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Dec. 3, 1946. J; R.’ PIERCE ETAL » v 2,411,913 ELECTRON DISCHARGE DEVICE Filed Sept. 21, 1942 as" as . 34 FIG. / . a5 a7 as // 2; 22 20 "19 I8 32' 26 l 25 I7 24 ‘ 2.9 27 - 40 I5 l3 I0 23 .20 | /6' so /5 ' )1! _ 2a ' u | '5 3 ' E 0: § 0. l'IVVfNTORS lasrzacr/iva'sLz-cmooe pdrgzvrugosmusmcq- ~ 8? SHEPHERD ATTORNEY 2,411,913 Patented Dec. 3, 1946 UNITED STATES ‘PATENT OFF-ICE 2,411,913 ELECTRON DISCHARGE DEVICE John E. Pierce, Millburn, and William 0. Shepherd, Summit, N.'J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. 17., a corporation of New York , Application September 21, 1942, Serial No.’ 459,12 \. 11‘ Claims. (Cl. 250--2"1.5) 2, v. range of frequency over which the device can be 1 This invention relates to electron discharge devices and more particularly to ultra-high fre quency oscillation generators of the re?ection type. tuned electronically. In general, the higher the transconductance, the greater is this frequency range and the greater the ratio noted the greater ‘ is this range. In oscillation'generators of the re?ection type, such as disclosed, for example, in Patent 2e06, 7' , Realization of a high transconductance ‘in volves, inter alia, attainment of strong ?elds effective upon the electrons in' both directions 850, granted September 3, 1946, to John R. Pierce, an electron beam‘is projected across a gap in a high frequency circuit element, such as a of their travel acrossthe gap. Such ?elds are cavity resonator, whereby it is velocity varied, 10 obtainable by employing grids across the ends of the gap. However, grids introduce a heat dissi and enters a region betweenthe gap and a re pation problem and the power obtainable from ?eeting electrode wherein the velocity variations the device is dependent upon the heat dissipat are converted into density variations and the ing limitations of the grids. In order to pre direction of electron travel is reversed. The elec vent overheating of the grids; a reasonably low trons are then ‘againprojected into the gap in 15 current density over the grids must be main the direction opposite to that of their initial tained. The heat dissipating capacity of the projection acrossv the gap and deliver energy to grids is dependent, of course, uponthe size of the circuit element to sustain oscillations. The the grids. However, the capacitance between the operating frequency of such oscillation gener grids also is dependent upon the size of the grids ators may be'valried over. a wide range by alter 20 and, therefore, the grids cannot be increased ing the high frequencyrcircuit ‘element or cavity unduly in size to increase their heat dissipating resonator. Also, as pointed out in . the Pierce capacity because of the attendant increase in the patent,‘ vdevices of this type are tunable electron capacitance therebetween. ' ' ically, that is, theloperating- frequency can be . As noted heretofore, the operating 'frequency varied through a moderate range by varying the 25 of re?ection type oscillation generators can be potential of the re?ectinge'lectrode. The ampli varied over a fairly wide range by varying the tude of the oscillation changes as the frequency high frequency circuit element’ associated with is varied by changing the potential of the re the gap. Thus changing v the operating fre quency, however, requires for attainment of op It has been found that in such devices the 30 timum operation substantial variation in the amplitude of the oscillations is not a single valued ?ector. ‘ ' transit time for the electrons in the region be tween the gap and the re?ecting ‘electrode, the function of the potential of the reflecting elec trode. As this‘potenti'al is varied from small ' transitv time including the time ofv both forward and reverse motion of the electrons. This transit time is dependent. upon the potential of there values through the rangewhere oscillations occur » and to large values Where ‘oscillation is stopped, and then decreased, a form of hysteresis occurs atone or several regions in the potential range. Hence over certain ranges of potentialof the. reflecting electrode, once the oscillation has ?ecting electrode and, in known devices, realiza tion of optimum operation with large changes in the operating frequency effected by changes in the high frequency circuit element,.has required 1 reached a high amplitude level it .will. maintain relatively-large changes in the potential of the re?ecting electrodes. One general object of: this invention is- to im ‘itself although over the same ranges mcillations will'not build up ‘from an. initial non-oscillating condition. This non-uniform operating. charac teristic is, of course, undesirabie. For example, if during the operation-of.thedevice, the volt~, 45 age supply for the device is interrupted, oscilla-v tions may not build up even after the supply is again connected and the voltages are restored to the values extant-before‘ the interrupticnof the Voltage supply. ' v ' ' Desiderata for. reflectiontype osciilation ‘gener-_ . ators 'are a“ hightransconductance‘ and‘ a‘ high ration of “transconductance to'the capacitance‘ prove the operating characteristics of electronic oscillation generators of the re?ection type. More speci?cally, objects of this invention are to substantially eliminate hysteresis e?ects in elec tronic oscillation generators‘ of the re?ection type, to increase the operating frequency range 50 thereof and to increase the electronic tuning , range thereof, to obtain a high transconductance and a high ratio of transconductance to ‘capaci ' tance for such generators, and to reduce the of varia ion in re?ecting electrode between the gap de?ning electrodes. Boththe 55 Imagnitude potential requisite'for optimum operation with transconductance and‘ the ratio‘noted a?ect the 3 2,411,913 changes in the operating frequency of such generators. In one illustrative embodiment of this inven tion, an electron discharge device comprises a pair of grids de?ning a velocity variation gap, an electron gun opposite one of the grids and a. re?ecting electrode opposite the other of the rids. g In accordance with one feature of this inven tion, the electron gun is constructed and ar ranged to produce a hollow cylindrical beam which is projected across the gap substantially parallel to the axis thereof. More speci?cally, in accordance with one feature of this invention, the electron gun comprises a cathode having a 4 I8, of greater diameter than the grid I8 and in juxtaposition thereto to define a gap 22. The two grids I8 and 2| together with the sup ports therefor and the portions of the enclosing vessel between the annular members It and 20 bound a resonant cavity 23 into which a coupling loop or pick-up 24 projects, the loop being con nected to one of the conductors I4 and to a metal lic sleeve 48 coaxial with this conductor. The 10 resonant cavity may be tuned in various ways to change the operating frequency of the device. For example, it may be tuned by flexing the wall member 60, as disclosed in the application Serial No. 439,375, ?led April 17, 1942, of Robert L.‘ Vance. laterally continuous electron emissive surface, for Mounted within the cylindrical portion E1 is a example circular and provided with a central for cylindrical beam forming electrode 25 having a wardly projecting portion, facing the grid oppo ?aring end 26 and supported upon a platform site the gun and a beam forming electrode adja 21 which is in turn supported from the header cent the cathode which in cooperation with the 20 I2 by a plurality of insulating strips 28, only one grid structure concentrates the electrons emanat of which is shown. The‘ beam forming electrode ing from the emissive surface into a hollow elec 25 encompasses a cathode which comprises a tron beam wherein, adjacent the grid, substanu heater ?lament 2s and a cylindrical cathode tially parallel electron flow obtains. In a par member 36 only the end surface SI of which ticularly advantageous construction, the for 25. toward the grid I8 is coated with electron emis wardly projecting portion is in the form of a cusp. sive material. This emissive surface which, in However, it may be of other forms, for example the construction shown, is circular, is provided conoidal or cylindrical. with a central forwardly projecting portion which In accordance with another feature of this may be in the form of a cusp, as shown, or of invention, the re?ecting electrode and the grid 30' other form, for example conoidal or cylindrical. to which it is opposite have opposed surfaces of Because of the form of the emissive surface 3!, predetermined con?gurations such that the elec 32, the ?aring end portion 26 of the beam form tron stream projected across the gap is formed ing electrode 25 and the curved end wall I9 of into a hollow beam of greater diameter which the grid structure, the electrons emanating from is reflected across the gap and is substantially 3.5 the surface 3i, 32 are concentrated into a hollow focussed upon an annular imperforate region of cylindrical beam coaxial with the electrode sys the grid structure opposite the gun, beyond the tem and in which in the region adjacent the grid boundaries of the grid in this structure. 58 the electron motion is substantially parallel. The invention and the above-noted and other Inasmuch as the emissive surface 3i, 32 is lat features thereof will be understood more clearly erally continuous, it will be appreciated that all and fully from the following detailed description ’ elemental areas thereof contribute to the space with reference to the accompanying drawing in current so that a high current beam with a rela which: tively small diameter cathode is obtained and, Fig. 1 is an elevational view mainly in section further, substantially uniform space charge of an electron discharge device illustrative of one effects in front of the cathode are obtained. It embodiment of this invention; " Will be noted, further, that as illustrated in Fig. 2, Fig. 2 is a diagram showing the con?guration the electrons are concentrated into a hollow beam of the electrodes in the device illustrated in Fig. l of an outer diameter slightly less than the diam and illustrating the equipotential lines in the eter of the grid I8 and which traverses a region region between the re?ecting electrode and the 50. of the grid 18 near the periphery thereof. The grid to which it is opposite and also the. electron current density in the beam at this region is rela trajectories in the device; and tively low so that local heating of the grid is Fig. 3 is a graph showing typical output power small. Such heating as occurs is in a region of reflecting electrode potential relations in devices the grid adjacent the support member I7 and, wherein hysteresis effects occur. hence, relatively rapid heat ?ow from this grid ' occurs. Referring now to the drawing, the electron dis Consequently, excessive heating of the grid I 8 is prevented and a relatively small grid charge device shown in Fig. 1 comprises a cylin in relation to the total beam current may be drical metallic enclosing vessel It having an end employed. The capacitance between the grids portion ii of reduced diameter, and closed by a metallic header I2 provided with eyelets I3 to 60 I8 and 2| will be correspondingly small. Mounted opposite the grid 2| as by a leading which leading-in conductors I 4 are sealed her in conductor 33 sealed to an eyelet 34 on the end metically by vitreous beads I5. Mounted within portion II by a vitreous bead 35, is a re?ecting the vessel I0 is a metallic grid structure including , electrode, which is coaxial with the cathode and a laterally extending, annular, metallic member grid structures. The re?ecting electrode includes I6 secured to the inner wall of the vessel, a cylin an outer cylindrical portion 36, an intermediate drical portion H which may be integral with the dished or inclined portion 31, the convex surface member I6, and a mesh grid l8 extending across of which faces the grid 2|, and a central cylindri one end of the cylindrical portion I1, the portion cal portion 38 projecting toward the grid 2|. I’! being imperforate and having a rounded end 70 During operation of the device, the beam form wall I9. ing electrode 25 is maintained at cathode poten A second metallic grid structure is mounted tial or at a small negative potential with respect within the vessel and comprises an annular sup to the cathode, the grids I8 and 2| are biased at port 28 af?xed to the wall of the vessel I0 and a positive potential with respect to the cathode a vcentral mesh grid 2| convex toward the grid and thare?ecting. electrode is maintained. ate 25411213911311‘ 6‘ negative potential with 3respect; to ,the cathode,__ flectingielectrode, and to subsequent bunching; of theielectrons-in the space between the.__grid_ 2|; and the reflecting, electrode.- The other is that The " electrons emanating fromq the ,1 cathode _; are" concentrateddntoearhollowrrdrlmdrical been? as not'édih“ ‘ étdfbrél; and projected.acrossthe- can I 2.2.’ wherein they’. are...’ velocity, varied. ‘ The . velocity.v due‘to' the, density and velocity varied stream, which crosses thegap 22 in thereverse direction. 'variedstrca'm isgconvertedhin? the space between If thegbunched and velocity variedistream of the, gridv 2| .andl'the. reflecting.,electrode, into va electrons ., passes, through the grid l8v into the region between this grid and the cathode, be? d¢n§ity<variedstream-Whichis-pmiectéd through’, thejgrid 2] ,.in._ the , reversoldirectiflnt, The reverse, electron .str'eamdelivers. energy. to. thefield with . c ' the“ forward1 direction, , that 1 is, , toward; the-re 10 cause ofacombination ofspace charge in?uences, in the resonant. cavity23, wherebyzoscillation itsv re?ection, and . grouping and interception by the‘ sustained- . inthe stream being projected toward the grid l8.‘ Thisdensityvariation:v corresponds to a second cathodefthis stream produces acvdensity variation 'Thenopposred ‘surfaces: of,‘ the. , grid 2 l l . and the i re?ecting. electrode. are, of. suchv con?guration that the, eljectronsprojectedinto the region be tween, the grid" 2] and the, reflecting. electrode, 15 the'electrons in the. space between the grid 2| and the reflecting electrode. For small ampli tudes of oscillation, thertwoconduction factors, havemtheir, direction of motion reversed and are. projectednthrough the grid 2|,inv the, form of a hollow, cylindrical beam of a diameter greater than thatofthe forwardly projected beam, which are in opposition so that the tendency for osoilla-_ tion is weak. However, as the amplitude of oscil is substantially focussed upon thewall IS. The. requisite: con?guration _ of these surfaces ,in any lation. is‘ increased, the second opposing. con ductance factor decreases and the device tends particular device can be determined in known ways, for example, by determination, in an elec-' trolytio tank, of the equipotential lines in the tof- oscillate increasingly strongly until an equilibrium... is reachedat a high amplitude of region _,be._tween these surfaces and calculation of ‘the electron trajectories. ,In the particular construction illustrated in Fig. 2, the lines E represent 'the'equipotentials, the numeral on each of;these vlines indicating its potential as a frac conductance factor, in addition to that due,to the, initial velocity, variation and the grouping of ' oscillation.‘ ' . t . In, devices‘ constructedin accordance with this invention, the reverse electrons are intercepted 30 tionof-the total‘direct'current potential differ ence between thegrid 2] and there?ecting elec-, trode. "' Thein'ner diameter of the electron beam by the imperforate wall 19 end, ‘therefore, sub stantially noneof thereverserelectrons enters the-region between the. cathode and the grid I8. Hence,v the second opposing conductan‘ce'factor notedabove is eliminated, the hysteresis effect is. in; this construction is approximately 100 mils likewise eliminated and, av uniform operating, and the outer diameter thereof is approximately characteristicis obtained. . 200 mils; The ‘other dimensions in ,Fige2fare to scale; ’ 7 It: will benotedgthat the, opposed surfaces of ‘the grid_2l_‘ and they intermediate portion 31 of} , ~ ' It may. bev notedfurtherthat prevention-of flow of . the reversed. electrons into the cathode region eliminates the possibility- of - bombardment of the - cathodegby such electrons ~. and thus prevents the/re?ecting electrode are convex withrespect 40 overheating. or variation of the cathode heating to thecathode andthat the surfacesof the re ?eeting electrode toward the, grid 2'. ,bOund an annular recess; toward which the electronv ‘beam. iswinitially projected, Because of‘ the con?gura tion of-thesurfaces involved, the electrons,,typ1 cal trajectories of which are illustrated by the linesrL in'Fig, 2,jprojected_linto the region be-v tween-the grid 21 and re?ecting electrode are, as noted heretofore, “reversed in direction, concen trated intoahollow cylindricalbeam of greater diameter than the grid 18, and projected through the-"gridZI to the annular wall portionl9,‘ the reverse beam being substantially focussed upon. the lwalliportion» l9. ' ‘ ' ’ ' Wherebvtheoperating life.v of , the cathode is in ‘creased._,and uniformity of cathode emission is, assured. : . _ As has been pointed out heretofore,theoper » ating; frequencyrof, .thegdevice, can beer-altered by varying the resonant- cavity.- When the frequency: is thus variedthegtransit time of the electrons in the regionbetweenvthe- grid 2| and the re?ecting electrode, both, the, forward and . reverse vmove mentyo?the electrons beingconsidered, must be varied .a1s0to obtain optimum operation, This involvesqvarying the potential of the re?ecting electrode inasmuch ,as/it is this potential which is_,.1arg,ely.determinative of the transit time, It As has been noted heretofore, in_ known oscillaT ; . will»v hie-‘noted; from Fig. 2 that .the equipotential tion generators'of the-re?ection-type a hysteresis lines of the ?eld betweenthe grid 2| and the effect occurs and a non-uniform operatingwchar reflecting, electrodes» are not uniformly r spaced,; ' acteristic'results.v Typical plots of power?output thisibeinggdueito the shielding effect of the cen tral portion Stand the outer cylindrical portion versus potential of ‘the re?ecting electrodes for such devices'are shown in Fig. 3 wherein plot a, (if) 36 of the re?ecting electrode. As shown in Fig. 2, theaequipotentials nearest the’ ‘re?ecting elec indicatesvthe characteristic as the reflecting elec trode potential is made progressivelycmore nega- , trodetarespacedz-a greater distance'apart than tiveywith respectto the cathode, and plot b in dicates. the-characteristic as the reflecting elece those ,nearest the.:grid,.2l.. Hence, a ‘relatively large-,variation of path length and transittime-i trodegpotential is made progressively less negative with respect to the cathoderthe range of potential for ’ the, electrons in, the region ‘between the grid being the same for both plots. Hysteresis, it‘will' re?ectingyelectrode potential results.- 'Conse one? when the operating frequency of ~_ the de-._. viceasa teredby varyingthe resonant ,cavity only . be noted, may occur‘at either‘ofvthe regions or :cL-y' .or- at both. Although this~invention is not to- be-limited thereby, the following theory ‘is believedto be ex-." planatoryofthe hysteresiseffect. There are two sources of conductance vacross theugapw?; one. OI swhighia?hat' due?ethe .gvelocity.variatioapi . »- and re?ecting electrode,- with'variation; .in the; arelativelypsmall change in there?ecti-ng eleci, ' tredepgétéhtial isnecessary'to maintain optimum operation so. thatthe operating frequency may. bevaried vover azwide range and optimum Zopera-V . tionmadntainedby. smallchangesin theqre?octg. . a? SignLegit’.ieereiestedaemss reggae "he. .75 mesa-creamer.. f 2,411,919 7 a ‘re?ecting-electrode having a convex surface‘ ' Furthermore, because‘ of the relatively wide spacing of the equipotentials as compared with the spacing in a uniform ?eld of the same extent and potential, the electron transit time in ‘the re— gion between the grid 2! and the re?ecting elec facing said one grid, 4. An electron discharge device comprising a_ high frequency circuit element including‘, a pair of grids mounted in juxtaposition anddefining a trode is affected to a'relatively large extent by gap, means for projecting a hollow substantially parallel ray electron beam across said gap in the velocity variation the electrons receive in crossing the gap 22 ‘in the ‘forward direction, that cluding a cathode opposite one of said grids, and, is, toward the reflecting electrode. This, in effect, enhances the transconductance. As has been a re?ecting electrode‘ opposite the other of said grids, said re?ecting electrode having therein an, noted heretofore, the transconductance is en-' hanced also due to the fact that the grids l8 and annular recess facing said other grid. 5. An electron discharge device comprising-a: 21 assure subjection of the electrons to strong high frequency circuit element including a pair ?elds in both directions of their traversal of the of grids mounted in juxtaposition and de?ning a gap 22. Hence, and because of the relatively 15 gap, means including a cathode opposite one of small size of the grids, with consequent small in I said grids for projecting an electron stream across tergrid capacitance, it will be appreciated that in said gap, the surface of the other of said grids, devices constructed in accordance with this in facing away from said cathode being dished, and vention a high ratio of transconductance to ca a re?ecting electrode opposite the dished surface pacitance is obtained whereby a wide range of 20 of said other grid, said re?ecting electrode in electronic tuning is realized, cluding an annular intermediate portion and Although a speci?c embodiment of this inven- ' central and outer cylindrical portions projecting tion has been shown and described, it will be from said intermediate portion toward said other understood, of course, that it is but illustrative grid. 7 and that various modi?cations may be made 25 6. An electron discharge device comprising a therein without departing from the scope and highv frequency circuit element constituted - in spirit of this invention as de?ned in the append part by a pair of grids mounted in juxtaposition ed-claim's. ' ' and de?ning a gap, means including a cathode ‘ What is claimed is: opposite one of said grids for projecting a hollow >1.'An electronic oscillation generator compris cylindrical beam across said gap substantially ing a high frequency circuit element constituted in part by a pair of reticulated members mounted in juxtaposition and de?ning a gap, means oppo site one of said members for projecting across said gap anelectron beam in which, adjacent said ‘ one member, the motion of the electrons consti tuting said beam is substantially parallel, and means for reversing said beam after it has crossed said gap "and projecting it across the gap in the reverse direction in the form of a stream directed upon an area laterally beyond the periphery of said one member, said last-mentioned means in cave surface. cluding a reflecting electrode opposite the other of said members. ' “2. 'An electronic oscillation generator compris- _ ing a high frequency circuit element including a pair of grids mounted in juxtaposition and de?n ing a gap, means for projecting a substantially cylindrical, hollow electron beam across said gap in one direction, said means comprising a cathode ' opposite one of said grids, a beam forming elec trode adjacent said cathode and an electrode member having an imperforate portion encom passing and extending outwardly from the pe riphery of said one grid, and means for re?ecting said beam after it has crossed said gap, in the form of a stream substantially focussed upon said ' imperforateportion, said re?ecting means includ ing a re?ecting electrode opposite the other-of said-grids. _ 3. An electronic oscillation generator compris ing a high frequency circuit element constituted, in part by a pair of circular grids mounted‘ in jux tapos'ition and de?ning a gap, one of said grids being dished away from and of greater diameter than the other of said grids, an imperforate mem ber extending outwardly from the periphery of said other grid, means'for projecting an electron stream across saidgapthroughregions of said other grid removed from the central portion thereof, said means including a cathode opposite said other grid, and means for reversing said. parallel to the axis thereof, the other of ‘said grids being concavo-convex and having its con vex surface toward said cathode, and a' re?ecting electrode opposite the concave surface of said other grid, said re?ecting electrode including an annular intermediate portion having a convex surface facing said concave surface and including also inner and outer cylindrical portions project ing from said annular portion toward said con ' ' ' v '7. An electronic oscillation generator of the re ?ection type comprising a resonator bounded in part byv a pair of juxtaposed grids de?ning a gap, means for projecting a hollow cylindrical electron beam across said ‘gap in one direction, said means including a cathode opposite one of said-grids and beam forming electrode means in cooperative relation with said cathode, and means for re ?ecting saidbeam after it has traversed said gap in said one direction and projecting it into said gap in the opposite direction in the form ‘of a hollow stream, said second means including a re-v ?ecting electrode opposite the other of said grids, the facing surfaces of said electrode and said other grid having portions dished and convex with respect to said cathode. . . ‘ 8. -An electron discharge device comprising means for producing a hollow cylindrical elec tron beam comprising a cathode having a sur-' GU face including a central forwardly projecting por tion and a laterally extending portion surround ing said projecting portion, both "of the project ing and laterally extending portions being highly electron emissive, a cylindrical beam_ forming electrode encompassing said cathode and having; a portion extending forwardly from adjacent the: periphery of said surface, and an electrode mem bér adjacent said beam forming electrode and having an annular portion overl?ngjsaidj-for wardly extending portion. 9. An electron discharge device comprising ‘means for producing a hollow cylindrical electron beam after ithas crossed said gap and projecting beam comprising a cathode having a circular it‘in‘the reverse direction to impinge .upon ‘said . , electron emissive surface provided with a central imperforate member, said lastnreansincluding .75. cusp; a beam "formirigelectrode encompassing" 2,411,913 9 , said cathode and having a cylindrical outwardly ?aringportion extending from adjacent the pe¢ riphery of said emissive surface, and a cylindrical electrode member encompassing said beam form ing electrode and having an annular'concave sur face adjacent said ?aring portion. 10. An electronic oscillation generator of the reflection type comprising a high frequency cir cuit element constituted in part by a pair of elec trode members having juxtaposed apertured por 10 11. An electronic oscillation generator of the re?ection type comprising a high frequency cir cuit element constituted in part by‘ a pair of juxtaposed apertured members de?ning a gap, an an electron gun opposite one of said members for projecting a hollow cylindrical electron beam in one direction across said gap, electrode means op posite‘the other of said members and cooperating‘ therewith for forming said beam after its pro 10 jection across said gap into a hollow reversed electron stream of greater diameter than said tions de?ning a gap, means opposite one of said beam and projecting said hollow stream across portions for projecting an electron stream across said gap in the reverse direction, and means for said gap, and means opposite the other of said intercepting said hollow stream after it has been portions for producing in the region adjacent said projected into said gap, said electrode means in other portion a reflecting ?eld non-uniform in cluding an annular reflecting surface opposite potential distribution in the direction of projec tion of said stream thereinto, said re?ecting ?eld ' said other member and shielding means extend ing from the inner and outer edges of said sur producing means including a re?ecting electrode face toward said gap. surface in alignment with said other portion and shielding means electrically integral with said ~ electrode surface and extending from the pe riphery thereof toward said other portion. JOHN R. PIERCE. WILLIAM G. SHEPHERD.