JPS5958736A - Electron gun for indirectly-heated type impregnated cathode - Google Patents

Abstract

PURPOSE:To effectively use the heat diffused from a cathode substrate and a support cylinder by integrating a compound body consisting of a cylindrical body for heat reflection and a primary grid. CONSTITUTION:A cathode support rod 12 is secured on an insulating plate 7 such as alumina with holes for mounting cathodes in the position where the upper part of a cylinder centering around the holes for mounting the cathodes is trisected. A support cylinder 2 is secured to the cathode support rod 12 through a cathode support plate 9. A primary grid that is opposed to a cathode substrate 1' and has holes through which an electron beam passes and a compound used additionally as a cylindrical body for heat reflection that effectively uses the radiated heat diffused from the cathode substrate 1' and the support cylinder 2 are provided at the outside of the cathode substrate 1' and the support cylinder 2. The power consumption of a heater 3 can be reduced by using this electrode structure.

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 invention]

The cathode of the so-called impregnated or supplemented type is used in an image pickup tube,
It is seen as promising for use in photoelectric conversion tubes such as 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-emitting substance and a sleeve, and is heated by a heating element such as a heater. This impregnated cathode is made of a porous cathode substrate made by sintering powder containing W as the main component under appropriate sintering conditions, and Ba0-A/203.
A molten compound made of CaO or the like is impregnated into the pores of the cathode substrate as an electron emitting substance. When using, M
The cathode substrate is held in a cylindrical sleeve made of a high-melting point metal such as O or Illa, and a heater for heating the cathode is installed inside the sleeve, making it 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, as electron radiation sources such as image pickup tubes and cathode ray tubes,
An oxide cathode containing (Ba, Sr, Ca)O as a main component is used. The oxide h-sode is an electron source that can obtain a saturation current density of 10 A/cm2 at 1000°;

Because Sr, Ca) 0 powder is used, it is vulnerable to ion bombardment, and because the electrical resistance is high (the specific resistance of a fully activated oxide cathode is approximately 104 Ωcm), it operates with a large amount of radiation current, and the oxide is heated by self-heating. The drawback is that the cathode itself deteriorates. Therefore, the radiation current density of the oxide cathode during steady operation is set to a low value of about 0.5 A/cm (!).

On the other hand, impregnated cathodes use metals with high high temperature strength such as W, Mo, Re, or their alloys as the cathode substrate, so they are resistant to ion bombardment and have low electrical resistance (
Since the resistivity of W is small (approximately 4.9×1ff"Ωcm), the temperature of the cathode substrate does not rise due to self-heating even when operated at a high radiation current density.

However, in order to obtain a saturation current density of 10 A/cm2 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 explained, taking as examples the case where an oxide cathode is used and the case where an impregnated cathode is used.

Example 1: Figure 1 shows the most common structure of an electron gun using a conventional indirectly heated oxide cathode. (I3a.

An oxide consisting of Sr, Ca)0 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, A/etc.) added thereto. 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 supported by a holding base 8.
It is fixed to a cathode support 4 which also serves as a heat reflecting cylinder, and attached to an insulating plate 7. Heater 3 for cathode heating
is used by being inserted inside the support cylinder 2. A practical electron gun includes a first grid '5 facing the cathode substrate 1 and having holes through which electrons do not flow, and a second grid 6 for extracting electrons.
In addition, multiple electrodes are used to project an electron stream onto a fluorescent surface. The disadvantage of this electron gun configuration is that the supporting cylinder 2
has a large heat capacity and a long length, and a large amount of heat escapes to the holding table 8 and the cathode support 4, so 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 thermal expansion due to temperature rise will also increase, resulting in fluctuations in the distance between the cathode surface and the first grid 5 (cathode surface (!: When the distance between the first grid and the first grid is 00 μm) (It is said that the permissible value for fluctuation is 10 inches or less) also increases.

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 designed 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 has 3 points on its circumference.
It is fixed to the upper part of the cathode support 4 by cathode support plates 9 attached at one or four locations. The other electrode structures are much the same in Example 1. The feature of the wooden sword type is that the time required for the cathode surface temperature to reach a steady value is shortened (reduced to about 174 in the case of Example 1) due to the decrease in the heat capacity of the cathode part. Furthermore, the cathode support plate 9 expands to absorb deformation of the support cylinder 2 due to thermal expansion, thereby maintaining a constant distance between the cathode surface and the first grid 5.

The two examples given here are electron-emitting substances (Ha,
When using oxides such as 8r, Ca)0.

Therefore, since the temperature of the cathode substrate 1 is as low as 800°C at most, there is no need for any special operation on the cathode cylinder 4, which also serves as a heat reflecting cylinder to effectively utilize the heat radiated from the cathode. There are no major obstacles.

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

Example 3: FIG. 3 shows an example of the structure of an indirectly heated electron gun using an impregnated cathode. Ba0-A as an electron emitting material in porous W
The cathode substrate 1' impregnated with l2O2.CaO is made of a thin plate (20 to 30 μm) of a heat-resistant metal such as Mo, Ta, or W.
It is supported by a support cylinder 2 made of (m thickness). This support cylinder 2 is held at one end ζ 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 fixedly attached to the insulating plate 7.1. Ru. When using such an impregnated cathode as an electron gun, the cathode base 1'
The electron beams are projected onto a fluorescent surface or the like using a first grid 5 which faces the electron beam and has a hole through which the electron beam passes, a second grid 6 which is a pole for extracting the electron beam, and a converging electrode.

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 to 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 does not reflect radiant heat from around the cathode base 1' to 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 comprises a cathode base made of a porous metal, a cylindrical support cylinder supporting the cathode, and a heating element; In an electron gun, the electron gun is composed of a heat-reflecting cylinder that reflects heat dissipated to the cathode side, and a first grid facing the cathode and having holes through which electrons flow. It is characterized by making one grid into an integrated complex.

[Embodiments of the invention]

The present invention will be explained below using examples.

Example 1 The structure of an electron gun according to the present invention will be explained with reference to FIG. 4. Porous W with a porosity of 20 to 25 inches. B a O・Al
Cathode substrate 1 impregnated with an electron-emitting substance called 2O3.CaO
' (ii diameter 1.4 mmφ, thickness 0.6 nun
) is a support cylinder 2 made of Mo with a wall thickness of 25 μm and a length of 6 mm.
I supported it. In addition to MO, the material for the support cylinder 2 may be W, Ta, or Re as long as it is a 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 17 inside the support cylinder 2 and used. A barrier plate 10 is provided on the side where the cathode substrate 1' is in contact with the heater 3 in order to prevent breakdown of insulation of the heater 3 due to evaporation of It and electron emitting substances. As with the support cylinder 27, it is desirable to use a heat-resistant metal with high high temperature strength as the barrier plate 1°. In this example, a Mo plate with a wall thickness of 25 μm was used. Cathode substrate 1'
The supporting cylinder 2 and the barrier plate were fixed with R, u-Mo brazing material. An insulating plate 7 made of alumina or the like having a hole for attaching a cathode (multiple holes when there are multiple cathodes like a color cathode ray tube) is divided into three equal parts on the circumference with the hole for attaching the cathode as the center. The cathode support rod 12 is fixed at the (or quartered) position. A support cylinder 2 was fixed 17 to the cathode support rod 12 with a cathode support plate 9 interposed therebetween. 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 may be used.

W, Ta, 1Le, Pt, or an alloy thereof may be used. In this example, Mo was used. Further, one of the cathode support rods J2 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 are first lids that face the cathode base 1' and have holes through which electron beams pass, which make 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 composite body 11 may rise by 500 to 600"O# due to the radiant heat of the cathode substrate 1' and the support cylinder 2, the material for the composite body 11 should be a heat-resistant alloy with high high-temperature strength and low thermal expansion. Ba Mo.

W, '['a, lLp, Pt, Ni or (
Alternatively, alloys of these may 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 a suitable range is 50 to 200 μm. The composite body 11 of this example has 10 Mo blue hooks.
Although a material cut into a shape with a wall thickness of 0 μm was used, the composite body 11 may be manufactured by deep drawing, or by brazing or welding a cylinder and a perforated disk corresponding to the first grid.

In addition, the distance between the first crid and the cathode substrate 1' is 100 μm,
The support cylinder 2 and the composite body 11 were assembled so that the distance between them was 1, Qlnm. A first crib 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 6 is provided outside the complex 11.
Grid lead wire 15 was connected. Reference numerals 18 and 19 denote mounting fittings for fixing the composite body 11 and the second grid 6 to the insulating plate 7. In addition, in FIG. 4 (bl, some parts such as cathode lead wires are omitted).

By using the electrode structure described above, the power consumption of the heater 3 to heat the cathode substrate 1' of the same size to the same temperature can be reduced by about 15 times.

Similar results were obtained when a different metal was used as the coating material for composite 11.

Embodiment 2 FIG. 5 shows an embodiment of the present invention aimed at reducing the power consumption of the heater 3 and the change in the distance between the first grid 5' and the cathode substrate 1' due to thermal deformation of the composite 11. Give an example.

The composite body 11 includes a first grid 5' made of a disk having a hole through which an electron beam passes, and a heat reflecting cylinder 16 made of a cylinder having a ring-shaped side surface.

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. Moreover, the composite body 11 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. A circular plate with a wall thickness of 100 μm was used as the first crid 5'. Heat reflecting cylinder 1
6 has a radius of curvature of 0.5 + on the side of a cylinder with a wall thickness of 50 μm.
A mold made by press-shaping a ring-shaped die 17 facing outward with a diameter of nm was used. The first grid 5' and the heat reflecting cylinder 16 are made of Ru.
- Connection was made using a Mo brazing filler metal. Alternatively, spot welding may be used. An effective radius of curvature of the annular mold 17 is 0.5 to 1 mm. Further, the annular shape 17 of the heat reflecting cylinder 16 is effective for the purpose of the present invention even if it is convex to the inside of the cylinder, but the distance between the supporting cylinder 2 and the heat reflecting cylinder 16 is reduced. From a practical point of view, it is better to make the single ring mold 17 convex to the outside of the cylinder.

The diametrical elongation of the disc of the first grid 5' and the heat-reflecting cylinder 1 are achieved by cutting the composite 11 of the structure of the invention.
6 could be alleviated by the cedar folds 17. By using the composite body 11 having the ring-shaped mold 17, compared to the case where a composite body without the ring-shaped mold 17 is used,
The amount of deformation due to thermal expansion could be reduced by a factor of about 10, and as a result, the change in the distance between the first grid 5' and the cathode substrate 1' could also be reduced.

Furthermore, by using the electron gun structure having the composite body 11, the power consumption of the heater 3 could be reduced by about 15% compared to the case of a conventional electron gun structure.

〔Effect of the invention〕

As explained 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 shape, deformation due to thermal expansion of the first grid can be reduced. Can 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 cand, and Figure 3 is a cross-sectional view showing the structure of a conventional indirectly heated electron gun using an impregnated cathode. Fig. 4 fa
l, (bl is a sectional view and bottom view showing the structure of an electron gun for indirectly heated impregnated cathodes in one embodiment of the present invention, and FIG. 5 is an electron gun for indirectly heated impregnated cathodes in another embodiment of the present invention. It is a sectional view showing the structure of 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, 1
DESCRIPTION OF SYMBOLS 1... Composite, 12... Cathode support rod, 13... Cathode lead wire, 14... First grid lead wire, 15...
...Second grid lead wire. 16... cylinder for field reflection, 17... ring-shaped, 18...
Mounting bracket, 19...Mounting bracket. Figure 1 Figure Z Figure J 3 Figure S Figure

Claims (1)

[Claims] 1. An indirectly heated impregnated cathode consisting of a cathode base made of porous metal, a cylindrical support cylinder supporting the same, and a heating element, and heat radiated outward from the cathode base and the support cylinder. In an electron gun consisting of a heat-reflecting cylinder that reflects electrons toward the cathode, and a first grid facing the cathode and having holes through which electrons flow, the heat-reflecting cylinder and the first grid are integrated. An electron gun for indirectly heated impregnated cathodes, which is characterized by a body. 2. In the indirectly heated impregnated cathode electron gun according to claim 1, a heat reflecting cylinder having annular folds on the side surface and a first
An electron gun for indirectly heated impregnated cathodes, which is characterized by having a grid as an integrated composite.