US2939995A - Traveling wave tube - Google Patents

Description

2 Sheets-Sheet 1 Filed Nay 19, 1958 June 7, 1960 w. E. DANlELsoN 2,939,995

mmm um: TUBE /NVE/vron IM E. DAN/ELSON ZM/Z@ ted States 'I'RAVELING WAVE TUBE Filed May 19, 1958, Ser. No. 736,251

20 Claims. (Cl. S15-3.5)

This invention relates to traveling v/ave tubes, and more particularly, to a support structure for the wave propagation circuit or helix of such tubes.

ln such devices, an electron beam is projected along a slow wave circuit a plurality of wavelengths long, and interaction takes place between the beam and an electromagnetic wave propagating on the circuit in synchronism with the beam over a substantial portion of lthe length of the circuit. The cumulative interaction between the beam and the wave on the slow wave circuit results in an interchange of energy and produces alternating-current components ofelectron velocity, known as velocity modulations. During this process, some of the electrons are slowed down while others are speeded up, which produces bunching lof the electrons, or density modulations of the beam. These bunches, in turn, interact with another portion of the same circuit, generally to produce amplification of the wave energy.

Gne of the most commonly used slow wave circuits in traveling wave tubes is a conductive wire helix, the reason being that it lends itself readily to precision grid winding techniques, permits effective wave retardation characteristics to be attained, is compatible with various types of coupling arrangements, exhibits an extremely wide frequency bandwidth because of its nondispersive forward wave characteristics, and permits effective disposition of the beam current over the cross-section of the circuit.

At very high frequencies, eective operation dictates that the helix be of extremely ne dimensions. For example, at a midband operating frequency of 55,000 megacycles, a 2 mil by 41/2 mil wire may advantageously be utilized to form a tape helix having a 15 mil inside diameter. These dimensions coupled with the fact that such helices often have a length ranging from 50 to 300 times their diameter makes them very fragile.

lt thus becomes apparent that virtually all of the helices utilized in traveling wave tubes, and certainly those designed for high frequency operation, are, because of their small dimensions, very fragile and incapable of self-support. Accordingly, a more rigid support structure for the helix is required to provide suitable rigidity during fabrication and permanent placement of the helix thereafter. Moreover, since the helix diameter is very small, extremely accurate positioning of the helix is required in order to prevent excessive heat caused by impinging electrons from seriously impairing the operation of the device if not rendering the device inoperative. Similarly, even a tolerable amount of heat generated on the helix by either axial misalignment or distortion of the helix would result in a reduction from the maximum attainable efiiciency of the device. Further, with the inutely dimensioned helices required at high frequencies, pitch uniformity becomes quite critical, and thus, fragile helices require a supporting structure which minimizes external forces or over-constraining of the helix during assembly as Well as thereafter.

Such helix support structures, heretofore, have comrice prised two basic forms. One conventional form of helix support has been a hollow cylinder of insulative material surrounding the helix, which cylinder often comprises the envelope of the tube. A modification of this arrangement has comprised a long support' member having a polygonally-shaped central aperture. ln these structures, the helix is normmly either bonded, as by glazing, to the centrally apertured member or frictional forces and mechanical clamping are relied upon to hold the helix in place. Examples of such structures are disclosed in F. H. Best Patent 2,706,366, issued April 19, 1955. Disadvantageously, in either ofthe above-mentioned arrangements, the helix straightness and alignment depend basically upon the uniformity in diameter and alignment of either the hollow tubing comprising the envelope or of Vthe member with the polygonally-shaped central aperture. In addition, neither -of the aforementioned types of helix support arrangements allows of the incorporation Within the tube of various other elements, such as attenuation means, between the helix and the envelope that often may be desired, nor do such structures by encompassing the Aperiphery of the helix allow for easy measurement of helix straightness. Similarly, and significantly, neither of these helix support arrangements permits the utilization of conlined coaxial beam ow whereby one portion Vof the beam is within and another portion without the periphery of the helix which would -result in a substantial increase in signal gain as well as a consequent improvement in the signal-to-noise ratio. This is especially true at very high frequencies where the necessity of an extremely small dimensioned helix drastically limits the value of beam current which may be transmitted axially through the heiix in the normal case. Moreover, in multi-contact helix support arrangements a fragile helix is very susceptible to being over-constrained because of the transverse forces set up, particularly during the fabrication ofthe device.

The second basic type of helix support structure priorly utilized to avoid some of the aforementioned difficulties comprises two or more insulative support rods uniformly spaced in a symmetrical manner about the periphery of the helix` and extending along the helix in a direction parallel to the axis thereof. As in the aforementioned structures, the helix is normally either bonded, as by glazing to the support members or frictional forces and/ or mechanical clamping are relied upon to hold it in place. Such a structure is disclosed in I. A. Morton Patent 2,790,926, issued April 30, 1957. Disadvantageously, in this type of structural arrangement, as in the case with the first-mentioned helix support arrangements, helix straightness and alignment depend primarily upon accurate dimensoning of a number of interrelated elements,

namely, the uniformity in diameter and straightness of the support rods. Since these support lmembers have a longitudinal length considerably greater than their diameter, and because of the type of material utilized, they do not afford the degree of rigidity desirednor are such members of a type conducive to manufacturing techniques which will assure precise dimensioning as matched machined parts. Moreover, in the fabrication of such a helix support structure, over-constraining or transverse stress between the helix and the support rods often tends to distort or weaken the supporting bonds.

A helix support rod arrangement designed to bond more securely the supporting members to the helix as well as to reduce transverse stress during assembly is disclosed in G. H. Robertson Patent 2,812,499, issued November 5, 1957. In that patent, there are disclosed two pairs of ceramic rods, the two pairs being positioned adjacent to the helix at diametrically opposite regions and the rods of each pair being positioned contiguous to each other. The rods are then glazed to the helix in such a contact. Y Y

E way that the glaze fills the volume defined by the arcuate Y sided triangle between the two Ycontiguous rods and the Y'ment is ydependent'basically upon theY straightness and uniformity 'or' diameter ofV a plurality of support rods.,

Similarly, the support structure does not readily lenditself to easy measurementsof helix straightness because of the multi-rod arrangement on opposite sides thereof;

Another signicant probleminvolved in traveling Wave normally cause the helix Vtemperature to rise to a point Yhigh enough to render the device inoperative if a thermalV heat flow path of some Ysortjaway from the helix were not provided. The bonds between 'the helix and support rods in certain of the aforementioned structures are intended toA transfer the thermal power from the helix Vto the'rods. However, an effective thermal path from the rods Yto a fsuitableheat sink is still required. r y Y One way'of accomplishing this transfer of thermal heat Y tubes, and particularlypertaining to the helixand support rangement of simple and unique design and which may be manufactured with accurate dimensions by conventional machining operations. Y

In a specic illustrative embodiment of my invention, an electron discharge device ofthe traveling wavev type comprises anY evacuatedY envelope with removable end portions, an elongated slow wave helical conductor dis- Y posed longitudinally within lthe"3en'velolgrefand supported vbya single insulative-.support member` extending along a4 line parallel to the axes of the helix, anelectron gun and'target positioned beyond opposite ends of the vhelical conductor for forming and projecting Aan electron beam along an extended path in close proximity to the helical conductor, signaly inputy output circuitsat opposite ends of the helicalV conductor and a magnetic focusing system for establishing and shaping a uniformY longituhelix is rigidly held inV precise axial alignment and with heating of the helix. VThese two sources of heat would Y from thesupport rodsV to a suitable heat sink is disclosed in J, P. Laico Patent 2,772,939, issued December 4, 195.6. i

Vsupport, structure. AThese forcesV areY very likely either to weaken the bonds or'actually displace the multi-support rod arrangement and,fthus, seriously distortthefhelix. r l. An associated problem encountered with minutely Y dimensionedIhelicea-is the manner in which the direct-V ;.current Vvoltage is applied thereto. Heretofore, metallic contact with the fragile helix has been utilized with con-Y siderable ditliculty often being encountered in preventing a Vdiscontinuity in the helix Accordingly, it is an object of this invention to insure precise Y and rigid helix alignment in high frequency traveling wave tubes. f

It is another object of this invention to minimize Aoverwire Vat the point ofY However, 'the Y pitch uniformity, by a single substantially wedge-shaped insulative helix support rod. Successive turns of the helix are Yglazed to a narrow edge of the support rod along a line parallel to the axis of the helix. This type of single support rod arrangement minimizes the tendency of the helix to beover-constrained. Moreover, lsuch an open helix lsupport assembly allows for easier measurement ofV helix straightness as well'as permits the utilization of'conined coaxial beam ow whereby an annular portion Yofthe beam'may be projected on either side of the helix periphery for increased gain. Similarly, with such a helix support arrangement, the helix is held in vsubstantially free-space relationship with respect to its surroundings which makes possible incorporation Yof circuit elements between the. helix and the envelope Wall, such as attenuation elements.

Yln accordance with another. aspect of this invention, the Ysingle substantially wedge-shaped support rod is sea-ted in an -accurately machinedst'ep offa rigid metal block, which may form aportion ofthe envelope. nSuch Y 1 and the straightness and parallelismrof ythe surfaces of the constraining of a helix during as well as after fabrication Y of thetube.

It is Vstill another object of this invention to support a :helix in a manner which is conducive to known techniques p for measuring helix straightness, allows of the incorporation of circuit elements between the helix and thejsurrounding envelope,V and permits the utilization of con-V ,fragile helix accurately "and rigidly witha structurale:-

single wedge-shaped support rod member which are in contact with either the metal block or the helix. Advantageously, these surfaces may` easily-be machined with extreme accuracy by conventional grinding or milling operations. v Y Conductive spring contacts, in accordance with my invention, produce la pressure Contact between flat `surfaces of the ,metal blockand the wedge-shaped` insulative support rod, Vwhich'assures adequate thermal conductance away from the helix through the support rod to lthe metal block while simultaneously providing ani effective way to ensure precise and rigid helix alignmentv during as well as after assembly'of the helix.

Further, in accordance withmy invention, Yan, applied Yloss coating on the support rod between Vthe helix and one or more of the conductivespring contacts provides anV V,eective and advantageous vway to -apply direct-current Itis another'feature ofV my invention that'the support Y rod Vb e of substantially wedge shape, VtheV helix being mounted, as by glazing, to the thin 'edgeof thesupport rod. Y 4

isanother feature of Vmy. invention that theV spring ntenrbersbe mounted onthesupport'merdber anddeine,

together with a conductive coating on the sloping surface of the support rod, a conductive path for the application of direct-current potentials to the helix. Further in accordance with this feature of the invention, the conductive coating may be of a lossy material.-

It is a further feature of this invention that the mounting member be substantially massive relative tothe minute fragile helix and comprise a heat sink for the removal of heat from the helix through the large area contiguous surfaces of the support rod and themounting member, the spring bias of the support rod against the hat surface of the mounting member'serving to assure good thermal conductance between these two members,

It is still la further featureA of my invention that lthe mounting member supporting' the helix extend continuously between two endplates to which endplates the electron gun and collector assemblies are secured. Further in accordance with this feature of my invention accurate axial alignment of the helix can be attained by radial adjustment of the mounting member between the endplates.

A complete understanding of this invention and of these and other features thereof may be gained from consideration of the following detailed description taken in conjunction with the accompanying drawing, in which:

Fig. l is a sectional view of a traveling wave -tube amplifier illustrative of one specific embodiment of this invention;

Fig. 2 is a partial sectional View in detail of the helix support structure depicted in Fig. 1; and

Fig. 3 is a cross-sectional view of the helix support struct-ure depicted in Figs. l and 2.

Referling now to Fig. l, there is depicted a traveling lwave tube 10, comprising an elongated. evacuated central envelope portion 1l, comprised of two sections 12 and 13, preferably of non-magnetic material, such as copper, brazed together at a flange 14 as a step in the fabrication of the tube described in greater detail hereinafter. The end of envelope section 12 opposite the ange 14 is positioned within a circular groove 15 in a conductive member 16 of an input endplate assembly 17, and similarly the corresponding end of envelope section 13 is positioned within a circular groove 13 in a conductive member 1,9 of an output endplate assembly 2t?. A

In accordance with an aspect of this invention, there is positioned axially within the envelope portion 11 la metallic block 21 abutting conductive endplate members 16 and 19 of endplate assemblies 17 and 20, respectively. The conductive 4block 21 maybe of any suitable conductive material, such as molybdenum, as long as it is rigid, has good thermal characteristics, and is machinable. A single substantially wedge-.shaped insulative support rod 22, ybest seen in Figs. 2 and 3, is seated into an accurately machined step 23 of block 21, and supports an elongated conductive helix 24. The single insulative supportrod 22is advantageously of ceramic or other suitable material of low radio-frequency loss and having approximately the same coefficient of thermal expansion as the material comprising the helix 24 so as to minimize pitch distortion during a subsequent heat treating process of the helix before assembly. By way of example, a ceramic known as F-66 Steatite `or a material such as synthetic v sapphire has been found quite adequate for the purpose intended with a helix made of molybdenum. It is to be understood that while the support rod is shown as being substantially wedge-shaped, other geometric configurations may lbe utilized with equal electiveness.

In accordance with another aspect of this invention, one or more conductive spring contacts 25, brazed to an indented flat surface of the conductive block 21, best seen in Fig. 3, extend toward and are in contacting relationship with the sloping frat surface ofthe wedgeshaped insulative support rod 22 ensuring precise and rigid helix alignment after the support rod 22 is positioned withina machined step of the conductive `block 21. Such spring contacts correspondingly afford an effective pressure contact between at surfaces of the conductive block 21 and support rod 22 which provides an adequate thermal conductance path for transferring heat from the helix 24 through the support rod 22 to the metal block 21. Any suitable non-magnetic conductive material with ay Ycertain amount of spring resiliency and good thermal `characteristics may be utilized for the spring contacts- 25,' such as a material known as -lnconel-X.

' Surrounding and extending along the central envelope portion 11 is a succession of apertured magnetic discs 30 of high permeability material separated from each other by aluminum spacers 31 as seen in Fig. l. The significance of and thepatentable features of such an arrange- Vment of magnetic discs are disclosed in a copending application of C. C. Cutler, Serial No. 664,015, led June 6, 1957. Briefly, these discs constitute a field straightener assembly for straight eld permanent magnet structures and effectively remove thestray magnetic fields encountered in the focusing structure so that a strong, straight magnetic field is assured along the path of electron ow. The straight magnetic field is established by a permanent magnet structure 32, shown in partial section in Fig. 1 as being semicircular, however, it is to be understood that other shapes and types of magnetic focusing systems may be utilized with equal effectiveness.

On the side of input endplate l'assembly 17 opposite the helix 24 is'V another evacuated envelope portion comprised of two sections 33 and 34 Abrazed together at an overlapping region 3S. These envelope sections may be of the same non-magnetic material Yas central envelope portion 11. lnclosing the extreme end of this evacuated portion is a suitable insulative `base 36, such as glass or ceramic, or a combination thereof, brazed along the outer periphery to one end of a support member 37. Insulative base 36 supports a plurality of lead stem connections 38. For convenience and simplicity, the connections from a suitable voltage source through the lead connections 3S to to the various tube elements are not shown. An exhaust tubulation 39 extends from the insulative base 36 allowing for the evacuation of the envelope after assembly of the tube elements, described in more detail hereinafter.

Attached'to the input endplate assembly 17 opposite the yhelix 24 is an electron gun assembly '4G for forming and projecting an electron beam along an extended path past thehelix 24 to a target 41 which has an inclined cavity 42 therein forminimizing secondary emission effects. `An evacuated envelope portion 28 encloses the collecting portion of target 41 and is brazed to a conductive member 29 forming a part of output endplate assembly '24?, The electron gun 4G comprises a heater element 43encl'osed byV a conductive cathode sleeve 44. The heater element 43 and cathode sleeve 44 are positioned axially with respect tothe helix 24 by a number of Wirelike members 45 in contact with an outer cylindrical member 46 which is brazed to a ceramic support member 50. At the end of cathode sleeve 44 is the emitting surface 48 of `the cathode and positioned in axial alignment therewith is a beam forming electrode 49 also held in spaced relationship by the ceramic member Si?. A beam accelerating electrode 51 is heldin spaced axial relationship with respect to the electron beam by an insulative member 52. A beam shaping electrode 53 is positioned between the accelerating electrode 51 and the input end of helix 24 so as to remove any stray electrons from the path of ow before the #beam enters the magnetic focusing region along the helix. Excessive heating of the fragile helix normally caused by impinging electrons is thereby minimized.

Advantageously, the electron gun assembly 40 is arranged so that Vthe entire unit is held in proper position on the side `of endplate assembly V17 opposite the helix 24 by a pluralityY of fastening screws 56 arranged in a symmetrical circular manner near the outer edge of pole piece member S7 which is a part of endplate assembly 17, Two or more conductive spacer rods 58 together with the supship withrespect Vtothe electron gun assembly 40`befor'e Vassembly of orduring removal thereafter'of envelope sections' aild 34. With this arrangement, i t becomes apparentjthat onecan replacea 'defectiveelec'tron lgurl assembiyifwitliia completely'nevi gun.as'sembly,jfor l example, by the Vsiizflpl'e expedient of reducing tlievaouum, y Ythen removing the envelope sections .33 and 34 by Known techniques .and then removing lthef. f as'tening screivsf56 which attachthe electron'gun assemblyfll) tothe input @anglais assembly-17. i j 1 An external input waveg'uide se'c'tio'r'tV 59,i`s :`x1nected'- through a'suitablemica window 6 0t'o aitaperedlwaveguide.

section VJr'or establishing thefproper impedance trailsformation toa reduced size intenaliilput waveguide passage62 lo-'r'medVv between the conductive member 16and a conductive member 63, bothbeingintegra;l parts f put endp'late Yassembly 17.YV l AquarterAlvave.fcndiictiye1 sleeveV '6d extends YacrossV a ibid-band resonant cavity 65 Y' for effecting an eicient'input coupling. impedance match.

Similarly, van vadjustable membervalies. the position of a metal block 67 within the extended .portion of the internal 'wave'guidey passage 62 .soas toiobtail a' ,s'l 1itab1e impedance match between the guide and the helix. A

similar configuration is utilized at' 'th"e.otput end of helix 24. Ail 'output section 69 is colipl'edfpthrou'gh 5a` micaY Vwindow 76 rto a tapered waveguidesecton. 7-1for V-es'tablishing the proper inipedancetransformation 'toareducedv size. internal output .waveguide .passage 7 2formed be- Ytween the conductive member 1`9 ,a`n d member 73'o'f out# put Vendplat'e assembly 20. AV quarter. Waite.'condl'lctiveVY i sleeve 74V extendsacross anlidfbandifresonarit cavityV 75' for VeffectingV an efficient output coupling impedance match An 4adjustable member v76V varie s the position of Va 'metal block 77 within lthe extendedpoftion of theiuternalwave 'Y guide passage 72 so as tobbtain a suitable.''nrl'pedan'cev match between the helix'and the output guid'ek.Y

YAsseen in Fig; 2, the Yspring contacts ZSmaybeofcol sideliablelongitudinal length; .and as shown inrFig.f. 3,

known 4glazing,materials utilized 'for such. purposes; as

can be seen the'helix is thus situated in a groove 83 in the block 21. Y ofthe support rod 22 defined between the surface of the rbd 22 abutting step`23 and the sloping surface ofthe rod 22 against which the springs 2S bear. This edge 'ati thenters'ection of the two surfaceswill have Va finite widthV The helix 24 is thus glazed to a narrow c dge but may advantageously be quite small.v i

- Similarly, in accordance with another'aspect of this ;iiivention, a thin coating of lossyirnaterial r256, suchas aquadag', as applied to certain portions of the single support rod 22 wherevoneor more ofthe spring contacts 25 aein contacting relationship therewith. Preferably,

a's seen Yil :l.Fig.3, this coating- 26 is appliedto'the support Lrod 2 2f'ov'er Ya short longitudinal region. near the center, thereof between the helix 24 andthe one or more In this manner, the. applied loss' spring .'"co'ntacts 12S. coating willn'otbnlylaiord al1-effective and ad'i'la'iitageous Y Vway'to apply directcurrentvoltage to the @fragile helix 24, Ybut will minimizethe tendencybf selfoscillationy and thereby increasethe operatingjstability ofthe tube `In-jfabricatihg the helix support assembly, the Vhelix is 'wound upon 'ahiandrelby any known ziethod, 'with thefra'ndrel being of ya materialsuch Y'as copper, if -Vthe helix s'tf a material'such as Ymolybdenum which 'would 5 permitthe'mnd'rel "to be dissolvedy chemically before treatment; Alternatively,"thefrhandrel 'might y'be Qftlie saine aisiiiiilar mateiial'asfne helix V2 4 having 'ap- Yproxiiiiately. fthe saine 'Coiiicient of .thermal expansion iftlle linandrelis't snppotthelielx duringia subsequent 1b `nor'maliing vheatfr eatingkprocess so as` to minimize distel-fen ef the ghelixfpitch. 1 Similarly, the single insula-V Y it' slpiorft rod 2 2fs'ho'uld have a coefficient ofitherrnal ve pansior'l; pproximately'equal Vto Vthatoi the helix'rla# A.; f iial as inculate glaze zintilized lebend the helix lsfzftilliejsuppertted-zzz.;- The gla`z`e27 istli'e'n applied tothe support r'odZZ along'a line conciding'lwith ltheare'a toV be in'contac't withV the periphei'ylof the Yhelix by spraying or any'of the Vother,knownmethods. Similarly, the applied loss coating'Z, suchfas a'qudag, is applied to the surface i of the insulative support rod 22 between the helix and winding process as well astobond the helix to the 'support ,-rodby melting the'glaze material 27. Themandrel is then removed, ifjnot previously. removed, 'and the VB fsingleY insulative support rod V22Y` and the helix 24, Yas an .integral unit, is'placed in tne accurately machinedstep 'Y 23 'of theconductive block 2l, firmly held in place'by thefsp'ring contacts 25. i :.The-.conl'plete helx support assembly, VVincluding the Yiiie'tal block .21, isA then 'attached vvto the Vinput en'dplate Vassembly/17. by a plurality of suitable fastening I screwS, Y Y- not shown; QIlie two/intermediate envelope sections 12 and 13,7.5to 'b'e subsequently rbrafzed' at Ythe ange 121,' together'wlth the permeablelmagnetic discs S'Qiand alumi-k @animi spacers lcoaxiallytherewith, are positioned Yto they are in contact with the wedge-shaped support Yrod 22 ai Y' along the ilat tapering side thereof;` Ihespringcontacts Y25l are securelyY positioned between ailiat surface ofthe, rigid metal block 21V and ailongitudinall'y extending 'con-'f1 ductiye member 7S Aabutting thereagains't'Yundenbompresl sion offastening elements 79. r Asalso seen inl-iig. 3, the. substantially wedge-shaped support rod 22 is'seated alongV an accurately machined step 230i the conductive. block 21 which assures precise axial aligflmeritfofth'efnarrow edge of support rodf22' in contactwith the'he'lix'24`; sup.- port rod 22 also bears against side wall 82 of the'V block 2,1;Vv

The Vsupportlrod 22 is attached tothe helix 24 by atl1in v V.glaze 27, seen in Fig.`3, which may comprise :anyof the ofnputenclplate assembly r11.7. The Vout'putendplate as V4.5serrlbly 20is thenfatta'chedito the .other endf'of thecon- 'ductiveblock 21 by meansof 4a plurality Vof suitable fasteningjscfrews,YV not shown The'etivelope section 1 3 4 isv Y Vthen fittedfwithin the circular groove `18gof VVconductive member 19 whichis Valt integral part'ofthe output end- 59 plate assembly 20.

Advant'ageousl pole pieceY memberfSTof input vendplate assembly 17 .and pole Vpiece Vmember 29 of `o'utput endplate assembly 20 may,' before V being permanently secureihgbe Vadjusted axially until,` as ldetermined by 'known' optical techniques, they Vare suitably yaligned vwith respect to the helix.' Similarly, the gun assembly 40 'may beadjusted axially by means of the fastening elements 56 Yto insure precise alignment with vrespect Yto Ythe helix beforelinal assembly of the device.

50 Fabrication ofthe helix assembly in this manner advantageously results in azlnini'mum of'stress'being placed i upon the input andoutput endplate assemblies as the ilange 14 of envelope'portionll is Vcapable of being com-4 pressed slightly so as to adjust readily to the exact longi` tudinal length betweentlie two endplate assemblies 17 and 20 'denned by the longitudinal 'length' ofthe conf ductive'block 21.Y The gunfa'ssembly 40 may thenjb'e attached to .the'input endplate assembly 17,V if notpren viously.attachedthereto'fby'the fastening screws 56. The

one or more ofthe spring 'contactsf2`5, preferablyV alongV conductive fljnernb'er 1'6'which`conlprises anintegra'l 'part regions of overlap between the various envelope portions and points at which the envelope sections are abutting the input and output endplate assemblies are brazed, such as by the heliarc process.

, It is to be understood that the specific embodiment disclosed and the method of fabrication described herein are merely illustrative of the principles of the instant invention. Numerous other arrangements and variations in fabrication could be devised by those skilled in the art without departing from the spirit or scope of the invention,

What is claimed is:

1. A traveling wave tube comprising an evacuated envelope, an electron gun and collector spaced apart within said envelope, a slow wave propagation circuit positioned axially therebetween, and means for accurately aligning and supporting said wave propagation circuit in substantially vfree space relationship with respect to said envelope, said means including a wedge-shaped insulative support member, one edge of which is glazed to said wave propagation circuit along the length thereof, a rigid conductive member extending longitudinally along said support member and having means yfor aligning said support member, means for retaining the `alignment of said support member with Vrespect to said longitudinally extending conductive member and simultaneously providing a portion of a conductive direct-current voltage path between said conductive'member and said wave propagation circuit, and low resistance means for completing the conductive direct-current voltage path between said conductive member and said wave propagation circuit.

' 2. A traveling wave tubev in accordance with claim l wherein said wave propagation circuit comprises a helix and -said'conductive member comprises a metal block having a Hat surface extending longitudinally of and in contiguous relationship with one surface of said substantially wedge-shaped support member.

3. A traveling wave tube in accordance with claim 2 wherein said means for retaining the alignment of said support member with respect to said metal block and for simultaneously providing a portion of a conductive direct-current voltage path comprises at least one metal spring Contact between said metal block and said support member, respectively, and said low resistance means for completing the direct-current voltage path comprises an applied loss coating on said support member.

4. A traveling wave tube comprising an evacuated envelope, an electron gun and collector spaced apart within said envelope with a slow wave propagating helix positioned in axial alignment therebetween, and means for accurately aligning and supporting said helix, said means including an elongated wedge-shaped insulative support rod, one edge of which is glazed to successive turns of said helix along the length thereof, a conductive blocl: extending longitudinally of said support rod and having means for aligning said support rod, and means for retaining the alignment of said support rod with respect to said conductive blk and simultaneously providing a portion of a conductive path through which direct-current voltage is applied to said helix.

5. A traveling wave tube in accordance with claim il wherein said last-mentioned means comprises at least one metal spring contact extending between said cond-uctive block and said support rod and further including a short longitudinal region of applied loss coating along the intermediate portion of said insulative support rod between the helix and at least said one metal spring contact for completing the conductive path through which direct-current voltage is applied to said helix.

6. A traveling wave tube comprising an evacuated envelope, an electron source and collector spaced apart within said envelope with a slow wave propagating helix positioned in axial alignment therebetween, means for accurately aligning and supporting said helix, said means including an elongated wedge-shaped insulative support rod, one edge of which is glazed to successive vturns o f said helix along the length thereof, a conductivefblo'clc having means for aligning said support rod, said means comprising an accurately machined step extending longi tudinally of said conductive block, and meansV for securely holding said support rod in said step and simultaneously providing a portion of a conductive path for applying voltage to said helix, said last-mentioned means including at least one metal spring contact between said conductive. block and said support rod, respectively, and resistance means for completing said conductive path for applying voltage to said helix.

7. A traveling wave tube in accordance with claim 6 wherein said resistance means for completing said con-` ductive path for applying voltage to said helix comprises a short longitudinal region of applied loss coating along the intermediate portion of said insulative support rod between the helix and at least said one metal spring contact. l Y

8. A traveling wave tube comprising a helix and means for supporting said helix, said means comprising a support member having a at surface, a substantially wedgeshaped insulating support rod having a first surface abutting said at surface and a second surface at an angle to said rst surface, said helix being secured to said support rod along the edge intersection of said first and second surfaces, and sp-ring means mounted on said support member and bearing against said second surface to position said support rod against said flat surface.

9. A traveling wave tube in accordance with claim 8 wherein said support member is of a conducting material, and conducting means on said second surface and con-v tiguous to said helix, said spring means and said conducting means deiining an electrical connection between said support member and said helix for applying adirectcurrent potential to said helix. v

l0. A traveling wave tube in accordance with claim 9 wherein said conducting means comprises a coatingof a lossy material.

1l. A traveling wave tube comprising a conductive helix and means for supporting said helix, said means comprising a conductive support member having a at surface and a side surface at an angle to said fiat surface, an insulating support rod having a rst surface abutting said at surface and a sloping surface at an angle to said first surface, said conductive helix being secured to said support rod along the edge intersection of said rst and sloping surfaces, and spring means mounted on said support member and bearing against said sloping surface and biasing said support rod against said hat andside surfaces.

l2. A traveling wave tube comprising a helix and means for supporting said heiix, said means comprising a conductive support member having a flat surface, a side surface to one side of said Hat surface, and a groove to the other side of said at surface, an insulating support rod having a rst surface abutting said flat surface and a sloping surface at an angle to said first surface, said helix being secured to said support rod along the edge intersection of said first and sloping surfaces and positioned in said groove, and spring means mounted on said support member and bearing against said sloping surface and biasing said support rod against said iirst and side surfaces.

13. A traveling wave tube in accordance with claim 12 wherein said spring means comprises a plurality of wide dat spring members.

14. A traveling wave tube in accordance with claim 13 further comprising lossy conductive means positioned on said sloping surface and electrically connecting said spring means to said helix whereby direct-current potentials can be applied to said helix from said support member.

15. A traveling wave tube comprising a helix and means for supporting said helix along its entire length,

`said 'means comprising a support member at least coextensive with said helix and 'extending adjacent thereto, said support 'member having ia at surface, an insulative support rod having a flat portion positioned on said at surface, said 'helix being attached to said support rod, and spring'mreans 'mounted on said support member and biafsi'ng said support rod against said at surface.V

"116. A traveling wave tube comprising a slow wave jn'o'pagationVV circuit and means Vfor supporting Ysaid circuit along "its entire length', Ysaid means comprising a conductive 'support member at leastrcoextensive with said slow wave circuit and extending adjacent thereto, saidl support member having a plane surface, an insulative t support member having a surface extending along and in contiguous relationship with said plane surface, said slow wave Ypropagation circuit being secured to said insulative support member, and means mounted on saidY support member and biasing Ysaid insulative support member against saidv conductive support member. 'Y Y 17. 1A traveling wave tube Vcomprising a rst VendplateV member,` a second endplate member, a conductiversupport-member extending between said endplate members l and Vcontiguous thereto, said conductive VsuPPOrtrmember having ra at surface, an insulative support member positioned on .said at'rsurface, a slow wave propagating cir- Y cuit 'secured' to said insulative support member, spring conductivecsupport member'toY said endplate membersY after radial adjustment of the position of said conductive support member.Y Y

. 18.,A Ytraveling wave tube 1n accordance with claim Y 17 further comprising a rst metallic envelopejportionr around Vsaid conductive support member and vsecured to 12 said ''rst endplate member and a second metallic 'envelope portion around said VVconductive support member landsecured to said `second endplate member, said `metallic en` velope portions having abutting deformablev ange's.

19. A traveling wave 'tube lcomprising ajrst and second jendplate, a substantially massive conductive support -memberextending between rvsaid endplates and -adjustably secured thereto, Vsaid conductivemember having awlon'gi-V tudinal groove therein and a at surface longitudinally extending adjacent said V'grooveya substantially Y Wedgeshaped insulating Vsupport member having a first surface on said Vfiat sur-face;and,a slopingjsurface at an angle to said rst surface, a small conductive wire helixmounted byY said insulating support member at the `edge intersection of said first and sloping surfaces and positioned in said groove, spring means bearing against said Ysloping Ysurface and biasing` Vsaid 'rst surface against said at surface, electron gun meansV mounted by said iirst endplate to the, other side thereof than said'conductive "support member,'and electron collector means mounted by said second endplate to lthe Yother side thereof than said g conductive means.

20. A traveling wave tube in accordance with' claim 19 further comprising a conductive lossy coating on said sloping surface continuous `to said 'helix and said spring means for applying adirect-current potentialto said helix from said conductive support member.

References Cited in the le of this patent UNITED STATES PATENTS 2,740,068 Robertson et al. Mar. `27, 1956 2,788,465 Bryant et a1. Apr; 9, 1957 Y FOREIGN PATENTS

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