US2600196A

US2600196A - Gaseous-discharge make-alive device

Info

Publication number: US2600196A
Application number: US218584A
Authority: US
Inventors: John L Boyer; Slepian Joseph
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1951-03-31
Filing date: 1951-03-31
Publication date: 1952-06-10
Anticipated expiration: 1969-06-10

Description

June 10, 1952 J. BOYER ErAL GAsEous-DISCHARGE MAKE-ALIVE DEVICE Filed Maren 51, 1951 3 Sheets-Sheei l VWITNEsslzs:

8 n. S .u ia. yw Y TOI. E .NBS N E. R VLh O N n.. T .lne T hm A m3 V| B y@ Mm.

June 10, 1952 y J. L. BOYER ETAL 2,600,196

GASEOUS-DISCHARGE MAKE-ALIVE DEVICE Filed March 5l, 1951 3 Sheets-Sheet 2 Fig.2.

WITNESSES: INVENTORS ZM, .John L. Boyer 8| Jose h SIe ian. BY P P dm@ y ATTORNEY June 10, 1952 J L BOYER ETAL GASEOUS-DISCHARGE MAKE-ALIVE DEVICE Filed March 51 1951 3 Sheet's-Shee 5 Contro| L a JL74 WITNESSES: lINVENTORS John L. Boyer 8 BYJoseph Slepan.

ATTORNEY Patented June 10, y1952 UNITED STATES PATENT OFFICE GASEOUS-DIS'CHARGE MAKE-ALIVE DEVICE John L. Boyerand Joseph Slepian, Pittsburgh,

Pa., assignors. to' Westinghouse ElectricCorporation, East Pittsburgh, Pa., a.y corporation' of" Pennsylvania Application'MarchBi, 1951, SerialNo; 21S-,584. acclaim; (C1. 313-170)- Our invention4 relates to single-anode, pool'- type vapor-arc rectiiiersior asymmetrically conducting devices, having a new make-alive meansand method, for-initiatingV the cathode-spark ofan arclat thebeginningof 'each conducting period of` the device. Our invention is an improvement over, or analternative for, the broad invention which is described andi claimed in` thel Boyer application, Serial-No. 206,434, led'January 17rv 19511, forfavapor-arc device, which was characterized: by havingf aspaced starting-anode, as disti'n guished fromzavhigheresistance orsemiconductive; ignitor-bo'dywhich dips down into` the catl'1odeA pool' asfdescribedfand claimed-'in an earlier Slepian and'V LudwigA ignitron Patent 220693283; granted February 1937i The vapor-arc device covered by theA above-- mentioned Boyer-4 application was characterized by-a relatively-large spacing-between thestarting anode and the` cathode; asl compared withk the` spacing between the main*anodefand-thecathode; in-combinationwith suitable :shielding-means for' causingl thefbreakdown-discharge from thev start"-y ing anode to. always: terminate on the cathode, rather than ontheA mainanode; In this Boyer device, the-largc startingsanode spacingior dis= tanceldfrom theV cathode; was' the means fory reducingfthefvoltage necessary: t'o break-downA the gapbetweenv thestarting-anod-zc andi the cathode,-` because it produced" a relatively largevaliieA off the. pressure-distance prcduct'pd; since -thesam'evaporepressurenris: applicable, of "course, to -bothi the main anode-Y and the startingf-anode:

In accordance with our presentinvention,l we' dispense withthe-necessity=for having a relativelyT large startinganode spacing; byusing, instead1 a magnetic'ii'eld which causes the electrons to' moveiwith-an-oscillatoryrorspiral motion in reachingrA the starting-anode,l therebyy increasing" thev distancesathrough whichtherelectrons-move; and' thus; greatly increasing the: probabilityf of colli sions, so that the breakdown-voltage of the starteing-anode is: relatively low, notwithstanding f the fact thatsitmay havel a relatively-small l'physicai spacing from@ the cathode;

Qurl` invention isf desirablaas*` a substituteforthe` higheresistancedip-in typeoff igniterf make alive; in:asymmetrically'conductingJvapor-arc fda-i vices in:` whichV the cathode i comprises a pool' of mercury as:V described' in the'v above-mentioned S.lepang-Ludwig` patent; However, a probably moreimportant field loir/application'of our 'present inventionfis-in-connection with sing-le-anode'pcoltype; alkalismeta-l.. tubes, wherein: the discharge-- metalLiiszazmetalchosen:ironytha-{ncupcomprisingl the three heavier stable light metalsl of* the alkali-metall group, comprising cesiuin, rubiclifinnl and" potassium, asmore' particularly described' and claimed' invv an application of' Boyer andEMV Colaiaco, Serial No. 144,354', filed" lebruary" 15?,-r 1950; In` single-anode pool-type alkali-metal rectiers, some Vsort of spaced` starting-anode-y is a necessity,V because the previously knownl sein-i1 conducting ignitor-materials Hhave notibeenlusable in contact with the extremely chernic'aall'fyfactive` alkali-metals, cesium, rubidium or potassium.y which wet-almostanythinge, andsoalrupfnto the pores of'theI-igniter. Y

Ourinvention can be usedl with any one ci several' discharge-metals for; for-miner they vapor# izablereconstructing cathode -niateria'l, including` anymetals capable' ofi formingA a liquid pool? at" a' reasonable` temperature, andi also havingl; the necessary low-arc-drop characteristics; The-best" known discharge#metalsofI this type include m'er# cury, cadmium, cesium, rubidiunxr` and potassium: Our novel excitation-method@ is particularlwsigni'cant' in connection withl alkali-metal tubes;V of;` a type using- `a pcoltype'varopizablereconstruct@ ingfcathod'e-material' consisting ofi eithencesiurn; rubidiuni orpotassium. By a' pool-type'- tube or valve, we mean any tubegor valve in which thel actve cathode-material is both vaporiaableY and.

` reconstructing. It may'v bev` eitherA an operr pooli-V orfa spongeeheld' pool vinwheh'a` porous sulcsta-nv tially non-vaporizable material-` holds f at'j least* the" active: portion' of the vaporizable reconstructing; cathode-material; or #antlopen-pool havingther'ei-'n many'vertically=disp-osed liaiii'esiwhich` are spaced by Ydistances `:larger than the-capillary dimensions which distinguishaispongei-lkematerial Several illustrative formsof embodimentof'our present invention are shown in the accompanying drawings, wherein:

Figures 1` and zare-somewhat diagrammatic and? much simplified vertical elevations,l nott'o scale; illustrativeoi two different iormsof emibodiinentfofourinvention; and$4 VFigi 31 a schematica diagram ofi illustrative circuits and connections; which 1 are: usabile' with;

any ofthe forrnsfoff'embodiment of-rourjinvention and, which areishown in-Y Fig. 3,` in' connection with a siinpliiiec'ldiagrammaticfilli'istration:- not to fscale; of' a' third form 'ofembodiment off" our tube.

AsY shown inA Fig. 1, ournovelrectier-tube'is anasymmetrically conducting' vapor-arcdevice" which comprises-an evacuated'container-'Bhavmg two, and only two, main `el'ectrodes'l-andf3 thereV in; Ther main? metallic-portionsf oiftliefveva'cuated container 6 (as distinguished from the insulator or insulator-seal portions thereof, which will subsequently be described), are preferably made of iron or steel, although other metals could be used. Each tube thus constitutes a single-phase rectifier, for interchanging power between two circuits, such as an alternating-current circuit, and a direct-current circuit. In Fig. 3, the alternating-current circuit is illustrated as a threephase supply-circuit IB, and the direct-current circuit is indicated as a direct-current load-circuit Il; and a separate rectiiier-tube 6 is used for each of the three phases of the supply-circuit IB.

Each tube B is also provided with an auxiliary starting-anode I2, for the purpose of exciting the tube at the beginning of each conductingperiod of the two main electrodes l and 8. In accordance with my present invention, the cathode 8 is a pool type of cathode, and hence it is necessarily or preferably disposed below the main anode so that it is the lower one of the two main electrodes 'l and 8. The cathode-pool I3 'consists of a vaporizable reconstructing cathodematerial, which is preferably selected from the group comprising mercury., cadmium, cesium, rubidium and potassium, and which still more preferably is selected from the group comprising cesium, rubidium and potassium, with particular emphasis on cesium as the vaporizable recons tructing cathode-material.

As will be described in connection with Fig. 2, this cathode-pool I3 may be .an-open pool, but it is preferable, for a number of reasons, that the pool-material, or vaporizable Vreconstructing discharge-metal, should be held by a porous substantially non-vaporizable material in the form of a sponge or partition-filled structure with spaces of capillary dimensions between the partitions, as indicated at I4 in Fig. 1. This porous material can be one of the high-temperature conductors, such as molybdenum, tungsten, tantalum, ruthenium or carbon. The discharge-metal I3 saturates the cathode-sponge I4, but if there is a small amount more than necessary-it can collect in the space around the-rim ofV the sponge, or in any other suitable space which might be provided. f y

It is necessary that the discharge-metal I3 should wet the sponge, so that it will ow readily through thev capillary spaces thereof. When mercury is used as the vaporizable cathode, the sponge has to have a preliminary treatment with hydrogen at a high temperature, in order that the mercury may wet the sponge-material readily, but when either cesium, rubidium or potassium is used, it is not necessary to preliminarily treat the sponge since these alkali-metals wet other materials so easily. Y Y

The main anode l and the auxiliary starting-- anode I2 have to be separately insulatingly supported so that both are spaced and insulated from each other, and from the cathode 8. In the form of embodiment of my invention shown in Fig. 1, both of these insulating supporting structures are a part of the evacuated container 6. Thus, the main anode 'l is separated from the main cathode 3 by a glass-metal-seal- I3, I9, 2o, in

which thin metal spinnings I8 and 20 are sealed between a tubular glass memberA I9 and the main anode and cathode structures I and 8, respectively. When a chemically active dischargemetal is used, such as cesium, rubidium or potassium, the metal spinnings i3 and 20 of the seal should be plated internally with either titanium or zirconium, or perhaps with beryllium, or even chromium, as described in the aforesaid application of Boyer and Colaiaco, in order to prevent the reduction of the oxides of the glass by the chemically active discharge-metal when the tube is up to the correct operating-temperature.

Our starting-electrode I2 is disposed in the space between the main anode 'I and the cathode I3, and is illustrated as being supported by a stili rod 22 which extends through an inclined tubular projection 23 which extends out, on one side of the device, from the side Walls of the cathodemember 8, immediately above the cathode-pool I3.V This side-projection 23 is provided with a starting-anode glass-metal seal-

portion

25, 26, 21, which extends out from the tubular metal projection 23. The thin metal spinnings 25 and 2l are sealed between-the tubular glass member 2u` and the'starting-anode supporting-rod 22 and the tubular metal projection 23, respectively, in a manner already described in connection with the main glass-metal seal I8, I9, 2li.A

In the form of our invention Vwhich is shown in Fig. l, the upper main electrode or anode I has a hollow or tubular reentrant-portion 3| which extends down into the device from the top of the container. The active portionr of the main anode 'l is a flat metal piece l', which is secured to the bottom of the reentrant portion 3|. The main anode 'i is cooled by means of a cylindrical balile 34, which extends down into the reentrant anode-structure, so that a cooling-uuid (either gas or liquid) may enter over theY top. of the rectifier-tank 6, as shown by the'arrow 35,-being then directed downwardly,V by the `anode-baffle cylinder 34, so as to play on the active mainanode portion 'l' at the bottom ofr the anode, after which the cooling-duid is discharged upwardly out of the rectier-tank. Tovfacilitate the heat-exchange, the upper portion of the active anode-portion or main anode-plate I may be in good thermal contact with a heavy copper heat-exchange member 36, which is provided with fins 3l for facilitating the heat-transfer from the cooling-huid to the copper plate 36.

As explained in the previously mentioned Boyer application, the cathode-pool I3 should preferably be the coolest portion of the device, so that its temperature will be the condensation-temperature of the vaporizable reconstructing cathode-material, thus determining the vaporpressure p of the device. As set forth in said Boyer application, the cathode-cooling may be effected by means of a heavy copperA plate 38 which is secured in good thermal contact to the bottom of the cathode-header 8 which'lies underneath the cathode-pool I3. VThe, bottom of the heavy copperV plate 38is'in turn in good thermal contact with a removable copper plate 39 which is provided with cooling-fins 39 for keeping the cathode at the desired operating temperature according to the desired vaporpressure p of the device. I

Inaccordance with our Ypresent invention, we use some sort of magnet-means forestablishing a magnetic iield in the -vicinity iof'the startinganode I2, so as to facilitate a breakdown'between said starting-anode and the cathode-pooleV I3, in order thereby to initiate an arc between themain anode 1 and the cathode I3 at the beginning of each conducting period of the device. Various structures and arrangements may be used for providing a make-alive means which is composed of the combination of a starting-anode'andsome sort of magnet-means. V'Ihe general principle is that the starting-anode I2 shall be so'disposed' anode 'I.

that atleast a. portion of-themagnetic. eld 40. of themagnet-meansshall extend atan angle with respect to at least a portion of the electrostatic iield 4I between the starting-anode I2V and the cathode I3.

Thus, in the form of embodiment of our invention which is shown in Fig. l, the magnetemeans comprises two vertically disposed permanent

barshaped magnets

43 and 44. The top .magnet 43 is, disposed centrally within the reentrant anode with one of its poles, such as the south pole S (the polarity being immaterial), disposed on top of the flat active anode-portion I of the main The lower magnet 44 is disposed underneath the cathode-header 8', so that it presents, to the bottom of the cathode header 8", a pole (such as a north pole N) having apolar.- ity. opposite to the pole of the upper'. magnet 43 which is presented to the topof the active-anodeportion l of the main anode T.

Although the starting-anode I2 may have any shape and disposition that will produce an electrostatic field 4I which has a substantial component which is cut, at an angle, by some part of the magnetic eld 4G, we prefer to use some sort of' loop or ring-shaped arrangement for the active end or tip of the starting-anode I2. The inactive portion of the starting-.anode supporting-rod 22, which extends in the space between the main anode 'I and the cathode-poolV I3, is preferably shielded by a metal shield 46 which may be at substantially the cathode-potential, so as to prevent breakdown from this rod 22 to the cathode I3, as shown in each of the ilgures of our drawing.

In the form of embodiment of our invention which is shown in Fig. 1, the starting-anode I2 hasan active portion in the form of a horizontally disposed ring or loop-shaped member which consists essentially of two spaced electrically connected portions I2 and I2, which are joined at one or both of their ends by means of an end portion IZ". This loop is so disposed that a substantial portion of the magnetic eld 40 of the magnetic-means lt-44 flows through between the two spaced starting-anode portions I2' and I2.

When itis desired' to re the tube, the' startinganode I2 is made positive with respect to the cathode-pool l2 by about 3,000l volts, or any other suit-able make-alive voltage or voltage-impulse. The free-electrons in the electricor electrostatic field 4I will be accelerated, by said field, toward the positive ring, along the lines of the electrostatic; field, but because ofthe vertical magnetic eld 4i), the electrons are forcedv to move mostly at an angle tothe electric field. In doing this, the electrons move in a spiral or oscillatory path', going from side to side, and back again, before reaching the ring, so that the effective length of the electron-path is made large, in a small space, thus greatly increasing the probability of collisions, whereby more electrons and positive ions are-formed. The positive ions move tothe anode l" and'to the cathode I3, butmost of the positive ions moveto the cathode, because the anode is positive with respect to the cathode.

The resulting positive-ion bombardment, on both the anode and theY cathode, in this-abnormal magnetically induced glow-condition, causes a cathode-spot to quickly form on the cathode.

Occasionally, a cathode-spot may momentarily snot; has formed thereon, the .main anode 1 een pick up `an arc` therefrom, and instantly begin to .carry the main load of the device.

It ie desirable to prende some means fp r nre.- venting theV formation of a cathode-spot on the main anode 'I' duringthe non-conductinggperiods ofthe device, Various means to this end. maybe adopted. In Fig. 1, it will be noted that the ,ver-V tical magnetic eld of 4I! is substantiallyin.: align,- ment with the, vertical electrostatic ileld (notl indicated) between the main anode-.portion 'If and the cathode-pool I3,v so Athat the magnetic flux- 40' does not materially cut the electrostatic lines of force between the main anode andthe. cathode, and hence does not deflect the electrons moving in this eld, and does not'substantially reduce the normal breakdown-.voltage in the gap betweeny the main anode and the cathode, sothat this main-anode breakdown-voltage is considerably higher than the inverse or negative voltage which is applied to the main anode I during lthe non-,conducting periods of the device.

In al1 of' the forms of embodiment of our in:- vention, because of or use of a magnetic field, it is usually desirable to use non-magnetic mate! rial, such as stainless steel, for at least those portions of the container which are in the vicinity of the magnetic eld 4U. Thus, the active plateportion E of the main anode and thecathodeheader 8' may be made. of-stainless steel, or even the whole main anode I and the Whole cathode 8 may be made of stainless steel.

Fig. 2 shows a modiiied form of our invention, using a `sort of anode and grid-structure which is more similar to the typewhich has become standard in ignitrons of the kind covered by the Slepian-Ludwig patent. In this form of our invention, the cathode-portion 8 ofthe container G" is shown as a metal tank 48 having a metal top 49 which is provided with a central hole or perforation Eil. The main anode is shown as a solid anode-member 52, having an upwardly extending stem 53 which is supported from theupper, cap-Shaped spinning i8' of a tubular .upwar-dly extending glass-metal seal-portion I8?- I'f-Zil' which extends up from around the hole Sil in the top 49 of the tank 43. l

In Fig. 2, the main anode 52 is surrounded by a spaced conducting grid-.member 55, which is shown as being suspended from a metal ring 55 which is secured to the bottom of `the top 49 of the tank 48, so that the grid 55 is at substantiallyV the tank-potential, which is the cathodepotential of the device. The active reconstruct, ing cathodeematerial, in Fig. 2, is shown as an open-type. pool I3'.

In'Fig. 2, the magnet-means isshown as a permanent magnet 56 which lies horizontally, immersed in the cathode-pool I3', with its north and south poles N and S pointing upwardly and lying just below the surface of the pool; The starting-anode ring I2a is now disposed in a .vertical plane, so that the magnetic iux, from the magnet 5G, will flow horizontally through the ring, so as to increase the length of theelectronpaths in a manner already described.

By reason of the use of the anode-shielding grid E5, it is feasible to Vuse a larger spacing between the main anode 52 and the cathode-'pool I3', in Fig. 2, as compared to the spacing in Fig. 1, and hence there is ample room for the vertical disposition of theV starting-anode ring-IZa. According to this construction, a cathode'spot can be: formed on the poolesurface above either-pole of the magnet: if i` acconto If desired, in Fig. 2, suitable shielding-means may be provided, for preventing the formation of cathode-spots outside of the main or central cathode-surface. This shielding-means may take the form of an insulating ring 51, immersed in the cathode-pool I3 and surrounding the magnet 56. The insulating ring 51 may extend above the top surface of the pool and may be connected to the bore of an insulating washer 58 which overiies the top edges of the bore for preventing a cathode-spot from forming in this region.

In the form of our invention which is shown in Fig. 2, it will be noted that the starting-anode ring [2a. lies in a plane which is substantially in alignment with the electrostatic field between the main anode 52 and the cathode i3', so that the magnetic field extends at an angle to the electrostatic field of the main anode 52, as well as being at an angle to the electrostatic field of the starting-anode l2a. This circumstance might tend to produce cathode-spots on the main anode 52 during the non-conducting periods of the device, When the main anode is negative with respect to the cathode i3', if it were not for the shielding eiiect oi the grid 55, which is substantially at the cathode potential, and which thus kills the electrostatic field between the main anode 52 and the cathode-pool i3. With the cathode-potential grid 55 in place, the electrostatic field surrounding the main anode 52 extends only to the grid 55, and does not extend on, through the magnetic eld, to the cathodepool I3'. In this way, backiiring is prevented, during the nonconducting periods oi the device.

In Fig. 3, we show another means whereby backring may be prevented during nonconducting periods of the device, without having to rely, for this purpose, upon an anode-shielding grid such as is shown at 55 in Fig. 2. In Fig. 3, we show the magnet-means as a U-shaped electromagnet 6l, which is provided with an energizing-coil 62 so that the magnet can be deenergized during the nonconducting periods of the device, so that its magnetic field will not be present to reduce the breakdown-voltage of the main anode during the times when that breakdown-voltage is needed in order to enable the tube to remain nonconducting during the nonconducting periods when a negative voltage is applied to the main anode. The tube-construction which is shown in Fig. 3 is similar to that which is shown in Fig. 1, except that the two permanent magnets 43 and d4 of Fig. l are removed, the startinganode loop i2 is turned into a vertical plane as shown at I2a in Fig. 3 and as described in Fig. 2, and the electromagnet is placed underneath the cathode-header 8, so that it produces magnetic flux which threads horizontally through the vertically disposed starting-anode loop l2a.

Fig. 3 also shows a form ci electrical connection which is presented for merely illustrative purposes, as there are many forms of electrical connections which could be used with our invention. I It will be understood, of course, that the-electrical connections (minus the electromagnet-connections) which are shown in Fig. 3 could be used with either of the other forms of embodiment of our invention, which are shown in Figs. 1 and 2.

Fig. 3 shows the essential parts oi a complete three-phase system, using three tubes 6 of the type which we have just described. Current from the three-phase supply-line I0 is fed to the three main anodes 1 through a main transformer 53. in any of several well-known ways. The three 8 cathodes 8 are connected to a common cathodecircuit B4, which constitutes the positive terminal of the direct-current load il. The negative terminal of the direct-current load is the secondary neutral of the main transformer 63.

An exemplary excitation or iiring-system for the starting-anodes I2 or |2a consists essentially of a firing transformer 66, which is energized from the polyphase supply-line I6, and charges three firing-capacitors 61 through chargingrectiers E8. rI'he respective firing-capacitors 51 are discharged, at suitable times, to the respective starting-anodes l2 or 12a, by means of gridcontrolled tubes 69 which are provided with suitable phase-controlling means 1B for controlling the portion of the cycle in which each of the tubes 5 is started or iired, thus controlling the output-voltage of the rectifier-assembly. This is only one of several suitable firing-circuits which could be used for the single-anode rectiers 6.

Usually, it is desirable to provide, also, some sort of sustaining keep-alive means for keeping the main rectifier-tubes 6 from going out under very light load-conditions in the directcurrent load-circuit H. A suitable means for this purpose could include a line-energized lowvoltage transformer 13, the secondary terminals of which are connected to the three startinganodes i2 or ia through suitable isolatingrectiiiers 14.

Where electromagnets t! are used, as shown in Fig. 3, the three energizing-windings 62 may be energized, preferably only during half-cycle periods, or even shorter portions of each cycle, by means of a suitable step-down transformer i5, having primary windings which are energized from the supply-line iii, and having secondary windings which are connected to the respective electromagnet-windings 52 of the three tubes 6 through rectiers I8. Preferably, as shown, the secondary windings of the magnet-supplying transformer i5 are phased slightly in advance of the corresponding main anodes 'i of the respective tubes, so as to give the magnetic ux of the electromagnets 6l time to build up in time for the beginning of the half-cycle of positive voltage which is applied to the respective main anodes.

While we have described our invention in several much simplied and diagrammatically indicated exemplary forms of embodiment, with a single exemplary form of embodiment of a suitable electric-circuit connection therefore, we wish it to be understood that our invention is not limited to these details. We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

We claim as our invention:

l. An asymmetrically conducting vapor-arc device comprising an evacuated container having' two, and only two, main electrodes therein and also having an auxiliary starting-anode therein, the operating portion of one of said mainelectrodes including a vaporizable reconstructing cathode-material, the operating portion of the other one of said main electrodes including an active face-portion comprising the active main anode of the device, means for separately insulatingly supporting said main anode and said starting-anode so that both are spaced and insulated from each other and from the cathode, and make-alive meansV including a magnetmeans for establishing a magnetic eld whichls accepte tween said-starting-anode and said cathode `so as to facilitate a breakdown between said starting anodeand said cathode in order thereby toiniti- 'ate an 'are between the main anode and the cathode.

l2. The invention as defined lin claim 1,'char'actei-ized bya disposition of the starting-anode such that at least a substantial portion of the electrostatic 'field between the starting-anode and the cathbde is Substantially Out f alinement 'With the electrostatic neld between the main .anode and l'the cathode, and a disposition ef the inagnet-"means such that its magnetic Siield is .subvsta'nti'ally 'iin alinement with the electrostatic field between the main anode and the cathode.

3. The invention fas defined in claim 1, characterized by a disposition of the starting-anode such that at least a substantial portion of the electrostatic field between vthe 'staring-anode and the cathode is substantially in alinement with the electrostatic field between the main anode and the cathode, and a disposition of the magnet-means such that its magnetic field is substantially out of alinement with both of said electrostatic fields, in combination with means for preventing a formation of a cathode-spot on the main anode during the non-conducting periods of the device.

4. The invention, as defined in claim 1, characterized by a disposition of the starting-anode such that at least a substantial portion of the electrostatic field betwen the starting-anode and the cathode is substantially in alinement with the electrostatic field between the main anode and. the cathode, and a disposition of the magnet-means such that its magnetic field is substantially out of alinement with both of said electrostatic fields, in combination with an anodeshield for at times preventing a formation of a cathode-spot on the lmain anode during the nonconducting periods of the device.

5. The invention as defined in claim 1, characterized by said magnet-means being an elecfi.

tromagnet.

6. The invention as defined in claim 5, in combination with means for energizing said electromagnet in readiness for a make-alive operation and deenergizing said electromagnet during times when a cathode-spot might otherwise be produced on the main anode during the nonconducting periods of the device.

7. The invention as defined in lclaim J characterized by a disposition of the starting-anode such that at least a substantial portion of the electrostatic field between the starting-anode and the cathode is substantially in alinement with the electrostatic eld between the main anode and the cathode, and a disposition of the magnetmeans such that its magnetic field is substantially out of alinement with both of said electrostatic fields.

8. The invention as defined in claim l, characterized by the operating portion of said starting-anode comprising two spaced electrically connected portions, and a disposition of said magnet-means such that a substantial portion of its magnetic field flows through between said spaced starting-anode portions.

9. The invention as defined in claim 8, characterized by said spaced starting-anode portions lying in a plane which is substantially out of alinement with the electrostatic field between the main anode and the cathode, and a disposition of 1U the Vmag'net-lmearis such that its vn'la'gneti'c Yfield is substantially in alinement with the electro:- static field between the main anode and Vthe cathode.

10. The Yinvention as defined in claim 8, char--4 acterized by said spaced starting-anode portions lying in a .plane which is substantially Aparallel to the Vvactive 'cathode surface.

:1-1. The invention asV dened in claim V8, char-I acterized by saidspaced starting-anode Lportions lying ina .plane which is substantially -in 'aline- 'ment V'with 'the electrostatic field between the main'ano'd'e andthe cathode, and a disposition of themagnet-rneans such that its magnetic Vfield is substantially vout of :alinement with both of 'said electrostatic 'elds, -i-n combination with me'an's for preventing a frmaticn 'of yacathoda'spdt on the m'ain Vanode during the non-conducting periods `of thedevice.V :I l

."12. Theinvention as Vd'ened iin claim '8,clfiar'fi acterized by saidspaced starting-anode portions lying in a plane which is substantially in alinement with the electrostatic field between the main anode and the cathode, and a disposition of the magnet-means such that its magnetic field is substantially out of alinement with both of said electrostatic fields, in combination with an anode-shield for at times preventing a formation of a cathode-spot on the main anode during the non-conducting periods of the device.

13. The invention as defined in claim 8, characterized by said spaced starting-anode portions lying in a plane which is substantially normal to the active cathode surface, in combination with means for preventing a formation of a cathode-spot on the main anodes during the nonconducting periods of the device.

14. The invention as defined in claim 8, characterized by said spaced starting-anode portions lying in a plane which is substantially normal to the active cathode surface, in combination with an anode-shield for at times preventingl a formation of a cathode-spot on the main anode during the non-conducting periods of the device.

15. The invention as defined in claim 8, characterized by said spaced starting-anode portions lying in a plane which is substantially normal to the active cathode surface, and further characterized by said magnet-means being an electromagnet disposed outside of the evacuated container and having two spaced pole-pieces disposed so that north and south magnetic poles are formed at spaced places on the active cathode surface.

16. An asymmetrically conducting vapor-arc device comprising an evacuated container having v two, and only two, main electrodes therein and also having an auxiliary starting-anode therein, the operating portion of one of said main electrodes .including a vaporizable reconstructing cathode-material, the operating portion of the other one of said main electrodes including an active face-portion comprising the active main anode of the device, means for separately insulatingly supporting said main anode and said starting-anode so that both are spaced and insulated from each other and from the cathode, the operating portion of said starting-anode being substantially ring-shaped, and a magnetmeans for establishing a magnetic field extending substantially in an axial direction through said ring-shaped operating portion of the starting-anode so as to facilitate a breakdown between said ring-shaped portion and the cathode in 1 i" order thereby to initiate an arc between the main anode and the cathode.

17. The invention as defined in claim 16, char-- acterized by said ring-shaped starting-anode portion lying in a plane which is substantially parallel to the active cathode surface.

18. The invention as defined in claim 16, characterized by said ring-shaped starting-anode portion lying in a plane which is substantially normal to the active cathode surface, and further characterized by said magnet-means having two spaced pole-pieces disposed so that north and south magnetic poles are formed at spaced places on the active cathode surface, in combination with means for preventing a formation of a cathode-spot on the main anode during the nonconduoting periods of the device.

19. The invention as defined in claim 16, characterized by said ring-shaped starting-anode portion lying in a plane which is substantially normal to the active cathode surface, and further characterized by said magnet-means having two spaced pole-pieces disposed so that north and south magnetic poles are formed at spaced places on the active cathode surface, in combination with an anode-shield for at times preventing a formation of a cathode-spot on the main anode during the non-conducting periods of the device.

20. The invention as dened in claim 16, characterized by said ring-shaped starting-anode por.- tion lying in a plane which is substantially normal to the active cathode surface, and further characterized by said magnet-means being an electromagnet disposed outside of the evacuated container and having two spaced pole-pieces disposed so that north and south magnetic poles are No references cited.