US2579654A - Electron-discharge device for microwave amplification - Google Patents

Description

P. P. DERBY Dec. 25, 1951 ELECTRON DISCHARGE DEVICE FOR MICROWAVE AMPLIFICATION Filed June 4, 1947 Dec. 25, 1951 P. P. DERBY 2,579,654

ELECTRON DISCHARGE DEVICE FOR MICROWAVE AMPLIF'ICATION Filed June 4, 1947 2 SHEETS-SHEET Mama/7a wave.

Patented Dec. 25, 1951 ELECTRON-DISCHARGE DEVICE FOR MICROWAVE AMPLIFICATION Palmer P. Derby, Weston, Mass, assignor to Raytheon ManufacturingTCompany, Newton, Mass, a corporation of Delaware Application June 4, 1947, Serial No. 752,346 l This invention relates to an electron-discharge device in which electrons are caused to react with an electromagnetic wave in a waveguide so as to give up energy to said wave, thereby producing amplification of said wave.

An object of this invention is to devise an electron-discharge device capable of amplifying electromagnetic waves of very high frequency, for example waves in the microwave range.

Another object is to provide an amplifying device of the above character which has a rather .broad frequency-response band.

A further object is to devise a travelling wave amplifier which is of simple construction, yet is highly eflicient in operation.

The foregoing and other objects of the inventionwill be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a central vertical cross-section of a microwave amplifier embodying this invention;

Fig. 2 is a vertical cross-section taken at right angles to that of Fig. 1; and

Fig. 3 is a partial sectional view taken along line o:--a: of Fig. 2, looking in the direction of the .with respect to said waveguide at such a rate that the motion thereof is in phase synchronism with the electromagnetic wave being propagated through said guide, an interchange of energy can and will occur between said electron and said The direction of this interchange (that is, whether the electron imparts energy to, or abstracts energy from, the wave) will depend upon the relative phase relation existing between the wave and the electron when the latter is injected into the waveguide.

Generally, accordin to this invention, an elec- .tromagnetic wave of the transverse electric (TE or H) type, the electric field lines of which extend transversely substantially at right angles to the waveguide walls, is propagated through a waveguide having a portion of constricted crosssection, the reason for such shape appearing hereinafter; a plurality of electrons is injected into the waveguide and caused to move transversely thereacross through said constricted porlinear velocities that the electrons move in synchronism with an angular phase velocity of the 17 Claims. (01. 31539) wave. Therefore, the electrons react with the wave to interchange energy therewith, the structure of the device being so arranged that the electrons of such phase relative to the wave as to be capable of abstracting or absorbing energy therefrom are effectively removed from the waveguide, leaving effective only those which are of such relative phase as to impart energy to the wave; therefore, a net energy increase or amplification of the wave results. In the device of this invention, means are also provided for reversing the original transverse direction of movement of the electrons to cause them to return toward the injection side of the waveguide, thus enabling those,

of proper phase for wave amplification to impart a maximum proportion of their available energy to the wave.

It is desired to be explained at this point what is meant herein by the expression, the angular phase velocity of a wave in a waveguide. The

angular phase velocity is the velocity at which the phase of an electromagnetic wave in a waveguide propagates alon a non-linear path with respect to said waveguide, said non-linear path being so related to the longitudinal axis of said waveguide as to provide a substantially periodic angular component of motion with respect to said axis for a point moving along said non-linear path at a uniform rate.

It is know that angular velocities of a fixed and predetermined value may be imparted to elec trons by magnetic fields. An expression has been developed in the copending application of Elmer J. Gorn, Serial No. 744,143, filed April 26, 1947, for the value of magnetic field necessary to produce a helical motion 'of an electron in synchronism with an angular phase velocity of the wave,

this expression defining the magnetic field strength in terms 01 the angular velocity of the wave, the mass of the electron, the electronic charge, the linear velocity of the electron, and

the linear phase velocity of the wave in the waveincreasing radius. This increase in radius of the orbits of these electrons is utilized to effectively remove such electrons of unfavorable phase from the waveguide, as will be more fully explained hereinafter.

Now referring to the drawings, numeral l generally designates an electron-discharge device according to this invention. A central block 2, of copper "or other highly-conductive materialand of generally rectangular prismo'idal outer conjfiguration, has hermetically sealed thereto, at opposite sides thereof, two similar hollow rectangu lar waveguide sections 3 and 4, also of copper or similar material (see Fig. 2). Blockkz'has-a centrally-located H-shaped aperture extendi'ng-longi tudinally therethrough, so that said block can actas a waveguide of H-shaped.icross section; the said aperture in said block communicates, at its opposite ends, with the openingsin the corresponding waveguide sections 3a'nd'"4. Although;

in Fig. 1, the aperture in block 2 appears. tosbei' in the shape of the letter I, this is merely for convenience in illustration; when Fig 1- :is turned on its side,. this aperture. willlassume the shape of the letter H; Waveguides ofithisccnfig-uratlon are generally referredlto as. H-shaped waveguides by those skilled inthe art'towhichthisinvention relates, so the term H-shaped will-herused herein. The cross-bar or constrictedlportionof.the.H- shaped wave uide 2 extends vertically inl igql 1, andsaid. portibnhasawidth or. waveguide in.- ternal d mension defined. or delimitedby thet'wo oppositely-disposedwalls-2a and 2b.

The larger internaldimension of. rectangular waveguide sections 3 ands-extends vertically in Fig. .2, and this dimension .is substantially. larger than the total height-f the H -shapednaperture in block 2 as shown. I

In order to seal off from the atmosphere the interiors of waveguides 2 3, and 4',.:a substantially cup-shaped. metallic .elementdentirelysurrounds waveguide 3-andtis brazed-thereto and sealed thereto and to block .l at its inner end;

element i has sealed therein .a. similar circular window 3- which istransparent. to microwave energy; The outer diameter r of. cup-shaped ele ments 5 and. I is-preferably substantially equal to. the overall or external". heightof block 2, u'rhich height is the-largest dimensionotsaid block;

Upper and lower coaxialcircularapertures-9 and ML; respectively, .aredrilledthrough there spective upper and: lower: walls of block. 2, said apertures a and is communicating; with :the. H sha ed T aperture. in block 2; being". of approximately the" same'diameter as eachflother and the axisof' apertures 1-9 and. I0 extend-ingtransversely ofeguide' 2 .orvertically inFig's. l andl2i; the" longitudinal axis .01 waveguides 2 3,. and! extends horizontally in Fig. 2'. The diameter of apertures-Band Illis. somewhat greater than the distance (measured horizontally imFig. 1.) between faces 2a. andibt 1 .A- cathode structured-[ is mountedrin aperture 9 axially thereof. Said-s structurepreferably comprises arr elongated: sleevel2, conventionally made of nickel, or the like, and havingareduced portion l3; the lowerendof which .terminates in substantially the same horizontal plane .as the lower end of aperture!) (ortheupperedgeof the 4 t H-shaped aperture in block 2), said portion being provided with a highly electron-emissive coating 14, for example, of the well-known alkaline-earth metal-oxide type.

In order to support a lead-in conductor 15 centrally with respect to sleeve 12, said sleeve has, at. its upper end,.. a ferrule lfi 'closed by a glass bead sealll through" which said conductor passes. The inner (lower) end of said conductor I5 is connected to the upper end of a heating filament l8, which is substantially coextensive withth'e: cathode coating [4 and the opposite (lower) end of which is electrically connected tothe. cathode sleeve l2.

Current may be conveyed to the filament [8 by; connecting the upper end of the lead-in conductor l5, through a conductor 19, to a positive-tap on a suitable source 2!) of electromotive force; the negative terminal of said source being connected, through a conductor 2!, to the sleeve [2.

The positive. terminal of. the: source 20. may be grounded, as shown; as: maybe" the" block; 2, whereby'a" potential difference is established be tween the cathode structure 1 l. andf'the' block or Waveguide 2.

In order. to insulate and sup-port tli'e'c'athode structure 5 i fromithe 'blo'ck"2', I provide the sleeve l2 with a cup-like bushing; 22" whicli'isfused into the upper end .of a'glass insulatingmember 23, the lower end. of saidinsulating'member'hav ing a tubular bushing 24' fused' therein "which,

in turn,. is secured in a: recess formed in the upperend of'a pole'piece 25.

The'pole piece '25 ishermeticaHy' sealed; as :at 26, into a suitablerecess provided in the'upper wall ofib1ock'2,.andisprovidedwitha bore 21,. of substantially'the same diameter :as. aperture 9 andcoaxial therewith, through Whichthe cathode structure! I 'may'enter the device;-

A cooperating pole. piece 28 is hermetically sealed; as at 29, into aisuit'able recess provided in the lower wall. of block 2", and is providedwith a bore 30; of'substantialiy'"the same diameter as aperture [6 and coaxial therewith. Pole piece 28 and'pole piece. 25 are fixed, for example; at theends ofa suitable source of magnet'omotive force (not shown), so that a magnetic'fiel'di's established, betweensaidpole pieces; in -a-direction transversely offwaveguide' 2, substantially parallel. to the crossebarportion .of the H, or substantially vertically in Figs. I and2'. The inner ends of pole pieces 25 andZB'have a reduced cross-section, as shown,,in order to increase the flux densityv of said magnetic. field;

Ahollo open-ended cylindricall electrode element 3Lis mounted axially in aperture'i), said element surroundingcathode' l3 and"being"co'ncentric. therewith. and with said aperture. Element 3| preferably has an. axial (vertical) length equalto the distancebetween. the lower edgeof pole piece 25and the-upper edge oi'iithe HI-Tshape'd aperture. in. block 2,. .so that I the. lower,v face. of said element lies ina common..horizontal.v plane withv the lower. face of cathode. l3. and. the. upper edge otthe- H-shaped, aperture...

The-inner. diameter of" electrodeelement 3| is made equal to the internal. dimension of .waveguide 2 between faces 2a andZb v(measured horizontally, i1o.Fig...1),v or,.in other words, is.made equal to the width of the crossebar portion of the H,

Electrode 31' is secured to a. still" supportwire fat-10,001

hermetically sealed to block 2, a horizontal bore 35 being provided in the upper wall of block 2 for the passage of said wire 32 to aperture 9 and electrode 3|. The electrode 3| is connected, by wire 32and a conductor 36, to an intermediate tap on the source 2!], this connection raising electrode 3| to a potential which is positive with respect to cathode l3 but negative with respect to ground or the potential of block 2.

A disk-shaped repeller electrode 37 is positioned axially of aperture l0, and has its upper surface lying in the same horizontal plane with the lower edge of the H-shaped aperture; this electrode may have a diameter substantially equal to the horizontal distancebetween faces 2a and 2b, or said diameter may be somewhat larger than said distance. In order to insulate and support electrode 31 from the block 2, and also to allow electrical connection to be made tosaid electrode,

I attach a stifi support wire 38 to said electrode,

said wire 38 passing axially downwardly through bore 3!). Wire 38 is provided with a cup-like bushing 39 which is fused into the lower end of a glass insulating member 40, the upper end of said insulating member having a tubular bushing 4| fused, therein which, in turn, is secured in a recess formed in the lower end of pole piece 28.

Electrode 31 is connected, by wire 38 and a conductor 42, to an adjustable tap 43 on the source 20, by means of which connection a potential is applied to said electrode 31, this potential being on the order of that applied to cathode l3 but being capable of variation therefrom for proper operation of the device, as described below.

The electron-discharge device of this invention is designed to amplify microwaves propagating in a waveguide system, and is adapted to be coupled directly into such a system by means of windows 6 and 8, with the input to the device coupling through window 6 and the amplified output therefrom coupling through window 8, or vice versa. In either event, it is intended that the microwave energy propagate axially through waveguides 2, 3, and 4, which means from right to left or from left to right in Fig.2.

The microwave amplifier of this invention is intended to be used with TEo,1 waves, the electric field lines of which extendtransversely to the waveguide walls, specifically in a horizontal direction in Fig. 1 or in a direction perpendicular to the paper in Fig. 2. In the constricted portion of the H-shaped waveguide 2, that is, in the portion thereof defined or delimited by faces 2a and 2b, the electric field lines of such a wave extend horizontally, transversely between faces 2a and 2b, perpendicularly to both faces. In the rectangular waveguide sections 3 and 4, the electric field lines of the wave extend perpendicularly to the paper in Fig. 2, or in a direction perpendicular to the longer cross-sectional dimension of said waveguide sections.

When heater I3 is energized by source 29, a copious supply of electrons is thermionically emitted from the cathode coating 4, these electrons originally proceeding radially outwardly toward electrode 3| because of the positive potential thereon with respect to the cathode. As described above, pole pieces 25 and 28' produce a magnetic field transversely of waveguide 2 (and also transversely to this original. radial motion), in a substantially vertical direction. Due to the transverse motion of each-electron across this magnetic field, each electron is caused to move in an orbital substantially circular path, at an diameter of this cloud will be substantially equal to the inner diameter of electrode 3| (and therefore also substantially equal to the horizontal distance between faces 2a and 2b), since if the diameter of the cloud tended to. increase beyond this value, the outer fringe .of electrons would strike, and be captured by, electrode 3|;

The above discussion has neglected the effect of the potential applied to waveguide 2. How- 'ever, due to the presence of this structure which is biased positively with respect to cathode l3, each electron of the cloud is caused to move or drift downwardly, transversely of waveguide 2, in a direction along the cross-bar portion of the H, to, into, and through said cross-bar or constricted portion of said waveguide 2; the linear velocity of the electrons, or the velocity of this drift, being determined by the potential of waveguide 2. Each electron of the cloud, as a result of its circular orbital motion combined with its drift or motion along the cross-bar portion of the H, follows a substantially helical path with respect to waveguide 2; all of the electrons taken together can be pictured as a hollow substantially cylindrical cloud which is rotating at a prede 'termined angular velocity and is moving down- .wardly along the cross-bar portion of the guide at a predetermined linear velocity.

The strength of the magnetic field in the dcvice of this invention has such a value, and the potential on waveguide 2 has such a value, that the electron angular velocity (determined by the strength of the magnetic field) and the electron linear velocity (determined by the potential on waveguide 2) are made such that the electrons of the cloud move in synchronism with an angular phase velocity of the wave. As a direct result of this synchronism, the electrons of the cloud react with the electromagnetic wave propagating axially through waveguide 2, to interchange energy therewith.

As described above, in a waveguide amplifier excited with a TE mode wave, through which electrons are moving transversely along a nonlinear path in phase synchronism with the wave.

energy is abstracted from, or imparted to, the orbital motion of the electrons, by the wave, in the first case decreasing the orbital radii of the electrons, and in the second case increasing the orbital radii of the electrons. Due to the fact that the cloud of electrons is solid or is a complete circle (the electrons are emitted from the cathode at all times, and not only at instants when the electrons if emitted would have a desired phase relative to the wave), there would be substantially as many electrons abstracting energy from the wave at any instant on one side of the circle as there would be imparting energy thereto on the other. Therefore, in order to increase the net energy level of the Wave, itis necessary to eifectively remove from the wave:- guide the electrons of such phase relative to the wave as to be capable of abstracting or absorbingenergy therefrom, leaving eii'ective only those ant/opts 'whichareo: such phase; relativeto. the waveas apable Of impartin energy 1 0 said-wave.-

Th sis done n; the followin way:

:It-will be-recalledthat the electrons whi h ab -sorb ener y from the wave have their, orbital radii increased, and that the outer diameter of the electron cloud, is substantially equal to the horizontal distance between waveguide walls 2a and 2?). As the cloud of electrons proceeds down wardly between waveguide walls 2a andzb in ;a synchronous fashion, those electrons of the "cloud which; absorb energy from the wave have theradiiof their orbits increased and, since the distancebetween walls ,zawanduzb is such thatch-y increase in the radius of the cloudv causes the outer electrons to strike said wall the wave :theposihve; potential on said walls, thereby eficctively r, ring-these electrons (ii-unfavorable phasef roin he interior: of. the waveguide 2;. or removing them: fr m. ener y-absorbing relation tothewave- Theenersv imoantinc' elec r ns-give up ner y to, the wave; resulting in a net increase in. the ener y level of; or amplification of, the wave; this givingup of ener y by the electrons causes their orbital radilito decrease.

As. the cloud: of electrons. proceeds downwardly, below. the lower end of the cross-bar-por- :tion of the H,:it approaches the, zone of the repeller, electrode 31, which-is-at the opposite side of: the waveguide 2 from the electroninjecting means 13,; 314, etc. Electrode .37 -is at a potential on-the. order ofgt-hat, of the, cathode, and acts as asnegative electrode to reverse the direction of movement. of the electron, cloud, thereby causing the same to move upwardly toward the cathode 13; By proper adjustment of the potential on electrode 31, the electrons can be made to move upwardly transversely of waveguide 2 in phase :synchronism with the wave, and with the proper {phase relative, to the wave as to impart energy thereto. Thus, by causing each electron to traverse at least two energy-imparting paths through the device, a larger proportion of its total available energy is abstracted by the wave from each electron, thus making the device as a wholemoreefiicient.

Due to the fact that the device has no resonant cavities or other tuned elements, it has a rather broad frequency-response band.

It should be brought out why it is preferable to'use an H-shaped waveguide for the energyinte-rchanging waveguide section 2. As is known, the cutoff Wavelength for a TEo,1 mode Wave in a rectangular waveguide is twice the larger internal dimension of the guide, where the electric field lines of the wave are perpendicular to the longer side-of said guide. The cutoff Wave- "length for the same type of wave in anH-shaped guide, on the other hand, is only very indirectly dependent on. the height of sucha guide, so that. for the same cutoff wavelength, an -H -shaped waveguide can have a substantially smaller in ternal total height than a rectangular guide. Height, here, refers to the vertical dimension in Figs. 1 and 2. Since theheight of waveguide section 2 determines the length of the air gap between pole pieces 25 and 28, this means a shorter air gap is possible with an H-shaped guide than with a rectangular guide having; the same cutoff wavelength. It is desirable to do: crease the length of the air gap in the magnetic circuit-as much as possible, in order to decrease the; totarreluctanceott mak-ing it easier, to achieve therequired mag. ti

field strength.

Anotherreason for usin H s aped, wave.- guide is. in order to; easily obtain the required small horizontal internal dimension of the waveguidei, so as. to effectively eliminate from the waveguide those electrons" whose; phase is 1111;- favorable for wave amplification. This required small -dimension; can be obtained readily by providing a constricted portion, in an H-shaped waveguldeyfa't, the Same; time, this constriction act aI-lvc HSesan;increase in he. cutoff. wavelength of the-guldelwhiehis to; be desired.

. -01 coursaitisrto beaunderstoodhat this inventionis. not limited. to: the particular details esdesc ibed abo :as-manvcquivalentswill susr estlth mselveszz ;-thoserslsill d in: he art, It is acoordinelvrdesiredthat the appended claimsbe given a: broad interpretation commen urate; with the-scope. crawls-invention within the art.

What is claimed-is: i

com inati ns.- wa-veguide throughwhich anelectromagnetic wave may-be propagated, said waveguide havingaportion of constricted ore section, means; adjacent. said waveguide, for injecting a substantially uniformly cylindrical cloud of electrons into said constricted portion, the. outer diameter oi;.,said.. cloud being substantially equal; to the: internal dimension of said waveguide at lsaidconstrictedportion, and means adjacent said waveguide for applying aforce to move the electrons-of said cloud in a direction having-a componenttangent to the circumference of a cross-seotionzofi saidcylindrical cloud;

2. In combinations waveguide through which an electromagnetic wave. may be. axially propagated,.said;waveguide'having a portion of com stricted cross-section, means adjacent said waveguide for injecting a substantially cylindrical cloud ofelectrons-transversely of said guide into said constricted portion, the .outer diameter of said cloud beingy'substantially equal to the in"- ternal dimension. of said. waveguide at said. constrlcted portion, and means adjacent said waveguide for applyingv a. force tormove the electrons of said-ioloud ina directlonhaving a component 7 tangent: to the. circumference of a cross-section .of said cylindrical cloud.

3. In combination, a waveguide through which an electromagnetic wave may be axially propagated, said waveguide having a portion of constricted cross-section, the electric field lines of the wave extending"transversely to the waveguide walls defining said'constricted portion, means ad'- j'acent said waveguide for injecting a substantially cylindrical cloud of electrons transversely of said guide into saidconstricted" porticn, the

outer diameter of said cloud being substantially equal to the internal dimension of saidwaveguide at said constricted portion, and means. adjacent said waveguide for app'lyin'g a force to move the "electronsof saidcloud'in a direction having a component t'ange'ntto the circumference of a he-imagnetic-olrcuit;thus

trons of said cloud in a direction having a component tangent to .the circumference of a crosssection of said cylindrical cloud.

5. In combination, a waveguide through which an electromagnetic wave may be propagated, means at one side of said waveguide for injecting an electron thereinto and for moving it in a first direction transversely thereacross toward the opposite side of said guide, means adjacent said waveguide for applying a force to move said electron in a second direction perpendicular to said first direction, means adjacent said waveguide for applying a force to move said electron in a third direction having a component perpendicular to both said first and second directions, and means at the opposite side of said waveguide for reversing said first direction of movement of said electron to cause it to move toward said one side.

6. In combination, a waveguide through which an electromagnetic wave may be propagated, said waveguide having a portion of constricted cross-section, means at one side of said waveguide for injecting a substantially cylindrical cloud of electrons thereinto and for moving the entire cloud transversely thereacross in a first direction through said constricted portion toward the opposite side of said guide, the outer diameter of said cloud being originally substantially equal to the internal dimension of said waveguide at said constricted portion, means adjacent said waveguide for applying a force to move the electrons of said cloud in a direction having a component tangent to the circumference of a cross-section of said cylindrical cloud, and means at the opposite side of said waveguide for reversing said first direction of movement of said cloud to cause it to move toward said one side.

7. In combination, a waveguide through which an electromagnetic wave may be propagated, said waveguide having an H-shaped cross-section, means at one side of said waveguide for injecting a substantially cylindrical cloud of electrons thereinto in a first direction along the cross-bar portion of said waveguide and for moving the entire cloud across said guide toward the opposite side thereof, the outer diameter of said cloud being originally substantially equal to the width of the cross-bar portion of said guide, means adjacent said waveguide for applying a force to move the electrons of said cloud in a direction having a component tangent to the circumference of a cross-section of said cylindrical cloud, and 'meansat the opposite side of said waveguide for reversing said first direction of movement of said cloud to cause it to move toward said one side.

8. In combination, a waveguide through which an electromagnetic wave may be propagated, said waveguide having a portion of constricted crosssection, means adjacent said waveguide for injecting a substantially cylindrical cloud of electrons into said constricted portion, the outer diameter of said cloud being substantially equal to the internal dimension of said waveguide at said constricted portion, and means for applying force to move the electrons of said cloud along substantially helical paths with respect to said waveguide at angular and linear velocities at which the electrons move in synchronism with a chosen angular phase velocity of the wave.

9. In combination, a waveguide through which an electromagnetic wave may be axially propagated, said waveguide having a portion of constricted cross-section, the electric field lines of the wave extending transversely to the waveguide walls defining said constricted portion,

means adjacent said waveguide for injecting a substantially cylindrical cloud of electrons transversely of said guide into said constricted portion, the outer diameter of said cloud being substantially equal to the internal dimension of said waveguide at said constricted portion, and means for applying force to move the electrons of said cloud along substantially helical paths with respect to said waveguide at angular and linear telocities at which the electrons move in synchronism with an angular phase velocity of the wave. a, l

10. In combination, a waveguide through which an electromagnetic wave may be propagated, said waveguide having an H-shaped cross-section,

means adjacent said waveguide for injecting a substantially cylindrical cloud of electrons into said waveguide along the cross-bar portion thereof, the outer diameter of said cloud being sub stantially equal to the width of the cross-bar portion of said guide, and means for applying force to move the electrons of said cloud along sub-.

stantially helical paths with respect to said waveguide at angular and linear velocities at which the electrons move insynchronism with a chosen angular phase velocity of the wave.

11. In combination, a waveguide through which an electromagnetic wave may be propagated, means at one side of said waveguide for in ecting an electron thereinto and for moving it transversely thereacross toward the opposite side of said guide, means for rotating said electron in addition to its said transverse motion so that it moves in a substantially helical path with respect .to said waveguide at angular and linear velocities at which said electron moves in synchronism with a, chosen angular phase velocity of the wave, and means at the opposite side of said waveguide for reversing the transverse direction of movement of said electron to cause it to move toward said one side. i

12. In combination, a waveguide through which an electromagnetic wave may be propagated, said Waveguide having a portion of constricted cross section, means at one side of said waveguide for injecting a substantially cylindrical cloud of electrons thereinto and for moving it transversely thereacross through said constricted portion toward the opposite side of said guide, the outer diameter of said cloud being originally substantially equal to the internal dimension of said Waveguide'at said constricted portion, means for rotating the electrons of said cloud in addition to thesaid transverse motionthereof so that said electrons move in substantially helical paths with respect to said waveguide at angular and linear velocities at which the electrons move in synchronism with a, chosen angular phase velocity of the wave, and means at the opposite side of said waveguide for reversing the direction of movement of said cloud to cause it to move toward said one side.

13. In combination, a waveguide through which an electromagnetic wave may be propagated, said waveguide having an H-shaped cross-section, means at one side of said waveguide for injecting a substantially cylindrical cloud of electrons thereinto in a direction along the cross-bar portion of said waveguide and for moving it transversely across said guide toward the opposite side thereof, the outer diameter of said cloud being originally substantially equal to the width of the cross-bar portion of said guide, means for rotating the electrons of said cloud in addition to the said transverse motion thereof so that said elec-.

' from energyeabsorbing.relation to the wave trons move in substantially helical -paths with respect to said waveguide .at angulargand linear velocities at whichothe electrons move in syn,- chronism with a chosen angular phase velocity of the wave, and meansat the opposite sidelof said waveguide for reversing the direction of movement of said cloud to cause it .to move toward said one side. l 1

114. A microwave amplifier, comprising a waveguide through which an electromagnetic wave may be propagated, said-wayeguide having a,,p or tion of constricted cross-section, means adjacent said waveguide ioriniectinga substantially cylindrical cloud ofeelectrons into. said constricted portion, the outer diameter ,oisaid clo.11d,hein originally substantially .equal .to the internal dimension of said Waveguide at said constricted portion, andmeansfor movingthe elQQtlQH o said cloud along substantially helical orbital paths with respect to said waveguide at angular and linear velocitiesat which the electrons move in synchronism with a, chosen angular phase velocity of the wave, the electrons. t ebyreacting with the .Wave to mterchan eenorey therewith, the electrons of suchphase relative to the wave as to becapableof absorbing energy therefrom by such reaction havinglth ii of their r sr no a d so that th y 5th the wa su d wa ls finin saidcon tricted port on an m a s onnected to wsaid'wavosui t t remo e electrons which strike said Wa ls from ,Stti 9 91 and hence from energyrlahsorbinsrllatiQn F9 1 wave. p

15. A microwave amplifier, ,comprifiiil Q WW6" guide through which an electromagnetic wave y b p pa ated saidvta esulds htW' i H s ap cro n q means adl qentsa d guide for injectin .a substantiall oy iiidriqe cloudof electronsinto said waveguide along th 01105574031 portion thereof, t e .oute ha 40 said cloud being originally substantially equal to the widthoflthe cross-harpor io -pi ai and means for moving the ,ele along'substantially helical orb spect tosaid waveguide a an ula velocities at which .the electrons move in syr chronism with .;a;0h0$811 an ular hase. te g iy of the wave, theelectrohstherebv re ct n with the wave to interchange energy-ti; w th, the electrons of suchlphaserelative to thevga to be capable forabsorbingte sl l .thersitom such reaction having the radiiloftheirorbits in; creased so that they strike the wavegui at the cross-bar portion ..of.,saldpglli.dt,.? ld in? connected to said waveguide to remove electrons Which'strike said wallsrfrom saidcl ud and .192%? 16. A microwave amplifier, comprising a waveguide through which an electromagnetic wave may be propagated, said waveguideehaving 1a portion of constricted crossesectiom means 1.31 one side of said waveguide for injecting galsulostanr tially cylindrical cloud of electrons thereinto and for moving it transversely thereacross through said constricted portion toward the opposite side of said guide, the outer diameter of'said cloud being originally substantially ;equal to the-in ternal dimension of :said waveguide at lsaid. con-1;

stricted portion, means for-rotating the electrons of said cloud in addition to .the said transverse motion thereof so that said electrons move iILSUbz. stantially helical orbital paths :with respectto. said waveguide at angular. and linear velocities at: which the electrons movein synchronismwitha chosen angular phase ,velocity ofthe wave, the

electrons thereby reacting with the wave to intere change energy therewith, the electrons of, such. phase relative to the wave as to, be capable of, absorbing. energy therefrom by such reaction.

having the radii of their orbitsxincroased sou-that they strike the waveguide :walls defining said constricted portion andare-thereby remoyedirom 1 energy-absorbing relation-tothe wave. and means at the opposite side of said'waveguide for rev rse,

ing the direction of movement of said cloud-to cause it to move towardsaid one'side 17. A microwave amplifier, comprising, a waveguide through which an electromagnetic wave m y e pr p ated-said waveguide havinean' H- shaped crosssection; means at one sideof'said,

waveguide for injecting a substantia y y indrica cloud of electrons thereinto in a direction-alone the crossebar portionof said waveguide andior movin it tra sve se a oss sa d uid towardthe opposite side thereof.- the outer diameter 9? said cloud bein originally subst ntially-edual t oi s d uide,

the width of the cross-bar por i meansfor rotating theielectronspf-said cloud in addition to the said transver e. mo i n he Oi so that said electronsmove insubstantially holi;

cal orbital paths with respectto, s ai d waveguide 1 at angular and linear velocities at Yllliflh 131 6 trons move in synchronism witha chosen angu- I lar phase v ityofthe wave, the ele trons th reby'reactin wi h he wave. to. interchan ener therewith, the electrons of such phase relative to'the wave as to-becapable o -.ab 7h ne energ therefrom by such-reaotion having the radii or their orbits "mcreajsed so that they strike the waveguide walls atthe'cross har portion 0f said guide and are thereby removed irom energy,- abs rb n relat on to. thewwave a d means at e opposite sideof-said waveguide ,for reversing the I direction of movernontof -s aidcl oudt o-cause it to move toward said one side.

' P-DEEBY- The following references are of'record in the file of'this patent:

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