US2876379A

US2876379A - Traveling wave tube structure

Info

Publication number: US2876379A
Application number: US583669A
Authority: US
Inventors: Lauer Anton; Bruck Lothar
Original assignee: Telefunken AG
Current assignee: Telefunken AG
Priority date: 1955-05-12
Filing date: 1956-05-09
Publication date: 1959-03-03
Anticipated expiration: 1976-03-03
Also published as: GB798622A; NL207090A; DE1209662B; FR1153479A

Description

March 3,1959

A. LAUER ErAL TRAVELING WAVE TUBE STRUCTURE SSheets-Sheet 1 Filed May 9, 1956 .Irlllllllllllllllllflllll:illlllllflllllllri w w W QNx March 3, 1959 A.LI- \UER ETAL 2,876,379

TRAVELING WAVE TUBE STRUCTURE Filed May 9, 1956 3 Sheets-Sheet 2 v Inventors 472 for: Lauef XLaf/fanBr'cfi March 3, 1959 A. LAUER ETAL' 2,876,379

TRAVELING WAVE TUBE STRUCTURE Filed May 9, 1956 3 Sheets-Sheet 3 Inuemans; flnforz ldver zflafzdrfrick 2 M United States Patent TRAVELING WAVE TUBE STRUCTURE Anton Lauer and Lothar Briick, Ulm (Danube), Germany, assignors to Telefunken G. m. b. H., Berlin, Germany Application May 9, 1956, Serial No. 583,669

Claims priority, application Germany May 12, 1955 11 Claims. (Cl. BIS-3.5)

The invention relates to the electrode structure for a traveling wave tube having a delay line built up as a helix.

7 With the well known traveling wave tubes of this kind, the wire helix, serving as a delay line, is embedded between at least three ceramic rods serving to support the helix line. That is because the helix line is generally made from a relatively thin wire which does not ensure the necessary stifiness of the helix. Theassembling of .the tube system is hereby doneas is for instance clearly .shown in Fig. 1 of the French patent specification .954,964---in a way that the ceramic rods together with the helix are pushed into a gaged glass tube into which .there are likewise pushed corresponding structural parts of the electron gun as well as the electron catcher of the tube. With said well known arrangement, the helix line together with its supporting means, therefore, forms a structural part separate from both the electron gun and the electron catcher. Moreover, this kind of helix support requires a most exactly calibrated glass tube. This will be extremely difiicult if the tube is to be operated with very short waves at which the helix line has a diameter of only a few millimeters. Consequently, even the dimensions of the other parts of the tube, such .as those of the calibrated glass envelope, of the electron gun system, etc., will at the same time decrease. Said well known structure has been put into practice only with traveling wave tubes to be operated with relatively longer waves. Therefore, another method has already been used as for instance shown in the journal Die Telefunken-Rohre, No. 32, page 4, Fig. 1, consisting in the fact that the cage of the helix line support, formed by the ceramic rods, is maintained, whereby said cage in itself is self-supporting. In order to obtain a proper location of the axis of the electron gun with respect to that of the helix line, there is, with said well known arrangement, provided a further cage of ceramic rods into which both the electron gun and the cage of the helix line support are built. Thus, there is obtained a rigid structural unit which can be assembled and adjusted as a whole, before being mounted in the vacuum vessel. In some respects, even this structure of a traveling wave tube does no longer fully meet the requirements for very short waves, because the double ceramic cage requires a relatively great diameter of the tube, which, it is true, is advantageous with tubes for relatively longer waves, but which, ,on the other hand, with tubes for very short waves, for instance within the range of about 4 cm., may require a disadvantageously high precision of the single structural parts. In order to prevent said difliculties concerning the helix support, there has been proposed a new method according to which the helix line, in spite of its "favorable electrical properties, may be dispensed with. Instead of said helix line, a metallic block, provided with longitudinal and transversal slots, is used as a delay line, whereby said block does not require any special support- "ingmeans." In'order toachieve, with said metallic block being provided with longitudinal and transversal slots, quite handy dimensions, so-called spatial harmonics have been used for operating the tube, said spatial harmonics, as well known, occurring with delay lines having a periodical structure. Such a type of tube has for instance been described on the pages 1035 to 1043 of Proc. of the I. R. E., 1951.

It is the object of the invention, even for the operation with very short electro-magnetic waves, to provide traveling wave tubes having helix-shaped delay lines,

whereby the difiiculties, arising above all in this frequency range, such as the alignment of the electron beam axis with respect to the helix line axis, shall be overcome.

The invention is hereby based on the well known method of supporting a helix line wherein said helix line is embedded between several rod-like supports of insulating material, such as ceramic, quartz, or glass. For the purpose of adjusting the structure of the electrode system outside the tube envelope, said supports of the helix line are, in accordance with the invention, fastened to a part of the electron gun system or of the electron catcher of the tube by soldering or cementing said part which serves as a structural base. That is why the cementing or soldering tothe part, serving as a structural base, can be easily done with such a precision that the helix line will always be properly embedded between the rods. i. e. by properly locating it to the above mentioned rodlike helix supports, it is at the same time assured that the electron gun will be located in the position desired, i. e. that the axis of the electron gun coincides with the axis of the helix line. It is recommended to choose the diameter of the helix support rods, in particular when using ceramic material, within the same range as that of the helix diameter, since hereby, on one hand, the necessary rigidness is ensured, and, on the other hand, an almost complete dispersionlessness is obtained, which is most advantageous with respect to the operation of the tube. While it is, when using a soldering joint without applying any special measures, in general not recommended to fit the rods into the structural base by means of a snug fit, the latter is applicable without any disadvantage, when cementing. The soldering may for instance be done as a butt soldering. But it is even possible to fasten the ends of the rods in the structural base by means of a solder or a well known cement suitable for the use in a vacuum, i, e., it is not fastened in a snug fit, said rods having diameters somewhat smaller than the diameter of the -aperture or recess within said structural base.

Through the German Patent 887,848 it is already known to locate both the electron gun and the delay line within the structure of the tube with respect to one common part, but the therein described well known arrangements have not the essential feature of the invention, viz. the ceramic rods, serving as helix supports, are soldered to a part which serves as mounting base. Contrary to the design according to the invention, with the arrangements in accordance with the German patent specification 887,848, the single structural parts of the tube system do not form a structural unit which can previously be mounted and adjusted outside the vacuum vessel.

w The following embodiments are to illustrate the invention:

Figure 1 is a schematic drawing showing a side view of a traveling wave tube according to the present invention, this figure including wave guide means for feeding into and out of the tube a signal to be amplified.

Figure 2 is a sectional view through the electron gun end and part of the delay line of a practical embodiment of a tube according to the present invention.

By using said part, serving as a structural base,

Figure-.3is,a sectional View through a jig of thetype used-to assemble part ofthe elements of the embodiment of Figure 2. t

Figure 4 is a sectional view through the electron catcher end and part of the delay linesupportsof a practical embodiment of a tube according tothc present invention.

Fig. 1 shows a schematic diagram 'of a traveling wave tube according to the invention. With said embodiment the fvacuum vessel of the tube consists of a metal-cup 1 which contains the electron gun, and which is followed by a tubular cylinder 2 of insulatingmaterial, such as glass or ceramic material.- Said tubular part 2 is tapered at the end adjacent to the metal cup 1 in order to reduce the lever effect at the joint, i. e. at the glass-tometal seal or" at the estimate-metal seal, when introducing the tube in the amplifier. At its other end, said tubular part 2: is terminated by means of the electron collector 3. The feeding ofthe radio frequency waves is done by a schematically indicated wave guide 4 which may be connected to the metal cup for instance through springy contacts 5, and which maybe connected to the helix line through a quarter-wave length resonator 6. The

coupling oht device

7, 8, 9, which likewise contains a wave guide, is designed in a similar way. For the purpose of avoiding a radiation of radio frequency waves along the helix line, the tubular part 2 of the vacuum vessel is surrounded by a metallic screen 10. The bundled guidance of the electron beam along its way through the helix line 11 is done by means of the coaxial magnetic field of a solenoid 12 which, however, may be replaced by'a corresponding arrangementof permanent magnets or. by electrostatic focussing means known per'se. The sun line is embedded between three ceramic rods 13 only two'of which are to be seen in Fig. I. Said ceramic rods 13am soldered to a metal part arranged within themetal cup 1, said metal part serving as a mounting base, whereas at their other ends they are merely axially guided in the collector 3. In the embodiment described, the ceramic rods 13 are soldered to the mounting base 15 atjsuch reciprocal distances that the helix line 11 may be with sliding contact introduced between the rods. Thus, any damage to thehelix line, such as the slightest bending of single windings, is practically prevented. The fitting of the helix will then be efiected during the assembling of the structuralunit by means ,of a clip 50 which slightly presses the ceramic rods 13 against the helix line 11. In the embodimentdescribed, said clip 50 is arranged within the range of an attenuatingdevice 14 to prevent. any field disturbation on the helix lines It goes without saying that, instead of one clip, even several clips distributed along the overall length of the helixline. or other suitable devices, such as mica rings or ceramic disks, may be provided. The ceramic rods 13, however, may also be soldered to the mounting base as such reciprocal distances that the diameter of the inscribed circle, resulting fromj such distances, is equal to the diameterof the helix line, so that the ceramic rods are to be slightly bent oil when introducing the helix. In this case, the.

clips 50 may be dispensed with, but even here it is useful providing at least one clip or any corresponding means if the rods shall be brought in a particularly uniform touch with the helix line. The attenuation device 14 consists in a 'spirally shaped graphite strip' to bedeposited onat leastone ofthe rods 13, said strip serving to absorb the waves recurring from the output of the tube to its input. The design of said attenuation arrangement corresponds to that shown in Germany Patent 932,731. Therefrom results a particularly high degree of reflectionlessness with ashort structurallength, which .in practice, es ially with the embodiment of a traveling ,wave tube shown in Fig. 1, isrn ost useful.

"In Fig; .2 there are shown details .of theconstruction ffihse s t i side i e re b in we gierutisa..9r uss i a ama with J Huma the metal cup 1 of the arrangement of Fig. 2, there is arrangcdthe electron gun which is contained in-thc interior of a further metal cup 15 which is here used as an accelerating electrode/or anode. Said metal part 15 is, at its front surface facing the helix, provided with recesses in which the ceramic rods 13 have been soldered by using a jig. As regards the solder, a silver solder may hereby, insa. well known way be used, which, after an appropriate preparation of the ends of the ceramic rods 13, results inv asufficiently good joint.

Thesoldering of the ceramic rods .13 to the mounting base 15 may for instance be done in the following way:

The mounting base 15 isas shown in Fig. 3s1id over-a soldering jig, which has a cylindricalyor tube-like projection 42 extending in the direction of the helix axis. Said projection 42 is surrounded by three guiding-rods 43 parallel to the axis, whereby only two of them are to be seen in Fig. 3. After sliding the mounting base 15 over thepart 42, a rod-shaped jig 44-, having the same directionas the helix line, is introduced in a centrical boring 'of the part 42; Thereupon, the ceramic r0 ds "13, being exactly ground with respect to their diameterfare fittedfin therecesses provided for the soldering joints in the bottom of the mounting base 15, said ceramic rods 13 being at the same time pressed, by means of springy clips 45, against two sections 46 of the rod-shaped'jig 44, having a somewhat greater diameter. According to oneof the two before mentioned embodiments, the diameter of said sections 46 has hereby been chosen such that the diameter of the inscribed circle between the ceramic rods, resulting from the diameter of said sections 46, is slightly greater than the outer diameter of the helix later on to be embedded between said ceramic rods 13. After said ceramic rods 13 have been fitted in the mounting base 15, and after the solder has'at the same time been inserted, e. "g. in the form of a solder ring, the upper part 47 ofthe jig is slid over the guiding rods .43, said part 47, by means of guiding borings, preventing ajtwistr ing of the ceramic rod cage from that side, at the same timeslightly pressing the ceramic rods 13 against the mounting base 15. For the pur'pose of securing the cage, on its side adjacent to the mounting base, against any twisting, the position of the mounting base is fixed in the place 48 by means of a groove and a tongue. After that, the soldering, can be done, e. g. in an inertgas 7 atmosphere, by heating withthe help of an induction loop 49 of a radio frequency soldering device. After the soldering process, the

parts

44, 47 of the jigas well as the clips 45 are removed, whereafter the ceramic cage together with the mounting base can be used as a structural unit fortheassenibling of the electrode system.

Corning baek tojFigl 2, further details of a.tube iuac cordance the invention are shown. The further parts of theelectron gun, su ch as the,cathode.16 and the Wehnelt electrode 17, are, by means of ceramic distance pieces-18 and 19,.introduced 'in the metal part 15 servingas amounting base. The metal part 15 is then closed by a further metal part 20, which in the embodiment is likewise cup-shaped, in a way that by means ofboth the distance,

pieces

18, 19 and said part 20, the

electrodes

15 and 16 of the electron gun are properly aligned with respect to the accelerating Yanode 15. The difierent electrodes of saidelectron gun are connected, over

flexible conductors

21, 22, to the lead-ins 24 arranged in thesinter glass socket 23. Said sinter. glass socket 23 issealed to a .furthermetal cup 1', so that-there is obtained a complete structural unitconsisting of the ceramic rods and the helixlinc -system together, with its coupling devices, and theleleetronjgun contained in the mounting base 15; Sincethehelix linetogether with itscoupling devices 6, 7is already to be embedded between the ceramicfrods and adjusted, before, introducing it in the vacuum vessel,

order to ensure that, during the operation of the tube, too much radio frequency energy can escape through said aperture, there is, in the embodiment of Fig. 2, additionally provided a hat-like metal part 26 which has already been assembled to the structural unit to be introduced in the vacuum vessel. In order to ensure that said hat-like part 26 does not change its position with respect to the bottom of the metal cup 1, the whole structural unit in the ready-assembled tube is pressed with its shoulder 29 against the bottom 30 of the metal cup 1 by means of a pressure spring 27 which at one of its ends engages the plate-like part 28 arranged within the part 1', and which at its other end engages the bottom of the part 20.

The electrical connection of the helix 11 with its coupling devices is, in the embodiment shown, effected such that the free end 33 of the helix line 11 is electrically connected to a tubular metallic projection of the hatlike part 26, for instance by means of spot welding or soldering, and such that said hat-like part 26 is electrically connected to the cup-like metal part 1 of the vacuum envelope, for instance by giving it an elastic property in the respective joining place. In order to insulate the metal cup 1 together with the helix line 11 from the mounting base 15 which at the same time serves as an accelerating anode, a distance plate 31 of insulating material is inserted between the two parts pressed together.

The vacuum tight joint between the parts 1 and 1' is usefully done by means of a so-called concentrator soldering 25 with the metal part 1' being so far slid into the metal cup 1 that the pressure spring 27 with a sufiicient strength presses the electron gun against the bottom of the metal cup 1. Any lateral displacement of the electron gun during said process, firstly, by making the shoulder 29 of the cup bottom sufiiciently large, and secondly, by providing an axial guidance of the ceramic rods 13 in the hat-like part 26. With the embodiment of Fig. 2, there is provided an additional ceramic guiding axis 32 which at one of its ends is fixed in the metal cup 20 closing the mounting base 15, and which at its other end is axially guided in the metallic disk 28 of the part 1. Taking into consideration the small diameter of the whole tube, which for instance corresponds to the dimensions shown in Fig. 1 at the scale of 1:1, it is furthermore recommended to use, as socket for the tube, a so-called pico-socket, since said socket can be directly sealed to the metal part 1, which ensures simple manufacturing.

The dimensions of the essential structural parts of an embodiment of an arrangement according to the invention, i. e. the diameter of the helix line system together with its coupling devices, the diameter of the electron gun, etc., are furthermore usefully to be chosen such that there is a sufliciently great distance between the vacuum envelope and said structural parts, so that merely the central position, within the bottom 30 of the cup, of the before mentioned structural unit, consisting of the electron gun and the helix line system together with its coupling devices, is determined by the hat-like part 26 by means of the guiding borings for the ceramic rods 13. This is obtained by the fact, as is to be seen from Fig. 2, that the dilatation of the structural unit is possible in two directions, one of which refers to the ceramic rods and extends towards the electron catcher, and the other one of which refers to the electron gun and extends toward the socket side of the metal cup 1. As already shown in Fig. 1, the ceramic rods 13 are for this reason at the catcher-side end of the tube only guided in axial direction.

Fig. 4 shows the details of an embodiment for said design according to the invention. The tubular section 2 of the vacuum vessel, which may for instance consists of glass, is sealed to a shoulder of a cup-like metal part 34. Thus, the approximately equal diameters for the tubular vacuum -envelope 'andfor the'cup lik'e metal part 34 may easily be realized. The three ceramic rods 13 rest in borings provided in the cup-like part, whereby said bor- .ings are to be recognized at the lower end of the drawing.

'As' to their length, the rods are dimensioned such that they have a certain play in the axial direction of the tube, whereby it is ensured that they cannot hitthe electron catcher 35 itself. The electron catcher 35 itself is pro vided with a tubular cylindrical part 37 made of metal, said part 37 being vacuum tightly sealed to a corresponding cylindrical part 36 of the metal cup 34 by means of a sinter glass seal 38. The tubular inserts 36, 37 are vacuum tightly joined to their respective parts by means of soldering. Since the design of the exhaust tube is made similar to that of well known constructions of traveling wave tubes of this kind, it is not fully shown in Fig.

4. At the upper end of the metal cup 34 engaging the ceramic rods, there is again arranged a metal hat 40 to whichthe free end of the helix line not shown in Fig. 4 is to be conductively connected, by spot welding or soldering, similar to the arrangement shown in Fig. 2.

The before mentioned embodiment is to illustrate that with the construction of the electrode system according to the invention it is possible to assemble the helix system, including its coupling devices, and the electron gun to be} come a rigid structural unit by means of a metal-to-ceframic soldering, which can be easily made with high precision, even with verysmall dimensions of the helix line and the-different structural parts. Thereby it is possible to properly align said parts already outside the vacuum vessel, and thereupon to insert them in an exactly prede termined way into said vacuum vessel. Any mechanical stresses inside the vacuum vessel, which may for instance occur with the well known arrangement described in Fig. 1 of the above French patent specification 954,964, are

thereby entirely prevented.

ized such that part of the electron catcher of the traveling wave tube, e. g. the cup-like metal part 34, is used as a mounting base, and that the electron gun is directly fastened, e. g. by means of clips, to the other free ends of the ceramic rods 13. Instead of said clip or of a corresponding cement joint, even a further metal-to-ceramic soldering may, however, be used in this case, similar to the arrangement according to Fig. 2. In this case, however, it should be observed that the tube envelope has free space for dilatation in axial direction, independent of both the electron gun and the helix system together with its coupling devices, for the purposes of preventing unde sired mechanical stresses. It is, therefore, useful designing the feeding conductor between the tube socket e. g. 23 in Fig. 2 and the electron gun to be flexible. The construction, having an electron gun which is directly built in between the ceramic rods 13, is above all suitable with tubes having a small cathode diameter, i. e. for socalled initial stages or low-noise tubes. In this case it is, moreover, easily possible to keep the diameter of the vacuum vessel at least approximately constant over its whole length, which, with traveling wave tube amplifiers, is often required for reasons of construction.

It goes without saying that the electrode system according to the invention is extremely advantageous with traveling wave tubes having helix lines of a very small diameter, i. c. with traveling wave tubes to be operated within the range of the shorter cm.-waves. However, the electrode system according to the invention may also be advantageously used with traveling wave tubes to be operated with somewhat longer waves, since said system, compared to other well known systems for said range, can be manufactured in a considerably simpler and more exact way.

asst-ne tgr nsss se ua sert:t gsl s qnssyn sheulstbe res t d s slsstronzsst atsure. h iwslslet o inst ce obtained by ,makingsthe u'netal cnp 1' .in Fig. 2, co nlng, the electron gun, :andjor the mounting base Bis: 2.v ..m sns iga s sn s ma a e of iron o1nKf gvz 1r-.

Weclaim:

1. A, traveling wave tube comprising a vacuun envelope; anelectroh gun sub-assembly; an electron catcher sub-assembly; a delay line including an elongated helix disp sed, between said sub-assemblies in the assembled traveling wave tube; and a. delay linesupportingcage including a plurality t of rods of insulating material, said rods being disposed parallelto the axis of the lhelix and touching the outerpefriphery thereof; the rods-at oneend ofthe cagebeing all rigidly .fixed sto one of said subassernblies toaxiallyalign the helix therewith, and the other sub-assembly beingrigidly fixed to said. envelope and having rod tguide meansfor slidably receiving-the rods at ..t bther end of saideageand supporting them transverselyof said axis, theenvelope having abutment centering means for: receivipgsaidone of said subassemblies and forsupporting it in spaced ,axialalign ment withsaid other sub-assembly, closure means for Closing the, envelopeafter insertion of. saidone of said sub-assemblies and 'delaytline in axial alignment with said other sub-assembly, means operative between the envelope and sai d on e.of said sub-assemblies for maintaining the latter engaged in said abntrner tv and v centering n eans and said. one sub-assembly being the, electron/gun sembly and comprising -,electron stream vemitting H and latleast one anode electrodebetweensaid emittingmeans and said delay line, said anode electrode senvingas a mounting base to whichsaid rods are directly attached 2. In a tube as set forth in claim; I, saidanode electrode being, cup-shaped and opening away from said delay line said rods being'attachedtothe outer surface atthe closed endoftheelectrode; insulated-spacers insertable in said cupshaped electrode and shaped; tosupport said electron stream emitting means; and retaining means receivable vvithin said cup-shaped electrode for ,securing said spacers and saidemitting rneans therein.

3. In ,altube as set forth in claim .1, said abutment and centering means being complementary in shape with at least ajportion of said anode electrode, andsaid means operatiye between said envelope and said .pnesub-asserm lyi c mp is n r n m ans-" om r ss d n tsaid anode electrode and 'urging it toward said electron 1 4.1a a tubeas set, forth in; claim, 3, an insulator disposed between said anode electrode andsaid abutment l ii qii l a 5. A traveling, wave tube comprising a vacuum envelope; an electron gun sub-assembly; an electron catcher subi-assemblyra delay line including an. elongated helix disposed between said sub-assemblies in theassembled traveling. wave tube; and a delay line supporting cage including a plurality of rods of insulating material, said rods being disposed parallel to the axis of the helix and touching the outer periphery thereof the rods atone end of the cage being all rigidly fixed to one of said sub.- assemblies to axially align the .-helix;therewith, and the other sub-assembly being rigidly fixed to said envelope and havingrod guide means for slidably receiving the rods at the otherv end of said cage and supporting them transversely of said axis, the envelope having abutment e s atstias mea f rlr s xi s idl w Said ubssi hli l arrant it ce axi l mentiwitlr said other sub-assembly, closure means for closing the envelope after insertion: ofsaid one of said ing the latter engaged in said abutment and centering g5 meang andsaid envelope comprisinga vessel of insulatingumaterial closed at one ,endby said electron catcher sub-assembly,andasealed. at its other end. to a metal sleeve, said abutment and centering means being located in the sleeve and said envelope closure means being fixed at the open end of the sleeve.

6. In a tube as set forth in claim 5, said closure means comprising an annular member of such diameter as to telescope into said open end of the sleeve and be sealed thereto, and said annular member carrying a plurality of connection pins, the latter being connected to the parts of the electron gun by flexible conductors.

7, In a tube as set forth in claim 6, said means operative between said envelope and said one sub-assembly comprising a spring compressed between the latter and the said annular, member when telescoped into the open end of said sleeve.

8. A traveling wave tube comprising a vacuum envelope; an electron gun sub-assembly; an electron catcher sub-assembly; a delay line including an elongated helix disposed between said sub assemblies in the assembled traveling wave tube; and a delay line supporting cage including a'plurality of rods of insulating material, said rods being disposed parallel to the axis ofthe helix and touching the outer periphery thereof; the rods at one end of the cage being allrigidly fixed toone of said sub-assemblies to axially align the helix therewith, and the, other sub-assembly being rigidly fixed to, said envelope and having rod guide means for slidably receiving the rods at the other end of said cage andsupporting themtransversely of said axis, the envelope having abutmentand centering means-forvreceiving said one of said sub-assemblies and for supporting it inspaced axial alignment, with said other sub-assembly, closure means for closing the envelope after insertion of said one .of said sub-assemblies and delay line in axial alignment with said other sub-assembly, means operative between the envelope and said one of said sub-assemblies for maintaining the latter engaged in said abutment and centering means, and said envelope comprising a vessel of insulating material containing said electron catcher sub-assembly and containing said abutment and centering means in spaced axially aligned relation, and said catcher sub,- assembly comprising a supporting plate connected with said vessel and having a guide portion disposed normal to said axis and having apertures to receive the rods at said otherend of the cage, the rods, being reciprocable in said apertures to allow for thermal expansion.

9. In a tube as set forth in claim 8,,said supporting plate having an opening therethrough spaced equi-distant from said apertures; and a catcher electrode, behind said plate and aligned with said opening.

v 10. A traveling wavetube comprising a vacuum envelope; an electron gun sub-assembly; an electron catcher sub-assembly; a delay line including an elongated helix disposed between said subrassemblies in the assembled traveling Wave tube; and a delay line supporting cage including a plurality of rods of insulating material, said rods being disposed parallel to the axis of the helix and touching the outer periphery thereof; the rods at one end of the cage being all rigidly fixed to one ofsaid sub-assemblies to axially align the helix therewith, and the other sub-assembly being rigidly fixed to said envelope and having rod guide means for slidably receiving the rods at the other end of said cage and supporting them transversely of said axis, the envelope having abutment and centering means for receiving said one of said sub-assemblies and forsupporting it inspaced axial alignment'with said-othensub-assembly, closuremeans for closing the envelope after insertion of said'one of, said sub-assemblies and delay line in axial alignment with said other sub-assembly, means operative between the envelope and said one of'said subsassemblies forl main: r sin t att re sased in,s id.a tmeutandcenzenns means, and cement disposed in the joints between said rods and said one sub-assembly.

11. A traveling wave tube comprising a vacuum envelope; an electron gun sub-assembly; an electron catcher sub-assembly; a delay line including an elongated helix disposed between said sub-assemblies in the assembled traveling Wave tube; and a delay line supporting cage including a plurality of rods of insulating material, said rods being disposed parallel to the axis of the helix and touching the outer periphery thereof; the rods at one end of the cage being all rigidly fixed to one of said subassemblies to axially align the helix therewith, and the other sub-assembly being rigidly fixed to said envelope and having rod guide means for slidably receiving the rods at the other end of said cage and supporting them transversely of said axis, the envelope having abutment and centering means for receiving said one of said subassemblies and for supporting it in spaced axial alignment with said other sub-assembly, closure means for closing the envelope after insertion of said one of said sub-assemblies and delay line in axial alignment with said other sub-assembly, means operative between the envelope and said one of said sub-assemblies for main taining the latter engaged in said abutment and centering means, and solder disposed in the joints between said rods and said one sub-assembly.

References Cited in the file of this patent UNITED STATES PATENTS 2,727,179 Lally et a1. Dec. 13, 1955 2,740,068 Robertson et a1. Mar. 27, 1956 2,765,421 Robertson et al Oct. 2, 1956