US2201818A - Electronic discharge device - Google Patents

Description

May 21, 1940. c. 6. SMITH.

ELECTRONIC DISCHARGE DEVICE Original Filed Feb. 16, 1926 Z7wefeaz' warms G: SW'Z'eJZY-L 5y Patented May 21, 1940 PATENT OFFICE ELECTRONIC DISCHARGE DEVICE Charles Grover Smith, Medford, Masa, assignor, by mesne assignments, to Raytheon Manufacturing Company, Newton, Masa, a corporation of Delaware Application February 16, 1926, Serial No. 88,558 Renewed August 3, 1929 20 Claims.

This invention relates to gaseous conduction space-discharge devices which contain an attenuated ionizable gas. Objects of the invention are to lower the voltage drop between anode 5 and cathode, to increase the ourrent'or electronic discharge in tubes of this type and in general, and to produce a unidirectional gaseous conduction device operating with an arc-like discharge that has a voltage drop between cathode and anode below that required to maintain a glow discharge, no cathode dark space, low normal cathode voltage drop. Herein the term-arc-like discharge-and equivalent phrases mean, a discharge in which the cathode voltage drop is of the order of the ionization voltage of the gas in the device or less.

According to this invention the region surrounding a part or all of the active cathode surface is confined and the radiation and conduction 20 of heat from this part is retarded so that the surface may be maintained at a high temperature by the discharge whereby the cathode operates at a temperature at which rectification is dependent on thermionic emission. For example the cathode may be hollow, with a restricted opening through which the anode is presented to its interior, and the thermionically active surface of the cathode may be in the form of a projection or plate extending from the cathode wall into the 39 interior of the cathode and opposed thereto. In conjunction with this confinement of the active cathode surface the intervening gas space adjacent this surface preferably has a small dimension perpendicular to the surface so that the cathode 35 end of the discharge is disposed between two relatively closely spaced surfaces, both at approximately the same potential, whereby the discharge isfurther facilitated and intensified. The length of ,the spacing or gap between the opposed surfaces should be of the order of that of the dark space which would exist in the absence of one of the surfaces. This spacing corresponds to the mean free path of the gas filling in the tube. By inclining the surfaces relatively to each other to 45 partition off a narrow tapering cell from the interior space of said cathode, the space between said surfaces varies in width and the tube is more adaptable to different conditions of operation, the discharge extending farther into the tapered 50 space upon increase of gas pressure and automatically shifting to the area affording most eflicient operation in the event of change in pressure due to absorption or liberation of gas during operation.

68 In the accompanying diagrammatic drawing,

Fig. 1 is a central longitudinal section of one embodiment of the invention:

Fig. 2 is a similar view of another embodiment;

Fig. 3 is a section on line 3-3 of Fig. 2 and Fig. 4 is an enlarged longitudinal central sec- 5 tion of one of the anodes and associated parts.

The particular embodiment shown in Fig. 1 comprises a tube or envelope '1, preferably formed of glass, a hollow cathode K of suitable conducting material such as iron or nickel, and anodes A and A of tantalum, molybdenum, carbon or other suitable material. The cathode is formed in two parts, the upper part being in the form of an inverted cup with an exterior flange around its mouth and the lower part D being in the form of a disk secured to said flange as by welding and closing said cup. The disk has two spaced anode apertures or openings 0 and 0 (Fig. 3) with depending flanges therearound, these flanges preferably being spaced from the anodes a distance less than or comparable to the mean free paths of ions or atoms in the gas. The anodes A and A extend through the openings 0 and 0 respectively into the cup. Each anode comprises a metallic tube B (Fig. 4) having a lead-in wire E extending therethrough, the two being pinched together at their upper ends to secure them together. Insulating sleeves F, of quartz lava or the like, surround the lead wire and substantially close the lower ends of the flanged openings, the re-entrant stem S of the tube having recesses to receive the sleeves. While the cathode may be supported on the sleeves F it is preferably supported independently of the anodes by lead G and wire H, although the sleeves F position the cathode relatively to the anodes so that the cathode openings are concentric with the anodes respectively. For many purposes; such a rectifying 110 volt 60 cycle current for the filament circuits of radio receiving sets, the tube 4 may be filled with an inert monatomic gas such as helium at 17 mm. pressure and a small quantity of mercury vapor, caesium or other readily ionizable gas may also be incorporated in the tube. The gaseous atmosphere in the tube during operation has a substantial pressure sufiiciently high to supply suflicient positive ions to the space discharge to neutralize the space charge of the electron current between the cathode and anodes to the desired extent and at which an arc-like discharge takes place between the anodes and the active surfaces within the cathode structure.

In accordance with this invention active cathode surfaces are providedupon the interior of the thermionic cathode structure, preferably spaced close together. As shown in Fig. 1 these surfaces are provided by a series of rings R secured to the cathode and having their central openings aligned to permit the discharge to pass between the respective rings and the anodes. Thus the upper portion of the cathode cup cooperating with the lowermost ring R forms a cathode enclosure. In this enclosure there is an opening in the lowermost ring R for the passage of electrons from the cathode to the anodes A and A and said anodes are spaced away from the cathode to permit ionization therebetween. The aligned central openings of the rings R. provide a common discharge space or crater into which the relatively narrow intercommunicating cells or spaces between the rings terminate or open. The inner surface of the cathode enclosure is at least twice the area of said opening in the lowermost ring and thus the spaces between the rings are bordered by a relatively large surface area. Rings may be formed of-material such as tungsten, which withstands extremely high temperatures, although under many conditions of operation they may be made of nickel or even iron. The spacing between the rings may vary considerably but when operating at a pressure of the order of 17 mm. the spacing is preferably of the order of 2 mm. which is approximately the mean free path of the gas. The rings may be caused to emit more efficiently if they are coated with a material of high electron emissivity such as an alkali metal or alkali earth metal or oxide of an alkali metal or alkali earth metal or if they have metallic thorium incorporated therein. Preferably this coating material, which enhances the electron emissivity of the cathode, should be one which is substantially solid at the normal operating temperature of the tube envelope T. Materials which are solid under these conditions will be termed herein-solid substances or materials. The hollow cathode may also be similarly constituted. Due to the above configuration the cathode structure as a unit when heated has a substantially smaller effective outer heat radiating area than electron-emitting area. Decrease of gas pressure due to absorption of the gas by the hot cathode surfaces is also substantially avoided by coating the surfaces as herein described, assisted under some conditions by the presence of mercury vapor as described in my prior application, Serial No. 55,262.

The modification of Figs. 2 and 3 is like the embodiment shown in Fig. 1 except in that the plate constituting the active cathode surface, instead of being in ring form as in Fig. l, is in the form of a ribbon which is anchored at one end to the inside of the cathode, is oppositely disposed thereto, and spirals inwardly therefrom. By virtue of the spiral the dimension of the gas space adjacent the ribbon varies in thickness throughout the length of the ribbon. The area of the openings left between the convolution or ribbon R and the walls of the cathode cup is less than the internal area of said cup and saidconvolution.

In operation the discharge passes between the anodes and the interior of the hollow cathode structure which constitutes an enclosure confining a part of the space in the tube. The plate surfaces inside the cathode (rings R of Fig. l or spiral R of Fig. 2) become highly heated to thermionic emission by the discharge owing to the fact that they are enclosed by the cathode and are juxtaposed or spaced close together and close to the wall of the enclosure; consequently these surfaces function as thermionic electron emitters with marked efliciency and most of the electronic discharge emanates therefrom rather than from the interior of the enclosure. Thus the enclosure need not be formed as a part of the cathode. With the region around the hot cathode surfaces R or R closely confined the excitation and ionization of the gas within the enclosure becomes suiiiciently intense to produce ions and electrons capable of carrying the discharge current. Thus I have discovered a unique method of producing an arc discharge by heating the cathode to a temperature at which the oxide coating has an effective electron emission to produce thermionic emission from a closely confined area by heat from the discharge terminating at the area.

The oxide coating in the cathode is relatively non-volatilizable and remains substantially intact at an effective electron-emitting temperature. Moreover, by virtue of the location of the oxide coating inside the hollow cathode with only a restricted opening therefrom, particles of the coating which may be dislodged by ion bombardment are redeposited upon the inside of the oathode, little if any of the dislodged particles escaping through the restricted opening through which the spaces between the rings R communicate with the exterior. Thus the closely adjacent walls of the rings, which are positioned in heat-shielding relation to one another, also provide deep contracted spaces whereby the oxide coating is conserved in the cathode enclosure at a temperature of thermionic emission. This not only conserves the coating but it avoids the deleterious effects which would result from the particles redepositing upon the inside wall of the glass container or vessel or upon other surfaces inside the container.

For many purposes improved operation is obtained by forming the cathode coating at least in part of alkali metal or alkali earth metal instead of an oxide of the metal. Such a coating may be effected by first applying an oxide coating and then operating the tube on heavy current while still on the vacuum pump, thereby reducing the oxide to metallic form by removing the oxygen. This reduction may be partial or complete depending upon the intended use of the tube but for most purposes I prefer not to reduce the oxide completely. The reduction product appears to amalgamate with the cathode and forms a remarkably durable and eflicient emitting surface.

I claim:

1. A gaseous conduction device comprising an envelope containing an attenuated atmosphere, a hollow cathode, forming a cup, a disk closing the cup, spaced apertures extending through the disk, a plurality of anodes projecting through the apertures into the cup, and a thermionically active surface projecting from the cup interiorly thereof and opposed thereto, forming an intervening gas space between the said thermionically active surface and the said cup interior, the width of said space being of the order of that of the dark space which would exist in the absence of one of said surfaces.

2. An electrical space discharge device comprising a vessel containing an anode, a cathode structure constituting an enclosure confining a part of the space in said vessel, said cathode structure having in the interior of the enclosure oppositely disposed tapering conducting wall ill;

members having juxtaposed electron emitting surfaces to be heated to thermionic emission during operation and partitioning oil a narrow tapering cell from the interior space of said enclosure, and an ionizable gas having during operation a pressure at which an arc-like discharge takes place between said anode and the interior of the tapering cell within the enclosure of said cathode.

3. An electrical discharge device comprising the combination of an envelope, an attenuated gas filling at a pressure sufficiency high to neutralize space charge, a cathode therein operating at a temperature at which rectification is dependent upon thermionic emission, said cathode comprising an enclosure of conducting material having a solid material of high electron emissivity in said enclosure, and an anode spaced away from said cathode to permit ionization therebetween, said cathode enclosure having an opening for the passage of electrons to said anode and having closely adjacent walls providing a deep contracted space, whereby said electron missive material is conserved in said enclosure at a temperature of thermionic emission, the inner surface of the enclosure being at least twice the area of the opening leading therefrom.

4. An electrical discharge device comprising an envelope, electrodes therein, including a thermionic cathode having walls providing contracted spaces communicating with the exterior, a ma terial in said spaces which is capable of enhancing the electron emissivity of said cathode, said cathode being adapted to be heated during operation to a temperature at which said material has an effective electron-emission, and a gas in said envelope at a pressure which is sufficiently high to neutralize space charge during the operation of the device.

5. An electrode for an electrical discharge device, said electrode having a plurality of adjacent wall members positioned in heat-shielding relation to one another and separated by deep contracted spaces which are open to the exterior, a material on each of said wall members which is relatively non-volatilizable at an effective electron-emitting temperature Within said spaces for enhancing the electrical emissivity of said electrode, said electrode being adapted to be heated to a temperature of thermionic emission during operation.

6. An electrode for an electrical discharge device constituted of conducting material formed into a hollow body having a convolution within its confines, the area of the openings left between said convolution and the walls of said hollow body being less than the internal area of said hollow body and said convolution, and a thermionically active material coating said electrode, said material being conserved at a temperature of effective electron emission, said electrode being adapted to be heated to a temperature of thermionic emission during operation.

7. An electrical discharge device comprising cooperating electrodes, one of which is provided with a cavity having an opening for the escape of electrons, and having a projection extending into said cavity, the surface of which is in communication with the exterior through said opening, and an activating material on said projection which will be conserved in said cavity during the operation of said device, said activating material being adapted to be heated to temperature of thermionic emission during operation.

8. An electrical space discharge device comprising a vessel having therein an anode, a cathode structure comprising conducting members surrounding a plurality of spaces bordered by a relatively large surface area having thereon an activating material adapted to be heated to thermionic electron emission during operation, said cathode structure as a unit having, when heated, a substantially smaller effective heatradiating area than electron-emitting area, and an ionizable gas in said vessel at substantial pressure at which suflicient positive ions are supplied during operation to the space discharge to neutralize the space charge and secure low cathods voltage drop,

9. An electrical space discharge device comprising a vessel having therein an anode, a hollow cathode structure having an extended interior solid electron-emitting wall surface of substantially greater area than the outer heat-radiating surface of the cathode, said wall surface having thereon an activating material adapted to be 10. An electrical space discharge device com- 1 prising a vessel having therein an anode, a cathode structure comprising a hollow conducting member having in the interior a plurality of projections having thereon an activating material adapted to be heated to thermionic electron emission during operation, the surfaces of said projections constituting, in conjunction with the interior surfaces of said hollow member, an extended electron-emitting area larger than the heat-radiating area of said cathode, said cathode having a discharge opening for passing a space discharge between the interior electron-emitting surfaces thereof and said anode, and an ionizable gas in said vessel at substantial pressure at which sufficient positive ions are supplied to the space discharge during operation to neutralize the space charge and secure low cathode voltage drop.

11. An electrical space discharge device comprising a vessel containing an anode and a cathode structure having a plurality of conducting wall members with relatively extended juxtaposed electron-emitting surfaces bounding spaces therebetween designed to be heated to thermionic emission during operation, an activating material on said surfaces during operation to enhance the electron emission thereof, an ionizable gas having during operation a pressure suflicient to sustain a discharge at low voltage drop between anode and cathode, said cathode structure also comprising a hollow enclosure member surrounding said wall members for maintaining said electron-emitting surfaces at temperature of electron emission during operation of the device, the gas between said surfaces to be simultaneously maintained in sufficiently excited condition sothat a discharge at low cathode voltage drop is secured between said cathode and anode.

12. An electrical space discharge device comprising a vessel containing an anode, a cathode structure constituting an enclosure, said cathode structure having in the interior of the enclosure oppositely-disposed conducting wall members having juxtaposed electron-emitting surfaces adapted to be heated to thermionic emission dursaid enclosure and subdividing the same into a plurality of cells opening into a common discharge space within said enclosure, an anode for maintaining through said common discharge space a discharge with the surfaces of said projections, and a gas filling at a pressure sufilcient to sustain a discharge by gas ionization between said electrodes.

14. A unidirectional gaseous discharge tube comprising a vessel containing a gaseous atmosphere to be ionized to maintain a discharge, a cathode structure constituting a hollow chamber with an interior electrode surface in said vessel, the interior of said cathode chamber having an electrode surface formed of a plurality of closely-spaced projecting wall portions consti' tuting a plurality of intercommunicating cells terminating into a common space within said hollow chamber, said wall portions having thereon, during operation, an activating material for enhancing the electron emission thereof, said wall portions being adapted to be heated to thermionic electron emission during operation, and an anode disposed outside said cells to maintain a discharge through said atmosphere with the interior conducting surfaces of said cathode through said common space.

15. An electrical space discharge device comprising a vessel having therein an anode, a cathode structure having oppositely-disposed wall members with relatively extended juxtaposed thermionic emitting areas bounding a narrow space therebetween, said areas being adapted to be heated'to thermionic emission during operation, an ionizable gas inert with respect to said electrodes in said vessel at a pressure sufllcient to supply during operation the requisite number of ions necessary to neutralize the space charge of the electron current between said cathode and anode, said juxtaposed thermionic emitting areas being spaced from each other by a distance of the order of that of the dark space which would exist in the absence of one of said areas.

16. A crater cathode for a discharge tube, comprising a plurality of parallel disks having alined perforations forming the crater, said disks being :lpaced to provide a discharge region between 1'7. An electrical discharge device comprising a vessel containing a gas, cc-operating electrodes, one of which is provided with a cavity, an opening for the escape of electrons, and having a projection extending into said cavity, the surface of which is in communication with the exterior through said opening, and an activating material on said projection which will be conserved in said cavity during the operation of said device, said activating material being adapted to be heated to temperature of thermionic emission during operation.

18. An electrical discharge device comprising a vessel containing a gas, mercury vapor, co-operating electrodes, one of which is provided with a cavity, an opening for the escape of electrons, and having a projection extending into said cavity, the surface of which is in communication with the exterior through said opening, and an activating material on said projection which will be conserved in said cavity during the operation of said device, said activating material being adapted to be heated to temperature of thermionic emission during operation.

19. An electrical discharge device comprising a the surface of which is in communication with the exterior through said opening, and an activating material on said projection which will be conserved in said cavity during the operation of said device, said activating material being adapted to be heated to temperature of thermionic emission during operation.

20. An electrical discharge device comprising a vessel containing a gas, co-operating electrodes, one of which is provided with a cavity, an opening for the escape of electrons, and having a projection extending into said cavity, the surface of which is in communication with the exterior through said opening, and an activating material on said projection which will be conserved in said cavity during the operation of said device, said activating material being adapted to be heated to temperature of thermionic emission during operation, said gas having a pressure at which an arc-like discharge occurs.

CHARLES G. SMITH.

' Patent No. 2,201,81

"CERTIFICATE OF CORRECTIONa May 2;, 191m. CHARLES GROVER SMITH.

;It is hereby certified that error appears in the printed specification of the above hamoeredpatent requiring correction as follows: Page 1, first column, line 7, strike out the word "am"; and second column, line 59, roi- "a" read --as--; page 2;, firstcolummline 21, for "Rings" read --The rings--; page 5, first columri, line 11, claim}, for "smfficieney' read --sufficiently-- 1-ine 25, same claim, for "mi-salve" read --em1ssiVesame page, second column, line 12-15, claim 8, for "cathods" read "cathodeand that the sa id Letters Patent should be read with this correction therein that the same may conforin to the record of the case in the Patent Office.

Signed and sealed this 2nd day of July, A. D. 19L o.

Henry Van Arsdale, I (Seal) -Acting Commissioner of Patenta.

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