US2620451A - Heated anode gaseous electric discharge device - Google Patents

Description

W. DALLENBACH HEATED ANODE GASEOUS ELECTRIC DISCHARGE DEVICE Dec. 2, 1952 34 Sheets-Sheet 2 Filed Dec. 4, 1950 INVENTOR WALTER D'ALLENBACH BY C 1' a w. DALLENBACH 2,620}451 HEATED ANODE GASEOUS ELECTRIC DISCHARGE DEVICE Dec. 2, 1952 3 Sheets-Sheet 3 Filed Dec. 4, 1950 fly. 7 I

INVENTOR, WALTER D'A'LI-ENBALH Patented Dec. 2, 1952 I HEATED ANODE GASEOUS ELECTRIC DISCHARGE DEVICE Walter Diillenbach, Zollikon-Zurich, Switzerland,

assignor to FKG Fritz Kesselring Geratebau' Aktiengesellschaft,Bachtobel-Weinfeden, Switzerland, a Swiss company Application December 4, 1950, Serial No. 198,942 In Switzerland December 6, 1949 12 Claims. (Cl. 313-45) My invention relates to gaseous electric discharge devices with an incandescent cathode in an atmosphere of inert gas or metal vapor, and particularly to discharge devices whose cathode has a thermo-ionically highly active surface and whose atmosphere contains vapor of alkali metal preferably of potassium, rubidium or cesium.

Such alkali metal vapors facilitate obtaining a high specific electron emissivity of the cathode surface and. reduce the voltage drop of the discharge between cathode and anode.

The emission of electrons from the cathode has a cooling effect on the cathode. The ingress of electrons into the anode causes heating of the anode. That is, due to the emission of electrons, heat of evaporation is drawn from the cathode, while heat of condensation is given off to the anode. In gas discharge devices operating with a high specific electron emission at the cathode surface and a low voltage drop of the discharge between cathode and. anode, this transfer of heat from cathode to anode plays a considerable role compared with the heat losses within the gas discharge proper. The vaporization heat of the electrons must be constantly refurnished to the cathode, and the heat of condensation must be constantly carried off from the anode. Thisheat transfer therefore increases the losses in thegas discharge device and aggravates the cooling requirements.

It is an object of my invention to minimize or virtually eliminate these disadvantages. In other words, my invention aims at improving the heat economy of gaseous discharge devices, especially those containing an alkali vaporous atmosphere, and thus to improve the stability of operation.

Another, ancillary object is to simplify the cooling requirements of such tubes or to do away with the necessity of providing special cooling means.

In order to achieve these objects, and in accordance with one of the features of my invention, I couple the anode in thermally radiative respects closely with the cathode and give the anode such a normal operating temperature that a considerable portion of the condensation heat caused by the flow of electrons into the anode is returned to the cathode by heat radiation and contributes essentially to maintaining the cathode at its normal temperature, thus providing a considerable portion of the vaporization heat required at the cathode.

Of course, this is possible only if the anode has a higher operating temperature than the cathode and if there is a close thermal radiative relation between the two electrodes. For a sufliciently large range of variation of the new of electrons, these conditions can be realized only if, according to the invention, the anode is heated from without either directly or indirectly and if the temperature needed for the electron emission is sustained at the cathode by virtue of the'heat radiation from the anode. If the voltage drop between cathode and anode and the current heat loss caused by that voltage drop were negligibly small and if the entire condensation heat of the electrons were returned from the anode to the cathode, then the proper temperatures of anode and cathode, in this special case, could be sustained, without aid from an extraneous heat source and' independently of the transmitted electron current, merely by heating the cathode by radiation from the anode. This limit condition, however, cannot practically be realized because there is always a voltage drop between cathode and anode and. because, generally, the quantityof condensation heat at the anode exceeds the quantity of vaporization heat at the cathode.- Nevertheless, the radiative return of condensation heat from the anode to the cathode improves the temperature conditions to such an extent that the steady-state operation becomes more independent of the transmitted electron current so that the performance of the discharge device attains a higher degree of stability.

If the gas discharge device serves as a rectifier. which upon polarity reversal blocks the flow of inverse current, then the cathode and anode surfaces must bedifferently constituted, that, for instance, in contrast to the behaviour of a completely pure metal surface, the more highly heated anode surface has an electron emissivity of a lower order of magnitude than the cathode surface having a considerably lower temperature. Such conditions can be secured, for instance, by means of tungsten electrodes within an atmosphere of alkali metal vapor of suitable density. The less heated and slightly oxidized cathode surface is coated with an alkali metal film while the carefully cleansed anode surface has an operating temperature sufliciently high to prevent a sectional side elevation of an anode structure for discharge devices according to the invention;

Fig. 4 is a sectional side view of another modification of a heated anode structure suitable for devices according to the invention;

Fig. 5 is a section through a thyratron-type gas discharge device with a separately heated anode and an auxiliary electrode serving as a control grid;

Fig. 6 is a section through a gas discharge device according to the invention with two heated anodes; and

Fig. 7 is a schematic circuit diagram ofa threephase transformer-rectifier apparatus equipped with discharge devices according to Fig. 1.

Referrin to the embodiment of Fig. 1, theillustrated discharge tube has an envelope 2| consisting, preferably, of an alkali vapor resistant boro-silicate glass such as known under the trade name Pyrex. The envelope is evacuated and contains a quantity 'of'cesium, A cup-shaped cathode structure 22 is mounted on a sealed-in carrier rod 23. The anode consists'of a helical tungsten filament 24 with its appertaining two inleads "25. The leads 25 are sealed throughtheenvelope wall. The anode is rated for an operat-- i-ng temperature of about 2000 abs. when the anode leads 25 are connected to a source of fila-- ment heating current.

sure corresponding to this. temperature, the surface of the highly heated anode 24 is virtually free of cesium so that its specific emissivity is at about 10* amp./cm.

In this embodiment, the cathode 22, consist in -for instanceof oxidized tungsten sheet metal, is:shaped/substantially as a hollow cylinder and has an opening in which the anode. helix 24 islocated: Anode and cathode are surrounded by a radiation shield ZT secured to a sealed-incarrier 28. This tube design has the effect that the cathode is heated by radiation fromthe-anode to the required operating temperature ofyfor-instance, 1300 abs. At that temperature, the cathode surface is coated with a layer of cesium which, due to dynamic equilibrium between evaporation and condensation, ism-aintained at or nearan optimum degree of coverage, thus securing a persistent high emissivity. Under such conditions a specific-cathode.-emission: of about 10 amp/cm.- is obtainable sothatthe ratio of cathode emission to anode emission would be in the order of 10 A cathode of the hollow-design exemplifiedby:

Fig.1 has. theadvantage of a very good adsorption of heat radiation from the anodepossibility that the electrons issuing from the cathode surface may. directly reachthe anode without contributing to the ionization of the vapor space; the design promotes a repeated back and forthtravel of the electrons within the oathode chamber and a correspondingly strongionization of the vapor space.

While the heating of the anode 24' secures an operating temperature high enough to prevent the anodesurface from being coated with an alkali metal layer appreciably increasing the emissivity of the anode metal, zones of reduced temperature may occur along the anode leads 25.

This may lead to the deposition of cesium at the cooler places with an ensuing increase in emissivity which decreases the peak inverse voltage and may cause arcback. To prevent this, the anode leads 25 within the vessel are prefer- At' a vessel temperature of 400 to-450 C., i. e. at the cesium'vapor pres-- Sucha cathode design also minimizes or prevents the ably protected from the formation of emissive coatings by a suitable surface treatment or design. For instance, as shown in Fig. 1, the

anode leads 25 may be covered by coatings 28 of refractory. insulating material such as zirconium oxide or aluminum oxide.

It will be recognized that in the above-described embodiment the electron condensation heat given off at the anode is radiated back to the cathode where it is needed for the further electron release and vaporization, the required operating temperature of the cathode being dependent upon this return radiation without whichlthe cathode. would cool below the needed temperature level.

A particular advantage of a discharge device accordingto. the invention is the fact that the energy released by the electrons collected by the anodecauses heating of just that electrode which is intentionally to be kept at a high temperature, contrary to conventional electronic tubes-whose anode heat losses must be-carried off by cooling. means.- This advantage can furtherbe utilized under certain conditions, especially whenthe. tube is to operate undera constant plate load,-

inhaving the anode maintain its requiredop-- eratin-g temperature by self heatin so that an external source of heating energy isneeded only for starting the operation of the discharge vessel. An example of such a self-heating anode tube is shown in Fig. 2.

According to Fig. 2, the tube envelope 3| encloses a hollow cylindricaland generally cup-.. shaped cathode 32 mounted on a sealed-in.con-. ductor rod 33. A plate-shaped anode 34 is- 10-, catedwithin the cup opening of thecathode and mounted on an inlead-rod 35.. For the reasons previously given, rod 35 is coveredwith aninsulating coating36a A high-frequency heating. coil 30, shown in cross section, is arranged at the outsideof the envelope 3| for the inductive eddy current-heating ofthe anode plate 34. Cathode 32 and anode 34 are surrounded bya radiation shield 31 mounted on sealed-in carriers 38. To prevent the cathode and shield from being heated by the induction coil 30, the cathode cylinder-32 and theradiation shield -31 are longitudinally subdivided or have longitudinal slots such as the one denoted by 39. The heating coil 30 is. energized during starting periods to raise the electrode temperatures up to the norm-aloperating values. Thereafter the coil 30 can'be partly. or wholly deenergized, letting theanode retain its temperature by self-heatin due to theload current. The heated anode, in turn, then causes the cathodev to maintain its required lower tempera-. ture as-explained with. reference to the firstdescribed embodiment.

Figs. 3a and 3b show an example of. an indie rectly heated anode suitable for discharge tubes according to theinvention. In these figures, the

anode structure proper is denoted by 44. This v A separate lead 49a is.con-.

5. the-filament leads and'has a separate lead 55. A voltage source can thus be connected between the anode lead 55 and one of the. leads 59a in order to heat the anode 54 by electronic, action up to the desired operating temperature. The three leads of the anode assembly are non-conductively coated within the vessel to prevent emission from these leads.

'In' devices according to the invention, the anode-may consist of metals other than tungsten. It is, as a rule, of advantage to select an anode material whose emission characteristic for a given operating temperature is as low aspossible. If a discharge device according to the invention is supposed tohave especially high safety from arcback, :the operating pressure of the alkali vapor is kept relativelyv low because at lower vapor temperatures the ratio between the emissivity of the cathode and the emissivity of the anode is larger than in the range of higher alkali vapor pres-.

sures. Conversely, if especially high current densiti'es are aimed at, the vessel temperatures may be given a higher value because then the absolute value of cathode emission is correspondingly increased."

In the thyratron-type discharge device shown in Fig. 5, a hollow cathode structure 6| is heated exclusively by the passage of the discharge current and by radiation from the anode. The anode structure 62 is indirectly heated by a helical filament 63. A centrally perforated auxiliary electrode 64 surrounds the anode structure to serve as a control grid. The cathode 6| is surrounded' by a radiation screen 66. The current conducting inleads 69 for the anode 62 and the control grid 64 are prevented from becoming emissive by protecting insulating tubes 61, for instance of aluminum oxide, as described previ ously in conjunction with the embodiments of Figs. 1 to 4. The entire electrode arrangementis enclosed in'a' sealed glass envelope 68 contain ing an atmosphere of potassium, rubidium'or cesium vapor. During the normal operation of the tube, the temperature of the anode 62 is higher than that of the substantially radiation heated cathode 6i, and'the control grid 64 assumes a temperature between the respective temperatures of anode 52 and cathode 6|, thisgrid temperature being still high enough to prevent the formation of an'electron emission coat of alkali metal on the grid electrode.

The embodiment shown in Fig. 6 is designed as a by- 'phase rectifier valve and is equipped with two anodes T0 and H within a, hollow cathode structure'IZQ The electrodes are disposed within a sealed glass envelope 13. The envelope wall is that of the embodiment according to Fig. 1.

When using discharge devices according to the invention for multi-phase rectification, the rectifier circuit connection may be suchthat the anodes are connected with one another to assume the same potential rather than the cathodes as heretofore customary. The three-phase rectifier according to-Fig. 7 is designed in this manner.

The transformer-rectifier circuit of Fig. 7 is equipped with three rectifier tubes each designed according to Fig. 1'. The three anodes 90, 9| and 92 of the respective tubes are directly connected with one another. This permits heating the three anodes from a common source 93 of filament current. The appertaining hollow cathodes'aredenoted by 94, 95 and'Q B, respectively. The other details of each tube'a're as shown i'n'Fig. 1 and, for simplified illustration, are" omitted in Fig} 7. The three tubes are connected to the -res"p'ective secondary windings 98', 99, I06 of a three-phase power transformer 9! whose primary windings- Hll, I62 and I03 are connected to an alternating current line. The primary'windings are deltaconnected, for instance, whilethe secondary windings arestar-connected. The rectifier load is de notedbylll l. v A

It will be understood by those skilled in the art after a study of this disclosure that various modifications and changes as regards details and design features other than those specifically mentioned can be applied without departure from the essence of the invention and within the" scopeof its features set forth in the claims annexed hereto.

1. A gaseous discharge device, comprising an envelope containingan alkali'metal vapor atmosphere, a hollow cathode structure in said envelope having a cathode surface of h h Electronic emissivity,"and a heatable anodehavlng an operating temperaturehigherjthan that of traversed by the inleads M and '15, for the anode 1n, and the corresponding leads 16 and TI of the anode "H. The cathode 12 is connected to an inlead 18. A heat radiation screen 19 is fastened to carrier rods 86 and 8| which are sealed through the envelope. In the interior of the envelope (3, the anode leads 14, l5, l6 and l! are coated with a layer 82 of zirconium oxide or aluminum oxide,

signed as a closed hollow cylinder with openings for the passage of the anode leads. The two anodes I0 and H are located completely within the said cathode structure and being" disposed in close thermic radiation coupling with said cath ode structure for heatingsaid structure by heat radiation from said anode.

2. A gaseous discharge device, comprising an envelope containing an alkali metalfvaporjate mosphere, a hollow cathode structure disposed in said envelope and having a cathode surface of high electronic emissivity, an anode'having a normal operating temperature higherthanthat of said cathode structure and beingdisposedin close thermic radiationcoupling with said cathode structure for heating said structure by heat radiationfrom said anodaaheating circuit ,en-, ergizable from without said envelope and'ther-f ITally arme hs'a' .d f rntain n it at said higher temperature. l

3. A gaseous discharge device, comprisingan' envelope containing an alkali metal vapor atmosphere, a hollow cathode structure in said envelope having a cathode surf-ace of high elec tronic emissivity, and a plurality of heatable anodes havin a higher operating temperature than said cathode structure and being disposed in close thermic radiation coupling with said cathode structure for heating said structure by heat radiation from said anodes.

4. A gaseous discharge device, comprising an envelope containing an alkali metal vapor atmosphere, a hollow cathode structure in said envelope having a cathode surface of high electronic emissivity and having anopening, an anode, heating means thermally related to said anode for supplying heat. thereto in addition to the heat due to the discharge between said cathode structure and said anode, said anode having in normal operation a higher temperature than said cathode structure and being disposed in said opening and in close thermic radiation coupling withsaid cathode structure for heating said structure by heat radiation from said anode.

5. A gaseous discharge device, comprising an envelope containing an alkali metal vapor atmosphere, a hollow cathode structure in said envelope having a cathode surface of high electronic emissivity, an anode, heating means thermally joined with saidanode and having a heating circuit separate from the discharge path between said cathode structure and said anode, said anode having-due to said heating means a higher operating temperature than said cathode structure and'being disposed in the interior of the hollow cathode structure and in close thermic radiation coupling therewith for heating saidcathode structure by heat radiation from said anode.

6. A gaseous discharge device, comprising an envelope containing an alkali metal va or atmosphere, a hollow cathode structure disposed in said envelope and having a cathode surface of high electronic emissivity, and a heatable anode filament adapted for connection to a heat filament circuit and having in normal operation a higher temperature than said cathode structure, said filament being disposed in close thermic radiation coupling with said cathode structure for heating said structure by heat radiation from said anode.

7. A gaseous discharge device, comprising an envelope containing an alkali metal vapor atmosphere, a hollow cathode structure disposed in said envelope and having a cathode surface of high electronic emissivity, an anode structure having indirect heating means comprising a heater filament within. said anode structure, said anode structure having a, higher operating temperature than said cathode structure and being disposed in close thermic radiation coupling with said cathode structure for heating saifl structure by heat radiationfrom said anode.

8.. In a, gaseous discharge device according to claim 4, said heating means comprising auxiliary discharge means within said envelope.

9. A gaseous discharge device, comprising an envelope containing cesium vapor, a hollow cathode structure disposed in said envelope and having a cathode surface of high electronic emissivity, and a heatable anode having a higher operating. temperature than said cathode structure and being disposed in close thermic radiation coupling with said cathode. structure for heating said structure by heat radiation from said anode.

10. In a discharge device according to claim 1, said envelope consisting of material resistant to said vapor'at its entire surface exposed to said vapor, said anode comprising a structure having a part of a temperature normally lower than said anode operating temperature, and a non-conductive protective coating disposed on said part within said envelope and consisting essentially of refractory inorganic material selected from the group of aluminum oxide and zirconium oxide.

11. A gaseous discharge device, comprising an envelope containing an alkali metal vapor atmosphere, a hollow cathode structure disposed in said envelope and havin a cathode surface of high electronic emissivity, a heatable anode having in normal operation a higher temperature than said cathode structure and being disposed in said envelope in a close radiative relation to said cathode structure for heating said structure by heat radiation from said anode, and a control grid between said cathode and said-anode having a normal operating temperature between the temperatures of said cathode and said anode.

12. A gaseous discharge device, comprising an envelope containing a cesium vapor atmosphere, a hollow cathode structure disposed in said envelope and having a cathode surface of high electronic emissivity, an anode, having means thermally coupled with said anode and adapted to be connected with a heating circuit for supplying to said anode heat in addition to that due to the discharge between said cathode structure and said anode, said anode havin a normal operating temperature higher than that of said cathode structure and being disposed in a close thermic radiation coupling with said cathode structure for heating said cathode structure by heat radiation from said anode, and a control grid disposed between said cathode and said anode having a normal operating temperature between the respective temperatures of said cathode and said anode.

WALTER DALLENBACH.

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

UNITED STATES PATENTS Number Name Date 1,878,024 Strigel Sept. 20, 1932 2,020,724 Fritze et al. Nov. 12, 1935 2,066,170 Barton Dec. 29, 1936 2,489,891 Hull Nov. 29, 1949 OTHER REFERENCES Article by-Lawrence E. McAllister, Physical Review, p. 123, vol. 21, 1923.

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