US2011372A - Glow-discharge vessel filled with gas or vapor - Google Patents

Description

J. NIIENHOLD Aug. 13, 1935.

GLOW DISCHARGE VESSEL FILLED WITH GAS OR VAPOR Filed Dec. 16, 1952 A a/elven;

Patented Aug. 13, 1935 UNITED STATES GLOW-DISCHARGE VESSEL FILLED WITH GAS on VAPOR Johannes Nienhold, Berlin-Charlottenburg, Germany, assignor to Siemens & Hals'ke, Airtiengesellschaft, Siemensstadt, near Berlin, Ger.. many, a corporation of Germany Application December 16, 1932, Serial No. 647,554

In Germany December 18, 1931 12 Claims.

This invention refers to an improvement of gasor vapor-filled glow-discharge vessels, having a hollow cathode. Where in the following description and in the appended-claims reference is made to a glow-discharge hollow cathode, this. is understood to be a cathode subdivided so as to form spaces or compartments, the different component parts of such cathode being arranged in such a manner and at such a distance apart that the electrons liberated from one portion of the cathode by the impingement ofpositive ions are shot into the cathodic fall space of the opposite part of said cathode and are stopped in this fall space, thus giving rise to a concentration of electrons in the hollow spaces of the cathode and, consequently, to a reduction of the cathode fall.

A glow-discharge hollow cathode is more particularly understood to be also such a one of the type characterized above, in which the distances separating the opposite hollow cathode surfaces are equal or inferior to the fall space thickness at a simple cathode.

In the accompanying drawing, Fig. 1 is a diagram illustrating the discharge conditions; Figs. 2, 3, 5, 6, '7 and 8 are vertical sections illustrating various embodiments of my invention; and Fig. 4 is a perspective view of 'a perforated hollow cylinder such as I employ in some of the embodiments shown.

' In glow-discharge vessels having such glowdischarge hollow cathodes, the operating conditions employed prior to my invention are such as are represented, for instance for small gas pressures in Fig. 1.

The discharge current i has been plotted as abscissa and the filament voltage e as ordinate. On applying a voltage to the vessel the voltage must, for instance, be raised to 300 volts (section a-b). At this voltage, a low discharge, known vto-day usually as preliminary discharge, is started, while the voltage simultaneously decreases to 200 volts (section b-c). For further increase of the filament voltage the discharge current increase is comparatively slight, so as to give a steep rise of the characteristic line (section cd) At 900 volts, point 11, the preliminary discharge suddenly becomes the glow-discharge strictly speaking, the voltage dropping from 900 volts to about volts (section d-e) The voltage of 180 volts depends, of course, on the series resistance. The discharge current intensity decreases considerably with increasing filament voltage (section e-f). At point the glow-discharge is converted into the are disways.

charge (section ;f g), which involves a voltage drop of from say 400 volts to 15-20 volts. The range g-h is the arc discharge range. As may be seen from the characteristic line, a very high voltage should be applied at least once, in orderto obtain appreciable discharge currents, i. e. at least one glow-discharge. In the case of the example, it was necessary to raisethe voltage once up to 900 volts for a mean operating voltage and for a glow discharge of 200-400 volts.

The smaller the gas pressure, the higher the maximum voltage tobe applied before the starting of the glow-discharge The same holdsfor small cathode distances. The dotted curve c-k indicates, for instance, such a characteristic for l charge hollow cathode, as defined above, suitable means for obtaining a supplementary thermal production of electrons in the hollow spaces. For this purpose devices well-known in themselves are available. The method of making hollow cathodes highly emissive by the use of adequate material is well-known in the art. The inner surfaces of hollow cathodes are, for instance, coated with alkali earth metals or oxides of electro-positive' substances or finely sub-divided compounds of the two. priate design of the cathode, with respect to the working current, permits one also to obtain a certain self-heating efiect, which is, however, only obtained after at least the range of high glow-discharge currents has been reached. Thus these means do not result in a considerable reduction of the voltage peak (point d in Fig. 1;). Only an additional source of thermions, as employed in this invention, enables a direct passage tobe obtained from point 0 to point e sothat th peak is avoided (hatched range).

The thermionic source can be designed in two Either use is made of an incandescent cathode, of a type known in the art, for instance, an oxide-coated, distillation or thoriated cathode, orprovision is made for additional heating enabling the hollow cathode or at least parts of it to emit ions thermically.

The first case in which use is made of a directacting incandescent cathode has been represented An approby the electrode holding wire 2 or its extensionin Fig. 2. The holding wire 2 sealed into the squash l carries the glow-discharge hollow cathode 3 which has been given the shape of a box. It consists of a casing 4 surrounded by a heatprotecting envelope 5. Within the cathode there are located the intermediate sheets orpartitions 6, '1 and 8, which are bored through in the middle, so as to enable the helical filament [0 carried 9 to project into the whole of-the compartments formed by the said partitions, which compartments in this particular example are designated by l I; I2, l3 and M. The helical'filament is atone end supported by the holdingwire I'5, whichis"insulated by means of an insulating tube. ILB .andled through the casing 4 and the heat-protecting envelope 5. Of course the filament cani'be given. any other form. The lead to the filament, which may also be a stretched filament, may be insulated at both ends, afact which is of importance for A. C.

" operation. It is -also' possibleto establish an electric connection 'between the electric center of the "filament and thelhollow cathode system.

' 'Another example of the use of a directly heated cathode is given by' Figs. 3 and 4. The two elec- '-trode holding wires l'a' are sealed into the squash l'l. Theycarry the hollow cathode'which is, in

"this case, builtupo'f concentrical cylindersZl and 22 arrangedin the-casing T9 surrounded by the heat-protecting envelope-.20. These cylinders. are shapedas indicated in Fig. 4, i. e. they. have slots enabling the various compartments of the cathode 'system to communicate with one another. Within thehollow cylinder, 2l, there is located a "double-wound helical "filament 23 carried by the -two electrode holding :wiresflkand 25. The slots'of the different 'hollow cylinders are designed-so as i to enable the electrons emitted within the hollow 1 cylinder 2 I =to i penetrate into the other compart- 'ments. The'barium vaporrcloud formed 1 byithe thermite pill 26 (compound:of barium-oxide and aluminium) can also during the manufacturing process penetrate -through i the-slotsinto all the compartments.

When starting a'hot cathodersuch as'indicated in Figs. 3 and 4, it'isifound that the glow-discharge "within cylinder irisfirststarted and that dueto I the superposed dischargecurrent; thehot cathode a is then brought to a brighterglow (additional "hollow cathode 29 which, .as showniin ,the concaused to emit electrons.

I self-heating). The dischargeshifts to the re- -=maining hollow cylinders,"the-hot (cathode again assuming its normal temperature.

When the glow-discharge'is started, it is, with suitable design of the cathode, possibletto switch the hot-catho'de-o'fi" or to keep it burning at a "dark-red glow. V r 1 Figs. 5-8 show thehollow cathodes,-as heated-ine directly according to" the invention.

In Fig. '5, the electrodeiholding wire i28 sealed into the squash 21 carries 'the "glow-discharge structional example of Figs. 24,- consists ofiiacas- *ing or cylinder39 whichmay be surmund'ed'by a -heat-protectingenvelope '3 I. Wi'thin30, there is, for mstance,= a ho'llow cylinderfj32, and, in its center a convex bulge-53 containing within its inner concave part a "heater 34 "heated, for instance,

"through :the lead 36 surrounded by-tan insulating -tube 35. After switching on the .heater, .34, the' 'part 33 is heated up,'so thatitszouter surface is In the case of C. heating, lt mayfbe electricallyrecommendable to .separate the heating wire 34 completely :fromthe hollow cathode system. .In the casepf the above- ':described:glowedischarge .hollowacathodez also.,%the

- same :manner as :in the previous ,-example. ..heater:52 whichiisplacedwithinthe met/a1 19012259 7 inner cylinder 32 or the partitions should be equipped with openings, so as to enable the electrons proceeding from the outer surface of the cylinder 32, to penetrate into all the compart-- ments under consideration. 7 I W Fig. ,6 shows another constructional example of the glow-discharge hollow'cathode. The squash 31 carries the holding wire 38 for the hollow cathf ode 39. "4.8cloSeda-atthertop and containing a heater it! "heated in a manner well-known in the art. The tube 40 carries spaced circular ribs 42 so that 41 :between theribs 42 with an electron emitting material, e. g. oxide .or the like, in order to obtain, withinthe'liniits' possible, a high electronic outalso heated and it may then be desirable to coat these ribsas well with an electron-active material This hollow cathode consists of a tube.

' compartments-"43,"!4545 etc. are formed. It may Y gbeisuitable in this .case to coat the tube parts t6,

-put. FIf the heating is suflicient, the ribs are. 1 c c or to' construct them ithroughout o'f such material i for example thoriated tungsten or the= like).

Figsfl'l and 8 show dischargeives'sels :according to my invention,- -in which the heating "is indi rect, the heater, "however, being locate'd' outside H the discharge vessel, that is notwithin the vacuv um. In this way-"the heaters can be-readily interch'anged and the discharge vessels canxmore particularly "be adapted for any given working conditions by the insertion of 'anadequate'heat'er body. I J

3mg; shows-a vessel in which theI heaten-is located within .a smallxbay zof itheqdischarge :vessel. Themetalpot 50 is =sealedat-49 &into the :discharge vessel 48vconsisting :for :iinstancel of glass and carrying the glow-vdischarge ihollowrcathede This cathode is constructed in much-rt-he {The as arin-g. isyplaced-aroundithe=metalrpoti-from the outside, andrraises the temperatureqof the cath- .ode .to a degree ssuitable for emission-purposes,

'A tapered cross-section maybezprovidediforwat "26! in order to block the transmissionzof heat.

On account-ref the -g-reatstraln produced by the :heating, thej'metalnpotsfill. 0fIF ig.1' 7 and-510i :8 shouldbe madezof metal -:not :readilyroxidized, for instance ."Of .chromic 'iron, xnickel-iiron or the alike, or :they should he coated with: nickel-.,-:chr.o-

'miumtor platinum-l-ayem'on, he side-'exposed 'to ithe ratmosphere.

Asitothematei'ial forithe cathnde, Ifmayuse tnickel, iron, molybdenumxungsten, .:or the ilike, either in the compactcondition-or in 'thesshape 60f *a netting. nsshaseibeen stated above, theemis- :sive material should i'be either thorium in: any of its 7 difierent forms orealkali earth metalslas well *as the oxides 'theredf. -?More particularly in the constructional examples shown in :Figs. 7 8,

-mate'ria'ls should he :used .which event at ex 1 treme'ly -lowtemperatures 'willyield a "high emis--- sion of-electrons. .Bariumf'finel-y sub-:divided-with oxide; 'which 'evenf.:at temperatures below ;red-

glow will yield an appreciable emission, is of special suitability. The use of nettings (nickel) is here'preferable, as it suits the emission-material particularly well. From the manufacturing standpoint nettings are also recommendable, since, for instance, barium-oxide can easily be rubbed into the meshes, and pure barium is present in the nettings after disintegration in vacuo.

As to the construction of the hollow cathode. the following is important: the distances separating the opposing hollow cathode surfaces should be in a definite ratio to the filling gas and to the gas pressure, i. e., the distances should be inferior or equal to the width or thickness which the fall space has in the case of a cold simple cathode under corresponding conditions as to kind and pressure of the gas or vapor employed. By a simple cathode, I mean one made of sheet metal, a so-called plate cathode, opposite to which an anode is located at a relatively considerable distance. This distance varies with the kind of gas or vapor employed and with the pressure under which such gas or vapor is contained in the vessel. These distances, insofar as they cannot be determined by experiment, can be calculated roughly, by making them equal to 10 to 20 times the length of the mean free gas-kinetic electron path.

The electron path length within a gas or vapor having a pressure of 19 mm. is:

, perature of C., are as follows:

I-Ig Ar Ne Iie By multiplying these values by -20 we approximately obtain the fall space thickness at a gas pressure of 1 mm.

A distinguishing feature of my invention is the production of a peculiar effect known as the hollow cathode effect. Investigations have shown that this effect is obtained when using a subdi vided cathode having compartments the adjacent walls of which are spaced from each other a distance smaller than twice the thickness of the fall space. An explanation of this peculiar effect is found in various publications, see for instance Engel & Steenbecks book Elektrische Gasentladungen Berlin 1934, Section 49 (pages 114 to 116).

What I claim as my invention is:

1. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode, provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, means for the additional thermic production of electrons within the compartments of the cathode.

2. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode, provided with compartments, the distance between the adjacent walls of such cornpartments being smaller than twice the thickness of the fall space, a hot cathode located within vapor, a glow-discharge hollow cathode provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, said cathode containing an electric heater.

4. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode, provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, a heater located outside the discharge vessel.

5. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode, provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the i all space, a heater located outside the discharge vessel and surrounding said glow-discharge hollow cathode.

6. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode, provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, a heater located outside the discharge vessel within a bay of the walls.

7. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode, provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, a heater located outside the discharge vessel and within a bay having the shape of a sealed-in pot.

8. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode a heater, provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, located outside the discharge vessel in a bay having a tapered cross-section.

9. In a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, and means for the additional thermic production of electrons in the compartments of said cathode, openings connecting said hollow spaces with one another and enabling the thermically produced electrons to penetrate into several compartments.

10. Glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode provided with compartments, the distance between the adjacent walls of such compartments being smaller than twice the thickness of the fall space, and means for the additional thermic production of electrons within said compartments, means for insulating said hollow cathode from heat.

11. A device of the character described, comprising a glow-discharge vessel filled with gas or vapor and having a glow-discharge hollow cathode provided with compartments and in which the opposing surfaces of the different component parts are at distances from each other inferior or equal to the thickness which the fall space has in the case of a simple cathode under corresponding conditions as to kind and pressure of the gas or vapor employed, and means for the additional thermic production of electrons within: said cathode.

12. A deviceof the characterdes'cribed, comprising a glow-dischargeevessel filled with gas or 5 vapor and having. a glow-discharge hollow cathode. having opposing surfaces the distance WhichthefaILspaceLtmsJ-in the case ofa simple cathode under corresponding conditions as to kind and pressure of the gas or vapor employed, and means for the additional thermic production of electrons-within'said cathode.

JOHANNES NIENHOLD.

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