US2937302A - Electric-discharge device and cathode - Google Patents

Description

May 17, 1960 s. GOLDBERG 2,937,302

' ELECTRIC-DISCHARGE DEVICE AND CATHODE med may 21, 1957 SEYMOUR GOLDBERG BY Z ' ATTORNEYS United Sme Parent@ C@ ton, Germeshausen & Grier, Inc., Boston, Mass., a corporation of Massachusetts l t Application May 21, 1957, Serial No.`660,592

Claims. (Cl. 313-212) The present inventionv relates to electric-discharge devices and cathodes therefor, and, more particularly, toimproved cathode structures for use in gaseous-discharge tubes and the like. Y

Various approaches have been proposed for solving the problem, particularly associated with high-power gaseous discharge devices and the like, such as hydrogen thyratrons that switch, pulse or key high-voltage circuits, of providing a cathode ofsmall physical dimensions that, nonetheless, has a large electron-emissive surface area. Several types of cathode configurations have been evolved to try to accomplish this end, including the'utilizativon of a'plurality ofparallel cathode-element electron-emitting surfaces disposed within a cup. Y Y

It hasV been found, however, that all portions of suchi cathode elements do not actually eiectively emitfele'ctrons toward the anode of the discharge device at the instant that a sudden electrical discharge is initiated in the switching or keying circuits, before mentioned, and is applied to the discharge device. Once such an electrical discharge is initiated, the current flowing between the anode and cathode rises very rapidly to its final value; but, since a nite time is required for the plasma-to penetrate to all regions of the cathode, most of the electrons are drawn from'the portion of the cathode nearest to the anode. Operation at high pulse repetition rates results in relatively rapid deterioration of the cathode. After the current in the discharge device reaches its nal value, more.v

over, there is a voltage drop in the gas of the device that causes a non-uniform distribution of current to be drawn from the cathode, whereby most of the current continues to be drawn from those portions of the cathode nearestv to the., anode. It has been found, accordingly, that improved operationcan behad With'cathode elements ofv where R0 is the specific resistance at the electron-emitting surface, having a nominal value of four ohm-centimeters squared; iT is the total current discharged cumulatively to the anode in the discharge device; Ep is'the electrical eld in the plasma between the anode andthe cathode, having a nominal value of fourteen volts per centimeter; Vs is th potentialdrop across the cathode sheath;

is the potential gradient in the cathode sheath with 4a 937302 Patented May 17, ,195o

. 2 n nominal value of -77 volts per square centimeter; and `P is the total perimeter of the cathode in a plane substantially parallel to thev surface of the anode. Y

Through the utilization of cathode elements having the above length or height L in the direction from the cathode to the anode and each comprising a thin enclosure housing heater windings therein andcontaining electron-emissive external coatings, therefor, more uniform utilization of cathode-emitting surface has been obtained. Such cathode structures have been found to operate admirably well. There are also cases, however, where the utilization of a plurality of heater elements, one for each of the cathode elements, is undesirable, and where the thermal variation inherent in this type of cathode structure over the complete cathode must be held within more uniform limits. It has accordingly been proposed, in co-pending application,V Serial No. 580,551, tiled April 2S, 1956, by Kenneth I. Germeshausen and. Seymour Goldberg, for Electric Discharge Device and Cathode, to provide a cathode, preferably having an electron-emitting surface of length given substantially by equation (l) above, that comprises a base member carrying a plurality of spaced vanes each having electron-emitting surfaces extending along a direction away from the base member, with the cathode preferably being heated by the base member. Such construc-y tions have also operated well, in practice, providing not only an improved cathode that eliminates the necessity for a` separate heater winding for each of the cathode elements but, also, a greater uniformity in temperature variation over the complete cathode area. The cathode Y structure, moreover, inherently is capable of providing greater electron-emissive area.

Y There are'occasions, however, where it is desirable that the' cathodevanes be directly instead of indirectly heated. structure may be simplified and the structure may involve a continuous vane configuration rather than separate vane segments, simplifying construction andrassembly of the apparatus.

An object of the present invention, accordingly, is to provide a new and improved cathode lof the directly or Y electrodes 1 and 3 are sealed to the envelope walls by,-

Fig. 2 is a view similar to Figure l of a modcation; i

Fig. 3 is a perspective view, upon an enlarged scale, of a portion of the cathode of Fig. l, and Fig. 4 is a plan view of modified constructions.

Referring to Fig. 1, an electric-discharge device, illus, trated as of the thyratron type, comprises a sealed preferably ceramic-walled envelope 21gbounded at its top by an inverted cup-shaped anode 1, and containing a controlgrid 3, illustrated as of inverted cup-shape form andprovided along its preferably substantiallyl planar top surface, that is disposed near and substantially parallel to the substantially planar bottom surface of the anode, with a plurality 'of apertures 5. The envelope 21'may'be filled with an ionizable medium such as hydrogen gas. The tlanges 1 and 3 of the respective anode and control-grid for example, a `titanium-hydride-silver-nickel-eutectic solder seal, not shown, and they extend outside the envelope walls to conduct heat to the outside and also to permit the easy external electrical connection to the electrodes. The lateral vertical walls of the anode 1 and ln such cases`,'the cathode-vane supporting.

sacamos` control-grid 3 are shown disposed close to the envelope walls to provide long arc-discharge paths therebetween.

A cathode 2 isgshown disposed Within the control-grid cup 3. The cathode 2 comprises a preferably insulative base member 11-supporting or carrying upon itsupper surface a plurality of thin substantially planar conducting vane segments 13, 15, 17, etc., that, in accordance with the present Vinvention form a continuous vane surface, shown of spiral configuration in Figs. l and 3. Juxtaposed vane segments 13, 415, 17,'etc. are thus spaced from oneanother preferably uniformly, and, in regions, substantially parallel to one another. The continuous vane surface 13, 15, 17, etc. extends upward from the basemember 11 along the direction from the cathode 2 to the `anode 1, substantially perpendicular or normal to the lower surface of the anode 1.l While the vane surface 13, 15, 17, etc. is shown reversely curving only a few times, it is to be understood that a large number of bends may be employed and that the surface may also assume other configurations, as hereinafter described, including a zig-zag configuration. A heat radiation shield 9 may surround the cathode.

The lateral at surfaces of the thin vane segments 13, 15, 17, etc. are coated with electron-ernissive material and the vertical length or height of the vanes preferably conforms substantially to the dimension L of equation (l) herein, as before explained. The cathode is preferably heated by passing heater current between end portions or terminals of the continuous cathode-vane surface, as by means of the conducting struts 41 and 43. The struts 41, 43 serve, also, to support the cathode 2 in position, yand they connect by sealed terminal posts 45 outside the base 35 of the envelope for connection to a source of heater current.v The strut 43 is shown connected to the inner free edge of the vane segment 13 and the strut 41 is connected to the outer free edge of the vane surface. A suitable circuit for operating this discharge device is disclosed, for example, in United States Letters Patent No. 2,592,556, issued April 12, 1952, to Kenneth I. Germeshausen, and in which a source of high voltage is discharged between the anode 1 and cathode 2 under the control of an impulse fed to the grid 3.

With the aid of the above construction, the continuous cathode-vane surface, as of nickel, serves as a self-heated cathode-emitting surface. The vane segments may be extremely thin, say of the order of 0.02 inch in thickness, and hence permit the utilization of a large number of vane segments within a small cathode volume, resulting in a very large effective electron-emitting surface area. The successive vane segments, furthermore, may be very closely spaced from one another, with spacings of the order of from 1 to 2 millimeters, more or less. The continuous cathode vane surface, moreover, unlike other types of self-heated cathodes, has excellent thermal conductivity, eliminating the development of hot spots leading to the cumulative destructive Vcycle that normally plagues self-heated cathodes of the prior art.

The cathode of the present invention is, of course, useful in other thanthe particular hydrogen discharge Vdevice before referred to. It may, as but a further illustration, be employed in gaseous rectiliers, as shown in Fig. 2, wherein the continuous vane surface 13, 15, 17, etc. is supportedv Within a cup 9 that is shaped somewhat in the form of the control grid 3 of Fig. l. Heater current may be applied between the strut 43, which connects through an aperture in an intermediate plate 12 with the inner edge of the vane segment 13, as in Fig. 1, and the flange 9' of the cathode cup 9,' which connects at 14 to the outermost end or edge portion of the cathode vane surface.

Other cathode-cup orv base configurations and other anode or control-electrode structures may also be employed. As before stated, in addition, it is not necessary that the vane surface be of the configuration discussed in connection with the embodiments of Figs. l and 2. It may, for example, be of other configuration, such as in the re-entrant spiral form of Fig. 4, which is similar to concentrically or coaxially disposed annular or cylindrical Vanes, but is of a continuous conductive nature to permit of self-heating. In Fig. 4, a heater transformer H, which may be used with the cathodes of the other embodiments of Figs. l to 3, also, Yenergizes the continuous re-entrant spiral cathode vanesurface. This re-entrant conguration has the further advantage of cancelling out magnetic fields emanating from the passage of current through the cathode vane surface. The primary Winding P is shown energizing the secondary winding S the outer terminals 2" and 2" of which connect to the free edges of the vane surface. The center 2 of the vane surface is connected by conductor 16 to an intermediate or center tap T ofthe secondary winding S and cathode potential may be applied at the arrow terminal.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A gaseous electric-dicharge device having a plurality of electrodes including an anode and a cathode spaced from one another along a predetermined direction within an ionizable medium, the cathode comprising a continuous solid vane shaped to provide a plurality of juxtaposed spaced vane segments having electron-emitting surfaces .extending substantially along the predetermined direction,

and the length L of the vane, measured along the said predetermined direction, being given substantially by is the potential drop across the emitting surfaces of the cathode vane;

. VdVs is the potential gradient along the emitting surfaces of the cathode vane; and P is the total perimeter of the cathode vane in a plane substantially parallel to the surface of the anode, and means connected between end portions of the continuous vane for passing heater current therethrough.

2. The discharge device of claim l,`said cathode vane being of spiral configuration.

3. The discharge devicek of claim 2, said spiral configuration being re-entrant.

4. The discharge device of claim 1, further comprising a cup-shaped grid electrode containing said cathode, said cathode further comprising a flat insulating base member carrying said vane.

5. The discharge device of claim l, said cathode having a cup-shaped portion enclosing a iiat plate over which said vane is mounted.

References Cited in the le' of this patent vUNITED STATES PATENTS 1,999,806 Eitel et al.k Apr. 30, 1935 2,212,827 Etzrodt Aug. 27, 1940 2,567,369 Edwards et al Sept. 11, 1951 2,653,265 Coolidge Sept. 22, 1953

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