US2001548A - Cathode for electric discharge devices - Google Patents

Description

May 14, 1935.

E. RMHILD CATHODE FOR ELECTRIC DISCHARQE DEVICES Filed Jah. l5, 1952 His Attorney.

Patented May 14, 1935 UNITED STATES CATHODE FOR ELECTRIC DISCHARGE v DEVICES Edgar Rmhild, Berlin-Steglitz, Germany, assignor to General Electric Company, a corporation of New York Application January 15, 1932, Serial No. 586,933 In Germany January 22, 1931 6 Claims.

The present invention relates to cathodes for electric discharge devices and more particularly to cathodes designed to carry large current at relatively low voltage.`

5 Heavy current cathodes of large power tubes are sometimes constituted of metal strips having a serpentine, loop or spiral conguration and presented edgewise to the anode. These shapes are desirable in vorder to obtain large cathode sur- 10 faces in relatively small spaces and to minimize radiation of heat. When cathodes of this sort are heated, the folds or convolutions, upon expansion, tend to distort and to change their relative position with respect to one another and also with respect to the cooperating electrode, thus causing deleterious koperating effects. Furthermore, these cathodes are subject to mechanical distortion by rough handling.

An object of the present invention is to provide an improved arrangement for holding a cathode structure of the type referred to rigidly in shape under unheated conditions, i. e., during manufacture; also under heated conditions as when being operated. This object is attained in brief, by forming the strip into a series of recurring reverse loops of which the inner portions are held rigidly between two grooved insulating disks. The latter may be supported on a central rod to which they are rigidly secured.

The invention will be better understood when reference is made to the following description and accompanying drawing in which Fig. 1 is a cross-sectional view of a cathode bent to form and shown as being tted into one of the insulating disks or plates; Fig. 2 is a cross section taken along line 2 2 in Fig. l; Fig. 3 shows the disposition of the improved cathode with respect to an anode of an electron discharge device; Fig. 4 is a diagrammatic view of an improved cathode provided with a control member and a cooperating anode; Fig. 5 shows plan and eleva- .tional views of the insulating plate.

Referring to Fig. 1, numeral l designates a strip form of cathode constituted of a member of bent and straight portions which take the general design of a clover leaf. The cathode may be fabricated of any suitable metal, for example, nickel, and if desired, coated with electronically active material. As shown more clearly in Figs. 2 and 5, the inner portions of the cathode are held rigidly between two circular plate members or disks 2 constituted of insulating material. These members are held at the proper distance apart by a spacer member 3 of insulating material and the entire assemblage arranged on a metal rod 4 to which it is rigidly secured by a washer 5 and pins 6 driven through the rod. The plates 2 are provided with channels or grooves l which receive snugly the inner loops.

As shown in Fig. l, one of the inwardly projecting loops of the cathode may be broken to provide terminals 8 for the application of alter' nating or direct current. If desired, the loops mays be entirely unbroken so as to form a continuous annulus and provided with connections at symmetrically disposed points on the cathode tok which a multi-phase voltage may be applied. It is evident that regardless of the manner in which current is passed through the` cathode, the structural arrangement, including the supporting disks 2, the spacer 3 and the central rod is such as to preclude any movement of the cathode as a Whole, or the individual portions thereof in any direction. As the cathode is heated, the resulting expansion is taken up by the lengthening of the individual convolutions, which simply results in a slightly increased outer diameter of the cathode and does not produce distortion of the individual loops because the metal is free to move longitudinally through the grooves. It is also apparent that a cathode of the type shown, when presented edgewise to an anode is capable of producing a large electron current 'by reason of its active surface and configuration which tends to prevent undue heat radiation; also on account of the f large extent of the surface. A cathode of this type is relatively easy to manufacture and assemble.

In Fig. 3, I have indicated the spacial relation of the improved cathode with respect to an anode of an electron discharge device. Numeral 9 design nates an anode of symmetrical shape such as a frustum of a cone, and presented endwise to the cathode. In order to prevent the anode from being coated with active material sputtered from the cathode, the latter may be provided with a metal shield Il) in the form of a shallow dish with the concave surface presented to the cathode. The shield member may be provided with a raised portion l I secured to the central rod Il in any suitable manner, for example, by a pin I2 driven through the rod.

The improved form of cathode lends itself to electron discharge devices of the electrostatically controlled type. Thus, in Fig. ll, I show a metal cylinder I3 surrounding a loop cathode of the improved type and closed at both ends except for perforated portions for the escape of electrons. The cylindrical member terminates in a metal tube I4 which may be sealed to the glass envelope of an electron discharge device. 'I'he central rod member 4 may also be secured to a stem. The upper end portion of the electrostatic control member is provided with a ange extension l5 which carries a pin I 6 driven through the central rod. The structure as a Whole, i. e., the improved cathode and grid member, is thus arranged in a compact and rigid unit which precludes relative movement between the cathode and grid so that small spaces may be accurately maintained between the electrodes. A combined cathode and grid structure of this sort may be employed in connection with a symmetrical form of anode 9 to which it is presented endwise.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A cathode for an electron discharge device comprising a metallic strip member bent into recurrent inner and outer loops and arranged about a central support member, means for securing the inner loops to the support member, said means comprising a pair of insulating plates containing grooves which receive the loops.

2. A cathode for an electron discharge device comprising a metallic strip bent into recurrent inner and outer loops and arranged about a. central support member, means for securing the inner loops to the support member, said means comprising a pair of insulating plates spaced apart by an insulating member, said plates serving to clamp the strip between them.

3. A cathode for an electron discharge device comprising a metallic strip having recurrent loops which form in the aggregate, roughly a cylinder, a support member mounted in the axis of the cylinder, and extending over and secured to the edges of said loops.

4. A cathode for an electron discharge device comprising a metallic strip having recurrent loops which form in the aggregate, roughly a cylinder, a support member mounted in the axis of the cylinder and secured at both ends to said loops.

5. A cathode for an electron discharge device comprising a metallic strip bent into recurrent loops and forming a complete annulus, said annulus being provided with terminals, greater in number than two, equidistantly spacedabout the periphery of the annulus for the application of multi-phase alternating current to the cathode.

6. An electron discharge device including a cathode, an electrostatic control member and an anode, said cathode and electrostatic control member secured together as a unit, said cathode being constituted of strip material presented edgewise to said anode and having recurrent loops arranged about and supported from a central member, said control member being constituted of a perforated cylinder secured to said central support member.

EDGAR ROMHILD.

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