US2498775A - Cathode construction - Google Patents

Description

Feb. 28, 195G W. W. WATROUS, JR

CATHODE CONSTRUCTION Filed Jan. 16, 1948 INVENTOR WMW ATTORNEY Patented Feb. 28, 1950 CATHODE CONSTRUCTION Ward W. Watrous, Jr., Chatham, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 16, 1948, Serial No. 2,570

8 Claims. (Cl. 250-27.5)

This invention relates to cathode construction, and particularly toindirectly heated cathodes.

The objects of the invention comprise generally the inclusion of all possible desirable features in a single cathode for obtaining high heating efl'lciency with a relatively large area of cathode and copious emission, and one that is sturdy, reliable and readily manufactured.

More specifically stated, an object of the invention is to provide an improved cathode of high heating efiiciency determined by the ratio of active cathode area to the heating energy required.

Another object of the invention is to obtain a high accessibility ratio, which is the ratio of the projected cathode area to its depth.

A further object of the invention is to minimize localized heating or hot spotting of the cathode.

Still another object of the invention is to provide a copiously emissive cathode having as low a mass of the heated portion thereof as possible for emission obtained.

Again, an object of the invention is to provide a. construction capable of handling current in excess of its normal requirement.

Yet again, an object of the invention is to provide a cathode of extensive area, yet compact and of a character lending itself to easy coating thereof with emissive material.

The invention has a further object of gaining advantages heretofore expressed in Whole or in part and at the same time enable the cathode to have a configuration that lends itself to easy coating with emissive material.

A'feature of novelty of the present invention is provision of a single tube, coaxial to a lead-in wire, said tube having the triple function of supporting the cathode, of conducting cathode current, and of passing heater current.

The invention, by the construction shown, accomplishes the advantageous limitation of heatconducting paths to the exterior of the device from the cathode.

The inventive concept further makes use of very thin material for reduction or heat-loss from the cathode by way of the metallic stem which is unavoidably of heat-conductive character, but at the same time to provide a stem aflording' adequate support and rigid maintenance of the oathode in its appointed place.

Still further objects .of the invention will appear to those skilled in the art to which it appere tains. as the description proceeds, both by direct reference thereto and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views;

Figure 1 is an elevation, with the envelope in part broken away, of an electron discharge device wherein my improved cathode is mounted;

Figure 2 is a view partially in elevation and partially in radial-axial section of my improved cathode and showing the mounting and enclosure therefor in section;

Figure 3 is a cross-sectional view as on line III-III of Figure 2;

Figure 4 is a diametric-axial section af a cathode and showing modified heater construction;

Figure 5 is another modified construction shown in diametric-axial section; and

Figure 6 is a partial sectional view of a still further modified construction.

In the specific embodiment of the invention illustrated in said drawing, a thyratron H! has been depicted as the particular electron discharge device chosen for purposes of this disclosure within which my improved cathode is employed. The cathode may, however, be used in other electron discharge devices, so it is to be understood that the invention is not confined to the selected device exemplifying herein use of the improved cathode.

Except for the cathode structure, the general organization of the thyratron here illustrated, is shown and described in my prior Patents 2,424,293 of July 22, 1947, and 2,381,632 of August '7, 1945, both of which are assigned to the same assignee as the present invention. Briefly, the thyratron shown comprises a glass or vitreous envelope H which is evacuated and provided with a small quantity of filling material, such as mercury vapor or inert gas. The envelope is provided with a reentrant stem l2 through the press l3 of which extend lead wires making connection with external prongs M on the bottom of an attached base I5. The opposite end of the envelope is constricted and capped with a terminal member it, which makes connection with a depending rod l1 sealed through the glass at the upper part of the constricted portion or dome 18 of the envelope and carries an anode l9 within and coaxial to the envelope.

The improved cathode 20 of the present invention is located in opposition to and on a common axis with said anode, within the envelope and situated between said anode and the re-entrant stem and having support, as will hereinafter appear, from the stem. The device further more includes a grid of the character described in said prior patents, namely a centrally apertured transverse plate 2| at the outer periphery of which is a cylindrical member 23 in proximity to the envelope wall and constituting a heat-dispensing radiator. The said plate 2| of the grid is interposed between the cathode and anode and is coaxial to the common axis thereof. The discharge between the cathode and anode is desirably confinedby a sectional shield of which one cylindrical lower section 24 is located coaxially around the cathode and extends almost to grid plate 2! and of which another cylindrical upper section 25 is located coaxially around the anode from just above the grid plate to a position well above the anode, both of said shield sections being of substantially equal diameter and carried by common posts 26 longitudinal thereof welded or Otherwise secured thereto and in turn carried by a collar 21 clamped on the stem.

The cathode of the present invention, inclusive of its heater andheat-shield may be variously constructed. The thermionically functioning portion of the cathode however, in the several views, is similar throughout and comprises a body of generally frusto-conical overall configuration with the metal thereof formed in deep corrugations of successively smaller diameter having successively further protrusion in an axial direction,

the body thereby being formed with a plurality of annular ridges 28 and valleys 29 directed toward the upper or forward end of the cathode.

In accomplishing this formation of cathode body,

it will be noted that the portion 3|] of each corcessibility ratio or projected cathode area depth.

Furthermore, said wall portions slope with respect to each other so that the several valleys widen toward the peaks. Said peaks are round at their forward extremities to definitely avoid any sharp edges which might engender hot spots and loss The most forward peak of emissive material.

preferably forms an end plateau 32 transverse to the axis of the cathode.

Devoting attention now to the specific structures shown in Figures 2, 3, and l, the most rearwardly extending portion of the cathode body I is provided at its rearward edge with a flange 33 projecting radially outward therefrom. The outer surface of the cathode body, inclusive of the peaks and valleys thereof, is rendered electron jemissive, as by having a coating of emissive material thereon, examples of which are barium,

strontium or the oxides thereof, and other known emitting'elements or compounds. A disc 34 is provided at the bottom or rear end of the cathode body, said disc having its margin juxtaposed to the flange 33 and secured thereto by welding or otherwise. At the middle of disc 34 a hole 35 is provided'for passage of a coaxial center lead wire or rod 36 therethrough. Secured by welding or otherwise to the under or rear face of the disc, as by a flange 31, is a tubular metallic stem 38 coaxially disposed with respect to the disc and hole and preferably somewhat larger in diameter .than said hole so as to mount a ceramic or other insulator 39 therein. The insulator is held from longitudinal displacement in said stem by engagement at one end with the margin of the disc next the hole, and at its other or rearward end byan indentation 40 in the stem. If desired, however,

as shown in Figure 5, the hole in the disc and the interior diameter of the stem 38 may be of equal size and insulator 39 may protrude from both ends of the stem and be retained from longitudinal displacement by pressing indentation 40 thereof into a peripheral groove 40' in the insulator.

Figure 5 shows a, further modification of the cathode in that a cylindrical housing 4| is provided around the generally conical and corrugated portion of the cathode, said housing being shown integral at its rearward or bottom edge with disc 34 and extending forwardly therefrom a distance substantially equal to the overall length of the cathode body. The inner cylindrical surface of said housing is likewise coated with the same electron emissive material as the oathode body, so as to render said cylinder copiously emissive and to thereby materially increase the electron discharge.

The heater for the cathode may be variously constructed. As shown in Figure 2 a spiral filamentary heater 42 is provided within the conical body of the cathode, said heater spiralling from large convolutions at the rearward larger part of the cathode progressively in smaller convolutions toward the forward smaller end of the cathode. In this showing, the rearward end of the filament heater 42 is connected to the lead-in wire 36, which enters the cathode body coaxially through insulator 39, and the forward end is connected to the inside surface of plateau 32 of the cathode body. Stem tube 38, therefore constitutes electrical connection both for the cathode and for one end of the filamentary'heater.

In Figure 4, the filamentary heater 42 is likewise formed as a spiral, but is shown supported upon a spirally grooved conical insulator 43 coaxially within the cathode body, the larger end of the insulator being directed rearwardly and located next said disc 34. The forward or small end of the insulator is formed with a neck extension 44 which is held within the small plateau .end of the cathode body. As shown, the largest convolution of the heater terminates next the largest wall portion 30 of the cathode body and is secured thereto, as at 45. The "final smaller convolution of the heater is extended back through the neck 44 of the insulator 43 and connects with lead-in wire or post 36. As in the previously described construction, therefore,'the stem tube, though differently connected with the heater, constitutes electrical connection for both the cathode and heater. Figure 5 shows another variation of heater construction and mounting. In this instance, insulator 39 carried by the stem continues forwardly above the end disc 34 coaxially within the cathode to the plateau end 32 thereof. That part of said insulator which is within the cathode body has the heater 42 coiled therearound. The insulator furthermore is longitudinally cored or otherwise provided with longitudinal holes to receive and pass both ends of the heater? wire or extensions thereof to the lower end'of the insulator where they can be separately attached to lead-in wires. In this arrangement, lead-tin con? nection, through agency of stem '38? for the oathode, is electrically separate 'from eitherle'a'd in connection for the heater. I f

In Figure 6, cathode 20 and heater 42 are reversed in position from'the showing-of FigureI, that is, the inside of the generally frusto-conical body has its larger end toward theanode 'and' it's plateau 32 more remote from the anodet Th'e ridges 28 and valleys 29arepresentpasi beiore,

' cathode.

. made copiously emissive of electrons as explained in connection with previously described figures. The larger end .of the cathode body may have a cylindrical flange 33 which fits within :and is welded or otherwise secured to a cylindrical hous- -ing 4| c the lower or rear end of which is integral with disc 34. The smallest convolution of the heater 42 terminates at and is secured to a lead-in wire 36 which enters through insulator 39 carried in a thin-metal stem 38 as described above in connection with Figure 1. The largest convolution of the heater 42 is secured to the .housing 4| in suitable manner as by use of a connector 42 In all forms of the invention, it will be noted that the cathode is a hollow body symmetrical about its axis and has a wall with outer and inner surfaces with the wall corrugated or formed with alternating valleys and ridges. One of the said surfaces is rendered electron emissive for its entire area, inclusive of the said valleys and ridges. A construction is therefore shown wherein a line normal to the emissive surface may be resolved into components, one longitudinally parallel to the axis of the cathode and another radial thereto. The entire area of the selected inner or outer surface in axial component is therefore directed entirely toward a single end of the cathode and is referred to herein as the forward direction, and is the direction of predominating flow of electrons from any part of the emissive surface.

Heat shielding of the cathode body is shown accomplished by a plurality of convolutions or cylinders 45 of sheet metal girdling said cathode body out of contact therewith and substantially coaxial thereto. These convolutions or cylinders are kept separated from each other by punch pricks or other protuberances 41. A plurality of centrally apertured forward shields 48 are provided cross-wise of the cylindrical shields beyond the forward or plateau end of the cathode body.

Similarly a plurality of transverse rear shields 49 are provided behind the cathode body and are severally supported from the stem 38 and in turn support the cylindrical shields. As shown, the

most rearward transverse heat shield is in the form of a header and the outermost cylindrical shield laps over and is secured to said headerlike shield. Said header-like shield has tabs 50 bent down therefrom in the vicinity of the stem and said tabs are secured, as by welding, to ears projecting from the stem. The transverse shields, both those forward of and those rear- Ward of the cathode body are kept separate by protuberances 41 as above referred to in describing the cylindrical shields. Suitable posts 52 sealed in the press l3 extend upward at the outside of outer cylindrical shield 46 and are welded thereto for supporting the shield, and the shield in turn, by tabs 56, supports the cathode stem.

Attention is directed to the fact that the oathode body has metallic support only by cylindrical stem 38 (or 38 That stem is preferably very thin metal, within the thickness range of only two to five mils, and therefore affords a low heat mass and a highly restricted path for heat con duction. As a result, escape of heat by way of the metallic stem is negligible. The ceramic 39 (or 3%) within the metallic stem is even more resistive to heat conduction, and because of its shielding need not be considered as a source of heat loss. 'The cathode is therefore isolated and ."heat-shielded and for that reason and because of its large emissive area develops a high heating and heat retention efficiency. The cylindrical character of the metallic stem 38 gives rigidity of support for the cathode notwithstanding the very thin metal constituting the same, and the ceramic therein affords a degree of support for the metallic portion of the stem and the metallic portion of the stem affords protection for the ceramic. On the subject of strength, it may also be stated that the corrugated conical formation of the cathode body not only permits necessary expansion when hot, but also gives self-sustaining strength and rigidity to the cathode even at the high temperature to which it is subjected in. use. The stem has adequate cross-section of metal to accommodate high overcurrent flow should such be applied due to accidental faults or other inadvertance. I

I claim:

1. A cathode comprising a body of generally over-all conical configuration the outer wall whereof is provided with deep corrugations the walls of which are spaced from each other providing hollows therebetween, the hollows of said corrugations opening toward a forward end of .said body, and said body having its surface directed toward said forward end, inclusive of the surfaces of the hollows of said deep corrugations, rendered electron emissive, and all parts of the electron emissive surface of said corrugations having components of normal line emissive path in a direction toward the forward end of said body.

2. A cathode comprising a body of generally over-all conical configuration and provided on the surface thereof with a plurality of rounded ridges circumferentially of the body and with a plurality of deep valleys between successive ridges, and said body throughout said ridges and valleys having its surface rendered electron emissive, and all parts of the electron emissive surface of said corrugations having components of normal line emissive path in a direction toward the forward end of said body.

3. A cathode comprising a body symmetrical about an axis and constituted by a wall having inner and outer surfaces, said body having an end disc transverse to said axis, a metallic hollow cylindrical stem projecting from said disc in a direction opposite from the body and coaxial therewith, said stem constituting the sole support for said body, and said body having the entire area of one of said surfaces in axial component directed away from said stem and having that area electron emissive.

4. A cathode comprising a body of generally frusto-conical shape having its smaller end closed by a plateau and its sides formed in successive ridges and valleys each including a part of the body coaxial therewith, a stem at the one end of said body projecting in a coaxial direction therefrom, said stem constituting the sole support for said body, and ears on said stem mounting the stem for use and for lead-in connection to the stem.

5. A cathode comprising a body of generally frusto-conical shape having its smaller end closed by a plateau and its larger end provided with a supporting disc and its sides formed in successive ridges and valleys, a stem projecting from said disc in a direction away from the plateau, said stem constituting the sole support for said body, a heat shield around said body having tabs next said stem, and ears on the stem secured to said tabs thereby supporting the said body from the heat shield.

6. A cathode comprising a hollow body of generally frusto-conical shape having its smaller end closed by a plateau, a transverse disc at the larger end of said body, a metallic stem secured to said disc, an insulator in said stem, a lead-in passing through said insulator and stem and having an end within the cathode body, and a spiral heater in said body having one end connected to said lead-in and its other end secured to said plateau.

7. A cathode comprising a hollow body of generally frusto-conical shape having its smaller end closed by a plateau, a transverse disc at the larger end" of said body, a metallic stem secured to the disc and projecting therefrom outside said body, an insulator of generally conical shape having its larger end next said disc and an extension at its smaller end projecting into engagement with said plateau, the conical surface 'of said insulator having a spiral groove therein,

and a heater having convolutions in said spiral groove.

8. A cathode comprising a body of generally frusto-conical shape having its smaller end closed and having its larger end forwardly open for REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,695,746 Stark Dec. 18, 1928 1,750,238 McIlvaine Mar. 11, 1930 1,879,159 Foulke Sept. 27, 1932 1,968,608 Lowry July 31, 1934 2,006,081 Anderson, Jr., et al. June 25, 1935 2,020,727 Gaidies et al Nov. 12, 1935 2,372,037 Watrous, Jr Mar. 20, 1945 2,430,309 Spencer Nov. 4, 1947

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