US2489298A - Velocity modulation electron discharge device - Google Patents

Description

No 1949 J. M. LAFFERTY 2,439,298

VELOCITY MODULATION ELECTRON DISCHARGE DEVICE Filed Nov. 16, 1946 Inventor:

16 James M. Laffer-ty,

42 1,: y 43' g/ His Attorney.

Patented Nov. 29, 1949 James MLLafferty, Schenectady, N. Y., assignortoiGeneral'Electric c mpany, a corporation of ApplicationNovemberalfi, 1946-,SerialNo. 710,336

3 Claims. (Cl. 250'27.5')"

This invention pertains to. electron" discharge devices, suchas, oscillators, amplifiers, or the like, employing a velocity modulated .beam of electrical particles and has forits object the provision of an improvedconstruction capable of substantially greater power output and substantially higher frequency than devices of the type hitherto known in theart.

For various usages in the high frequency electrical arts, such as-for the purpose of generating or amplifying high frequency oscillations, there have been. developed, in recent years, numerous electron tube constructions-employing the princiresonator to-- be excited butalso to provide a cathodeconstruction which will permit the use of an active cathode surface of maximum areain order thatthe maximum current density obtainable from such-area will not in itself act to limit the total amount of current in the beam.

In accordance with my invention there may be provided a construction which obviates the aforementioned limitations to a considerable degree.

Generally speaking, the objects of the-invention are accomplished by constructing the discharge devicein such a manner that the geometry of ple of velocity modulation. of an electron beam for example constructions in which a moving electronbeam havinginduced periodic density variations along its length is caused'topass in the vicinity of a resonant circuit element, such as a cavity resonator in. such -manner that the density variations will induce and sustain oscillations in the resonantelement. Such constructions have not been assatisfactory. as could be the. electrodes, the cavities and of the beam is symmetrical with" respect to an extended plane rather than to the axis of-a narrow electron beam as. in the constructions heretofore known. For example, the various; elements of the device may besoconstructedthat the elec tron beam prodesiredfor the aforesaidpurposes principally because the maximum power output and the 4 maximum frequency-obtainable have not alwaysbeen sufiicient to satisfy the progressively increasing demandsgof-the artfor generators and amplifiers of the highestpossiblepower output and highest possible frequency. I have found that any such shortcomings may-be attributed largely to restrictionson-the sizean'd density of the electron beam imposedby the-geometrical configurations of the various electrodesand res-.

duced' is in the shape of a flat wedge or sheet having considerable planar area with the resonant"cav ities themselves positioned on opposite sides .of the planeofthe beam. Such geometry permits of the use ofan electron beam having considerablygreater total current because the beam is extended over a considerable area. At thefsarn'e time it permits the use of a cathode of extended active surface area corresponding to the cross section of the wedge shaped electron beam.

Thefeatures of the" invention desired to be protected are set forth in the appended claims.

" The invention itself together with further objects onantcircuits-heretoforeemployed For example,

in the. constructions heretofore common; in the art, an electron beam of generally circular cross section emanates from a cathode of similarcross section and passes-axially through toroidal cavity resonators forming the resonant "circuit element of the device, theconstruction therefore being symmetrical with respect to the axis of the electron beam. sincegfor agiven'electron beam voltage, the amount of power whichcan be'ob tained from the'device'ls limitedby'the amount of electron beam current which can be passed through the'cavity resonator; and" since that current is in turn limitedbyth'e'maximum current density which may be" derived 'from the surface of the cathode used in the electron gun from which the beam emanates, such axially and advantages thereof -may be best understood by reference to the following specification when takenin connection with the accompanying drawingin which Fig. 1 is a schematic illustration ofthe construction heretofore common in the art; Fig.. 2 represents .in cross section 7 an electrical discharge device embodying the principles of the invention; Fig. 3 represents in cross section a view ofithe device taken along the line 3-3 of Fig.

2; while Fig. 4 represents-a View of the device ofFigJZ'looking from the outputconnections into thelcavity resonatorsection of the device.

In'Figrl thereis shown for purposes of illustratiofi a velocity 'modulated electron discharge device of the reflex type which may include withinan evacuatedenvelope I, a cathode -2 having the" usual disk shaped active surface, a cylindrical focusingelectrode 3, a cavity resonso-ator'in the formbf 'a toroidal cavity 4 having a symmetrical arrangements impose geometric" limitations on thenet power output; Therefore;- it becomes desirable notonlyto provide a cavity construction which will permit a much greater amount ofelectron-curiient to flow past the'cav'ty central aperture there'through; a second cylindrical focusingfelectrode 5; and a reflecting anode 6. As is well understood'inthe art, a narrow electron beam of circular"crosssection may be caused to pass from thecathode it through the O electrode 3, the cavity 4, the second focusing electrode whereupon it is reflected by the anode 6 back through the central aperture in the cavity 4, whereupon it will excite resonant oscillations within the cavity 5 It will be understood, of course, that periodic density variation lengthwise of the beam will be induced in the beam after its first passage through the cavity 4 and that such density variation will sustain oscillations within the cavity 4 during the return of the beam to the cavity on its reversed motion. To eifect such behavior appropriate electrostatic potentials may be applied to the various electrodes by any suitable means such as the battery 'I which, by means of the connections indicated, imposes with respect to the cathode a high positive potential on the cavity 4, a negative potential on the focusing electrode 3, a negative or slightly positive potential on the focusing electrode 5 and finally a negative potential on the reflecting anode 6.

It will be apparent that all of the various electrode elements and the cavity 4 are symmetrical about the axis of the electron beam and concentric therewith. Under such circumstances the amount of power which may be derived from the cavity 4 will be dependent upon the total amount of electron current which can be passed through its central aperture by the beam and, moreover, the total amount of current which can be gotten into the beam will be limited by the maximum current density obtainable from the active surface of the cathode 2. It will be understood that these limiting conditions are equally applicable to velocity modulation tubes of other than the reflex modulation type, for

example those in which the density variations of the electron beam induce oscillations in a second cavity resonator similar to resonator 4 but positioned farther along the beam path.

Although it will be understood that the principles of the invention are applicable to all types of velocity modulation discharge devices, there is shown in Figs. 2 and 3, as one illustration of the inventive principles, an electron discharge device of the velocity modulation type employing reflex principles. The device shown may comprise generally a preferably metallic hermetically sealed envelope 8 in the form of a parallelepiped or other geometrical shape having considerable extension in one plane such as the plane of Fig. 3. Within the envelope 8 there is provided a cathode 9, an accelerator anode structure comprisin the symmetrically positioned blocks I0 and II provided with a focusing grid comprising parallel Wires I2, a cavity resonator structure comprising the blocks I3 and I4 mounted integrally within the corresponding blocks of the accelerator electrode and having cavities I5 and I6 formed therein, and a reflecting electrode I'I. As indicated more clearly in Fig. 3 all of these elements Will have considerable extension in the direction perpendicular to the plane of Fig. 2, for example they will be elongated to extend completely across the width of the envelope 8.

The cathode 9 may comprise any suitable structure which presents to the accelerator anode structure a concave cylindrical sector portion I8 capable of focusing electrons emanating from a thermionically active coating on the surface of portion I8 into the accelerator anode slot formed by the opposin surfaces of blocks I6 and H. For example, it may comprise the box-like structure I9 having the concave cylindrical sector portion I8 as an end Wall facing the accelerator anode structure. The surface of portion I3 may be coated with any of the suitable thermionically emissive substances known in the art. Any suitable means for raising that surface to an electronically emissive temperature may be provided such as the heater wires 20 embedded within a ceramic or other insulating material 2| Within the interior of the box-like structure I 9 of the cathode. Suitable means for energizing the said heater wires may be provided such as a battery 22 connected to the heater by the externally accessible leads 23 and 24 extending through and insulated from the envelope by hermetic sealing beads 25 and 26 of glass or like material. The cathode may be supported in insulating relationship to the envelope 8 by any suitable means such as the insulating wall 27 afiixed to the envelope 8 by means of the metallic clamps 28 spot welded or otherwise aiiixed to envelope 8. The cathode 9 may be supported within suitable slots in the insulating wall 2'! and rigidly aflixed thereto by metallic clamps 29 spot welded or otherwise affixed to structure I9.

The blocks ID and I I comprising the accelerator anode structure may be directly affixed to the wall of envelope 8 in conducting relationship therewith by any suitable means such as by brazing or welding thereto. Since the major portion of the energy losses dissipated as heat by the device is dissipated in these accelerator anode blocks and the cavity blocks I3 and. I4, the construction indicated is particularly advantageous in that heat may be directly conducted to the metallic envelope 8 and thereby dissipated externally in order that the electrode structure may not operate at too high a temperature. The focusing grid wires I2 may each be conductively affixed at their opposite ends to one of the anode blocks I0 and II and formed in a generally arcuate shape conforming closely to and generally concentric with the concave shape of the cathode. In order to provide optimum electron beam focusing effects by the grid Wires, it is preferable that the spacing between Wires I2 be small in relation to the distance from the grid wires to the cathode surface. For example, the distance between any two wires I2 is preferably less than one half the distance from those wires to the cathode surface. While these grid wires are indicated as preferably being parallel to each other in order that parallel interstitial spaces may be presented to the electron beam, it will be understood that this grid structure may be also formed of a mesh of mutually perpendicular wires in the manner'of grid constructions known in the art. The dimensions of the interstitial space should however, be small by comparison with the distance from the grid to the cathode for optimum focusing effects. The opposed surfaces of the anode blocks I0 and II will preferably be formed in such manner as to present a generally wedge shaped opening between the blocks formed by the opposing surfaces 30 and 3!. As is well understood in the art appropriate shaping of these surfaces as well as the concave surface of the cathode Will result in desired shaping of electron beam configuration.

The cavity blocks I3 and I4 may :be formed by any construction which presents cavities of the desired configuration necessary .to oscillate :at the desired frequencies. For example, they are shown as comprising blocks having cavities of semi-circular cross section extending laterally to the envelope and having laterally extending d gaps 32 and 33 j-uxtaposed to the electron beam hereby forming 'enirfgQfor communication 3 be eenfthespace in the cavities l5 and I6 and ,the regions ofthe electron beam. If desired such cavity constructions may beformed by laminated stamped sheets each having the desired cavity ha .The reflecting anode ll may comprise any suitable formwhich presents a concave surface 134 adapted to reflect and focus the electron beam 'fbaclr into thevi'cinity of the cavity gaps 32 and 1331 For example,.fit is shown as comprising a :bar tendinglaterally'to the envelope and having cylindrical concave surface formed in the side resented to thecavityresonators. ,That elecode or anodemay be supported in insulating lationship tofitne envelope 8 by. any suitable "means such as the rod 35 welded thereto and extendin .throughsthe glass sealing head 36 in the envelope wall.

It will be apparentto those skilled in the art that when suitable potentials corresponding to those imposed on corresponding electrodes of velocity modulation devices heretofore known are applied to the various electrodes described above, a thin substantially wedge shaped electron beam having substantial extended area in a direction transverse to the direction of motion of its electron particles will be formed along a path extending from the cathode through the opening in the anode structure and past the cavities toward the reflecting anode. Thereupon it Will be reflect'ed back into the vicinity of the cavity along its entire width. B means of reflex velocity modulation principles, oscillations :will thereby be induced in the cavity blocks. For the *purpose of applying those potentials any suitable means may be employed such as the battery 31 which imposes with respect to the cathode, a relatively high positive voltage upon the accelerating anode structure and a negative voltage on the reflecting anode.

For the purpose of extracting useful energy from the cavities or for the purpose of introducing energy for amplification or like urposes, any

suitable means may be provided. For example, suitable coupling loops may be inserted within the cavity and attached to appropriate external coupling lines. Alternatively, a wave guide may be coupled to the cavities through an iris or slot formed in the wall of the envelope adjacent; to one end of the cavities. Such a means is shown for example in Fig. 3 and comprises a cylindrical wave guide or cavity resonator 3B hermetically attached to the external surface of the wall of the envelope 8 which has an appropriate slot-like opening 39 exposing the ends of the cavities to external view as indicated in Fig. 4. A suitable coupling loop 40 connected to the closed distal end of the cylindrical wave guide 38 and to the inner conductor M of a coaXial transmission line comprising the inner conductor 4| and the outer conductor 42 may be provided for delivering energy derived from the wave guide to suitable external utiliziation circuits not shown. For the purpose of maintaining hermetic sealing of the discharge device at these output connections, the coaxial transmission line may be hermetically sealed :by a head 43 of glass or like vitreous material sealed across the outer conductor 42.

The resonant frequency of the cavities may be controlled and tuned by a cylindrical wave guide or cavity resonator 44 of variable length attached to the opposite wall of the envelope and juxtaposed to the other end of the cavities through an, iris or slot.4 5 uilmto the ll of .theen- 'v'eiepe at that so "6. in a manner similar to that offthe slot 39. Thelen'gtl'i of this cylindrical wave gide may befcontrolled' and varied by "means or the""pis'ton;46. In orderto'maintain the hermetic sealing "of the device at this point of connection between the wave guide 54 and the envelopaflthe glass window 41 maybe provided across the cross'section' of the cylindrical wave guide and hermetically sealing the same. It Will be understood that movement 0f the piston 46 in either direction[will result in a corresponding "change in the; inductive or capacitative properties ofthe cavities and thereby result in a desired change in he ueney. "Alternatively, the cavities "may be provided with a tuning system similar to that shown and claimed in my copending application Serial No,] 7 20, 250 filed January 4-, 1947. in the latter casejthe accelerating anode and. resonators will be tormed' by a laminated confstruction in thernannershown in the'mentioned application.

" In order that the device may operate at optimum emciency it is preferable that the "wave guide-like structure formed by cavities l5 and J6 operatehear' itscutofi' wave 'lengthso' that the phase w-ave' lengthalong the longitudinal direction of the structure] is long. Thelength ofthe vities lfi and l6 isthen only a small fraction ""o phase wave length and as a result the high flif requency electric iield across the gaps 32-133 maintains a high percentage of its maximum cavities. For example-if the cavity ection l5'l6 is made 70 electrical degrees in length and sections comprising guides 38-44 are 55 electrical degrees each, the electric field at the ends of the gaps 32 and 33 only drop to 82 per cent of the maximum value at the center.

While I have shown and described a particular embodiment of my invention, it will the obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects 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 electrical discharge device of the reflex velocity modulation type comprising a pair of spaced cavity resonators, an elongated anode structure extending between said resonators, said anode structure having extending therethrough a longitudinally extending cavity resonator symmetrical relative to a longitudinal axis thereof and tuned along with said pair of resonators to the frequency of oscillation of said device, said anode structure also having a transverse passageway with an elongated cross section extending therethrough in a plane perpendicular to the axis of said last-mentioned resonator and communicating with said last-mentioned resonator, and means for directing a relatively wide and thin electron beam through said passageway to excite said resonators at said frequency comprising an elongated cathode and an elongated reflector electrode disposed on opposite sides of said anode structure and disposed substantially in the plane of said passageway.

2. An electrical discharge device of the reflex velocity modulation type comprising a pair of spaced cavity resonators, an elongated anode structure extending between said resonators, said anode structure having extending therethrough "tam at the center along' the entire lengthof the.

a longitudinally extending cavity resonator sym- Jnetrical relative to a longitudinal axis thereof and tuned along with said pair of resonators to the frequency of oscillation of said device, said anode structure also having a transverse passageway with an elongated cross section extend- "ing therethrough in a plane perpendicular to the axis of said last-mentioned resonator and communicating with said last-mentioned resonator, means for directing a relatively wide and thin electron beam through said passageway to excite said resonators at said frequency comprising an elongated cathode and an elongated reflector electrode disposed on opposite sides of said anode structure and disposed substantially in the plane of said passageway, and means for varying the resonant frequency of said cavity resonators comprising a tuning plunger movably mounted in one of said pair of cavity resonators.

3. An electrical discharge device of the reflex velocity modulation type comprising a pair of spaced cavity resonators, an elongated anode structure extending between said resonators, said ;anode structure having extending therethrough ;a longitudinally extending cavity resonator symmetrical relative along with said pair of resonaztors to a longitudinal axis thereof and tuned to (the frequency of oscillation of said device, said \way with an elongated cross section extending itherethrough in a plane perpendicular to the axis (of said last-mentioned resonator and communiecating with said last-mentioned resonator, and

means for directing a relatidelfy wide and thin wanode structure also having a transverse passageelectron beam through said passageway to excite said resonators at said frequency comprising an elongated cathode and an elongated reflector electrode disposed on opposite sides of said anode structure and disposed substantially in the plane of said passageway, the phase wave length of said last-mentioned resonator being of the order of 70 electrical degrees and the phase wave length of each of said pair of resonators being of the order of 55 electrical degrees whereby the high frequency electric field across said last-mentioned resonator where said passageway communicates with said last-mentioned resonator is a high percentage of its maximum value along the length thereof and efficient density modulation of said electron beam is obtained along its entire width.

JAMES M. LAFFERTY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,259,690 Hansen et al Oct. 21, 1941 2,293,151 Linder Aug. 18, 1942 2,410,822 Kenyon Nov. 12, 1946 2,410,863 Broadway et al Nov. 12, 1946 2,413,963 Fiske et a1 Jan. 7, 1947 2,414,785 Harrison et a1 Jan. 21, 1947

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