US2479529A - Electron discharge device - Google Patents

Description

Aug. 16, 1949 w. WATROUS, JR, ET AL 2,479,529

ELECTRON DISCHARGE DEVICE Filed Nov. 23, .1945

ATTORNEY Patented Aug. 16, 1949 ELECTRON DISCHARGE DEVICE Ward W. Watrous; Jr.,

Herbert Gleason, Bloo Chatham, and Charles infield,

N. J assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 23, 1945, Serial No. 630,340

7 Claims.

This invention relates to electron discharge devices and more particularly to devices wherein an ionizable medium or atmosphere is present. Such devices include the so-called glow discharge tube and gaseous rectifiers and thyratrons.

In discharge devices of the character indicated, particularly in those wherein a control electrode is employed, it is necessary to control the initiation of the discharge. It is desirable in this type of electron discharge devices, especially those for heavy current and voltage industrial use, to utilize cathodes and anodes of as large a size as practicable in order to provide for the desired'high rating for the tube. A desideratum for controlled discharge devicesof-the gaseous or vapor type, inter alla, requires that the grid potentials for control should be of a convenient order of magnitudeeven for tubes designed to operateat high values of anode voltage; and also requires that the grid geometry should be such as to minimize the tendency to surge. Surging is the term used in the art to designate the sudden extinction of the discharge. That extinguishing of the discharge probably is the result of a very sudden deionization of the discharge region, Such very sudden cessation of the flow of current in the circuit of which the device is a part, may induce abnormally high voltages of destructive magnitude in the equipment associated with the tube.

We have found that for a given discharge cur- I.

rent the tendency of the tube to surge increases both with decrease of the open grid area through which the discharge current flows during operation, and with decrease of the density of the gas or vapor.

Generally speaking, the ionizable medium in a discharge device of the character indicated is obtained by introducing a specific gas, of which neon, argon, xenon and krypton are examples, into the previously evacuated envelope, and sealing the gas therein. Such a device is known as a gaseous type tube distinguishing it from the vapor type of tube which is made by evacuating the envelope and introducing mercury, zinc, tin, or other material having sufiiciently low vapor pressure that it will produce a vapor of that material in the device when heated. Each type has limitations. For instance, the high voltage gasfilled thyratron requires a low gas density, and conventional designs which permit low values of grid bias voltage, are prone to surge. On the other hand, conventional high voltage vapor type thyratrons using mercury are limited in condensed mercury temperature operating range, because too high bias voltage is required at high our invention;

2 temperatures and surging occurs at low temperatures.

Broadly stated, the present invention is directed to the provision of an electron discharge device having an ionizable medium, wherein ade-. quate ionization for starting purposes is obtained but with a limitation imposed upon the discharge path for initiation of the discharge current.

A further general object of the invention is to increase materially the operating temperature range for a device of the character described.

Again, a general object of the invention is to provide a construction which will permit reduction of gas density in a gaseous type discharge device.

More specially. an object of the invention is to provide an improved control electrode.

Yet another object of the invention is to pro-. vide a control electrode constituting a partition and said partition providing regions for control of the discharge initiation and for the operating discharge following initiation.

Other objects of the invention will appear to those skilled in the art to which the invention appertains as the description progresses, both by direct recitation thereof and by implication for the context.

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

Fig. 1 is an elevation, with part of the envelope broken away and internal parts shown in section, of an electron discha ge device embodying Fig. 2 is a cross-section taken on line 11-11 of Fig. 1; and

Fig. 3 is a perspective view of the control electrode partition.

In the specific embodiment of the invention illustrated in said drawing, the reference numeral l9 designates a sealed envelope which has been evacuated and supplied with an ionizable medium, either as a gas such as recited above or a vapor of a reconstructing or other vaporizable source such as mercury and analogous substances. The envelope is shown cylindrical and at one end is provided with stem I l projecting longitudinally therein for introduction of usual lead-in wires l2 for a cathode l3 and lead-in wire M for a grid l5. At the opposite end of the envelope is provided longitudinally thereof a coaxial post 16 carrying at its inner end an anode ll of carbon or other suitable material which provides a surface directed toward the cathode and perpendicular to the axis of the envelope. Said post connects through the end of the envelope to a metallic connector cap I8 at the exterior of the envelope.

The cathode I3 is here illustrated as of the corrugated ribbon type such as described in Patent 1,968,608 of July 31, 1934, to Lowry, and mounted with its axis perpendicular to the axis of the envelope as in prior patent of co-inventor W. W. Watrous, Jr., herein, No. 2,254,922 of September 2, 1941 (both said patents being assigned to the same assignee as the present invention). The ends of the ribbon constituting the cathode are welded or otherwise secured to the aforementioned lead-in wires [2 which also function as rigid supports therefor. The cathode is rendered electron emissive, as by a coating of barium, strontium and the like, or otherwise.

Around the cathode is a shield It which is here shown of generally frusto-conical shape situated axially of the envelope and provided with bulges 20 in its tapered wall to afford clearance opposite the ends of the cathode. This shield is closed at its bottom and supported by eyelets 2! of which one is secured to one lead-in wire l2 and another to a dummy or other supporting post 22. Of course, the second lead-in wire for the filament is electrically free from the shield to avoid a short circuit. The smaller end of the frusto-conical shield is shown open and directed axially toward the anode.

The grid l5 preferably comprises, coaxial with the envelope, a hollow cylindrical shield portion 23 and a transverse partition 24 therein. The smaller end of the frusto-conical cathode shield [9 projects, with clearance, into one end of the cylindrical shield portion 23 of the grid, and the anode is located, with circumferential clearance, entirely within the other or upper end of the shield portion of the grid. Partition 24 is a metallic disc located between said smaller end of the cathode shield and the anode. The disc has a peripheral cylindrical flange 24* which fits within and is secured to the inside cylindrical surface of the shield. Upper end of the shield portion of the grid is preferably closed, suitable insulated passage for the anode post It being provided therethrough. The grid is supported by rods 25 longitudinally thereof secured on the inside cylindrical face of the shield portion below the partition and carried by a clamp collar 28 on the stem H.

The grid partition 24 is, for its greatest area, a solid wall fully blockin electron or ion flow, but provides two general regions through which discharge may pass. As shown, the first of these regions is provided by a slot 21 extending in a diametric direction of the partition and parallel to the axis of the cathode thereby locating the slot in the direct path of electron flow from cathode to anode. The second region is offset from such direct path and is shown as obtained by provision of arcuate slots 28 near the rim, or marginally of the partition, and symmetrically situated on opposite sides of the diametric slot 21. The center of curvature for the arcuate slots is coincident with the center of the partition. Preferably the length of the diametric slot is not greater than the diameter of the smaller end of the frustoconical cathode shield, whereas the diametric distance between the arcuate slots is greater than the smaller end of the cathode shield with the slots separated by solid material of the partition greater than the width of the slots, and thus deviation in fiow path from cathode to anode through the 4 arcuate slots due to the described geometry is required.

The essential feature of the grid is accordingly satisfied in provision of the diametric slot to constitute what we have termed above as the first region, and the arcuate or off-set slots to constitute the second region. The first region is for the purpose of controlling the discharge initiation and to pass a part of the discharge current. The second region is substantially exclusive to any initiating discharge and has a minor effect on the control of initiation, but furnishes an additional path for the discharge current. The influence of this second region on the control is kept small by using a geometrical relationship between the cathode, anode and this region which results in small contribution to the off-cathode field gradient as compared with the off-cathode field gradient resulting from the presence of the first region. By using a grid partition comprised of two such general flow-passage regions, and solid elsewhere, sufficient discharge area through the grid may be obtained to prevent surging, while maintaining grid control potentials of convenient magnitude even for very high potentials. It may furthermore be pointed out that the diametric slot 21 representing th first region, for controlling the initiation discharge, is much smaller than the second region exemplified by arcuate slots 28. Said diametric slot 21, though small, obtains control with low potentials, whereas discharge once initiated then utilizes the diametric and arcuate slots which offer sufficient area to prevent surging. A specific example of device employing a grid partition constructed as herein shown and described operated at mercury-vapor temperature of ten to fifteen degrees centigrade lower than similar devices not employing such partition.

We claim:

1. An electron discharge device comprising an envelope having an ionizable medium, a cathode and an anode opposed one to the other, and an interposed partition between the cathode and anode, said partition having separated co-planar openings therethrough each open at one face of the partition to the cathode and at the other face of the partition to said anode, said openings constituting discharge passage regions one for passage of discharge inclusive of initiating discharge and the other for passage of discharge substantially exclusive of initiating discharge.

2. An electron discharge device comprising an envelope having an ionizable medium, a cathode and an anode opposed one to the other, and an interposed partition between the cathode and anode, said partition having an opening in direct line between the cathode and anode, and having another opening for discharge passage from cathode to anode off-set from direct line between cathode and anode.

3. An electron discharge device comprising an envelope having an ioniza'ble medium, a cathode having an axial length, an anode having a surface parallel to the axis of the cathode, and a grid partition interposed between said cathode and said parallel anode surface, said partition having a slot parallel to said cathode axis and interposed in direct line between the cathode and anode, said partition having another slot off-set from the first said slot and out of direct line between the cathode and anode.

4. An electron discharge device comprising an envelope, a cathode therein having an axial length, an anode opposed to said cathode, and a grid partition between the anode and C thode and parallel to the axis of said cathode, said grid partition having an opening in direct line between the cathode and anode and having elongated arcuate openings offset in their entirety from direct lines between the cathode and anode and offset from the first said opening.

5. An electron discharge device comprising an envelope, a cylindrical hollow grid shield therein, a cathode shield having one end projecting into the grid shield, an anode at an opposite end part of the grid shield from said cathode shield, a grid partition in said grid shield transverse thereto and interposed between said cathode shield and anode, said grid partition having openings therethrough spaced from each other distances greater than the width of the openings measured on an intercepting radius of the partition, and a cathode in said cathode shield.

6. A grid partition comprising a metallic disc having a diametric slot therein and having elongated arcuate slots therein on opposite sides of and symmetrical with respect to said diametric slot.

7. A grid partition comprising a metallic disc having a diametric slot therein and having elongated arcuate slots therein adjacent the periphery thereof and having the center of curvature of said arcuate slots coincident with the center of said disc.

WARD W. WATROUS, JR. CHARLES HERBERT GLEASON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Number Name Date 1,997,831 Mitsuda Apr. 16, 1935 2,121,591 Gessford et al June 21, 1938 2,144,505 Mouromtsefi' et a1. Jan. 1'7, 1939 2,175,894 Hutchings Oct. 10, 1939 2,225,645 Kuipers Dec. 24, 1940 2,245,998 Pietsch June 17, 1941 FOREIGN PATENTS Number Country Date 321,197 Great Britain Nov. 4, 1929 334,256 Great Britain Sept. 1, 1930

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