US2892115A - Cathode structures - Google Patents

Description

June 23, 1959 P. RUDNICK I CATHODE STRUCTURES Filed Dec. 20, 1955 IN VEN TOR. PAUL RUDNICK United States Patent CATHODE STRUCTURES Paul Rudnick, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation Application December 20, 1955, Serial No. 554,542

5 Claims. (Cl. 313-85) This invention relates to cathodes, and is particularly directed to indirectly-heated sleeves with a planar-type emitting surface at the end of the sleeve, from which surface a beam of electrons may be emitted.

Cathode-ray tubes of various kinds each require a cathode with a small emitting area having well-defined boundaries, from which a beam can be obtained. The

emplary, so that the placement of the coating material and control of the area may be technically difficult.

Attempts to decrease cathode size by wiping the carbonate from around the periphery of the coated area tend to fail for tworeasons. First, the edge material cannot be wiped off cleanly without disturbing or contaminating the central portion of the coated area. Second, any ordinary mechanical wiping operation will not leave the edge area chemically clean. Residue of the peripheral coating apparently will reduce and activate along with the coating material at the center. sired boundaryof the emitting area becomes indistinct and the accurate placement of beam-forming electrodes in front of the cathode does not achieve a well-defined beam.

In cathode assemblies. of the Pierce. type, it is particularly desirable to locate the collimating anode precisely With respect to the emitting area of the cathode so that a maximum of the emitted electrons enter the beam and a minimum of the electrons move to the anode. Unless the cathode boundary can be controlled, the electron focusing properties of the assembly cannot be controlled in manufacture.

An object of this invention is an improved extended cathode for electron beams.

A more specific object of this invention is a cathode in which the emitting area may be accurately and easily controlled in manufacture.

The objects of this invention are attained by coating the end of a thimble (preferably of nickel) with electron emissive material, or otherwise preparing the area for electron emission at elevated temperatures, and then fitting a collar over the thimble with an inwardly extending flange for masking the peripheral portion of the thimble bottom. The collar may extend if desired beyond the flange and be interiorly shaped to cooperate with the beam-forming anode of the assembly to produce the desired collirnated beam.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description The deice of an embodiment of the invention taken in conjunction with the accompanying drawing, wherein the single figure ofthe drawing shows, in half section, a cathode assembly embodying this invention.

Thecathode thimble 10 shown in the drawing is drawn preferably from special cathode grades of nickel, the bottom or end plate of the thimble being integral with or welded to the sleeve of the thimble. Theheater 12 may be folded or coiled, as shown, and comprises tungsten wire coated with alumina or other highly refractory insulating ceramic. The heat from the coil is transmitted by conduction and radiation to the Wall of the thimble and hence along the wall to the end plate 11 of the thimble. The exterior surface of the end plate is activated to copiously emit electrons at elevated temperatures. To support the cathode thimble and to minimize the loss of heat to the supports, aceramic disk 13 is employed. In the particular example illustrated, theceramic disk 13 is centrally apertured at 14 to receive the sleeve of the thimble.Bosses 15 and 16 are upset or swaged in the wall of the thimble to bear against the opposite faces of the ceramic disk.

Theceramic support 13 for the cathade may, in turn, be supported directly on themetal cylinder 20 which, in the case of the Pierce type cathode, may comprise the focusing anode for the beam. The end ofcylinder 20 is rolled inward to form theopening 22 mathematically determined in diameter and in spacing from the emitting surface to produce, at a low positive potential, a collimated beam of electrons in the aperture. Theend wall 21 may in some cases be conical (as shown), spherical, or-- otherwise shaped.

In the particular example illustrated, theceramic support 13 is telescoped into the cylinder and is held in place by thecollar 23 spot welded to the cylinder on one side of the ceramic disk. Movement in the other direction is prevented by themetal spacer 24 anchored, as shown, to thecylinder 20.

The bottom of the thimble 11 is prepared for electron emission preferably by coating the end area of the thimble with alayer 30 of barium-strontium carbonate. Such material is mentioned because of its wide use in the art, and not by way of limitation. The powdered carbonates in a wet slurry are conveniently sprayed on or applied with a brush to the area to be activated. Such a carbonateis desirable particularly because it is stable in air for relatively long periods of time. Later, when the coated cathode is degassed in an envelope, the temperature of the carbonates may be elevated to reduce them to the oxides of barium-strontium. Minute quantities of reducing materials in the cathode metal backing or in the coating then cause copious electron emission at a wide range of elevated temperatures.

According to an important feature of this invention, irregularity in the boundary of thecoating 30 need cause no concern. Thecollar 40 is slip-fitted over the end of the thimble and the inwardly extendingflange 41 thereof is brought to bear against the coated end of the thimble. The diameter of the opening defined by theflange 41 is easily and accurately controlled by drawing dies or by machining so that only a measured portion of the coated area is exposed. Where the cathode thimble is to be used in a Pierce-type cathode assembly, as illustrated, the collar may be extended beyond the flange and the interior surface of the extension shaped to properly complement the field established by theanode 21 to produce the desired beam inaperture 22.

Inasmuch as emission is not desired from thecollar 40, the collar is preferably machined or drawn from relatively pure, passive nickel. That is, the nickel should be suificiently free of such trace reducing elements as silicon, magnesium, iron, manganese, copper, and carbon as to produce no emission at the operating temperature of the cathode. Commercially obtainable coated cathodes or cathode-and-ceramic assemblies may be fitted with thecollar 40, mounted in theceramic disks 13 if need be, and then fastened in thecylinder 20. This assembly. is then placed in its envelope together with other tube components and pumped out while degassing heat is applied. At the proper time the cathode temperature is elevated to break down the carbonates to oxides and after removal of the gaseous by-products of this step, including gettering if desired, the tube is sealed off and the cathode is ready for operation. The boundary of the emitting surface is sharply defined and by proper placement of I theanode 21, and by proper adjustment of the potential ofanode 21 and other electrodes with respect to thecathode 10, a minimum of electron current flows to the anode. Currents of the order of A ampere per square centimeter have been obtained from small cathodes constructed according to this invention with but negligible loading of I the cathode circuit by the currents to theanode 21.

While the principles of the invention have been described in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of cylinder coaxial with and surrounding said sleeve, one end of said cylinder having a portion formed inwardly toward one end of said sleeve, one end of said sleeve being integrally closed by a plate, electron emissive material exteriorly coated on said plate; and a collar slipfitted over said one end of said sleeve, said collar having an inwardly extending flange bearing against the coated area of said plate and exposing a part thereof, said collar having a portion extending outwardly and toward said cylinder-portion to form with said cylinder an electron lens.

4. The cathode structure comprising a thimble of a commercial cathode grade of nickel, a coating of electron emissive material on the exterior surface of the closed end of said thimble, a collar slip-fitted over said closed end of said thimble, said collar having an inwardly extending flange bearing against said exterior surface of said closed end of said thimble and exposing a portion thereof.

' 5.' In combination in a cathode assembly, a metal cylinder with an inturned end portion, said end portion having a central opening, a ceramic spacer positioned transversely across said cylinder, a cathode sleeve supported in said cylinder by said spacer with one end of said sleeve adjacent said opening, said one end being integrally closed and having cathode coating material thereon opposite said opening, a collar slip-fitted over said one end and extending therebeyond toward said cylinder inturned end,

' and an inwardly extending flange on said collar bearing being electron-passive at said elevated temperatures and a being slip-fitted over said one end of said sleeve, said collar having an inwardly extending flange of measured inner diameter bearing against said exterior surface of said plate and exposing a part thereof.

2. A cathode structure comprising a cathode thimble, the closed end of said thimble having electron emissive collar having an inwardly extending flange of measured inner diameter bearing against said exterior surface of said closed end of said thimble and exposing a portion thereof.

3. A cathode assembly comprising a nickel sleeve, an insulated heater in said sleeve, a ceramic disk, said sleeve extending through and being attached to said disk, a metal against the coated area of said one end of said sleeve and exposing a part thereof.

References Cited in the file of this patent UNITED STATES PATENTS Benjamin et al. Aug. 2, 1938 2,131,204 Waldschmidt Sept. 27, 1938 2,244,358 Ewald June 3, 1941 2,310,811 Schantl et al. Feb. 9, 1943 2,436,265 Pohle et al. Feb. 17, 1948 2,604,599 Breeden July 22, 1952 v 2,640,950 Cook June 2, 1953 2,667,598 Linder Jan. 26, 1954 I FOREIGN PATENTS 395,660 Great Britain July 20, 1933 400,351 Great Britain Oct. 26, 1933 438,343 Great Britain Nov. 14, 1935 47,944 Holland Mar. 15, 1940 1,093,817 France Nov. 24, 1954

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