US2924738A - Electron beam apparatus - Google Patents

Description

9, 1960 M. CHODOROW ELECTRON BEAM APPARATUS Filed Jan. 14, 1954 fIIEI l 2 2 //A r W 7 w e m v FIFE-:3:-

IN VEN TOR. MARI Ml .CHODOEOW ELECTRON BEAM APPARATUS Marvin Chodorow, Menlo Park, Calif.,-assignor to Varian Associates, a corporation of California Application January 14, 1954, Serial No. 404,040 Claims. (Cl.315-3.5)

This invention relates in general to electron beam discharge apparatusand methods and, more particularly, to

novel devices of the slow wave type such as, for example,

of interdigital fins are maintained at difierent relative values of potential.

Another object of the present invention is to provide anovel electron beam device having a slow wave structure which electrostatically focuses the beam, whereby the use of permanent or electromagnets for focusing is either unnecessary or the amount of magnetic field required for focusing is substantially reduced.

1 Still another object of the present invention is to pro- .vide a novel device of the above character having a slow wave structure of thevinterdigital type wherein one set of interdigital fins is structurally difierent from the associated second set of fins to compensate for the alternate changes in beam velocity due to the beam focusing electric field components parallel to the electron beam which are directed in alternately opposite directions between successive pairs of fins.

These and other objects and advantages of the present invention will be more apparent after a perusal of the followingspecification taken in connection with the accompanying drawings, wherein Fig. 1 is a longitudinal sectional view of an electron beam device illustrated as a traveling wave tube amplifier of the interdigital ffin type construction wherein the electron beam passing through the tube is electrostatically focused,

,Fig. 2 is a cross-section view of the traveling wave tube amplifier taken along section line 22 in Fig. 1,

Fig. 3 is a diagrammatic view showing the electric field lines between successive pairs of the interdigital fins of the traveling wave amplifier device shown in Fig. 1, and Fig. 4 is a diagrammatic section view of an embodiment of the pesent invention wherein alternate fins in the interdigital structure are of a different configuration than the fins in the remaining set of interdigital fins to compensate for velocity changes in the beam due to the electric field lines. i

Referring now to Figs. 1 and 2, the traveling wave tube amplifie riwhich embodies the novel interdigital structure ."ofithis invention comprises a main body portion 1 of substantially an elongated U-shape configuration and a top portion 2 alsoof Ushape cross section which is adapted tofitonto the main body portion 1 and form the hollow elongated tubebody, these bodies being of a good con- United States Patent 0 ice ducting metal such as copper or plated with a good conducting metal. Mounted on the right-hand end of the body is a collector assembly which comprises a metallic electron collector 3, an end adapter 4 and an insulating seal 5 as of glass. Secured on the left-hand end of the tube body is a cathode assembly which comprises the gun anode 6, the cathode gun assembly 7 including the cathode button 7', and the insulating mounting seal 3 as of glass.

Secured on the main body portion 1 and extending upwardly within the tube body are a plurality of equally spaced metallic fins or loading members 9. Mounted within the tube body is a substantially U-shaped elongated member or plate 11, the plate being mounted on the main body 1 and insulated therefrom by insulating spacers 12. The plate 11 is spaced from the wall '2 of the body and electrically insulated therefrom by suitable spacers 13 as of ceramic. Mounted on this plate 11 and extending downwardly within the tube are a plurality of equally spaced fins or loading members 14, these fins 14 being so arranged as to form a uniform interdigital structure with the fins 9 along the length of the tube. A small aperture 15 is located in each of the fins 9 and 14, these apertures being in axial alignment with the cathode button 7 and the collector 3 so that a clearpath is provided for the electron beam from the cathode through the interdigital structure to the collector. A substantially L-shaped member 16 is provided on either side of the tube for utilization as a choke.

An input waveguide 17 having an associated window seal 18 is coupled through an aperture in the body portion 1 to the space between the first set of fins 9 and 14 on the left-hand side in Fig. 1. An output waveguide 19 with its associated window seal 21 is coupled through a second aperture in the main body portion 1 to the space between the furthermost set of fins 9 and 14 on the righthand side of the tube. The cathode is connected to a source of potential 22 which places the cathode at a negative potential with respect to the main body of the tube and the collector 3. The insulated plate '11 and associated fins 14 are connected to a source of potential 23 which maintains this plate and fin assembly at a positive potential with respect to the main body portion 1 and associated fins 9.

In operation, a stream of electrons, shown in dot-dash lines in Fig. 1, is emitted from the cathode button 7 and is accelerated by the positive voltage on the gun anode, the stream of electrons being focused into a beam while passing through the aperture in the gun anode 6. The beam of electrons proceeds along the path defined by the apertures 15 in the interdigital structure. The expended beam of electrons is then collected by the positively charged collector electrode 3. The wave energy to be amplified is transmitted into this traveling wave amplifier through the input waveguide 17, the wave energy traveling in a sinuous path along the interdigital structure defined by the fins 9 and 14 such that the wave travels along the tube at the same velocity as the electron beam in a well-known manner and extracts energy from the beam. The amplified wave energy is extracted from this traveling wave tube through the output waveguide 19.

This novel construction of a. slow wave tube is utilized in cooperation with selected electric potentials to electrostatically focus the electron beam so that the beam retains its small cross-section as it proceeds along the length of the tube, thus eliminating the necessity for a magnetic field focusing means such as a permanent magnet or electromagnetic coils. As stated above, the plate 11 and fins 14 are at a potential positive with respect to the niain body portion 1 and fins 9 and thus an electric field is produced between the fins 9 and the fins 14. The electric field pattern set up between the interdigital finswhich would produce the optimum electron beam focusing is shown in partinFig. 3"by the arrowe'd' lines. "The electric field lines are shown in the direction of electron deflection. In the absence of the apertures, the electric field lines"between"thef'fins Wouldbeparallel withthe' axis of the beam and essentially constant across the position of the apertures. With the apertures present the electric field pattern in the beampathhas both longitudinal .and circularly symmetric radial components of elect-ric'field. The'longitudina'l component causes 'the velocity of the electrons in the axial direction to vary. "When theelectron'velocity is smaller than the average, the radial component of electric field produces an inward force, and when the velocity is larger, the radialelectriefielfd produces an outward force. Because o flthe velocity va'riatio'n, however,' the electrons spend more time in the region of inward force and -hence acquire a, net inward momentumfrom the focusingffield. This canlbe used -to"balance"'the outward momentumldue to electronicpulsion forces which co'ntinually act within the beam, and would. cause the beam 'toldiverge if no'focusing forces were. present.

One other effect Which may, in somelrinstances ermilization'ofthe novel electrostatic focusing schemeflgive riseto undesired operation'is that .Ithe electric,.field" between one interdigital 'fin9an'd its immediately preceding associated fin14 is'in .one particular directionwhile the electric field' between "the same interdig-ital'fin 9 and '-the immediately succeeding interdigital fin 1'4isin thejopposite'direction. Thus the'first mentionedfieldis' in'the 'di-re'ction which opposes theielectron flow while theother field is in the direction which; aids: the electrontfiow and therefore the velocity 'ofithe electrons asthey enter -any one interdigital'lfin 9 is less than the velocity when they enter the succeeding interdigit'a-l'fin' 14. Thus, the transit angle through the 'fins 9 is greater than theitransit angle through the fins 14, the cumulative e'ifect of which "may be sufficient to destroythe. required;phase relationship With the radio-frequencytwave To remedythis 'eifectthe novel structure shown in 'Fig."4" maybeutilized Where the thickness ofv the fins 14 is greater .than-thethickness of"thefins"9 sothat the transit 'angles'through the-"fins '9'and' 14 maybe made equal.

interpreted as illustrativeand not in a limiting sense.

What is claimed is:

1. A slow-wave electron beam device of the-type wherein an electromagnetic wave is made to -travel through"-the"device' coupled to'and substantially at'the velocity of an electronbeam thereintsu'ch that an energy exchange occursbetween' the beam" andthe-Wave comprising means 'for producing a beam of electronsdirected through said device, a -'slow-'wave"structure associated with the'beampath comprising an interdigital structure having a first plurality of loading members electrically coupledtogether and a second plurality'of loading memberselectrically coupled together, said'loa'ding members {having apertures'therein aligned with-the beam patln'said loading members "being" interdigitally' ;space'fcl*along the beam path'"whereby a sinuous wave-energy path is formed defined by the loading members for the transmission' of said electromagnetic wave 'in a-sinuous path-directed along and coupled to saidbeam; means'electrically insulating said first pluralityof'loadingymernbers from said second plurality, Land means for applying-"different 'direct current electrical potentials to said-two'pluralities of loading m'emb'erssuch' that electrostatic focusing fields extend between adjacent -loadi-ng meI'n-bers at the; beam ipath apertures'forfocusingthe b'eam.

s same 2. A slow-wave electron beam device of the type wherein an electromagnetic wave is made to travel through the device coupled to and substantially at the velocity of an electron beam therein such that an energy exchange occurs between the beam and the wave comprising means for producing a beam of electrons, a base member having a plurality ,o f equally spaced loading members mounted thereonand'extending inwardly into the oatemplatezposinonedimms ssddz her in apl a ity. o 51 l r pac d st s sts mounted thereonandeiitendin toward thefbase member, said latterloading members be'ing in -interdigital relationp tsaii ten-n teas n members tal jih tth a sinuous wave-energy path isjform ed through the'device defined by the loading--member"s', s'aid loading members each having an aperture therein, the apertures being aligned within the device so as to be aligned with the electron beam path therethrough such that the electron beam {is coupled to the electromagnetic-wave passing along "the W sinuous pa-th for' energy exchange, means -for mounting said top plateon said" base member including insulation {electrically insulating the top plate trom the base member, and[-means-=-for applying different direct current electricalpotentials to said base and top plate wherebyan electrostatic focusing field-may extend betweenadjacent loading members at the beam -path apertures.

' 3. A'slow-wave elect-ron beam device-ofthe type-whereinan electromagnetic wave is made to travel through-eke device; coupled --to--and; substantially at the-.velocity of an electron beam thereinsueh th'atan energy exchange occurs between the beamand the wave-eomprisingmeans for producing a-beam -of-electrons=dire'cted;-through' said de- Vice, a slow-wave structure associated withfth'e beampath comprising a first plurality of loading members electrically coupled together and a secpnd;p1urality of-leading members electrically coupled togethen -the-members;of the two pluralities; being alternatelyspaceda-long-the beam path in interdigital;relationship such that a sinuouswaveene rgy path is formed 'througlithe-device defined by the loading members, said loading m embers having apertures therein 'aligned-with'the beam path, and means electrically insulating saidffirst pluralityof loading members from; said second plurality, a source of electrical potentials m'eans for coupling thefirst and second pluralities of members to s'aid source whereby said first and second pluralitiesareatdifferent relative potentials such 'tha't focusingelectrostatic fields extend between adjacent loading members at the beam path apertures, the dimension of the loading members inthe direction of thebeam path oi Qneplfirality of loading. members being greater'than the ,dimension in :the direction of the beam path of] the loading members ofthe other plurality. i i

V 4,1A slow-wave electron beam device of the typewhere- ,in an electromagnetic wave is made tq-travel through'the .dQYiCQ coupled to and sub V s t a y atith vi l i i' P a electron beam therein such that an energy'exchange occurs ,betwe emthe beam and the wave comprising meansjfor p uc ng a be m pt e sct g sisl r q fi re-u h sa z c a s o -w e ,st ta e t ma e w t 1. 6 l mr c mp i ing-a fir t plu a it 9. ,,lea in membe ss ss tco n t p h ruan l assg a hers. ele trical y,cquulsdt fllq r the membe s h 1 i interdigit l relatio sh p such. t a .v a" m Q J r y pathv orme th ought dqvis fls a ns Wi oadi amem e aid cai i ..-ms be sha in apertures ,lec r cal poten a qf a ti Pluralities o ca ing membersl suc a ha ett9$t focusing fields extend between adjacent loading members at the beam path apertures.

5. A slow-wave electron beam device of the type wherein an electromagnetic wave is made to travel through the device coupled to and substantially at the velocity of an electron beam therein such that an energy exchange occurs between the beam and the wave comprising means for producing a beam of electrons, a base member having a plurality of equally spaced loading members mounted thereon and extending inwardly into the device, a top plate positioned above said base member having a plurality of equally spaced loading members mounted thereon and extending toward the base member, said latter loading members being in interdigital relationship with said former loading members such that a sinuous wave-energy path is formed through the device defined by the loading members, said loading members each having an aperture therein, the apertures being aligned within the device so as to be aligned with the electron beam path therethrough, the dimension in the direction of the beam path of each of said latter loading members being difierent from the like dimension of each of said former loading members, and

means for mounting said top plate on said base member including insulation electrically insulating the top plate from the base member whereby difierent direct current electrical potentials may be applied to said base and top plate such that electrostatic focusing fields extend between adjacent loading members at the beam path apertures.

References Cited in the file of this patent UNITED STATES PATENTS 2,289,756 Clavier July 14, 1942 2,489,082 De Forest Nov. 22, 1949 2,545,595 Alvarez Mar. 20, 1951 2,645,738 Coeterier July 14, 1953 2,653,270 Kompfner Sept. 22, 1953 2,679,615 Bowie May 25, 1954 2,800,606 Ping King Tien et a1 July 23, 1957 2,842,704 Van Iperen July 8, 1958 2,845,571 Kazan July 29, 1958 FOREIGN PATENTS 1,006,336 France J an. 23, 1952 1,034,007 France Apr. 8, 1953

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