US2666880A - Gaseous-discharge device - Google Patents

Description

atented Jan. 19, 1954 GASEOUS-DISCHARGE DEVICE Paul W. Stutsman, Needham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application June 16, 1950, Serial No. 168,426

2 Claims.

This invention relates to gaseous-discharge devices, and more particularly to discharge devices which may be used as voltage regulators. In the construction of voltage regulator tubes of the sub-miniature type, several problems are encountered.

Because or" the small size, it is diiiicult to produce a device which will carry relatively large currents, for example, up to twenty-five milliarnperes. It has been discovered that, by utilizing the device wherein the cathode surrounds the anode, a large cathode area is exposed such that a relatively wide range of currents may be drawn from the cathode surface without appreciably changing the cathode fall potential thereof.

In previous sub-miniature discharge devices, it was found that when a sub-miniature bulb was used insufficient quantities of the gaseous medium were available to produce a long life of the discharge device, since the gas become occluded in the metallic elements of the device thereby lowering the pressure to a point where stable operation was no longer possible.

rIhis invention discloses a structure and gaseous nlling whereby a relatively high pressure may be used, thereby providing a sufficient reserve of a gaseous medium so that the discharge device may be operated for a long period of time, for example, in excess of ve thousand hours, without seriously decreasing the supply oi the gaseous medium.

Brieiiy, this is accomplished by using a gaseous mixture comprising approximately forty per cent argon and sixty per cent neon. It has been found that this mixture causes considerably less sputtering ot the cathode surface than may be had with either pure argon or pure neon.

In addition, this invention discloses a cathode support member which eiiectively shields the cathode surface in such a way that the discharge is conned to the desired area between the cathode and the anode, thereby eliminating sputtering and condensation of cathode material on insulating supports which would eventually produce a short circuit, and eliminating variations of the voltage drop of the discharge due to variations in the position of the discharge path which would be encountered in the absence oi the shielding support member.

ln addition, this invention discloses the substantial elimination of the positive column drop normally encountered in the discharge. This is accomplished by placing the anode substantially at the minimum breakdown distance from the cathode. This will place the anode in or adanode support rod jacent the Faraday dark region of the discharge, and, for the particular electrode configuration and gaseous medium disclosed herein, the position of the anode is substantially at the junction of the Faraday dark space and the positive column. Since the positive column drop has a negative voltage current characteristic which might produce oscillations in the circuit being regulated, substantially eliminating the positive column drop produces a nonoscillatory circuit. Any portion of the positive column drop which still remains will have its negative characteristic more than compensated for by the slight positive voltage current characteristic oi the remaining glow discharge phenomena.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawing, wherein:

Fig. 1 illustrates a longitudinal, cross-sectional View of a gaseous-discharge device embodying this invention;

Fig. 2 illustrates a transverse, cross-sectional View of the discharge device shown in Fig. l taken along line 2 2 of Fig. i; and

Fig. 3 illustrates a graph demonstrating the characteristics of various mixtures of argon and neon.

Referring now to Figs. l and 2, there is shown a sub-miniature envelope ii! which may be, for example,y of glass. Extending upwardly from the bottom of envelope iii through a glass press H are three leads E2, i3 and It, respectively. Lead I3, Which is the center lead, is connected to an l5 which is coaxial with envelope li). Attached to anode support rod I5 are two anode support cups IG, said cups surrounding anode rod l5 and being rigidly secured thereto by any desired means such as by a friction t or by welding.

Extending over a portion of anode rod i5 and both support cups is an anode cylinder il which is coaxial with anode support rod l5, said anode cylinder l1 being rigidly attached to support cups I6, as by welding. Each of cups lo has small hole i3 in the bottom thereof which allows gases to pass freely in and out of anode cylinder Surrounding anode cylinder il, spaced therefrom and coaxial therewith is a cathode cylinder i!! which may be made, for example, of molybdenum. Anode cylinder il is somewhat longer than cathode i9 and extends out of cathode cylinder i9 beyond both ends thereof. Closely surrounding cathode is and attached thereto, as

by welding, is a nickel cathode support cylinder which is substantially the same length as anode cylinder il' and consequently extends out of the ends of cathode cylinder I9.

Support cylinder 20 is rigidly attached, as by welding, to a pair of side support rods 2| and 22 whose lower ends are attached to leads I2 and I Li, respectively. Both anode support rod I5 and side support rods 2| and 22 are somewhat longer than anode cylinder Il and cathode support 2G and consequently extend out beyond the ends thereof.

A pair of mica spacers 23 and 24 is placed over the lower ends of side support rods 2| and 22 and anode support rod I5, thereby rigidly maintaining the correct spacing between the lower end of anode I1 and cathode I9. Similarly, another pair of mica spacers and 26 is positioned over the upper ends of side rods 2l and 22 and anode support rod I5 to maintain the correct spacing' therebetween. Axial movement of spacers 23, 2t, 25 and 2S on side rods 2i and 22 is prevented by a plurality of metallic tabs 21 welded to side rods 2l and 22. Similarly, longitudinal movement of anode support rod I5 relative to spacers 23, 251, 25 and 25 is prevented by a metallic tab 28 welded to anode support rod I5 at a point just above upper mica spacer 26 and by a metallic tab 29 welded to anode support rod I5 just below lower mica spacer 24. Thus, both axial and transverse movement of the anode structure relative to the cathode structure is prevented.

Mica spacers 23, 24, 25 and 26 extend outwardly and engage the walls of envelope I0, thereby preventing movement of the tube elements within the envelope.

Attached to the upper end of anode support rod I5 is a getter structure which may be of any well-known type, for example, a U-shaped metallic member 30, across which is connected a bar of getter material which is flashed by induction heating.

Since molybdenum cathode cylinder I9 is surrounded by the support cylinder 20, the discharge is confined to the inner surface area of the molybdenum cathode cylinder I9 with possibly a small amount extending over the ends of the molybdenum cylinder I9. However, the discharge cannot move around to the outside of cathode cylinder I9 as would be possible in the absence of the supporting shield member 2G, and hence changes in the voltage drop between the cathode and anode during the discharge, and due to changes in the length of the discharge path, are substantially eliminated. Moreover, with the spacing between the molybdenum cathode I9 and the anode as shown, the anode is positioned substantiaily at the minimum breakdown distance from the cathode, thus substantially eliminating the positive column drop with its associated negative voltage current characteristic from the discharge.

Referring now to Fig. 3, there is shown a graph illustrating the voltage drop across a discharge using various percentages of argon and neon. Along the axis of ordinates is plotted the voltage drop in volts, and along the axis of abscissas is plotted the percentage of argon, with the remainder of the mixture being made up of neon, the particular curve being taken for a gaseous pressure on the order of ive centimeters of mercury.

At a zero percentage of argon, which corresponds to a mixture of pure neon, a voltage drop of approximately one hundred and six volts is encountered, as shown by point 3| on the graph. When one per cent of argon is added, the voltage drops to approximately eighty-rive volts, as shown 4 by point 32 on the graph, this voltage being the lowest drop which is encountered for a gaseous mixture of argon and neon at this pressure. '1' his particular mixture of one per cent argon and ninety-nine per cent neon is well known and used in many discharge devices. However, if it is desired to construct a tube having a voltage drop of substantially one hundred volts, a mixture of one per cent argon and ninety-nine per cent neon at a pressure of five centimeters of mercury produces a drop which is too low. While the potential drop for this mixture could be raised by decreasing the pressure, this results in an insufcient quantity of gas within the envelope to produce a long-life tube.

Similarly, if either a mixture of one hundred per cent argon or one hundred per cent neon were used, and the pressure raised to thereby lower the voltage drop of the discharge, sputtering of the cathode surface is so intense that a short may be quickly produced, for example, within one hundred hours of operation. This sputtering occurs by reason of concentration of the area of emission of electrons to a particular spot on the cathode surface, and results in stalactite formations which extend outwardly from the anode surface until they reach the cathode and short the device.

It has been discovered that a large range o1 voltage values may be had for a given pressure by varying the percentage of argon in the neon mixture. For example, when the mixture comprises forty per cent argon and sixty per cent neon at a pressure of ve centimeters of mercury, a voltage drop of substantially one hundred volts occurs across the discharge. When the gases are mixed, the emission area on the cathode spreads out over an extended area, and hence there is very little sputtering in the cathode surface, and there is no concentration of sputtering of the type which would build up shorting stalactites.

Furthermore, since the shape of the curve as it passes through the mixture of forty per cent argon at one hundred volts, as shown by point 33 on the graph, is relatively at, hence production tolerances of the gaseous mixture and pressure need not be held to extremely high accuracies in order to result in a large number of tubes which have substantially the same voltage regulating properties.

This completes the description of the invention illustrated herein. However, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, other materials could be used for the cathode and cathode support cylinder instead of molybdenum and nickel. Other support structures could be used, and other mixtures of the gaseous medium could be used to produce diiferent regulating voltages in accordance with the teaching of the graph of Fig. 3. Therefore, it is desired that this invention be not limited to the particular details of the species of the invention illustrated herein, except as defined by the appended claims.

What is claimed is:

1. A gaseous discharge device comprising an envelope having therein a hollow cylindrical anode, an anode support rod extending through said anode spaced therefrom, a molybdenum cathode spaced from said anode by a distance substantially equal to the distance from the cathode to the outer edge of the Faraday dark region whereby the positive column drop of the gaseous discharge is substantially eliminated, a nickel cathode support member surrounding said cathode and coaxial therewith, said cathode support member and said anode extending axially beyond both ends of said cathode member, and a gaseous lling comprising substantially three parts of neon to two parts of argon at a pressure on the order of i'ive centimeters of mercury.

2. A gaseous discharge device comprising an envelope having therein a hollow cylindrical anode, an anode support rod extending through said anode spaced therefrom, a molybdenum cathode spaced from said anode by a distance substantially equal to the distance from the ycathode to the outer edge of the Faraday dark region whereby the positive column drop of the gaseous discharge is substantially eliminated, said distance also being substantially equal to the minimum breakdown distance, a nickel cathode support member surrounding said cathode and co- 6 axial therewith, said cathode support member and said anode extending axially beyond both ends of said cathode member, and a gaseous lling comprising substantially three parts of neon to two parts of argon at a pressure on the order of live centimeters of mercury.

PAUL W. STUTSMAN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,815,762 Charlton July 21, 1931 1,871,344 Rentschler Aug. 9, 1932 1,893,304 Rentschler et al. Jan. 3, 1933 2,071,748 Hund Feb. 23, 1937 2,103,031 Foulke Dec. 21, 1937 2,414,450 Chevigny Jan. 21, 1947 2,449,697 Graves et al. Sept. 21, 1948 2,507,696 Depp May 16, 1950

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