US2332428A - Electron flow device - Google Patents

Description

Oct. 19, 1943. 2, J. ATLEE ET AL ELECTRON FLOW DEVICE Filed March 26, 1942 w ww l lll -|Ill|ll Ill & Q9042. mrozzmsy Patented Oct. 19,1943 I gum-m STATES BA arl;

ELECTRON FLO QD l 1 Zed J.-Atlee, Elmhurst,lIll., and Robert'-F'. Wilson;

' Washingtom'D. C.,-assignors to General Eleca ,trici'X-Ray Corporation, Chicago,'Ill.,-a corpoii 1 p, rationof NewYork v V Application March 2c,194g,'sena1N0.436,2so

7 y 3 Claims. romeo-27.5)

'The Present invention relates in general to electronics and has morelparticular referenceto improved electronic rectifier means.

An'important object of the invention isto pro vid'e' an electron flow device embodying an extremely efficient electron emission source; a furv ther' object being to provide an. emission element adapted to be heated 'for electron emission at relatively low temperature; astill furtherobject being toutilize an emission element comprising thorium forhighly efilcient electron emission.

' Another important object is toprovidean electron emision element comprising thorium supported on a suitable mountingpsuch as a tung sten filament; a further object being to support the thorium as a surface filmonthe supporting filament. v

Another important object isto carbonize the tungsten filament whereby to carry the thorium thereon in a sheath of tungsten carbide on said ame Anotherimportant object is-to provide an electron flow device embodying the improved elecing means to prevent endiproducts of the gettering operation from settling upon the anode and cathode elements'oithedevicen These andnumerous, other} portant objects,

* advantages, and inherent iun'ctions of the: inven tionwill be, fully understood 'frjom'the following description, which, takenin'connectionwith the accompanying drawing, discloses a preferred embodiment of the invention.

' Referring to the drawing:]

Figure 1 is a sectional View t akenliongitudinally through an electronic rectifierembodying the invention, the'figure including a diagrammatic representation of externalelectrical connections I for the operation of the rectifier; and

Figure 2 is a s ectionalview taken the drawing an electronic' devicecomprising a tron emission element asa cathode, inicornbi nation with a co-operating anode, enclosed; in a sealed evacuated envelope, and to preserve the thorium by providingmeansformaintaining the exhausted envelope at a highdegree of vacuum of the order of 0.02 micron of mercury or better;

a further object, to this end, being to provide l getteringmeans within the envelope and supported on a mounting preferably comprising a part ofllthe cathode structure, ,said gettering means being operable to produce agettering material such, as barium in vaporized condition at intervals during the service life of the device to maintain the desired degree of'vacuum within the envelope for the preservation of the electron rectifier ll, although the several featuresof the inventionare not necessarilyliinited torectifiers I but may beutilized to advantage 'generallyjin,

electronic devices embodying means forming an electron emitting source,

The rectifier ll,'as shown on" the drawing; may comprise'a sealed envelope lt 'containing;

an anode l5 and a co-operating cathode 'll; "The envelope I3 may bev forniedof any suitablelen velope material and may be arranged inflariy convenient or pr'eferred'iorm; As; shown, thejenvelope may comprise atub lar gl as's'zshell' hav ing re-entrantnecks 19 at thefoppositeendsof the shell,the anode"lilandlcathode'l'l,being, 7

s respectively, supported on saidnecksat thefop emission element for operation at'high efficiency. a c

Another important objectisto provide means withinthe envelope, operable as an ionization gaugaior the determination of vacuum conditions within the envelopejduring the operating life of the device; a furtheriobjectbeing to form the gauge as a plate havinga connection extending outwardly of the:sealed-envelope for attachment in 'an external measuring circuitand oper- 4 able'as an ionic collector, said plate servin in conjunction with the external measuring circuit,

, to measure the degree, of ionization andjhence,

, vacuum conditions within the envelope; a further object being to form the ionization gauge plate as a part of the cathode structure'iofthe device; a still further object being to utilizefthe' said gauge plate as a housing or enclosure for gettervelopethrough an opening formed the s'e'al,

" said",

preferably" comprises v an; electron emiss fila lament. A 7 The posite ends of the envelope, The necks H! de-] fine openings which areclosedby seal members-Ii 2i and 23of generally cup-shaped coniig' ra+'f tion. These members preferably comprise sheet metaLandeach has an annular rim which iormsf a glass-to-metal seal 25 with: the inwardly .fac f I neck is 'on which'the' seal merri berisfmounted to thuss'ealthe endoi t ing end of the velope.

JTheinernber 23,]at end of the'envelope, carries the anode i5, which preierablyfcomprisesj a; cup shaped element-formed with ajstem 25 which projectsoutwa'rdly'oi the1end'of theien;

member 23, the stem 26 being sealed opening. o j f 1 Thelmemberf'r I, at the other end of velope, 'carries"thecathode llfwhich,'as shownp- I r subs tan- H tially along the lines 25-2 in'Figurel'.

To illustrate the invention, thereis'shown on fitment n ethane solicited in tungsten with the thorium component substantially uniformly distributed in the filament. By operating the filament at high temperature, the thorium is driven to the surface of. the filament to form a thorium film on, the surfaces of. the

filament. The heating of the filament to form a thorium film thereon need not be accomplished until the filament has been assembled in the electron flow device and may be' accomplished as a part of the process of conditioning the finished device for service. The process of thus conditioning the filament merely comprises the he'atingof the filament to a temperature of the order of 2900 Kelvin; somewhat below the melting temperature of tungsten. v

A thoriate'd filament "oi the character herein described is characterized by the ability to' emit efiective electron quantities at' a temperature substantially lower than the effective operating temperature of a pure tungsten filament. Asa consequence, an electron flow device embodying a thoriated filament, in'accor'd'ance with the teachings of the present invention, is capable of functioning at a lower' temperature 'and hence at appreciably higher efficiency with, substan tially longer life thanisi'the case with electron flow devices containing electron emission elements of the character heretofore knowing In order to aid in holdingthe thorium on the filament during the serviee'liieoithe cathode and t6 therebymaintain the cathode as a highly eflicient electron' 'source', itis desirableto car boniz'e the filament in order toprovide a surface coating of carbide, specifically a tungsten carbide layer, where the filament comprises tungsten, since the thorium has a greater aflinity and'will be heldlnore securely on the filament by the carbide tha'n'onfpure tungsten. iTo this end, the filamentis preferablycaiibonized by heating it to a temperature of the order of2 ,000 degrees centigrade in a hydrogen bottle or container in the presence'of a carbonizing gas such as acetylene.

In this fashion, a sheath of tungsten carbide may be applied wine surface of thefilarnent to serve as a'foun'dation for holding the thorium on the filament. The carbonizing process Should be limited to the surfaces and should not penetrate completely to the center of the filament in order to avoid extreme brittleness, In performing the carbonizing process, the degree of carbonization may be determined'bymeas'uring the electrical resistance of the filament from time totirnefthe resistance of tungsten carbide being substantially higher than that of pure tungsten,.so thatadesired degree of carbonization may be readily determined by measuring the resistance of the 'filament being treated and by terminating carbonization when a predetermined resistancefhas been reached. f l

'The'cathode structure includes a disk-like head 43, preferably of metal, which head is mounted on a stud l5 extending in an opening formed in the seal member 2|, the stud being sealed in said opening and havingportions extending outwardly or the envelope. Thehead ,43 carries a tubular skirt 41 secured at one end on the head and extending at the other end in position enclosing the glass-to-metal seal 25. The skirt thus encloses a space 49 between the seal member 2| and the head 43, which space is in open communisurethe maintenance of a high degree of vacuum within the envelope.

The cathode comprises the filament H which,

, at oneend, is mounted on, electrically connected to, andsupported by a conductor stem 21 which extends through: an opening 28 formed in the head 43. The end of the stem 21 is mounted on the seal member-2| which is formed with an opening fitted with a grommet 29 which receives the stem '21. The stem 21 is supported in and electrically insulated from the grommet and the seal member 2| by means of a globule of glass which supports the stem and seals the grommet opening around the stem. outwardly of the grommet, the stem 21 is electrically connected to a conductor 3|. The other end of the filament E1 is mechanically and electrically connected on a mounting member comprising a wire 33 which has a hclically coiled portion 35 embracingthe filament and a supporting portion 31 which is supported on and electrically insulated from the head 43 by means of a grommet 33 sealed in an opening in the head, the stem 31 being secured i electrically connected with the conductors 3| and 4| which extend outwardly of the envelope, such connection being accomplished by way of the stems 21 and 31 which are electrically insulated from the head 43.

It should be understood, of course, that an electron flow device functions by the flow of electrons emitted at the cathode and traveling to and impinging'upon'the anode. When the flow device is constituted as a rectifier, the stream of electrons passing between the cathode and anode form a conduction path along which electrical current may flow in one direction only between the anode and cathode. This uni-directional flow phenomena is utilized for the purpose of rectifying alternating or fluctuating electrical energy in order to provide uni-directional electrical power.

For efficient operation of the electron flow device, the atmosphere within the envelope I3 is preferably maintained at pressures of the order of 0.02 micron of mercury, and the maintenance of low vacuum conditions is of particular im-.

portance where the electron flow, device embodies x qfidi ervlce life, it is necessaryto reducethe possibility of ionic impact on the cathode filament-and consequent dislodgment of thorium by eliminating, as far aspossible, the presenceof gaseous matter within the envelope.- To this end,

means-is provided for insuring high vacuum conditions within .the envelope throughout the serv-' ice life of the device. To this end, the envelope is first thoroughly evacuated as apart of the' manufacture of the device, evacuation being acin the anode, cathode and envelope walls. After the devicehasthus been exhausted. to the greatest possible exte'nt, theenvelope may be sealed off and as a final operation to remove all remaining impurities, a gettering operation isperformedwithin the envelope. According to the present invention, gettering is accomplished by vaporizing a suitable gettering materialwithin the envelope, more particularly within the space 49. Barium may be utilized as a gettering ma-. terial, and by vaporizing the same within the en- 63 for regulating current flowjinthe'gettering circuit for gettering control through-regulation of vaporization of the gettering material in the chamber 49; It will be apparent, of course, that suificient 'gettering materialmay be supplied within-the chamber 49 to enable successive gettering operations to beperiormed within the envelope at intervals during theservice life of the device to thereby periodic'ally re-establishdesired operating life of the device.-

vacuum conditions within-the envelope 'inthe event that the'vacuum be impaired during the The device of the present 'nventio'n also includes means for testing and measuring vacuum conditions within the envelope from time to time by ionization gauge means, including the head 43 and skirt 41 which, it will be noted, are elec- 'tri'cally connected onthe stud 45 and otherwise insulated from the cathode and anode.

The degree of vacuum within the envelope I3 is a function of the number of gaseous particles present within the envelope, and the number of such particles, in turn, is a function of the degree of ionization developed as a result of collision between electrons emitted by the cathode with any such gas particles present withinthe envelope. By measuring the degree of ionization within the envelope resulting from a measurable velope, all remaining impurities may be caused to unite with the barium vapor to form innocuous i solid end pro-ducts which, upon condensation of the gettering material, will become deposited within the envelope is. =Byproviding a head 43 and the skirt ll, the end productswill be deposited upon the internal surfaces-defining the get tering chamber 49. and thus will be prevented from depositing either upon the wall surfaces of the envelope I3 or upon working surfaces of the anode and cathode. I

Barium or other suitable gettering material may be supported within the chamber 49 and evaporated therein by any suitable or preferred means. Preferably, however, the gettering material is supported by a carrier wire 5| electrically connected at one end on the stud 45 and at the other end of a conductor 53, the carrier wire 5| having portions intermediate the anchored ends thereof arranged in loops within the chamber 49. The conductor 53 extends through the seal member 2| and is sealed, as by means of a globule of glass, in a grommet 59-similar to the grommets 29 and 39 and, like them, sealed in the member 2|. outwardly of the envelope, the conductor 53 is electrically connected to a conductor 55.

The gettering material may be supported in any suitable or preferred fashion uponthe carrier wire 5|, which preferably is a hollow conductor wire enclosing the gettering material and having weakened wall portions. By passing electrical current through the wire 5|, as by connecting a suitable electrical power source 51 between the stud 45 and the conductor 55 outwardly of the envelope, the hollow carrier wire 5| may be heated to thereby vaporize the gettering material carried by the wire, the material thus vaporized being projected outwardly of the wire through its weakened wall portions to perform the gettering operation within the chamber 49, resulting end products being deposited upon the inner walls of the head 43 and tubular skirt 41.

The gettering circuit between the stud 45 and the conductor 55, in addition to the power source 51, preferably includes a meter 6| for measuring current flow in the gettering circuit, an adjustable control rheostat 65, and a control switch electron flow between cathode andanode; it is possible accurately to determine the presence of gas particles within the envelope and thereby determine the vacuum condition at any time during the service life of the device. This may beaccomplished by promoting a known electron flow between cathodev and anode and then measuring the resulting ionization by collecting resulting positive ions onthe head and skirt 43 and 41 and quantitatively measuring the ions thus collected. To this end, an ionization gauge circuit comprising a meter 61 and a power source 69 may be connected between either of the conductors 3 or 4| and the anode stem 26, preferably under the control of a switch 1| and an adjustable current flow regulating device, such as a rheostat 13. By adjusting the rheostat, a known electron flow, as indicated by the meter 61, may be estab lished between the cathode and anode. I

By applying a negative bias to the head 43 and skirt 41 with respect to the cathode H, as by means of a power source 15 connected between i one of the cathode leads 3| or 4| and the stud 45which is electrically connected with the head 43 and the skirt 41, positive ions produced within the envelope will be caused to impinge upon the head 43 and skirt 41, the extent of such ionic.

impingement being accurately measurable upon the meter 11 which is included with the power source 15 in the biasing circuit between the stud 45 and the cathode I1. Whenever the meter 11 shows ionization above a predetermined minimum, it will be known that the desired vacuum condition within the envelope |3 has been impaired and that the device should be reconditioned by theperformanoe of a gettering operaf tion in orderto recondition the device for operation at maximum efiiciency,

It will be understood, of course, that the circuits shown in solid lines, namely, the ionization circuit including the meter 51, the ionization measuring circuit including the meter 11, and the gettering circuit including the meter 5!, are connected with the device in the manner shown only when it is desired to measurevacuum conditions within the envelope |3 and recondition the device by the performance of a gettering operation. When the device; is in: service,- i tlmay be connectedin any preferred rectifier system. For example, the'rectifier may ordinari1y=be connected as indicated-in:dotted lines, illustrating ;a filament transformer, 19 connected;to supply'filament current through the filament'conductors 3i and II and an alternating ,currentpower input ransformer: 8| connected between -.the;: anode a I 5 and cathode I1 through aunidirectional @power outlet connections. a

It is thought that-the invention andits ;nu-

merous attendant advantages will berfully under-v stood from the foregoing description, and it is obvious that numerous changes may. be made-in the form, construction and arrangement of the several :parts without departing from :the spirit .or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed hein'ga preferred embodiment for the purpose of illustrating-the invention.

The invention is hereby claimed as-follows:

1. An electron flow devicecomprising asealed evacuated envelope containing an anode and a co-operating'ecathcde comprising gthorium on a suitable support, means forming an enclosuretin communication-with the space; in said envelope,

arsupply of evaporablegettering. material in said enclosure, meansoperable'outwardlyof the envelope for the controlled evaporation of said material withinsaid enclosure, said enclosureserving as a collectorin and on which the gettering materialmay condense after evaporation tothus prevent condensation of. gettering material on the anode and cathode, saidgmeans forming-the enclosure comprising electrical conductingmaterial forming an: ionization gauge plate -inthe envelope and electrically insulated from said .anode and cathode, and means for connecting said plate in an ionization measurement circuit outwardly of the envelope.

2. Anelectron flow device comprising a sealed evacuated envelope containing an anode and a "co-operating cathode comprising thorium on a suitable support, and means for measuring ionization within the envelope to determine the evacuated condition therein comprising conductor.means forming an ionization gauge plate in the envelope in position to collect positively charged ions produced by electron flow between anodeand cathode, said plate being insulated from said anode and'cathode, and means for connecting the plate in an external electric circuit-for the quantitative measurement of ions collected thereon.

3. A high voltage, high vacuum electronic rec- -tifier comprising a sealed evacuated envelope, an

able upon predetermined expansion of the material therein, and means connected with said enclosure and operable outwardly of said envelope to cause the material to expand within the enclosure to rupture said wallportion and at intervals thereafter to evaporate the material in the envelope to maintain high vacuum conditions within the envelope and thereby preserve the thorium in situ on the support means.

ZED J. ATLEE. ROBERT F. WILSON.

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