US1814711A - Electron discharge device and method of fabricating the same - Google Patents

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K. H. KINGDON ELECTRON DISCHARGE DEVICE AND METHOD OF FABRICATING THE SAME July 14;, 1931,

Filed March 6, 1926 Inventor Kenneth HKinQdon,

b Hus Attorney.

. Patented July 14, 1931 UNITED STATES.

PATENT OFFICE KENNETH H. KINGDON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK ELECTRON DISCHARGE DEVICE AND METHOD OF FABRICATING THE SAME Application filed March 6, 1926. Serial No. 92,946.

. The present invention comprises improvetion which are set forth with greater parments in electronlc devices containing a conducting material of relatively high vapor pressure, such as an alkali metal, and its main object is to prevent impairment ofthe efliciency of such devices by the formation of a conducting film on the inner surface of the container, which would permit electrical leakage to occur between sealed-in conductors. As the conducting film is mainly deleterious when formed on the glass stem of these devices, through which the leadingin wires are sealed, the phenomenon will be referred to herein as stem leakage.

' In a bulb containing electrodes operating at a higher temperature than the bulb, an easily vaporizable material is continually vaporizing at the electrodes and condensing on the cooler bulb. Under some conditions the condensed material forms a continuous film which, even when it is so thin as to be invisible to the unaided eye, has a sufiiciently high electrical conductivity to cause serious electric leakage.

I have found that under other controllable conditions the vapor will condense in detached specks between'which there is no electrical contact, and which will not cause electrical leakage.

It is my present opinion that the continuous deposit occurs when tthe vapor is adsorbed by a layer of oxide or a thin metallic film on the surface of the stem, or other part of a tube, over which leakage occurs. The formation of this adsorbing film apparently is promoted by the deposition of the products of ionization of gas on the stem.

In accordance with the present invention discontinuity in the condensed metal on the surface of the stem, or wherever electrical.

leakage is like to occur, is obtained by carrying out the exhaust in accordance with a procedure hereinafter described and also by a construction whereby ionization in the space adjacent the stem is avoided. The exhaust procedure appears to owe its effectiveness to the actionof water left in the glass which converts the deleterious oxide to hydroxide.

The novel structural features of my inventicularity in the appended claims are illustrated by the accompanying drawing in which Fig. 1 shows in perspective one form of a complete device; Fig. 2 shows the electrodes in perspective on a somewhat larger scale, the anode being shown in part broken away, and Fig. 3 is a fragmental perspective view of a modification, the enclosing bulb being omitted in Figs. 2 and 3.

Referring to the drawings, the device shown in Figs. 1 and 2 comprises a sealed envelope 1, commonly consisting of glass on the stem 2 of which are mounted the electrodes of the device. The electrode leading-in conductors are sealed into the stem and connected to the exterior contacts of a base 3. As shown in Fig. 2, the cathode of the device consists of a filament 4 which has in the main a rectilinear extension but which actually consists of a fine spiral wire. This cathode, which may consist of tungsten is connected to a support 5 which serves also as a current supply conductor and therefore is sealed into the stem 2. The opposite end of the cathode filament is connected to the sealed-in leading-in conductor 7. As indi cated in the drawings, the ends of the cathode may be connected to short pieces of somewhat heavier nickel wire which in turn are connected to the still heavier wires 5, 7 The anode 8 is cylindrical in form and inclosesthe cathode substantially throughout its length. The anode is provided upon its interior with four vanes 10 which extend radially toward the cathode. The anode is supported by stout anchor wires 11, 12, one of which passes through the stem 2 and serves as a leading-in conductor. Between the vanes 10 there is provided a second set of vanes which are constituted of metal plates 9, 13 bent in such a way as to extend radially from the cathode filament toward the anode. The vanes 9, 18, are supported by a plate 14.- which is conveniently made circular in form and is positioned closely adjacent but out of contact with the lower end of the cylindrical anode 8. The vanes 9, 13 therefore are electrically at the same potentialv and together constitute the control electrode of grid of the device. Both the anode and the control electrode may consist of nickel. The plate 14, together with the grid members 9, 13, are supported upon wires 15, 16, one of which is sealed into the stem 2 and serves to impress potential changes upon the grid. The plate 14, WhlCh is rovided with a hole through which the cat ode wire passes, serves to prevent the'escape of electrons from the space between the electrodes and thus Erevents ionization from occurring around t e stem.

e device is also provided with a capsule 17 consistin of two metal Iplates, a cavity being rovided in one of t e lates in which is p aced a small quantity 0 a reaction mixture capable of yielding an alkali metal, such as caesium. For example, a mixture of caesium chloride and metallic calcium the formation of a continuous,

or magnesium may be used. The capsule 17 is supported any convement way as by a wire 18 connected to the anode. As shown in Figs. 1 and 2, the capsule 17 is in a position somewhat above the anode so that it may be heated by a high frequency field independently of the anode.

The bulb should not be subjected during exhaust to the high temperature bake-out to which vacuum devices usually are subjected. It may be baked for about half an hour at a temperaturesomewhat below 300 C. During or after this partlal dehydratlon of the bulb, gas may be driven from the electrodes, by heating the same by high freuency induction or other convenient way. 2 liquid air trap in the vacuum system s a somewhat too energetic agent for removing water vapor. Pre erably aside bulb containing phosphorous pentoxide is used instead of a liquid air trap, care being taken to avoid introduction of the pentoxide into the bulb. It is my present opinion that moisture left in the glass by this procedure converts traces of oxide or alkali metal deposited on the stem to hydroxide and thus produces a surface condltion unfavorable to electrically conducting film.

The tungsten cathode preferably should be provided with an oxygenous surface by heating in an atmosphere of attenuated oxygen or air so as to render its surface suitable for the adsorption of a thin film of caesium during operation. For example, after exhaust oxygen at a pressure of about 100 microns of mercury may be admitted to the bulb, the filament is then heated to about 2000 K. for about one minute to produce a thin adherent film of oxygen. The oxy then is exhausted and the capsule 17 is heated to liberate caesium. The thin film of caesium adsorbed by the cathode permits of efiicient emission of electrons when the cathode is operatedv at a temperature of about 950 K. which would otherwise be too low to produce gen' appreciable electron emission from ordinary tungsten in a vacuum. The phenomena involved in the emission of electrons from a tungsten cathode in the presence of caesium vapor are described in apers in The Proceedings of the Royal iety, A Vol. 107, p. 61, 1925, and Physical Review, Vol. 24,p. 510, 1924, and therefore will not be described in detail in the present specification. It is desirable also to have present in the bulb a source of oxygen, such as a small piece of oxidized copper indicated at 19. During the operation of the tube some of the caesium reacts with the cop r oxide to form caesium oxide and the resulting mixture of caesium and caesium oxide eliminates deleterious gases such as hydrogen and carbon monoxide when evolved in minute quantities from metal and glass parts of the device.

The shield 14 may assume various forms and modifications within the scope of my invention. In Fig. 3, I have illustrated a modified shield 20 which surrounds the stem 2 leaving the electrodes 21 (shown in part) otherwise unshielded. This shield '20 is supported by the nickel wire which in turn forms an anchor for the lower end of the cathode. The two members constituting the anode are connected together by a wire (not shown) across the top and similarly the two grid members, which are inserted between the slots of the anode elements, are also connected together at the top by a wire (not shown). The stem shield 20 largely prevents contact of products of ionization with the stem, and thus preserves discontinuity in the deposits of alkali metal condensed thereon device.

Devices containing caesium constructed and exhausted as above described have been operated successfully as amplifiers for 1000 hours or more with 60 volts on the anode, and the grid being connected to the negative end of the cathode filament.

at I claim as new and desire to secure by Letters Patent of the United States, is,-

An electrical discharge device comprising an evacuated container, electrodes having supply conductors sealed closely adjacent one another into said container, and a charge of alkali metal in said container, the inner surface of said container adjacent the seals for said electrodes containing suflicient water to cause alkali metal condensed on said surface to assume the form of discontinuous specks incapable of causing substantial electrical leakage between said electrodes.

In Witness whereof, I have hereunto set my hand this 5th day of March, 1926.

KENNETH H. KIN GDON during the operation of the

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