US2396807A - Discharge device and cathode therefor - Google Patents

Description

March 19, 194e. w. w.' WATRUS, JR 2,396,807

DISCHARGEV DEVI-CE AND CATHODE `THEIREFOR ATTORNEY Patented Mar. 19, 1946 i DISCHARGE DEVICE AND CATHODE THEREFOR Ward W. Watrous, Jr., Chatham, N. J., assigner' to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 27, 1943,. Serial No. 477,383

17 Claims'. (Cl. Z50-275) This invention relates to cathodes, and more particularly to such for use in connection with discharge devices,

The primary object of my invention, generally considered, is to provide an improved form of directly-heated cathode for electrical discharge devices.

Another object of my invention is to provide a directly-heated type of cathode operating ina heat-shielded enclosure and so arranged that the intermediate or central portion of the cathode is presented to the anode, in order to minimize op.- erating variations due to phase changes resulting from cathode energization by alternating current.

A further object of my invention is to provide a directly-heated cathode structure whichV has a very small thermal mass.

A still further object of my invention is to provide a directly-heated cathode structure which allows for high heating e'iciency, and at the same time has sufficient space, in the region adjacent to the electron emissive surface, to provide a multiplicity of paths, greater than the mean freeY path, for ionization.

An additional object of my invention is to provide a cathode structure in which themass thereof is low but which is nevertheless relatively rigid- Another object of my invention is to provide a cathode structure the operating voltage for which is readily changeable to predetermined values.

Other objects and advantages of theinvention, relating to the particular arrangement and construction of the various parts, will become apparent as the description proceeds.

Referring to the drawing:

Fig. 1 is an elevational view, Withk parts broken away, of a thyratron embodying my invention.

Fig. 2 is a perspective view, on' an enlarged scale, of the shield and cathodev structure of the thyratron illustrated in Fig. 1.

Fig. 3 is a longitudinal sectional View of one of the corrugated cathode elements;

Fig. 4 is a transverse sectional view on the line IV-IV of Fig. 3, in the direction of the arrows.

Fig. 5` is .a fragmentary perspective View' of a corrugated cathode element, showing a modification.

Fig. 6 is a diagram showing how the cathode elements are connected for operation at relatively high voltage.

Fig. 7 is a diagram showing how the cathode elements are connected for operation at relatively low voltage.

Referring to the drawing in detail, like parts being designated by like reference characters, and first considering the embodiment of my invention illustrated in Figs. 1 to 4, inclusive, there is shown a thyratron Il consisting of a vitreous orrglass envelope l2, preferably containing inert gas at a desired pressure, closed at one end by a nare tube I3, having a press IQ through which pass lead-in conductors I5 and i6 (shown double) for the cathode, generally designated as il. By makingprovision for the necessary insulation between the electrodes, the insulating envelope IZ may be replaced by one of metal. The press also receives supporting lead Wires I8 and I9 (which unite outsidey of the press I6) for the cathode shield 2l, shown double cylindrical in the present embodiment.

Through a side of the rflare tube I3, passes .a lead-in conductor 22 uniting` with a collar 23 which is clamped to embrace the flare tube I3, as by means of bolts or the like 23, and from which extend supportingA lead wires 2d to the grid 25. The thyratron is based `as indicated at 2G, said lead-in conductors I5, I6, 22 and I8--I9 connecting, respectively, with contacts 2l, 28, 29, and 3| 4of said base. The other end of the lamp is provided with a contact cap 32 to which an electrode 33, adapted to function as an anode, is connected, as by means of'lead-in conductor 34.

In general, the cathode Il consists of one or more laments of special conguration, the present embodiment being illustrated specifically in Figs. 1, 2, 3, and 4, located radially in the interior of the heat-shielding device 2i. In the form of construction illustrated in these iigures, it is proposed that currentv flow from the lead-in conductors I5 through connector 3l] and lead lill, (desirably square in section and which passes through correspondingly shaped hole in insulating bushing 50 in the bottom walls of the shield 2l), to half disk 35, then divide, one-half continuing through each filament 3t and 3i., across the top circular, apertured, and slotted connector disc 38, (which is outwardly anged for connecting with and partly closing the outer or upper end of the inner heat-shielding cylinder Eil) onehalf also continuing through each lament 39 and lli, uniting at half disk i2, and passing out of the envelope along lead El, desirably square in section, through corresponding hole in bushing 50, and connector B2', and out along lead-in conductors I6. It Will thus be seen that the uppermost portion of the cathode structure is electrically midway between the inlet and outlet leads and, therefore, always at an operating voltage midway between that of said leads.

Therefore, even when heating the laments with alternating current of a relatively high potential, the cathode region around the area bordered by the top disc 38 and adjacent portions of the laments 36, 31, 39 and 4I is always substantially unipotential, that is, it does not even vary appreciably as the phase of the heating current changes. Thus, regardless of said heating current, the field conditions at the mouth of the cathode, or opening 6s are constant, so that ionization sufficient to cause breakdown will occur at a uniform value of anode potential.

Low cathode mass with mechanical rigidity is obtained by employing a thin (of the order of a few mils) cathode base material of suitable composition, such as nickel, and forming it in such a way that increased area and reasonable rigidity and resistance to warping are obtained. A preferred construction is shown fragmentarily in detail in Figs. 3 and 4, and another is shown as an alternative in perspective, fragmentarily and in detail in Fig. 5, like the cathode element 36 in Fig. 2, and designated 36a. Thecathode elements when finished are, of course, coated with suitable electron-emissive material, such as the oxides of barium and strontium.

Specincally, each filament of the cathode is desirably formed with transverse corrugations 43. each of which is in turn bent, as shown most clearly in Fig. 4, as it extends from side to side, so that its intermediate portion is to one side of the plane of the flat end portions 44 of each filament, and its end portions 45 and 46 lie on the other side of said plane. This is equivalent to corrugating each filament both ways, that is, longitudinally and transversely, insofar as rigiditying the same is concerned.

It will also be understood, that although I have shown the small corrugations 43 extending between the near sides of the cathode plates, yet if desired said corrugations 43a may extend between the far sides, or longitudinally rather than transversely of each plate, in this case desirably terminating short of the ends, as shown in Fig. 5, so as to leave at end portions for attachment to the members 35, 38 and 42, which attachment may be effected by welding or soldering, asin the first embodiment.

The intermediate attaching member 38 is secured to the upper or outer end portion of the inner hollow cylinder 60, as by welding or soldering a peripheral flange 41 to the upper edge portion thereof (Figs. 1 and 2). The lower edge of said cylinder 60 is desirably connected in a slmilar manner to a closure member 48, spaced from the lower wall of the outer heat-shielding hollow cylinder 62 by the peripheral Ilange 5| of the insulating bushing 58 through which the leads 4U and 6l pass.

The hollow outer cylinder 62,; of heat-shielding device 2l, encloses the hollow inner cylinder 60, as illustrated most clearly in Figs. 1 and 2, with just a convenient gas space therebetween. It is directly connected to end support by the leads VI8 and I9, which are soldered or otherwise suitably connected thereto, and closed at its lower end by bottom plate B3, Iprovided with an outer peripheral flange 64 soldered or otherwise suitably connected toits lower edge portion. The plate 63 serves to support the insulating bushing 50 and the inner cylinder B0, as by dimples or upwardlyextending corrugated portions 35, desirably spot welded or otherwise metallicly connected to the lower surface of the closure plate 48 of said cylinder Sil. thereby making a good electrical connection therewith.

The upper end of the outer cylinder 62 is partly closed by circular `plate 68 provided with outstanding peripheral flange 6l soldered or otherwise suitably secured to the outer edge portion' of said cylinder. The plate 66 may be provided with a central circular aperture 68, or cathode mouth corresponding in size with the central aperture in the plate 38, to allow for the escape of electrons. All parts of the shielding cylinders, including the circular end closure plates, are desirably formedof polished nickel, or other similar metal, for conserving the heat radiated by the cathode elements during operation of the device. Y

The grid 25 is formed generally as a hollow cylinder carrying a transverse foraminous wall 52 which functions as the grid proper with respect to the anode 33. The upper end of the grid 25 is braced by connected tab members 53 and 54 which are adjusted so to snugly t within the dome or constricted'portion 55 0I the envelopes l2. The grid 25 is desirably formed of sheet metal, nickel for example, provided with a coating of carbon or other material which is low in electron emissivity and high in heat-radiating power. Although the cylindrical portion of the grid 25 is also shown foraminous, it will be understood that this is not necessary as the grid cylinder is equally efficacious when unperforated.

The wiring diagram for the arrangement shown in Figs. l and 2 is illustrated in Fig. 6. That is, when it is desired to operate the cathode at a relatively high voltage, current passes through a switch member 56, leads l5 (connector B, lead 48, shown in Figs. 1 and 2), dividing to pass through cathode elements 36 and 3l, then after passing through the top connection 38, continuing through cathode elements 39 and 4l, and returning through (lead 6 l, connector 62', shown in Figs. 1 and 2) leads It, and switch element 5l.

If it is desired to operate the cathode at half voltage, it is only necessary to tie the leads l5 and I6 together, as indicated by switch member 58, and pass current between this juncture, as one terminal, and the shield member 2l, which is electrically connected through the top disk 38, as the other terminal. The current will then double but the power input remains the same. This connection is illustrated in Fig. '7, the current passing through switch element 56 and leads I8 and I9 t0 the top disk 38, dividing through the four filaments 35, 3T, 39 and 4l, and nally passing out through return leads l5 and I and switch element. In order to use voltages different from the normal voltage which should be applied to the cathode filaments, in accordance with Fig. 6, or the half voltage of Fig. 7, a rheostat 59 (which may be cut out entirely when the supply voltage is correct for the filaments) may be employed in series with the cathode supply, if desired.

The operating voltage can be determined when the tube is being manufactured, thus oifering devices with cathodes of two potentials, while using similar cathode parts, or the leads can be brought out from the tube as separate connections and the lament potential selected by `the user. With the parallel connection, it willbe noted that the equipotential (or intermediate) cathode surfaces are not presented to the anode, (which may be designated as the random-phasing advantage) so one advantage of the connection, illustrated in Fig. 6, disappears.V However, in. such instance the voltage being only half, the effect of cathode potential phasing is minimized.

From a consideration of the foregoing, it will be seen that although both faces of each cathode section are heat shielded, they are readily accessible to emit electrons. This avoids some diiiiculties previously encountered due to heat shielding because of space charge effects and the inability of` the eld from the anode to act upon all parts of the cathode surface.

It will also be seen that I have devised a discharge device and cathode therefor in which the cathode is directly heated, and its eiective potential, as compared with the anodeis independent of the supply potential phasing. I have likewise provided a cathode with elements of small thermal mass, rigid, and adjustable to one or another voltage, the lead, sections which connect directly to the lower plates thereof being desirably non-circular or square, so that they not only tend to maintain their desired positions in the receiving insulator, but present flat upper surfaces for accurate connection with said plates.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

I claim:

1. An electrode for a discharge device comprising a strip of metal connected for direct heating to electron-emitting temperature by the passage of electric current therethrough, and formed with a rigidifying corrugation extending longitudinally between the pair of remote opposite edges thereof.

2. An electrode for a discharge device comprising a strip of metal connected for direct heating to electron-emitting temperature by the passage of electric current therethrough, and formed with a longitudinally extending corrugation.

3. An electrode for a discharge device comprising a generally straight corrugated strip of metal connected for direct heating to an electronemitting temperature by the passage of electric current therethrough, and with its corrugations curved as viewed in a transverse section of said strip.

4. An electrode for a discharge device comprising a generally nat strip of metal connected for direct heating to an electron-emitting temperature by the passage of electric current therethrough, and formed with corrugations extending from side to side and curved as viewed in a transverse section of said strip.

5. An electrode comprising a generally flat strip of metal connected for direct heating to an electron-emitting temperature by the passage of electric current therethrough, and formed with corrugations extending at an angle to one another.

6. An electrode for a discharge device comprising a heat-conserving enclosing shield, and a strip of electron-emissive material formed with corrugations, extending parallel to the axis of said shield, and connected for direct heating by the passage of electric current therethrough.

7. An electrode for a discharge device comprising a double heat-conserving enclosing shield of bright metal, and a strip of electron-emissive material formed with corrugations, extending parallel to the axis of said shield, and connected for direct heating, by the passage of electric current therethrough.

8. An electrode for a discharge device comprising a plurality of. corrugated strips of metal extending in generally the same direction. as the axis of said device, means extending transversely of said device and connecting the inner ends of said strips, and means connecting thek outer ends of said strips to a source of electric power for energizingl said strips to electron-emitting temperature by passage of electric current therethrough.

9. An electrode for a discharge device comprising a heat shield, an insulator mounted in a bottom aperture thereof, a plurality of strips of` metal enclosed in said shield and extending in generally the same direction as the axis of said device, means extending transversely of said device and connecting the inner ends of said strips, and means connectingthe outer ends of said stripsV to a source of electric power for energizing said strips to electron-emitting temperature, said means including transversely extending plates, and lead sections square in section, connected to said plates, and passing through corresponding apertures in said insulator.

10. An electrode for a discharge device comprising a generally cylindrical shield disposed axially of an enclosing envelope, a plurality of shield-enclosed corrugated strips of metal extending in generally the same direction as the axis of said shield, means extending transversely of said shield and connecting the inner ends of said strips, and means connecting the outer ends of said strips to a source of electric power for energizing said strips to electron-emitting temperature by passage of electric current therethrough.

l1. An electrode for a discharge device comprising a plurality of corrugated strips of metal extending in generally the same direction as the axis of said device, means extending transversely of said device and connecting the inner ends of said strips, andmeans connecting said transversely extending means and the outer ends of said strips to a source of electric power for energizing said strips to electron-emitting temperature by passage of electric current therethrough.

12. An electrode for a discharge device comprising a generally cylindrical shield disposed axially of an enclosing envelope, a plurality of corrugated strips of metal extending in generally the same direction as the axis of said shield, means extending transversely of said shield and connecting the inner ends of said strips, and means connecting said transversely extending means and the outer ends of said strips to a source of electric power for energizing said strips to electron-emitting temperature by passage of electric current therethrough.

13. A discharge device comprising a vitreous envelope, a flare closing one end of said envelope, a grid supported from said are and with its other end braced with respect to the opposite end of said envelope, an anode passing through said opposite end for cooperating with said grid, a cathode device disposed within said grid and comprising a corrugated strip of metal, and a heat shield surrounding said strip and enclosed in said grid.

14. An electrode comprising a strip of metal connected for direct heating to an electron-emitting temperature by the passageof electric current therethrough, and curved to cylindrical form about a longitudinally disposed axis and provided with corr-ugations transverse to said aX1s.

15. An electrode comprising a strip of metal connected for direct heating to an electrcn-emitting temperature by the passage of electric curreni; therethrough, and corrugated longitudinally and transversely. Y

' 16. An electrode for a discharge device comprising a plurality. of corrugated strips of metal extending in generally the same direction as the raxis of said device, means extending transversely envelope, a flare closing one end thereof, a grid supported from said are and with its other end braced with respect to the opposite end of said envelope, an anode supported on means passing through said opposite end for cooperating with said grid, and a cathode device disposed within said grid and comprising a plurality of strips of metal .extending longitudinally from said flare with their remote ends connected, and a pair of leads passing through said flare and respectively Yconnected to the adjacent ends of said strips, and

a third lead also passing through said flare and united to said remote ends connection, whereby said cathode is adapted for operation on either of two voltages.

' WARD W. WATROUS, JR.

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