US2719240A

US2719240A - Cathode structure

Info

Publication number: US2719240A
Application number: US654498A
Authority: US
Inventors: Laurence R Walker
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-03-14
Filing date: 1946-03-14
Publication date: 1955-09-27
Anticipated expiration: 1972-09-27

Description

Sept. 27, 1955 1 R. WALKER 2,719,240

CATHODE STRUCTURE.

Filed March 14, 1946 FIG. I.

VENTOR. LAUREN R. WALKER BY W ATTORNEY United States Patent CATHODE STRUCTURE Laurence R Walker, Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application March 14, 1946, Serial No. 654,498

17 Claims. (Cl. 31337) This invention relates to a cathode structure and more particularly to an improved axial cathode structure for magnetrons.

The use of magnetron tubes in high frequency radio equipment at increasingly higher voltage levels has made improvement of certain features of the cathode structure mandatory. The method of dissipating the excess heat developed at the cathode, because of electron bombardment, by means of radial leads known to the art is inadequate. In addition, suificient protection of the leads and elements carrying the high voltages from areing or electrical breakdown is very difficult with known cathode structures.

It is an object of this invention to overcome the abovementioned difficulties.

It is another object of this invention to provide an axially mounted cathode structure for magnetrons.

Another object is to provide a magnetron cathode structure capable of large heat dissipation.

Another object is to provide a magnetron cathode structure which reduces the danger of high voltage electrical breakdown.

Another object is to provide a magnetron cathode structure with magnetic rings to shape and strengthen the magnetic field.

Still another object is to provide a cathode structure for magnetrons with traps in the magnetic rings to minimize migration of the electron emitting material from the cathode to the rings.

A further object is to provide a magnetron cathode structure including an input jack at one end for receiving a plug carrying high voltage.

A still further object is to provide a cathode structure for magnetrons which is capable of pre-assembly into a compact unit.

These and other objects will become apparent from the following specification when taken in conjunction with the accompanying drawings in which:

Fig. l is a cross-sectional view of one embodiment of this invention; and

Fig. 2 is a partially cut-away view showing the orienta tion of the cathode structure with respect to the magnetron block.

In Fig. 1 is disclosed a heavy nickel sleeve whose outer surface is covered with a cathode coating of electron emitting material. Nickel sleeve 10 is brazed at one end to a tapered cylindrical copper piece 12 and is also brazed, as shown in Fig. 1, to two

toroidal rings

13 and 14 which are made of Permendur, a magnetic alloy composed of equal parts of iron and cobalt wtih a Curie point of 1000 C. While other alloys having similar characteristics may be employed in place of Permendur, this alloy will be referred to throughout the specification as illustrative of the characteristics of the alloy to be employed.

Permendur rings

13 and 14 are undercut to form

annular slots

16 and 18 respectively. A molybdenum sleeve 20 is brazed to the other end of Permendur ring 14, and is zirconium coated to make it a good heat radiator.

Tapered cylinder 12 is brazed as shown in Fig. 1 to copper tubing 22, which is in turn brazed to a circular Kovar piece 24 that has a flange at its base end. Kovar is an alloy having a coefficient of thermal expansion such that it permits permanent sealing of meal to glass. Again, other metals having this characteristic are well known. However, the description of the invention will be simplified by referring simply to Kovar, leaving it to the reader to interpret this term as suggesting other materials having similar characteristics. A Kovar tube 26 is secured to a Kovar cup 28 as shown in Fig. l and a glass seal 30 is formed between cup 28 and flange-like piece 24.

Kovar

pieces

24, 26, and 28 with glass seal 30 form an input jack at the base of the cathode structure to receive a coaxial plug. One lead 34 of heater coil 32 is securely welded to Kovar cup 28 and is insulated in the region of tapered cylinder 12 and nickel sleeve 10. The other end of heater coil 32 fastens to the end of nickel cathode sleeve 10 which is brazed to sleeve 20.

In Fig. 2 is disclosed an iron block pole piece 35, which contains a tapering circular hole through its center thus forming a part of the magnetron block cavity into which the cathode structure is inserted. The remaining part of the above-mentioned cavity, formed by other parts of the tube assembly, is not shown. A Kovar ring 36, which is glassed first, fits into the hole in pole piece 35 and is brazed to it along the circumference of the hole. Kovar ring 36 then is sealed to glass envelope 38 which in turn is sealed to Kovar ring 40.

The cathode structure including nickel sleeve 10, tapered cylindrical piece 12, copper tube 22,

Permendur rings

13 and 14, sleeve 20,

input jack components

24, 26, 28 and 30, heater lead 34 and heater coil 32, is preassembled as a unit, which can then be slipped as a whole into the magnetron block and the final seal made by brazing Kovar ring 40 to flange-like Kovar piece 24.

In operation a coaxial plug carrying the heater voltage and cathode high voltage connects into the input jack formed by Kovar

pieces

24, 26 and 28. Nickel sleeve 10 heats, causing electrons to be emitted from its coating. When the magnetron is operating properly, a large number of these electrons are returned to the cathode with sufficient force to generate considerable amounts of heat. This heat is dissipated through nickel sleeve 10, tapered cylindrical copper-piece 12 and copper tube 22 by conduction and by radiation from zirconium-coated molybdenum sleeve 20. In addition to increasing the total heat dissipation, sleeve 20 serves to equalize the amount of heat dissipation at each end of the cathode. The amount of heat conduction from the cathode is increased by making the walls of nickel sleeve 10 and copper tube 22 thick and making good contact between nickel sleeve 10, copper-piece 12 and copper tube 22. The amount of heat conduction can be controlled by controlling the dimensions of copper tube 22.

Copper tube 22 is of sufficient size to insure mechanical rigidity if the brazed joints are properly made. Good electrical breakdown properties are achieved by making the whole structure consist of inter-locking cylinders, which present no sharp points. The radii of the cylinders are as large as consistent with the clearances required inside the tube, thus making the field gradients at the cathode structure as low as possible.

The

Permendur rings

13 and 14 serve to prevent leakage of electrons along the axis of the tube. From this function they derive the name of hats. By using Permendur with a Curie point of 1000 C., the hats retain their magnetic properties when the magnetron is operating.

Permendur hats

13 and 14 are shaped to produce a nearly uniform magnetic field over a large fraction of the center of .the inter-electrode :gap and a focusing field over the remainder. Because they are located between the north and south poles of the magnet, Permendur

hats

13 and 14 also contribute substantially to the strength of the magnetic field in the anode-cathode gap and thereby allow a decrease in total magnet weight.

Annular slots

16 and 18 increase the path length of migration of cathode coating material from the cathode to Permendur

hats

13 and 14 respectively, and thereby cut down possible emission from the hats. Such emission is undesirable from the standpoint of loss of efliciency andother possible effects deleterious to good operation of the magnetron.

The method of dissipating heat by inter-locking cylinders of large areas is readily seen to be far superior to that of using radial leads. By introducing the high voltage onto the cathode through thehigh voltage coaxial jack at one end of the cathode structure only, the problem of clearance and shielding of the high voltage lead is greatly simplified.

The novel features .of this invention include a cathode structure for magnetrons which (a) can be completely pre-assembled before inserting in the magnetron, with no welding operations required in mounting the cathode in the tube; (b) gives large, and controlled heat dissipation; (s) can be made rigid mechanically; (d) eliminates all sharp points which might contribute to electrical breakdown; (2) includes magnetic alloy rings to shape and strengthen the magnetic field; and (f) terminates at one end in a high voltage coaxial jack.

This invention is only to be limited by the appended claims.

What is claimed is:

1. A unitary cathode structure comprising a cylindrical cathode provided with a coating of electron emitting material, supporting means secured to one end of said cathode in axial alignment therewith and adapted to support said cathode, said cathode being supported solely by said supporting means, and heat dissipating means secured to said cathode at the end of said cathode opposite said supporting means, said heat dissipating means being supported solely by said cathode.

2. An improved axial cathode structure comprising a cathode with a coating of electron emitting material, and means shaping and strengthening a magnetic field, said means being disposed on either end of said cathode in axial alignment therewith, said means and said cathode being formed as interlocking cylinders rigidly fastened together.

3. A cathode structure comprising, an elongated cathode having an axial opening therein, and means constructed of magnetic material for shaping and strengthening a magnetic field disposed on the end of said cathode in axial alignment therewith, said means being shaped to prevent leakage of electrons along said cathode structure.

4. A cathode structure of the type described in claim 3 wherein said means is provided with an annular slot concentric with said cathode.

5. An improved axial cathode structure comprising a cathode formed with a coating of electron emitting material, supporting means secured to said cathode structure in axial alignment therewith and heat dissipating means secured to said cathode at the end of said cathode opposite said supporting means, said supporting means, said cathode and said heat dissipating means being formed as interlocking cylinders, rigidly fastened together.

6. An improved axial cathode structure comprising a cathode with a coating of electron emitting material, means shaping and strengthening a magnetic field, said means being disposed on either end of said cathode in axial alignment therewith, heat dissipating means positioned as an axial extension of one of said field strengthening means, said aforementioned elements being formed as interlocking cylinders rigidly fastened together.

7. A unitary cathode structure for a magnetron comprising an elongated cylindrical cathode formed with a coating of electron emitting material, a supporting means secured to said cathode structure in axial alignment therewith, said supporting means being formed with a portion thereof remote from said cathode adapted to be fastened to a magnetron anode, said supporting means further including means electrically insulating said last-mentioned portion from said cathode, and an elongated cylindrical heat dissipating means secured to said cathode in axial alignment therewith at the end of said cathode opposite said supporting means.

8. An improved axial cathode structure for magnetrons capable of preassembly into a single unit comprising, a cathode formed with a coating of electron emitting material, supporting means secured to said cathode at one end thereof and in axial alignment therewith, the end of said supporting means remote from said cathode being formed as the outer shell of a coaxial connector, magnetic field shaping and strengthening means mounted on said cathode intermediate said coating of said emitting material and said supporting means, said field strengthening means being formed to prevent leakage of electrons along the axis of said cathode structure, said field strengthening means being securely fastened to said cathode whereby good electrical breakdown properties and rigidity are obtained, and means mechanically and insulatively securing said supporting means into a magnetron block.

9. An improved axial cathode structure comprising a cathode formed with a coating of electron emitting material, means shaping and strengthening a magnetic field, said means being disposed on either end of said cathode in axial alignment therewith, said field strengthening means being shaped to prevent leakage of electrons along said cathode structure, heat dissipating means positioned as an axial extension of one of said field strengthening means, said aforementioned elements being formed as interlocking cylinders rigidly fastened together whereby said structure is mechanically rigid and has good electrical breakdown properties.

10'. A cathode structure as in claim 9, said structure further comprising a coaxial connector disposed in axial alignment with said cathode, means electrically and mechanically connecting said structure to the outer shell of said coaxial connector thereby to form a pre-assembled unit, and means securing said pre-assembled unit into a magnetron block, said means including means for insulating said pre-assembled unit from said block.

11. An improved axial cathode structure for magnetrons, capable of pre-assembly into a single unit, comprising a cathode with a coating of electron emitting material, a heater coil disposed internally of said cathode, connector means having one terminal thereof connected to said cathode and first and second terminals thereof connected to opposite ends of said heater coil whereby said cathode may be connected to a source of high voltage and said heater coil may be connected to a source of low voltage, heat dissipating means disposed adjacent said cathode in axial alignment therewith, means shaping and strengthening a magnetic field, said means being disposed as axial extensions of said cathode, means intermediate said cathode and said field strengthening means preventing leakage of electrons along the axis of said cathode, said aforementioned elements being rigidly fastened together, and means securing said pre-assembled unit into a magnetron block, said last mentioned means including means for electrically insulating said pre-assembled unit from said block.

12. An improved axial cathode structure for magnetrons capable of pro-assembly into a single unit comprising a cathode formed with a coating of electron emitting material, supporting means secured to said cathode at one end thereof and in axial alignment therewith, the end of said supporting means remote from said cathode being formed as the outer shell of a coaxial connector, heat dissipating means secured to said cathode in axial alignment therewith and at the end, of said cathode opposite said supporting means, magnetic field shapingand strengthening means mounted on said cathode intermediate said coating of emitting material and said supporting means and said coating and said heat dissipating means, respectively, said field strengthening means being formed to prevent leakage of electrons along the axis of said cathode structure, said aforementioned elements being formed as interlocking cylinders securely fastened together whereby good electrical breakdown properties and rigidity are obtained, a heater coil mounted internally of said cathode, and having one end thereof electrically connected to said cathode, an electrically conductive member insulatively mounted within said supporting means and having one end thereof connected to a second end of said heater coil, the end of said conductive member remote from said heater coil being formed as the inner member of a coaxial connector, said above-recited elements comprising a unit capable of pre-assembly, and means mechanically and insulatively securing said supporting means into a magnetron block.

13. A cathode structure as in claim 12 wherein said last mentioned means is in the form of a cylinder surrounding said supporting means and sealed about its peripheries to said magnetron block and said supporting means respectively thereby providing a vacuum seal of the opening in the block within which the cathode structure is located.

14. A unitary cathode structure adapted to be secured in an opening formed in the anode block of a magnetron, said cathode structure comprising an elongated cylindrical cathode having a coating of electron emissive material, a supporting means having the form of two cylindrical concentric members electrically and mechanically joined at one end thereof, the inner member of said two concentric members being supported solely by said joined end, said cathode being secured to the unjoined end of said inner cylindrical member in axial alignment therewith, the unjoined end of said outer cylindrical member being formed for attachment to said anode block at said opening therein, said cathode structure being adapted to form a gas tight closure for said opening in said anode block, said outer cylindrical member including means electrically insulating said unjoined end of said outer cylindrical member from said joined ends of said inner and outer cylindrical members, said cathode and said inner member of said supporting means having communicating axial opening therein, said joined ends of said inner and outer cylindrical members of said supporting structure being formed as the outer member of a coaxial jack, said cathode structure further comprising a heater coil disposed within said cathode, means forming the inner member of a coaxial jack insulatedly supported within said inner member of said supporting means, and means electrically connecting said means forming the inner member of said coaxial jack and one terminal of said heater coil, and a second terminal of said heater coil being connected to said cathode.

15. An improved axial cathode structure for magnetrons, capable of pre-assembly into a single unit, comprising a cylindrical cathode including a coating of electron emitting material, an input jack, a heater coil, one lead of said heater coil connecting to one terminal of said input jack, said input jack being located at one end only of said cathode structure, a second lead of said heater coil connecting to said cylindrical cathode internally, said leads being ultimately connected to a source of heater voltage, said cylindrical cathode being brazed to a tapered cylindrical copper plate, said tapered cylindrical copper plate being brazed to a cylindrical copper tube, said cylindrical copper tube being brazed to a second terminal of said input jack, said input jack being adapted to receive a coaxial plug, said cylindrical copper tube being of sufficient strength to support said cathode structure rigidly, means disposed at either end of said cylindrical cathode shaping and strengthening a magnetic field, means associated with said cylindrical cathode preventing leakage of electrons along the axis of said cathode structure, and means securing said pre-assembled unit into a magnetron block.

16. An improved axial cathode structure for magnetrons, capable of pre-assembly into a single unit, comprising a cylindrical cathode including a coating of electron emitting material on its outer surface, a heater coil, an input jack, a lead connecting heater coil to a center terminal of said input jack, said input jack being located at one end only of said cathode structure, a second lead of said heater coil connecting to said cylindrical cathode internally, said leads being ultimately connected to a source of heater voltage, said cylindrical cathode being brazed to a tapered cylindrical copper plate, said tapered cylindrical copper plate being brazed to a cylindrical copper tube, said cylindrical copper tube being brazed to a second terminal of said input jack, said second terminal being connected ultimately to a source of high voltage and to one side of a source of heater voltage, said input jack being adapted to receive a coaxial plug, said cylindrical copper tube being of suflicient strength to support said cathode structure rigidly, said cylindrical cathode, tapered cylindrical copper plate, and cylindrical copper tube being of sufficient area and being brazed together sufficiently well to provide an adequate path for conduction of large amounts of heat, said cylinders overlapping to present smooth, even surfaces with good electrical breakdown properties, a pair of hats, toroidal in shape, brazed to said cylindrical cathode, said hats being of magnetic material to help shape and strengthen a magnetic field which lies parallel to said cylindrical cathode, said hats being oriented to prevent electrons from escaping along the axis of said cathode structure, said hats being undercut to lengthen the path of migration of said electron emitting material along said external surface of said cylindrical cathode, and means for securing said pre-assembled unit into a magnetron block.

17. An improved axial cathode structure for magnetrons, capable of pre-assembly into a single unit, comprising a cylindrical cathode including a coating of electron emitting material, a heater coil, an input jack, a lead to said heater coil connected to a center terminal of said input jack, said input jack being located at one end only of said cathode structure, a second lead of said heater coil connecting to said cylindrical cathode internally, said leads being ultimately connected to a source of heater voltage, said cylindrical cathode being brazed to a tapered cylindrical copper plate, said tapered cylindrical copper plate being brazed to a cylindrical copper tube, said cylindrical copper tube being brazed to a second terminal of said input jack, said input jack being adapted to receive a coaxial plug, said cylindrical copper tube being of sutficient strength to support said cathode structure rigidly, said cylindrical cathode, tapered cylindrical copper plate, and cylindrical copper tube being of sufficient area and connected together sufiiciently well to provide an adequate path for conduction of large amounts of heat, said cylinders overlapping to present smooth, even surfaces with good electrical breakdown properties, a pair of hats, toroidal in shape, brazed to said cylindrical cathode, said hats being of magnetic material to shape and strengthen a magnetic field which lies parallel to said cylindrical cathode, said hats being oriented to prevent electrons from escaping along the axis of said cathode structure, said hats being undercut to lengthen the path of migration of said electron emitting material along said external surface of said cathode, a zirconium coated molybdenum heat radiator, cylindrical in shape, being brazed to one of said pair of hats, a cup being brazed to a magnetron block, a glass envelope, a second cup, said first cup being sealed to said glass envelope which is sealed to said second cup, said second cup being brazed to said input jack for final seal of said pre'assembled unit to said magnetron block.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Holhnann Mar. 28, 1939 Bondley June 17, 1947 Nelson July 22, 1947 8 McArthur Aug. 10, 1948 Spencer Oct. 26, 1948 Derby Mar. 8, 1949 Wax Apr. 12, 1949 Kather Aug. 9, 1949