JPH07312180A - Thermoelectronic cathode for electron beam pipe - Google Patents

Abstract

PURPOSE: To provide a thermal electron emitting negative electrode which heats an object to operating temperature more rapidly than usual negative electrode, requires less power, is miniaturized, and is manufactured at lower cost. CONSTITUTION: A negative electrode consists of a supporting structure 32, an electron emitting material layer 34 which is thermally connected to the support structure, and a heating element 45 which heats the supporting structure 32 and the electron emitting material layer 34 up to a desired temperature, and the heating element 45 is thick or thin film which is adhered on the surface of the supporting structure 32 opposite to the electron emitting material layer 34. This structure causes thickness W to be smaller to heat the electron emitting material layer 34 rapidly and efficiently.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermionic cathode for an electron beam tube, and more particularly to a thermionic cathode which utilizes a thin film heating element to heat the cathode to provide a cathode having reduced volume and excellent operating characteristics.

[0002]

The operation of electron beam tubes depends on the electron flow in the tube. The electron stream is generated by the cathode. The electrons are emitted from the cathode in the tube as a result of one of four conventional processes, distinguished by the mechanism by which they can leave the cathode structure. These processes include thermionic emission produced by the temperature rise of the cathode structure, secondary electron emission produced by the bombardment of the cathode structure with electrons, and field emission produced by exposing the cathode structure to a strong electric field. And photoelectron emission produced by the incidence of photons on the cathode structure.

Traveling wave tubes (TWTs), klystrons, and other high frequency and high power tubes use thermionic cathode structures to produce the required electron beam. In such a cathode structure, thermionic emission occurs when the electrons of the cathode material have sufficient thermal energy to escape from the cathode surface. The thermal energy provided to such a cathode is provided by a heating filament that is thermally coupled to the electron emitting surface. Thus, when the electron beam tube is first used, there is a delay from the time the heating element is powered to the time the heating element raises the emitting surface of the cathode to the proper operating temperature. In other words, the cathode needs time to "warm up" before the electron beam tube can function properly.
The amount of time it takes to properly heat the cathode is a function of the power of the heating filament, the materials used in the cathode, and the total mass of the cathode.

To reduce the amount of time it takes for the filament to properly heat the cathode, the current conducted through the cooled filament is typically increased to an excess of the filament's normal operating current. When the filament heats the cathode, the current is reduced to normal operating values.
The current passing through the heated filament produces a magnetic field that mechanically stresses the filament. Thus, when the current through the filament is increased, the mechanical stress experienced by the filament is also increased and the life of the filament is shortened. Therefore, excess starting current cannot be used in a normal filament without shortening the total life of the cathode, ie the functional life of all electron beam tubes.

[0005]

Referring to FIG. 1 (Prior Art), there is shown a cross section of a conventional cathode 10 of a traveling wave tube. In this prior art cathode 10, the impregnated tungsten electron emitter 12 is located at one end of a cylindrical molybdenum body 14. The heating element 16 is located in the cylindrical body 14 behind the impregnated tungsten electron emission 12. The heating element 16 is embedded in an aluminum oxide pot material 18 which is thermally coupled to the tungsten electron emitter 12 which is impregnated with the heating element 16. The molybdenum rhenium sleeve 20 is located around the molybdenum body 14 on the side opposite to the electron emitter 12, and is soldered to the molybdenum body 14.

In the cathode 10 shown, the heating element 16 is formed by a wound wire. In the manufacture of the cathode 10, the wire is typically wound by hand and the wound wire is manually placed in the molybdenum body 14. Numerous parts of cathode 10 of the prior art require that each cathode 10 be time-consuming and labor-intensive in the manufacturing steps required to manufacture the cathode 10.
Greatly increases the price per unit of.

When electron tube devices are miniaturized to suit certain applications, the cathodes used within these electron tube devices are also miniaturized. A small cathode does not require much space to heat the device. Therefore, the heat output of the miniaturized heating element is insufficient to rapidly heat the remaining cathode structure without passing excessive current through the heating element, which adversely affects the life of the heating element. . The cathode 10 shown in FIG. 1 is for a miniaturized traveling wave tube currently produced by ITT. Such a cathode 10 has an emitter diameter of about. 0785 inches, with a typical length of 0.30 inches. In addition, the heating element 16 requires about 4 seconds to heat the cathode structure to the proper operating temperature.

Considering the prior art on thermionic cathodes, it can be heated to operating temperature more rapidly than conventional cathodes, can be miniaturized to smaller dimensions without loss of power, labor and cost. There is a need for a cathode structure that can be manufactured down.

[0009]

The present invention relates to a thermionic cathode for use in electron beam tubes such as traveling wave tubes, klystrons and the like. The present invention includes a ceramic body of high thermal conductivity. One side of the ceramic body is metallized and the thermionic radiator is soldered to the metallized surface so that the thermionic emission and the ceramic body are thermally interconnected. A thick film or thin film heating element is deposited on the surface of the ceramic body opposite to thermionic emission. In the preferred embodiment, the thin film heating element is aligned directly behind the thermionic emission so as to miniaturize the heat conduction path from the thin film heating element to the thermionic radiator through the ceramic body.

In order to keep the mass of the ceramic body small, both the thermionic radiator and the thin-film heating element are formed on a common central area of the ceramic body, from which the central area extends radiatively. It is supported in the electron beam tube by the above ceramic arm. The ceramic arm may also include a metallization region that electrically connects to the metallization region under the thermionic emission. By providing a metallization region on the ceramic arm, an electric potential can be applied to the metallization on the arm, thus applying a potential to the metallization region below the thermionic emitter and the electron emitter. In addition, thin film microstrip lines may be formed along the ceramic arms. The microstrip line is electrically interconnected with the thin film heating element and provides a means by which current can pass through the thin film heating element.

The use of a low mass ceramic body in conjunction with a thin film heating element that is directly attached to the ceramic body enables thermionic cathodes to be manufactured with reduced labor and cost. The further reduced size and efficient heat transfer design allows the thermionic cathode of the present invention to have superior operating characteristics over prior art cathodes of comparable power.

[0012]

For a better understanding of the present invention, an exemplary embodiment is described in detail below with reference to the accompanying drawings. Figure 2
With reference to, there is shown an exemplary embodiment of a thermionic cathode 30 of the present invention having a ceramic body 32 with a pellet 34 of electron emission centered therein. In the embodiment shown, the ceramic body 32 has a circular central area 36 in which three elongate arms 32 extend radially. The ceramic body 32 is made of a ceramic material with high thermal conductivity such as aluminum nitride, beryllium oxide, alumina, etc., and can be easily metallized. It will be appreciated that the use of three arms 38 is merely one example, and any number of arms or porous discs may be used. However, the radially extending arms or perforated discs can be replaced by a solid structure to reduce the mass of the ceramic body 32, and the radially extending arms or perforated discs can be properly vacuumed. Is preferably used for

The upper surface 42 of the central region 36 below the electron emitting pellets 34 is metallized with a conductive material 47 such as copper, nickel, gold or the like. Similarly, at least one elongated arm 38
The upper surface 44 of the metallization is also provided with a metallization and the metallization on the elongated arm 38 is electrically coupled to the metallization 47 on the central region 36.
Thus, by applying an electrical bias to the metallization on the elongated arm 38, an electrical bias can be applied to the metallization area under the electron emitting pellet 34.

Electron emitting pellets 34 are the same type of electron emitters used in the prior art for certain applications. Thus, the diameter D1 of the electron emitting pellet 34 is the same as that used in the prior art cathode, and the electron emitter is the impregnated tungsten, thoriated tungsten, alkaline rare earth oxide, etc. used in the prior art cathode. Can be made from such known electron emitting materials.

Referring to FIG. 3 in conjunction with FIG. 4, heating element 46
It is noted that is located on the lower surface 45 of the circular central region 36 directly below the electron emitting pellet 34. The heating element 46 is formed as a thick film or thin film structure on the lower surface 45 of the circular central region 36. In the embodiment shown (FIG. 4), the heating element 46 is attached to the ceramic body 32 in a concentric or spiral pattern connected so as to evenly cover the lower surface 45 of the circular central region 36. However, it will be appreciated that the thin film heating elements 46 may be deposited in any suitable pattern on the lower surface 45 of the ceramic body 32. The length of the spiral structure determines the resistance of the heating element and thus the heat generated. As is well known, the longer the heating element wire, the greater the resistance. Resistance also increases with decreasing conductor cross-sectional area. In this way an efficient heating element can be provided by using a coil or spiral film structure as shown. The electric current is applied to the two thin film microstrip lines 48, 50 extending along the lower surfaces of the two elongated arms 38.
Is applied to the thin film heating element 46 via. Microstrip lines 48, 50 are electrically coupled to the two ends of thin film heating element 46. Thus, by providing a potential between the ends of the elongated arm 38 and the microstrip lines 48, 50, a current can be passed through the heating element 46. Non-magnetic or magnetic patterns can be used. The electron emitting pellet 34, the ceramic body 32, the metal coating portion 47 on the ceramic body 32, and the thin-film heating element 46 attached on the ceramic body 32 are arranged close to each other so that the cathode 30 of the present invention can be manufactured. Give the total thickness W. As described below, the thickness W of the cathode 30 of the present invention is greatly reduced over that obtained in the prior art for cathodes of comparable power.

Heating element on the lower surface 45 of the circular central region 36
46 can be provided on the ceramic body 32 using known thin film deposition techniques. Similarly, the metallization region on the upper surface 42 of the ceramic body 32 can be created using known metallization techniques such as vapor deposition. Adhesion of thin film materials to the ceramic substrate and the metallization of the ceramic substrate are well practiced and will not be described in detail here.

The operation of the thermionic cathode 30 of the present invention will be described with reference to FIGS. The cathode 30 is assembled into an electron beam tube, such as a traveling wave tube, the metallized area on the upper surface 44 of the elongate arm 38 is coupled to a potential source, and the microstrip lines 48, 50 on the bottom of the elongate arm 38 are electrically connected. Is bound to the source. Using the structure shown, the cathode 30 of the present invention can be manufactured with a thickness W as small as one-third that used in the prior art embodiment of FIG. Most of the space savings is attributed to the use of thin film heating element 46 rather than the prior art wound heating coil. The heating element 46 is heated as current passes through the heating elements 46 through the microstrip lines 48,50. The heat generated by the heating element 46 is conducted to the ceramic body 32. The cathode of the present invention
Because the ceramic body 32 of 30 has less mass than a conventional prior art cathode, the cathode 30 of the present invention can heat up more rapidly than the prior art cathode. In addition heating element 46
Is a thin film structure located directly on the ceramic body 32 of the cathode 30, so that almost all heating elements 46 are in direct contact with the ceramic body 32 and the
Allow efficient transfer to 32. Further, the heating element 46 is located directly below the area of the electron emitting pellet 34. Therefore, the heat conduction path between the heating element 46 and the electron emitting pellet 34 is miniaturized.

In order to provide the cathode 30 of the present invention with a shorter heating time starting at a cooler state than prior art cathodes, a combination of reduced mass, improved heating element structure and short heat transfer paths. For example, the electron emitter diameter as shown in FIG. The 0785 inch prior art cathode takes approximately 4 seconds to start utilizing overvoltage technology. The cathode 30 of the present invention having the same size electron emission diameter heats to the desired operating temperature within 1 second. Since the cathode 30 of the present invention heats the electron emitters to operating temperature more rapidly than the comparable prior art cathodes, the cathode of the present invention utilizes less power and is therefore more efficient.

In the prior art cathode, much effort is required to wind the heater element and to house the heater element in the rear of the electron emitter. Such efforts greatly increase the manufacturing cost of prior art cathodes. Thin film heating element of the present invention
By utilizing 46, the cathode 30 can be manufactured inexpensively with less effort. Further, the thin film heating element 46 of the present invention is mechanically applied to the ceramic body 32 of each cathode 30. Thus, the reliability of the entire cathode is improved by winding the heating element and reducing the need to manually house the element in the cathode structure.

It will be appreciated that the embodiments described herein are merely exemplary, and that one skilled in the art will make many variations and modifications to the described embodiments that utilize functionally equivalent components. In particular, it will be appreciated that any form of ceramic body can be used with a thin film heating element and an electron emitting body to manufacture the cathode of the present invention. All such modifications and applications are included within the scope of the invention as defined in the claims.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a prior art miniaturized cathode of an electron beam tube.

FIG. 2 is a perspective view of a preferred embodiment of the thermionic cathode of the present invention.

3 is a cross-sectional view of the embodiment of FIG. 2 taken along line 3-3.

FIG. 4 is a bottom view of the thermionic cathode of the present invention shown in FIGS. 2 and 3.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01J 9/08 (72) Inventor Kenneth S. Kirsten, Junior, USA 18017, Bethlehem, Maine 2219 (72) Inventor Richard Sea Wortman 18103, Pennsylvania, USA, Allentown, Meadowbrook Circle 2913 (72) Inventor Wayne El Orlinger Georgia, USA 30084, Tucker, Chelsea Common 4007

Claims (20)

[Claims] 1. A heating structure comprising: a support structure; an electron emitting material thermally coupled to the support structure; and a heating element for heating the support structure and the electron emitting material to a desired temperature. The device is a thermionic cathode having a structure of a thick film or a thin film deposited on the support structure. 2. Thermionic cathode according to claim 1, further comprising means for supplying an electric potential to the electron emitting material. 3. The thermionic cathode according to claim 1, wherein the support structure is a ceramic body. 4. The ceramic body has a first surface on which the electron emitting material is located and a second surface opposite the first surface to which the heating element is attached. 3. The thermionic cathode according to 3. 5. Thermionic cathode according to claim 4, wherein the heating element on the second surface is aligned directly opposite to the electron-emitting material on the first surface. 6. Thermionic cathode of claim 4, wherein a metallic coating is deposited on the first surface of the ceramic body under the electron emitting material. 7. The thermionic cathode of claim 6, wherein the ceramic body comprises a central region having a plurality of arm members radially extending away from the central region of a common plane. 8. The thermionic cathode according to claim 7, wherein the electron emitting material and the heating element are arranged on the opposite side of the central region. 9. The thermionic cathode of claim 8 further including means coupled to at least one of said arm members for supplying an electric current to said heating element. 10. The thermoelectron according to claim 8, further comprising means for coupling to at least one of said plurality of arm members to provide an electrical potential to said metallization deposited under said electron emitting material. cathode. 11. A thermionic cathode according to claim 3, wherein the ceramic body is selected from a group consisting of aluminum nitride, beryllium oxide or alumina. 12. The thermionic cathode of claim 2 wherein the electron emitting material comprises impregnated tungsten. 13. A method of providing a thermally conductive body, coupling a thermionic radiator to the thermally conductive body, and attaching a thick film or thin film heating element to the thermally conductive body, the thick film or thin film heating. A method of manufacturing a thermionic cathode, characterized in that the element is capable of heating the heat conducting body and the thermionic radiator to an operating temperature. 14. The method of claim 13, further comprising the step of metallizing a surface of the heat conducting body and coupling the thermionic emission to the metallized surface. 15. The method of claim 13 wherein said thermionic emission and said thick film or thin film heater are directly aligned on opposite surfaces of said heat conducting body. 16. The method of claim 14, further comprising the step of providing means on said heat conducting body for supplying an electric current to said heating element. 17. The method of claim 14 further comprising the step of providing a means on the heat conducting body for applying an electrical potential to the metallized surface. 18. The method of claim 13, wherein the heat conducting body is composed of a ceramic material. 19. The method of claim 18, wherein the bonding step comprises soldering the thermionic emitter to a metallized surface on the heat conducting body. 20. The method further comprises depositing a microstrip line on the heat conducting body, the microstrip line being electrically coupled to the thick film or thin film heating element to provide an electric current to the thin film heating element. 14. The method according to claim 13, wherein means are provided.