US2428661A - Electric discharge device of the gas filled type - Google Patents

Description

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BLEc'rnIc DISCHARGE DEVICE oF THE GAS FILLED TYPE 'Fnea'nprl 1?, 194s i? @l il PRESSURE TIMES DISMNCE Ihvevrwtov: Stahleg R. Fitimarris,

bg JM Hi: Attorneg.

Patented Oct. 7, 1947 ELECTRIC DISCHARGE DEVICE or 'rnE cas FILLED TYPE Stanley R. Fitzmorris, Schenectady, N. Y., assignor to General Electric Company, a corpi)-v ration o! New York Application April 17, 1943, Serial No. 483,409

29 Claims. (Cl. Z50-27.5)

My invention relates to electric discharge devices, and more particularly to electric discharge devices of the controlled type which employ ionizable mediums such as gases or vapors.

It is an object of my invention to provide new and improved electric discharge devices.

It is another object of my invention to provide new and improved electric dischargev devices of the controlled type wherein ionizable mediums,

such as gases or vapors, are employed.

It is a further object of my invention to provide new and improved electric discharge devices wherein the electrodes of the devices are spaced in close relationship, and wherein the pressure oi the ionizable medium ls maintained at a relatively large value while maintaining a large maximum forward voltage rating, a relatively large inverse or arc-back voltage, and stable operation.

It is a still further object of ymy invention to provide new and improved electric discharge devices wherein the transfer of current between the anode and the cathode is effected by an arc discharge or glow discharge phenomenon and wherein the immediate region within which the ionization takes place is limited to a relatively small proportion of the total volume of enclosed ionizable medium.

It is a still further object of my invention to provide new and improved structure for electric discharge devices of the type employing ionizable mediums wherein the spacing between the enclosed electrodes is very small and wherein the ionization region is confined by mechanical means and by virtue of the establishment of a relatively small mean free path of the ions constituting the medium.

Briefly stated, I provide new and improved electric discharge devices of the type employing an ionizable medium, such as a gas or a vapor. More particularly, I provide discharge devices of the controlled arc-discharge type wherein a gas or vapor pressure of relatively large value is used while maintaining a large maximum peak forward voltage rating, a large inverse or arc-back voltage rating, and stability of operation.

The electric discharge devices which I provide` are characterized by the utilization of very small electrode spacings and the use of a gas or vapor pressure of relatively large value, thereby obtaining a small value for the product of anodecathode spacing and the gas or vapor pressure whereby large forward and inverse voltage ratings are afforded. Forward voltage rating may be defined as the positive anode-cathode voltage which a discharge device will withstand, Iwith proper grid voltages applied, without effecting the establishment of an undesired or uncontrolled discharge between anode and cathode.v By inverse voltage rating is meant that instantaneous value of voltage that the discharge 'device will safely' withstand in the direction opposite to that in which it is designed or intended to transmit current. l

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. 1 of the accompanying drawing diagrammatically illustrates my invention as applied t'o a construction, certain features of which are disclosed and claimed in copending patent application Serial No. 436,633 of James E. Boggs, filed March 2,8, 1942, and which is assigned to the assignee of the present application. Fig. 2 represents details of a cathode construction which I employ. Fig. 3 represents generally the relationship existing between the sparking potential and the product of pressure and distance between electrodesV within an ionizable medium,` which relationship is now somewhat generally known as Paschens Law. Fig. 4 is a modiiied electric discharge device construction employing my invention. i

Prior to a detailed consideration of the illustrated embodiments of my invention, it is believed appropriate to review certain general aspects thereof. Heretofore, the substantial utilization of the inhibiting eect on evaporation of the cathode material in electric discharge devices operating under relatively high pressure of an ionizable medium, such as a gas or a vapor, has not been attainable in high voltage devices, that is devices having high forward and inverse voltage characteristics, by virtue of the fact that structures of reproducible characteristics were not available for maintaining relatively close space relationships between the anode and cathode of the discharge devices and for establishing a single discharge path between anode and cathode. The use of vapor or gas pressures of relatively high value is desirable since such pressures inhibit the evaporation of cathode material, that is inhibit the evaporation of the cathode emissive surfaces such as alkaline earth metals or oxides thereof. Furthermore, the use of relatively high pressures is desirable in order to reduce the amount of gas clean-up. The term gas cleanup is somewhat generally used to denote that phenomenon which occurs in discharge devices 3 y O 1 employing ionizable mediums, particularly gases, whereby upon operation the bombardment of the cathode by the positive ions incident to the are discharge causes absorption of the medium by the enclosed parts, the dislodged cathode material and internal surface of the enclosing envelope. By the useof relatively high gas or vapor pressure, this absorption is substantially reduced, consequently resulting in increased life of the discharge devices.

While heretofore someof the prior ari;` discharge devices have employed relativelyv high f pressures, these devices have been subjected to a definite limitation of having relatively low forward and inverse voltage ratings. By virtue lof the discharge device constructions and the relationships described hereinafter, I provide electric discharge devices of the type employing ionizable mediums wherein the advantages vof inhibiting cathode material evaporation and relatively large forward and inverse voltage ratings are both attainable. In an electric discharge emloying a plurality or pair of electrodes such as an anode and cathode within an ionizable medium, there is a definite relationship between the sparking or break-down'voltage and the product of the pressure of the medium and the distance between the electrodes. This relationship is shown generally in Fig. 3 where the ordinates represent the breakdown voltage and abscissae represent the product of pressure and distance. Of course, for each gas or vapor, or combinations thereof, a distinctive individual curve will be representative of this relationship. The characteristics depend, among other factors, on the configuration of the electrodes, the materials or metals of which the electrodes are constituted and the nature of the electrode surfaces. Furthermore, there is a definite minimum or critical sparking or break-down potential as illustrated by the general characteristic J shown in Fig. 3.

By the use of the term sparking potential or break-down potential is meant that phenomenon in which a discharge is established in the absence of local ionization or arc producing means. For example, this phenomenon is somewhat generally referred to as a Townsend discharge and is not of the self-sustaining type requiring the application of an external source of energy to maintain it. This type of phenomenon, of course, usually precedes and is distinguishable from a glow discharge or an arc discharge wherein the potential differences across given electrodes are substantially less than in the sparking region due to the fact that appreciable ionization of the medium occurs, effecting a reduction 'in the voltage appearing across the electrodes.

In accordance with one aspect of my invention, I provide electric discharge devices wherein the structural spacing is correlated with respect to the operating pressure of the medium, such as a gas, to obtain a relatively small product of pressure and distance, thereby giving to the discharge device a large break-down voltage characteristic, except for the controlled arc discharge in the desired direction of conduction. Furthermore, by virtue of the fact that the medium or gas pressure is maintained at a relatively high value during operating conditions, the mean free path of the ions constituting the gas may be maintained at a relatively small value with respect to the anode-cathode spacing, preferably Within the neighborhood of one-sixth of the anode-cathode spacing, resulting in a substantial transverse or radial localization of the region Within which the .4 i arc discharge phenomena between the anode and cathode occur. Due to the fact that the gas pressure is relatively large, the mean free path of the ions is small with respect to the anode-cathode spacing, resulting in a confinement of the arc discharge path, which may be considered from an elementary point of view as arising from the recombination .of thel ions as they tend to depart from the localized arc discharge region. It will be appreciated that as the ions tend to move from the localized region, upon moving into the relatively highpressure region of the non-ionized gas, the ions re-combine with the relatively inactive gas surrounding the ionized region.

The immediately above described feature may be considered as augmenting, to a certain extent, a gas focusing phenomena established primarily by the fringing effect of the electrostatic field extending from edge or periphery of the cathode surface to the anode surface. g

In order to accentuate the above described phenomena whereby the ionization of the medium is localized, I provide electric discharge device constructions wherein the amount of gas actively or immediately engaged inthe arc discharge or glow discharge and which is most susceptible to clean-up is localized within a particular part,

or parts, of the discharge device enclosure without limiting the total volume of gas or medium available, thereby lending to the device the desired long life. The anode and cathode cooperating surfaces, as illustrated in the embodiments of my invention described hereinafter, are preferably located within a confined part of the structure, and additional means such as mechanical means is provided for limiting the effective longitudinal cathode area over which the glow-dischargephenomena may occur. Furthermore, the discharge device constructions, and particularly the enclosed envelope constructions, are arranged -so that the total enclosed volume of the ionizable medium or gas is substantially greater than the volume of the region within which the immediate are discharge phenomena and glow discharge phenomena take place. For example, I have found that the desired arc discharge and the glow discharge phenomena may be effectively localized without sacrificing the desired life of the discharge devices by employing constructions wherein the total enclosed volume of the medium or gas is at least ve or ten times the volume of the region within which the above phenomena occur. Of course, it is to be appreciated thatthis ratio is not critical and that an important aspect is the provision of a sufficiently large reservoir of medium or gas within the enclosing envelope to afford the desired replenishment of the gases absorbed by the clean-up process during operation.

Referringl now particularly to Fig. 1', one embodiment of my inventionA is there illustrated which comprises a plurality of planar electrodes, such as an anode, a cathode and a grid, enclosed within an envelope andv in which an ionizable medium such as a gas is employed. 'I'he discharge device comprises a plurality of transversely extending metallic members I, 2 and 3 which constitute parts of the enclosing envelope and also may serve to support the cooperating electrodes of the discharge device. Members i and 2 may be of substantially disk formation provided with apertures 4 and 5, respectively, and transverse member 3 may comprise a part of a cylindrical member 6 of which member 3 comprises an inwardly extending ange. The cylindrical member E is preferably sealed to a base amaca:

member 'l which is provided with a plurality of' 4 terminal prongs B-I I, inclusive, and an orienta-1 tion protuberance I2 which are arranged for insertion into an appropriatesocket. Transverse -members I, 2 and 3 a're maintained in illustratedv or a plurality of lead-in or rigid supporting conductors III and 3l which are connected to terminal prongs! and II, respectively.

` I also contemplate in a discharge device of the Yabove described nature the provision of suitable getteringl means which may` comprise. a ribbon 32 ofgettering material which is supported by a pair of lead-in rods or .conductors 32 and 34 smaller longitudinal dimension than the cylinder v I4 for the purpose of dening a' relatively small region 'between transverse members I and 2 for purposes which will be explained in detail here-y inaiter.

An anode I5, preferably comprising a solid disk of metal such as nickel or molybdenum, is provided with an appropriately formed shoulder. to engage transverse member I to which it is welded or soldered, and is provided with a planar anode` surface I8. In close proximity to the anode surface I8 and supported on the upper surface vvoit which are connected to suitable terminal prongs (not illustrated). The gettering operation is effected by the transmission of electric current through the ribbon 32 to effect substantial vaporl ization of the material included thereon or therein transverse member 2, I provide a gridl I1 preferf ably of the mesh type and which may be deformed upwardly to have the configuration illustrated.

Transverse member 2 also serves the purpc'isel of affording an externally accessible connection.

to the grid Il, and connection to the anode of the discharge device may be obtained eitherv through a direct connection to the disk I5 or toA the transverse member I which is in electrical contact therewith.

I employ a cathode construction, which permits l the provision of closely positioned anode and cathode cooperating surfaces, and which extends through aperture 5 in transverse member 2. The cathode construction may comprise a metallic cathode cylinder I8, shown in detail in Fig. 2,

having a closed end I9 which constitutes the cathode emissive surface. This surface preferably lies in a plane above the upper surface of member 2 and may be coated with an electron emissive material such as an alkali or alkaline earth metal, or oxides thereof. Suitable operating temperatures for the cathode structure may be obtained by the provision of a fllamentary cathode heating element 20 which is positioned within the cathode structure, and more particularly within a cylinder 2i, which telescopes and is conl centric with cathode cylindery I8, being provided with a metallic end disk 22 seated upon the inner surface of the end part I9 of cylinder I8 to adord the desired thermal connection with the closed end of cylinder I8.

'Ihe above described cathode construction may be supported by a ilanged tubular member 23, illustrated in Fig. 2, and which comprises a ange part 24 and an integral tubular part 25 provided with a dared section 26 upon which the lower end of the cathode cylinder I8 rests, thereby providing a structure readily adaptable for .manu.

facturing operations andfor obtaining a desired localization of the heat incident to the element 20. The above described cathode heating structure may be supported directly by transverse member 3 or cylinder 6 or may be supported by and insulated therefrom by means of an annular insulator 21. Alternatively, the cathode structure may be supported by rigid cathode conductors to be described presently.

The circuit for energizing the cathode heating element 20 may comprise a pair of lead-in conductors 28 and 29 which are connected to terminal prongs 9 and I0, respectively, and connection to the cathode may be obtained by a single which cooperatesl with undesirable gases within the envelope andl which it is desired to absorb either during the evacuation process or immediately thereafter.

As a means for further localizing the glow discharge phenomena, that is for limiting the eiective area of the cathode cylinder I8 which maybe involved in the glow discharge phenomena, I provide means, such as a dielectric disk 35.

which surrounds the cathode cylinder I8 and whiclris of greater dimension than the aperture .5 in ltransverse member 2. Disk 35 may be constructed ofa suitable material, such as mica, and may be displaced a small distance from the under ysurface of transverse member 2. Disk 35 may be supported by any suitable construction and is illustrated as being supported by a metallic cylinder 36 which is welded or soldered to the upper surface of ilange 24 of the cathode supporting structure.

In electric discharge devices which I have built and tested, I have found that anode-grid spacings preferably lie'within the range of 10 to l5 mils and the grid-cathode spacing is preferably Within a range of 2 to 10 mils. In the latter case, the distance between the cathode and thegrid is that measured from the closed end of the cathode cylinder I8. Considering the range of pressures, it may be generally stated that I prefer to utilize a sufciently high pressure of the gas or` vapor to obtain a product of pressure and distance equal to or less than one-half the product which corresponds to the minimum sparking potential for the particular medium. More speciiically, I prefer to employ a sufficiently large pressure to obtain long life in conjunction with the maximum inter-electrode spacing, particularly between the remotest sections of anode and grid, or anode and cathode and supporting structures therefor, to obtain a product of pressure and distance which establishes large spark breakdown or arc-over voltage characteristics.

In obtaining the large forward and inverse voltage ratings by operating at a relatively small product of pressure and inter-electrode spacing, itis important to maintain the distances between the electrode supporting structure as well as the cooperating surfaces of the electrodes at relatively small values where the desired range of high pressures is employed. Stated in other words, the maximum distance between the elecis small for the pressure employed. Furthermore, since transverse member 2 is intermediate disk 35 and the anode l5, the meets this criterion.

' The mesh-type grid l1 may completely cover aperture 5 and be constructed of a wire or a. plurality of wires of relatively small dimension, such as a diameter of 2 mils, providing a large number of relatively small openings. For example, one type of mesh grid which I have found to serve satisfactorily is .a mesh grid comprising a plurality of 2.mi1 wires defining one hundred openings per linear inch, that is, providing a plurality of 8 mil square openings.

The ionizable medium employed within discharge devices of the above described character may be an ionizable vapor or an inert gas such as argon, neon, xenon, or helium, preferably having an operating pressure lying Within or above the range of 1.5 to 2.0 millimeters of mercury.

Curve A of Fig. 3 represents the relationship existing between the break-down voltage and the product of pressure times distance for a pair of electrodes placed within an ionizable medium, such as a gas. Where the pressure is expressed in millimeters of mercury and the distance in centimeters, the minimum or critical ionizing potential appearing at point b for argon is approximately 0.9. As stated above, in discharge devices built in accordance with my invention, the pressure is correlated with respect to the relatively short structural spacing to obtain a break-down or sparking potential lying preferably within the neighborhood of 0.2 such as that indicated at point c.

Considering one particular example, in a discharge device constructed in accordance with my grid-anode structure invention, argon was employed as the ionizable medium at an operating pressure of 1.6 millimeters. The arc drop, that'is the voltage drop across anode and cathode, was substantially 13 volts at 50 milliamperes of anode-cathode current, providing a high voltage rating, having been successfully operated within the neighborhood of 1000 volts. f

In other types of discharge `devices built in accordance with my invention, I have found that high forward and inverse voltage ratings are obtained by employing anode-cathode spacing of substantially 20 mils and using a gas, such as argon, having an operating pressure ranging from 1.8 to 2.0 millimeters of mercury.

Of course, the grid control characteristics of discharge devices of the type shown in Fig. 1 indicate the necessity of employing an increasingly negative voltage on the grid as the anode-cathode voltage is increased. In this connection, for the application of a given negative voltage to the grid, an increase in plate voltage above a predetermined value or range of values will initiate an arc 0r glow discharge. Conversely, if it is desired to maintain the discharge device nonconducting, upon the application of increased anode voltage the grid potential must be correspondingly increased in accordance with the grid-control characteristic to prohibit the establishment of an arc discharge.

Another modification of my invention is illustrated in Fig. 4 which is similar in many respects to that shown in Fig. 1, and corresponding elements have been assigned like reference numerals. In the arrangement of Fig. 4, a, shell or hood-type cylindrical grid connection member 31 is provided which comprises an integrally formed shoulder or collar 38 which surrounds transverse Vthe elect-ric discharge device.

. member 31.

8 member 2 and is electrically connected thereto. If desired, an additional annular metallic spacer 39 may be placedintermediate transverse member 2 and collar 38 to act as a rigid support therefor and which may be welded or soldered thereto. The anode structure comprises a metallic cylinder 40 having a closed end 4|, the surface thereof facing the cathode constituting the anode for Cylinder 40 is supported by and sealed to an annular vitreous part 42 which is also sealed to the inner surface of The above described constructions for electric discharge devices offer definite advantages. One of these advantages is the establishment of a single confined or isolated path along which the arc discharge phenomenon occurs. It will be noted that by virtueof the close spaced relationship between the end I9 of cathode cylinder I8, the region through which an arc discharge may take place is isolated from the surrounding structure. Another advantage incident to the above described structure is that thegrid l1 shields the structure therebelow including the cathode, portions of transverse member 2 and the mechanical arc or glow discharge confining means, thereby protecting these elements or parts during the application of inverse voltage to the anode and cathode and consequently serving to relieve the electrostatic stress thereon incident to the applied voltage.

A further advantage incident to the above described structure is the resultant reduction in arc drop during normal operation of the discharge device incident to the relatively high gas pressure. I have found that in discharge devices employing argon this .decrease in arc voltage ranges from 2 to 3 volts.

A still further advantage resides in the fact that the structure affords relatively large surfaces exposed to the medium which has undergone ionization as compared with the volume within which the ionization takes place. Thisaspect is of considerable importance in controlling the deionization time of a discharge device of this character. For example, it will be noted that the inner surface of the enclosing envelope, the face or anode surface and the inner surfaces of transverse member '2 immediately surrounding the aperture 5 are relatively large compared with the volume above the upper surface of disk 35, thereby providing a relatively large effective area for the neutralization or collection of ions after the intended period of conduction by the discharge device. Of course, due to the increased operating pressure of devices of this character, there is present in a unit volume of medium or gas a larger number of ions than would be present with smaller operating pressures and the diffusion rate is correspondingly slower. This, of course, in itself would result in an increased deionization time. However, the advantage obtained by the increased eiTective area compensates for the increase in deionization time due to the increased pressure.

Although the yembodiments of my, invention illustrated are shown as including a control element or electrostatic grid placed between the anode and the cathode, it will be appreciated that the broader aspects of my invention, whereshield grid.

While my invention has been illustrated as applied to a particular type o f electric discharge devices employing elements or electrodes having particular configurations, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device employing an ionizable medium and including a plurality of electrodes comprising an anode and a. cathode having extended surfaces in opposed closely spaced relation, an envelope structure enclosing said electrodes comprising means supporting said electrodes including a pair of transverse metallic members in spaced relation and means comprising an insulating member sealed between said members, and a member surrounding said cathode and extending outwardly therefrom adjacent the extending surface of the cathode, said member extending in closely spaced relation with respect to one of said transverse members, said member, said one transverse member, said anode and said cathode providing a, chamber of relatively small volume enclosing the extended surfaces of said anode and cathode and opening into the interior of said envelope through the space between said member and said one of said transverse members.

2. An electric discharge device employing an ionizable medium and including a, plurality of electrodes comprising an anode and a cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a pair of transversely extending members and means including a sealed insulating member between the transverse members, the product of operating pressure of said medium and the spacing between said anode and said cathode being substantially less than the value of such product corresponding to the minimum break-down voltage between the electrodes to obtain a large forward voltage characteristic and means including a portion of said envelope dening a localized region around said anode and cathode surfaces in which the discharge takes place, the volume of said envelope being several times the volume of said localized region to provide a reservoir of said medium substantially in excess of that employed in the immediate arc discharge phenomenon between said anode and said cathode.

3. An electric discharge device employing an ionizable medium and including a plurality of electrodes comprising an anode and a. cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a, pair of transversely extending members and means including a sealed tubular insulator extending therebetween, the operating pressure of said medium and the spacing between said anode and said cathode providing only a limited region of ionization of said medium and the enclosed volume dened by said envelope structure being at least ve times as great as said region within which the immediate arc discharge phenomenon takes place.

4. An electric discharge device comprising an l0 inert gas as an ionizable medium and including a plurality oi! electrodescomprising an anode, a grid, and a cathode, said anode and grid being mounted in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a pair of transversely extending metallic members and means comprising a sealed insulating cylinder between said members, the operating pressure of said gas'being in excess of a pressure of 1.5 millimeters of mercury andthe product of said gas pressure and the spacing between said anode and grid being substantially less than the value of such product for minimum breakdown voltage between the electrodes thereby to obtain large forward and g inverse voltage ratings.v

5. An electric discharge device comprising an ionizable medium and including a plurality of electrodes comprising an anode and a cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a. pair of transversely extending members and means comprising a sealed insulating cylinder between said members, said cathode being of cylindrical conguration supported by one of said members and extending within said cylinder towards said anode providing an electron emissive vsurface for cooperation therewith, the operating pressure of said medium being in excess of a pressure of 1.5 millimeters of mercury and the product of said operating pressure and maximum spacing between cooperating surfaces of said electrodes and the supporting structure therefor being substantially less than the value of such product corresponding to minimum breakdown voltage between the electrodes.

6. An electric discharge device comprising an ionizable medium and including a plurality of electrodes comprising an anode, a grid and a cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including three transversely extending metallic members for said envelope structure comprising an insulating cylinder sealed between the transverse members supporting said cathode and said grid and a second insulating cylinder of substantially smaller longitudinal dimension than the first mentioned cylinder and sealed between the transverse members supporting said grid and said anode, said cathode being of cylindrical conguration and extending through an aperture provided by the transverse member supporting said grid, the product of the operating pressure of said medium and the maximum spacing between said anode, grid, and said cathode being substantially less than the value of such product corresponding to minimum break-down voltage between said electrodes.

7. An electric discharge device comprising an ionizable medium and including a plurality of electrodes comprising an anode, a grid and a cathode in close spaced relation, an envelope structure enclosing said electrodes comprising means supporting said electrodes including three transversely extending metallic members and an insulating cylinder sealed between the transverse members associated with said cathode and said grid and a second insulating cylinder of substantially smaller longitudinal dimension than the first mentioned cylinder and sealed between the transverse members supporting said grid and-said anode, said cathode being of cylindrical conilgllration and extending through an aperture provided by the transverse member supporting said grid,

anode, a grid and a cathode, said anode and said grid being in close spaced relation, an envelope structure enclosing said electrodes comprising means supporting said electrodes including a series of transversely extending metallic -members and a plurality of insulating cylinders respectively sealed between the various members, and means for conning the ionization region between said anode and said cathode including means extending transversely of the envelope near the planar surface of the cathode and cooperating with the transverse member supporting one of said electrodes. y

9. An'electric discharge device comprising an ionizable medium and including a plurality of electrodes comprising a planar anode, a grid and a cathode, said anode and said grid being mounted in close spaced relation, an envelope structure enclosing said electrodes comprising means supporting said electrodes including a series of transversely extending metallic members and a plurality of insulating cylinders respectively sealed between the various members, and a transversely extending member supported by the cathode structure and longitudinally displaced from the surface thereof parallel to said anode for limiting the'ionization region. l

10. An electric discharge device comprising an ionizable medium and including a plurality of electrodes comprising a planar anode, a, grid and a cathode, said anode and said grid being mounted in close spaced relation, an envelope structure enclosing said electrodes comprising means supporting said electrodes including a series of transversely extending metallic members and a plurality of insulating cylinders respectivelysealed between the various members, the operating pressure of said medium being in excess of 1.5 milli` meters of mercury the product of said operating pressure and the maximum distance between said anode and said cathode and supporting structure therefor being substantially less than the value of such product for minimum break-down voltage between said electrodes.

11. In an electric discharge device of the type employing an ionizable medium and including a plurality of electrodes, the combination comprising an enclosing envelope comprising in part three transversely extending members, a llair of insulating cylinders sealed in end-to-end relationship between said members and constituting partof an envelope enclosing said electrodes, said elec` trodes comprising an anode supported by one end transverse member, a mesh electrostatic control member of the grid type supported by the intermediate transverse member and a cylindrical cathode supported by the other end transverse member and having an electron emissive surface i lying substantially in the plane of said intermediate member and extending into anv aperture provided thereby, and means for establishing a coni-'med ionization region comprising a transverse member supported by the cathode structure.

12. An electric discharge device employing an ionizable medium and including aplurality of electrodes comprising an anode and a cathode in close spaced relation, and an envelope structure `enclosing said electrodes comprising means supporting said electrodes including a pair of tra-nselectrodes comprising an anode and a cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a, pair of transversely extending metallic members and means for supporting said members comprising anv insulating member extending longitudinally therebetween, the product of the operating pressure of said medium in millimeters of mercury 'and the maximum interelectrode spacing in centimeters being substantially 0.2.

14. An electric discharge device employing an inert gas as an ionizable medium and including a plurality of electrodes comprising a planar anode and a planar cathode separated by a distance ranging from 18 to 20 mils, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a pair of transversely extending metallic members and means comprising a sealed insulating member extending therebetween, the product of the operating pressure of said gas in millimeters of mercury and the maximum spacing between said anode and said cathode and supporting structures therefor in centimeters being substantially less than that value corresponding to the minimum break-down voltage between said electrodes.

15. An electric discharge device employing argon as an ionizable medium .and including a pair of electrodes comprising an anode and a cathode spaced substantially 20 mils apart, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a pair of transversely extending members and means comprising a sealed insulating member extending therebetween, the operating pressure of said argon gas being substantially 1.8 millimeters of mercury.

16. An electric discharge device employing an inert gas as an ionizable medium and including a plurality of electrodes comprising an anode, a grid and a cathode, the cathode-grid spacing being substantially 6 mils and the grid-anode spacing being substantially 12 mils, and an envelope structure enclosing said electrodes comprising means maintaining said electrodes in spaced relation including three transversely extending metallic members, said envelope structure comprising an insulating member sealed between the transverse members associated with said cathode and said grid and a second insulating member of substantially smaller longitudinal dimension than Athe first insulating cylinder and sealed between the transverse members supporting said grid and said anode, the product of the operating pressure of said inert gas and the maximum spacing between 13 a plurality of electrodes comprising an anode, a grid and a. cathode, the cathode-grid spacing being substantially 6 mils and the grid-anode spacing being substantially 12 mils, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including three transversely extending metallic members and an insulating member sealed between the transverse members associated with said cathode and said grid and a second insulating member of substantially smaller longitudinal dimension than the ilrst insulating member and sealed between the transverse members supporting said grid and said anode, the operating pressure of said inert gas lying within the range of 1.6 to 2.0 millimeters of mercury.

18. An electric discharge device employing an ionizable medium and including a plurality of electrodes comprising an anode and a, cathode in close spaced relation, and an envelope structure enclosing said electrodescomprising means supporting said electrodes including a pair of transversely extending metallic members and means forsupporting said members comprising an insulating means extending therebetween, the operating pressure of said medium being such that the mean free path of the ions constituting said medium is substantially one-sixth of the spacing between surfaces of said anode and said cathode.

19. An electric discharge device employing an ionizable medium and including a plurality of electrodes comprising an anode, a grid and a cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including three transversely extending metallic members and a pair of insulating members sealed in end to end relation between the transverse members, the operating pressure of said medium being such that the mean free path of the ions constituting said medium is not greater than one-fourth of the spacing between cooperating surfaces of said anode and said cathode.

20. An electric discharge device employing an ionizable medium and including a plurality of electrodes comprising an anode and a cathode in close spaced relation, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including a pair of transversely extending metallic members and means for supporting said members comprising an insulating member extending therebetween, the total enclosed volume defined by said member being at least ten times as great as the volume of the region defined between planar cooperating surfaces of said anode and said cathode and the operating pressure of said medium and the spacing between cooperating surfaces of said anode and said cathode being correlated with respect to the pressure times distance sparking characteristic t'o produce a mean free path of the ions constituting said medium having a value substantially one-sixth the interelectrode spacing thereby eiecting a concentration of the ionization phenomena within said region.

21. An electric discharge device employing an inert gas as an ionizable medium and including a plurality of electrodes comprising an anode, a grid and a cathode. the cathode-grid spacing being substantially 6 mils and the grid-anode spacing being substantially 12 mils, and an envelope structure enclosing said electrodes comprising means supporting said electrodes including three transversely extending metallic members and comprising a pair of insulating members sealed in 14 end-to-end relation between said members, said grid being o! the mesh type comprising a plurality of 2 mil wires deilning substantiallyone hundred openings per linear inch and being supported bythe transverse member intermediate said insulating members.

22. An electric discharge device employing argon as an ionizable medium and including a. plurality of electrodes comprising an anode, a grid and a cathode, the cathode-grid spacing being substantially 6 mils and the grid-anode spacing being substantially 12 mils, and an envelope structure enclosing said electrodes comprising means supporting said electrodes in longitudinal spaced relation including three transversely extending metallic members and comprising a pair of insulating cylinders sealed in end-to-end relation between 'said transverse members, said grid being of the mesh type and the operating pressure of said argon being correlated with respect to the anode-cathode spacing to produce an ion mean free path substantially one-sixth the spacing between cooperating surfaces of said anode and said cathode, and a, vtransverse dielectric member surrounding said cathode and displaced from the intermediate transverse member towards the cathode base for limiting the distance the glow discharge extends along the cathode toward its base.

23. An electric discharge device of the type employing an ionizable medium and comprising a plurality of electrodes including an anode and a cathode in close spaced relationship, an enclosing envelope structure said electrodes including three longitudinally spaced transverse metallic members and a vitreous cylinder sealed between one end transverse member and the intermediate member and a second vitreous cylinder sealed between said intermediate member and the other end transverse member, said intermediate member being provided with a centrally positioned aperture through which said cathode extends in proximity to said anode, and a transverse dielectric member surrounding said cathode and having a dimension greater than said aperture to provide a localized region within which the glow and arc-discharge phenomena are confined.

24. An electric discharge device of the type employing an ionizable medium and including a plurality of electrodes, and an envelope structure enclosing said electrodes comprising three transversely extending metallic members supported in spaced relation by a pair of vitreous insulators sealed in end-to-end relationship with said transverse members, a thermionic cathode of cylindrical form supported by one of the end trans- `verse members and extending to the vicinity of an anode supported by the other end member through an aperture in the intermediate transverse member, a grid supported by said intermediate member and in spaced relation between said anode and said cathode, and means for establishing a localized region within which the glow and arc-discharge phenomena occur comprising a transverse dielectric member spaced below said transverse member and having a dimension substantlally greater than the dimension of said aperture.

25. In an electric discharge device employing an ionizable medium, the combination comprising a plurality of electrodes including an anode, a cathode and a grid, an envelope enclosing said electrodes including inpart a transverse disk provided with an aperture through which the cathode extends, agrid supported by said disk over said 15 aperture and spaced intermediate said cathode and said anode thereby shielding said cathode during application of voltage across said anode and said cathode and means cooperating with said disk to conne the arc discharge phenomenon to the region between saiddisk and said anode.

26. In an electric discharge device of the type employing an ionizable medium, the combination comprising a plurality of electrodes including an anode, a cathode land a grid, and an envelope enclosing said electrode and comprising in part a transverse metallic disk provided with an aperture through which said cathode extends, said grid being of the mesh type attached to the surface of said disk facing said anode and curved towards said anode to obtain relatively small spacing therebetween.

27. In an electric discharge device of the type employing an ionizable medium.' the combination comprising a plurality of electrodes including a disk metallic anode, a cylindrical cathode and a mesh-type grid, and an envelope enclosing said electrode comprising in part a. transverse disk sealed to insulated supporting structure and being provided with a centrally located aperture through which one -end of said cathode extends towards said anode, said grid being attached to the surface of said transverse disk facing said anode and curved to lie in spaced relation between an emissive surfaceA oi the cathode cylinder and the face of the disk anode.

28. In an electric discharge device of the type employing an ionizable medium, the combination including a, plurality of electrodes including a disk-type anode and a cathode, an envelope enclosing said electrodes including a transverse metallic disk provided with an aperture throughl which said cathode extends thereby deilning with anode and said cathode opening `into saidanode a localized region within which the arc-discharge phenomenon occurs, and a. partition member extending from said cathode in closely spaced relation to said transverse disk and providing with said transverse disk, said anode and said cathode a confined region between said the interior of the remainder of said envelope through the space between transverse member and said partition member.

29. In an electric discharge device of the type employing an ionizable medium at a pressure equal to or greater than 1.5 millimeters of mercury, the combination comprising a plurality of electrodes including an anodek and a cathode, and an envelope structure enclosing said electrodes comprising means defining a localized region within which the arc discharge and the glow discharge phenomena occur, the total volume enclosed by said envelope being at least ve times the volume of said localized region.

STANLEY R. FITZMORRIS.

REFERENCES CITED The following references are of record in the;

` le of this patent:

UNITED STATES PATENTS Smith Nov. 15, 1938

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