Electron gun and method of manufacturing an electron gun

Abstract

The present application relates to an electron gun, which has a cathode having an electron emission surface, a planar shape of which is circular, and which emits electrons, a heater which warms the cathode, and an anode which applies a positive potential to the cathode and extracts the electrons in a certain direction. The cathode has a through-hole along a central axis of the cathode in a central portion thereof, and at least one of an opening edge portion of the through-hole on the electron emission surface side and an inner surface of the through-hole has a non-emission layer, or the opening edge portion of the through-hole on the electron emission surface side is a chamfered C face or a chamfered R face.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electron gun, and particularly relates to an electron gun for supplying electrons to an electron beam generator, a Linac (linear accelerator), a TWT (traveling wave tube), a klystron, and the like, and a manufacturing method of the electron gun. BACKGROUND

[0002] In the electron beam generator, the Linac, the TWT, the klystron, and the like, which are applications using an electron beam, as shown in FIG. 1, an electron gun 101 is provided, which heats a cathode 102, on which a hot electron emission substance such as a thermionic emission substance is sprayed, applied, or impregnated, by a heater 105, thereby causing hot electron emission. The existing electron gun 101 is used by applying a positive potential to the cathode 102 with respect to an anode 103 and a Wehnelt 104 in order to move the electrons in a certain direction and focus the electron beam. In addition to the diode structure shown in FIG. 1, as shown in FIG. 2, there is a method of forming a triode by providing a grid 106 and applying a positive control voltage to the cathode 102 to control the electron flow. In addition, a negative potential is applied to the grid 106 with respect to the cathode 102, thereby blocking the electron flow using an electric field, and the cutoff state can be controlled, and the electron flow can be more simply controlled than when a high voltage between the cathode 102 and the anode 103 is controlled. Figure 18 Figure 18 Figure 19 In any case, the electrons are emitted from the electron gun 101, and the emitted electron beam is focused in a certain direction using an electric field or a magnetic field, and is applied to applications such as directly using the electrons, or indirectly using energy when the electrons collide with a target to generate X-rays or the like, and in order to obtain higher energy of the electrons, the energy is increased by accelerating the electrons using a high-frequency electric field or the like as in the Linac, or the electron flow, travel / delay is modulated using a high-frequency electric field as in the TWT and the klystron.

[0003] In any case, the electrons are emitted from the electron gun 101, and the emitted electron beam is focused in a certain direction using an electric field or a magnetic field, and is applied to applications such as directly using the electrons, or indirectly using energy when the electrons collide with a target to generate X-rays or the like, and in order to obtain higher energy of the electrons, the energy is increased by accelerating the electrons using a high-frequency electric field or the like as in the Linac, or the electron flow, travel / delay is modulated using a high-frequency electric field as in the TWT and the klystron. Figure 18 Figure 19

[0004] ​​​​Even in any of the above applications, not all of the emitted electron beams are transferred to the next section (e.g., Linac, TWT, etc.), but reflection will certainly occur, and a part will return to the electron gun 101 side (see Patent Document 1). In addition, secondary electrons are generated due to the impact of electrons, and sometimes the secondary electrons travel to the electron gun 101 side. Furthermore, ions that receive energy from the electrons also sometimes flow back to the electron gun 101 side. In any case, the energy possessed by the electrons, secondary electrons, or ions collides with the grid 106 and the cathode 102, and typically causes damage to the grid 106 and the cathode 102 due to impact or overheating. Thus, in order to avoid the temperature rise of the cathode due to the return of a part of the electrons emitted from the cathode, secondary electrons generated by the impact of the electrons, and ions to the cathode, a method is known in which, as a configuration in which a through-hole is formed in the center of the cathode and is called a hollow cathode or a ring-shaped cathode, back-bombardment to the cathode (a phenomenon in which a part of the electrons emitted from the cathode, electrons in an acceleration phase return to the cathode and collide with the cathode from the high-frequency electric field to obtain energy) is prevented (see Patent Document 2).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2016 / 029065A1

[0008] Patent Document 2: CN202633200U SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] However, even with the method of Patent Document 2, in the hollow cathode / ring-shaped cathode, there are problems in that the electrons emitted from the inner surface of the through-hole formed in the cathode or the like disturb the orbits of the electrons, or hinder the formation of the electron beam, or generate unnecessary leakage current called dark current that flows from the cathode to the anode direction. In addition, there are problems in that when the emitter material scattered due to evaporation or sputtering is attached inside the through-hole formed in the cathode, electron emission occurs from the emitter material, and similarly there are problems in that the orbits of the electrons are disturbed, or the formation of the electron beam is hindered, or dark current is generated.

[0011] Thus, an object of the present disclosure is to provide an electron gun and a manufacturing method of an electron gun that can suppress the emission of electrons from an edge portion formed when a through-hole is opened in a cathode electron emission surface and in a through-hole formed in the cathode.

[0012] MEANS FOR SOLVING THE PROBLEMS

[0013] To achieve the above object, in one embodiment, the present disclosure relates to an electron gun having: a cathode having an electron emission surface and a planar shape of a circular shape; a heater; and an anode disposed opposite to the cathode, wherein a through-hole along a central axis of the cathode is provided in a central portion of the cathode, and at least one of an opening edge portion of the through-hole on the electron emission surface side and an inner surface of the through-hole has a non-emission layer.

[0014] According to this embodiment of the present disclosure, the non-emission layer is provided, so that the electron emission substance can be absent from the opening edge portion of the through-hole on the electron emission surface side of the cathode or the inner surface of the through-hole, and thus the emission of electrons from the through-hole of the cathode can be eliminated. As a result, the disturbance of the electron beam formation or the generation of the dark current can be prevented.

[0015] In addition, in another embodiment, the present disclosure relates to an electron gun having: a cathode having an electron emission surface and a planar shape of a circular shape; a heater; and an anode disposed opposite to the cathode, wherein a through-hole along a central axis of the cathode is provided in a central portion of the cathode, and an opening edge portion of the through-hole on the electron emission surface side is a chamfered C face or a chamfered R face.

[0016] Effects of Invention

[0017] According to this other embodiment of the present disclosure, the opening edge portion of the through-hole of the cathode is chamfered in the C face or the R face, so that the emission of electrons from the opening edge portion of the through-hole can be eliminated, and the generation of the dark current can be prevented. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a cross-sectional view showing a schematic configuration of a structure of a base portion of the electron gun of the present disclosure.

[0019] Figure 2 is a cross-sectional view showing the electron gun of Embodiment 1 of the present disclosure, particularly the cathode, in an enlarged manner, and is a view showing a manner in which a cylindrical metal layer is formed as a non-emission layer in the through-hole of the cathode.

[0020] Figure 3 is a cross-sectional view showing the electron gun of Embodiment 1 of the present disclosure, particularly the cathode, in an enlarged manner, and is a view showing a manner in which a ring-shaped metal layer is formed as a non-emission layer in the opening edge portion of the through-hole of the cathode on the electron emission surface side.

[0021] Figure 4 is a cross-sectional view showing the electron gun of Embodiment 1 of the present disclosure, particularly the cathode, in an enlarged manner, and is a view showing a manner in which a metal tube and a cylindrical metal layer are provided as non-emission layers in the through-hole of the cathode.

[0022] Figure 5is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 2 of the present disclosure, and is a view that shows a manner in which a cylindrical metal layer after melting and solidification of a metal matrix is formed in a through-hole of the cathode as a non-emission layer.

[0023] Figure 6 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 2 of the present disclosure, and is a view that shows a manner in which an annular metal layer after melting and solidification of a metal matrix is formed in an opening edge portion of the cathode on the electron emission surface side of the through-hole.

[0024] Figure 7 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 3 of the present disclosure, and is a view that shows a manner in which a cylindrical layer composed only of a porous metal matrix is formed in a through-hole of the cathode as a non-emission layer.

[0025] Figure 8 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 3 of the present disclosure, and is a view that shows a manner in which an annular layer composed only of a porous metal matrix is formed in an opening edge portion of the cathode on the electron emission surface side of the through-hole as a non-emission layer.

[0026] Figure 9 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 4 of the present disclosure, and is a view that shows a manner in which a cylindrical layer in which a ceramic is impregnated in a fine hole of a porous metal matrix is formed in a through-hole of the cathode as a non-emission layer.

[0027] Figure 10 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 4 of the present disclosure, and is a view that shows a manner in which an annular portion in which a ceramic is impregnated in a fine hole of a porous metal matrix is formed in an opening edge portion of the cathode on the electron emission surface side of the through-hole as a non-emission layer.

[0028] Figure 11 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 5 of the present disclosure, and is a view that shows a manner in which an opening edge portion of the cathode on the electron emission surface side of the through-hole is a C face that is chamfered.

[0029] Figure 12 is a cross-sectional view that enlarges and shows a cathode of an electron gun of Embodiment 5 of the present disclosure, and is a view that shows a manner in which an opening edge portion of the cathode on the electron emission surface side of the through-hole is an R face that is chamfered.

[0030] Figure 13 is a cross-sectional view that shows a schematic configuration of another structure of a base of an electron gun of the present disclosure.

[0031] Figure 14is a graph showing the relationship between the ratio of the diameter of the hole of the grid of the electron gun of the present disclosure to the diameter of the through-hole of the cathode and the cathode leakage current.

[0032] Figure 15 is a graph showing the relationship between the ratio of the diameter of the hole of the grid 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 hole of the grid and the diameter of the electron beam.

[0033] Figure 16 is a cross-sectional view showing a schematic configuration of still another structure of the base of the electron gun of the present disclosure.

[0034] Figure 17 is a perspective view showing the heat-resistant member of the electron gun of Figure 16 .

[0035] Figure 18 is a cross-sectional view showing a schematic configuration of a conventional two-pole electron gun.

[0036] Figure 19 is a cross-sectional view showing a schematic configuration of a conventional three-pole electron gun. DETAILED DESCRIPTION

[0037] Hereinafter, the present disclosure will be described based on the embodiment shown in Figures 1 to 17 . Note that each drawing is merely a view for illustrating a schematic configuration of the electron gun 1 of the present disclosure, and does not strictly show the detailed configuration of each part or the dimensional relationship with each other.

[0038] (Common Mode)

[0039] Figure 1 is a cross-sectional view showing a schematic configuration of the structure of the base of the electron gun 1 of the present disclosure. Note that the electron gun 1 shown in Figure 1 is a two-pole electron gun. The main difference of this electron gun 1 from the structure of the conventional electron gun is that, after forming the through-hole 2a in the cathode 2, a measure of suppressing electron emission is implemented on the inner surface of the through-hole 2a and its surroundings. Regarding this measure, it is not specifically shown in Figure 1 , and in Figures 2 to 12 , it is shown as a non-emission layer 11 or a chamfered C-face or R-face. In the present specification, the term "non-emission layer" means a layer that prevents exposure of electron emission substances from the cathode and does not emit electrons. Regarding the structure equivalent to the past, detailed description thereof is omitted, but Figure 1 The electron gun 1 shown in

[0040] 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 connection with a vacuum device and with the interior maintained under vacuum.

[0041] 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."

[0042] 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.

[0043] 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.

[0044] 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. A high thermal conductivity is preferred for the metal substrate; for example, tungsten has a thermal conductivity of 173 W·m³. -1 ·k -1). At the cathode 2, a predetermined negative potential is applied to the anode 4 and the Wehnelt 5 by a power source (not shown).

[0045] In the cathode 2, a through-hole 2a is formed in the center portion thereof along the central axis of the cathode (in a direction perpendicular to the circular shape of the planar shape of the cathode 2). The through-hole 2a is used to prevent deformation of the energy cathode 2 or deterioration of the electron emission substance and the metal base itself due to back bombardment of returning electrons and the like traveling toward the electron gun 1. The through-hole 2a is formed as a hole in the center portion of the cathode 2, the cross section of which orthogonal to the central axis of the cathode 2 (arrow A direction) is circular, and penetrates the cathode 2 along the central axis of the cathode 2 (in the arrow A direction (traveling direction of electrons)). The diameter of the circular cross section of the through-hole 2a orthogonal to the central axis of the cathode 2 is usually set to about 1 to 3 mm, for example, but is set in consideration of the electron beam diameter and the focusing electric field. The outer diameter of the cathode in this case is about 3 to 15 mm. Note that the cross-sectional shape of the through-hole 2a need not be circular, but only needs to be the same size.

[0046] The heater 3 is used to heat the cathode 2. The heater 3 is surrounded and held by an insulating material 8. The insulating material 8 is formed of a material having insulating properties and heat resistance, and is formed of alumina, for example.

[0047] The anode 4 is disposed opposite the cathode 2, and is used to cause the electrons emitted from the cathode 2 to travel in such a manner as to pass through the opening portion 4a. A predetermined potential is applied to the anode 4 by a power source (not shown).

[0048] The Wehnelt 5 is an electrode used to focus the electron beam by causing the electrons emitted from the cathode 2 to form an electric field distribution together with the anode 4 and to bend the electron orbits. A predetermined potential is applied to the Wehnelt 5 by a power source (not shown).

[0049] According to the electron gun 1 of this structure, the cathode 2 is heated by the heater 3, thereby generating hot electron emission, the directionality of the movement of the electrons 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 Wehnelt 5. That is, the electrons emitted from the cathode 2 are focused toward the opening portion 4a of the anode 4 using the voltage that is the difference between the potential applied to the anode 4 and the potential applied to the cathode 2, while traveling.

[0050] Note that the structure / configuration of the base of the electron gun 1 of the present disclosure is not limited to that shown in each figure. Specifically, for example, the arrangement of the heater 3 and the insulating material 8 is not limited to that shown in each figure. That is, a portion of the electrons emitted from the cathode 2 passes through the opening portion 4a of the anode 4, further travels mainly in the direction of the arrow A, and goes to the next stage (e.g., Linac, TWT, etc.) using the electron beam. Then, in the next stage, the electrons collide with a small amount of gas or ions, etc. that exist inside the tube bulb which is originally supposed to be a vacuum, or a portion of the electrons is reflected due to the influence of an electric field, or return electrons such as secondary electrons, etc. that are generated by the impact of the electron beam flow back to the cathode 2. Therefore, if 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, and therefore the heater 3 and the insulating material 8 can also be arranged not on the same axis as the through-hole 2a of the cathode 2.

[0051] (Embodiment 1)

[0052] Optionally, in Embodiment 1, a metal layer 11a is provided as a non-emission layer 11 at the opening edge portion on the electron emission surface side of the through-hole 2a of the cathode 2, or the inner surface of the through-hole 2a. Figures 2 to 4 is a cross-sectional view that specifically shows the electron gun 1 of Embodiment 1, and in particular, the cathode 2. In other words, the metal layer 11a as the non-emission layer 11 fills or covers the fine holes and irregularities on the opening edge portion on the electron emission surface side of the through-hole 2a of the cathode 2 and the inner surface of the through-hole 2a, and functions to prevent the electron emission substance from being exposed to the surface and to prevent the emission of electrons from that surface.

[0053] Optionally, Figure 2 The electron gun 1 shown has a cathode 2 having an electron emission surface and a planar shape that is circular, a heater 3 that warms the cathode 2, and an anode 4 that applies a positive potential to the cathode 2 and extracts electrons in a certain direction (see Figure 1 ); wherein, at the center portion 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 as a non-emission layer at the inner surface of the through-hole 2a.

[0054] The metal layer 11a is formed, for example, by adhering a metal in the form of a powder or a thin film to the inner surface of the through-hole 2a, melting by, for example, in-furnace heating, and solidifying by subsequent cooling. The metal layer 11a is applied to adhere the metal so as to cover the entire inner surface of the through-hole 2a in the entire circumference, and the metal is melted and solidified to form a cylindrical shape. At this time, the outer surface can be melted to completely cover the entire inner surface of the through-hole 2a, for example, by laser irradiation or the like, in a state where the metal is applied or adhered to the metal base of the inner surface of the through-hole 2a of the cathode 2. The thickness of the metal layer 11a is not limited to a particular size, and is appropriately adjusted to an appropriate size, for example, on the basis of consideration of use as a seal or the like of the inner surface of the through-hole 2a. The thickness of the metal layer 11a is specifically adjusted to, for example, about 0.3 to 2 mm.

[0055] Figure 3 The illustrated electron gun 1 has the same structure as the above-described Figure 2 illustrated electron gun 1, except that the metal layer 11a as the non-emission layer 11 is provided in a ring shape at the opening edge portion of the through-hole 2a on the electron emission surface side of the cathode 2. Figure 3 In the above-described , it is described that the metal layer 11a as the non-emission layer 11 is formed inside the outer shape of the cathode 2 (inside the cathode 2), but the metal layer 11a can be provided so as to cover the opening edge portion of the through-hole 2a on the electron emission surface side of the cathode 2, and the metal layer 11a can further be provided so as to cover the opening edge portion of the through-hole 2a on the electron emission surface side of the cathode 2 throughout the inside of the cathode 2.

[0056] Figure 3 The metal layer 11a is formed, for example, by adhering a metal in the form of a powder or a thin film to the opening edge portion of the through-hole 2a on the electron emission surface side, and solidifying after melting by, for example, in-furnace heating or laser irradiation or the like (thereby, as illustrated in , the metal layer 11a is formed inside the cathode 2). The metal layer 11a is applied to adhere the metal so as to cover the entire opening edge portion of the through-hole 2a in the entire circumference, and the metal is melted and solidified to form a ring shape. The cross-sectional size (thickness of the ring) of the metal layer 11a is not limited to a particular value, but is specifically adjusted to, for example, about 0.3 to 1 mm.

[0057] Figure 4 The illustrated electron gun 1 has the same structure as the above-described Figure 2 illustrated electron gun 1, except that the non-emission layer 11 is a metal pipe 11e fixed to the through-hole 2a. The metal pipe 11e is fixed to the through-hole 2a with a metal layer 11a that is melted and solidified between the metal pipe 11e and the inner surface of the through-hole 2a, for example, by in-furnace heating or the like, and the metal pipe 11e and the metal layer 11a form the non-emission layer 11.

[0058] The metal pipe 11e is formed as a tubular (cylindrical) metal member, and is adjusted to a size that is the same as the axial direction length of the through-hole 2a. The wall thickness of the metal pipe 11e is not limited to a particular size, but is specifically adjusted to, for example, about 0.3 to 2 mm. The outer diameter of the metal pipe 11e is adjusted taking into account that a metal layer 11a is formed between the outer peripheral surface of the metal pipe 11e and the inner peripheral surface of the through-hole 2a in a state in which the metal pipe 11e is inserted into the through-hole 2a. The metal pipe 11e is fixed to the through-hole 2a using the metal layer 11a that is formed by metal solidification between the metal pipe 11e and the inner peripheral surface of the through-hole 2a. Note that the metal pipe 11e can not necessarily be formed as a cylinder, but can be a tubular metal foil that does not need to be self-supporting like a cylinder.

[0059] The metal pipe 11e is formed of a material that has high heat resistance, and is preferably formed of a material that can be used stably without causing thermal deformation or gas release even at a temperature assumed for the metal pipe 11e when the electron gun 1 is used. The metal pipe 11e is also preferably formed of a metal that has a high work function and a low secondary electron multiplication coefficient. Thus, the generation of secondary electrons and tertiary electrons when return electrons and the like that travel to the electron gun 1 side collide with the metal pipe 11e can be suppressed, and the electron beam emitted from the electron gun 1 can be prevented from being affected. The metal pipe 11e is specifically formed of, for example, molybdenum, tungsten, tantalum, or hafnium, or an alloy containing these substances, or a compound or mixture of these substances, or the like high heat-resistant member.

[0060] In this mode, the metal layer 11a is formed by, for example, causing a powder or thin film-like metal or the like to adhere between the outer peripheral surface of the metal pipe 11e and the inner peripheral surface of the through-hole 2a and to be melted by in-furnace heating, and then being cooled and solidified, or causing a powder or thin film-like metal or the like to adhere to at least one of the outer peripheral surface of the metal pipe 11e and the inner peripheral surface of the through-hole 2a, and after being melted by in-furnace heating or laser irradiation, inserting the metal pipe 11e into the through-hole 2a, and then solidifying the melted metal by cooling. The metal layer 11a is formed by disposing a metal that fills between the outer peripheral surface of the metal pipe 11e and the inner peripheral surface of the through-hole 2a in such a manner that 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 particular size, but is appropriately adjusted to an appropriate size, for example, on the basis of the total size including the wall thickness of the metal pipe 11e. The thickness of the metal layer 11a is specifically adjusted to, for example, about 0.3 to 2 mm.

[0061] As the metal used to form the metal layer 11a in this embodiment 1, a material having high heat resistance is preferable, and a material that can be stably used without causing thermal deformation or gas release even at a temperature assumed for the cathode 2 when the electron gun 1 is used is preferable. As the metal used to form the metal layer 11a, specifically, for example, molybdenum, an alloy containing molybdenum, or a compound of molybdenum is used. By using molybdenum, an alloy containing molybdenum, or a compound of molybdenum, the opening edge portion of the electron emission face 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 emission of electrons can be formed. As the metal used to form the metal layer 11a, an alloy containing tungsten, tantalum, or hafnium, or a compound or mixture of these substances can also be used.

[0062] Note that, for the cathode 2, on the basis of the cylindrical metal layer 11a or the metal tube 11e fixed to the through-hole 2a, a ring-shaped metal layer 11a can also be provided.

[0063] (Embodiment 2)

[0064] Optionally, in the cathode 2 of embodiment 2, the opening edge portion of the electron emission face side of the through-hole 2a or the inner surface of the through-hole 2a is provided with a metal layer 11b formed after the metal base of the cathode 2 is melted and solidified as a non-emission layer 11. Figure 5 、 Figure 6 is a cross-sectional view that specifically shows the electron gun 1 of embodiment 2, and in particular, the cathode 2. In other words, the metal layer 11b formed after the metal base of the non-emission layer 11 is melted and solidified blocks the fine pores at the opening edge portion of the electron emission face side of the through-hole 2a or the inner surface of the through-hole 2a of the cathode 2, and functions to prevent the electron emission substance from being exposed to the surface and to prevent emission of electrons from the surface.

[0065] Figure 5 The electron gun 1 shown has a cathode 2 having an electron emission face, a planar shape of a circle, and provided with a metal base and an electron emission substance; a heater 3 that warms up the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and extracts electrons in a certain direction (see Figure 1 ); wherein, at the center portion of the cathode 2, a through-hole 2a along the central axis (arrow A) of the cathode 2 is provided, and at the inner surface of the through-hole 2a, a metal layer 11b formed after the metal base is melted and solidified is provided as a non-emission layer 11.

[0066] The metal layer 11b after melting and solidification of the metal base is formed by melting the metal base of the edge portion on the opening edge of the through-hole 2a on the electron emission surface side of the cathode 2 to generate molten metal, and solidifying the molten metal. The metal layer 11b after melting and solidification of the metal base is formed by melting the metal base of the edge portion on the entire circumference of the opening portion of the through-hole 2a to generate molten metal, and solidifying the molten metal to form a ring shape. The cross-sectional dimension (size of the ring) of the metal layer 11b after melting and solidification of the metal base is not limited to a particular value, but is specifically adjusted to about 0.3 to 2 mm, for example.

[0067] Figure 6 The electron gun 1 shown has the same structure as the above-described Figure 5 The electron gun 1 shown has the same structure as the above-described

[0068] The metal layer 11b after melting and solidification of the metal base is formed by melting the metal base of the edge portion on the opening edge of the through-hole 2a on the electron emission surface side of the cathode 2 to generate molten metal, and solidifying the molten metal. The metal layer 11b after melting and solidification of the metal base is formed by melting the metal base of the edge portion on the entire circumference of the opening portion of the through-hole 2a to generate molten metal, and solidifying the molten metal to form a ring shape. The cross-sectional dimension (size of the ring) of the metal layer 11b after melting and solidification of the metal base is not limited to a particular value, but is specifically adjusted to about 0.3 to 2 mm, for example.

[0069] The method of melting the metal base to generate molten metal in this embodiment 2 is not limited to a particular method, and a suitable method is appropriately selected on the basis of the material of the metal base and the like. Specifically, for example, a method of melting the metal base by using a laser to generate molten metal can be given. In a method of melting and solidifying the powder or thin film-like metal or the like adhered to the through-hole 2a by in-furnace heating or the like as in embodiment 1, the metal after melting enters the cathode 2. In contrast, according to the method of directly melting the metal base by using a laser, it is possible to generate molten metal only by melting the surface layer of the metal base without impregnating excess metal in the metal base, and thus it is possible to impregnate a larger volume of the cathode 2 than in embodiment 1, and the life is long. Furthermore, by using a laser, it is possible to reduce the time and effort required to generate molten metal from the metal base.

[0070] Note that, with the cathode 2, on the basis of the metal layer 11b that is melted and solidified after the cylindrical metal base, a metal layer 11b that is melted and solidified after a ring-shaped metal base can also be provided.

[0071] (Embodiment 3)

[0072] Optionally, in Embodiment 3, the opening edge portion on the electron emission face side of the through-hole 2a of the cathode 2, or the inner surface of the through-hole 2a, is provided with a layer 11c composed only of the metal base that constitutes the cathode 2 as a non-emission layer 11. Figure 7 , Figure 8 is a cross-sectional view that amplifies a specific mode of the electron gun 1 of Embodiment 3, and in particular, the cathode 2.

[0073] Figure 7 The electron gun 1 illustrated in FIG. 10 has a cathode 2 that has an electron emission face, a planar shape that is circular, and that is provided with a porous metal base and an electron emission substance that is impregnated within the fine pores of the porous metal base; a heater 3 that warms the cathode 2; and an anode 4 that applies a positive potential to the cathode 2 and extracts electrons in a certain direction (see FIG. 10). Figure 1 In the center portion of the cathode 2, a through-hole 2a is provided along the central axis (arrow A) of the cathode 2, and on the inner surface of the through-hole 2a, a layer 11c composed only of the porous metal base is provided as a non-emission layer 11.

[0074] The layer 11c composed only of the porous metal base is formed by removing the electron emission substance from the surface layer portion of the inner surface of the through-hole 2a in the metal base that constitutes the cathode 2. The layer 11c composed only of the porous metal base removes the electron emission substance from the metal base of the surface layer portion on the entire circumference of the inner surface of the through-hole 2a to form a cylinder. The thickness (wall thickness of the cylinder) of the layer 11c composed only of the porous metal base is not limited to a particular size, but is specifically adjusted to be around 0.3 to 2 mm, for example. Due to this, the electric field that is generated between the cathode 2 and the anode 4 does not enter the inside of the cathode 2, so electric field emission of electrons from the electron emission substance that exists in a deeper position does not occur, and the leakage current (dark current) can also be suppressed.

[0075] Figure 8 The electron gun 1 illustrated in FIG. 10 has the same structure as the electron gun 1 illustrated in FIG. 9, except that the layer 11c composed only of the porous metal base as the non-emission layer 11 is provided in a ring shape at the opening edge portion on the electron emission face side of the through-hole 2a. Figure 7

[0076] ​The layer 11c composed of only the porous metal base is formed by removing the electron emission substance from the opening edge portion of the electron emission surface side of the through-hole 2a in the metal base constituting the cathode 2. The layer 11c composed of only the porous metal base is removed of the electron emission substance from the metal base of the edge portion of the entire circumference surrounding the opening portion of the through-hole 2a to form a ring shape. The cross-sectional dimension (thickness of the ring) of the layer 11c composed of only the porous metal base is not limited to a particular value, but is specifically adjusted to about 0.3 to 2 mm, for example.

[0077] The method of removing the electron emission substance from the metal base in this Embodiment 3 is not limited to a particular method, and a suitable method is appropriately selected based on the material of the metal base and the like. Specifically, for example, a method in which, after the electron emission substance is impregnated in the metal base, pure water, ethanol, or a mixture of pure water and ethanol is impregnated in the surface of the porous metal base of the predetermined portion of the cathode 2 (specifically, the inner surface portion of the through-hole 2a, the opening edge portion of the through-hole 2a on the anode 4 side) to remove the electron emission substance impregnated in the metal base from the metal base can be given. By using a particular substance in this way, the electron emission substance can be more appropriately removed from the predetermined portion of the cathode.

[0078] Note that, with respect to the cathode 2, a cylindrical layer 11c composed of only the porous metal base can be provided, and a ring-shaped layer 11c composed of only the porous metal base can also be provided.

[0079] (Embodiment 4)

[0080] Alternatively, in Embodiment 4, a layer 11d in which ceramic is impregnated in the pores of the porous metal base constituting the cathode 2 is provided as a non-emission layer 11 on the opening edge portion of the electron emission surface side of the through-hole 2a of the cathode 2, or the inner surface of the through-hole 2a. Figure 9 、 Figure 10 is a cross-sectional view that specifically illustrates the electron gun 1 of Embodiment 4, and in particular, the cathode 2. In other words, the layer 11d in which ceramic is impregnated in the pores of the porous metal base as a non-electron emission layer 11 fills or covers the pores and irregularities of the opening edge portion of the electron emission surface side of the through-hole 2a of the cathode 2 and the inner surface of the through-hole 2a, and functions to prevent the electron emission substance from being exposed to the surface and to prevent the emission of electrons from the surface. The ceramic is preferably a material that does not generate gas even in a high-temperature vacuum environment, and alumina (AI2O3) or the like can be used, for example.

[0081] Figure 9The 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.

[0082] 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 is formed by impregnating the ceramic onto the surface portion of the metal substrate covering the entire circumference of the inner surface of the through-hole 2a, thus forming a cylinder. 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.

[0083] 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.

[0084] 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 entire circumference of the edge portion 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.

[0085] 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.

[0086] (Implementation Method 5)

[0087] Figure 11 as well as Figure 12is a cross-sectional view showing an enlarged representation of the electron gun 1 of Embodiment 5, particularly a cross-sectional view of the cathode 2. Optionally, the electron gun 1 of this Embodiment 5 has: the cathode 2 having an electron emission face, and a planar shape of a circular shape; the heater 3 which warms up the cathode 2; and the anode 4 which applies a positive potential to the cathode 2 and extracts electrons in a certain direction (refer to Figure 1 ). In the center portion of the cathode 2, a through-hole 2a along the central axis (arrow A) of the cathode 2 is provided, and the opening edge portion of the through-hole 2a on the electron emission face side is a C-face (symbol 22 in Figure 11 ) which is chamfered or an R-face (symbol 23 in Figure 12 ) which is chamfered.

[0088] The chamfering processing to form the C-face or the R-face is performed in a manner to surround the opening edge portion of the through-hole 2a of the cathode 2 over the entire circumference. The size and degree of the C-face or the R-face are not limited to a specific numerical value, and are appropriately adjusted to a suitable numerical value, for example, on the basis of consideration of a range in which the electrons emitted from the opening edge portion of the through-hole 2a are not easily affected by the electric field between the cathode and the anode.

[0089] Note that, for the cathode 2, the opening edge portion of the through-hole 2a can be chamfered to a C-type or chamfered to an R-type on the basis of the cylindrical metal layer 11a of Embodiment 1 described above, the metal tube 11e fixed to the through-hole 2a, the metal layer 11b after the cylindrical metal base is melted and solidified of Embodiment 2 described above, the cylindrical non-emission layer 11c composed only of a porous metal base of Embodiment 3 described above, or the cylindrical layer 11d in which a ceramic is impregnated in the fine pores of the porous metal base of Embodiment 4 described above.

[0090] (Embodiment 6)

[0091] Figure 13 is a cross-sectional view showing a schematic configuration of another structure of the base of the electron gun 1 of the present disclosure. In Figure 13 , the electron gun 1 is the same as the electron gun 1 shown in Figure 1 except that the grid 6 is connected to the Wien filter 5. That is, the electron gun 1 shown in Figure 13 is a triode electron gun. Note that, regarding the structure identical to the electron gun 1 shown in Figure 1 , the description thereof is omitted by attaching the same symbol.

[0092] The grid 6 for controlling the cathode current is installed on the side of the cathode 2 of the Wien filter 5. The grid 6 is driven by an electric potential applied to the Wien filter 5. The grid 6 is formed of a material having conductivity, for example, in a mesh shape or a punched shape having an opening ratio through which electrons can pass. In the grid 6, a negative voltage is applied to the anode 4 (thereby, a positive control voltage to the cathode 2 is applied to the grid 6 to control the electron flow), and the cathode current can be controlled by applying an electric field that draws more electrons from the cathode 2.

[0093] The cathode current, that is, the flow rate of electrons passing through the grid 6 from the cathode 2 and traveling in the direction of the arrow A, is controlled by the grid 6 using the electric potential applied to the Wien filter 5, and the operability of the electron gun 1 can be improved.

[0094] Furthermore, the electron gun 1 of Embodiment 6 has the grid 6 for controlling the flow rate of electrons between the cathode 2 and the anode 4, and a hole 6a is provided in the grid 6 on the same axis as the through hole 2a of the cathode 2.

[0095] The hole 6a is used to prevent the grid 6 from being thermally deformed or deteriorated due to the energy of back sputtering by passing backflowing return electrons and the like to the side of the electron gun 1. The hole 6a is formed in the central portion of the grid 6 as a circular hole that penetrates 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 formed at positions coaxial in the emission direction A of electrons.

[0096] 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 to 97% with respect 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 is a graph showing the relationship between the ratio of the diameter of the hole 6a of the grid 6 with respect 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 grid 6. If the ratio of the diameter of the hole 6a of the grid 6 with respect to the diameter of the through hole 2a of the cathode 2 is 97% or more, the cathode leakage current becomes large, and the cathode current cannot be cut off. Also, when a positive potential is applied to the cathode 2 by the grid 6 to control the cathode current, that is, the flow rate of electrons, similarly, if the ratio of the diameter of the hole 6a of the grid 6 with respect to the diameter of the through hole 2a of the cathode 2 is 97% or more, the control cannot be performed unless the grid control voltage is set to be very large. Figure 15is a graph showing the relationship between the ratio of the diameter of the hole 6a of the grid 6 to the diameter of the through-hole 2a of the cathode 2 and the difference between the diameter of the hole 6a of the grid 6 and the diameter of the electron beam. If the ratio of the diameter of the hole 6a of the grid 6 to the diameter of the through-hole 2a of the cathode 2 is 75% or less, the limit of the difference between the diameter of the hole 6a of the grid 6 and the diameter of the electron beam is 0.5 mm or less, and it is difficult to adjust the position. Therefore, the ratio of the diameter of the hole 6a of the grid 6 to the diameter of the through-hole 2a of the cathode 2 is preferably 75 to 97%, the electrons emitted from the vicinity of the center of the cathode 2 do not leak from the hole formed in the grid, and generation of dark current can be prevented, and in addition, damage to the grid caused by back-bombardment, which is the original purpose, can be prevented. In the case where the through-hole 2a of the cathode 2 and the hole 6a of the grid 6 are not circular, the average diameter can be used.

[0097] The electron gun 1 is provided with the grid 6, and the hole 6a is formed in the grid 6, so that the return electrons and the like flowing back to the electron gun 1 pass through the hole 6a of the grid 6. According to such an electron gun 1, the hole 6a is provided in the grid 6 on the basis of the grid 6 being provided, so that the cathode current, which is the flow rate of the electrons passing through the grid 6 and proceeding from the cathode 2, can be controlled, and the operability of the electron gun 1 can be improved, and in addition, local heating at the center of the grid 6 can be prevented, and damage to the grid 6 can be prevented.

[0098] (Embodiment 7)

[0099] Figure 16 is a cross-sectional view showing a schematic configuration of still another structure of the base portion of the electron gun 1 of the present application. In Figure 16 In the electron gun 1 shown in Figure 1 In addition to the structure identical to that of the electron gun 1 shown in Figure 1 Note that the description of the structure identical to that of the electron gun 1 shown in

[0100] Figure 16 The electron gun 1 shown in is configured to be provided with the heat-resistant member 9 having the first portion (the protruding portion 92 in this embodiment 7) that plugs the through-hole 2a of the cathode 2 and the second portion (the flat portion 91 in this embodiment 7) that is located between the cathode 2 and the heater 3.

[0101] The heat resistant member 9 is used to diffuse heat generated by impact while preventing return electrons and the like flowing back through the through hole 2a provided in the cathode 2 from entering and damaging the article. The heat resistant member 9 is preferably formed as a member that covers and blocks the through hole 2a provided in the cathode 2 without gaps, is attached to the bottom surface of the cathode 2 (the end surface on the side of the heater 3), and is in contact with the bottom surface of the cathode 2. In addition, the heat resistant member 9 is preferably provided so that a portion thereof is in contact with the sleeve 7. The heat resistant member 9 is in contact with the bottom surface of the cathode 2 or the sleeve 7, and thus heat of the heat resistant member 9 is conducted to the cathode 2. In addition, the heat resistant member 9 blocks the cathode 2 and the side of the heater 3 including the insulating material 8, and thus prevents occurrence of insulation failure due to inflow of barium ions, which are electron emission substances included in the cathode 2, to the side of the heater 3.

[0102] The heat resistant member 9 is formed of a material having high heat resistance, and is preferably formed of a material that can be used stably without causing thermal deformation or gas release even at a temperature assumed for the heat resistant member 9 when the electron gun 1 is used. The heat resistant member 9 is also preferably formed of a metal having a high work function and a low secondary electron multiplication coefficient. Thus, generation of secondary electrons and tertiary electrons when return electrons and the like flowing to the side of the electron gun 1 collide with the heat resistant member 9 can be suppressed, and the electron beam emitted from the electron gun 1 can be prevented from being affected. The heat conductivity of the heat resistant member 9 is preferably greater than that of the cathode 2. This is because it is preferable to avoid local heating and diffuse heat generated by back-bombardment to the entire cathode 2. However, even if the heat conductivity of the heat resistant member 9 is the same as that of the cathode 2, it is effective in terms of avoiding impact of return electrons and the like on the surface of the cathode 2. The heat resistant member 9 is specifically formed of, for example, molybdenum (heat conductivity 138 (W m -1 ·k -1 ), tungsten, tantalum, or hafnium, or a compound or a mixture of these substances, or an alloy including them, or the like high heat resistant member. Alternatively, the heat resistant member 9 can be formed of ceramic or SiC (silicon carbide).

[0103] By forming the heat resistant member 9 of a metal and electrically connecting it to a portion that should be at the same potential as the cathode 2 (the heat resistant member 9 can also be attached to the cathode 2), the heat resistant member 9 and the cathode 2 can be made to be at the same potential. Thus, the action of electrons emitted from the cathode 2 traveling toward the opening portion 4a of the anode 4 by the voltage that is the difference between the potential applied to the anode 4 and the potential applied to the cathode 2 is not hindered. That is, the heat resistant member 9 can be provided while avoiding hindrance of the function of the electron gun 1.

[0104] Here, the insulating material 8 is formed of a material having heat resistance, and thus the heating of the cathode 2 is not direct radiation from the heater 3, but is mostly heat conduction or heat radiation via the insulating material 8 and the sleeve 7. According to the inventors' studies, it was confirmed that the heating efficiency of the cathode 2 by the heater 3 does not significantly decrease by appropriately adjusting the thickness or the like of the heat-resistant member 9. That is, the heat-resistant member 9 is configured to be adjusted so as to allow the return electrons or the like of the backflow to collide with the surface of the cathode 2 to appropriately perform heat diffusion, and does not significantly decrease the heating efficiency of the cathode 2 by the heater 3.

[0105] Although it also depends on the physical properties of the heat-resistant member 9, according to the inventors' studies, it was confirmed that the heating efficiency of the cathode 2 by the heater 3 does not significantly decrease by 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. Note that, in this case, the thickness of the convex portion (the thickness of the portion protruding from the flat plate portion) can be set to 0.3 to 2.5 mm.

[0106] The heat-resistant member 9 can also be formed of a simple flat plate having flat surfaces on both sides (in other words, can also be formed to have a constant thickness in the electron emission direction A), but in order to effectively prevent mechanical degradation such as deformation or change in surface state of the heat-resistant member 9 due to the energy of the back-bombardment of the return electrons or the like, and not significantly decrease the heating efficiency of the cathode 2 by the heater 3, the portion (the portion opposite to the through-hole 2a) where the return electrons or the like of the backflow collide with the through-hole 2a of the cathode 2 can be thickened, and the other portion (the portion not opposite to the through-hole 2a) can be thinned.

[0107] The heat-resistant member 9 can specifically be formed, for example, in the shape as shown in Figure 17 Figure 17 The heat-resistant member 9 shown in Figure 17 Figure 17

[0108] Optionally, the circumferential end 93 of the circular flat plate portion 91 of the heat-resistant member 9 is in contact with the sleeve 7 over the entire circumference. Thereby, the heat conduction of the heat-resistant member 9 to the sleeve 7 is favorably ensured.

[0109] ​​​One or more holes can also be formed in the flat portion 91 of the heat-resistant member 9. By forming holes in the flat portion 91, it is possible to ensure that heat from the heat-resistant member 9 is conducted to the sleeve 7 while effectively conducting the radiant heat from the heater 3 (heat via the insulating material 8 and the sleeve 7) to the cathode 2 and ensuring the heating efficiency of the cathode 2.

[0110] The heat-resistant member 9 can be formed integrally (as one member) or can be composed of a plurality of members as long as it is formed of a material having heat resistance at a portion (a portion opposite to the through-hole 2a. In the example shown, a portion opposite to the through-hole 2a including the convex portion 92) that is struck by return electrons and the like that reach the heat-resistant member 9 through the through-hole 2a of the cathode 2. Figure 17 The heat-resistant member 9 can be formed integrally (as one member) or can be composed of a plurality of members as long as it is formed of a material having heat resistance at a portion (a portion opposite to the through-hole 2a. In the example shown, a portion opposite to the through-hole 2a including the convex portion 92) that is struck by return electrons and the like that reach the heat-resistant member 9 through the through-hole 2a of the cathode 2.

[0111] Here, a part of the electrons emitted from the cathode 2 passes through the opening portion 4a of the anode 4, mainly travels further in the direction of the arrow A, and goes to the next stage (for example, Linac, TWT, or the like) using the electron beam. Then, in the next stage, the electrons are struck by a small amount of gas or ions and the like that exist in the tube bulb that is originally supposed to be vacuum, or a part of the electrons are reflected by the influence of an electric field, or return electrons and the like such as secondary electrons that are generated by the impact of the electron beam flow back to the cathode 2. However, in the case of the electron gun 1 of this embodiment 7, the return electrons and the like that flow back to the cathode 2 are struck by the heat-resistant member 9 through the through-hole 2a, the heat generated by the back-bombardment of the return electrons and the like is diffused by the heat-resistant member 9, and is mainly transferred to the bottom surface of the cathode 2 and the sleeve 7 side. A part of the heat contributes to the temperature rise of the cathode 2, but is transferred from the bottom surface of the cathode 2 or the inner surface of the through-hole 2a, and although it is small relative to the heating heat by the heater 3, the heating by the heater 3 also contributes to the heating of the entire cathode 2. Thus, unlike in the past, local heating does not occur at the center of the cathode 2, and abnormal evaporation of the thermionic emission material that is impregnated in the space (voids and pores) of the cathode 2 and the porous metal substrate can be prevented.

[0112] According to the electron gun 1 of this embodiment 7, even in the case where return electrons and the like that flow back from the next stage (for example, Linac, TWT, or the like) using 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, and thus it is possible to suppress local impact and heating at the center of the cathode 2, and the return electrons and the like that have passed through the through-hole 2a are struck by the heat-resistant member 9, and thus the heating caused by the back-bombardment of the return electrons and the like is diffused by the heat-resistant member 9. Thus, even in an electron gun designed with a very high electron beam current density, it is possible to prevent damage to the cathode 2, and furthermore, it is possible to reduce the temperature rise and deterioration of the heater 3 and the insulating material 8. As a result, it is possible to prevent changes in the characteristics of the electron gun 1, and it is possible to prevent insulation failure and ensure stable thermionic emission for a long period of time.

[0113] 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.

[0114] 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).

[0115] 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.

[0116] 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.

[0117] According to the disclosure of Embodiments 1 to 5 described above, at least one of the opening edge portion on the electron emission surface side of the through-hole of the cathode or the inner surface of the through-hole is provided with a non-emission layer in which no electron emission substance exists, and thus emission of unintended electrons from the through-hole of the cathode can be suppressed. As a result, interference of electron beam formation or generation of dark current can be prevented.

[0118] In addition, according to the disclosure of Embodiments 1 and 2 described above, optionally, the inner surface of the through-hole of the cathode has a cylindrical metal layer or a metal layer after melting and solidification of a metal base or a metal tube, or the opening edge portion on the electron emission surface side of the through-hole has a ring-shaped metal layer or a metal layer after melting and solidification of a metal base, and thus the inner peripheral surface of the through-hole and the opening edge portion of the cathode can be sealed, and no electrons are emitted from the inside of the through-hole and the opening edge portion of the cathode, and no electrons exist in the range of application of an electric field. In addition, interference of electron beam formation by unnecessary electrons or generation of dark current by leakage current can be prevented, and an electron beam of an electron orbit as in a desired design can be ensured.

[0119] Explanation of Symbols

[0120] 1 Electron gun

[0121] 2 Cathode

[0122] 2a Through-hole

[0123] 3 Heater

[0124] 4 Anode

[0125] 4a Opening portion

[0126] 5 Wehnelt

[0127] 6 Grid

[0128] 6a Hole

[0129] 7 Sleeve

[0130] 8 Insulating material

[0131] 9 Heat-resistant member

[0132] 91 Flat plate-shaped portion

[0133] 92 Protruding portion

[0134] 93 Peripheral end

[0135] 11 Non-emission layer

[0136] 11a Metal layer

[0137] 11b Metal layer after melting and solidification of a metal base

[0138] 11c layer consisting of a porous metal matrix only

[0139] 11d layer in which the pores of the porous metal matrix are impregnated with ceramic

[0140] 11e metal tube

[0141] 22 chamfered C-face

[0142] 23 chamfered R-face

[0143] 101 electron gun of prior art construction

[0144] 102 cathode

[0145] 103 anode

[0146] 104 Wien

[0147] 105 heater

[0148] 106 grid

[0149] A direction of emission (direction of travel) of electrons

Claims

1. An electron gun comprising: a cathode having a curved, 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. A non-emission layer is provided at the opening edge on the electron emission surface side of the through-hole, or at the opening edge and on the inner surface of the through-hole. The cathode comprises a porous metal substrate and an electron-emitting material impregnated within the pores of the porous metal substrate. The non-emission layer is a porous metal layer consisting only of the porous metal substrate from which electron-emitting material has been removed from the pores of the porous metal substrate.

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

3. The electron gun as described in claim 2, 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% to 97% of the diameter of the through hole in the cathode.

4. 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.

5. A method for manufacturing an electron gun, comprising the method for manufacturing the electron gun as described in claim 1, wherein, The method includes: The process of immersing the electron-emitting material in the pores of the porous metal substrate to obtain the cathode, and The process of removing the electron-emitting material impregnated in the metal substrate from the metal substrate by impregnating a predetermined portion of the cathode with pure water, ethanol, or a mixture of pure water and ethanol.

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