled R-surface 101 Existing Electron Gun Structure 102 cathode 103 anode 104 Wijnal 105 heater 106 gate The direction of electron emission (direction of travel)

Claims

1. An electron gun comprising: a cathode having a concave electron emitting surface and a circular planar shape for focusing an electron beam; a heater; and an anode disposed opposite to the cathode, wherein, The cathode has a through hole at its center, along the central axis of the cathode. The opening edge portion on the electron emission surface side of the through hole, or the opening edge portion and the inner surface of the through hole, have a non-emission layer; The cathode has a porous metal substrate and an electron-emitting material impregnated in the pores of the porous metal substrate. The non-emissive layer is a metal layer comprising the porous metal matrix and at least some metal molten and solidified within the pores of the porous metal matrix. The porous metal matrix is ​​tungsten, tungsten compounds, or raw materials doped with other elements in tungsten. The metal that melts and solidifies in the pores of the porous metal matrix is ​​molybdenum, molybdenum-containing alloys, or molybdenum compounds.

2. The electron gun as claimed in claim 1, wherein, The cross-section of the through hole, orthogonal to the central axis of the cathode, is circular with a diameter of 1–3 mm.

3. The electron gun as claimed in claim 1, wherein, The opening edge of the through hole on the electron emission surface side is either a chamfered C-surface or a chamfered R-surface.

4. The electron gun as claimed in claim 1, wherein, A gate is provided between the cathode and the anode.

5. The electron gun as described in claim 4, wherein, A hole is provided on the same axis as the through hole of the cathode, on the gate. The diameter of the hole in the gate is 75-97% of the diameter of the through hole in the cathode.

6. The electron gun as claimed in claim 1, wherein, It is equipped with a heat-resistant component having a first portion that blocks the through hole of the cathode and a second portion located between the cathode and the heater.

7. A method for manufacturing an electron gun as claimed in claim 1, the method comprising: The process of coating a metal onto the opening edge of the through-hole, or the opening edge and the inner surface of the through-hole, and heating it in a furnace to melt it, wherein the metal is molybdenum, a molybdenum-containing alloy, or a molybdenum compound; and The process of cooling and solidifying molten metal to form the non-emissive layer.

8. A method for manufacturing an electron gun as described in claim 3, the method comprising: The process of coating a metal onto the opening edge of the through hole, or the opening edge and the inner surface of the through hole, and heating it in a furnace to melt it, wherein the metal is molybdenum, a molybdenum-containing alloy, or a molybdenum compound; The process of cooling and solidifying molten metal to form the non-emissive layer; and The process of performing C-beveling or R-beveling on the edge of the opening.

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