US2909777A - Gaseous-discharge device - Google Patents

Description

Oct. 20, 1959 Fig. 1

2 Sheets-Sheet 1 Fig.2

KENNETH J GERMESHAUSEM INVENTOR.

ma/Mm ATTORNEYS Oct. 20, 1959 K. J. GERMESHAUSEN 2,909,777

GASEOUS-DISCHARGE DEVICE Original Filed Feb. 7, 1946 2 Sheets-Sheet 2 Fig.3 23

Paschen Curve For He 11 um Voltage Breakdown Pressure in mm x spacing m cm.

Fig. 4

KENNETH J GEHMESHAUSEW, INVENTOR.

ATTORNEYS United States Patent 53 cc GASEOUS-DISCHARGE DEVICE Kenneth J. Germeshausen, Newton Center, Mass.

Continuation of application Serial No. 646,066, February 7, 1946. This application October 5, 1956, Serial No. 614,323

14 Claims. (Cl. 313193) V The present invention relates to gaseous-discharge de-v 2,909,777 Patented oer. no, 1959,

, vention resides in reducing the amount of the sputtered cathode material that travels out of the metal cathode cup, during the operation of the tube, and along a path toward the space between the anode and the inner walls of the carbon-spool electrode. A preferred method of accomplishing this result is to intercept the sputtered material during its travel along the said path, but withvices, and more particularly to gaseous-discharge devices of the cold-cathode, especially the strobotron type. The present application is a continuation of application, Serial No. 646,066, filed February 7, 1946.

An object of the present invention is to provide a new.

and improved gaseous-discharge device, particularly of out interfering with the operation of the tube resulting from the difierence of potential established between the cathode pill 8 and the anode 5. This method may be carried out with the aid of an annular ring-shaped metal cover for the metal cathode cup. The metal cover may be placed upon the open end of, an insulating cup in which the metal cathode cup is disposed, and the upper end of which extends above the upper end of the metal cathode cup. The metal cover may thus be insulated from the metal cathode cup.

As some of the sputtered cathode material does leave the metal cathode cup through the central opening in the annular or ring-shaped cover, however, an additional A sputtered-material intercepting barrier, in the form of the strobotron tube comprises-an anode 5, a grid 4, which may be in the form of a carbon or graphite spool or hollow cylinder, and a cold cathode 8, disposed at the bottom of a metal cathode cup. The cold cathode 8 is in the form of a compressed pill of caesium powder. and

the anode 5 inside the carbon or graphite spool or hollow cylinder 4, but suitably spaced from the inner 'walls thereof. As described in the said Letters Patent 2,592,556, the distance between the inner walls of the carbon or graphite spool or hollow cylinder 4 and the anode 5 is such that the product of the said distance and the pressure of the gas in the tube is represented by points of the Paschen curve for the said gas to the left of its lowermost portion, thus providing a high breakdown voltage between the grid 4 and the anode 5.

The caesium or other material of low work-function compressed in the cold-cathode pill 8, however, sputters away in a plurality of directions during the operation of the tube; and it is found that, if this cathode-pill 8 is disposed in a cold-cathode metal cup that is fully open, there is danger of the sputtered cathodeparticles leaving the fully-open cup, to travel along a path toward the space between the anode 5 and the inner walls of the'carbon-spool electrode 4. Some of the sputtered material entering this space may then become deposited a metal sputtershield, may also be interposed in the said path, spaced from this ring-shaped or annular cover, between this cover and the anode 5. The tube is thoroughly operative without the sputter shield, but the I sputter shield may serve to enhance the life of the tube.

Other and further objects will be explained hereinafter, and will be-particularly pointed out in the appended claims. I

The invention will now be more fully explained in connection with the accompanying drawings, in which Fig. 1 is a longitudinal section of a gaseous-discharge device embodying the present invention, the parts being shown diagrammatically, and not to scale; Fig. 2 'is a similar view of a modification having the advantages" of small size and ease of construction; Fig. 3 is a diagrammatic view of a circuit with the tube of the present invention connected therein; and Fig. 4 is a graph rep resenting the Paschen curve for helium, the abscissae representing the product of the gas pressure, in millimeters, and the spacing of the-electrodes, in centimeters, and the ordinates representing the breakdown voltage between the electrodes, in volts.

The electric-discharge tube illustrated in Fig. 1, shown of the strobotron type, comprises an evacuated glass envelope 1 filled with a suitable gas, at a relatively low pressure, and containing a plurality of electrodes, as

upon the inner walls of this carbon-spool electrode 4.

discharge between this inner surface of the carboncylinder-grid electrode 4 and the anode 5. The consequent break-down of the tube naturally defeats the object of increasing the voltage at which the strobotron should yield the high currents.

An objection of the invention is to reduce the amount I follows: a solid cold cathode 2, a control-grid electrode 3, in the form of an annular or ring-shaped metal cover, and a second control-grid electrode 4, in the form of a hollow-cylinder spool or tube of carbon or graphite, concentric with and surrounding an anode 5. The anode 5 is constituted of the free end of a lead-in-wire conductor 21 that extends into, but is spaced from the inner walls of, the spool-shaped or tubular carbon or graphite electrode 4. The space separating the anode 5 from the inner walls of the spool-shaped electrode 4,'as is explained in the said Letters Patent 2,592,556, is small. The cathode 2 is provided with a cathode-lead conductor 23. The cylinder grid 4 is fixed to a grid-support element 12, in the fOlTl'lzOf a metal strap wrapped around the carbon cylinder 4, and supported by a support-wire rod or rods, shown at 14 and 14a. The rod 14 may also constitute a lead conductor for the grid 4.

The lead-in-wire conductor 21 is sealed in a glass or other insulating sleeve or tube 16 so as to .be surrounded by the glass or insulation of this tube. The carbon or graphite cylindrical-grid electrode 4 is supported by the glass sleeve 16 by means of a tight fit between them. The glass sleeve 16, the anode 5 sealed therein and the carbon electrode 4 supported thereby constitute a unit sub-assembly, the parts of which are held temporarily together during the subsequent steps of manufacture of the tube. In the complete tube, the parts are held together by the grid-support element 12 and the tube envelope 1.

The cathode 2 is shown comprising a pill 8, held in place by a wire-mesh screen 9 at the bottom of a metal cathode cup 18. The ring electrode 3, which may serve as a control grid for the discharge, constitutes a metal cover for the part of the cathode 2 facing the discharge. The cup 18 is surrounded by an insulating cup 10 for the part of the cathode 2 away from the discharge. The insulating cup 10 serves to support the grid 3 and to prevent the occurrence of a discharge to the outside of the cathode-cup structure. The pill 8 may be constituted of compressed caesium chloride and aluminum filings or powder, or other material of low-work function, and forms the active material of the cathode.

Electrons from the cathode 2 may travel through the central opening of the annular or ring-shaped cover 3, into the upper region of the envelope 1, and into the axially disposed opening of the carbon cylindrical spool 4 to the anode 5. The discharge therefore takes place from the lower region of the envelope 1, in the interior of the metal cup 18, into the upper region, to the anode 5.

Glass or other insulating sleeves 6 surround the support wires 14 and 14a of the grid 4 to prevent breakdown from the support wires to the grid 3 and to insure that the breakdown shall occur directly between the grid 4 and the grid 3. As explained in the said Letters Patent 2,592,556, the spacing between the grid 4 and the anode 5 inside the concentric spool cylinder 4 is such that the operation, when helium is the gas employed, is represented by the points of the left-hand-portion of the Paschen curve of Fig. 4, to the left of its lowermost portion, according to which the breakdown voltage may be high even for close spacings and low pressures. As appears from this lowermost portion of this curve, the breakdown voltage between the electrodes is very low, on the order of 150 volts, and it does not vary very rapidly, with changes in pressure or spacing, over a considerable range of both pressure and spacing. As an example, for a typical tube, a pressure of 10 millimeters of helium, and a spacing between the grid 4 and the anode 5 of 0.05 centimeter, would yield a product of 0.5. The corresponding breakdown voltage is shown in Fig. 4 to be approximately 2000. With the same low pressure, on the other hand, a spacing between the grid 4 and the grid 3 of 0.4 centimeter would yield a product of 4 and a corresponding breakdown voltage of approximately 175.

The anode 5 is preferably constituted of a material of refractory nature, such as tungsten or tantalum, to prevent excessive sputtering of the anode under highcurrent-discharge conditions. This sputtering, if excessive, would result in the disappearance of the gas in the tube. The use of tungsten for an anode, as compared to nickel, results in a greatly increased tube life.

The anode 5 and the cathode 2 of the tube 1 may be connected by the conductors 21 and 23, in series with a load impedance 13, across a condenser 11. The condenser 11 may be continuously charged from a suitable source 22 of direct current, shown as a battery, through an impedance 7. The grid 3 is shown connected by a conductor 17, through an impedance 28, shown as a resistor, to the positive terminal of the battery source 22. The grid 4 is shown connected by the conductor 14, through the secondary winding of a transformer 15, to the cathode 2.

The condenser 11 is charged from the battery 22 through the impedance 7, the tube 1 being non-conductive. When a pulse of power is desired in the load impedance 13, the grid 4 is energized by means of the transformer 15. Upon the attainment of a potential on the grid 4 of about volts positive with respect to the cathode, a glow discharge is initiated between the grid 4 and the cathode 2, causing the gas in the gridanode space to become partly ionized. This results in breakdown between the anode 5 and the cathode 2, producing an arccharacteristic discharge to the cathode 2. The current first fiows to the cathode 2 in the form of a glow discharge. When this current flow reaches sufiicient density at the surface of the cathode, a cathode spot is formed on the surface of the pill 8. The action of the cathode spot causes the caesium chloride to break down, aluminum being substituted for the caesium and forming aluminum chloride. This reaction results in the formation of a thin surface layer or coating of caesium on the pill and the mesh 9, which has a great tendency to adhere to the surface. It is on this layer that the cathode spot is formed.

A surge of current then flows from the condenser 11 through the load impedance 13 and the tube 1, discharging the condenser 11. The tube 1 thereafter becomes extinguished, and the condenser 11 again becomes charged from the battery 22, in readiness for the next desired surge of power through the load impedance 13.

The material of the pill 8 furnishes enough free caesium so that advantage can be taken of the ease of spot formation on caesium. The formation of the cathode spot is greatly facilitated by the presence of the caesium or other material of low work function present on the cathode.

Other material than caesium chloride and aluminum may be used for the pill 8; for example, mixtures of caesium chloride and rubidium chloride and aluminum, cadmium or zinc.

The gas pressure, though relatively low, should be as high as possible to insure proper formation of the cathode spot. Helium is therefore preferred as a gas filling; its characteristics are such that, for a given spacing of the electrodes, the gas pressure can be much higher than for gases such as argon.

At the time of formation of the cathode spot, some caesium is sputtered on to the grid 3, thus lowering the breakdown voltage between the grid 4 and the grid 3.

In the absence of the annular metal ring 3, there would be danger of a large amount of the sputtered caesium entering the space between the anode 5 and the inner walls of the carbon spool 4, and this would cause a breakdown in the space between these inner walls and the anode 5. In accordance with the present invention, the annular metal ring 3 and/or other means such as, for example, the later-described sputter surface 19, oriented with respect to the cathode 2 at least partially to intercept or obstruct the travel of a substantial quantity of sputtered cathode material that otherwise might reach the said space between the anode 5 and the inner walls of the carbon electrode 4, considerably reduces the amount of this sputtered caesium that enters this space. As the grid 4 is constituted of carbon, any residual sputtered caesium that may reach it, in the presence of the annular metal ring cover 3, will not lower the breakdown voltage from the grid 4 to the anode 5. Further to reduce the amount of sputtered caesium from the cathode 2 that shall enter the space between the anode 5 and the inner walls of the carbon or graphite hollow-cylinder electrode 4, however, a metal sputter shield surface 19 may be interposed along the path of travel of the electrons between the cathode 2 and the anode 5, shown attached to the grid support 12 by means of a wire support 20, spaced from the annular cover 3. The tube is perfectly operative, however, even in the absence of the sputter shield 19.

According to the modification of Fig. 2, the controlgn'd electrode 3, with its connection through the impedance 28, and the support wire 1411, are entirely omitted, and the tube is made of smaller size. Conduction is started by exceeding the breakdown voltage between the grid 4 and the cathode 2, shown supported and centered by a mica disc 22.

The mica disc 22, like the insulating cup of Fig. 1, prevents a discharge from forming on the outside of the cathode structure 2. The lead 21 to the anode 5 is brought out or sealed through the base of the tube instead of, as in Fig. 1, fromthe apex, and it is surrounded by the glass sleeve 16 for preventing breakdown between the anode lead 21 and the grid lead 14 and the cathode lead 23. A metal cap 26 carried by the support wire 14 serves to hold the grid 4 in place on the glass sleeve 16.

The glass sleeve 16, as in the construction of Fig. 1, serves to prevent a discharge between the anode 5 and the grid lead 14, the cathode lead 23 or the cathode structure. The cathode lead 23 is shown covered by a glass or other insulating sleeve 24. The operation is substantially the same as that described in connection with Fig. 1 when the before-mentioned sputter-obstructing means is provided.

Further modifications will occur to persons 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:

1. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a solid cold cathode between which electrons may flow, a control electrode having a Wall separated from the anode by a small space, the cathode comprising material that, during the operation of the device, sputters out of the cathode in a plurality of directions including the direction toward the said space and on which material a small cathode spot is formed from which electrons are adapted to travel toward the anode and into the said space, and means for obstructing the travel of substantial quantity of the said sputtered material toward the the said space.

2. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a caesium-containing cathode between which electrons may flow, a control electrode having a wall separated from the anode by a small space, and means for obstructing the travel toward the said space of a substantial quantity of the caesium that sputters out of the cathode in a plurality of directions including the direction toward the said space, during the operation of the device.

3. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a solid cold cathode between which electrons may flow, a hollow-cylinder control electrode in the hollow space of which the anode is disposed with a small separation from the walls of the said space, the cathode comprising material that, during the operation of the device, sputters out of the cathode in a plurality of directions including the direction toward the said hollow space and on which material a small cathode spot is formed from which electrons are adapted to travel from the said cathode spot into the said hollow space toward the anode, and means for obstructing the travel of a substantial quantity of the said sputtered cathode material toward the said hollow space.

4. A gas-filled device having a plurality of electrodes in the gas of the device comprising a wire anode and a 6 -from which electrons are adapted to travel from the said cathode spot into the said hollow space toward the anode, and means 'for obstructing the travel of a substantial quantity of the said sputtered cathode material toward the said hollow space.

5. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a solid cold cathode between which electrons may flow, a control electrode having a wall separated from the anode by. a small space, the cathode comprising material that, during the operation of the device, sputters outof the cathode in a plurality of directions including the direction toward the said space and on which material a small cathode spot is formed from which electrons are adapted to travel toward the anode and into the said space, and a sputter shield interposed in the path. of travel of the said sputtered material out of the cathode toward the said space for partially obstructing such travel.

6. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a solid cold cathode between which electrons may flow, a control electrode having a wall separated from the anode by a small space, the cathode comprising material that, during the operation of the device, sputters out of the cathode in a plurality of directions including the direction toward the said space and on which material a small cathode spot is formed from which electrons are adapted to travel toward the anode and in the said space, and an apertured cover disposed over the cathode for obstructing the travel of a substantial quantity of the sputtered material toward the said space.

7. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a solid cold cathode between which electrons may flow, the cathode being contained in a cathode cup, a control electrode having a wall separated from the anode by a small space, the cathode comprising material that, during the operation of the device, sputters out of the cathode in a plurality of directions including the direction toward the said space and on which material a small cathode spot is formed from which electrons are adapted to travel toward the anode and into the said space, and an annular cover partially closing over the open end of the cathode cup to obstruct the travel of a substantial quantity of the said sputtered material toward the said space.

8. A gas-filled device having a plurality of electrodes in the gas of the device comprising a wire anode and a solid cold cathode between which electrons may flow, the cathode being contained in a cathode cup, a hollow cylinder carbon control electrode in the hollow space of which the wire anode is disposed 'with a small separation from the walls of the said space, the cathode comprising material that, during the operation of the device, sputters out of the cathode in a plurality of directions including the direction toward the said hollow space and on which material a small cathode spot is formed from which electrons are adapted to travel into the said hollow space toward the anode, and an annular cover partially closing over the open end of the cathode cup to obstruct the travel of a substantial quantity of the said sputtered material toward the said hollow space.

9. In a gas-filled electric discharge tube, a carbon grid electrode, an insulating support therefor, a lead-in wire anode sealed through the support and extending into, but spaced from, said carbon grid electrode, and a cathode of material capable of forming a cathode spot, said material being comprised of caesium chloride and aluminum compressed into a pill, an insulating cup for the part of said cathode away from the discharge, an annular metal cover for the part of said cathode facing the discharge, and a metal shield interposed between said anode and said annular metal cover.

10. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode, a control electrode, and a solid cold cathode between which electrons may flow, an insulating cathode cup in which the cathode is contained, the cathode comprising material that, during the operation of the device, sputters out of the cathode in a plurality of directions and on which material a small cathode spot is formed from which electrons are adapted to travel toward the anode, and an annular metal cover partly closing over the open end of the cathode cup to obstruct the travel of a substantial quantitity of the said sputtered material.

11. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode, a control electrode, and a caesium-containing cathode between which electrons may flow, an insulating cathode cup in which the cathode is contained, and an annular metal cover partly closing over the open end of the cathode cup to obstruct the travel of a subsantial quantity of the caesium that sputters out of the cathode in a plurality of directions during the operation of the device.

12. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a caesium-containing cathode between which electrons may flow, an insulating cathode cup in which the cathode is contained, and an annular metal cover partly closing over the open end of the cathode cup to obstruct the travel of a substantial quantity of the caesium that sputters out of the cathode in a plurality of directions during the operation of the device, the annular metal cover acting as a control grid during the operation of the device.

13. A gas-filled device as claimed in claim 1 and in which the said obstructing means comprises a surface oriented with respect to the cathode to receive thereupon the said substantial quantity of the said sputtered material.

14. A gas-filled device as claimed in claim 1 and in which the said control electrode is a carbon electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,190,308 Blackburn Feb. 13, 1940 2,201,166 Gerrneshausen May 21, 1940 2,212,88l Lecorguillier Aug. 27, 1940 2,320,949 Myers et al. June 1, 1943 2,433,813 Hilliard Dec. 30, 1947

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