US3041492A - Gaseous discharge device - Google Patents

Description

June 26, 1962 w. J. KEARNS GASEOUS DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed April 11, 1960 FlG.l.

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Tuas cunnsnr uv MILLIAMPERES VOLT-AMPERE CHARACTERISTIC CURVE INVENTOR: WILLIAM J. KEARNS, BY VMQQM HIS ATTORNEY.

June 26, 1962 w. J. KEARNS GASEOUS DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed April 11, 1960 LllrlLlllLrLl-l l-llhll WALL TEMPERATURE IN DEGREES CENTIGRADE 432 mooow VOLT- TEMPERA TURE CHARACTERISTIC CURVE FIG.6.

HIS ATTORNEY.

United rates Fatent 3,041,492 GASEOUS DISCHARGE DEVICE William Joseph Kearns, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Apr. 11, 1960, Ser. No. 21,507 14 Claims. (Cl. 313-185) My invention relates to gaseous discharge devices of the glow discharge type and more particularly to an improved glow discharge tube having a very low temperature coefiicient of voltage.

Conventional glow discharge tubes generally comprise a gas-filled envelope containing cathode and anode electrodes. When a direct voltage is applied between the electrodes, the current flow through the tube can vary and yet the voltage drop across the tube will remain generally uniform or will experience relatively small variations. Consequently, such tubes have been effectively employed as voltage regulating and voltage reference tubes. However, the construction of the conventional glow discharge tube does not generally adapt it for high temperature applications. For example, the conventional device cannot withstand an ambient temperature range of 65 C. to 400 C. for an extended operating life. Additionally, it has been found that the voltage drop of a device of the above-described type tends to vary considerably when the device is employed in a high temperature environment, which variations render the device ineffective as a voltage regulating or a voltage reference device in such an environment. Furthermore, in prior art devices voltage jumping, or, in other words, sudden increases in voltage drop as the glow expands and current increases, has been excessive.

My invention contemplates the provision of a glow dis charge device which overcomes the above-noted difficulties and, thus, is adapted for operation as a voltage regulator or voltage reference tube over a wide ambient range of envelope temperature and substantially independently of the temperature. Additionally, my invention contemplates the provision of structure adapted for minimizing voltage jumping and for extending the effective operating life of a device.

Accordingly, the primary object of my invention is to provide a new and improved glow discharrge device, the voltage characteristic of which is substantially independent of ambient temperature.

Another object of my invention is to provide a new and improved glow discharge device adapted for use as a voltage regulator or voltage reference device over a wide ambient temperature range.

Another object of my invention is to provide an improved glow discharge device having a temperature coefficient closely approaching zero.

Another object of my invention is to provide a new and improved glow discharge device adapted for operating over an ambient temperature of approximately 65 C. to approximately 400 C. with only slight variations in voltage drop per degree centigrade and while maintaining a substantially constant voltage with variations in current.

Another object of my invention is to provide a glow discharge device adapted for application as a voltage regulator or voltage reference tube in high temperature environments without the need for special cooling or temperature controlling means.

Another object of my invention is to provide a glow discharge device including improved means for minimizing voltage jumping.

Another object of my invention is to provide a new and improved glow discharge device unit which is particularly adapted for being utilized in combination with other similar units to provide a unitary device adapted for regulating any desired high voltage.

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Another object of my invention is to provide a glow discharge device which can be constructed to occupy a relatively small space without thereby being subject to adverse operating effects from either self-generated heat or high ambient temperature.

Another object of my invention is to provide a new and improved glow discharge device which is particularly rugged and adapted for withstanding high amplitudes of shock and vibration.

Still another object of my invention is to provide a new and improved glow discharge device which is relatively simple in construction, includes improved mounting and contact means and can be easily and inexpensively manufactured.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention I provide a glow discharge device comprising a ceramic-and-metal envelope structure containing a single highly purified inert gas at a predetermined pressure, a planar anode and a discrete cup-like cathode formed of a substantially gas-free high refractory metal. The anode and cathode can comprise wall members of the envelope. The rim of the cathode and the anode define a suitable annular breakdown gap adapted to effect a discharge at a minimum voltage. Predetermined relations between the depth and diameter of the cathode and between the volume of the cathode and the volume of the envelope, the use of predetermined electrode materials, the texture of the active surface of the cathode, and other particular structural features of the device adapt .the device for desired high temperature applications. Additionally, the individual units can be combined with others to provide a unitary series construction adapted for operating capabilities not obtaining with a single unit and for heating dissipating capabilities not obtainable with prior unitary series constructions.

For a better understanding of my invention reference may be had to the accompanying drawing in which:

FIGURE 1 is a vertical cross-sectional view of a single glow discharge unit constructed in accordance with one form of my invention;

FIGURE 2 is a voltage-current characteristic curve of a device as illustrated in vFIGURE. 1 and constructed in accordance with my invention;

FIGURE 3 is a voltage-temperature characteristic curve of a device of the type illustrated in FIGURE 1;

FIGURE 4 is a vertical cross-sectional view of a unitary series construction including a plurality of units of FIG- URE 1;

FIGURE 5 is a vertical cross-sectional view of a single glow discharge device constructed in accordance with a modified form of my invention; and

FIGURE 6 is a vertical cross sectional view of a unitary series construction including a plurality of units of FIGURE 5.

Referring to FIGURE 1, there is shown a glow discharge unit generally designated 1. The unit 1 comprises an envelope formed by a straight cylindrical ceramic insulator 2 having planar metal discs 3 and 4 hermetically joined to the upper and lower ends thereof, respectively. The ceramic can advantageously be the spinel-forsterite ceramic disclosed and claimed in co-pending U.S. application Serial Number 831,510 of R. H. Bristow, filed August 4, 1959 and assigned to the same assignee as the present invention. Due to the known highly desirable gettering qualities of titanium the discs 3 and 4 can be advantageously formed thereof.

The disc 3 serves as a planar anode and can advantageously include an integral laterally extending tab 3a arrangement the lip or rim 6 of the Cathode is predeterminedly and'uniformly spaced fromthe anode to define an annular breakdown gap therebetween.

, 'The cathode is formed of a highly refractory metal such, for example, as molybdenum, tungsten, tantalum,

niobium, rhodium, rhenium, and the softer materials such as titanium, zirconium, nickel, iron or copper. The pri- -mary requisite of the cathode material is that it be as gas 'free as possible. 'Vacuum melted or zoned refined metals have been found particularly suitable. The cathode is bonded at the bottom thereof'at 7 to the disc 4, and

the bond 7 is intentionally limited to a central'restricted area of the cathode to avoid thermal expansion mismatching between these elements and associated distortions which could-adversely affect the predetermined uniform spacing between the cathoderim and anode in the dischargegap defined thereby. The disc 4 can be advantageously formed with an integral tab 4a for making electrical contact with the cathode. Additionally, a centrally threaded nut-likemount-ing member 412* can be bonded to the outer surface of the disc 4 whereby the device can be rigidly mounted on a threaded stud as on a chassis of equipment'incorporating the device. This arrangement provides forsubstantially sturdy mounting of the tube and is also efiectivein dissipating heat from the device. If desired the circuit through the device can be completed through the member 4b instead of through the tab 4a. Additionally, the member 4b is formed to include at least a=pair of diametricallyopposed flat lands 4c to enable the use of a wrench in mounting the device on'a threaded'stud. If providedon both discs '3' and 4 the members 4b can be employed with oneor more interconnecting threaded studs to enable. easyassembly of a stacked series of the' described units.

The cathode Sincludes straight cylindrical side walls and fitspsnuggly in the insulator 2. Additionally, the cathode is substantially deep, with the diameter ofthe cathode 'being only approximately 1.3 times its depth. Further,

the volume defined by the cooperating cathode and anode :closely approaches the'volume of the envelope defined by the insulator '2 andthe disc 3 and 4. Preferablythe ratio between'these volumes is unity or as close to unity asis practical. Stillfurther, the active or inner surface of the cathode 5 is uniformly'texture'd and macroscopically smooth-or devoid'of scratches or other markings or protrusionswhich would represent even small irregularities or non-uniform discontinuities in the smooth 1 surface.

a The envelope is filled with a highly purified inert gas the ra'nge of approximately'40 to 60 mm of mercury. Additionally, the atmosphere comprises only the single known Paschen curves forthe gas and pressure used.

In'o'peration of theunit 1 at approximately IOO'volts, a' dis'char'ge orbreakdown' occurs .between the rim of the cathode and theanode. This-Idischargeinitiate's the formation of a. glow discharge between the'anode and the inner surface of' the cathode in much the same .rnanner asillus'trated inthe drawing and'which column includes an ion sheath designated 8' spaced approximately '10 mile from the inner surface of the cathode.

As seen in FIGURE-2, the voltage of theunit l'varies only slightly and substantially smoothly'with increases in current; 'Duetothe cup-like configuration of the cath- 'atmosphere'which is preferably neon and ata pressure in trated in FIGURE 1. Thus, the glow column is not restricted to discrete areas of the cathode and is not subject to jumping from one area to another, which in prior art devices, has caused undersirable voltage jumping or abrupt changes in the volt-ampere characteristic curve. The smoothly textured: active-surface of the cathode also contributes to the avoidance =of abrupt movements of the glow from one 'area 'of the cathode to another. I have found, for example, that scratches or slight irregularities in the'active surface of the cathode can cause localization of the glow, and undesirable voltage jumps when thejglow expands sufiiciently to bridge'the scratch or irregularity. The extremely smooth active surface provided in my structure minimizes any tendency for the glow to localize at any particular area of the cathode.

As shown by the curve A in FIGURE 3, ideally the voltage of a unit would be identical regardless of changes in ambient or Wall temperature. As shown by the curve B in this figure, with my invention one can obtain a signal which is substantially constant or varies only slightly from the ideal over a substantially wide temperature range. For example, over the range of approximately C. to approximately 400 C. the voltage is constant 'to within approximately 1%, the maximum variation being approximately 1 volt over the temperature range or only 2. to 3 millivolts per degree centigrade. Expressed another way, my invention enables the provision of a glow discharge device having a'temperature coetficient of approximately 2.5 millivolts or less per degree Centigrade. Thus, my device is particularly adapted, 'for example, as a voltage reference tube in maintaining constant to within a very small percentage, the voltage in equipment adapted for use in low as well as very high temperature environment.

A full understanding of the phenomena acting toenable the unit 1 to operate over such a Wide ambient temperature range with such relatively small voltage variations as those described above is not currently had. However, the substantial stability of the above-described structure is believed attributable to the various described features in the manners now about to be discussed in detail.

Changes in ambient temperature are believed ordinarily to affect the temperature of a gas filler in a gas-filled device which is believed, in turn, to aifect the voltage of such a device. More specifically, twodischarge processes which are very likely to be operating in a gas-filled device and which are believed sensitive to gas temperadissociative recombination process in the temperature range, of approximately -65 C. to approximately 400 C The. charge exchange and dissociative recombination processes may wellbethe dominant. generation and loss mechanisms in the plasma volume between the edge of "the cathodesheath 8 and'the. anode 3. At the cathode boundary a sheath only a few mils thick exists across a 65 ions are generated inthis sheath to produce the electrons which almost all of the tube voltage develops. Enough required by the external circuit by ion bombardment. The

; energies of ions and electrons in their sheath being of the region of the sheath. At the anode boundary only elecode and the planar configuration ofthe anode the glow f 'column is fiective for' covering substantially completely" .efllfli active surface of the cathode im the manner: illustrons can be absorbed plus those ions which have enough -kinetic energyto moveagainst the field. To describe these processes qualitativityat this time-is quite difiicult because not all aspects of the steady state D.C. discharge are understood in the art.

However, qualitativity it reasonable to consider the voltage across the tube as determined by the cathode fall plus any additional amount required to overcome losses due to radiation, recombination and wall losses. It is believed that to achieve the proper plasma energy balance wherein temperature changes in the gas produce no eifect on the total tube voltage the proper tube dimensions, geometry and filling pressure would be required so that no temperature sensitive processes such as dissociative recombination can predominate or so that a compensating phenomenon is also present. The device of FIGURE 1 is adapted for meeting these requirements and thus minimizing temperature coefiicient.

In the present structure the cup-like configuration of the cathode provides for a substantial cathode area required to afford the substantial plasma volume but at the same time enables the device to be reduced in diameter for a given cathode area. It will be seen that if the cathode were fully planar rather than cup-shaped the outside diameter of the unit would be substantially increased. Additionally, the cup-like configuration of the anode and specifically the substantial depth thereof, enables the conservation of approximately of the energy which would be lost by radiation if the cathode were shallow or planar. Specifically, by being cup-shaped and of substantial depth, the cathode is adapted for trapping ions, electrons and photons and effectively utilizing the interactions of same with the gas in the device.

As pointed out above, the atmosphere of the unit is constituted of only a single gas. The presence of other gases is undesirable due to the fact that different gases can have different mobilities at the same temperature and a mixture of gases would eifect variations in operating voltages with temperature changes. Thus, I have provided a cathode which is substantially gas-free and which is refractory and therefore not subject to the release of any appreciable amount of absorbed gas due to the influence of impinging ions and metastable atoms. Also, in the presently disclosed structure the side walls of the cathode serves to shield the inner surface of the insulator 2. Thus, the plasma is prevented from seeing or having charged particles thereof impinge upon the ceramic and releasing impurities which could contaminate the atmosphere and result in undesirable variations in the voltage.

The cup-like configuration of the cathode and the snug fit thereof in the insulator are also effective for disposing a substantial area of the cathode member in high heat transferring relation with the wall of the ceramic insulator. Thus, the cathode is adapted for radiating substantial quantities of heat to the ceramic insulator for dissipation thereby. This has the desirable effect of reducing the internal temperature which could affect the gas atmosphere and thereby deversely affect the voltage variation. Additionally, the presently described structure reduces substantially the required dissipation through the end caps or metal discs 3 and 4 of the envelope thereby better adapting the units for being assembled in series as shown in FIGURE 4. Without this decreased dissipation through the end caps a stocked series of units would be subject to greater heating with a tendency toward adverse efiects on the voltage variation. 7

The limited area bond 7 between the bottom of the cathode 5 and the end cap 4 is effective for holding the cathode in place and producing a heat and current conducting path to the end cap 4- without introducing distorting stresses in the end cap which could adversely affect both the seal between the end cap and the ceramic 2 and the discharge gap.

As also pointed out above, the ratio of the discharge volume to the total volume of the unit envelope is desirably as close to unity as practicable. This is to avoid local gas density variations in the vicinity of the cathode ion sheath 8 from contributing to the total temperature coefficient.

Illustrated in FIGURE 4 is a unitary combination structure generally designated 10 and which includes a plurality of units each substantially identical to the unit 1 described above and illustrated in FIGURE 1. The combination structure It is adapted for employment where a higher operating voltage is desired than can be satisfactoriiy obtained with a single unit. The structure of FIG- URE 4 comprises a plurality of devices of FIGURE 1, including the above-described predetermined single inert gas atmosphere and electrode arrangements and materials stacked in a vertical array or series. In the drawing identical numerals are used to identify elements which are identical in the structures of both FIGURES 1 and 4.

In view of the fact that there is no need for both an anode disc 3 and a cathode contact 4 for the intermediate units, a single disc '11 is provided for serving as both the anode and the element to which the cathode is bonded for adjacent units. The structure of FIGURE 4 is adapted for the same stable operation, or, in other words, a voltage characteristic substantially independent of ambient temperature, as the device of FIGURE 1 but is adapted for higher operating voltages than the previously described device. In practice, the operating voltage can be increased, as desired, by increasing the number of units stacked in the series.

FIGURE 5 illustrates a modified form of the glow discharge unit shown in FIGURE 1. The unit of FIGURE 5 is generally designated 12 and is adapted for increased cooling capacity. The unit 12 includes an anode disc 3 and a cup-like cathode 5 which can be identical to those of the unit of FIGURE 1 and, therefore, carry identical numerals. In the structure of FIGURE 5, however, the envelope of the device is completed by a short ceramic washer 13 which is sealed between the planar surface of the disc 3 and the lateral surface of the cathode rim, as at 14. In this arrangement the rim of the cathode is inserted in the ceramic washer before sealing and to a point where the rim defines an annular breakdown gap with the planar anode. Protruding embossements 5a formed in the side wall of the cathode a predetermined distance from the rim can be utilized for controlling the insertion of the cathode in the ceramic.

The remainder of the cathode 5 is exposed to the normal atmosphere and thus is adapted for substantial heat dissipation. This has the desirable eifect of reducing internal temperatures and avoiding undesirable voltage variations which can result from substantial heating of the internal gaseous atmosphere. Additionally, this structure can result in substantial cost reductions. The structure in FIGURE 5 is adapted for all the operational advantages of which the device in FIGURE 1 is capable and, additionally, because of its high heat dissipating capabilities,

it is particularly adapted for mom a stacked series high voltage construction now about to be described. If desired a connector tab 3a can be formed on-the disc 3 in FIGURE 5. Also, if desired, a threaded nut-like mounting member 5b can be employed on either or both the anode disc and cathode bottom surface for mounting the unit or enabling easy assembly of a stacked series thereof with the use of interconnecting studs.

In FIGURE 6 is illustrated a unitary combination structure designated 15 and comprising a series or stack of the units designated 12 in FIGURE 5. In this structure a plurality of the units of FIGURE 5 are stacked vertically and joined by central bonds 16 between the bottoms of the cathodes 5 and the outer planar surfaces of the anodes 3 of the adjacent units. The structure 15 is adapted for operating in the same manner as the structure 10 in FIG- URE 4 but is adapted for greater heat dissipation due to the exposure of the outer walls of the cathodes 5.

While I have shown and described specific embodiments of my invention I do not desire my invention to be limited to the particular forms shown and described and I intend by-the-appeuded claims to cover alimodifications Within the spirit and scope of my invention.

what l claimes new and desire to secure by Letters Patent of the United States is:

1. A glow discharge device adapted for having a voltage characteristic substantially independent of ambient'tem- .pcrature comprising, a hermetically sealed high refrac- .tory-envelope containing an atmosphere of only a single inert gas at a pressure oftapproximately 40 to 60 mm. of mercury, a disc-shaped anode member, a discrete metal cup=shaped :cold cathode, an annular ceramic insulator comprising a wall portion of said envelope and maintaining-the rim of said cathode in predetermined spaced relation with said anode member for defining an annular breakdown gap, and said cathode having a depth closely :approaching-the diameter thereof and cooperating with said anodeto provide a substantial glow volume which extends over the major portion of the surface of said cathode during a glow.

I '2. glow discharge device according to claim .1, wherein the diameterof said cathode is approximately 1.3 times the depth thereof.

,3. A glow discharge device according to claim 1, Whereinlthe ratio of the discharge volume defined by said anode and cathode and the volume of Said envelope closely approach unity. 4

4. A glow discharge device according to claim 1, wherein the cathode material is substantially gas-free and the inner surface of said cathode is uniformly textured and macroscopically smooth: for minimizing voltage jumps.

' 5. A- glow discharge device accordingto claim 1, Where- 7 in: the inert. gas is neon.

6 A1 glow discharge device comprising a straight cylindiical ceramic-insulator, a-metal disc bonded to each end of-said insulator to provide hermetically sealed envelope, :said envelope containing an atmosphere of only, a single highly-purifiedinert gas at a pressure of approximately to 60 mm. ofmercury, one of said discs constituting an anode, al-discrete metal cup-shaped nonthermionic cathode forrncd f a substantially. gas-free refractory metal, said cathode being-positionedinsaid envelope with the rim thereoiprcdeterminedly spaced relative to said anode for defining an annular breakdown gap therebetween and having the bottom surface of said cathode bonded to the .otherof said discs, the depth of said cathode closely approaching the dia-meter of said cathode, and the ratio of the volumr'sdefined'by saidanode and cathode and by said envelope being approximately unity. 7

7'. A.glow discharge device according to'claim 6, wheree in -at least said anode disc includes an integrally formed laterallyextendingconnector tab and a threaded nut-like -mounting member-isbonded to the outer surface of'at .least said other of said discs. 7 v v -18. A glow discharge device according to claim 6, Where- -in hebondbetween the bottom of said cathode and said other discis-restricted to only a relatively small central area thereof.

1'9. A;.-glowdischarge device comprising aunitary en velope structure including a plurality of axially aligned --ceramic cyIinder a-disc-Iike anode bonded to said adjasubstantially gas free refractory metal position in each compartment, said cathode being positioned in said compartment with the rim thereofdeterminedly spaced relativeto said anode for defining a breakdown gap therebetween, the bottom surface of each cathode being conductively connected to the disc opposite said anode in each compartment, the depth of each cathode closely approaching the diameter thereof and the ratio of the volume defined by each anode and cooperating cathode and the volume of the respective compartments being approximately unity.

10. A glow discharge device according to claim 9, wherein the connection between the bottom of each cathode and said disc opposite said anode is a metallic bond restricted to a relatively small central area thereof.

ll. A glow discharge device comprising, a disc-like anode, a discrete cup-shaped cold'cathode formed of a substantially gas-free refractory metal, a ceramic washer of substantially short length relative to the depth of said cathode bonded to said anode, said cathode being positioned in said washer with the rim thereof predeterminedly spaced from said anode to define a predetermined breakdown gap therebetween and bonded to said washer for completing a hermetically-sealed envelope, the depth of said cathode closely approaching the diameter of said cathode, the ratio of the volume defined by said anode and cathode and the volumeof said envelope being approximately unity, and said envelope containing an atmosphere of only a single highly purified inert gas at a pressure of approximately 40 to 60 mm. of mercury.

12. A glow discharge device according to claim 11,

I wherein said disc-like anode includes an integrally formed laterally extending connector tab and a threaded nut-like mounting member is bonded to the outer surface of the bottomof said cup-shaped cathode.

13. A glow discharge device comprising a unitary structure including a plurality of axially spaced disc-like anode members, each anode member having a cup-shaped cold cathode associated therewith and formed of a substantially gas-free refractory metal, a ceramic washer of substantially short length relative to the depth of said cathode bonded to said anode member, each said washer having the rim of one said cathodes positioned therein in prede- =termined spaced relation with its associated anode for defining a predetermined breakdown gap and bonded to said washer for completing a hermetically-sealed compartment, the depth of said cathode closely approaching the diameter of said cathode, the ratio of the volume defined by each said anode member and its associated cathode and the volume of said compartment being approximately unity, the bottom-of each said cathode being conductively connected to the next adjacent anode member, and said compartments being axially aligned and each containing an atmosphere of only. a single highly purified inert gas at a pressure of approximately 40 to 60 of mercury.

14. A'glow discharge device according to claim 13 wherein the connection between the bottom of each'cathode and the adjacent anode member is a metallic bond restricted to a relatively small central area thereof.

References Cited in the file of this patent 4 UNITED STATES PATENTS 1,749,423 Fenton Mar. 4, 1930 2,720,474 Myers Oct. 11, 1955 2,840,746 Price June 24,1958

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