US2556855A

US2556855A - Gaseous discharge device

Info

Publication number: US2556855A
Application number: US694057A
Authority: US
Inventors: Paul W Stutsman
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1946-08-30
Filing date: 1946-08-30
Publication date: 1951-06-12
Anticipated expiration: 1968-06-12

Description

June 12, 1951 P. w. sTUTsMAN GAsEous DISCHARGE DEVICE vFiled Aug. so, 194e;

. /NVENro/e PAM W STUTSMAN -BV Patented `lune 12, 1951 UNITED STATES PATENT OFFICE.

GASEOUS DISCHARGE DEVICE Application August 30, 1946, Serial No. 694,057

8 Claims.I (Cl. 313-209) This invention relates to gaseous discharge devices, and more particularly to gaseous discharge devices of the cold cathode type.

In some applications of gaseous discharge tubes, for example, in certain ignition systems for internal combustion engines, a grid controlled tube is required to pass high peak current in the primary circuit of a transformer whose secondary produces a radio frequency voltage. Accordingly, the ionization and deionization times of the tube must be sufliciently short to'permit the tube to function satisfactorily in such a circuit. Furthermore, in many such circuits, particularly in the ignition system of an air-craft engine, the tube is subjected to severe shock and prolonged vibrations.

Heretofore, attempts to use gaseous discharge devices in such circuits have not been successful due to the failure to provide the desired mechanical strength together with the necessary electrical characteristics.

It is among the objects of the present invention to overcome the defects in the prior devices of the type described and provide a gaseous discharge device suitable for use in a circuit where a high peak duty cycle is required, the peak current being much greater than the average current, and having such short ionization and deionization times as to be suitable for use in the primary circuit of a transformer whose secondary produces a radio frequency voltage.

It is a further object of the invention to provide a tube of the type described which is of rugged construction and which may be used for long periods in positions where it is subjected to continuous vih-ration and severe shock.

The above and other objects and features of the invention will be made fully apparent to those skilled in the art from a consideration of the following detailed description taken in conjunction lwith the accompanying drawing in which:

Fig. 1 shows a longitudinal section through a gaseous discharge device constructed in accordance with the invention;

Fig. 2 is a section taken on the line Z-Z of Fig. l; and

Fig. 3 is a section taken along the line 3--3 of Fig. 1.

Referring to the drawing, reference numeral II! indicates a metal envelope containing an ionizable gas, preferably helium, at a pressure of the vorder of fteen millimeters of mercury. The tube I!! is provided with short tubular projection I I at the upper end thereof providing an opening for the connection of suitable exhaust tubulation.

Cri

The opening H is sealed, as indicated at I2, and to protect the seal against breakage a cap I3 is Welded to the tube I0 in a position to cover the seal. The upper portion of the tube I0 constitutes a reservoir of gas for the purpose of maintaining a gaseous medium in the lower portion of the tube where the gaseous discharge takes place. Within the upper portion of the tube IQ a thin metallic strip i4 is secured to the inner wall which strip carries a plurality of hollow wires i5 containing a getter material. The strip is integrally secured to the tube, and the wires to the strip, for example by welding. The wires I5 are provided with a plurality of openings I5 from `which the getter material may be released in the course of manufacture of the tube.

.T n the central portion of the tube IQ a metallic disk il, having a downwardly projecting flange i8, is rigidly secured to the metallic wall of the tube, preferably by welding. The disk I'I provides a rigid support for a cathode structure comprising a thin metallic ring I9 which is welded or otherwise integrally secured to a me tallic disk 2G, also of thin metal. The ring I9 and the disk 2@ provide a cup-shaped member integrally secured to the lower face of the disk I 1.

A plurality of short metal tubes 2 I, also welded or soldered to the disk to, are arranged in closely packed relation to completely ll the ring I 9. Each of the tubes 2l is filled with a powdered activating material 22 such, for example, as caesium chloride crystals and aluminumV lings. Other activating materials which decompose to provide a material of low work function are known to those skilled in the art. The activating material is suiilciently tightly packed in the tubes 2l to prevent its being dislodged in the course of the manufacture of the tube.

A ceramic member 23, having an external diameter approximately equal to the internal diameter of the tube l? and therefore having a snug fit with the internal wall of the tube, is positioned immediately below the disk il, its upper portion being somewhat reduced to provide an annular space Z4. The annular space 24 is in communication with the space above the disk II through openings 25 provided in the disk, and the annular space is in communica* tion with the space below the ceramic member 23 by means of a plurality of grooves 2B in the circumferential wall and base of the member. Ceramic member 23 is rigidly secured in the tube i@ by means of the annular member 2l at the base thereof, Vwhich annular metallic member is welded to the tube l0 after the insertion of the member 23, and this member' is therefore held against longitudinal movement between the disk ll and the annular member 2l.

The upper end of the ceramic member 23 is recessed to accommodate the cathode structure with a small clearance therebetween. The lower portion of the ceramic member 23 is provided with a substantially larger recess 28, a partition 29 remaining between the two recessed portions, which partition is provided with an opening 3Q.

A tube 3l of glass or other vitreous material, and of somewhat less external diameter than the diameter of the recess 28, is formed integrally with or fused to a supporting base 32 of glass or similar material and projects upwardly into the recess 2S to a point adjacent but not in contact with the bottom of the recess 28. A plurality of grid support rods 33 sealed through the base 32 extend upwardly to points approximately flush with the upper end ci the tube 3l for supporting an annular grid 54. The grid 36 is preferably oi carbon and is provided with a center passage The grid 3d is rigidly secured in a metal tube 36 having an annular metallic member Si at its upper end and a sirnilar member 38 adjacent its lower end for rigidly1 securing the grid 3i therebetween. A plurality of metal strips 3e are welded to the upper part of the tube 3% and have outwardly projecting end tabs fili, which tabs are welded to the grid support rods 33 to rigidly secure the grid 34 in the desired position.

An anode support rod and lead-in conductor 43 is also sealed through the supporting base 32 and an anode sli, preferably oi carbon, is secured to the rod i3 by a metallic sleeve d5. An anode shield it is provided surrounding the anode lli and is fused at its lower end in the base 32.

rlhe base 32 is in the form of a button moulded into an annular metallic member te, which member is provided with an outwardly projecting flange Lli contacting the walls of the tube i and having upwardly projecting tabs i9 engaging the inner wall of the tube. An annular member 5% having an inwardly projecting flange 5l adapted to be welded to the lower face of the outwardly projecting flange il'i of the member 4S, and also having an outwardly projecting flange 5E adapted to be welded to an outwardiy projecting iiange 53 integral with the envelope Il), completes the seal of the tube.

In operation, when a suitable potential is applied between the cathode and the grid, a glow discharge is initiated between these two electrodes. The glow discharge so initiated is quickly converted into an arc discharge between the cathode and the anode f. The arc discharge originates in a small spot in the cathode surface, which spot is formed at the junction between the low work function material 22' and the cathode base material, and thereafter moves about over the active surface of the cathode, ln so doing, additional metallic caesium is evolved from the caesium chloride, thus maintaining the supply of low work function material upon the cathode surface. The activation of the cathode material tends to bind the material in the short tubes 2l with great rigidity so that the discharge device may be subjected to heavy shock and vizration without dislodging this material.

The tubular structure of the cathode provides numerous surface irregularities and junctures between the cathode base material and the activating material which facilitate the formation of lthe cathode spot and thus eiTect rapid conversion of the glow discharge between the cathode and grid to an arc discharge between the cathode and anode. The open ends of the tubes 2| tend to form small pockets in the course of the operation of the tube, which pockets favor rapid ionization and deionization in the region adjacent the cathode. Also, since the discharge space is conned, and the distance between the cathode and anode is relatively short, in view of the pressure of the gas within th-e tube, the gas in this space is ionized rapidly. A large portion of the discharge path lies within the passage 35 of the grid 34, which passage is of relative small diameter. Also, all parts of the discharge path outside the passage `35 are close to one or the other of the electrodes. The distance which any ion is required to traverse to arrive in the region of a deionizing surface, for example, the surface of the grid structure 34-36, or the anode structure M-d, or the cathode structure 2|- 22., is small, and accordingly, upon the termination of the discharge, the time required for deionization is very short.

The tubes 2| may be readily assembled and secured in the cup by rst placing a thin dis-k of silver solder in the base of the cup, then inserting as many of the tubes 2l as are required to fill the same, and heating the assembly to a temperature at which the solder is melted. Preferably, fine wires of the solder are also inserted in the interstices between the tubes 2l, prior to heating, so that the tubes are secured to each other and to the ring i9 to form a rigid integral structure. The structure thus not only provides numerous pockets of small cross-sectional area in which a substantial quantity of activating material is eiiectively stored for use during the life of the tube and from which it cannot be dislodged, but also provides ample heat-conducting paths from any point on the activating material to the disk I1 and thence to the metallic envelope lil of the tube. Thus, although the temperature at any point where an arc spot exists may be high, the temperature of th-e cathode as a whole is low. Since the cathode spot does not remain at any one point for a signicant period of time, moving about or occurring interruptedly. the activating material 22 is subjected only instantaneously to high temperatures at any point. Upon interruption of the arc spot or its movement from a given point, the heat at that point is quickly dissipated so that the temperature of the activating material quickly falls below the temperature at which vaporization or other destructive effects can occur. Without such ample heat-conducting paths in close proximity to all points on the surface of the activating material, the heat generated at the cathode spot would be dissipated slowly through the powdered activating material. Points on the cathode surface would remain at a high temperature for a much longer period, thus permitting greater vaporization of metallic caesium and other undesired effects.

In the course of the operation of discharge devices containing a Xed gas as the ionizable medium, the gas supply tends to become exhausted. As the ionizable medium is reduced or the content altered, the electrical characteristics of the tube vary. In order to provide a tube having substantially constant electrical characteristics over the useful life of the tube, a substantial reservoir of gas is provided by the space within the tube above the disk il. Thus, although the gaseous discharge is confined to a attacco relatively small space, permitting rapid ionization and deionization, the quantity of gas available for use during the life of the tube is many times the volume of the gas available in the discharge space.

The gas preferably contains a small amount of water vapor which tends to combine with any free caesium present. I have found that the water vapor reacts with the activating material, forming compounds which facilitate the formation of the cathode spot. As previously described, the caesium "chloride breaks down under the action of the cathode spot to form pure caesium. If the activating material originally provided `were pure caesium, the caesium would be sputtered or vaporized much more quickly. This would also be true if the activating material furnished too much free caesium. Also it is known that while the arc spot may be formed upon pure caesium, and while some free caesium should be present to provide a low work function material whereby the discharge may be maintained, the cathode spot is, nevertheless, more easily formed or initiated upon the caesium chloride and aluminum than on a surface of pure caesium. I have found that conditions particularly favorable to the formation of the arc spot exist at the junction between the caesium and the base material. It is, therefore, desirable to avoid the formation of a continuous surface area of pure caesium over the face of the cathode. The water vapor combining with some of the free caesium present on the cathode surface forms compounds, when conditions are favorable, which compounds are analogous to the original caesium chloride, breaking down under the action of the arc spot and reforming as the discharge is interrupted. The water vapor thus tends to pre-serve the electrical characteristics of the cathode surface. It limits the amount of free caesium present on the grid surface, and while free caesium still is formed by the action of the cathode spot and some of it is vaporized, this formation and con sumption of the caesium from the original caesium chloride is more limited. Also the water vapor tends to combine with any caesium vapor generated so that the caesium which may settle upon the grid or upon other elements within the tube is not in the form of pure caesium. As

is well known, caesium vapor settling on the grid can destroy its control characteristics. The presence of water vapor combining with the caesium either in a vapor state or after it has settled upon the grid results in a compound of higher Work function than the pure caesium l and thus preserves the control function of the grid.

It will be apparent from the foregoing that the invention provides a cold cathode type gaseous discharge device in which all of the electrode elements are of great rigidity, and in which the ionization and deionization times are relatively short. The invention also provides in such a device a tube in which the operating characteristics will remain substantially constant over a relatively long life.

Although there has been herein described a preferred embodiment of the invention, other embodiments thereof within the scope of the appended claims will be obvious to those skilled in the art from a consideration of the embodiment shown and the teachings hereof.

What is claimed is:

1. A gaseous discharge device comprising an envelope containing an ionizable medium, a cathode, and an anode, vsaid cathode comprising;an`

activating material, and metallic members *eirtending through said material providingpaths' of high thermal conductivity in close proximity to all parts of saidmaterial. ly v l 2. A gaseous discharge device comprising'an envelope containing an ionizable medium, a cath'- ode, and an anode, said cathode comprising an activating material, said ionizable medium come prising a iixed `gas containing water vaporv for reacting with said material.

3. A gaseous discharge device comprising 'an envelope containing an ionizable medium, a cath- 'de, and an anode, said cathode comprising 'a cup-shaped member of metal, said cup containing a plurality of metallic members extending therethrough and providing a plurality of cavities, said cavities containing a powdered activating material, the cross-sectional area of said cavities beingsuiciently small toretain sai-d powdered material.

4. A gaseous discharge device comprising an envelope containing an ionizable medium, a cathode, and an anode, said cathode comprising a plurality of hollow tubular members of metal, each of said tubular members being integrally secured at one end to a common supporting member and having their opposite ends open, said hollow tubular members containing an activating material.

5. A gaseous discharge device comprising an envelope containing an ionizable medium, a cathode, an anode, and a grid, said cathode comprising a plurality of hollow tubular members of metal, said tubular members being integrally secured at one end to a common supporting member and having their opposite ends open, said hollow tubular members containing an activating material.

6. A gaseous discharge device comprising an envelope containing an ionizable medium, a cathode, and an anode, said cathode comprising a plurality of hollow tubular members of metal, said tubular members being closed at one end and having their opposite ends open, each of said hollow tubular members containing an activating material, said open ends of said tubular members terminating in a common plane defining the active cathode surface.

7. A gaseous-discharge device comprising a metallic envelope containing an ionizable medium, a cathode, an anode and a grid, a metallic disk secured at its periphery to the interior wall of said tube and providing a partition dividing the interior of said envelope into two chambers, said partition having at least one opening providing restricted communication between said chambers, said cathode comprising a cup-shaped member secured to one side of said partition, an insulating member substantially filling the space surrounding said cathode with a small clearance therebetween, said anode being disposed on the same side of said partition as said cathode, said grid being disposed between said cathode and said anode and having an opening therethrough providing a portion of the discharge path between said cathode and anode.

8. A gaseous-discharge device comprising a metallic envelope containing an ionizable medium, a cathode, an anode and a grid, a metallic disk secured at its periphery to the interior wall of said tube and providing a partition dividing the interior of said envelope into two chambers, said partition having at least one opening providing restricted communication between said chambers, said cathode being secured to one side of said partition, said anode being disposed on the same side of said partition as said cathode, said grid being disposed between said cathode and said anode and having an opening therethrough providing a portion of the discharge path between said cathode and anode, a member of insulating material having an external diameter approximately equal to the internal diameter of said tube positioned on the same side of said disk as said cathode, said member having a recessed portion in each end thereof, one to accommodate said cathode, and the other to accommodate said grid, said member having a passage between said recessed portions.

PAUL W. STUTSMAN.

REFERENCES CITED Number 15 Number