Indirectly heated cathode and method for manufacturing the same

Abstract

To provide an indirect heated cathode capable of shortening the time up to a start of radiation of thermoelectrons, and a method of manufacturing the indirect heated cathode in which a heat absorption layer which has a uniform thickness can be easily manufactured.SOLUTION: An indirect heated cathode 10 comprises a cathode sleeve 1, a heater 2 arranged at a hollow part of the cathode sleeve 1, a black heat absorption layer 4 covering a hollow part inner surface of the cathode sleeve 1, and a cathode base body 3 carrying an electron emission substance arranged at the cathode sleeve 1. The black heat absorption layer 4 consists of a particulate substance including tungsten and aluminum oxide. The black heat absorption layer 4 is formed by arranging rod-like alumina ceramics, and a first tungsten heater and a second tungsten heater in the hollow part of the cathode sleeve 1 and heating it in a vacuum atmosphere.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an indirectly heated cathode and a method for manufacturing the same, and particularly to an indirectly heated cathode used in a magnetron, a klystron, a traveling wave tube, an electron gun, etc., and a method for manufacturing the same.

Background Art

[0002] Electron tubes such as magnetrons are widely used in medical equipment devices, radar devices, etc. Generally, in this type of electron tube, in order to emit thermoelectrons from the electron-emitting substance of the cathode provided in the electron tube, it is necessary to heat the electron-emitting substance. In order to shorten this heating time, cathodes having a structure for efficiently absorbing heat radiated from a heater have been proposed so far (for example, Patent Document 1, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] FIG. 8 is an explanatory diagram of an indirectly heated cathode used in a general magnetron. As shown in FIG. 8, in this type of indirectly heated cathode 30, a heater 32 is disposed in a hollow portion of a cathode sleeve 31 having a hollow structure, and a cathode substrate 33 in which an electron-emitting substance is impregnated in a sintered body of porous tungsten is disposed on an outer peripheral surface of the cathode sleeve 31. The cathode sleeve 31 and the cathode substrate 33 are heated by the heater 32, and when the cathode substrate 33 reaches a predetermined temperature, thermoelectrons are emitted by the action of the electron-emitting substance impregnated in the cathode substrate 33.

[0005] In order to efficiently absorb the heat radiated from the heater 32 into the cathode sleeve 31, a structure has been proposed in which a heat-absorbing layer is provided on the inner surface of the hollow portion of the cathode sleeve 31. For example, Patent Document 1 discloses an indirectly heated cathode in which a heat-absorbing film composed of a sintered film is formed by coating the inner surface of the cathode sleeve with a slurry containing tungsten powder and alumina and firing it in a reducing gas atmosphere. Generally, sintered films have poor thermal conductivity and are difficult to form thinly. Therefore, there was a problem that the time it took for the cathode substrate 33 to reach a predetermined temperature due to the heat radiated from the heater 32 became long.

[0006] Furthermore, Patent Document 2 discloses an indirectly heated cathode in which a tungsten oxide layer is formed on the inner surface of the hollow portion of a cathode sleeve made of a nichrome alloy by sputtering, and then aged (heated) to form a heat-absorbing layer of brown chromium oxide and black metallic tungsten on the inner surface of the cathode sleeve. The sputtering method allows for the formation of a thinner film than a sintered film. However, when forming a sputtered film on the inner surface of the hollow portion of a long, narrow cathode sleeve using the sputtering method, the thickness of the sputtered film decreases as it moves away from the opening compared to near the opening, making it difficult to form a film of uniform thickness.

[0007] Therefore, the object of the present invention is to provide an indirectly heated cathode that can shorten the time until thermionic emission begins, and a method for manufacturing an indirectly heated cathode that can easily produce a heat absorption layer of uniform thickness. [Means for solving the problem]

[0008] The indirectly heated cathode of the present invention comprises a cathode sleeve, a heater disposed in the hollow portion of the cathode sleeve, a black heat-absorbing layer covering the inner surface of the hollow portion of the cathode sleeve, and a cathode substrate disposed in the cathode sleeve and supporting an electron-emitting material, wherein the black heat-absorbing layer comprises at least tungsten and aluminum oxide. , diameter less than 0.1 μm It is composed of granular material.

[0009] The present invention relates to a method for manufacturing an indirectly heated cathode, comprising: a cathode sleeve; a heater disposed in the hollow portion of the cathode sleeve; a black heat-absorbing layer covering the inner surface of the hollow portion of the cathode sleeve; and a cathode substrate disposed in the cathode sleeve and supporting an electron-emitting material, wherein the black heat-absorbing layer comprises: a) a rod-shaped alumina ceramic, a first tungsten heater wound around the alumina ceramic, and a second tungsten heater wound around the first tungsten heater between the first tungsten heater and the inner surface of the hollow portion of the cathode sleeve. The configuration is formed by the steps of: a) arranging a tungsten heater and a) heating the alumina ceramics with the first tungsten heater and the second tungsten heater in a vacuum atmosphere, evaporating a portion of the alumina ceramics, and evaporating a portion of at least one of the first tungsten heater or the second tungsten heater, thereby laminating a granular material containing at least tungsten derived from the first tungsten heater or the second tungsten heater and aluminum oxide derived from the alumina ceramics on the inner surface of the hollow portion of the cathode sleeve. [Effects of the Invention]

[0010] According to the indirectly heated cathode of the present invention, the black heat absorption layer can be composed of a thin film of granular material containing tungsten and aluminum oxide. This shortens the time it takes for the black heat absorption layer to reach a predetermined temperature, thereby shortening the time until thermionic emission begins. Furthermore, the method for manufacturing the indirectly heated cathode of the present invention allows for the easy formation of a black heat absorption layer of uniform thickness. [Brief explanation of the drawing]

[0011] [Figure 1] This is an explanatory diagram of one embodiment (Embodiment 1) of the indirectly heated cathode of the present invention. [Figure 2] This is an explanatory diagram of another embodiment (Embodiment 2) of the indirectly heated cathode of the present invention. [Figure 3] This is an explanatory diagram of one embodiment of the method for manufacturing an indirectly heated cathode according to the present invention. [Figure 4] This is an explanatory diagram of one embodiment of the method for manufacturing an indirectly heated cathode according to the present invention. [Figure 5] This is a scanning electron microscope (SEM) image showing the surface state of the black heat absorption layer in the indirectly heated cathode of the present invention. [Figure 6] This is the result of elemental analysis of the black heat absorption layer of the indirectly heated cathode of the present invention by energy-dispersive X-ray spectroscopy. [Figure 7] This is the result of elemental analysis of the black heat absorption layer of the indirectly heated cathode of the present invention by energy-dispersive X-ray spectroscopy. [Figure 8] This is an explanatory diagram of an indirectly heated cathode commonly used in magnetrons. [Modes for carrying out the invention]

[0012] Next, embodiments of the indirectly heated cathode of the present invention and embodiments of its manufacturing method will be described with reference to the drawings. However, the present invention is not limited to these embodiments and embodiments, and the members, materials, etc. described below can be modified in various ways within the scope of the spirit of the present invention. In addition, the same reference numerals in the drawings indicate equivalent or identical components, and the sizes and positional relationships between each component are for convenience only and do not reflect actual conditions.

[0013] (Embodiment 1) FIG. 1 is an explanatory diagram of an embodiment (Embodiment 1) of the indirectly heated cathode of the present invention and is an explanatory diagram of an indirectly heated cathode used in a general magnetron. As shown in FIG. 1, the indirectly heated cathode 10 of the present embodiment includes a helical heater 2 disposed in a hollow portion of a hollow cathode sleeve 1 made of molybdenum, and a cathode substrate 3 is disposed on the cathode sleeve 1. In the present embodiment, as shown in FIG. 1, a cylindrical cathode substrate 3 in which an electron-emitting material is impregnated in a sintered body of porous tungsten is disposed on the outer peripheral surface of the cathode sleeve 1. As the electron-emitting material, for example, calcium barium aluminate or the like can be used. The cathode sleeve 1 and the cathode substrate 3 are adhesively bonded without gaps using, for example, a brazing material.

[0014] The indirectly heated cathode 10 of the present embodiment includes a black heat absorption layer 4 on the inner surface of the hollow portion of the cathode sleeve 1. The black heat absorption layer 4 according to the indirectly heated cathode 10 of the present embodiment has a structure in which particulate substances containing at least tungsten and aluminum oxide are laminated. Alternatively, the black heat absorption layer 4 further has a structure in which particulate substances containing at least one of magnesium or calcium are laminated. Such a black heat absorption layer 4 can be formed to a thickness of about 0.5 to 5 μm according to the manufacturing method described later. The composition and the like of the black heat absorption layer 4 will be described later.

[0015] As shown in FIG. 1, the indirectly heated cathode 10 of the present embodiment is configured to include a black heat absorption layer 4 on the inner surface of the hollow portion of the cathode sleeve 1, so that the heat emitted from the heater 2 is efficiently absorbed by the black heat absorption layer 4, and the heat is transmitted to the cathode sleeve 1 and the cathode substrate 3 to heat the electron-emitting material. Since the black heat absorption layer 4 is composed of a thin film having a uniform thickness, the time until the black heat absorption layer 4 reaches a predetermined temperature is shortened, and the time until thermoelectron emission starts can be shortened.

[0016] In the case of indirectly heated cathodes having the same structure, when comparing the electric power supplied to heater 2 until cathode substrate 3 reaches the same temperature (1050 °C) within a predetermined time (10 minutes), 130 W (10 V, 13 A) was required when the black heat absorption layer 4 was not provided, whereas 114 W (9.5 V, 12 A) was required when the black heat absorption layer 4 was provided. From these results, it was confirmed that power saving of approximately 10% is possible.

[0017] Note that the cathode substrate 3 carrying the electron-emitting substance is not limited to a sintered body of porous tungsten having the structure shown in FIG. 1. For example, a cylindrical cathode substrate 3 made of nickel may be disposed on the outer peripheral surface of the cathode sleeve 1, and the electron-emitting substance may be carried on this cathode substrate 3. In this case, if a concave portion such as a groove shape or an island shape is formed on the surface of the cathode substrate 3 on the cylinder and the electron-emitting substance is embedded in this concave portion, the electron-emitting substance can be carried. At this time, if an oxide of an alkaline earth metal such as barium, strontium, or calcium is used as the electron-emitting substance, an oxide cathode can be formed. When an oxide cathode is used, since the operating temperature is lower than that of the impregnated cathode described in the present embodiment, a configuration in which the black heat absorption layer 4 is provided on the inner surface of the hollow portion of the cathode sleeve 1 made of nickel can be adopted.

[0018] Furthermore, the heater 2 of the indirectly heated cathode 10 in this embodiment is not limited to the structure shown in Figure 1, and the first tungsten heater 7 and second tungsten heater 8 (shown in Figures 3 and 4) used in the method for manufacturing the indirectly heated cathode of the present invention, which will be described later, can also be used as is. In addition, the alumina ceramics 6 (shown in Figures 3 and 4) can also be used as is as a support member to prevent displacement of the first tungsten heater 7. When the first tungsten heater 7 and second tungsten heater 8 are used as the heater 2 of the indirectly heated cathode, they should be used at a temperature lower than the temperature of the first tungsten heater 7 and second tungsten heater 8 when forming the black heat absorption layer 4. In particular, when used with the alumina ceramics 6 in place, for example, if the temperature of the first tungsten heater 7 and second tungsten heater 8 when forming the black heat absorption layer 4 is 1400 to 1500°C, it is desirable that the temperature of the first tungsten heater 7 and second tungsten heater 8 used as the heater 2 of the indirectly heated cathode be 1300°C or lower so that the alumina ceramics 6 does not evaporate. Typically, the operating temperature of an impregnated cathode is approximately 1050°C, and the operating temperature of an oxide cathode is approximately 800°C, so there are no problems whatsoever.

[0019] (Embodiment 2) Figure 2 is an explanatory diagram of another embodiment (Embodiment 2) of the indirectly heated cathode of the present invention, and is an explanatory diagram of an indirectly heated cathode used in general klystrons and the like. In this embodiment, as shown in Figure 2, the indirectly heated cathode 20 has a hollow structure cathode sleeve 1 made of molybdenum, in which a helical heater 2 is arranged in the hollow part, and a cathode substrate 3 is arranged at one end of the cathode sleeve 1. In this embodiment, as shown in Figure 2, one end of the cathode sleeve 1 is sealed with a metal cap 5 made of molybdenum or the like, and a cylindrical cathode substrate 3, which is a porous tungsten sintered body impregnated with an electron-emitting material, is arranged via this metal cap 5. The electron-emitting material can be, for example, barium calcium aluminate. The cathode sleeve 1 and the metal cap 5, and the metal cap 5 and the cathode substrate 3 are bonded together without gaps, for example, using a brazing material.

[0020] The indirectly heated cathode 20 of this embodiment is provided with a black heat-absorbing layer 4 on the inner surface of the hollow portion of the cathode sleeve 1 and on the surface of the metal cap 5 that closes one end of the cathode sleeve 1 and is exposed into the hollow portion of the cathode sleeve 1. The black heat-absorbing layer 4 of the indirectly heated cathode 20 of this embodiment is also composed of a laminated granular material containing at least tungsten and aluminum oxide. Alternatively, the black heat-absorbing layer 4 may be composed of a laminated granular material containing at least one of magnesium or calcium. Such a black heat-absorbing layer 4 can be formed to a thickness of about 0.5 to 5 μm according to the manufacturing method described later. The composition of the black heat-absorbing layer 4 will be described later.

[0021] As shown in Figure 2, the indirectly heated cathode 20 of this embodiment is configured to have a black heat-absorbing layer 4 on the inner surface of the hollow portion of the cathode sleeve 1 and on the surface of the metal cap 5 that closes one end of the cathode sleeve 1 and is exposed into the hollow portion of the cathode sleeve 1. As a result, the heat emitted from the heater 2 is efficiently absorbed by the black heat-absorbing layer 4, and the heat is transferred to the cathode sleeve 1, the metal cap 5, and the cathode substrate 3, heating the electron-emitting material. Since the black heat-absorbing layer 4 is made up of a thin film of uniform thickness, the time it takes for the black heat-absorbing layer 4 to reach a predetermined temperature is shortened, and the time until thermionic emission begins can be shortened.

[0022] The cathode substrate 3 supporting the electron-emitting material is not limited to a porous tungsten sintered body with the structure shown in Figure 2. For example, a cup-shaped cathode substrate made of a metal such as nickel or molybdenum that supports the electron-emitting material can be placed on a metal cap 5 that closes one end of the cathode sleeve 1, and the electron-emitting material can be supported by this cathode substrate. In this case, the electron-emitting material can be supported by embedding it in the cup-shaped cathode substrate. If an oxide of an alkaline earth metal such as barium, strontium, or calcium is used as the electron-emitting material, an oxide cathode can be constructed. When an oxide cathode is used, the operating temperature is lower compared to the impregnated cathode described in this embodiment, so a black heat-absorbing layer 4 can be provided on the inner surface of the hollow part of the nickel cathode sleeve 1.

[0023] In this embodiment, a metal cap 5 is provided to securely adhere the cathode substrate 3 to one end of the cathode sleeve 1. However, the adhesion structure between the cathode sleeve 1 and the cathode substrate 3 can be modified in various ways. For example, instead of providing a metal cap 5, the end of the cathode sleeve 1 facing the cathode substrate 3 can be closed, and the cathode substrate 3 can be positioned within this closed structure (a structure in which a part of the cathode sleeve 1 constitutes the bottom). In this case, the black heat-absorbing layer 4 will be positioned to cover the inner surface of the hollow portion of the cathode sleeve 1, including the bottom.

[0024] (Method for manufacturing an indirectly heated cathode) Next, embodiments of the method for manufacturing an indirectly heated cathode according to the present invention will be described.

[0025] Figures 3 and 4 are explanatory diagrams of one embodiment of the method for manufacturing an indirectly heated cathode of the present invention, and are explanatory diagrams of the case in which a black heat absorption layer 4 is formed on an indirectly heated cathode having the structure described in Embodiment 1. The black heat absorption layer 4 is formed, for example, by a) a step of arranging a rod-shaped alumina ceramic, a first tungsten heater wound around the alumina ceramic, and a second tungsten heater wound around the first tungsten heater between the first tungsten heater and the inner surface of the hollow portion of the cathode sleeve in the hollow portion of the cathode sleeve, and b) heating the alumina ceramic with the first tungsten heater and the second tungsten heater in a vacuum atmosphere, evaporating a portion of the alumina ceramic and evaporating at least a portion of either the first tungsten heater or the second tungsten heater, and laminating a granular material containing at least tungsten derived from the first tungsten heater or the second tungsten heater and aluminum oxide derived from the alumina ceramic on the inner surface of the hollow portion of the cathode sleeve. Specifically, in step a) above, as shown in Figure 3, a rod-shaped alumina ceramic 6 and a first tungsten heater 7 wound around the alumina ceramic 6 to heat it are placed inside the hollow part of the hollow cathode sleeve 1, and a second tungsten heater 8 is wound around the first tungsten heater 7 and placed in the space between the first tungsten heater 7 and the inner surface of the hollow part of the cathode sleeve 1.

[0026] Alumina ceramics 6 contain 99% alumina and include magnesium oxide and calcium oxide as sintering aids. As an example, Kyocera Corporation's product (product name: A479) is used. The first tungsten heater 7 and the second tungsten heater 8 use, for example, pure tungsten wire (purity 99.95% or higher) with a wire diameter of φ0.46 mm. Alternatively, rhenium-tungsten alloy wire (for example, containing 3% rhenium) can be used instead of pure tungsten wire.

[0027] Next, as shown in Figure 3, the alumina ceramics 6, the first tungsten heater 7, and the second tungsten heater 8 are placed inside the hollow portion of the cathode sleeve 1, and then placed in a sealed container equipped with an exhaust device. Subsequently, in step b) above, the inside of the container is vacuumed to 1.3 × 10⁻⁶. -5 ~1.8×10 -6 Approximately Pa, for example, 2.7 × 10⁻⁶ -5 The air is exhausted to approximately Pa, and the current flowing to the first tungsten heater 7 and the second tungsten heater 8 is controlled to set the surface temperature of the first tungsten heater 7 and the second tungsten heater 8 to approximately 1400-1500°C. Since the alumina ceramics 6 are heated by the first tungsten heater 7 and the second tungsten heater 8, they are placed in the hottest part of the cathode sleeve 1. The inner surface of the hollow part of the cathode sleeve 1 is the coldest part of the cathode sleeve 1.

[0028] When the surface temperature of the alumina ceramics 6 reaches 1400-1500°C, the aluminum-containing material constituting the alumina ceramics 6 evaporates and diffuses into the hollow portion of the cathode sleeve 1. Meanwhile, the surface temperatures of the first tungsten heater 7 and the second tungsten heater 8 also reach approximately 1400-1500°C, and come into contact with the vapor of the aluminum-containing material evaporated from the alumina ceramics 6. As a result, evaporation of the tungsten-containing material from the surface of the first tungsten heater 7 and / or the second tungsten heater 8 is promoted. The evaporated material then adheres to the inner surface of the hollow portion of the cathode sleeve 1, where the temperature is lowest. By holding this state for 100 hours, a material of approximately 5 μm thickness is deposited on the inner surface of the hollow portion of the cathode sleeve 1, forming a black heat-absorbing layer 4. The thickness of the deposited material can be controlled to a thickness corresponding to the holding time by appropriately changing the holding time.

[0029] Subsequently, a cathode substrate 3, for example, made of porous tungsten and impregnated with an electron-emitting material, is bonded to the outer surface of the cathode sleeve 1 without any gaps using a soldering agent or the like. The cathode substrate 3 is bonded to the outer surface of the cathode sleeve 1, on which a black heat-absorbing layer 4 is formed, as shown in Figure 4.

[0030] According to this embodiment, a rod-shaped alumina ceramic 6 is positioned opposite the inner surface of the hollow portion of the cathode sleeve 1, and a first tungsten heater 7 and a second tungsten heater 8 are wound around it. At least the region of the inner surface of the hollow portion of the cathode sleeve 1 corresponding to the region where the cathode substrate 3 is formed, that is, the region where the black heat absorption layer 4 is formed, is heated at a nearly uniform temperature. As a result, evaporation occurs from the alumina ceramic 6 and the like in this region, reducing variations in the thickness of the black heat absorption layer 4 adhering to the inner surface of the hollow portion.

[0031] Furthermore, the black heat-absorbing layer 4 is visibly black, and it has been confirmed that it remains black even when a high temperature (e.g., 1050°C) is applied to operate the magnetron, etc. Therefore, in this specification, it is referred to as the "black heat-absorbing layer."

[0032] Furthermore, even when the first tungsten heater 7 and / or the second tungsten heater 8 are heated to 1400-1500°C without the alumina ceramics 6, the black heat absorption layer 4 is not formed. In this case, there is no change in the surface condition of the first tungsten heater 7 and the second tungsten heater 8, and it was not possible to confirm that tungsten-containing material evaporates from their surfaces. In contrast, as in this embodiment, when the first tungsten heater 7 and the second tungsten heater 8 are heated to 1400-1500°C, the temperature at which alumina can evaporate, with alumina ceramics 6 (99% purity) present, the black heat absorption layer 4 is formed. At this time, the surface condition of the second tungsten heater 8 changes significantly (the surface becomes rough with a pearlescent texture), and it has been confirmed that tungsten-containing material evaporates from its surface. From these results, it is considered that the evaporation of tungsten-containing material from the surface of the first tungsten heater 7 and / or the second tungsten heater 8 is promoted by contact with the vapor of material evaporated from the alumina ceramics 6.

[0033] Next, we will describe the material that adheres to the inner surface of the hollow portion of the cathode sleeve 1 and constitutes the black heat absorption layer 4. Figure 5 shows an SEM image of the surface state of the black heat absorption layer 4. As shown in Figure 5, the black heat absorption layer 4 is a layer of granular material with a particle size of approximately 0.1 μm or less. This black heat absorption layer 4 can be formed to a desired thickness in the range of approximately 0.5 to 5 μm by appropriately selecting the time for layering. For example, even when heated under conditions such as a temperature of 1050°C and a holding time of 100 hours or more, simulating the operating conditions of an electron tube such as a magnetron equipped with an impregnated cathode, the shape of this granular material does not change and it maintains its black color.

[0034] As shown in Figure 5, the granular material constituting the black heat-absorbing layer 4 is very small, resulting in the formation of a dense film. Furthermore, because the lamination rate is slow, it is formed at high temperatures, and the granular material is composed of multiple substances, the bonding between the granular material and the cathode sleeve 1, as well as the bonding between the granular material itself, is strong, resulting in a black heat-absorbing layer 4 with low thermal resistance. This black heat-absorbing layer 4 was confirmed to adhere to the cathode sleeve 1 and not easily peel off, compared to heat-absorbing films made of general sintered bodies.

[0035] The composition of this black heat-absorbing layer 4 will now be explained. Figure 6 shows the elemental analysis results of the black heat-absorbing layer 4 by energy-dispersive X-ray spectroscopy (EDS). As shown in Figure 6, it is confirmed that tungsten, aluminum, oxygen, and magnesium are present. Figure 7 shows the elemental analysis results of another part of the black heat-absorbing layer 4 that was formed at the same time by EDS. As shown in Figure 7, it is confirmed that tungsten, aluminum, oxygen, magnesium, and calcium are present.

[0036] As shown in Figures 6 and 7, the elements mainly contained in the black heat absorption layer 4 are thought to originate from the alumina ceramics 6, the first tungsten heater 7, and the second tungsten heater 8. The black heat absorption layer 4 contains the most abundant tungsten. Normally, tungsten heaters do not evaporate in a vacuum atmosphere at a temperature of around 1400-1500°C when alumina ceramics are not present. However, in this embodiment, since evaporation occurs under these conditions and in the presence of alumina ceramics 6, it is thought that the tungsten evaporates by reacting with the vapor of the substance evaporated from the alumina ceramics 6. The evaporated substance is thought to exist as tungsten on the inner surface of the hollow part of the cathode sleeve 1. In addition, some of the tungsten is thought to exist as an oxygen-containing compound. This is because these substances can exist stably at the high temperatures in which the electron tube operates.

[0037] The magnesium and calcium seen in Figures 6 and 7 are thought to originate from magnesium oxide and calcium oxide added to the alumina ceramics 6 as sintering aids. This magnesium and calcium are thought to exist as compounds composed of tungstic acid, a compound containing tungsten and oxygen, and magnesium or calcium, or as compounds composed of aluminic acid, an aluminum oxide, and magnesium or calcium. This is because these substances can exist stably even at the high temperatures in which the electron tube operates. Furthermore, since the black heat absorption layer 4 contains magnesium and calcium, it can be seen that the black heat absorption layer 4 also contains a layer of material evaporated from the alumina ceramics 6 (derived from the alumina ceramics).

[0038] According to the method for manufacturing an indirectly heated cathode of the present invention, a black heat-absorbing layer 4 can also be formed on the indirectly heated cathode having the structure described in Embodiment 2.

[0039] Although one embodiment of the method for manufacturing an indirectly heated cathode according to the present invention has been described above, the present invention is not limited thereto. For example, the purity of the alumina ceramics, the type of sintering aid included, the heating temperature, and the heating time can be appropriately selected and set. Since the indirectly heated cathode formed by the present invention is used in a vacuum atmosphere, it is necessary to prevent the inclusion of substances that may reduce the vacuum level, and a purity of about 99% for the alumina ceramics is preferable. In addition, the first tungsten heater 7 can be right-handed and the second tungsten heater 8 can be left-handed.

[0040] (summary) (1) One embodiment of the indirectly heated cathode of the present invention is an indirectly heated cathode comprising a cathode sleeve, a heater disposed in the hollow portion of the cathode sleeve, a black heat-absorbing layer covering the inner surface of the hollow portion of the cathode sleeve, and a cathode substrate disposed in the cathode sleeve and supporting an electron-emitting material, wherein the black heat-absorbing layer may be composed of a granular material containing at least tungsten and aluminum oxide.

[0041] According to the indirectly heated cathode of the present invention, the time it takes for the black heat absorption layer, which is composed of a thin film of granular material containing tungsten and aluminum oxide, to reach a predetermined temperature is shortened, and the time it takes for the electron-emitting material supported on the cathode substrate 3 to reach a predetermined temperature is also shortened, making it possible to shorten the time until thermionic emission begins.

[0042] (2) The black heat-absorbing layer may further include granular material containing at least one of magnesium or calcium.

[0043] (3) One embodiment of the present invention for manufacturing an indirectly heated cathode is a method for manufacturing an indirectly heated cathode comprising: a cathode sleeve; a heater disposed in the hollow portion of the cathode sleeve; a black heat-absorbing layer covering the inner surface of the hollow portion of the cathode sleeve; and a cathode substrate disposed in the cathode sleeve and supporting an electron-emitting material, wherein the black heat-absorbing layer comprises: a) a rod-shaped alumina ceramic, a first tungsten heater wound around the alumina ceramic, and a second tungsten heater wound around the first tungsten heater between the first tungsten heater and the inner surface of the hollow portion of the cathode sleeve. The alumina ceramics can be formed by the steps of: a) arranging a tungsten heater and a) heating the alumina ceramics with the first tungsten heater and the second tungsten heater in a vacuum atmosphere, evaporating a portion of the alumina ceramics, and evaporating a portion of at least one of the first tungsten heater or the second tungsten heater, thereby laminating a granular material containing at least tungsten derived from the first tungsten heater or the second tungsten heater and aluminum oxide derived from the alumina ceramics on the inner surface of the hollow portion of the cathode sleeve.

[0044] (4) The alumina ceramics comprises alumina and magnesium oxide and / or calcium oxide as sintering aids, and step b) may be a step of further laminating granular material containing at least one of magnesium or calcium by heating the alumina ceramics to 1400-1500°C in a vacuum atmosphere using the first tungsten heater and the second tungsten heater. [Explanation of symbols]

[0045] 10, 20, 30 indirectly heated cathode 1.31 Cathode Sleeve 2, 32 heaters 3, 33 Cathode substrate 4. Black heat-absorbing layer 5. Metal cap 6. Alumina Ceramics 7. First tungsten heater 8. Second tungsten heater

Claims

1. A method for manufacturing an indirectly heated cathode comprising a cathode sleeve, a heater disposed in the hollow portion of the cathode sleeve, a black heat-absorbing layer covering the inner surface of the hollow portion of the cathode sleeve, and a cathode substrate disposed in the cathode sleeve and supporting an electron-emitting material, The aforementioned black heat-absorbing layer a) A step of arranging a rod-shaped alumina ceramic, a first tungsten heater wound around the alumina ceramic, and a second tungsten heater wound around the first tungsten heater between the first tungsten heater and the inner surface of the hollow portion of the cathode sleeve, and b) A step of heating the alumina ceramics with the first tungsten heater and the second tungsten heater in a vacuum atmosphere, evaporating a portion of the alumina ceramics, and evaporating at least a portion of either the first tungsten heater or the second tungsten heater, thereby laminating a granular material containing at least tungsten derived from the first tungsten heater or the second tungsten heater and aluminum oxide derived from the alumina ceramics on the inner surface of the hollow portion of the cathode sleeve. Characterized by being formed by A method for manufacturing an indirectly heated cathode.

2. The alumina ceramics comprises alumina and magnesium oxide and / or calcium oxide as sintering aids. The aforementioned step b) is, The method includes heating the alumina ceramics to 1400 to 1500°C using the first tungsten heater and the second tungsten heater in a vacuum atmosphere. This process involves further layering granular material containing at least one of magnesium or calcium. A method for manufacturing an indirectly heated cathode according to claim 1.

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