JPS6350814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the structure of an electron gun for indirectly heated impregnated cathodes.

[Background of the invention]

The cathode of the method called impregnation or replenishment type is
It is seen as promising for use in photoelectric conversion tubes such as image pickup tubes and cathode ray tubes, traveling wave tubes, and microwave tubes such as klystrons and magnetrons. A conventional impregnated cathode is an indirectly heated cathode that consists of a cathode base impregnated with an electron emitter and a sleeve, and is heated by a heating element such as a heater. This impregnated cathode is made of a porous cathode base made by sintering powder containing W as the main component under appropriate sintering conditions, and is coated with BaO, Al ₂ O ₃ ,
A molten compound such as CaO is impregnated into the pores of the cathode substrate as an electron emitting substance. During use, the cathode substrate is held in a cylindrical sleeve made of a high melting point metal such as Mo or Ta, and a heater for heating the cathode is installed inside the sleeve, resulting in an indirectly heated structure. The heater usually uses a W wire with good heat resistance, and an alumina coating layer for electrical insulation is formed on the surface of the W wire.

Conventionally, an oxide cathode containing (Ba, Sr, Ca)O as a main component has been used as an electron radiation source for image pickup tubes, cathode ray tubes, and the like. Oxide cathode is
This is an electron source that can obtain a saturation current density of 10A/cm ² at 1000〓, but the electron source
Since O powder is used, it is vulnerable to ion bombardment, and the electrical resistance is high (the specific resistance of a fully activated oxide cathode is about 10 ⁴ Ωcm), so when operated with a large amount of radiation current, the oxide cathode itself will heat up due to self-heating. It has the disadvantage of deterioration. Therefore, the radiation current density of the oxide cathode during steady operation is set to a low value of about 0.5 A/cm ² .

On the other hand, impregnated cathodes use W or W as the cathode substrate.
Because it uses metals with high high temperature strength such as Mo, Re, or their alloys, it is resistant to ion bombardment and has low electrical resistance (specific resistance of W is approximately 4.9×10 ^-6
Ωcm) is small, so there is no temperature rise in the cathode substrate due to self-heating even when operating at high radiation current densities.
However, in order to obtain a saturation current density of 10 A/cm ² with an impregnated cathode, it is necessary to heat the cathode substrate to a high temperature of 1000 to 1100°C. Therefore, there is a need for an electron gun structure that can effectively utilize the electric power supplied from the heater as a heating element.

Below, the structure of a conventional indirect heating type electron gun will be described, taking as examples a case where an oxide cathode is used and a case where an impregnated cathode is used.

Example 1 Figure 1 shows the structure of the most common electron gun using a conventional indirectly heated oxide cathode. (Ba, Sr,
An oxide consisting of Ca)O is applied onto the cathode substrate 1. The material of the cathode substrate 1 is mainly Ni, with a small amount of other activators (Mg, Si, Al, etc.) added. The cathode substrate 1 is supported by a support cylinder 2 made of a heat-resistant alloy (for example, nichrome), and the support cylinder 2 is further fixed to a cathode support 4 which also serves as a heat reflecting cylinder with a holding table 8 interposed therebetween. It is attached to the insulating plate 7. A heater 3 for heating the cathode is inserted inside the support cylinder 2 for use. In a practical electron gun, in addition to a first grid 5 having holes facing the cathode substrate 1 through which electrons flow and a second grid 6 for extracting electrons, a plurality of electrodes are used on the fluorescent surface. It is designed to project an electron stream. The disadvantage of this electron gun configuration is that
The support cylinder 2 has a large heat capacity and a long length.
Furthermore, since a large amount of heat escapes to the holding table 8 and the cathode support 4, the heater 3 is also required to be large.
Furthermore, the time required for the cathode surface temperature to reach a steady value becomes longer. Furthermore, if the length of the support cylinder 2 is long, the amount of thermal expansion due to temperature rise will increase, resulting in fluctuations in the distance between the cathode surface and the first grid 5 (the fluctuation when the distance between the cathode surface and the first grid 5 is 100 μm). (The permissible value is said to be 10% or less) will also increase.

Example 2 FIG. 2 shows an example of an electron gun configuration designed to reduce the heat capacity of the cathode section and also reduce the amount of deformation due to thermal expansion. The cathode substrate 1 is supported by a support cylinder 2. As a result of the cathode heating heater 3 being devised to heat the cathode portion intensively, the length of the support cylinder is also less than half that of Example 1. The support cylinder 2 is fixed to the upper part of the cathode support 4 by cathode support plates 9 attached at three or four places on its circumference. The other electrode structures are almost the same as in Example 1. A feature of this method is that the time required for the cathode surface temperature to reach a steady state is shortened (reduced to about 1/4 of that in Example 1) due to the reduction in the heat capacity of the cathode section. In addition, the cathode support plate 9 expands to absorb deformation of the support cylinder 2 due to thermal expansion, and maintains a constant distance between the cathode surface and the first grid 5.

The two examples given here are cases where oxides such as (Ba, Sr, Ca)O are used as electron emitting materials.
Therefore, the temperature of the cathode substrate 1 is as low as 800°C, so
Even if the cathode tube 4, which also serves as a heat reflecting tube for effectively utilizing the heat radiated from the cathode section, is not subjected to any special operations, there is no major problem in practical use.

Next, an example of a conventional structure of an electron gun using an impregnated cathode will be shown.

Example 3 Figure 3 shows an example of the structure of an indirectly heated electron gun using an impregnated cathode. Porous W as an electron emitting material
The cathode substrate 1′ impregnated with BaO・Al ₂・O ₃・CaO is
It is supported by a support cylinder 2 made of a thin plate (20 to 30 μm thick) of heat-resistant metal such as Mo, Ta, or W. This support cylinder 2 is held at one end opposite to the cathode base 1' by a cathode support 4 which also serves as a heat reflecting cylinder that reflects radiant heat from the cathode portion. The heater 3 is inserted inside the support cylinder 2 and heats the cathode base 1' by thermal conduction and radiant heat. A barrier plate 10 is provided on the side of the cathode substrate 1' in contact with the heater 3 to prevent the electron emitting substance from evaporating toward the heater 3 and causing dielectric breakdown of the heater 3. The cathode support 4 is attached and fixed to the insulating plate 7. When such an impregnated cathode is used as an electron gun, there is a first grid 5 which faces the cathode base 1' and has holes through which the electron beam passes, a second grid 6 which is an electrode for extracting the electron beam, and a converging electrode. The image is projected onto a fluorescent surface, etc. using

The impregnated cathode is expected to be used as a high current density electron beam source, but since its operating temperature is as high as 1000-1100°C, an electron gun configuration that reduces the power consumption of the heater as much as possible is expected. When looking at the example shown in FIG. 3 from this perspective, the conventional electron gun structure has the following drawbacks. That is, the electron gun structure does not effectively utilize the heat consumed by heat radiation from the periphery of the cathode substrate 1'. In other words, the electron gun structure is not such that the radiant heat from around the cathode base 1' is reflected toward the cathode side.

[Purpose of the invention]

A first object of the present invention is to provide an indirectly heated impregnated cathode electron gun that can effectively utilize the heat dissipated from a cathode substrate and a support cylinder serving as its support, and that can simplify the electron gun structure. That's true.

Another object of the present invention is to provide an electron gun structure that reduces deformation due to thermal expansion of the first grid due to radiant heat from the cathode section.

[Summary of the invention]

The indirectly heated impregnated cathode electron gun of the present invention includes an indirectly heated impregnated cathode comprising a cathode substrate made of a porous metal, a cylindrical support cylinder supporting the cathode substrate, and a heating element;
In an electron gun, the electron gun is composed of a cathode base body, a heat reflecting cylinder that reflects the heat radiated outward from the support cylinder toward the cathode, and a first grid facing the cathode and having holes through which electrons flow. It is characterized in that the reflecting cylinder and the first grid are integrated into a composite body, and that an annular fold is provided on the side surface of this composite body.

[Embodiments of the invention]

The present invention will be explained below using examples.

Reference Example The structure of an electron gun, which is the basis of the present invention, will be explained with reference to FIG. Porous W with a porosity of 20-25%
The cathode substrate 1' (diameter 1.4 mmφ, thickness 0.6 mm) impregnated with an electron-emitting substance called 4BaO・Al ₂ O ₃・CaO is
It was supported by a supporting cylinder 2 made of Mo and having a wall thickness of 25 μm and a length of 6 mm. In addition to Mo, the material for the support cylinder 2 may be W, Ta, Re, or any other heat-resistant metal with high high-temperature strength.
Pt or an alloy thereof may also be used. The heater 3 as a heating element is inserted inside the support cylinder 2 for use. A barrier plate 10 is provided on the side where the cathode substrate 1' contacts the heater 3 to prevent dielectric breakdown of the heater 3 due to evaporation of the electron emitting substance. Barrier plate 10
As with the support cylinder 2, it is desirable to use a heat-resistant metal with high high-temperature strength. In this reference example, the wall thickness
The cathode substrate 1', the support cylinder 2, and the barrier plate, each made of a 25 μm Mo plate, were fixed with Ru-Mo brazing material. An insulating plate 7 made of alumina or the like that has a cathode mounting hole (or multiple holes if there are multiple cathodes like a color cathode ray tube) has a circumference divided into three (or four) with the cathode mounting hole as the center. The cathode support rod 12 is fixed at the equally divided positions. Cathode support rod 12
A support cylinder 2 was fixed via a cathode support plate 9. It is preferable that the cathode support plate 9 is made of the same material as the support cylinder 2, but if it is a heat-resistant metal with high high temperature strength and low thermal expansion, Mo,
W, Ta, Re, Pt, or an alloy thereof may be used. In this reference example, Mo was used. Furthermore, one of the cathode support rods 12 was provided with a cathode lead wire for setting the potential of the cathode base 1'. On the outside of the cathode base 1' and the support cylinder 2, there is a first grid which faces the cathode base 1' and has holes through which electron beams pass, and which makes effective use of the radiant heat radiated from the cathode base 1' and the support cylinder 2. A composite body 11 was provided which also served as a heat reflecting cylinder. Since the temperature of the composite 11 may rise to 500 to 600°C due to the radiant heat of the cathode base 1' and the support cylinder 2, the material for the composite 11 may be Mo, Mo, or a heat-resistant alloy with high high-temperature strength and low thermal expansion. W,Ta,
Re, Pt, Ni, or an alloy thereof may also be used. The thickness of the composite body 11 varies somewhat depending on the operating temperature of the cathode substrate 1' (the higher the operating temperature, the better the thickness), but it is suitably 50 to 200 μm. The composite 11 of this reference example was made by cutting a Mo block into a shape with a thickness of 100 μm.
The perforated disk corresponding to the grid may be soldered or welded. Further, the assembly was performed so that the distance between the first grid and the cathode substrate 1' was 100 μm, and the distance between the support cylinder 2 and the composite body 11 was 1.0 mm.
A first grid lead wire 14 for potential setting was connected to the complex 11. A second grid 6 is provided outside the complex 11, and a second grid lead wire 15 is provided.
connected. 18, 19 are the composites 11 on the insulating plate 7
and a mounting bracket for fixing the second grid 6. Note that some parts such as the cathode lead wire are omitted in FIG. 4b.

By using the electrode structure described above, the power consumption of the heater 3 required to heat the cathode substrate 1' of the same size to the same temperature can be reduced by about 15%. Similar results were obtained when a different metal was used as the material for the composite 11. The present invention is based on this example.

Embodiment FIG. 5 shows an example in which the purpose is to effectively utilize the radiated heat, reduce the power consumption of the heater 3, and reduce changes in the distance between the first grid 5' and the cathode substrate 1' due to thermal deformation of the composite 11. Examples of the present invention are shown below.

The composite body 11 is composed of a first grid 5' consisting of a disk having a hole through which the electron beam passes, and a heat reflecting cylinder 16 consisting of a cylinder having annular folds on its side.
This composite body 11 may be made of Mo, W, Ta, Re, Pt, or an alloy thereof, as long as it is a heat-resistant metal with high high-temperature strength and low thermal expansion. Also complex 1
1 may be constructed by combining the same types of metals or by combining different types of metals. In this embodiment, an example in which Mo is used as the first grid 5' and the heat reflecting cylinder 16 will be described. The first grid 5' has a wall thickness of 100μ
A disk of m was used. The heat reflecting cylinder 16 has a wall thickness of 50μ.
The outer ring-shaped folds 17 with a radius of curvature of 0.5 mm were formed by pressing on the side surface of a cylinder with a radius of 0.5 mm.
The first grid 5' and the heat reflecting cylinder 16 are made of Ru-Mo.
Connected with solder metal. Alternatively, spot welding may be used. An effective radius of curvature of the annular folds 17 is 0.5 to 1 mm. The annular folds 17 of the heat-reflecting cylinder 16 are effective for the purpose of the present invention even if they are convex toward the inside of the cylinder, but the distance between the support cylinder 2 and the heat-reflecting cylinder 16 is reduced. From a practical point of view, it is better to make the annular folds 17 convex to the outside of the cylinder.

By making the composite 11 of the structure of the invention, the diametrical elongation of the disc of the first grid 5';
The axial extension of the heat reflecting cylinder 16 is determined by the annular folds 17.
This could be alleviated by By using the composite body 11 with ring-shaped folds 17, the amount of deformation due to thermal expansion can be reduced by about 10% compared to the case where a composite body without ring-shaped folds 17 is used, and as a result, the first grid 5' and Changes in the spacing between the cathode substrates 1' could also be reduced.
In addition, by using the electron gun structure with the composite body 11, compared to the case of the conventional electron gun structure, the
% reduction in power consumption of heater 3.

〔Effect of the invention〕

As described above, according to the present invention, in an indirectly heated impregnated cathode, the power consumption of the heating element for heating the cathode can be reduced, and by providing the annular folds, deformation due to thermal expansion of the first grid can also be reduced.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views showing the structure of a conventional indirectly heated electron gun using an oxide cathode, and Figure 3 is a cross-sectional view showing the structure of a conventional indirectly heated electron gun using an impregnated cathode. Figures 4a and 4b are a sectional view and a bottom view showing the structure of an electron gun for indirectly heated impregnated cathodes as a reference example of the present invention, and Figure 5 is an electron gun for indirectly heated impregnated cathodes in an embodiment of the present invention. It is a sectional view showing the structure of a gun. 1, 1'...Cathode base, 2...Support cylinder, 3...
...heater, 4...cathode support, 5, 5'...first
Grid, 6...Second grid, 7...Insulating plate,
8... Holding stand, 9... Cathode support plate, 10... Barrier plate, 11... Composite, 12... Cathode support rod, 13
. . . Cathode lead wire, 14 .

Claims (1)

[Scope of Claims] 1. An indirectly heated impregnated cathode comprising a cathode base made of porous metal, a support cylinder that supports the cathode base, and a heating element, and heat radiated outward from the cathode base and the support cylinder. In the electron gun, the electron gun has a heat reflecting cylinder that reflects electrons toward the impregnated cathode, and a grid that has a hole through which the electron flow passes and faces the impregnated cathode. An electron gun for an indirectly heated impregnated cathode, characterized in that the composite body has an annular fold on the side surface thereof. 2. The indirectly heated impregnated cathode electron gun according to claim 1, wherein the annular fold is configured to form a convex portion on the outside of the composite.