US2082602A - Thermionic cathode - Google Patents

Description

June 1937- H. c. STEINER ET AL 2,032,502

THERMIONI C CATHODE Filed April 26, 1929 Inventors: Harry CSteiner, Orh'n W. Livingston, by Them Attorney.

Patented June 1, 1937 UNITED STATES PATENT OFFlCE 2,082,602 THERMIONIC CATHODE Harry 0. Steiner, Scotia, and Orrin W. Livingston, Schenectady,,N. Y., assignors to General Electric Company, a corporation of New York Application April 26,1929, Serial No. 358,354 11 Claims. (01. 250-275) The present invention relates to gas conduction tional area and for carrying the heavy current devices and more particularly to the cathode and for providing ruggedness. In the case of structure of such devices. filamentary cathodes of ordinary length which An article in the General Electric Review, April are designed for relatively low voltages, these con- 1929, vol. 32, No. 4, pages 211L223, describes a ditions may be satisfied by the use of metal ribform of electrical discharge apparatus termed a bon wound as a continuous helix either as a ver- Thyratron. The present invention relates to tical convolute or as a single, flat spiral. How apparatus of this type. ever, in the event the cathode is designed for The tube described in the article referred to,. higher voltages, in order to offer the proper reis essentially a three-electrode device, into which sistance, the filament is necessarily long on ac- 10 a small amount of an ionizable medium consistcount of its large cross sectional area and it is ing of an inert gas or a. vapor producing substance evident that the amount of space taken up by the has been introduced. The presence of the ionizhelical cathode of the requisite length may preable medium changes the discharge into an arcclude its advantageous employment in tubes of like discharge having a fiat or slightly negative limited interelectrode space. 15 volt-ampere characteristic. The starting of the Accordingly, one of the features of our invenarc may be controlled electrostatically by means tion contemplates an improved form of cathode of the grid member to which a, negative charge for controlled arc devices in which a relatively may be applied, the discharge ceasing only by the large electron emitting surface, constituted as a removal of the plate voltage. The removal or heavy conductor of long length, is confined in a 20 stoppage of the plate voltage conveniently is acrelatively small space and at the same time offers complished by energizing the plate circuit with the full measure of effectiveness in presenting alternating current which periodically drops the entire active surface to the anode. Accordthru zero. Such a tube may thus be used as an ing to another feature of our invention proelectrostatically controlled arc rectifier in which vision is made to separate the load current from 25 the charge on the grid determines the point in the cathode heating current in so far as the the alternating current cycle at which the arc lead-in conductors are concerned thus relieving discharge shall start and hence controls the avthe filament conductors of the burden of transerage value of the plate current. This current porting the plate current so that the size of these may have a magnitude almost without limit exconductors need only be large enough to carry 30 cept for apparatus cooling and cathode emission the heating current. This feature is accomconsiderations; the fiow of current may be inplished by providing an additional lead connected itially controlled by an expenditure of grid ento the center or mid-point of the filament and ergy of less than one microwatt. forming part of the load circuit.

In view of the arc-like character of the current It has been found in the operation of tubes of 35 stream, the various elements within the tube the kind described that when the ribbon filamust be carefully designed, particularly the ments are wound as a helix in the manner procathode. The heated member is normally subposed by the prior art the force exerted by the jected to considerable positive ion bombardment magnetic field of the filament, which is of an acin the larger size tubes and there is always prescumulative character, deleteriously affects the 4 ent the danger of developing localized hot spots movement of the positive ions and electrons,

, with consequent burning out. Hence, it is imtending to defiect these particles from their norperative to provide a filament of relatively large mal path between electrodes and generally to incross sectional area and of rugged construction. terfere with the starting of the device and oper- Morever, inasmuch as there is a large plate curation thereafter. As a further feature of our in- 45 rent involved which necessarily passes through vention, we propose to construct the cathode in some portion of the filament after traversing the such a manner that there are no magnetic forces are path, there is the problem of providing a filpresent or rather such forces tend to neutralize ament lead-in conductor capable of being heroneanother and hence the current is free to move metically sealed within the stem and of suffibetween the electrodes without impediment. 50 cient size to accommodate the combined heating Other objects and features will be apparent as and plate currents. The cathode must also be the specification is perused in connection with able to supply considerable quantities of electrons, the accompanying drawing which represents a hence calling for a large electron emitting surview partly in cross section of a preferred embodface in addition to the required large cross seciment of the invention. 55

Referring tov the drawing, numeralv i designates. an evacuated envelope which terminates in a press 2. Within thev envelope there are coaxially arranged a cathode structure, an electrostatic control member or grid 3 and an anode 4. In accordance withour invention,.the-cathode consists of a conductor,]preferably of strip material. formed as a plurality of portions,"layers or decks 5, 6 of similar contact pin I4 and at the other end-jis-ijoined,

' "ductors 21, one of as by welding, to a cap-like shield -l5iwhich iits over the cathode. It is appare'nt-thatinasmuch the spirals are :j'oined together as the centers of and the outer terminals 'are'eflectively-across the source of electromotive force the .current traverses one of the spirals in a direction opposite to the fiow .0!

whereby the magnetic fields of the helicessneu traiize one another. The cathode-is preferably made both sides with electronically. active substances such as barium carbonate (139 603)".ortotherf-suibv able salts of theialkaline earth metalsinorder to increase electron emission. The coatmay be formed by applying to theurface a paste of the carbonate mixed'with suitable binder and heating the fiiamenttoa proper "temperature.

The cap member it which also may comprise nickel'is closed'at thetop, pen at-the bottom andis of a length sufiicient to extend at least trons except at fairly to the lower edge'of the spiral 6. In addition to being supported at'the center by the lead in conductor IS the cap 'or shield i5 is joined at the outer surface to a rod lt which is fused in the stem 2 and hence is rigidly held at two places.- The function of the shield will be explained hereinafter. 'The.grid member 3 is fabricated preferably as a mesh or other perforated body of a metal' such as'a nickel-chromium auoy j (nichrome) which ordinarily does not emit'elece high temperatures. The

grid may take the general'shape of a cylindrical cap which fits over the shield member and ex-' tends a considerable distance below the cathode, being supportedat suitable distance from the cathode structure by means of metrically disposed rods H, which are secured to a band l8 of metal tightly embracing the stem 2. A lead-in conductor is may be attached to the band and taken out to a contact pin 20.

The anode 4 comprises a plate member preferably of nickel which is carbonized toJoffer a black body heat-radiating surface. In order to make contact with the anode, a terminal 2! is aflixed to the upper extremityof the envelope l and a lead connected in any suitable manner between the terminal and the anode, The envelope is of the tipless type so-called in order to accommodate the made for evacuating the envelope through a tube 22 in the well 'knownmanner.

During operation, the heat produced by the filament is intense and it is desirable to protect configuration :such. as spirals in opposed relatlon-andsinco ductor l1. The

H may be applied cl'udes aload 28 shown but which may constitute a relay or other circuit current in the other spiral ofnickel andmay be coated onr'oneaor trons are emitted through an equal number from two sets of dia--,

leakage atlthe terminal, provision being to azplate 25 and supported in the proper position by means of a wire 26 secured to the coniunction of the getter is well known. An inert gas, such as argon, at a pressure between 50-250 microns may be introduced into the envelope during and after evacuation but preferably a drop of mercury (not shown) is employed as the source of positive ion-producing vapor. The operating temperature of the device may be suchthat the mercury vapor has a pressure less than 1 millimeter.

The input. or control circuit comprises con- .which is connected to the pin i4 and hence to the mid-point of the filament while the other is connected to the grid contact 20. The outputlor controlled circuit inin the form of resistance controlling device and a source of alternating current 29 of suitable voltage to which connection can be made by means of a double pole switch 30.

It is found that during-operation, when the cathode and the anode are energized by the respective sources of electromotive force, electhe open or bottom end oi the cap member l5 and an electrical discharge of arc-like character is formed between the anode and cathode members. The starting of the discharge may be controlled by a negative charge on the grid of proper potential. The cap i5 serves not only to conserve the heat generated at the cathode thereby increasing the efficiency of this member but also to prevent the electronically active material on the cathode, i. e. barium and its oxides, from being deposited on the grid member 2 to cause deleterious grid emission therefrom as the'result of intense bombardment produced-by the arc. It is evident that the electrons emitted from the grid are equivalent as far as starting the tube is concerned to the cathode and if sufilcient in number to causestarting oi' the arc, no negativev voltage appliedto the grid can prevent it. A few microamperes of grid emission is generally suflicient to spoil control of the-tube.

An inspection of the circuit diagram will show that the load circuit through which a current, ordinarily of many amperes, may fiow, is electricallyseparate from the filamentary circuit and hence no conductor withinthe tube is required to convey the combined filament and plate currents, By reducing the current to aminimum in the various lead-in conductors ,the tendency for stem is reduced. Furthermore, it is .lessdiiheult' 'initially to seal hermetically small diameter. in glass than large. wire such as would be required to conduct the combined current; .The filament being formed as a doubledeck spiral in accordance with our invention and one portion being directly placed over the other, conserves the space member is w the fullest advantage. This ad- It is very diflicult to determine accurately the mid-tap of a filament transformer for What we claim as new and desire to secure by Letters Patent of the United States, is:

1. An electrical discharge device comprising an spective spirals in opposite directions and the magnetic fields produced in the two spirals will neutralize one another.

3. An electrical discharge device comprising 5. An electrical discharge device comprising an evacuated envelope containing a cathode, grid mounted adjacent to and coaxial with one another and cooperating with the grid and anode members.

6. An electrical system comprising an evacuated envelope containing a cathode, a grid and of the input and output connections.

8. An electrical system comprising an evacuated envelope containing a plurality of electrodes including a cathode,

put connections.

9. An electrical discharge device comprising an envelope containing vapor-producing material, a thermionic cathode of flat spiral configuration,

10. An electrical discharge device comprising an envelope terminating in a stem and containmaterial, a plurality of sup- HARRY C. S'I'EINER. ORR-IN W. IIVINGSTON.

cathode.

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