US2623191A - Electric discharge tube - Google Patents

Description

Dec. 23, 1952 A. H. REEVES 2,523,191

ELECTRIC DISCHARGE TUBE Filed March 18, 1948 I INVENTOR. 14. P551455 3m Patented Dec. 23, 1952 "UNITED PATENT OF FI'CE ."LELEDTRICLDISCHARGE TUBE :Alec Harley Reeves; London, England, assignor to 'lnternational' i'standard .Elect'ric -Corporation, NewiXo'rk, 5N; 155,11. :corporation ofJJeIaWare ,fApplicati'oniMarchlfi, 1948,."Serial No.115',582 I111 tjGreatlBritain March 20, 19.47

lThe jpresent? invention-relates to ecold' cathdde electric discharge 'devices.

f It is characteristic :6]? "cold cathode gas filled discharge tubes that the voltagerequire'd to in- :itiate-a "dischargebetween 'two' electrodes" depends 5 uponthe'nature and pressure ofthegasand its r state of ionisation, the shape: arid materialot'the discharge electrodes and 'the l distance between v.themthe gap "length. At low interelectrode voltages megligi-ble current' will flowit the *gas l is initially deionised. -As-the -voltage'- isT increased ":the molecules of the -gas become ionise'd' until eventually a discharge isset up v'Iith-arapid inrcrease 'in current 'fiow which' -may -typically rise and to .become to alargaextent independentzioi the discharge current. This approximatelyponstant-voltage. is called the maintaining voltage. Thus, in the familiar neon tubes used as ,voltage regulators and the like, the striking potential -may be of the orlder'of =100*volts'-or morefbut the maintaining voltage tends to be constant in" the region of 80 volts.

mentioned rabove, ions an'd relectronsitend Etc-migrate "T from the immediateneighbourhood "df-sthe discharge. This "phenomenon-Fhasbeenex- 'tensivelyused to lower the striking -poten'tial of :-another :discharge gap in the same"- tube-envelope. In one known device there is provided a main discharge gap .between a'main anode and'acathode and a trigger gap'between-an auxiliary anode and thesaid cathode. "The auxiliary *anode is much closer to the cathode than themain anode -so that-:theinitial: striking ,voltage of the-trigger 'gapri's' considerably -below' thatof the maingap.

vThetriggerrgapis-:used to lower thestrikingvolt- ;age:of,zor :to .iprime, the main gap by ionisation coupling.

It is also wellknown that Whereasgwhenstiiking voltageisi'appliedfto a gap, ionisation takes place ina very short:time, -measure'd in microseconds; if :the voltage acrossa -'discharging "gap he removed, deeionisation is not complete-until after a "substantial 1 period of time which "may ,oitengamountr to milliseconds.

; In:my :copen'ding' LU. SL PatentapplicationNo. 55

763,655, filed Ju1y 25, 1947, the phenomenon of "ionisation coupling is utilised to provide 22, .cold "cathode discharge tube having aniordered array "of gaps'of which -the"starting gap isarranged "to have "alower'striking voltage'than the re- 'mainder so that arecurrent voltage "appliedto each gap in turn or'to all gaps togethen'fires 'firstthe'starting. gap-and then theremainder in order. I Due toithefinite de-ionising time; it isnot necessary that a priming gap be discharging simultaneouslywith theapplicationiof therecur- :rent voltagesto aLneighbouring gap. 1Thus;'such a sequencedischarge-tube,"*as it may be'called,

may be operated by. a'trainiof 'pu1ses=applied-.:between acommon anode in the form of'a plate or wire and. an 'array'of cathodes,teach mounted; independently, oriorming thelhillsiof a. corrugated Jplate facing 'the anode, or, perhaps,-;taking the form *of rods' mounted uponia common plate 1 or wirelikeithe teethtof. a comb, and havingthegap leng'thior-agiven: gap, usually thefirst, shorter than the remainder. Then the "first or :starting :"gap .may be fired by the first pulse, while :the second pulsetre-ignites the starting gap ;:and the next fadiacent gap simultaneously. The third pulse-will:fireithezfirst three gaps and soon. On theother handif'a maintaining battery be'connected' across thegaps, once fired each. 'gap' will :remain discharging indefinitely. .Thus such a sequence discharge tube has been used, with'suit- .:.able .circuits to extract the information and to 'zrestore the initial zconditions as to ionisation, :aicounter-or/and as an..information storage device.

.My-scoj-fpending U. S. tPatent Application -Nc. 14,184,.filed :March11,.1948, is :ccncerned with that :a'spectxif ionisationmigration which :de- "pends :upon the finite time occupied. for ionisation to spread from one gap toanother and m'akes use of the phenomenon to provide auto- -matic "firing from gap to gap along "a sequence at-definitely'spaced time intervals'when once a :starti-nggap hasbeen fired. The present'inventionfiisrelated to both these prior co-pending *applicationsbut is-concerned particularly with phenomena associated with the-spreading of cathode glow along a surface inclined to its co-operating anode.

In cold cathode electric discharge devices in general, it is acomrnoniy observed phenomenon 'that,dependingupon'the operating voltage con- -diti-ons, the cathode glow may not cover the *whbleof the electrode and often maybe observed "to wander from point .to] point thereon. I "have observed that-onapplication of a voltage sufficient to initiate a discharge, the glow spreads along the surface of the cathode at a rate which is quite definite and depends inter alia upon the value of the voltage applied to the tube, upon the electrode spacing and also upon the inclination of cathode to the anode. On removal of the applied voltage the discharge is observed to collapse again at a definite rate, it will in general always be initiated and finally be extinguished at the gap between the two points of the cathode and anode which are closest together. In accordance with one aspect of the present invention there is provided a cold cathode gas filled electric discharge device comprising a pair of electrodes forming a discharge gap, said electrodes being inclined to one another at a definite angle, said angle being such as to give a predetermined rate of spread and/or rate of collapse of glow discharge along said electrode for given combinations of the other parameters such as applied voltagewhich eifect said rate of spread or collapse.

Possible fields of application and other aspects of the invention will become apparent from consideration of simple examples of the operation of devices according to the present invention having reference to the drawing accompanying the provisional specification in which:

Fig. 1 is a schematic circuit arrangement for explanatory purposes of a device according to the present invention.

Fig. 2 is a similar circuit including a modified form of device according to the present invention.

Figs. 3 and 4 show further modifications of devices according to the invention.

Fig. 5 shows a further modification of the devices according to the present invention.

In Fig. 1 the device I comprises two electrodes one of which is the anode and may conveniently be a flat plate 2 and the other is a cathode in the form of a small rod 3 inclined at an angle a to the plate. A battery 4 and limiting resistance 5 may be connected in series between these electrodes, the battery voltage being such that it delivers a potential at the tube terminals corresponding to the maintaining voltage. If the voltage applied between the electrodes is raised continuously a discharge will take place first at the gap 6 corresponding to the shortest distance between cathode and anode. If the applied voltage remains higher than the maintaining voltage for the tube, the glow will spread along cathode 3. Furthermore it will spread at a definite rate due to the time effect as described for discontinuous gaps in my aforementioned U. S. Patent application No. 14,184, filed March 11, 1948, and-depend-v ing, of course on the total voltage which is applied to the tube. I have found that on removal of the applied voltage in excess of the maintaining voltage the discharge tends to collapse more slowly along the cathode until it is maintained only at the gap 6. If the battery voltage is sufficient only for maintenance of a discharge and if a rectangular pulse of a given amplitude is superimposed upon the battery voltage on arrival of the pulse, as soon as the voltage rises above the necessary striking voltage for the shortest distance gap, the cathode glow starts to spread up the inclined electrode. This spread depends upon the duration and amplitude of the pulse. After the pulse has passed, the discharge collapses until the voltage drop in the limiting resistance has reduced the inter-electrode potential to the maintaining voltage. Increase in the angle a, though offset somewhat by the fact that, as the glow spreads, the total number of ions and 4 electrons striking the remainder of the cathode surface will increase, also tends to reduce the rate of spread as the glow moves up the inclined electrode, thus giving a progressive limiting action with a current curve against time that is not linear but is less steep towards the end of the pulse duration. 1 In some cases this limiting action is an advantage, but if a linear or other particular shape of curve be desired, it may be achieved by curving one or both of the electrodes so that the inclination between the electrodes increases or decreases according to any desired law. Another effect of increasing angle a is to augment the'increase of glow collapse rate of large cathode current as compared with small current, as withlarge current, the distance of cathode to anode at the initial collapse point is greater. This again tends to give progressive limiting action. If such limiting action is not desired, a should be small. In practice it will be found advisable to use a priming discharge across-another gap in the discharge tube, as shown at 1 in Fig. 2, in which a variable resistance 8 and a battery 9 are connected in series between auxiliary cathode I!) and anode 2, the gap being kept constantly discharging and the current passing through it regulating, as well as stabilising, the total ionisation in the tube. Thus, an increase in this priming discharge current will materially increased the rate of spread of glow. The, use of the priming dischargei-s described in my copending U. S. application No. 19,084, filed April 5, 1948, .now U. S. Patent No. 2,520,171.

Data for a typical tube according to this invention is given below:

With this tube the collapsing time of the discharge was found to be several times the spreading time.

,If the main cathode 3 has a normally smooth surface the collapse rate cannot in practice be made slower than agiven value, for example to microseconds for total collapse. A much lower stable collapse rate may, however, be obtained if the surface of the main cathode facing the anode is made artificially rough. The glow then tends to remain in turn on each of the slight surfaceprojections; also, other things being equal, the build up rate is reduced. This may be com pensated, if desired, by an adjustment of one or more of the other tube constants and without increase in collapse rate. A still slower collapse rate, including a zero rate, may be obtained by introducing definite and regular indentations or corrugations on the cathode surface as shown at 3' in Fig. 3. In this case we have a simple variant of the sequence discharge tube previously mentioned and described in my aforementioned U. S. Patent application No. 763,655, filed July 25, 1947 Y According to a further aspect of the invention therefore, there is provided a cold cathode electric se ier qd ri e 0 hfl equence discharge type comprising an anode rod or plate and a plurality of cathode electrodes connected together so as to form with said anode an array of discharge gaps of non-uniform length so that on application of a given voltage across the anode and common cathodes, cathode glow may spread along said array at a predetermined rate.

When the applied voltage is reduced the oathode glow tends to remain on the tips of the corrugations of the cathode so that if a maintaining battery be used, the glow may be caused to remain indefinitely on one or more of the projections.

Devices according to the present invention may be used to generate pulses of relatively large energy content which varies in accordance with the signal modulation of corresponding input pulses of small energy content. They may also be used as electrical integrating and information striking devices. Examples of such uses are described in our co-pending application No. 14,185, filed March 11, 1948, which is now U. S. Patent #2,541,099, granted February 13, 1951.

For some uses an inclined cathode having a large number of indentations or corrugations may be required, for example, for demodulating speech pulses in a pulse modulation system. A convenient practical construction is to use as the cathode a wire helix of the type generally employed in the .grids of ordinary types of vacuum tubes as shown at 3" in Fig. 4. Each turn of the helix acts as one tooth on an indented surface. The glow may be prevented from spreading circularly round each turn and confined to a small area opposite the anode plate by coating the helix, except over a line opposite to the anode, with a material which has the properties of insulating and/or raising the work function. An example is alumina which does both and is easily applied.

A further modification of the invention is shown in Fig. 5 wherein the electrodes are numbered with the same reference numerals utilized in the previous figures.

The cathode 3 in Fig. 5 is shown to be curved convexly with respect to the anode 2. One end of the curved cathode is in closer proximity to the anode 2 than any other point on said cathode. It can be seen therefore that the curved cathode provides an extended gap of variable length so that a discharge may spread along the electrodes at a predetermined rate of change.

I claim: 1. A cold cathode gas filled electric glow dist charge tube comprising a discharge gap formed by two electrodes at least one of which has an 1 uneven surface adjacent said other electrode, one

of said electrodes being a cathode of the cold type, the longitudinal axes of said electrodes being inclined to one another at an angle selected to provide a predetermined rate of spread and rate of collapse of the discharge along the said electrodes under specified operating conditions of the tube.

2. A cold cathode gas filled electric discharge tube comprising a sequence of discharge gaps of progressively varying length, all connected in parallel, successive gaps being positioned adjacent each other to provide ionization coupling therebetween so that on application to the gaps of a given potential, a glow discharge strikes and spreads along the sequence of gaps at a predetermined rate.

3. A cold cathode gas-filled electric glow discharge tube comprising a pair of extended electrodes, at least one of said electrodes curved convexly with respect to said other electrode and having one end thereof in closer proximity to said other electrode than any other point on said one electrode, said electrodes forming an extended discharge gap of variable length, such that, when a given striking potential is applied to said electrodes, a discharge is produced which spreads along the gap at a predetermined rate.

4. A cold cathode gas-filled electric discharge tube comprising a substantially smooth-surfaced electrode arranged opposite a corrugated electrode set at an angle to the smooth-surfaced electrode in such manner that a discharge betweenthe said electrodes is produced on the application thereto of a striking voltage the said discharge spreading along the corrugated electrode at a predetermined rate.

5. An electric circuit arrangement comprising a cold cathode gas filled electric discharge tube including two extended electrodes, at least one of which electrodes has an uneven surface adjacent the said other electrode, said electrodes arranged opposite one another to form an extended discharge gap of varying length, and leads connected to said electrodes for applying to the said electrodes a potential sufficient to start a glow discharge across the gap, the arrangement being such that the discharge spreads and collapses at a predetermined rate.

6. An arrangement according to claim 5 in which said electrodes are conductors inclined to one another at a given angle and the cathode electrode has an uneven or indented surface.

7. A gas filled glow discharge tube comprising a gas filled envelope enclosing two electrodes inclined to one another at an angle selected to provide a predetermined rate of travel of a glow discharge therebetween along the length thereof, one of said electrodes being in the form of a helix having portions thereof nearer to the other electrode than other portions of the helix.

ALEC HARLEY REEVES.

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

UNITED STATES PATENTS Number Name Date 836,071 De Forest Nov. 13, 1906 1,965,588 Foulke July 10, 1934 1,984,469 Ewest Dec. 18, 1934 2,003,493 Rentschler et al. June 4, 1935 2,149,093 Kingdon Feb. 28, 1939 2,221,644 Lucian Nov. 12, 1940 2,479,164 Inman Aug. 16, 1949 2,516,915 Reeves Aug. 1, 1950 FOREIGN PATENTS Number Country Date 370,967 Great Britain Apr. 11, 1932

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