US2400770A

US2400770A - Cathode for magnetron devices

Info

Publication number: US2400770A
Application number: US424316A
Authority: US
Inventors: Mouromtseff Ilia Emmanuel; Findlay John Hamley
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1941-12-24
Filing date: 1941-12-24
Publication date: 1946-05-21
Anticipated expiration: 1963-05-21

Description

1946 I. E. MOUROMTSEFF ETAL 2, 00,770

I CATHODE FOB MAGNETRON DEVICES- Filed Dec. 24, 1941 INVENTORS I. E. Mourom Ase ATTORNEY Patented May 21, 1946 Ni'l'E. stares cn'rnonn .ron AoNn'rnoN DEVICES Ilia Emmanuel Mouromtseif, Montclair, and John Hamley Findlay, Upper Montclair, N. J., as signors to. Westinghouse Electric Corporation; East Pittsburgh, Pa; a corporation of Pennsylvania Application December 24, 1941, Serial No. 424,316

'7 Claims. (01. 250-275) electron emitting cathode axially sustained therein with both elements enclosed within an evacuated glass envelope. It is found in such devices that the portion centrally of the length of the cathode element of the tube reaches a higher equilibrium temperature than the end portions of the length of said cathode, to which several reasons may be ascribed. One reason is that this central portion of the cathode is subjected to more severe electron bombardment than the end portions. Another reason is that the ends are more favorably situated for radiation. Yet another reason is that less bombardment occurs at the end portions than at the central portion. Bombardment results in the loss and destruction of the thermionically active material on the surface of the cathode. Also the higher temperature of the central portion of the cathode results in evaporation of the active material, and in either event the active material lost from the cathode is in greater part found to be deposited on the inner concave face of the anode. This deposit on the anode materially interferes with the operating characteristics of the magnetron device and shortens the operating life and efficiency of. the device.

One of the objects of the present invention is to eliminate this defect in an electron discharge device of the magnetron type thereby to increase the operating life and efiiciency of magnetron devices.

Another object is to provide an improved electron. emitting cathode for a magnetron device.

Still another object. is to provide an oxide coated cathode for an electron discharge device of the magnetron type whichis not deleteriously affected by electron bombardment.

Other objects and advantages will be apparent as the invention is more fully hereinafter disclosed.

In accordance with these objects, We have discovered that by locating the thermionically active material, adjacent the ends of the cathode leaving the intervening or central area of the cathode bare and exposed to electron bombardment, the defect hereinabove noted, not only iseliminated but that theoperating characteristics of the device are stabilized and remain substantially con stant for relatively prolonged periods of time as compared with devices provided with cathodes that arethermionically active over substantially their entire length. Wehave found that by 10- cating the thermionically active material on the cathode surface at a point remote from the area of intense electron bombardment and within the area wherein the temperature of the cathode remains substantially constant, the amount of such material on the cathode may be reduced material- 1y to an amount required to produce a sufficient quantity of electrons to initiate operation of the device and that the secondary emission of the uncoated area produced by electron bombardment plus the electron emissivity of the electron emite ting material on the cathode end portions is ample for continued operation of the device; and we have further found that by eliminating the evaporation of the electron emitting material onto the anode by so locating the electron emite ting material on. the cooler end portions of the cathode the operating characteristics of the device remain constant over a prolonged period of time as compared to prior art devices.

In accordance with these discoveries we have devised the electron emissive cathode of the type illustrated in the drawing for use in magnetron devices.

Referring to the drawing 'l Fig. 1 is a sectional view of a magnetron device showing the essential elements thereof;

Fig. 2 is a cross-sectional view of the same along plane 22 of Fig. 1;

Fig. 3 is a sectional view of the improved electron emissive cathode of the present invention;

Fig. 4 is a cross-sectional view of the same along plane 4-4 of Fig. 3; and

Fig. 5 is a contemplated modification of the present invention.

As indicated in the drawin a magnetron device comprises a split anode A'-A surrounding in the present instance an indirectly heated tubular cathode C sustained in concentric spaced relation within evacuated glass envelope G by means of lead-in support wires a-a and 0-0, respectively, passing through press P of the envelope G. Magnetic coil M is provided to produce a magnetic field of the desired character within the device.

In accordance with the present invention, cathode C is shown as comprising an elongated tubular metal base member It provided with a heater element H concentrically disposed therein as is customary in the art. A surfacecoatin E--E' of thermionically active material is present on the outer surface of each end portion of the base Ill, extending inwardly in each instance from the end portion towards the center a distance at least sufiicient to provide enough emission for energization and actuation of the device. The active material is therefore insufficient in extent to be located upon the central area of the tube subjected during operation to intense electron bombardment with consequent high temperature and evaporation.

It is believed apparent that the amount of thermionically active material E-E' deposited on the end portions of base I of the cathode C may vary widely without essential departure from the present invention, depending upon the nature of material employed and upon the field of use for which the device is designed. In general, the object is to locate the thermionically active material E-E on th area of the cathode surface which in the normal operation of the device has lowest temperature and is subjected to the least electron bombardment. This area obviously varies with respect to the tube design, such as anode length and anode-cathode spacing and for devices where the electron bombardment during normal operation may extend over the greater portion of the length of the cathode enclosed by the anode. It

is contemplated that the cathode C may be elongated at least sufiiiciently to provide an area at each end that is beyond the area of disruptive electron bombardment upon which the electron emitting material E-E may be located.

Irrespective of the fact that the electron emissive material E-E' is limited to the area of the base ill which is remote from the area of intense electron bombardment, and at a temperature sub stantially below the vaporization temperature of the electron emitting constituent thereof, the exposed or uncoated area of the base it still functions under theinrluence of electron bombardment as anemitter of secondary electrons. Accordingly, base it may be comprised of any one of a plurality of metals and alloys heretofore known in the art to be of utility as an emitter of secondary electrons under electron bombardment. Preferably, base if! is comprised of substantially pure nickel, but alternatively may be comprised of molybdenum or of one of the various nickel alloys heretofore found satisfactory as a base met l for thermionically active oxide coatings for such cathodes.

Within the contemplation of the present invention also is the provision of a cathode consisting of a tubular base it comprised of a metal or metal alloy highly reactive as an emitter of secondary electrons under electron bombardment but not necessarily suitable for use as a base for electron emittin material EE wherein material EE' is located on sleeve members 2 l--2 I comprised of material suitable for use as a base for electron emitting material E--E and adapted to be slipped onto the ends of tubular base 29 substantially as indicated in Fig. 5.

Having hereinabove described the present invention generically and specifically and described and illustrated one specific embodiment thereof, and for simplicity having omitted herefrom further illustration and description of other modifications and departures from the precise showing herein, but which might have been included in substitution for or in addition to the selected showing, applicants do not disclaim any such modifications and departures as may fall within the scope of the following claims.

base member, all active areas of the cathode being situated in the said concentrated field of the magnet.

2. A magnetron device having a magnet establishing a concentrated field, an anode having an electron-receiving face in said field and an envelope enclosing the electron-receiving face of said anode, an electron emitting cathode Within said envelope and opposed to said electron-receiving face of the anode, said cathode consisting of an elongated metal base member having the thermionically active surface area thereof restricted to the area adjacent each end of the base member and consisting of material resistant to eva orating under electron bombardment, all active areas of the cathode beingsituated in the said concentrated field of the magnet.

3. A magnetron device having a magnet establishing a concentrated field, an anode havingan electron-receiving face in said field and an envelope enclosing the electron-receivin face of Said anode, an electron emitting cathode within said envelope and opposed to said electron-receiving face of the anode, said cathode consisting of an elongated metal base member having the thermionically active surface area thereof re stricted to the area adjacent each end of thebase member, said base member in the area intermediate said thermionically active end areas consisting of material of relatively high secondary emissivity under electron bombardment, all active areas of the cathode being situated in the said concentrated field of the magnet.

4. An electron emitting cathode consisting of an elongated metal base member having the thermionically active surface area thereof reface beyond the area of intense electron bombardment and within the end areas of the said cathode.

5. A .cathode element consisting of an elongated tubular base consisting superficially in the center area thereof of material of relatively good secondary electron emissivity under electron bombardment and at each end thereof super ficially of material of relatively high primary electron emissivity, and means interiorly of said tubular base member to heat the end areas of the said tubular base member to the temperature of primary electron emissivity.

6. A cathode element comprised of an elongated tubular metal base member consisting of nickel, a thermionically active oXide coating dis posed on the surface of said base member within the area adjacent each tubular end remote from electron. bombardment during operation, and heater means disposed Within the said tubular member to heat the end portions of the said tubular member to the temperature of electron emissivity of said oxide coating thereon.

7. A magnetron device comprising an envelope, an anode in said, envelope, a magnet presenting a concentrated field within said anode, an electroni emitting cathode in said field and anode, said cathode consisting of an elongated metal base member having the thermionically active surface area thereof restricted to the area adjacent each end of the base member, said base member comprising an elongated metal tube consisting of substantially pure nickel and the said thermionically active surface area adjacent each end of the tube comprising a thermionically active oxide coating, said oxide coating being limited to the area of said tube surface beyond the area of intense electron bombardment during operation of said device and within the end areas of the said cathode, and means within said envelope for thereby heating the end portions of the tube and thermionioally active coating on the end areas thereof to the temperature of electron emissivity of said 10 coating.

ILIA EMMANUEL MOUROMTSEFF. JOHN HAMLEY FINDLAY.