US2796548A - Electrode structure - Google Patents

Description

June 18, 1

G. A. BECKER 2,796,548

ELECTRODE STRUCTURE Filed April 14, 1951' I I 40 x L36 INVENTOR.

ELECTRGDE STRUCTURE George A. Becker, Oakland, Calif., assignor to Research Corporation, New York, N. Y., a corporation of New York Application April 14, 1951, Serial No. 221,061

1 Claim. (Cl. 313-485) This invention relates to electrode structures and particularly to structures adapted for use in vacuum tubes of very high power, specifically tubes of the resnatron type such as are described in the concurrently filed application of David H. Sloan for patent on a High-Frequency Amplifier, Ser. No. 221,017, filed April 14, 1951, now Patent No. 2,653,273, dated September 22, 1953.

Tubes of the resnatron type are devised primarily to deliver very high powers (running into the megawatt range) at ultra-high and microwave frequencies. The power that can be delivered by tubes of this character is limited, ultimately, by the electron current which is released from the cathode and actually reaches the anode. In order to raise the electron emission to as high a total value as possible a large cathode emitting surface is necessary, while in order to assure that a maximum proportion of the emitted electrons reach the anode the crosssectional area of the electron stream, viewed in the direction of electron flow, which is occupied by grid or other control elements must be kept to a minimum.

Where grid elements are disposed in the electron stream there is certain to be some interception of electron flow by these elements and since at least some of the electrons which are intercepted will be travelling at high velocity, there is a considerable evolution of heat. Both for purely mechanical reasons and in order to facilitate the dissipation of the heat generated, the structure supporting the grid elements of this character is quite massive. Further reasons, both mechanical and electrical, in some cases require that a portion of this massive structure be supported wholly by the grid elements themselves. This argues that in spite of their small crosssection exposed to the electron stream they must have, at least collectively, a considerable degree of rigidity.

In one form of resnatron tubes described in the concurrently filed Sloan application the requirement for a cathode of large area has been fulfilled by an annular cathode assembly comprising a large number of stapleshaped cathode elements arranged radially, with their emitting surfaces positioned to discharge, on the average, in a direction parallel to the axis of the annulus. The emitting cathode surfaces are dished so as to be concave on the discharge side andto emit a converging annular beam of electrons toward the anode of the device. In a characteristic tube over three hundred such stapleshaped cathode elements are used, resulting in a spacing, center to center, of just a little over 1 of arc. In this particular tube each cathode element is formed of thoriated tungsten ribbon of such width that at their inner ends the elements are nearly touching, although of course they diverge toward the outer periphery of the annulus. In this tube, the outer abutment, supporting the grid structure, surrounds and projects beyond the cathode support. The inner abutment of the grid structure is a heavy copper disc which, for electrical reasons, is preferably supported solely by the grid elements. In order that constant operating conditions be maintained within the tube the spacing of grid and cathode must be accutates atent O rate and constant. Practically all of the heat developed in the grid structure is, however, localized in the annulus formed by the grid members themselves; these elements, therefore, expand with the result that buckling and mutual displacement of cathode and grid elements would take place if definite steps were not taken to prevent it.

The broad purpose of this invention is to provide an electrode structure which will meet, to a maximum degree, the problems posed by the conditions above enumerated. Accordingly, among the objects of this invention are to provide a grid structure offering a minimum area to intercept electron flow; to provide a structure wherein the grid elements can expand, differentially with respect to the remainder of the structure, without causing warping, buckling, or displacement which would alter the electrical characteristics of the device; to provide a structure whichis rigid in a direction normal to its plane but which oflers torsional flexibility in its own plane to permit differential expansion of its various parts; to provide a structure wherein a multiplicity of grid elements may be maintained substantially parallel to and between alike multiplicity of individual cathode elements while still permitting differential expansion as between the two classes of elements and, generally, to provide an electrode structure which is generallyapplicable to tubes of high power and is not limited to tubes of the resnatron type.

Considered broadly my invention comprises the combination with a cathode and anode which define an electrical discharge path of a pair of abutment members spaced on either side of the path and a fixed support for one of these abutment members. The abutment .memhere are so positioned that they define, between them, an opening of substantially constant width. The grid elements themselves bridge this gap and. are preferably formed of thin sheet material disposed edge-on to the direction of How of the electrical discharge. The ends of the grid elements are secured to the abutment members respectively but are so disposed that the two ends of each grid element do not lie upon the same line normal to the edges of the two abutments to which they are attached. In the special but most usual case where the abutment members are circular this same situation maybe stated as follows: the two abutments lie on opposite sides of a common radius. This requirement may be met in two slightly different ways; the grid elements may be either straight, from abutment to abutment, and so disposed that each element crosses a radius bisecting it at the same angle as the others, or, in a more general and preferred case, each element may consist of a major straight portion and an offset end portion, the offset being accomplished by bending the element through two opposite and substantially equal angles which should, preferably, be less'than t In What immediately follows the invention will he described as applied to a resnatron tube of a type fully disclosed in the copending application of David H. Sloan above identified. Only such portions of the device will Fig. 2A is a one-half transverse section on the line 22 of Fig. 1, illustrating one disposal of the grid elements in accordance with this invention; A

Fig. 2B is a one-half transverse section, taken in the same plane as that shown in Fig. 2A, illustrating a sec ond and preferred form of the invention; and Fig. 3 is an enlarged isometric view of a single grid element of the type used in the form of invention illustrated in Fig. 2B.

As is shown and more fully'described in the concurrently filed application aboved referred to, the tube structure comprises a cathode-end support disc 1 and anodeend support disc 3 which are sealed to and connected by a generally tubular glass insulating section 5. The cathode-end disc 1 is provided with a central aperture through which there projects a cathode terminal column 7 which is insulated from the disc 1 and the inner end of which flares outwardly to form a frustoconical cathode abutment 9. This abutment terminates in a substantially plane annular surface 11 facing the anode of the tube; the inner ends of each of a multiplicity of radially disposed cathode elements 13 are secured to this surface.

The outer ends of the cathode elements connect to the end of a cathode column 15 which surrounds the column 7 and its flaringend 9 and is electrically integral with the disc 1. In the specific tube mentioned each of the cathode elements comprises a staple-shaped strip of thoriated tungsten ribbon, the emitting surfaces of which are concave as viewed from the anode end of the tube. As these ribbons are flatWise-on as viewed from the anode and are initially concave, there is no tendency for them H to buckle as they expand, their concavity merely increasing somewhat. They are so designed that at the emitting temperature, when fully expanded, the concavity is such as to converge the electrons emitted from each element and direct the concentrated beam into the anode cavity as will next be described.

The electron collecting surface of the anode is a narrow V-shaped groove 17 formed in the end of a tubular ring 19, which projects from the anode disc 3 toward the cathode. The radius of the ring 19 is such that the apex of the notch 17 is on substantially the same radius as the center of the cathode elements 13. The inner edges of the anode ring project into an annular anode cavity 21. This cavity is defined by the anode, an accelerating electrode structure and an inner and an outer annular corrugated diaphragm, 23 and 25 respectively, which connect the anode with the accelerating electrode structure.

The accelerating electrode is carried by a column 27 supported externally of the disc 3 and projecting inwardly through an axial aperture therein. Near the end of the column is a flat circular flange 29 from which projects a skirt 31, frusto-conical as viewed from the anode end of the device. This skirt terminates in a flanged lip 33. A similar but inwardly projecting skirt 35, terminating in a flanged lip 37 is carried by an outer ring 39, to which the diaphragm 25 connects. The flanged lips 33 and 37 are spaced to form an annular slot through which the electrons emitted from the cathode elements 33 can enter the anode cavity, the edges of the lips forming the accelerating electrode.

The elements thus far described are not original with me but are characteristic of one class of high power resnatron tubes, comprising the electron emitting and collecting mechanisms for tubes of this class. In order that such tubes should operate properly the electron stream must be controlled by a grid structure spaced closely adjacent to the cathode and bearing a fixed spatial relation thereto which is substantially unaltered by thermal expansion due to the heating to which the grid elements are inevitably subjected. My invention relates specifically to this grid structure.

Projecting inwardly of the tube from adjacent the end of the cathode column 15 is a heavy tubular skirt 39, the end of which projects somewhat beyond the plane of the cathode elements 13. This skirt forms one abutment for a multiplicityof grid elements 41. The other abutment for the grid elements is formed by a rather massive disc 43 having an outer diameter smaller than the inner 5 *2: diameter of the ring of cathode elements so that the space between the abutments 39 and 43 is approximately centered over the center of the cathode elements. The grid elements 41 are preferably formed of sheet metal; in the tube here described they are of tungsten. They are set edgewise-on to the electron flow and are arcuate in form with a center of curvature which conforms approximately to that of the cathodes when heated. The grid elements are conveniently set into the abutments by slotting the edges of the abutments and then peening or swaging the slots so as to hold the grid elements in place. The characteristic feature of the instant invention is that the slots in which the individual grid elements are set are not on a common radius of the tube, considered as a whole.

Two conformations through which this may be accomplished are shown in Figs. 2A and 2B respectively. The simplest of these is that shown in Fig. 2A, wherein the edgewise-on grid elements are straight but are mounted at an acute angle to the radius which bisects them. When the grid elements expand the circular inner abutment merely rotates to a very slight degree it being freely floating and supported only by the grid elements themselves. Due to the edgewise-on mounting of these elements they are axially very stifi. Because of the Very large number of elements used the structure is reasonably rigid torsionally but when the elements expand there is nothing to restrain the rotation of the inner abutment which compensates for the expansion.

A slightly more complex structure is shown in Fig. 2B. In this case also the grid elements are formed of sheet material mounted edgWise-on to the electron stream. The slots in the abutments are, however, made substantially radial. A major portion of each of the grid elements is also radial. This is the portion through which the electron stream passes and in assembling the tube the parts are so positioned that the radial portions of the grid elements lie between the cathode elements and hence they are subject to minimum bombardment, not only because most of the electrons emitted from any one filament element pass between adjacent grid elements but also because the grid elements take the shortest path across the electron stream, being generally perpendicular to the abutment. Adjacent one end (preferably the inner end) of the grid elements each is bent twice, in opposite directions, so that the end where it attaches to the abutment is otfset. These bends are preferably positioned so that they lie wholly outside of the electron stream. Fig. 3 shows, in plan, and on an enlarged scale, the. preferred conformation of the grid elements when thus arranged. The deflection at each of the two bends forming the offset are, when the grids are cold, materially less than a right angle, '6. g., about 45, or so as to form. an internal angle of approximately 135 Substantially all of the expansion takes place in the radial portion of the grid elements, since this is a portion subjected to bombardment. Such expansion increases the deflection at the offset, decreasing the internal angle to.- ward The lengths are so computed that although the non-radial portions of the grid elements are longer than the separation between these elements the angles never reach the 90 value even under conditions of maxi-' mum expansion. the non-radial portions do not touch to form a firm abutment which could cause buckling of the radial portions. Where a floating abutment is used the expansion is taken up by a slight rotation thereof, although such rotation will not be as great as in the previous case. However, this construction permitsboth abutments to be fixed, in which case expansion results in a very slight deflection of the radial portion of the grid.

With either form of the device there will be some slight curvature of the nominally straight portions of the grid elements themselves. Experience has shown that this is so slight that it does not perceptibly affect the operation Consequently, under these conditions,

greases of the tubes. All of the grid elements being substantially identical and the structure being symmetrical the fiexures which occur are likewise substantially identical and the deviations from identity are too small to cause difficulty.

With elements as shown in Fig. 2A circular symmetry of the structure as a whole is practically essential. The offset-end grid elements can, however, be used in nonsymmetrical structures if desired; they may even be employed in structures wherein both abutments are rigidly fixed. Although it may be said in this latter case that some buckling does occur, it does not take place in haphazard fashion, with the greatest probability that maximum displacement will be at the center of the grid elements but occurs uniformly at the bends and preferably outside of the electron stream.

Where one abutment is floating it is immaterial whether this be the inner or the outer one. In the specific tube described it was more convenient that the inner abutment member float, but it should be obvious that structures are possible wherein the inner disc be fixed and the ring abutment float, supported only by the grid elements. It is also possible to ofiset both ends of the grid elements, but this is not preferred as it gives a less rigid structure.

I claim:

In an electrical discharge device, the combination with means for causing an annular electrical discharge of an electrode structure comprising a circular abutment member and an annular abutment member surrounding said circular member substantially coaxially and defining therewith an annular opening in the path of said discharge, a fixed support for one of said members, and a multiplicity of grid elements bridging said opening, each of said grid elements being of sheet material mounted edge-on to the general direction of electron flow through said opening so as to be relatively rigid to axial forces and flexible to torsional forces and comprising a substantially radial major portion positioned to span said discharge and secured to one of said abutments and a single diagonal portion extending at substantially the same angle from said radial portion toward the other of said abutments, said grid elements constituting the sole supporting means for one of said abutments whereby expansion of said elements tends only to rotate said last-mentioned abutment without changing its axial position.

References Cited in the file of this patent UNITED STATES PATENTS 2,261,154 Hansen et a1 Nov. 4, 1941 2,394,396 Mouromtseif et a1. Feb. 5, 1946 2,397,233 Bingley Mar. 26,; 1946 2,400,743 Clifiord May 21, 1946 2,460,120 Bondley Jan. 25, 1949 2,466,064 Wathen et al Apr. 5, 1949 2,515,267 Salisbury July 18, 1950 2,581,876 Parker Jan. 8, 1952 2,617,959 Fay Nov. 11, 1952

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