US2376439A - Insulating structure - Google Patents

Description

y 1945. R. R. MACHLETT ET AL 2,376,439

INSULATING STRUCTURE Filed June 18, 1945 a d M. a. 1945 l 2,376,439

UNITED .STATES PATENT OFFICE 2,376,439 INSULATING STRUCTURE Raymond B. Maehlett, New Canaan, and Joseph W. Bkehnn, Stamford, Conn., asslgnore to Machlett laboratories Incorporated, Springdale, Com, a corporation of Connecticut Application June 13, 1943, SerialNo. 491,888 5 Claims. (0]. 250-275) This invention relates to h-volta e equipsections per foot of column length. While such ment, such as high voltage electrical discharge sectionalizing oflcrs some advantages, it is for devices, and resides more particularly in a novel from the theoretical ideal and leaves much to be insulating structure for use in separating points desired. g operating at large diflerences of potential in such a The present invention is, accordingly, directed equipment. The new structure is especially suited to the provision of an insulating structure for high for use in apparatus in which the potential along voltage use, which is more highly sectionalized the structure from one end to the other is to be and, thus, approaches the theoretical ideal more accurately controlled. Such constructions have closely, than has heretofore been possible. In found application in high voltage X-ray tubes 30 addition, the new structure may be sealed from and in apparatus for nuclear research, and are the high vacuum pumps and will retain its high variously referred to as cascade, laminted, or vacuum indefinitely, sothat it may be employed seotionlized tubes. 1 for its intended purpose without continuous A sectionallzed tube for generating high voltpumping. Whereas prior sealed oflf tubes have age x-rays consists of alternate metal and inis been made with no more than three sections per sulating members interposed between the clos foot, the structure of the present invention may trodes to which the extremes of potential are be made with three sections per inch or even less applied, and means are provided for maintaining of column length. As a result, the total overall the metal sections at predetermined potentials dimension or a high voltage X-ray tube, for exrelative to the main electrodes. Such means may an ample, in which the new structure is employed, take the form of connections between the metal may be safely reduced to a small fraction of the sections and appropriate points on the secondary length previously required. of the high voltage transformer supplying high The new structure comprises a series of closely voltage to the main electrodes and resistance spaced similar thin annular discs of metallic ma connections and other expedients have also been as terial insulated from one another by sections of suggested for the purpose. By reason or their insulating material, preferably a hard glass, the sectionalized construction, such tubes, in general, sections being sealed vacuum-tight to the discs. may be operated at higher potentials than is pos- The metal 01 which the discs is made is one havsible with the more conventional construction, in 111 a coeilicient of expansion closely similar to which the full potential is applied to the principal so that or the material used for the insulating secelectrodes and no expedients are provided for intions, and the surfaces of the discs in contact suring a uniform potential gradient along the tube with the sections are oxidized so that good seals wall from one main electrode tothe other. It has are obtained. The discs are circumierentially also been found in high voltage X-ray work that distorted, as by having their outer edges dished, accurate control of the potential along the path 5 to prevent their being warped during the sealing of the electrons traveling between the cathode of the sections thereto. By employing the sevand the target is of considerable assistance in conare] features mentioned, the parts of the structrolling the focusing of the electron beam on the ture can be readily assembled by the use of a target. method and apparatus invented by us, in accord- The advantages mentioned, which are obtained so once with which the sealing of the insulating from sectionalizing the insulating column between sections to the discs is eilected by heat transthe main electrodes 01' high voltage apparatus, mitted'from the discs to the sections. such as a high voltage X-ray tube, are greatly better understanding f the n i n. increased by increasing the number of sections reference may be had to the accompanying drawper unit length 01' the column. In practice, no 45 inginwhich limittothe improvement dcrivabletrom increased Fig. 1 is a longitudinal sectional view of an sectlonalization has been found, and it appears X-ray tube which embodies the invention; that the practical limit imposed by mechanical Figs. 2 and 3 are plan and sectional views, re-

considerations will be reached before the theospectively, or one or the metallic discs;

retical ideal is attained. Heretofore, the sec-- so 8 4 n 5 are P n n Sectional vi w tionalizing oi "sealed-oil" tubes, that is, tubes spectively, of one of the insulating sections; and which are ca abl of holdi g a high va uum a d ig. 6 is a front elevational view or the cathode. ire n n s p ping during oper Thetube illustrated includes the new insulatu so far as 1 am aware, not progressed in: structure serving as the envelope oi the tube beyond the point or providing more than three as i consisting of a eries or thin annular discs :2

separated by tubular sections ll of insulating material, preferably of bore-silicate glass. The discs l are made of a material having a coefllcient of expansion closely similar to that of the material of which the insulating sections are made and when the sections aremade of borosilicate glass, the discs may be made of an alloy of nickel, iron, and cobalt, known commercially as Kovar." The discs are circumferentially stiffened to prevent their being warped when heated and the desired stiffness may be imparted to the rings in various ways, as by pressing a circumferential channel in one face with incident formation of a corresponding head in the other. Preferably, the discs are flat throughout the major portion of their faces, and they are stiffened by having their outer edges dished, as indicated at l2.

The glass sections II are formed with parallel fiat faces I3 and the inner diameter of the discs is substantially less than that of the sections, so that the inner edges H of the discs extend inward into the nvelope a considerable distance beyond the inner surfaces of the sections and define a substantially cylindrical surface. The dimensions of the insulating sections are such that the discs are closely spaced and there may be as many as thre discs or more to the inch in a practical construction. The overall length of the series of discs and sections depends on the voltage to which the tube is to be subjected and one construction suitable for use in a tube to be operated at a voltage in excess of two million volts, includes 172 discs separated by glass sections and has an overall length of about 5'7".

The tube is completed by closing the series of discs or rings and sections at its ends by metallic end caps i5 and It. These end caps are sealed to insulating sections at the end of the series and each cap includes a tubular portion with a flange at its inner end.

The cap contains a metallic tube i'l secured to the inner wall thereof at its outer end and provided at its inner end with a flange l8 extending outwardly close to the inner surface of cap l5. Within the inner end of tube 11 is mounted a metal block l9 having a recess in which is contained an incandescible filament 2|, here shown as helical in form. Outwardly from the block 20 is a second block 22 in contact with block IS. The lead 23 from the filament extends through an enlarged passage 26 in block I9 and out of contact with the wall of the passage and through a plug 25 of insulating material mounted in an opening through block 22. The other lead 26 of the filament passes through aligned openings in blocks 19 and 22 and is not insulated therefrom. The leads 23, 25 pass out of the envelope through a body of glass 21 closing an opening at the end of cap it, and the leads are sealed in the glass body. At its inner end, the cap I5 is provided with a flange 28 sealed to the end insulating section 29. It will be noted that the surface of the filament facing the interior of the envelope lies substantially parallel to a plane through the inner surface of flange 28.

The end cap l6 includes a tubular portion, at the end of which is mounted the anode 30 having a target surface of any suitable material. The cap is formed at its inner end with a flange 3i sealed to the insulating section 32. at the adjacent end of the series.

In the formation of the device in accordance with our method above referred to, the end cap it, nd insulating section 32, and one of the discs III are placed in contact and flange ll of the cap and the disc are then heated by high frequency current until the heat transmitted through the metal to the glass causes the latter to soften and adhere to the flange and disc. By this operation, the surfaces of the flange and disc facing the glass are oxidized and, as the glass softens and becomes plastic, the flange and disc are caused to approach each other to assume their desired final space relation. In this operation, the glass section is likely to be slightly deformed. It will be noted that, in the construction shown, the outer diameter of the glass section is slightly less than the outer diameter of the ring and flange and, as the deformation of the glass section occurs, the glass may flow to 1111 in the dished edge of the disc, as indicated at 33. When the cap has been secured to the first disc by the sealing of the glass section to the parts, another section and disc are placed in position, and the glass is sealed to the two discs. The operations are then repeated until a series of discs and sections of the desired length has been completed. The flange 28 of end cap I5 is finally sealed to the end section 39 and the tube is thereafter subjected to the usual processing operations to evacuate it and prepare it for use.

By making use of stiffened discs and forming the wall of the envelope of alternate discs and glass sections, the sealing together of the discs and sections by induction heating can be accomplished without distortion of the discs. During such heating, the oxidation of surfaces of the discs permits the glass to wet the discs properly to make good seals. As no distortion or the discs occurs during the heating, the discs can be assembled on accurate spacings and with the inner edges of the discs aligned as illustrated. In the operation of the tube, the presence of the discs makes it possible to cause charges to accumulate evenly on the envelope Wall and to insure such even distribution, it is important that the discs be evenly spaced and concentric. Since in a tube for high voltages, the series of discs and glass sections forming the envelope may be of substantial length, it is also of great importance that the faces of the discs be parallel to one another, since otherwise errors introduced by the nonparallel relationship might be additive and thus impair the functioning of the discs in insuring a uniform potential gradient along the wall.

In the operation of the tube in which the new structure is used, the discs serve an additional purpose, namely, that of assisting in focusing the electron beam. In any such tube, the electrons fall through the electric field between the anode and cathode along paths which cut the lines of force of the field at right angles. If the field is uniform, the electrons will move from the cathode to the anode along straight parallel paths but variations in the field will cause distortion of the paths. In tubes for extremely high voltages, it is of utmost importance that the paths of the electrons b controlled and predictable to avoid damage to the tube and, in one such tube, it is desired to have the electrons enter a uniform field upon leaving the cathode and travel in such a field and without divergence from straight paths until they reach the target. With the new structure, such a field may be maintained throughout the length of the structure by impressing the proper potentials on the metal discs. At the anode and cathode ends of the structure, there may be some distortion of the fleld by reason of a lack of symmetry in the construction.

nary production' methods and, in its finished form, it holds the desired high vacuum indefinitely. The use of the discs sealed by the glass sections in precise geometrical relations makes it possible to insure not only the uniform potential gradient along the envelope wall and the prevention of charge accumulations which might result in puncture, but also the proper contribution of the discs to the focusing of the beam.

While the new structure has been specifically described in the foregoing as applied to a high voltage X-ray tube, it will be evident that numerous other applications in the field of electronic tubes suggest themselves. For example, there are many instances of high voltage apparatus in which a vacuum-tight tubular duct is useful between points in the machine which must operate at high potential differences, and the new structure is suitable for such use. In the case of lower voltage tubes for application in the field of communication, direction finding, and industrial electronic controls, the use of columns along which the potential gradient can be accurately controlled is also indicated and the new structure may be advantageously employed in such tubes.

We claim:

1. .An evacuated electric discharge device which comprises an envelope made up of a series of closely spaced similar annular metallic discs and annular sections of glass sealed to opposite faces of the discs, each section joining a pair of discs together and insulating them from one another, the discs being made of a metal of approximately the same coefficient of expansion as the glass and of such gauge that the discs, if flat, would be subject to warping out of their plane when heated to the temperatures required to efl'ect the seals, the discs being circumferentially stiffened against such warping and having inner edge portions extending parallel and lying inward of the glass sections, closures for the ends of the envelope, an anode within the envelope mounted on one closure, and a cathode mounted within the envelope on the other closure.

2. An insulating structure which comprises a hollow column made up of a series of closely spaced similar annularmetallic discs and annular sections of glass sealed to opposite faces of the discs, each section joining a pair of discs together and insulating them from one another, the discs being made of a metal of approximately the same coeflicient of expansion as the glass and of such gauge that the discs, if fiat, would be subject to warping out of their plane when heated to the temperatures required to effect the seals, the discs being circumferentially stifiened against such warping and having inner edge portions extending parallel and lying inward of the glass sections.

3. An insulating structure which comprises a hollow column made up of a series of closely spaced similar annular metallic discs and annular sections of glass sealed to opposite faces of the discs, each section joining a pair of discs together and insulating them from one another, the discs being made of a metal of approximately the same coeillcient of expansion as the glass and of such gauge that the discs, if flat, would be subject'to warping out of their plane when heated to the temperatures required to efiect the seals, the discs being circumferentially stiffened against such warping and having inner edge portions extending parallel and lying inward of the glass sections, the faces of the discs to which the glass is sealed being oxidized.

4. An insulating structure which comprises a hollow column made up of a, series of closely spaced similar annular metallic discs and annular sections of glass sealed to opposite faces of the discs, each section joining a. pair of discs together and insulating them from one another, the discs being made of a metal of approximately the same coefficient of expansion as the glass and of such gauge that the discs, it flat, would be subject to warping out of their plane when heated to the temperatures required to effect the seals, each disc being formed with a circumferentially distorted portion lying at one side of the glass seals and effective to prevent warpins of the disc during sealing, the discs having inner edges lying parallel and inward of the glass sections.

5. An insulating structure which comprises an envelope made up of a series of closely spaced similar annular metallic discs having flat portions and circumferentlally distorted portions at one side of the flat portions, and annular sections of glass sealed to the opposite flat faces of the discs, each section joining a pair of discs together and insulating them from one another, the discs being made of a metal of approximately the same coefllcient of expansion as the glass.

and of such gauge that the discs, but for the circumferentiaily distorted portions, would be sub- Ject to warping when heated to the temperatures required to efiect the seals, the discs having parallel portions lying inward of the glass sections.

RAYMOND R. MACHLE'II. JOSEPH W, SKEHAN.

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