US 3308399 A
Description (OCR text may contain errors)
M. DREES ETA 3,308,399 NG SLEEVE WIT N RAL OUTWARDLY TING SUPPORT NGERS March 7, 1967 J. HELIX BUNDLE BANDI PROJEC 5 Sheets-Sheet 1 Filed April 30, 1963 INVENTORS H M. DRE H A. TER
ATTORNEY March 7, 1967 M. DREES ETA 3,308,399
HELIX BUNDLE BA D NG SLEEVE WITE IN GRAL OUTWARDLY PROJECTING SUPPORT FINGERS Filed April 30. 1963 5 Sheets-Sheet 2 m I INVENTORS JOSEPH M. DREES I l l JOSEPH A. TERESI ATTORNEY March .7, 1967 J. M. DREES ETAL 3,308,399
HELIX BUNDLE BANDING SLEEVE WITH INTEGRAL OUTWARDLY PROJECTING SUPPORT FINGERS Filed April 50. 1963 5 Sheets-Sheet 3 INVENTORS JOSEPH M. DREES. JOSEPH A. TERESI ATTORNEY 7K7 United States Patent tion of Delaware Filed Apr. 30, 1963, Ser. No. 276,881 1 Claim. (Cl. 333-31) This invention relates to traveling wave tubes and more particularly to rod mounted helix bundle for such a tube.
The helix of a traveling wave tube provides a delay circuit by which the forward velocity of a propagating radio frequency signal becomes synchronized with an adjacently located electron beam. The electric field of the signal interacts with the slow space charge mode of the beam in a manner well understood in the art to produce amplification of the signal.
In order to achieve maximum effective interaction between the electron beam and the radio frequency signal on the helix, accurate axial alignment of the helix and the electron gun is required. Ideally, the electrons should flow as closely as possible to the helix for its entire length without interception.
One aspect of the alignment problem is supporting the helix in such a manner that its axis is a straight line. One of the present techniques for so supporting a helix utilizes a so-called bundle consisting of a plurality of ceramic rods, usually three, within which the helix is supported, and several axially spaced sleeves or bands disposed tightly around the rods. Each sleeve is assembled about the rods by radially squeezing the sleeve so as to elastically deform it into a triangular shape when viewed axially, inserting the helix and rods into the sleeve, and releasing the sleeve so that it contracts on and binds the rods. This technique is more fully described in Patent No. 2,943,382, assigned to the assignee in this invention.
Sleeves of this type are difficult to manufacture because I the sleeve wall must be sufiiciently thin to permit elastic deformation and must have uniform thickness so as to apply equal radial forces to the helix.
An object of the invention is the provision of a reproducible precisely formed deformable sleeve having uniform wall thickness.
Another object is the provision of precisely dimensioned thin-'wall sleeves which can be produced at low cost and without special tools or skilled operators.
Another requirement for these sleeves is that they have substantially the same rate of thermal expansion and contraction as the rods and helix in order that the radial banding forces be uniform during temperature excursions incident to operation of the tube. This is accomplished by use of the same refractory metal (tungsten or molybdenum) in the sleeves and helix. However, sleeves formed of such refractory metals are exceedingly difficult to fabricate. Casting is impracticable because of the high melting point of such metals. Excursion of tungsten, molybdenum or the like is unsatisfactory because (1) the resultant sleeve is brittle because of inability to cold work the material, (2) sleeve diameters and wall thicknesses are not precise, and (3) forming die costs are high.
Another object of the invention is the provision of a ductile refractory metal sleeve having a precisely uniform wall thickness and diameter.
A further object is the production of such sleeves at low cost and without special apparatus or skilled operators.
A further disadvantage of prior helix bundles is that pockets of contaminant gases formed during the high temperature processing of the tube become trapped along the lines of contact of the rods and sleeves, and are difiicult to remove. These gases combine with other subsequently formed gases to cause arcing between gun electrodes of the tube.
A still further object of the invention is the provision of a helix bundle having sleeves that permit ready removal of contaminant gases from the tube envelope.
A still further object is the provision of a method and apparatus for forming a helix bundle of the type described.
In accordance with the invention, each of the sleeves which band the rods and slow-wave structure together in a bundle comprises a wire helix formed with adjacent turns in contact with each other and sealed together to form a cylinder. The wire is refractory metal, such as molybdenum, is Wound on a cylindrical mandrel and thereafter is coated with a metallic film to bond and seal adjacent turns. The thickness of the wall is equal to the diameter of the wire and therefore is as uniform as the wire diameter is constant. The inside diameter of the sleeve is that of the mandrel and is substantially as precise. The spiral groove formed on the interior of the sleeve provides a sort of directional passageway along which gas generated during the outgassing cycle passes out of the assembled tube. Another important aspect is that the sleeve wall may be diametrically squeezed or deformed without fracturing the thin refractory metal because the wire comprising the wall is stressed in the proper direction for its elastic deformation. Thus a deformable thinwall refractory metal sleeve having precise dimensions is made with standard helix winding equipment.
The invention will be more fully explained in the following description of a preferred embodiment, reference being had to the accompanying drawings in which:
FIGURE 1 is an elevation, partially cut-away, of a traveling wave tube embodying the invention;
FIGURE 2 is an enlarged transverse section taken along line 22 of FIGURE 1;
FIGURE 3 is an end view, partially cut-away of a jig by means of which the rod mounted helix is inserted into the banding sleeves, one of which is shown in the jaws of the jig;
FIGURE 4 is a side elevation of the jig;
FIGURE 5 is a section similar to FIGURE 2 showing the shape and dimension of the deformed sleeve relative to the rod mounted helix;
FIGURE 6 is an elevation of a sleeve on the helix bundle; and
FIGURE 7 is a greatly enlarged portion of the sleeve wall.
A traveling wave tube which uses a helix bundle is shown in FIGURE 1. The tube has a barrel 2 which encloses the slow-wave structure 4, shown as a helix, and a gun structure 6 which directs an electron beam along tube axis A through helix 4 to a collector at the other end of the tube. This beam interacts with the helix in a well-known manner so that a signal passing from input terminal 8 to output terminal 9 is amplified.
Helix 4 is part of a bundle 10, see FIGURES 2 and 6, mounted in barrel 2. Bundle 10 consists of the helix 4, three ceramic rods 12 extending longitudinally of and engaging the outside of the helix 4, and several axially spaced sleeves 11 clamped tightly around the rods. The rod mounted helix bundle is well known in the art and does not per se constitute my invention which is concerned with an improved construction of the banding sleeves 11.
Referring to FIGURES 2, 6 and 7, each sleeve 11 is cylindrical and has a wall comprising successive turns 11a (see FIGURE 7) of a closed helix of Wire preferably having a circular cross-section. The wire is made of refractory metal such as tungsten or molybdenum. In this closed helix, the turns abut and are sealed to each 3 other longitudinally and form therebetween external and internal helical grooves and 16. External groove '15 advantageously serves to distribute and retain molten brazing material with which the turns are sealed and secured together. Internal groove 16 facilitates axial flow of contaminants from the assembled tube during the final outgassing operation.
In order to support the helix bundle within the barrel 2 of the tube, outwardly projecting fingers 18 and 19 (see FIGURE 2) are formed at opposite ends of each sleeve. These fingers are extensions of the helix wire and are formed by radially outwardly bending equal lengths of wire in opposite directions at the ends of the sleeve. The fingers 18 and 19 have identical shapes as well as lengths and extend from the sleeve body at diametrically opposite points as shown in FIGURE 2. The radial distances from the sleeve axis to the ends of unstressed fingers 18 and 19 are equal and their sum is greater than the inside diameter of barrel 2. The fingers are sprung inwardly to permit insertion of the assembled helix bundle into the barrel and, when released, spring out against the barrel to resiliently hold the bundle concentrically of the barrel axis.
If desired, the fingers 18 and 19 may be omitted and other means may be employed to support the bundle in barrel 2.
By forming the sleeve 11 as a closed wire helix, several important advantages are gained. The thickness of the sleeve wall, being equal to the diameter of the wire is as uniform as the diameter of the wire is constant; i.e., $0.001 inch by well known wire drawing techniques. Refractory metal sleeves having wall thicknesses of 0.005 inch or less are readily formed by practice of the invention and, moreover, the thin wall of this normally brittle crystalline material is readily deformable from a cylindrical to a triangular shape without fracturing. This advantage obtains from circumferentially incorporating into the wall the characteristic longitudinal ductility of wire. Also, the diameter of the sleeve is uniform and is precisely controlled by use of a mandrel for forming the helix initially.
By Way of example, the helix bundle described above has been successfully fabricated and tested in a highpower traveling wave tube and has the following dimensions:
Helix 4 Material Tungsten wire Diameter inches 0.087
Rod 12 Material Quartz Diameter inches 0.100
Sleeve 11 Material s Tungsten Diameter inches 0.283 Wall thickness (wire diameter do 0.005 Length do 0.313
The sleeves are formed on a helix winding machine of the type described in co-pending application, Serial No. 226,982 filed September 28, 1962 and assigned to the assignee of this application. Briefly, refractory metal wire on a reel is fed to a rotating precision mandrel which moves along its axis of rotation relative to the reel so that a closed 'helix is wound thereon. After a helix of desired length is formed, the wire is severed, the ends of the helix are temporarily fastened to the mandrel, and the mandrel and helix are fired in a furnace to relieve stress in the wire. The assembly is then cooled, the sleeve is removed from the mandrel, and is thereafter plated with a thin film of copper.
If desired, fingers 18 and 13 are next formed by outwardly bending the ends of the sleeve. Axial pressure is then applied to the wire turns in a ceramic jig to insure tight contact between turns, and the latter are brazed together in a furnace, the copper plate serving as brazing material. The sleeve is then complete and is ready for application to the helix bundle.
It will be understood that several sleeves 11 may be cut from a single helix after the latter is removed from the mandrel.
The several sleeves 11 used to band the helix bundle together are applied to the bundle simultaneously in a jig 25 shown in FIGURES 3, 4 and 5. The jig (see FIGURE 4) has a length L slightly less than the length of the bundle and comprises side plates 26 and 27, end plates 28 and 29, a top plate 30 and a base plate 31. A pair of elongated jaws .33 and 34. within the jig enclosure are supported at their outer 'lower edges (as viewed in FIGURE 3) on longitudinal rods 35 and 36, respectively, about which the jaws may pivot toward and away from each other. The inner adjacent faces 33 and 34 of the jaws are spaced apart and the portions thereof which engage the sleeves 11 diverge downwardly and away from each other at an angle preferably of 60 degrees. Spring loaded screws 36 and 37 engage jaw 33 and similar screws 38 and 39 engage jaw 34, the springs acting so as to tend to pivot the jaws away from each other. Pressure plate 40 abuts the tops of the jaws and under the pressure of screws 41 in top plate 30 causes the jaws to pivot toward each other. A bottom jaw 44 is supported between the lower parts of jaws 33 and 34- on vertical adjusting screw 45 which engages threads in bottom plate 31.
In practice, the desired number of sleeves 11 are inserted into and are longitudinally spaced along the jig between jaws 33, 34 and 44 while screws 41 are withdrawn and jaws 33 and 34 are in their fully opened position. Fingers 18 and 19 on each sleeve are sprung inwardly in order to permit insertion of the sleeves into the jig. Plate 40 is next moved down by adjustment of screws 41 and pivots jaws 33 and 34 toward each other to deform the several sleeves simultaneously into the triangular cross-sectional shape shown in FIGURE 5. The inside dimension of each compressed sleeve is larger than the corresponding triangular profile of the rod mounted helix and the latter may then be inserted into the several sleeves. Screws 41 are then retracted and the springs on screws 36, 37, 38 and 39 act to open jaws 33 and 34. Sleeves 11 return to substantially their original shape and close upon and tightly band the rods against the helix. The banded helix bundle is then removed longitudinally from the jig.
The helix bundle is mounted in the barrel 2 and the assembled tube is finally processed by baking out gaseous contaminants at elevated temperatures. The outflow of these contaminants is aided by the helical sleeve construction because the internal groove 16 in each sleeve tends to direct the gas flow axially of the tube. As shown in FIGURE 7 the internal groove 16 provides a space between adjacent wire turns 11a of sleeve 11 and the ceramic rods gripped by it, so that gas can pass readily between the sleeve and the rods.
This invention is not limited to particular details of construction, materials or process, described above, as many equivalents will suggest themselves to those skilled in the art. The invention is defined in appended claim.
What is claimed is:
In an electron discharge device of the type described having a barrel, a helix bundle adapted to be inserted into said barrel comprising a refractory metal conductor wound into an inner cylindrical helix,
a plurality of rods circumferentially spaced around and engaging said helix and extending parallel to the axis of the helix,
a plurality of axially-spaced sleeves banded about and tightly engaging said rods,
each of said sleeves comprising a wire wound into a closed cylindrical heix and composed of a refractory metal identical to that of the inner helix, and
means for bonding adjacent turns of the sleeve helix together,
the inside diameter of each sleeve when rel-axed being less than the outside diameter of the rod-mounted helical conductor combination whereby the mounted sleeve exerts a radial clamping force on the rods and helical conductor,
each of said sleeves having a radially outwardly extending finger at each end, said fingers on each sleeve being integral with the sleeve wire and projecting equal distances from the sleeve in opposite 6 directions for resiliently engaging the interior of said barrel.
References Cited by the Examiner UNITED STATES PATENTS 3,026,445 3/1962 Staerck 3l5--3.5 3,242,375' 3/1966 Anderson et a1. 3153.5
FOREIGN PATENTS 10 245,903 11/ 1962 Australia.
HERMAN KARL SAALBACH, Primary Examiner.
R. D. COHN, Assistant Examiner.