US3569769A

US3569769A - Cathode with elongated heat dissipating and supporting member

Info

Publication number: US3569769A
Application number: US786112A
Authority: US
Inventors: Yukio Takanashi
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1967-12-27
Filing date: 1968-12-23
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09
Also published as: GB1191550A; DE1816807A1; DE1816807B2

Abstract

This dispenser cathode having a good heat efficiency consists of a round cylindrical envelope having an annular hollow chamber and accommodating a heating coil electrically insulated therefrom, an electron emitting layer mounted on the outer peripheral portion of the top wall of the envelope and a metallic cylindrical member fitted to the envelope in concentrical relationship therewith in such a manner that the outer circumferential wall of said cylindrical member is spaced at a prescribed interval from the inner circumferential wall of the envelope.

Description

O Umted States Patent l 13,569,769

[72] Inventor Yukio Takanashi 3,195,003 7/1965 Jagt 313/27OX HIralsuka-shl, J p 3,351,795 1 1/1967 Gronlund 313/346X [21] Appl. No. 786,112 3,369,145 2/1968 Domotor 313/346 Sued d 293,l19976l8 3,441,779 4/1969 Hubner 313/346 atente ar. [73] Assignee Tokyo Shibaura Electric Co. Ltd. 1 052 0 FOREIGN ENTS 313/346 Kawasakrshi Japan 00 12/ 1966 Great Brltam [32] Priority Dec. 27, 1967 Primary Examiner.lames D. Kallam [33] Japan Assistant Examiner-Andrew .1. James [31] 42/108,604 Attorney-Flynn & Frishauf [54] CATHODE WITH ELONGATED HEAT DISSIPATING AND SUPPORTING MEMBER 14 Claims, 4 Drawing Figs.

[52] US. Cl 313/346, ABSTRACT: This dispenser cathode having a d h ffi 313/270, 313/33 ciency consists of a round cylindrical envelope having an an- [5 l 1 Int. nular hollow chamber and accommodating a heating coll elec- J 19/06 trically insulated therefrom, an electron emitting layer Fleld of Search mounted rrthe outer peripheral portion of the top of the 340, 346 envelope and a metallic cylindrical member fitted to the envelope in concentrical relationship therewith in such a manner [56] References cued that the outer circumferential wall of said cylindrical member UNITED STATES PATENTS 2,280,980 4/1942 Samuel is spaced at a prescribed interval from the inner circumferential wall of the envelope.

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' Y m mun/45w CATHODE Wl'llll ELONGATED HEAT mssrrxrmc AND SUFPORTTNG MEMBER The present invention relates to a dispenser cathode.

A cathode heretofore used in high output applications has exclusively consisted of a type operable within the range of from 950 to 1050 C. While various modifications have been made to such types of cathodes, they are not much different in then essential properties. Accordingly, the present description will be taken only with reference to a typical one. The hollow interior of a cylindrical envelope made of metals, for example, molybdenum, is separated into two upper and lower independent compartments by a partition wall of the same material as the envelope. The lower compartment is packed with an insulating material mainly consisting of, for example, alumina powders. In this packed material is embedded a heating source consisting of refractory metal or metal of high melting point. Two terminals are conducted from the heating source to the outside of the envelope to form a heating member. On the other hand, in the upper compartment is accommodated an electron emitting material consisting of a porous metal such as tungsten, and a solid solution prepared from aluminum oxide and oxides of alkaline earth metals impregnated in the pores. Thus is formed an electron emitter.

in a dispenser cathode of the aforesaid arrangement, the heat generated by introducing a prescribed amount of electric current through the heating source is conducted to the electron emitting material of the upper compartment through the layer of electric insulation and partition wall. This heat causes electrons to be released from the electron emitting material. In this case, the heat from the heating source is transferred not only to the partition wall, but also to the circumferential wallof the envelope in appreciable amounts through the insulation layer, thus being lost without contributing to the emission of electrons. Namely, the heat from the heating source is not fully utilized in emitting the electrons, and reduces the effective heat ouptut of the heating source. As mentioned above, the cylindrical envelope is heated by the heating source, and if other parts are positioned close by the envelope, they will also be heated to evolve undesirable gases which will have a harmful effect on the apparatus in which the cathode is incorporated. Accordingly, where such type of cathode is used in a microwave tube such as a klystron tube or a travelling wave tube it will greatly degrade the properties of these tubes.

SUMMARY OF THE INVENTION The dispenser cathode of the present invention is prepared by accommodating a heating means in a round cylindrical envelope, defining an annular hollow chamber by the outer and inner circumferential walls of the envelope, and disposing a metallic cylindrical member at the envelope at a prescribed space from the outer surface of the inner circumferential wall so as to offset the loss of heat from the inner circumferential wall of the envelope by the radiation of heat from the central cylindrical member.

The present invention can be more fully understood fro the following detailed description when taken in connection with the accompanying drawing, in which:

F108. 1 to 3 respectively represent a dispenser cathode according to an embodiment of the present invention; FIG. 1 being a perspective view of the same, FIG. 2 being a sectional view taken along line 22 of FIG. 1 and FIG. 3 being a sectional view taken along line 3-3 of FIG. 2, as viewed in the direction of the arrows; and

FIG. 4 is a sectional view of a dispenser cathode according to another embodiment of the invention.

There will now be described the present invention first by reference to FlGS. l to 3. A round cylindrical member made of metal, for example, tungsten, molybdenum, niobium or thallium is so formed as to have an annular hollow chamber open at the top. The hollow chamber is filled with an electrical insulating material ll mainly consisting of, for example, alumina powders. In these powders is embedded a heating means 12.

The heating means 12 is a coil made of ordinary refractory metals or metals of high melting point, for example, tungsten, and assumes an annular shape as a whole so as to lit in with the annular hollow chamber. The coil 12 and the inner circumferential wall of the hollow chamber of the cylindrical member it) are electrically insulated from each other by the filler 11. Though not always necessary, the surface of the coil 12 is coated with alumina. Both ends of the'coil 12 are conducted to the outside through small holes bored in the bottom wall of the annular cylindrical member 10. The bottom wall of the cylindrical member 10 and coil ends are electrically insulated from each other by alumina insulators l3 brazed to the aforesaid small holes.

The opening of the annular cylindrical member 10 is covered with an annular (doughnut-shaped) plate 14 made of metal such as molybdenum, both cylindrical member 10 and annular plate 14 constituting an envelope. The central opening of the annular plate 14 has a larger diameter than that of the annular inner circumferential wall of the cylindrical member if). The annular plate 14 may consist of the same material as the annular cylindrical member 10 or a different material. While the bonding of the annular plate 14 and cylindrical member 10 may be made by the various known methods, this embodiment uses heliarc welding. On the annular plate 14 is integrally erected a cylindrical wall 15 rising right upward from the top surface of said plate M and in coaxial relationship therewith. This cylindrical wall has a larger diameter than that of the inner circumferential wall of the cylindrical member 10. On the outer peripheral portion of the top surface of the doughnut-shaped plate 14 confined by the upright cylindrical wall 15 is disposed an electron emitter 16. The emitter is made of porous metal such as tungsten, in the pores of which is filled a mixture mainly consisting of aluminum oxide and alkaline earth metal salts, for example, a mixture of barium oxide (SBaO), aluminum oxide (3Al O and calcium oxide (ZCaO). The emitter is heated to about l600 to 1700C. in the case of the aforementioned mixture. This method of preparing an electron emitting layer allows said mixture to pervade a large number of fine pores in the porous metal disc disposed upon the annular plate 14. The electron emitting layer 16 used in the cathode of the present invention is not limited to the aforementioned material, but may consist of any other material if it forms such a layer that emits electrons upon heating. It is also possible to compress in advance the mixtures of said materials and powders of tungsten and depositing them on the annular plate 14, followed by heating.

To the edge of the central open section of the doughnutshaped plate 14 is fixed, for example by heliarc welding, the top edge of the cylindrical member 17 made of metal which is inserted from below said doughnut-shaped plate 14, namely, from the side of the aforesaid annular cylindrical member 10. The lower portion of the member 17 projects further downwardly than the level of the bottom of the member 10. The dimensions of the central cylindrical member 17 and annular cylindrical member 10 are so determined as to allow the outer circumferential wall of the former and the inner circumferential wall of the latter to be kept at a prescribed space.

With a dispenser cathode of the aforementioned arrangement, the heat from the heating means is transferred through the doughnut-shaped plate to the layer of electron emitting material disposed thereon to cause the layer to emit electrons. In this case, the heat from the coil is also conducted to the annular cylindrical member accommodating the coil, where the heat is dissipated to the outside. However, since the central cylindrical member is positioned at a prescribed distance from the inner circumferential wall of the annular cylindrical member, the heat is also transmitted to the central cylindrical member, which in turn radiates heat back to the annular cylindrical member to reduce heat loss therefrom. This substantially decreases the consumption of power required to maintain the cathode temperature at a desired level as compared with that used with the prior cathode. For instance, the conventional apparatus consumes 200 watts, whereas the cathode of the present invention requires only 110 watts. Moreover, since the amounts of heat released from the cathode to the outside can be reduced, parts positioned close by the cathode are saved from exposure to excessive heat, preventing harmful gases from being evolved therefrom.

There will now be described another embodiment of the present invention as shown in FIG. 4. Since the cathode of this embodiment is of substantially the same arrangement as that of the preceding embodiment, the same parts are denoted by the same numerals and description thereof is omitted.

The envelope used is prepared by machining both annular cylindrical member constituting the outer peripheral portion of the envelope and doughnut-shaped plate 14 into an integral body as illustrated. The annular cylindrical member 10 has an opening at the bottom, thereof through which a heater 12 and an electrical insulating material 11 are inserted into said member. The open bottom is closed with a lid 18 and the heater 12 is conducted through an alumina insulator 13 to the outside. Numerals l6 and 17 respectively represent a layer of electron emitter and a central cylindrical member.

In this embodiment, the annular cylindrical member and doughnut-shaped plate are formed into an integral body. There is, of course, obtained the same effect as in the preceding embodiment.

Insofar as the present invention is concerned, the envelope is not necessarily limited in shape to a round annular cylinder, but may assume any other form, for example, a square annular member. Also the central cylindrical member may be formed into a square or hexagonal elongated member in addition to a round cylinder. Nor is it always necessary to position the central cylindrical member in coaxial or parallel relationship with the inner circumferential wall of the annular cylindrical member.

I claim:

1. A dispenser cathode comprising:

an envelope having an annular hollow chamber defined by outer and inner walls and a top wall of said envelope;

a heating means housed in the hollow chamber of the en-' velope in electrically insulated relationship from the envelope and having a plurality of terminals conducted outside of said envelope;

an electron emitter mounted at least on the outer peripheral surface of the top wall of the envelope and emitting electrons when heated by the heating means; and

an elongated metallic member mounted to the envelope with a spacing between the outer surface of said elongated metallic member and the outer surface of the inner wall of the envelope, a portion of the outer surface of the elongated metallic member being surrounded by the inner wall of the envelope, and another portion of the elongated metallic member extending from the level of the bottom of the envelope. g

2. A dispenser cathode according to claim 1 wherein the envelope comprises an annular top wall, an inner cylindrical circumferential wall projecting from the inner peripheral edge of the annular top wall, an outer cylindrical circumferential wall projecting the outer peripheral edge of the top wall, and an annular bottom wall to close up the opening of the annular hollow chamber.

3. A dispenser cathode according to claim 2 wherein the diameter of said inner cylindrical wall is smaller than that of said top wall, and the diameter of said outer cylindrical wall is larger than that of said top wall.

4. A dispenser cathode according to claim 2, wherein the emitter is made. of porous materials, the pores of the emitter being filled with electron emitting materials.

5. A dispenser cathode according to claim 4, wherein the emitter is comprised of tungsten.

6. A dispenser cathode according to claim 2, wherein the heating means includes a coil assuming an overall annular configuration.

7. A dispenser cathode according to claim 6, wherein the surface of the coil is coated with an electrically insulating material.

8. A dispenser cathode according to claim 1, wherein the heating means is embedded in insulating powders mainly consisting of alumina, thereby electrically insulating the heating means from the envelope.

9. A dispenser cathode according to claim 1 wherein said inner and outer walls of the envelope are circumferential walls.

10. A dispenser cathode according to claim 9, wherein the elongated metallic member is of a cylindrical member.

' 11. A dispenser cathode according to claim 9, wherein the elongated metallic member is mounted in coaxial relationship with the inner circumferential wall of the envelope, the outer circumferential wall of the elongated metallic member being spaced at a prescribed spacing from the inner circumferential wall of the envelope.

12. A dispenser cathode according to claim 11, wherein the elongated metallic member is a cylindrical member.

13. A dispenser cathode according to claim 12 wherein the spacing between the outer circumferential wall of the elongated metallic member and the inner circumferential wall of the envelope is substantially constant.

14. A dispenser cathode according to claim 9 wherein the elongated metallic member is a hollow cylindrical member.

Claims

1. A dispenser cathode comprising: an envelope having an annular hollow chamber defined by outer and inner walls and a top wall of said envelope; a heating means housed in the hollow chamber of the envelope in electrically insulated relationship from the envelope and having a plurality of terminals conducted outside of said envelope; an electron emitter mounted at least on the outEr peripheral surface of the top wall of the envelope and emitting electrons when heated by the heating means; and an elongated metallic member mounted to the envelope with a spacing between the outer surface of said elongated metallic member and the outer surface of the inner wall of the envelope, a portion of the outer surface of the elongated metallic member being surrounded by the inner wall of the envelope, and another portion of the elongated metallic member extending from the level of the bottom of the envelope.

4. A dispenser cathode according to claim 2, wherein the emitter is made of porous materials, the pores of the emitter being filled with electron emitting materials.

11. A dispenser cathode according to claim 9, wherein the elongated metallic member is mounted in coaxial relationship with the inner circumferential wall of the envelope, the outer circumferential wall of the elongated metallic member being spaced at a prescribed spacing from the inner circumferential wall of the envelope.