US 2853643 A
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A. H. lvERsEN ELECTRON DISCHARGE DEVICE sept. 2 3, 195s Filed March 1, 1955 IN VEN TOR.
- velope. side of each indentation. A cantilever beam spring ac `tion of the portions of the ferrule engaged with the i11- nited States f" atent f nice ELECTRON DISCHARGE DEVICE Application March 1, 195s, seria1N0.491,27s
6 claims. (ci. als-3.5)
This invention relates to electron tubes and more particularly to means whereby a hollow metallic cylinder may be securely mounted within a hollow dielectric cylinder.
- In a microwave tube, such as a traveling-wave tube, a conductive cylinder called a matching ferrule is employed Within the envelope of the tube adjacent an electron gun to prevent the loss of electromagnetic energy by radiation from a waveguide which is disposed about the envelope. In many cases, it is desirable to restrain the radial and axial movement of the ferrule within the envelope by making aV plurality of indentations in the envelope about its circumference at each end of the ferrule. lt is necessary, however, to heat the ferrule by induced currents to volatilize gases occluded by the ferrule which are constantly removed while evacuating the envelope. This and other methods of heating generally cause the envelope to break due to the different thermal expansion coefficients of the envelope and the ferrule. To make matters worse, the envelope in the above described outgassing process is maintained at room temperature.
It is therefore an object of the invention to provide a mechanically strong vitreous support for a metallic cylinder.
It is another object of the invention to provide an envelope support for the matching ferrule of a microwave tube.
In'accordance with the invention, a matching ferrule for a traveling-wave tube is disposed within the tube envelope between a plurality of indentations in the en- The errule is axially slotted at its ends on each dentations is then produced, whereby the dilerential thermal expansion between the ferrule and the envelope produced by heating the ferrule is prevented from breaking the envelope.
' The novel features which are believed to be char-v acteristic of the invention, both as to its organization Rand method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with,
is not intended as a definition of the limits of the invenl tion.
Fig.' lis a sectional View of a traveling-wave tube in which the mechanical support of the present invention is j incorporated;
Fig. 2 is a sectional view on the section line 2-2 inf`r j Y Fig. 1;
tion-of the travelingwave tube of Fig. 1 shown in Fig. 3;
Fig. 5 is a broken section of a traveling-Wave tube illustrating an alternative embodiment of the present invention; and
Fig. 6 is an enlarged broken-away section of the portion of the traveling-wave tube shown in Fig. 5.
Referring to the drawing, there is shown in Fig. 1 a traveling-wave tube 10 having a rectangular input waveguide 12 and a rectangular output waveguide 14. The traveling-wave tube 10Y is provided with an .evacuated envelope 16 which maybe made of glass having an enlarged portion 18 at its left end. Within the enlarged portion 18, there is shown an electron gun 20 comprising a cathode 22 which 'is provided with a lament 24, a frusto-conical focusing electrode 26, and an accelerating anode 28. Focusing electrode 26 has a frusto-conical internal surface of revolution disposed 671/2 degrees from its axis of symmetry.
In the direction of electron flow from the gun 20, there is shown disposed within the elongated portion 30 of the envelope 16 an input matching ferrule 32 which is connected over an antenna lead 34 to a conductive helix 36 which is employed to propagate electromagnetic Waves at a velocity substantially less than the velocity of light. Conductive helix 36 is in turn connected over an antenna-lead 38 to a conductive output ferrule 40. At the end of the elongated portion 30 of the envelope 16, a collector electrode 42 is positioned to intercept the stream of electrons.
A conductive sleeve 44is disposed about a portion of the elongated portion 30 of the envelope 16 coextensive with input ferrule 32. The conductive sleeve 44 is disposed adjacent the left side of the input waveguide 12. A conductive sleeve 46 is simifarly positioned adjacent 1 output waveguide 14 coextensive with output ferrule 40.
A sectional View of the tube 1t? is shown in Fig. 2 taken on the section line 2 2. In Fig. 2, the conductive sleeve 44 is disposed on the outside of the envelope 16 which is in turn disposed contiguous to the circumference of the matching ferrule 32 which has three cantilever beam extensions or tongues disposed 120 degrees apart at each end, only the left end of the matching v ferrule 32 being shown in Fig. 2. The cantilever tongues .is outjgassed. Envelope breakage is prevented for a number of reasons. Firstly, the energy represented by the diilerential thermal expansion is taken up bythe cantilever springs formed by the tongues 120. Secondly, the beveled surfaces 132 make the energy transfer a gradual one. Thirdly, heat is conducted away from the ferrule 32 at the point where the tongues 120 are in contact with the envelope 16. Fourthly, the slots 122 prevent the circulation of circularly induced electric currents directly Within the tongues 120, whereby the envelope 16 may be kept relatively cool at the indentations 130. This is important `because when-a relatively high vacuum is maintained within the envelope 16, soft heated spots, such as the indentations 130, may suck in or collapse and ruin the vacuum seal.
The exact structure of the envelope 16 near the indentations 13G is shown in Fig. 4. By having the end of the input ferrule 32 beveled as indicated by 132, the indentations in the envelope need not be made so deep that a direct axial stress will be imposed against it by the axial the envelope. 'heating the envelope 152 and makingthe indentations 154 expansion of input ferrule 32. This is important in that the smaller the radius of the bend in a glass, the weaker the glass is, that is, the smaller` its ultimate strength. The input,ferrule.,32 is in fact mounted within the envelope 16 by placing it concentrically within the .envelope and subsequently making the indentations 130. Onlytwo indentations, need `be made and only` two .cantilever tongues 120 needbeemployed. However,a more securemechan- `ical support may bevprovided for thetferrule 32 Whenthree cantileveltongueslZl lare used ,and three indentations 130 vin the 4envelope 16 are employed Yat each endof the ferrule ,32. The outputfferrule is constructed in ka manner .similar to input ferruleSZ witha plurality ofindentaltions-in theenvelope 16disposed about it.
.Fig. 5 .'shoWs an alternative embodiment of the inventionwhere a matchingtferrule 150 is showniwithin an envelope 15.2. The envelope hasa plurality of indentations 154 and 155fdisposed about each end of the'ferrule .150. similar to the indentations 130 in the envelope 16.
The indentation 154 is however disposed around a substantially right angle turn or bend in the ferrule 150 at the edge 156. 'The ferrule 150 has tongues V158 similar to 'the tongues'120 of input ferrule 132 and provided by slots 160 similar to the slots 122 in input ferrule 32. However, due to the right angle edge156 of the ferrule 15Dfand the lack of a beveled edge such as the edge 132, it is necessary to produce indentations 154 before the. ferrule 150 is inserted within the envelope 152. This requirement is made in order to avoid the production of a right angle or small radius turn in the inside surface of the envelope 152 at the sharp edges'156 of the ferrule 150. The right end of the ferrule 150, however, must necessarily be supported or restrained from axial and radial movement by making indentations 155 after the ferrule 150 ,is inserted within the envelope `152. Thiscauses the envelope 150. to have an unusually small radius which is indicated by an arrow 170 in Fig. 6 where an enlarged broken-away section of the right-hand portionof the ferrule 150 and the envelope 152 with the indentation 155 ,is shown` cause the envelope to break at 155 when a beveled end or beveled surface 132 isnot provided on the input ferrule 32 or when a slanting surface Asuch as a surface 172 is not provided inside the envelope 152. The slanting surface 172 near the indentation 154- in Fig. 5 serves the same purpose as thatof the beveledV surface 132 onthe ends of the input ferrule 32. The sloping surface 172 however cannot-be made when theferrule 150 is disposed within Hence, the indentations 154 are made by with a pointed tool. This istrue because the glass will ow around the corners 156 of the ferrule 150 in spite of what may be done to prevent it from happening.
A sturdy ferrule support may thusbe obtained by practicing vthe present invention and a ferrule may be heated for out-gassing purposes without fear of breaking the dielectric or glass envelope disposed about it, breakage being a current problem because of the thermal expansion of the ferrule.
" What is claimed is:
1. In an electron tube, a mechanical support comprising a hollow dielectric cylinder having a plurality of inndentations disposed about its circumference in a plane intersecting said dielectric cylinder, and a hollow metallic microwave matching ferrule cylinder having a predetermined length disposed withinv said dielectric cylinder having oneV endytouching said dielectric cylinder only at said indentations, means for restraining the radial and axial movement of the metallic cylinder within said vitreous cylinder at the other end of said metallic cylinder,said metallic cylinder having a plurality of slots extending raxially `into said metallic cylinder for an axial distance whichis short with respect to said length from the one gend-of said metallic cylinder adjacentV said indentations, :said slots being disposed on both sides of each of said rlhe axial expansion of the ferrule 150 may indentations whereby said slots provide a radial supporting tension in a manner such that said dielectric cylinder is not fractured when said metallic cylinder is heated by radio frequency currents.
2. In an electron tube, a mechanical supporting structure comprising a hollow vitreous cylinder having a plurality of indentations disposed about its circumference in a plane intersecting its length, and a hollow metallic microwave matching ferrule cylinder having atleast one beveled end disposedwithin saidvdielectric cylinder, said beveled end touching said vitreous cylinder only `at said indentations, means for restraining the radial and axial movement of ythe metallic cylinder within said vitreous cylinder at the other end of said metallic cylinder, said metallic cylinder having a plurality, of slots extending axiai-ly into said metallic cylinder from the one end of said metallic'cylinder adjacent said indentations, said slots being axially short compared. to the length of said metallic cylinder and being disposed Von either side of each of said indentations, whereby said slots provide a radial supporting tension in a manner such `that said Vviterouscylinder is not fractured when said metallic cylinder is heated by radio frequency currents asfor purposes of outgassing said electron tube.
3. In combination, in a traveling-wave tube ofthe character `including slow-wave` structure means f for propagating'traveling waves therealong, a vitreous evacuated envelope having a plurality of indentations disposed about its'circumference at a point along its length, and a hollow metallic cylinder microwave matchingferrule for-said slow-wave structure means disposed within-said evacuated envelope havingrat least-oneeendtouchingsaid evacuated envelope'only atsaidfindentations, means for restraining thev radial-and'a-xial movement-of`the metallic cylinder within said envelopeV at the-other end-of-sa-id metalliccylinder, said-metallic cylinder having a plurality of slots extending axially into Saidmetallic cylinderlfrom the one endof said-metall-ic-cylinder adjacent'saidindentations for a ldistance which -is short `compared to said predetermined length, said-slotsbeing disposed on 'both sides of each of said indentations whereby said slots provide a radial supporting tension in a manner suchthat said-vitreous envelope is not fractured .when said metallic cylinder is 'heated by radio frequencycurrents as for `purposes of outgassing said traveling-wave tube.
4. Av microwave tube comprising an evacuatedglass envelope, ay slow-wave ystructure means disposed therewithin, an electron gun disposed-.at one end `of said. e11- velope for producing `an electron streamfa waveguideldis- .posed about said envelope, a conductivesleeve disposed about said envelope adjacent-one side-of-said. waveguide, said envelope having a plurality of indentationsadisposed about its circumference at each endof saidv sleeve, andra conductive microwave matchingeferrulenfor said slowwave structure means disposed within said envelopegbetween the circumferential. indentations-at each end of said sleeve andcoextensive with said sleeve andfhaving its ends touching said envelope .only at said indentatiOnS, said conductive ferrule having a ,pluralityr ofslots which are short compared ,to the lengthof saidferruleextending axially into said conductive .ferrule from each, end .of said conductive ferrule adjacent'said indentationsysaid slots beingdisposed oneitherside-.of each of saidiindentations whereby said slots provide-,a radial supporting -tension in a rnannersuch` that said glass envelope is not -fractured when said conductive ferrule is heated by radio frequency currentsas for purposes yof foutgassing- `Suchnmicrotvave tube.
5. A traveling-wave tube comprising :an :evacuated glass envelope, a slow-wavestructure disposed therewithin, an electron gun disposed at one end of said envelope for producing an electron stream, Aa-,rectangulanwaveguide disposed about said'.,envelope,a..conductivefsleeve disposed about said ,envelopeadjacenbxone side, of said waveguide,.said envelope, having aplurality of indentations disposed about its circumference at each end of said sleeve, and a conductive microwave ferrule terminating at the end of said slow-wave structure and having beveled ends disposed within said envelope between said circumferential indentations Icoextensive with said sleeve and having its ends secured by said envelope at lsaid indentations, whereby the radial and axial movement of the metallic cylinder with respect to the vitreous cylinder is restrained, said conductive ferrule having a plurality of slots extending axially into said conductive ferrule yfrom each of its ends, said slots being axially short compared to the length of `said ferrule and being ydisposed on each side of each of said indentations to prevent the differential thermal expansion between said conductive ferrule and said envelope from breaking said envelope.
6. An electron tube comprising a hollow dielectric cylinder, a slow-wave structure disposed within and along the length of said hollow dielectric cylinder, a plurality of protuberances extending inwardly from the inside surface `of said dielectric cylinder in at least one plane perpendicu- 20 lar to the longitudinal axis of said dielectric cylinder, a hollow metallic cylinder forming a microwave matching ferrule for terminating `said slow-wave structure constrained within said dielectric cylinder and having at least one of its ends touching said dielectric 'cylinder only at said protuberances, means including said-protuberances for restraining the radial and axial movement of said metallic cylinder within said dielectric cylinder, said metallic cylinder being beveled on at least one end and having a plurality yof slots extending axially into said metallic `cylinder from the beveled end, said slots being axially short compared to the length Iof said metallic cylinder vand being disposed on both sides of each of said protuberances adjacent said slotted end of said metallic cylinder to prevent the differential thermal expansion between the metallic cylinder and the dielectric cylinder from breaking the dielectric cylinder when the metallic cylinder is heated by radio frequency currents as for purposes of outgassing said electron tube.
References Cited inthe file of this patent UNITED STATES PATENTS 1,581,520 Schwerin Apr. 20, 1926 2,417,061 Chilcot et al. Mar. 11, 1947 2,584,597 Landauer Feb. 5, 1952