US2812499A - Helix assembly for traveling wave tube - Google Patents

Description

Nov. 5, 1957 e. H. ROBERTSON ,8

HELIX ASSEMBLY FOR TRAVELING WAVE TUBE Filed July 11, 1952 FIG.

F IG. 4

INVENTOR G. H. ROBERTS ON A T TORNEV United States Patent 9 HELIXASSEMBLY FOR TRAVELING WAVE TUBE George- II. Robertson, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, NJ Y1, a corporation of New York Application July 11, 1952, Serial No. 298,230

1 Claim. (Cl. 333-31) This invention relates to traveling wave tubes and to a method forthe fabrication elements of such tubes. More particularly it relates tothe support of a wire helix for such tubes and the method of fabricating such support.

Inonetype of traveling wave tube that has become known-in the art, a wire helix is utilized to define the interaction circuit or transmission line along which the electron streamis projected. This helix is made'of a very fine wire'advantageously wound in helical form on a man drel. Its accurate positioning within the tube is of prime importance. Not only must the helix be accurately and firmly supported Within the tube but it must besupported in such a manner as to minimize the possibility of variations' in: the pitch of the helical Winding. At the same time, th'e' mounting of the helix assembly into a traveling wave tube'is made considerably more diflicult if the helix assembly'is relatively inflexible. Thus the assembling would be greatly simplified if the helix structure could admit. of some flexibility and variance in the circumference of the helix without damaging either the bond between the'helix and its supporting members or increasing the possibility of variations arising subsequently in the pitch or positioning of the helix.

In" certain types of priorhelix support structures, the helix has been supported and mounted simultaneously in rigid. assemblies, as by being supported by the walls of the traveling wave tube itself or by being positioned in a long support member having a polygonically shaped cen tral aperture; examples of these structures are disclosed in F. H. Best application Serial No. 197,589, filed November 25, 1950, now Patent 2,706,366 issued April 19, 1955, and British Patent 664,663. However, if the envelopeis to support the structure it must be of glass and thus. this structure is not applicable to ceramic or metal envelopes; further neither of these types of supports for the helix allows of the incorporation within the tube of various other elements between the helix and the envelope of the tube.

Therefore another support structure has been employed in which three support rods are positioned around the outsidef the helix in a tripod arrangement and glazed to the helix. Such a structure is disclosed in J. A. Mor'ton application Serial No. 208,204, filed January 27, 1951, now Patent 2,790,926, issued April 30, 1957. This, however, requires very accurate tolerances in the mounting members in the tube with which the structure is associated, and it is substantially impossible to try to fit the structure into the mounting memberswithout introducing some transverse stress between the helix and the rods that tends to disrupt or weaken the supporting bonds. Thus while this structure does have a degree of flexibility, in'

actuality that flexibility is attained at the sacrifice of subjecting the bond between the support rods and the helix to a shearing stress.

It is an object of this invention to provide an improved support structure for the helix of a traveling wave tube. It is another object of this invention to facilitate the assembling of traveling wave tubes by providing a support structure for'the helix thereof which allows'a greater:

degree of flexibility than priorly attainable whereby the tolerance requirements of the cooperating members may:

lix support structure wherein the helix is more securely bonded to the supporting members than in prior structures.

A still further object of this invention is to fabricate facilely the improved support structure of this invention.

In one illustrative embodiment of this invention, two;-

pairs of ceramic support rods are employed, the two pairs being positioned adjacent the helix at diametrically opposite regions and the two rods of each pair being positioned contiguous with each other. Strips of glaze are then positioned on the helix in the space beneath the two adjacent support rods, on one of the support rods in that space, and onthe other of the support rods of the set above that space. The assembly is advantageously placed ina jig and heated to melt the glaze which, on melting, fills thevolume defined by the arcuate sided triangle between the two rods and the helix thereby giving a much stronger bond. than has been priorly attainable. This not only enables the helix wires to be more securely held by support rods but also provides flexibility in the helix structure without the development of shearing stresses to the bonds between the helix and the rods. Pressure can be applied radially inward between the two sets of rods tocause the helix itself to compress slightly into an elliptical shape without in any way disturbing the bond between the helix and the rods. As it has been found that slight variati'onsofhelix circumference from circular to ellip-, deal will not introduce serious electrical variations, the mounting of the helix is thereby greatly simplified by this increased degree of flexibility without impairing the supporting bonds. The required tolerances on the mounting structure of the helix assembly are thus considerably reduced, with concomitant savings both economically and in simplifying the fabrication.

It is therefore a feature of this invention that the helix of a traveling wave tube be supported by a pair of con-. tiguous rods placed at one side of the helix and another pair of contiguous rods placed diametrically opposite the first pair, whereby there is defined between the contiguous rods and the helix a triangularly cross-sectioned volume which is, in accordance with this invention, filled with glaze to seal the rods to the helix and the rods to each other.

It is a further feature of this invention that this structure be fabricated by placing a strip of glaze on the portion of the helix within this thus defined volume, a strip ofglaze on one of the rods within this volume, and a strip of glaze onthe other of the rods directly above this volume and heating the assemblage in a jig so that the glaze can melt andrun into this volume.

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

Fig. l is a schematic of a traveling wave tube showing the essential elements thereof;

Fig. 2 is a perspective view of a helix and support assembly in accordance with one specific illustrative embodiment of this invention for incorporation into a traveling wave tube;

Fig. 3 is a side view of one jig that may be employed in the fabrication of the assembly of Fig. 2;

Fig. 4 is a sectional view of the jig of Fig. 3 along the lines 4-4 thereof; and

Fig. 5 is an end view of the helix and support rods showing particularly the location of the strips of glaze Patented Nov. 5, 7

prior to the glazing operation, in accordance with this invention.

Turning now to the drawing, a traveling wave tube as shown schematically in Fig. 1, comprises an envelope 10, which may advantageously be of glass, ceramic, or metal, an electron gun assembly comprising a cathode 11 positioned at one end of the envelope and having a cathode heater 12, an accelerating electrode 13, adjacent the cathode 11, and a collector electrode 14 positioned at the other end of the envelope 10. Positioned between the electron gun and the collector 14 is a wire helix 15. The electrical signal may be applied to the helix 15 and removed therefrom by direct lead connections through a coaxial terminal 17, as depicted, or by antennae from wave guides, as is known in the art.

In accordance with the invention, the helix 15 is supported in the tube 10 by four support rods advantageously of a ceramic material having the same coefficient of expansion as the helix 15. If the helix wire is of molybdenum a ceramic madev of zirconium oxide and known as zircon may advantageously be employed for the rods 20.. The rods 20 are glazed to the helix 15 by a glaze material, as explained further below. The glaze, which should be of such a coefficient of expansion as to match the expansivities of the helix wire and the support rods may advantageously comprise approximately 6.3 percent LizO, 5.9 percent CaO, 16.5 percent BaO, 21.4 percent Al2O3, and 50.4 percent SiO2 if the helix is of molybdenum and the rods of zircon.

In fabricating the helix support assembly the helix 15 is itself wound on a mandrel 22, which may be of steel or copper if the helix is of molybdenum so that the mandrel may subsequently be etched out without dissolving the molybdenum wire. The helix 15 on the mandrel 22 is then positioned in a jig 24, as seen in Figs. 3 and 4, the jig comprising an upper member 25 and a lower base member 26 each of which has a slot 27 milled into it and into which slots 27 the two pairs of ceramic rods 20 fit to be held in position on opposite sides of the helix 15. Prior to being placed in the jig 24, each of the rods 20 has had placed thereon a strip 29 of the glazing material and a similar strip 29 has been placed on the helix in the region directly beneath the adjacent rods. As clearly seen in Fig. 5, the strip 29 of glazing material on one of the rods 20 of the pair is positioned adjacent the strip 29 on the helix but the other strip 29 on the other rod 20 of the pair is above the volume defined between the helix and the adjacent rods so that when melted it runs down between the two rods 20, by capillary attraction thereby securely joining the rods together and also aiding to completely fill the volume thus defined between the rods and the helix with glaze.

After the rods and helix, with the strips 29 of glaze properly positioned, have been placed in the jig 24, the assemblage is heated to melt the glaze strips whereby the volume defined between the rods and the helix is completely filled with glaze material 30, as shown in Fig. 3, and the rods are securely bonded both to, the helix and to each other. Advantageously the jig is made of a material having a lower coetficient of thermal expansion than the helix and ceramic support rods whereas the mandrel 22 advantageously has a higher coefficient of thermal expansion than the other parts in order to aid in obtaining a tight and complete bond between the helix and the pairs of support rods by completely filling the volume defined between them with the glaze material 30.

the bond between the support rods and the helix. And

as each turn of the helix is not joined to each of the support rods at but a single point but over a wide area and further as the two support rods of each pair are securely bonded together by the glaze that fills the volume between the adjacent support rods and the helix, a much stronger helix support assembly is attainable in accordance with this invention than priorly attainable with support rods.

It is to be understood that the above-described arrangements are merely illustrative of the application of the principles of this invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

In a traveling wave tube, a helix assembly capable of being deformed slightly to vary its size and shape without introducing deleterious stresses therein comprising a wire helix; a first pair of distinct support rods positioned each adjacent said helix to one side thereof, contiguous to each other and defining with said helix a first volume; a second pair of distinct support. rods positioned each adjacent said helix to another side thereof, diametrically opposite said one side, contiguous to each other and defining with said helix a second volume; and glaze material in said first and second volumes thus defined between said contiguous support rods and said helix, substantially filling said volumes to bond said helix to said support rods and extending between said contiguous rods of each pair to bond said contiguous rods to each other.

References Cited in the file of this patent UNITED STATES PATENTS 2,174,853 Bowie Oct. 3, 1939 2,277,150 Scharfnagel Mar. 24, 1942 2,541,843 Tiley Feb. 13, 1951 2,549,551 Walsh Apr. 17, 1951 2,567,415 Walsh Sept. 11, 1951 2,602,148 Pierce July 1, 1952 2,611,102 Bohlke Sept. 16, 1952 FOREIGN PATENTS 984,959 France Feb. 28, 1951

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