US2340799A - Electronic discharge device - Google Patents

Description

Feb. 1, 1944.

w. A. DEPP I 2,340,799

ELECTRONIC DISCHARGE DEVICE Filed Dot. 19, 1942 INVENTOR W A. DEPP BV Ohda, 6 7M ATTORNEL Patented Feb. 1, 1944 UNITED STATES PATENT OFFICE 2,340,799 v ELECTRONIC DISCHARGE! mavron Wallace A. Depp, Elm'hurst; N. Y;, assignor to Bell Telephone Laboratories, Incorporated,

New York; N. Y., a corporation of New York Application October'19, 1942', Serial'No. 46am 10 Claims. (01. 250-27 5)- This invention relates to electronic discharge devices and more particularly to such devices of thejcaithode glowityp'e; v I

In devices'of this type it is a' common practice to provide a starting or ignition anode close to the cathode surface to initiate and sustain a glow discharge, whereby the discharge is readily transferred, or in' other words, the main gap in the device breaks downmore efiiciently when critical potentials are" applied to the control electrode. However, it has been found that variations in transfer current and, therefore, unstable operation usually occurs, dueto the variability' in the striking of the glowdis'charge on the surface of the" cathode to initiate the starting discharge.

Thedifi'icultyin this construction is the inherent lack of control of the striking path of the discharge so that the initiating glow wanders over Wide areas of the cathode, thereby varyingthe potential gradient in the initial glow discharge path in relation to the main discharge path, If attempts are made to overcome this difficulty by shielding the greater portion of the ignition anode to localize the striking path, a further difficulty arises in sustaining the glow dischargedue to the limited contact surface of the starting anodein spaced relation to the cathode surface.

The principal object of" thisinvention is to; stabilize theinitiating glow discharge whereby the main discharge pathbreaks down'at a minimum limit of control potential.

Another object of theinvention" is to anchor the striking glow discharge in the device so that the glow forms at thesame location each time whereby reproducibility is enhanced.

A further object of the inventionis to facilitate efficient operation of the device as a relay or switching element by controlling" the breakdown" characteristics withinja narrow range or operate ing voltages, whereby'an extremely sensitive device is attained;

These objects'are realized in accordance with" this invention'by providing an assembly of cooperating electrodes in a gasfllled vessel in which a cathode element is subdivided into major and minor proportions and separate anodes are associatedwith the-several parts of th'e'cathodeele ment. In a specificarrangementyinaccordance withthis invention, the cathode is formed'of a small disc member surrounded by an annular disc memb'erwith a, main anode disposed opposite the cathode and-an aui'iiliary anode-,in-the form of a ring; positionedcloseto and parallel with the small 'disc cathode member; This '-construction'- insures thelo'calization' ofthe" starting or initiattogether with the'a short distance'which is less thani the niimmu ,1

theaeeorimg revetmeing' discharge 'due to the symmetrical relationvof the ring and small disc memherswhereby" the" glow discharge'is always constant with respect tothe striking point on the sinall' discso thatiti el curve relating transfer current to main anode voltage remains constant'and a' low transfer' curf rent is obtained with regularity throughout the operating life of the device. I p A "feature of the invention" relates tothie'space' relation of the initiating discharge path involvingff the auxiliary anode ring and the small cathode disc section whereby the striking of the-glow'di charge is controlled. The auxiliary ring me'm is spaced above the small cathode disca relatively point in the sustainingflvoltsversusfifitahcecurv so that the glow discharge is 'converge'd at central, portion of the'idisc cathode; thereby loca izing the initiating discharge and condoning t, w I constancy of the striking point: and the density of currentflow in the starting discharge 7 P Another feature of this construction re1ates' to the isolation of the initiating discharg-so'thati the directionlof strikingi th'eglow' onth'e c'e'n ral" cathodejsurface is positively assured." This a pect of the'invent'ion'is' concerned with theg'e a metric'relation of the auxiliary an ode rlng a d the small cathode disc that t e discharge f induced to converge towards the enter of t e adjacent disc and peripheral discharge is pulsed. This feature is contemplated in thes di metrical relation 'of the'ring and disc elect, both'with respect to the minimum sustainin' current and the power output of the .devicel l Th: radius of the ring electrode should" be, Sumter-1; tially the same or not muc greater than.tl'ie distance for minimum sustainingcurrent for. tria I discharge' and the control' catho'de disc should havefa diameter only slightly greater than the, auxiliary anode ring so that the possible paths from the periphery of theiring electrode. to the-f periphery of the disc 1 electrode careless thari the" optimum'length for the establishment of a gicti discharge paththerebettveen. Furthermore; the slightly larger area of the control cathode dis simplifiesthe 'probler lliofjdegassing i'the" cath o e disc by high frequency heating Dart'icularlywhn' i the electrodes are assembledin anenclosiiig'ves se.

hese: and v the feature rid; adi'afita the invention will be inorefc a referring to the fioll'owing det dfun on Fig. 1 is a perspective View of one embodiment of this invention with a portion of the enclosing vessel broken away to show the disposition of the internal electrode assembly;

Fig. 2 shows the device of Fig. 1 in elevation and partly in cross section to illustrate the interrelation of the cooperating electrodes;

Fig. 3 is a plan view of the cathode sections and the auxiliary anode to show the spatial relation thereof;

Fig. 4 illustrates in plan view the reverse side of the larger cathode section and the disposition of the supports for mounting it in the device of Fig. 1;

Fig. 5 is a perspective view of the electrode shown in Fig. 4 with the depending support extensions;

Fig. 6 shows the initiating discharge electrodes in elevation, on an enlarged scale, to clearly illustrate the diametrical and parallel spaced relation for accomplishing the controlling action in accordance with this invention; and

Fig. 7 illustrates a modified arrangement of the device of Fig. 2, partly in cross section, in which the auxiliary anode is made discontinuous and a screen grid is positioned between the main gap electrodes.

Referring to the drawing, and particularly to Fig, 1, the electronic glow discharge device of this invention includes a cylindrical enclosing vessel I 0, of vitreous material, having the lower end hermetically sealed to the flare of an inwardly projecting stem H which terminates within the vessel in a flat press l2, and the stem is provided with a central outwardly-extending tubulation I 3 forevacuating the interior of the vessel and for injecting a suitable pressure of an ionizing gas therein. A plurality ofleading-ini conductors l4 extend within'the vessel and are sealed in the stem l2 for connection to various electrodes mounted on the stem.

The electrode assembly of this invention for facilitating the transfer of a large current and in which the control of the transfer is highly stabilized, comprises a pair of main discharge electrodes, such as a large area cathode metallic ring 15 with a slot l6 provided therein to offset distortion due to high frequency heating of the electrode surface, and a main anode l'l separated from the main cathode by a large gap and mounted'in coaxial relation therewith from the top of thenc'losingvessel I 0. The cathode I5 is provided with an electron emitting coating on the upper surface, such as barium and strontium oxides;to produce an emissive glow discharge across the main discharge gap between the cathode and the anode. The reverse surface of the cathode is provided with a non-emissive coating, such as aluminum oxide, to'preven't the glow spreading to the rear surface thereof. The cathode ring l5, as shown in Figs. 4 and 5, is provided with a plurality of angle-shaped support wires l8 mounted in spaced relation on the reverse side of the electrode and depending therefrom. One of these support wires is attached to an extension of the leading-"in conductor l4 projecting from the press l2, other support wires being attached to stub wires (unnumbered) in the press which are covered by insulating sleeves IS.

The large surface. area of the cathode l5 and the large gap between the cathode and the anode constitute a high resistance path which requires a fairly'high potential to create a glow discharge therebetween and the striking or initiating point is variable due to the numerous possible paths presented between the main electrodes. In order to overcome these defects and at the same time render the device highly sensitive to narrow limits of initiating and transfer control voltages, a separate control cathode surface 20 is provided so that the cathode is formed of two parts or portions, namely, the major portion and the minor portion 20. The control cathode is a small diameter metallic disc coaxially mounted within the boundaries of the ring cathode l5 and spaced therefrom by a relatively large gap to prevent the initiating discharge of the control cathode from spreading to the main cathode until the critical transfer voltages are applied to the main discharge path in the device. The small disc cathode 20 is coated on opposite sides in the same manner as the main cathode I5 whereby the upper surface is electron emitting while the reverse surface inhibits the spreading of the glow discharge thereto. The control cathode disc 20 is mounted in a parallel plane slightly above the surface of the main cathode and is attached to an extension of one of the leading-in conductors I4, the extension being covered by a glass sleeve 2| to prevent extraneous discharges between the extension and the main cathode I5.

In order to localize or anchor the initiating discharge on the small diameter control cathode and thereby stabilize the transfer characteristics of the device, so that the operation is reproducible throughout the life of the device and also to make the potential gradient in the initiating discharge constant, an auxiliary anode is mounted close to the control cathode surface. This auxiliary control electrode is in the form of an annular ring member 22 which is mounted parallel and close to the periphery of the control cathode disc 20. The annular ring 22 is mounted in rigid position by an upright wire 23 which extends from the press I 2 through the slot iii of the main cathode.

I5 and is surrounded by an insulating sleeve 24:

to prevent false operation of the device, due to theshort gap between the main cathode l5 and the:

from the end of the upright wire 23 and is attached to the annular anode 22, said Wire being surrounded by an insulating sleeve 26. The correlation of the electrodes mounted on the stem I2 and the space relation therebetween with the dimensional areas thereof can be realized from the showing in Fig. 3 of the drawing. This construction insures the concentration of the initiating glow striking the center of the control cathode 20 and prevents the glow from striking on the periphery of the control cathode. In view of the large gap between the control cathode and the main cathode surface I 5, the initiating glow is controlled until the critical potential is applied to the anode I1 to transfer the discharge to the main cathode whereupon the gap between the control cathode and the main cathode breaks; down and a large flow of current ensues between the anode and the cathode in the main discharge path of the device.

Fig. 6 shows the initiating discharge electrodes on an enlarged scale in cooperating relation with the main cathode ring l5, to illustrate the func tional characteristics of the diametrical and elevational relation of the respective electrodes for directing the initiating discharge towards the center of the control cathode and preventing the dispersion of the glow to other areas of the control cathode which would introduce unstable operation due to wander-effect in striking the glow on the cathode surface. As a first consideration itw'isadesirable that the diameter of the control in' either the breakdown or sustaining voltage characteristics. The thirdconsideration is that the diameter of the control cathode surface 20 should not be much greater than thediamet'er of the anode ring 22. The close spacing of the control anode 22 with respect to theperiphery of thecathode disc 20 provides an insulating path directly below the-ring which is-indicate'd by Aas representing a shadow border defined bydiagonals projected from the periphery of the crosssectional area of thering 22 which bisect the ed'ge'of the cathode disc 20"and'an equal distance on the opposite side of an axial line drawn throughthe cross section of thering. This area embracespaths of less than optimum length in which a striking of'the glow cannot occur since thepath'sare too short'to ionize the gap therebetween. The ions must therefore seek longer paths toionize the gap between the anode and thecathode and these paths are indicated by B so that the discharge is directed towards the center of the cathode and is'concentrated thereon to'insurea potential gradient of constant value and stable characteristics; The control cathode disc 20is preferably made slightly larger than the control anode diameter to facilitate high frequency heating thereof in the manufacturing process of the device to activate the emissive coatingthereon. It is, of course; understood'that the cathode surface may be made smaller with the'same operational characteristics noted above if other methods are employed in activating the cathode surface. It should be understood that it is not essential'to mount the control cathode 20 in a plane above the main cathode ring l5.

Iii-order that the critical relations of the electrode assembly employed inthe'device of this invention maybe realized a typical example of the dimensionalmeasurements of the electrodes and the'sp'acing therebetween is given as follows: The main cathodering I5 is formed of thin nickel sheeting having an outside diameter of inch andan inside diameter'of' inch with the slot l6; /g'inch. The anode I1 is a 30-mil diameter wire extending downwardly toward the main cathode with the inner end thereof spaced c'o axially from the cathode a distance of inch. The control cathode 20 is a thin nickel disc e inch in diameter and spaced coaxially with respect to the main cathode I5 and in a parallel plane therewith approximately 1 5 inch above the main cathode, the insulating gap between the edge of the control cathode 20 and theinner edge of 'themain'cathode [5 being substantially equal to'the radius of the control cathode. The control anode ring 22' is formed of circular wire having a diameter of .020 inch and formed into a ring having an inner diameter of .140 inch. This ring is mounted in parallel relation to the control cathode 20 so that the ring is wholly within the boundary of the outer diameter of the disc'20 with'a spacing therebetween of approximately 5 mils.

Since-the peripheral edge of the control cathode disc 20 is slightly beyond the outer diameter of the: ring. 22, the peripheral" edge of the disc glow exterior to the anode ring 22. Theperipheral edge of the disc projecting beyondthe outer diameter of the ring is approximately slightly more than /2 the distance between'the ring and the surface of the control cathode 20, the-exactdifference, in the typical exampledescribed, being an overhang of .00375 inch. This protrusion or extension of the disc beyond the control anode diameter is preferably not more than the spacing distance betweenthe control anode ring and the surface of the cathode which is much less than. the spacing corresponding to thepoint ofminimum voltage on a curve relating either to the breakdown or sustaining voltage of a glow discharge to the distance between the electrodes-.- It will be readily seen that the initiating glowdischarge is easily controlled to strike at substantially the centralportion of the cathode surface 29 substantially at a constant rate so that the potential gradient of the initiating discharge is constant and reproducible transfer characteristics may be realized in the operation of the device.

After the electrodes are suitably mounted in their cooperative relation on the stem of the vessel in association with the main anode IT, the vessel is highly evacuated through the tubulation I3, the active coating on the bi-part cathode surfaces is activated by bombardment, for instance by high frequency heating, and, at a suitable stage of the processing of the device, a getter" material supported on the mounting 21 is flashed, to absorb residual gases not easily removed by the pump system. The evacuated space of the vessel may be filled with an ionizing medium, for instance, an inert gas, such as argon or a mixture. of gases, such as argon and neon, in the proportion of 95 per cent argon and 5 per cent neon, at a pressure of between .1 to millimeters of mercury after which the tubulation l3 isseal'ed" off and the device associated in a switching 'circuit in which critical relay actionof the device is to be utilized in the transfer of large currents. Although the bi-part sections of the cathode sur faces I5 and 28 are shown connected to separate lead-in conductors l4 for functional operation in desired switching circuits, the control cathode surface 20 may be directly conne'ctedto the large cathode surface 15 within the vessel by a suitable strap wire.

A modification of the invention is shown in Fig. 7 in which the various electrodes, described in connection with Fig. l, are cooperatively arranged in the same relation except that the control anode ring 22 is shown split to overcome high. frequency heating thereof during the activation of the cathode surfaces 20 and [5. In addition, the structure shown'in Fig. 7 includes a screen grid electrode 28, in the form of a circular member of wire mesh material, reinforced at the periphery in the device. Such operation is an advantage-ininterlocking circuits in the telephone plant in which the firstcritical voltage applied to'the' control anode 22 initiates the discharge on the center of the cathode surface 20, then a critical po-' tential applied to the grid 28 transfers the initiating discharge to the main cathode l5 and finally, the discharge breaks down to the main anode" Ilwhen a suitable potentialis: applied. thereto to must be held within close limits in order toavoid: the establishment of a path to producea striking transfer the discharge to the main path between the main cathode I and the anode l1.

-While the invention has been disclosed with respect to particular embodiments of the invention as heretofore described, it is, of course, understood that various modifications may be made in the detail structure of the electrode assembly without departing from the scope and spirit of the invention as defined in the appended claims.

What is claimed is:

1. An. electronic discharge device comprising an enclosing vessel containing an ionizable medium, a plurality of electrodes therein including a cathode element formed of concentric surfaces with a relatively large gap therebetween, a small area output electrode spaced axially with respect to the outer concentric surface and forming therebetween a main discharge path in said vessel, and an annular auxiliary electrode closely adjacent the inner concentric surface and forming therewith an initiating discharge path in which the striking point of the discharge is localized near the axis of said inner surface.

2. An electronic discharge device comprising an enclosing vessel containing an ionizable medium, a plurality of electrodes therein including a cathode element formed of concentric surfaces with a relatively large gap therebetween, a, main anode spaced axially with respect to the outer concentric surface and forming therebetween a main discharge path in said vessel, and a rin shaped control anode substantially coextensive with the periphery Of said inner concentric surface and spaced therefrom a, distance less than the minimum sustaining point for establishing a glow discharge directly across the area between said ring anode and said inner surface.

3. An electronic discharge device comprising an enclosing vessel containing a gaseous medium, a plurality of electrodes therein including a cathode element formed of concentric surfaces with a relatively large gap therebetween, a main anode spaced axially with respect to the outer concentric surface and forming therebetween a main discharge path in said vessel, and an annular control anode closely adjacent the periphery of the inner concentric surface, said control anode being adapted to produce a border on said surface below it of an area defined by a shadow effect projected from the sides of said control anode to said surface, whereby the space relation therebetween inhibits the establishment of a glow discharge in said shadow and causes the discharge to strike over a longer path between said annular anode and an area of said surface surrounded by the shadow border.

4. An electronic discharge device comprising an enclosing vessel containing a gaseous medium, a plurality of electrodes therein including a cathode element formed of concentric surfaces with a relatively large gap therebetween, a small area output electrode spaced axially with respect to the outer concentric surface and forming therebetween a main discharge path in said vessel, and an electrode closely adjacent the inner concentric surface and forming therewith an initiating glow discharge, said electrode being so proportioned with respect to said inner surface that said glow discharge is projected and concentrated towards the center of said inner concentric surface and is inhibited from diverging outwardly to the periphery of said inner surface.

5. An electronic discharge device comprising an enclosing vessel containing an ionizable medium, a plurality of electrodes therein including a cathode, an anode, and an auxiliary electrodepsaidcathode being formed of a central disc member and a fiat ring member, said anode being associated with said ring member and constituting a main discharge path, said auxiliary electrode being closely associated with said disc member and.

forming therewith an initiating discharge path, the space relation between said auxiliary electrode and the periphery of said disc member being much less than the minimum point ofthe breakdown voltage characteristic and the space rela-.

therewith, the space relation between them being less than the minimum point of the breakdown voltage characteristic and the space relation between said disc and ring members being substantially equal to the breakdown voltage characteristic.

7. An electronic discharge device comprising an enclosing vessel containing an ionizable medium, a plurality of electrodes therein including a cathode, an anode, and an auxiliary anode, said cathode being formed of a central disc member and a flat ring member in concentric relation, said anode being associated with said ring member and constituting a main discharge path, and said auxiliary anode being mounted parallel to said disc member, the space relation between them being less than the minimum point of the sustaining voltage characteristic, said disc member having its periphery extending beyond the outer diameter of said auxiliary anode slightly greater than one-half the spacing distance between said auxiliary anode and said disc member.

8. An electronic discharge device, according to claim 7, in which the auxiliary anode is in the form of a wire ring having a cross-sectional dimension of .020 inch, the space relation between the auxiliary anode and the disc member being .005 inch, and the peripheral edge of the disc member projecting a distance of .003'75 inch beyond the outer diameter of said wire ring.

9. An electronic discharge device comprising an enclosing vessel containing a gaseous medium, a plurality of electrodes therein including a bi-part cathode consisting of a small disc section and a flat ring section disposed in concentric relation, said sections being in different planes, a main anode disposed opposite said cathode and forming with said ring section a main discharge path, and a split wire ring mounted parallel to and close to the edge of said disc sec-- tion, said wire ring and disc section forming an initiating discharge path in said vessel, said flat ring section being spaced from said disc section by an insulated gap more than five times the space relation between said wire ring and said disc section.

10. A gaseous electronic relay device compris-- ing an enclosing vessel having a stem, an inert gas filled therein, a plurality of electrodes mounted in said vessel and capable of producing an ionizing glow discharge in distinct steps depending on the initiating, sustaining and breakdown periods of the device, said electrodes involving a control cathode, a control anode, a main anode, and a main cathode, said control cathode being a small metallic disc axially mounted on said stem, said main cathode surrounding said control cathode and bein formed of a flat metallic ring having a slot therein, said main cathode being electrically connected to said control cathode, a plurality of supports extending from said stem to said flat ring, said control anode being a wire ring closely adjacent and parallel to the periphery of said control cathode, a support extending from said stem through said slot to said wire ring, and said main anode being mounted in the top of said vessel and projecting axially toward said control cathode and main cathode. WALLACE A. DEPP.

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