US3021447A - Electron tube apparatus - Google Patents

Description

Feb. 13, 1962 Filed Feb. 6, 1953 R. L. JEPSEN ETAL ELECTRON TUBE APPARATUS FIG.2

2 Sheets-Sheet 1 INVENTORS ROBERT L.JEPSEN FREDERICK L.SAL|SBURY CURTIS E. WARD RY M ATTORNEY Feb. 13, 1962 R. L. JEPSE-N ETAL ,ELECTRON TUBE APPARATUS 2 Sheets-Sheet 2 Filed Feb. 6, 1953 FlG.3

M m u m m U MN N V AD B NESR O I .A I T ELW fl .K A LmE TR EF DT BER ORU Y RFC B United States Patent Oilrice 3,021,447 Patented Feb. 13, 1962 3,021,447 ELECTRON TUBE APPARATUS Robert L. Jepsen, Palo Alto, Frederick L. Salisbury, Redwood City, and Curtis E. Ward, Palo Alto, @ahfi, assignors to Varian Associates, San Carlos, Calif a corporation of California Filed Feb. 6, 1953, Ser. No. 335,438 13 Claims. (Cl. 315-5.19)

This invention relates, generally, to electron tube apparatus and the invention has reference, more particularly, to novel apparatus of this type embodying component improvements appl'cable to velocity modulation tubes, traveling wave tubes and other tube types.

Ultra high frequency devices as of the velocity modulation type are being widely used as oscillators, amplifiers, modulators, etc., and heretofore have been delicate tubes assembled from a relatively large number of subassemblies having many small and delicate elements therein. The construction of these known devices has very often required the use of glass for the man body portion and has been such that careful handling and protection from even minor shock have been necessary when using these devices. These devices, because of their construction from multiple subassemblies and the number of elements in each device, have been larger and more cumbersome than necessary for eflicient operation. Present day requirements, especially in the fields wherein the tubes are subjected to rough usage, demand electron devices which will be both compact and extremely rugged While still possessing improved operating characteristics over known devices.

Several difficulties encountered in discharge devices of the electron beam type, such as, for example, klystrons and traveling wave tubes, heretofore employed arise from an interact'on between the electron beam and ions trapped along the path of the beam. These difiiculties may include:

(1) Modulation of output power, frequency, and beam current at the frequency or frequencies of continuous ion oscillation. These frequencies are, typically, in the range of .l megacycle per second to megacycles per second.

(2) Modulation of output power, frequency, and beam current at both (a) ion oscillation frequencies (in the megacycles per second range) and (b) low frequenc'es (typically in the audio frequency range). The low frequency fluctuations are associated with the high frequency ion oscillations.

(3) Changes in output power, frequency, and beam current as the frequency of an applied modulating voltage is varied. These changes occur when the modulating frequency is near one of the frequencies of inc pient ion oscillation. The changes may be abrupt or fluctuating.

As stated above, these difiiculties arise from an interaction between the electron beam and ions trapped along the path of the beam. In reflex klystrons these ions are trapped in the re-entrant tube portion between the accelerator grid and the first resonator grid.

It is, therefore a principal object of this invention to provide a novel electron tube apparatus that is both compact and extremely rugged, while at the same time operably improved over existing electron devices of this type.

Another object of this invention is to provide an electron beam tube which is made up of a relatively few number of small subassemblies securely and compactly assembled together to form a small and rugged structure, each subassembly being made up of a relatively few elements, each rugged in its own right.

Another object of this invention is to provide an electron beam tube having a novel structure located in the electron beam path and associated with a portion of the tube which ordinarily traps positive ions therein, this novel structure substantially reducing the number of ions trapped therein.

A further object of this invention is to provide an electron beam tube wherein one of the walls forming the portion of the tube in the path of the electron beam which normally traps ions is a novel grid structure which permits the escape of the ions from the trap.

A further object of this invention is to provide a novel electron beam gun assembly which is structurally better than conventional gun assemblies in that it is more compact and rigid while at the same time provides the maximum electron emission with relatively lower heater current.

Other objects and advantages will become apparent from perusal of the following specification taken in connection with the accompanying drawings wherein one embodiment of the invention is depicted.

In the drawings,

FIG. 1 is a plan View of a reflex klystron embodying this invention,

FIG. 2 is a longitudinal sectional view of the reflex klystron shown in FIG. 1 showing a novel cathode gun assembly n plan view,

FIG. 3 is a transverse sectional view of the tube in a plane indicated by section line 33 in FIG. 1, the arrows indicating the direction in which the view is taken,

FIG. 4 is a sect'on view of the novel cathode gun assembly shown in FIG. 2,

FIG. 5 is a transverse sectional View of the novel electron beam gun in a plane indicated by section line 55 in FIG. 4, the arrows indicating the direction in which the view is taken, and

FIG. 6 is a longitudinal part sectional view of the reflex klystron in a plane indicated by section line 6-6 in FIG. 1, the arrows indicating the direction in which the view is taken.

Referring to the drawings, the main body 1 of the reflex klystron is a unitary structure of metal such as steel comprising a block 2 having a rectangular shape and having oppositely extending end port ons 3 and 4 cylindrical in shape protruding from the larger sides of the block 2. The body has a multi-diarneter bore ex tending longitudinally through the body and axially aligned therein, the different diameter portions of the bore arranged in pyramided step-like relationship. Located in the wall of one other side of the block is an elongated pan-shaped recess 5 having tapering side walls and a flat bottom surface in which is located an elon gated opening 6 or iris extending into the smaller diameter portion of the bore of the body.

1 A unitary metallic header 7 serves the triple function of providing the mounting support for the accelerating grid 8 and the first resonator grid 9, providing boundary walls for the cavity resonator 10, and forming the reentrant tube 11 of this reflex klystron. This header 7 is ring-shaped with a projecting annular portion 12 and a two-step axially aligned bore therein, this bore forming the re-entrant tube of this klystron. Fixedly mounted as by gold brazing on one side of this header 7 and axially aligned with the bore therethrough is a round honey-cornbed accelerating grid 8. Fixedly mounted as by gold brazing on the opposite side of the header 7 on the projecting annular portion 12 is a round honey-combed copper resonator grid 9, the longitudinal thickness of this resonator grid being of the order ,of .04" thick, or approximately four times the thickness of the accelerating grid 8. This metallic header 7 and copper grids 8 and 9 form one subassembly, this subassembly being slipped into the portion of the body 1 having the. smallheader 14 having anaxiallyaligned bore therein.

second s'ubassembly is placed within the smallest diame-g a '3 estLdiameterat a point adjacent to the iris 6 and secured therein as by silver brazing.

A second round honey-combed resonator grid 13 is mounted as by gold brazing on a cup-shaped met ailklliic the headers, one surface of the header 7 and the annu-. lar' portionlZ thereof, the two resonator grids 9 and 13,

and one surface of the header 14.

The third or reflector "subassembly comprises a shallow cup-shaped metal, such as nickel, reflector 15 which may.

begspotwelded toithe end flange of a conducting collar 16,, this collar in turn encompassingone end of arhollow' conducting post 17,rthe post'beingsecured as by spot-. welding within the collar 16., The reflector mounting 'post 17 is fixedly secured and sealed within themounting cup-18; byva glass-to metaltype seal '19. .A wire reflector lead or terminal 21 extends into the hollow reflector post 17,the;e'nd' of the post being cn'mp'edaround the lead,

thcgjunction being sealed and secured as by silver brazing. T

This reflector subassembly is then mounted within the re-i flectorrendof the unitarytubebody 1,.the outer flange 22 r of ,the mounting cup 181 being fixedly secured Within the largest diameterbore' of the metal body 1 aslby silverbrazing. "A small hole 23in the reflector 15 permitsievacuation of the space within thehollow reflector post 17 during evacuation of the tube. a

a ,The fourth or cathodet subassembly is a novel cathode gun assembly which is extremely rugged and is more compact than heretofore existing gun assemblies.- It should be noted thatthis novel cathode gun assembly is mounted entirely within the small metaltbody or" the tube and. thus reduces thelength of'the tube device by about one-fourth as compared with klystrons having the samesize body l but utilizing conventional beamigun assemblies which protrudefromtthe end ofrthe body 1-.

FIG. 4) having a slightly concave shape and an annular flange 47 encircling the periphery thereof. This cathode button islcoated with a conventional electron emissive oxide, substance 1 and is. mounted on a cathode mounting member 48 made of a strong but poor thermal conducting materialsuchas a metal alloy; This member has a twostephollow' cylindrical-like shape closed at one end 49. The surfacexof the closed end preferably has the same concave'curvature asthevcathode'button. The cathode button is'niounted above this surface as by spotwel ding the inside wall of the cathodebutton flange 4710 the outer upper wall of the mounting member 48. The heater wire-51 is sandwichedrinrthe narrow space between the undertsurface ofv'the' cathode button 46 and the upper; surface of vthe end 49 of the mouting'member 48'. The sandwiched heater .wirer51 extends in a wavy or sinuous fashion to and-fro in this small space, doubling bacleon itselfjto thereby provide aniaximum length of wire under the cathodefbutton asshown in' FIG. 5. derstood that. the heater wire couldbe wound in a flat spiralunder the cathode button or. could assume other configurations. The ends or the heater wireextend down throughthe mounting member through two openings in the'closedtend thereofe A disk-like heat reflector 52 as of nickel is spotwelde'd or otherwise secured on theunder surface of the stepin the member 48. This reflector 52 also has two openings :therein to allow passage-through of the heaterwire 51.v This mounting-member 48 is then secured within the cylindrical focussing ring 53 as by spot- Welding theofuter surface ofithe larger diameter. portion This cathode gun-as-- sembly comprises a cathode button 46-as of nickel (see of the cylindrical mounting member 48 to the inside surface of the focussing ring 53. 7 One end of the heater wire is preferably spotwelded to a nickel ribbon 54, the other end of the nickel ribbon being similarly spotwelded to the heat reflector 52. The inner open end of the cathode assembly supporting cup 55is closed with a glass-to-metal seal through which five leads extend; three of theseleads a being combination electrode terminals and mounting wires and the remaining tw'obe'ing mounting wires. The cathode gun assembly is mounted on the lattertwo mounting wires 56 and 57 and one of the other wires 58, which is the common terminal for th getter, cathode and heater.

A' ribbon 59 as of nickelencircles the lower portion of the focussing ring 53 m the three wires; 56,- 57 and 58 andis secured'to each -aspby spot weldingr The getter 61 is secured at one end tothe common terminal lead '58 and at the other endto the getter terminal lead 62 as by spotwelding. The fifth ,terminal lead 63 is secured as'by' spotwelding toa ribbon 54 asof nickelwhich'in turn is spotwelded to one of the ends ofithe heaterwireSI. The

the vfocussing ring and the cathodemounting member 48 whileat the same time provides a large amount of heater wire in close associatioriwiththe cathode button The cathode button is thusmore uniforrnly and more intensely heated by the current in the heater wire,

greatly decreased lengths of the focussingvring and 'c'a'tliode mounting members the diameters of the'crosssece tions of the focussing ring 53 and, cathode mounting mem ber 48'are greater than the length of these elements and these elements are, thus far more ri gid than heretofore possible. The possibility of vibration of the cathode button and heaterwire assembly is therefore greatly reduced. .The fifth or; output wjaveguide assembly comprises a hollow rectangular metallic waveguide window, adapter 28. This adapter-is flanged, on oneendandhas four small shelf-like ;indentations .29 in theside; thereof. A rectangular windowcup -31 has a sheet'of glass 32- sealed across the openinginthe, end thereof, ,The window cup 31 is set within the open end of the window adapter, 28 resting-on the shelfl-like indentations 29, and is sealed therein as-by silver brazing. This window; assembly is then mounted on the surface of -the-tube body surrounding the iris 6, the flanged'endof thewindowl adapter 28 being secured asiby'copper goldbrazingto the body.- A rectangular sectiontof waveguide 33 made of; suitable alloys iorimetal; is secured {as by copper-gold brazing-l to a waveguide flange 34,'this flange 34,prc rvidingforconnec-v tion.to ;a standard output waveguidecir'cuit; A pair of tube support; brackets135v .and 36t are brazedtat one end thereof to ,the,:,fiange;34, thei -brackets extending flush against the larger sides of the block 2 and being fastened I and is secured ,thereinasby. brazing, this tube serving as It should be un from the cathode button 25.

the point' of evacuation; of :thetubem After-evacuation the end of the tube iscrimped and sealed closed.

In operation of this device, a heaters-current is supplied to.the heater'wiref26:topproduce arstream 10f electrons The accelerating grid-8 is at apositivepotential withiresp'ectlto the cathode'and the electrons are attracted.tosthisregionend accelerated, the electrons vreachingsa .constant'velocity in there-entrant tube '11 .formed by the header .7. The electrons pass the gap-to velocity v modulate these electrons} 1 The 'ne'ga- Because of the tively charged reflector 15 repels the approaching electrons and turns them about, the electrons then passing through the resonator gap between the resonator grids in bunches and giving up high frequency energy to the field in the cavity resonator 10. The electrons thereafter are collected on the walls of the tube and the first resonator grid 9. The first resonator grid is made thick to thereby intercept a large number of electrons passing through on their return trip from the reflector to the cathode area and thus reduce the number of multiple transit electrons. The high frequency power produced in the cavity resonator passes through the iris 6 into the waveguide section and then through the glass seal to the output waveguide circuit.

In heretofore existing reflex klystrons, an ion trap is formed in the re-entrant tube by the accelerating grid and the first resonator grid. The positive ions, produced, for instance, by collision of the electrons and gas molecules, are collected in the re-entrant tube and perturb the electron beam, thus giving rise to the above noted difiiculties. A novel structure is shown herein which greatly reduces the number of positive ions trapped within the re-entrant tube portion to thereby eliminate these difiiculties and in addition spread the center of the beam. This novel. structure comprises an accelerating grid 8 including an annular frame 41 (see FIG. 3) and a network of honey-combed vanes 42 as of copper supported by and extending within the frame 41. The interstices formed by the intersecting vanes 42 of the positively charged accelerator grid 8 provide a relatively intense.

electric field for coacting With the beam. Located approximately in the center of the honey-combed vanes is an enlarged polygonal opening 43. This polygonal opening 43 in the positively charged accelerator grid permits the positive ions in the re-entrant tube to pass therefrom through the positive region of the accelerating grid to the negatively charged cathode area where they are collected on the various tube elements. Neither the size, nor the position, nor the shape of this opening 43 in the grid is absolutely critical for any particular embodiment, the only requirement being that the opening is about in the center of the grid and is of the proper size and shape to prevent trapping an excessive number of positive ions in the remnant tube portion. In the present embodiment of this invention an accelerating grid having an overall diameter of about .26 was employed. The inside diameter of the grid frame 41 was about .19" while there were approximately 190 holes in the honeycombed vanes. The larger opening in the center of the honey-combed vanes was approximately .05". The size, shape and/ or position of the opening 43 will vary depending on each particular application of this invention. This special type of grid may be utilized wherever ion traps may occur in various types of electron discharge tubes other than this particular reflex klystron embodying the invention as, for example, in drift spaces in multi-cavity klystrons.

Since many changes could be made in the above construction of the novel electron tube apparatus and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an electron beam discharge device, a main body comprising a rectangular metallic block having oppositely extending cylindrical end portions protruding from two opposite sides of the rectangular block, the body having an axially aligned bore extending through the cylindrical end portions and the rectangular block, the body having a slit-like window opening on one other side of the rectangular block extending perpendicular to the axis of the bore, a metallic cylindrical header having an axially aligned bore therethrough defining a re-entrant tube within the header, an accelerator grid fixedly mounted on this header at one end of the bore and a first resonator grid fixedly mounted on this header at the opposite end of the bore, the header and associated grids being mounted within the bore of the body adjacent the window opening, a second round metallic header having an axially aligned bore therethrough and a second resonator grid mounted thereon, the second header being mounted within the bore of the body adjacent to and on the opposite side of the window from the first header and so positioned as to provide a predetermined spacing between the first and second resonator grids, whereby the bore of the body, the surfaces of the two headers, and the two resonator grids form a resonator cavity within the body having the window in the side wall thereof.

2. An electron beam discharge device including a main body comprising a rectangular metallic block and oppositely extending cylindrical end portions protruding from two opposite sides of the rectangular block, the body having an axially aligned bore extending through the cylindrical end portions and the rectangular block, the body having a slit-like window opening in one side of the rectangular block extending perpendicular to the axis of the bore, a metallic cylindrical header having an axially aligned bore therethrough defining a drift space within the header and an accelerator grid and a first resonator grid fixedly mounted on the header at opposite ends of the bore therethrough, the header and associated grids being mounted within the bore of the body adjacent the window opening, a second round header having an axially aligned bore therethrough and a second resonator grid mounted thereon over this bore, the second header being mounted within the bore in the block of the body on the opposite side of the window from the first header with the second resonator grid closely adjacent the first resonator grid, a reflector assembly comprising a reflector mounted on a mounting post, the mounting post being fixedly mounted within the bore in the outer end of one of the cylindrical end portions of the body with the reflector extending into the bore of the body and closely spaced from the second resonator grid, a cathode gun assembly mounted within the bore of the body at the outer end of the other cylindrical end portion with the cathode gun extending inwardly into the bore of the body and closely spaced from the accelerator grid, and

an output Waveguide section mounted at one of its ends on the block portion of the body and encircling the iris window, the other end of the waveguide being closed by a glass-to-metal seal.

3. A cathode gun assembly comprising a cylindrical focussing ring, an electron emissive cathode and a heater wire mounted within the focussing ring, a cylindrical cathode assembly supporting member having open ends and a glassto-metal seal across one of the open ends in the member, a plurality of mounting wires extending out from the supporting member and imbedded in the glassto-metal seal, the wires engaging the outer surface of the focussing ring at spaced points around the ring, and a metallic ribbon encircling the focussing ring and the mounting leads and securely aflixed thereto to thereby rigidly hold the focussing ring, cathode and heater wire in fixed position with respect to the supporting member.

4. A cathode gun assembly comprising an electron emissive concave disk-shaped cathode button having a flange around the peripheral edge thereof, a cylindrical cathode mounting member having a closed end with a concave surface, the cathode button being mounted over and spaced from the closed end of the mounting member with its flange engaging the outer surface of the cylindrioal mounting member and being aflixed thereto, a heater wire positioned between the cathode button and the closed end of the mounting member and arranged to occupy the major portion of the space therebetween, the ends of the heater wire extending through openings in the closed end of the mounting member, and a cylindricalcfocussing ring, the cathode mounting; memb eribt:

ing fixedlyrse'cured the focussing ring with its outer surface engagingthe inner surface ofthe ring, the cathode button extending within the lfocussi'ng ring.

SI'In anelectron beaml discharge device havingmeans for'producing a'beam of electrons, rahollow enclosure positioned in the'path of the beamzhaving open ends through which the beam enters and leaves the hollow enclosure a first grid closing one end of'said enclosureyand a second grid mountedover theother-open end of the enclosure, said second'grid' having aplurality of inter-= for producing a beam of electrons, are-entrant tube in the path of the'electron beam comprising side walls and a pair of grids mounted on each'end ofthe r e-entrant tube'transverse to' the path ofthe beam, on'e of said grids being. a honey-combed accelerator grid adjacent the cathode region ofthe device, said accelerator grid having a plurality of: intersecting vanes therein defining. small interstices there-i between providing a relatively intense electric" field in use forcoactingwith the beam and having anenlarged opening approximately in the center ofthe' grid vane'network greatly larger than -any of the other'interstices through which'ionstrapped in the re-entrant tube can be drained intothe' cathode region; 1 a I a, {-7-5Ai1 electrondischarge device comprisinga main body,

havingfan --axially' aligned-bore! extending therethrough and having-a slit-like window opening'inthe side thereof extending perpendicular to the axis of the bore, an an nular rnetallic headerlincluding -a hollow cylindrical reentrant 'tube portion, the bore of said re-entranttube being axially aligned-in the bore-of the main body, an accelerator grid mounted over one end of the re-entrant tube bore'and a first resonator grid mounted over the other end of the re entrant tube bore, the header and reentrant tube portions and the associated grids being mountedw-ithin the bore'of the body adjacent thewindow opening," a second metallic header having an axially aligned bore thereth'rough and a second resonator grid mounted overthe-bore thereof, the second header being mounted 'within-thebore of 'the body adjacent to thewindow on the opp'osite' side from the first header and so positioned as to provide a predetermined spacingbetween the first'a'nd'second resonator" grids whereby the bore oi the:bodyf-thesurfaces of the two headersiandihe two resonator grids forming a resonatorcavity-within the body having the' w-indow in thesidewallxthereof. 7 -8. An electron beam discharge device including a body "having an axially aligned bor'e'f extending} thei'ethroughith'e bodyhavingaslit-like window opening in the side extending perpendicular to the was of the bore,

.an annular metallic header'includinga hollowcyli'nd'rical re entrant tube} portion, the bore of said re-entrant tube being axially aligned "in thebore of' the main body; an

accelerator gr id mounted over'one' endof there-entrant tubeb'or'eand'a first resonator grid mounted'over "the one ter end-0f=the;body Wfihlhifl'fifiQCtQK x end ng-int he here etthebodyand clqse r pa e rolmit s e ond resona o ig c hode :gun assembly.,ng ume s the bo e-Let the b dy: t: h t e 0u en w t the cathodegun extending-inwardly into the bore of;the-body closely spaced from the accel eratoriglid and a wave energy-p eable; m erial c ve ins: he I -Wi I A r flex l y tronincluding soathodeadapted o pro: d ce abe m of. e ectrons; at rel-entrant; tu efm mb r, c vity, r n tor, a r flector elec o t ndem. c elerator grid coveringt-he open endof'iho re-entrant tube member near the cathode region,t.-the grid being a honeycombed accelerator gridrihaving a pl ia iW i intersecting grid vanes thereindefining small interstices therebetween and having an enlarged-openingapproximatelyin the center of the ,grid vane 'network'largerthanthe :other interstices through which ions in 5 the re-entrant tube 1 member may be drained into thecathode region. 1 a 1 I 1 T 10. A refiexk-lystron comprising cathode meansadapted, to producea beam-of electrons directed along a path in the klystron a .r'efl'ectorelectrode; positionedinthe path adapted to repel the electrons, a'hollow member forming a re -entrant tube positionedinathe beam path between thecathod'e means and thereflector, a cavity resonator member; positioned intheibeam path between the reentrant tube member. and the reflector including aresona-torgrid mounted on the ;rleflector.end.iof the hollow re-entrant tube 'memberand a honeycombed accelerator gridmounted on the cathode end of -the hollow re-entrant tube member having 'a plurality of intersecting vanes therein defining small interstices therebetween and having an enlarged opening approxhnately in the center oi the grid vanenetwork' through'whichxions that may normally be trapped between the gaccelerator grid and. the resonator grid in there-entrant tube f'member maybe drained to the cathode region. 7. j 1 3 V 11. An electron be 'Vdischarge'device includingta main bodyvcompzising a-metallic-blockhaving oppositely extending'cylindrical end portions sedan axially aligned bore a extending through the cylindrical end portions and the block a metallic cylindrical header mounted in the device having an ardally aligned bore'there'through defining a re-entrant ;tube:within the header; :an accelerator grid fixedly mounted'on-thisheader atone end of the bore and a first-aresonator-g'rid; fixedly mounted on this header at the .oppositea'end of the boreg'said accelerator grid being ahoneycombed grid having a'plurality of intersectinggrid vanes therein defining small interstices therebetween and having. an enlarged opening approximately in the center of th'e grid vane network larger than the other interstices through which' ions in the 're-entrant tube 'member may be drained-into the cathode-region, and a cathode gun assembly mounted in one cylindrical'end portion adjacent said accelerator gridicbmprising a cylindrical focusing rlngyan electron emissive cathode-and a heater wire mounted within the focusing ring, a cylindrical= cathode assembly "supporting member: having open'iends and an insulator seal across' one" of 'theopenends in the member, a-plurality of mountingwires extending' ouffrbm'the supporting member and'irnbedded'in the'insulator seal,- the wires engagi'ng' theo'uter surface of the focusing ring at spaced'pointsaround the ring, and a'metallic ribbon en circling the foeusin'g ring anddhemounting leads and securely afiixed thereto to thereby rigidly hold the focusing ring, cathode'and heaterwirein fixed-position with respea't' m nwmngmmsee f 12. electron' discharge 'f device jcomprising' a main body 7 having an axially i'aligne'd bore extending therethfroughgian annularlmetallicfhe'ader including a hollon c lindricalre-entranttube a v ionrnountedin body,

theborefo f tubeibeihg axially aligned in t ar f he main body, .a a q s at r e d i wi e e r n nd f h Rea ent-t bs Dema d a-fi s Yew tor and m unt d q erithe a; and, it h fl w sa r hf tube bore, and a cathode structure mounted in the bore of the body adjacent said accelerator grid comprising a cylindrical focusing ring, an electron emissive cathode and a heater wire mounted within the focusing ring, a cylindrical cathode assembly supporting member having open ends and an insulator vacuum seal across one of the open ends in the member, a plurality of mounting wires extending out from the supporting member and imbedded in the vacuum seal, the wires engaging the outer surface of the focusing ring at spaced points around the ring, and a metallic ribbon encircling the focusing ring and the mounting leads and securely afl'ixed thereto to thereby rigidly hold the focusing ring, cathode and heater wire in fixed position with respect to the supporting member.

13. An electron beam discharge device comprising a cathode gun assembly for producing a beam of electrons including a cylindrical focusing ring, an electron emissive cathode and a heater wire mounted within the focusing ring, a cylindrical cathode assembly supporting member having open ends and an insulator vacuum seal across one of the open ends in the member, a plurality of mounting wires extending out from the supporting member and imbedded in the vacuum seal, the wires engaging the outer surface of the focusing ring at spaced points around the ring, and a metallic ribbon encircling the focusing ring and the mounting leads and securely aflixed thereto to thereby rigidly hold the focusing ring, cathode and heater wire in fixed position with respect to the supporting membar, a hollow enclosure positioned in the path of the beam having open ends through which the beam enters and leaves the hollow enclosure, 2. first grid closing one end of said enclosure and a second grid mounted over the other open end of the enclosure adjacent the cathode gun assembly, said second grid having a plurality of intersecting grid vanes therein forming a honeycomb configuration defining small interstices between the vanes and having an opening approximately in the center of the grid vane network having a diameter greater than three times that of the other interstices through which ions trapped in the hollow enclosure are drained into the cathode region.

References Cited in the file of this patent UNITED STATES PATENTS

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