JPH083956Y2 - Impregnated cathode structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of Invention] (Field of Industrial Application) The present invention relates to an impregnated cathode assembly used for an electron gun of a microwave electron tube such as a high-power klystron.

(Prior Art) Microwave electron tubes such as klystrons tend to have higher output, and especially for those used for nuclear fusion and particle accelerators, their output is in the MW (megawatt) class,
Increasingly high output is desired.

Therefore, also in the cathode used for the electron gun, the emission value taken out is inevitably increased, the current value per unit area is increased, and the current density is being increased.

Therefore, in the conventionally used oxide cathode structure, the current value that can be taken out is small and the operating voltage is also high.In recent years, the impregnated type cathode structure has been replaced by the oxide cathode in terms of withstand voltage. Has become commonly used.

That is, the impregnated type cathode assembly is capable of operating at a current density of 3 A / cm ² , and its life is estimated to be tens of thousands of hours when mounted on a satellite. There is an increasing trend toward the use of impregnated cathode assemblies in high power microwave electron tubes.

 The general structure of this impregnated cathode assembly is shown in FIG.

1 is a porous cathode disk made of tungsten (W), the cathode disk 1 has a porosity of 15 to 20%, and the electron emitting material composed of BaO, CaO, and Al ₂ O _{3 in the} holes. Is to be impregnated.

Reference numeral 2 is a cylindrical storage container made of molybdenum (Mo) or the like. The storage container 2 has a function of supporting the cathode disk 1, and the back surface of the cathode disk 1 is brazed with a Ru-Mo brazing material. It is attached.

A heater 3 for heating the cathode disk 1 to an optimum operating temperature is housed in the container 2 together with an insulator 4 made of alumina or the like and embedded in the insulator 4. The object 4 is sintered by being heated in hydrogen or vacuum.

Then, after this, the surface of the cathode disk 1 which is concavely curved is filled with an electron-emitting substance, and the electron-emitting substance is heated and melted in a non-oxidizing atmosphere such as in hydrogen, whereby the electron-emitting substance is melted. Is impregnated in the hole of the cathode disk 1.

By the way, if the cathode is relatively small, there is no particular problem, but if it becomes large, the input power of the heater that heats the cathode disk increases, and the cathode disk efficiently reaches the optimum operating temperature. Various ideas have been made so that

First, the impregnated cathode has an operating temperature 100 to 200 ° C higher than that of the oxide cathode, and the temperature of the heater also rises to 1500 to 1600 ° C, so the heater is made of an insulator such as alumina. It is embedded to efficiently transfer the heat of the heater to the cathode disk and prevent the temperature of the heater from rising too much.

Then, in order to further improve the thermal efficiency, a heat reflecting cylinder is provided outside the cathode and a heat reflecting plate is provided at the rear of the cathode so that the heat of the heater is concentrated on the cathode disk. Due to its character, it is desirable to cover the part excluding the cathode disk as much as possible, but by doing so, the thermal efficiency is improved, but the gas emitted from the components that make up the cathode is eliminated. There is a problem that it takes time to exhaust.

In particular, the insulator in which the heater is embedded has a large surface area because it is made by sintering powder of alumina or the like and adsorbs a large amount of gas. Therefore, it takes time to exhaust.

This gas is discharged by energizing the heater in the exhaust process during the manufacturing process of the microwave electron tube. However, if the amount of gas discharged is large and the vacuum degree in the tube is poor, the cathode is contaminated and gas poisoning occurs. As a result, the emission after exhaust is affected, and the emission value becomes low.

FIG. 5 shows a specific structure of the large diameter impregnated cathode assembly.

Reference numeral 11 denotes a cathode disk, which is made of porous tungsten (W), has a diameter of 70 mm, has a circular through hole in the center, and has a curved surface.

12, 13 and 14 are three large, medium and small circular support cylinders made of molybdenum (Mo). These three support cylinders 12, 13 and 14 are concentrically arranged on the back surface of the cathode disk 11 and are made of Ru. -Brazed with Mo brazing material to form the container 15.

The innermost support cylinder 14 is slightly longer than the other support cylinders 12 and 13.

Reference numeral 16 is a heater, and this heater 16 is a tungsten wire having a diameter of 1.5 mm and forms two types of annular coils to be inserted between the support tubes 12 and 13 of the storage container 15 and between the support tubes 13 and 14. One coil is made by welding the ends of two coils into one continuous coil.
By connecting 16a to the innermost support cylinder 14, the cathode disk 11 is used at the same potential.

17 is an insulator made of alumina powder.
Is filled in a container 15 in which the heater 16 is housed, the heater 16 is buried therein, and after being dried, it is heated and sintered in hydrogen or vacuum.

Reference numerals 18 and 19 respectively denote reflecting plates, which are formed in an annular shape and are provided on the supporting cylinders 12 and 13 of the storage container 15, and the first reflecting plate 18 has the outer peripheral portion of the flange of the outermost supporting cylinder 12. The second reflection plate 19 is fixed to the first portion by arc welding, and the second reflection plate 19 is formed by bending a part of the outer periphery of the second reflection plate 19 to form the first reflection plate 18
Are fixedly arranged by welding the inner peripheral portion to a ring 20 provided on the outer periphery of the innermost support cylinder 14 above.

Reference numeral 21 denotes a reflecting cylinder, which is provided on the outer circumference of the storage container 15 and the reflecting plates 18 and 19, one end of which is brazed to the cathode disk 11 and the other end is a flange body.
22 is brazed.

The cathode is fixed to the electron gun via the flange body 22.

(Problems to be Solved by the Invention) By the way, in the above-mentioned conventional impregnated-type cathode assembly,
After fixing the outer peripheral portion of the reflecting plate 18 to the support cylinder 12, the inner peripheral portion of the second reflecting plate 19 is fixed to the ring 20 on the outer periphery of the supporting cylinder 14, and at this time, the outer periphery of the second reflecting plate 19 is fixed. Since the projection 19a bent in the direction forms a gap with the first reflector 18, the inner periphery of the second reflector 19 is curved, and the inner periphery of the second reflector 19 and the first reflector 18 are curved. There is a problem that it is difficult to stabilize the gap between the first reflector 18 and the fixed plate 18 and the fixed state.

Since it is difficult to stabilize the distance between the reflection plates 18 and 19 and the fixed state, if the distance between the reflection plates 18 and 19 is small, the reflection plate 18 is repeatedly expanded and contracted by turning the heater 16 on and off. , 19 are easily deformed and come into contact with each other, and when they come into contact with each other, thermal efficiency changes. Therefore, in order to prevent this, it is necessary to widen the distance between the reflection plates 18, 19.

Therefore, if the number of the reflectors 18 and 19 is increased in order to further improve the thermal efficiency, the spacing between the reflectors 18 and 19 and the fixed state may become more unstable,
It was difficult to provide many reflectors 18 and 19 in a narrow space, and it was difficult to increase the number of reflectors 18 and 19.

Further, when the number of reflectors 18 and 19 is increased, it becomes difficult for the gas in the insulator 17 in which the heater 16 is embedded to escape, and it takes time to bring the inside of the electron tube into a high vacuum.

The present invention has been made in view of such a point, and in the impregnated-type cathode assembly, it is possible to increase the number of reflectors by stabilizing the distance between the reflectors and the fixed state. Also, the purpose is to facilitate smooth gas discharge.

[Constitution of device]

(Means for Solving the Problems) The impregnated-type cathode assembly according to claim 1 is a porous cathode disk impregnated with an electron-emitting substance, a storage container provided on the back surface of the cathode disk, and the storage. An insulator that is housed in a container and sintered, a heater that is housed in the container together with the insulator and is embedded in the insulator, and a heater that covers the insulator in which the heater is embedded and is attached to the container. And a plurality of reflecting plates, wherein the plurality of reflecting plates are integrally assembled as a reflecting plate structure with a plurality of spacers spaced apart from each other in advance. is there.

In the impregnated-type cathode structure according to the second aspect of the present invention, each of the reflection plates has a gas vent hole formed at a position where they do not linearly communicate with each other.

(Operation) In the impregnated-type cathode assembly according to claim 1, since a plurality of reflectors are integrally assembled as a reflector assembly in advance, the distance between the reflectors is stable and the fixed state of the reflectors is strong. become.

In the impregnated-type cathode assembly according to claim 2, in addition to the function according to claim 1, the gas released from the insulator or the like during exhaust is
It escapes from the gas vent hole formed in each reflector. Then, the heat radiated through these gas vent holes is reflected by another reflector.

(Embodiment) An embodiment of the impregnated cathode structure of the present invention is shown in FIGS.
It will be described with reference to the drawings.

FIG. 1 shows the structure of an embodiment of the impregnated cathode structure of the present invention.

Reference numeral 31 is a cathode disk made of porous tungsten (W). The cathode disk 31 has a diameter of 70 mm, a circular through hole 31a is formed in the center thereof, and the surface thereof is concavely curved.

32, 33, and 34 are three large, medium, and small circular support cylinders made of molybdenum (Mo), and these three support cylinders 32, 33, and 34 are concentrically arranged on the back surface of the cathode disk 31 to make Ru- It is brazed with Mo brazing material, and thereby the storage container 35 is configured.

Then, when brazing the support cylinders 32, 33, 34 to the back surface of the cathode disk 31, a Ru-Mo brazing material is applied to the back surface of the same cathode disk 31, and the holes on the back surface are crushed. By
The electron emitting material impregnated from the surface is prevented from entering the heater 36 side described later and reacting with the heater 36.

Further, the intermediate support tube 33 is formed with a cutout portion 33a through which the intermediate portion of the heater 36 penetrates, and the innermost support tube 34 is formed by welding the inner end portion 36a of the heater 36 to another. It is slightly longer than the support tubes 32, 33 of.

The length of the innermost support cylinder 34 is the same as that of the reflection plate 4 described later.
In order to narrow the interval between 1,42 and increase the number of reflection plates 41, 42, 43, 44, it is preferable that the one end 36a of the heater 36 be welded as short as possible.

36 is a heater for heating the cathode disk 31, and the heater 36 is a tungsten wire with a diameter of 1.5 mm so that the cathode disk 31 reaches a predetermined operating temperature.
Two types of annular coils that enter between the support cylinders 32 and 33 and between the support cylinders 33 and 34 of 5 are made, and the ends of these two coils are welded into one continuous coil. Above storage container 35
And the inner end 36a is stored in the innermost support tube 34
When connected to the cathode disk 31, the cathode disk 31 is used at the same potential.

37 is an insulator made of alumina powder.
Is embedded in the storage container 35 containing the heater 36 up to the height of the support cylinders 32, 33, and the heater 36 is embedded.The insulator 37 is dried and then heated in hydrogen or vacuum to burn. By connecting the heaters 36, the heater 36 is fixed to the support cylinders 32, 33, 34 and the cathode disc 31 in an insulated state with a predetermined gap.

It should be noted that one end portion 36a of the inside of the heater 36 projects from the insulator 37, and after the insulator 37 is sintered, the innermost support cylinder 34
Be welded to.

The other end 36b outside the heater 36 is projected from an insulator 37 for applying a voltage, and a protective pipe 38 made of alumina is attached to the protruding portion from the insulator 37. Therefore, breakage at the root portion is prevented.

40 is a reflector plate structure, and this reflector plate structure 40 is the insulator
It covers the 37 and suppresses the escape of heat and increases the thermal efficiency by radiation. As shown in FIGS. 2 and 3, four reflection plates 41, 42, 43, made of molybdenum (Mo), are used. 44 is integrally assembled by four rivets 45 made of molybdenum (Mo) with a plurality of annular spacers 46, 47 made of molybdenum (Mo) spaced apart from each other.

The reflector plate structure 40 is obtained by sintering the insulator 37 and heating it.
After welding one end 36a of 36 to the support cylinder 34, the first reflection plate 41 is fixed to the flange portion 32a of the outermost support cylinder 32 of the storage container 35 by arc welding.
The other reflectors 42, 43, 44 are also fixed.

Then, the four reflectors 41, 42, 43, 4 of this reflector assembly 40
Of the four, only the first reflecting plate 41 has an annular shape with a through hole 41a formed in the center, and the through hole 41a is fitted to the outer side of the innermost support cylinder 34 of the storage container 35, thereby The reflection plate 41 of the support container 32, 33 of the storage container 35 and the insulator 3 in the storage container 35
It adheres to 7 and prevents the insulator 37 from falling off.

Since there is no through hole in the center of each of the second to fourth reflectors 42, 43, 44, the support cylinder protruding from the first reflector 41 is shown.
The heat emitted from 34 is reflected to the cathode disk 31 side, and the thermal efficiency can be improved.

In addition, in the reflectors 41, 42, 43, 44 of this reflector structure 40,
The opening 4 through which the other end 36b of the heater 36 passes
8 is formed in a position that communicates in a straight line,
A plurality of gas vent holes 49, 50 are formed at positions where they do not communicate linearly.

In this way, when a plurality of gas vent holes are formed at positions that do not communicate with each other linearly, the gas is radiated from the support cylinder 34 protruding from the first reflection plate 41, similarly to the through hole 41a provided in the first reflection plate 41. It is possible to improve the heat efficiency by reflecting the generated heat to the cathode disk 31 side.

Reference numeral 51 is a reflection cylinder made of rhenium (Re) -molybdenum (Mo). The reflection cylinder 51 is for covering the storage container 35 to suppress heat escape and to improve thermal efficiency by radiation.
One end thereof is located outside the flange portion 32b of the outermost support cylinder 32, and is fixed by brazing to the cathode disc 31 with a brazing material of Ru-Mo-Ni, and the other end is A flange member 52 made of molybdenum (Mo) is fixed by brazing with a Ru-Mo-Ni brazing material, and the flange member 52 is fixed to an electron gun (not shown).

Then, after this, by placing an electron emitting substance composed of BaO, CaO, and Al ₂ O _{3 on} the curved surface of the cathode disk 31 and heating it in hydrogen to 1600 to 1700 ° C. ,
The electron emitting substance is melted and impregnated in the void portion of the cathode disk 31.

In such a structure, the four reflection plates 41, 42, 4
3,44 is a reflector plate structure before being attached to the storage container 35.
Since it is integrally assembled with the rivet 45 via the spacers 46 and 47 as 40, the distance between the reflection plates 41, 42, 43 and 44 is stable and the reflection plates 41, 42, 43 and 44 are fixed to each other. And the thickness of the first reflection plate 41 for fixing the entire reflection plate structure 40 to the storage container 35 is increased.
By preventing bending and deformation, the entire reflector plate structure 40 can be stably attached to the storage container 35.

Therefore, by narrowing the spacing between the reflectors 41, 42, 43, 44,
Since many reflection plates 41, 42, 43, 44 can be provided in a narrow space, the thermal efficiency can be further improved.

Further, when the number of the reflection plates 41, 42, 43, 44 is increased, the gas of the insulator 37 in which the heater 36 is buried is less likely to escape in the exhaust process of the microwave electron tube as it is, and the inside of the electron tube is made to have a high vacuum. Although it takes time to do so, here, since the gas vent holes 49, 50 are formed in the reflection plates 41, 42, 43, 44, it is easy for the gas to escape and the exhaust is performed smoothly, so it takes time. It does not hang.

The thickness of the first reflection plate 41 is 0.2 to 1.0 mm, the thickness of the second to fourth reflection plates 42, 43 and 44 is 0.1 to 0.5 mm, the first reflection plate 41 and the second reflection plate The height of the spacer 46 between the plates 42 is 1 to
5 mm, second reflector 42, third reflector 43, and fourth reflector 4
The height of the spacer 47 between 4 is 1 to 5 mm.

[Effect of device]

According to the impregnated-type cathode assembly according to claim 1, in the impregnated-type cathode assembly, the plurality of reflectors covering the insulator in which the heater is embedded are integrally assembled beforehand as a reflector assembly via a spacer. The distance between the reflectors is stable, and the reflectors are firmly fixed to each other, so that the entire reflector structure can be stably attached to the storage container. Therefore, the distance between the reflectors can be narrowed and many reflectors can be provided in a narrow space, so that the thermal efficiency can be further improved.

According to the impregnated-type cathode assembly of claim 2, in addition to the effect of claim 1, when the number of reflectors is increased, it is difficult for gas such as an insulator in which a heater is embedded to escape during the exhaust process as it is. It takes time to make the inside of the electron tube high vacuum, but since the gas vent holes are formed in the reflector, it becomes easier for the gas to escape and the gas is exhausted smoothly. It does not hang. Also,
The heat radiated through these degassing holes is reflected by another reflector, so that the thermal efficiency can be improved.

[Brief description of drawings]

1 to 3 show an embodiment of an impregnated-type cathode assembly according to the present invention, FIG. 1 is a side view of a part of which is shown in cross section, FIG. 2 is a side view of the reflector assembly, and FIG. FIG. 4 is a bottom view of the reflector plate structure, FIG. 4 is a vertical cross-sectional view showing an integrated structure of the impregnated-type cathode structure, and FIG. 5 is a partial cross-section of a conventional large-diameter impregnated-type cathode structure. It is a side view. 31 …… Cathode disk, 35 …… Storage container, 36 …… Heater, 37…
… Insulator, 40 …… Reflector structure, 41,42,43,44 …… Reflector, 46,47 …… Spacer, 49,50 …… Gas vent.

Claims (2)

[Scope of utility model registration request] 1. A porous cathode disk impregnated with an electron emitting material, a storage container provided on the back surface of the cathode disk, an insulator housed in the storage container and sintered, and the insulation. An impregnated-type cathode assembly including a heater housed in the storage container together with an object and embedded in an insulator, and a plurality of reflectors mounted on the storage container to cover the insulator in which the heater is embedded. An impregnated-type cathode assembly, wherein the plurality of reflectors are integrally assembled as a reflector assembly with a plurality of spacers spaced apart from each other in advance. 2. The impregnated-type cathode assembly according to claim 1, wherein each of the reflection plates is formed with a gas vent hole at a position where they do not linearly communicate with each other.