US2679597A - Ion source - Google Patents

Description

May 25, 1954 c. M. TURNER ION SOURCE 2 Sheets-Sheet l` Filed Jan. 28, 1953 E] wwe/wwf' C/o/ence M Tar/7er May 25, 1954 M TURNER i 2,679,597

` 10N SOURCE Filed Jan. 28, 1953 2 Sheets-Sheet 2 e f M C/orence Turner* I m, 65M @iw Patented May 25, 1954 ION SOURCE Clarence M. Turner, Stony Brook, N. Y., assigner to the United States of America as represented by the United States Atomic Energy Commission Application January Z8, 1953, vSerial No. 333,709

13 Claims. (Cl. Z50-41.9)

This invention is a continuation-in-part of the invention disclosed in application Serial No. 574,156, filed January 23, 1945, now abandoned, and relates to gaseous electric` discharge apparatus and especially to an electric arc discharge apparatus capable of producing in quantity a substantially continuous supply of gaseous ions under vacuum. More particularly, the electric arc discharge apparatus of the present invention is designed primarily for generating substantial quantities of metal ions, as are required, for example, in apparatus for separating or concentrating the isotopes of metals such as copper 63 and 65, cobalt 59 and 60, or uranium 234, 235, 237 and 238 by appropriate selective operation upon ions of different atomic mass in an ion beam. The separation of such isotopes is important to provide quantities of a selected isotope for research, medicinal or industrial purposes such as radiography. This may be accomplished in accordance with this invention by bombarding a vapor containing the several isotopes of the metal with the electrons of an arc discharge established between noniilamentary electrodes one of which is thermionically emissive and maintained so by the alternate electron bombardment of this electrode and another thermionically emissive electrode that results when these electrodes are connected to an alternating voltage.

One type of isotope separating or ion-classifying apparatus in which the ion source of the present invention may be advantageously used may be found described and claimed in a Patent 2,606,291 issued August 5, 1952, to Robert R. Wilson. This ion-classifying apparatus may consist essentially of an evacuated and sealed chamber, that may be cylindrical and of predetermined proportions, for supporting the ion source and its ion accelerating electrodes at an end thereof, and for supporting equipotential bunching electrodes at a predetermined distance spaced from said accelerating electrodes and maintained at the steady state potential to provide a iield free space intermediate the accelerating electrode and the buncher structure for the flow therethrough of the accelerated ionized particles. An alternating radio frequency potential of small amplitude and preferably saw-tooth wave form is applied to the bunching electrode for periodically impressing increments of velocity both positive and negative upon the ionized particles passing therethrough to cause these particles to bunch together in accordance with their mass. A radiofrequency alternating potential is applied also to a deiiecting electrode that is supported within the chamber at a distance spaced from said buncher electrodes to yprovide a substantial field free space of definite length immediately following and adjoining said bunch electrodes. This alternating potential is synchronized with the buncher potential to deflect the grouped ions enriched with the desired isotope of the ionized material into a collecting pocket or cup positioned at or adjacent the end of said chamber.

That the operation of an ionic mass separating device such as that described above (or other types employing cooperating electric and magnetic fields for classifying ions) may be eectively employed on a production basis it is essential that the ion source utilized in the device be capable of continuous operation for long periods without serious deterioration of the arc lelectrodes, to supply the ions necessary for large scale separation of the isotopes of the ionized material.

Prior to the present invention one effective procedure for producing ions of a metal has been to bombard the vapors ofthe metal or of suitable volatile salts of the metal by the accelerated electrons of an arc discharge established between a lamentary cathode and an anode. In these procedures, particularly the procedures where metallic vapors are generated by depositing controlled quantities of the metal on the anode. the filament becomes contaminated with the source metal since it is exposed directly to the anode where the source metal is being vaporized. This contamination has in certain instances caused the filament to burn out after an operating time of only two hours.

Furthermore, when a fllamentary cathode is used with direct current heating, the effect of the arc current flowing through the filament is to make one end hotter and the other end cooler, since in one end the filament and arc current are in the same direction while in the other end they are in opposite directions. This increase in heating of one end causes the lilament to burn out more quickly than if the heating were uniform. Attempts to eliminate this unequal heating by utilizing an alternating current, for example, for heating the filament, have been unsuccessful because the alternating current produced large fluctuations in the ion output.

It has been discovered from observing the results of arc operation on the lament that ode.

considerable amount of powermustbe-supplied to the filament to heat it to desired emission temperature. When direct heating of the cathode is used, as in the filament type of arction sources, the power required represents many hundreds of amperes preferablypdirect;current, at the relative low potentialo'f avolt or `two. Suitable low voltage sources "capable Jof sup-- plying this current magnitude present power supply problems that are :t-avoided 1in -this invention.

In the course of investigations undertaken rto extend the life of the electrodes of an arc discharge capable Aof producing gaseous zions ,of "a material that' is normally'solid and vaporizable undervacuum4 only with the application .ofrhigh temperatures, it was discovered :that a .satisfactory operating timefor these arc electrodes,

greater by Aa factor of three,:than that iobtained formerly, could be realizedby utilizinganf'arc 'cathodesheated to electron emissive temperatures byzthebombardment-thereof of accelerated electrons emitted from a lamentarycathode. .It

waszfound that a'platform cathode could'thus be' `utilizednand'heated` uniformly by .the electron vbombardment `from ,a heated filament -so `that the platform could be vpositioned intermediate theanode and'filament to protect orlshieldvthe -filamentary .cathode from 'the' vapors within the varc region, thus'reducing ,the contamination of filament by .these vapors. IIt will be observed,

Aof course, 'thatthe unequal heating ofthe ila- ,ment vby ,the arci-and heating `current'is eliminated through the employment of such an;in

directly heated arc cathode.

`Ion' generatingiapparatus developed as a. result of this discoveryand of ya type `similar `to that described'and claimed in a copending application,` S. Nul-371,981, filed May 241946,was found :also to'havezotherconcomitant advantages. .It

and -concomitant advantages possessed .by `this arc source of ions employing .the vindirectly heatedcathode,it'wasfound that this source failed to avoid entirely the disadvantages attendant the use ofa heated filament, e. g. it was found .that after prolonged operation the `arc vcathode would eventually allow suflicient vapor to get to the heating filament vto establish an arc between this filament and the main cath- Furthermore, although alternating current could -be used to heat the filament the necessity for a low voltage power source capable hundred amperes was `not avoided.

When 4these disadvantages were .noted to pergist, further research leadingto the present invention was undertaken. It occurred to me that`the necessity for continuing the supply of heating current to the filament could be dispensed with if the arc cathode could be heated by using an alternating current between the filament and the arc cathode. Attempts to so heat the cathode by means of alternating current were initially unsuccessful however because the relectron bombardment of the filament on the'reverse cycle `was suflicient tomelt the lament. After the idea of utilizing two somewhat 1-10 rmassive non-lamentary cathode structures for alternate bombardment with electrons was hit upon, and found to avoid the previously encountered 'di1iculties; it appeared desirable for =reasons of greater stability and longer life of '15 the 'heating element, to attempt the development of an indirectly heated arc cathode which 5would=preventat least for a prolonged period of operation, the penetration of the isotope metal vapors to the heating element; accordingly it was proposed to make the arc cathode @completely lcontain 'or enclose the intermediate or secondary cathode and to be so thick as to ,be substantially impenetrable.

-Thus :thearc electrodes of the ion source of the presentinvention were developed and com- -prise specifically an'arc cathode constructed vof a'largerod of tungsten, for example, provided ywithan axial hole in one end thereof for containing a second intermediate cathode also pref- .30 erably of tungsten. A loop filament surrounds the arc cathode 4for producing the electron ybombardment-for initially heating the arc cath- Iode to electron emissive'temperature, after which the filament is turned off and the heating maintained by connecting between the hollow lthimble- `likefarc cathode and the rod a source of alternating potential.

It was observed that, as a result of its smaller `mass, the intermediate rod cathode was heated .4U :to 1a higher temperature than .the outer and larger arc cathode upon equal electron bombardment. lIt was discovered that .this inequality in heating could be eliminated by having the source vof A. C. feeding the cathodes controlled by'thyratrons, or other gaseous discharge device f4" insuch a waythat the power fed into the thimble fand that fed into the1rod could be independently controlled.

.It `will be apparent from the foregoing there- 'fore vthat thisinvention has for its purpose the attainment Aof the following objects:

First, Vto provide an improved non-lamentary sourceof electrons for an arc discharge device;

Second, to provide an improved nonlamentary source of electrons having a large emitting area for supplying a uniform and copious supply o'f electrons to an electric arc discharge device `thereby .enabling .the 4arc to be started more fjeasily;

lfI'hird,..to provide an improved electronxsource v:for usein .an Varc discharge device capable of Acontinuous `operation 'for long periods in the presence of `corrosive vapors through which the -arc .discharge is established;

5 Fourth, to vprovide a non-lamentary source of electrons for an arc discharge device that is operable on alternating currents at moderate voltage magnitudes to avoid the disadvantages concomitant with the electron sources operable of supplying continuously currents of Vseveral 570 omyfrom 10W voltage Sources capable of sup- Vv arc discharge, is heated to electron emissive temperature as a result of mutual and alternate electron bombardment produced between it and another electrode spaced from the arc cathode and shielded from the region of the arc discharge by being contained within said arc cathode;

Sixth, to provide a control means in a source of electrons for an arc discharge device which will permit an independent control of the emission temperature of each of two spaced electrodes that are maintained electron emissive by mutual and alternate electron bombardment on alternate half cycles of an alternating potential supplied to these electrodes.

A further and more specific object of this invention is to provide an efficient andl copious arc source of ions of a material that is normally solid and vaporizable under vacuum only with the application of high temperatures that employs an improved electron source for the arc that is operable on alternating current and of increased life.

Further objects and many of the attendant advantages of this invention will be appreciated more fully as the same become better understood by reference to the following detailed description of a preferred embodiment, when taken with the accompanying sheets of drawing wherein:

Figure 1 is a detailed elevational View of a preferred embodiment of the present invention shown largely in cross-section the section being taken on lines I--I of Figure 2;

Figure 2 is a cross-sectional end view taken on lines II-II of Figure 1; and

Figure 3 is a Wiring diagram illustrating the operation of the present invention.

Referring now to the drawings and more particularly to Figures l and 2, the ion source illustrated is to be positioned within one end of an evacuated chamber housing the ion utilization apparatus, preferably by being supported within the insulated tubing I of quartz, porcelain, or other suitable refractory insulating material, to insulate the ion source unit from the evacuated chamber so that it may be maintained at a high positive potential, of the order of 20,000 volts,

relative to an accelerating electrode II which isv indicated only schematically, to provide the electric eld for withdrawing the ions from the region of the arc and accelerating these ions to a high velocity. More specifically, the ion source electrodes are shown supported and sealed in a water cooled metallic end plate I2 in insulated relation therewith, and this end plate is provided with a circular groove I2 into which the ceramic supporting cylinder Ill is inserted and sealed by means of the gasket ring I3 adapted to be cornpressed by an annular packing gland, not shown, to maintain the air tight integrity of the chamber.

The end plate I2 is shown provided with a centrally disposed opening I4 drilled therein for supporting the refractory insulating bushing I5 and the concentric and spaced apart metallic tubes I6 and II that are partitioned longitudinally for a substantial distance of their length to provide a supply and return conduit for the circulation of a cooling fluid for cooling a chuck I8 that is shown inserted into the ends of these tubes and a cathode 20 which it supports. The chuck I8 has a central opening I9 for receiving the thimble arc cathode 20 of tungsten or other suitable electron emissive material which is held in place by radially directed set screws of which 2| is representative. As an aid in the support of the insulating bushing I5 and the concentric tubes I E and I'I a cylindrical metallic sleeve 22` is shown welded to the outside surface of the end plate I2 concentric with the drilled opening I4. The opening in the free end of this sleeve 22 is enlarged and tap threaded to receive the packing gland 23 for forcing a gasket material 24 into intimate contact with the insulating bushing to provide an airtight seal at the end of the bushing that projects through the end plate and to the high pressure end of this sleeve.

In the interests of simplicity of illustration no seal is provided for the surface between the insulating bushing I5 and the outer metallic tube I6 although it is apparent that in the eventi an airtight fit between the contacting surfaces of these members cannot be maintained otherwise, a suitable sealing gland may bel easily installed.

An intermediate auxiliary or second rod cathode 25, also of tungsten, is shown supported to extend Within an opening 21 drilled in the end of the main arc cathode 20 preferably by means of the electrolytic drilling process in spaced and insulated relation with the arc cathode and its supporting structure. Accordingly a chuck 26 for supporting the rod 25 is shown supported coaxially within the tube I'I through a flanged insulated bushing 28 and metallic sleeve 29.

More precisely, a pair of coaxial and spaced' apart tubes 30 and 3| support the chuck 26 Within the sleeve 29, to provide conduits for circulating cooling fluid through the space 32 intermediate the tubes to cool the cathode rod 25 where it is supported in the chuck to prevent warping of this rod at its support. One effective l way of providing for the flow of the cooling uid through the space 32 is to have the annular space formed by the coaxial tubes partitioned circumferentially by means of a pair of diametrically spaced wires having a diameter equal to the radial spacing of the tubes and of a length substantially equal to the tube lengths so that they will extend longitudinally down the space 32 to terminate just short of the end of the tubes. Accordingly the tubes 3|| and 3| are shown provided with entrant and exit tubes 33 and 34 respectively for this cooling fluid.

Inasmuch as the space between the rod 25 and thimble cathode 20 must be evacuated if heating by electron bombardment is to be effective, the chuck I8 is shown provided with a plurality of radial openings 35 that extend from this space to the exterior surface of the arc cathode to communicate with the chamber of the ion utilization apparatus that is connected to a suitable pumping apparatus for continuous evacuation.

Furthermore, the high pressure ends of each pair of tubes I B, I1 and 30, 3| are shown provided with packing glands 36, 31 for sealing the ends of each surface of tubes I6 and 30, respectively, to the flanged insulated bushing 28, and the metallic sleeve 29. Furthermore the high pressure ends of the tubes 30 and 3| are sealed olf as at 38. To complete the insulation between thimble and rod cathode, and to secure an inner airtight seal of the space between the metallic sleeve 29, and the insulated bushing 28, as well as the space between the chuck I 8 and insulated bushing 218, the chuck and flanged bushing are each shown provided with circular recesses 4I and 42 formed in their end surface for receiving sealing rings 43, 44 and opposite ends of a glass cylindrical insulating sleeve 40. The insulated bushing 28 is provided with a ange 45 against which the packing gland nut 36 is forced to sealithe glasssleeve' 40= betweenthe opposite sure facesfcontaining` thef recesses 4I .and .42 by com-V consisting cfa-tungsten wire 50 encircling the.

thimble .cathode 20 and spaced radially a short distance from it, and at one side of the region. of the anode wherein the arc is established. Opposites` ends-ofthe-.,lamentary vstartingcathode 50 are. supported .by the. lead-in conductors.

5I which are sealedzandinsulated in.:their pas.

sagefthrough'theend:plate-..I2;V by a bushing39.. of, suitable refractory insulating.V material and. gland 49, shownin. cross-section. in-Figure 1, as: being similar in construction `to that employedI forsealing and insulating the tube-.IE-in the pas?- sagethrough theY end: plate- I2; It being understood thatfother'insulated seals-4 may be employed:

and-also. thatan-.additionalfseal for each bushing 39. and conductor 5I may-be provided if necessary to maintainthe chamber airtight. ".l'heY atitssupport towpreventwarping ofeither the` cathode orthe anode.

To feed metal tothearcas needed, an. appropriate supply,device.has-been provided. By Way of example, one suchdevicemay comprise a'feefly tube or duct-` 53 .extending thrQugnthe-tube 5d A which is -sealed andsupp0rted tinthe .endplate I2 by means of the packinggland-55, said ductbeing shown .terminating-ata .point at .the .edge of and slightly. abovethe. platform 46. A wirei orribbon of metal 56 which maybecopper, ura i nium or cobalt .for example, mayv beadvanced continuously or in.l successive steps` as. desired, through this -tube..53 .to the-.upper surface of the platform. A.cooling.tube..51 is shown extending,- through thetube 54 in contact-With the feed tubel 53 .for the circulation therethrough. `of a` cooling iiuid for preventingr the` W-irefrom becomingheatedin theieedtube--to deleteriously effect the feeding operationthereof.

It .will beappreciated thatvarious-.supporting and feeding structures tobeamounted. inf-the end plate. I2 may include. suitable insulating sealing or packing means (not shown) whereneeded, `in accordance with theusualpractice for vacuum typeapparatus. Although mechanical wire-advancing means, e. g. including a reel and .motor driven rollers drawingthe wire. from the reel and pushing it through the tube53 (such Vparts being insulated. and enclosedv in a communieating evacuated housing if desired) may be employed in some cases to feed the wire continuously, Satisfactory` resultsv canbe obtained also by utilizing a. timing device set to operate the. feeding mechanism intermittently at the desired time intervals.v

" cathode of the tube 6I.

Referring.. now4 to.Figure.3.fof` the. drawings. thereis..shown.in. the wiring diagram.one..conf. venient .way of yconnecting an. alternating, volt-I age to the two/cathodes -toproduce the alter.- nate electron bombardment on opposite half.V cycles thereof that includes also a means Whereby the power input.into..each.of. the. cathodes may be independently. controlled. It willV be. clear that the cathodes20. and25 areconnected.

l* tothe A. C. supplyA source throughavariable.

autotransformer 60, for example, to provide .a control of the magnitude of the applied. alter nating voltage. As shown,A the rod. cathode 251 isfconnected directlyto the A. CL supplywhereas. the thimble cathode 20 is connected. tothe A.l C. supply through a pair of gaseous discharge tubes 6I and62, oneofwhichisinverted. rela.- tive to the other to provide` a currentconductive path onV alternate cycles. The discharge.

tube 62 is merely a rectier tube .connectedto provide a conductive path for ow of electrons: from the rod cathode 25 to the thimble arc cathode 20 during the `portion of the cycle. of the alternating voltage applied r thereto,` that I the thimble is positive relative to the rod. Theballast resistor 63 is provided merely to limit the current to a sale value. The gaseous discharge tube 6I is grid controlled-and may be rendered conductive at selective points in the cycle of-the alternating voltage when the rod 25 is positive relative to the thimble 20-by adjusting the phase of the grid and platel potential for example, to control the heating of the rod 25 independently. of the heating of the. thimble 20. A suitable phase control circuit consisting of an adjustable series resistance 65, and adjustable reactance 65 is provided and is shown energized from a secondary 61 of a transformer 68 in series with` a center-tapped resistor 69 connected to the The grid 'I0 of the tube 6I is connected into the phase control circuitat the junction of the series connected resistor 65 and reactor 66 through a resistance 'II vwhich is provided merely to limit the grid current to a safe value after the tube res.. This series resistor 1I may of course be omitted if both impedances 65 and 66 are at all times large enough to limit the grid current. The phase of the grid voltage and time4 of firing of the tube 6I is of course controlled byv changing the magnitude of the resistor 65 or of the reactor 66 in accordance with well-known practice.

In operating the apparatus a switch S1 isv rst closed to connect the filament of the starting cathode 5U to a source of heating voltage 'I2ito supply 'I3 so that the thimble 20 is. at a positive electrical potential relative to the filament to provide the accelerating voltage for the thermionic emission of the cathode 50 to cause the electrons thereof to bombard the thimble to heat 1 the thimble to electron emissive temperatures.

After the thimble 20 is thus heated to a desired electron emissive temperature, switch S4 may be closed to connect the thimble cathode 2G' and rod cathode 25 to the source of alternating voltage the amplitude of which is controlled through the variable autotransformer 60, to cause the electrons of the thimble to bombard the rod to heat it also to an electron. emissive temperature, after whichthe emission of each the. thimble.26.and rod 25 may be sustained by the'mutualbom- 9 bardment by electrons of the tllimble and rod on alternate half cycles. The switches Si and S3 are then opened to remove the source of heater voltage from the filament and to disconnect the filament from the source of electron accelerating voltage. Switch S5 may then be closed, in the event this connection has not been previously established, to connect the arc voltage between thimble arc cathode 20 and the platform anode 46. The establishment of this arc running to the anode upon which has been deposited controlled amounts of the isotope source metal, results in the vaporization and subsequent ionization of this metal by electron bombardment of the vapors thus produced. The

CII

ions thus formed are withdrawn and accelerated in the form of a beam through a suitable accelerating electrode schematically indicated by the cylindrical shell Il by means of the high negative potential 13 to which this electrode is connected.

In View of the foregoing description, it will now be apparent that what is illustrated and described is but a preferred embodiment of this invention that has been constructed and successfully operated wherein the main arc cathode' comprises a tungsten thimble made by electrolytically drilling a hole 1A; inch in diameter and 11/2 inch deep centered in a tungsten rod 1/2 inch in diameter by 2 inches long; and wherein the intermediate cathode comprises a 15G-milA rod, also of tungsten which projects into this hole to within l/g inch of the end and serves as the heater for the arc cathode in the manner described above. It is conceived that this structure illustrated may be modified in substantial meas" ure and applied to other uses without departing,

however, from the spirit of and scope of this invention as deiined in the subjoined set of claims.

I claim:

1. In an arc source for producing ions an electronic discharge device comprising an anode, a first and second thermionically emissive electrode, starting means for initially heating at least one of said electrodes to an electron emissive temperature, means for applying analternating voltage between said first and second electrodes to cause the electrons emitted by an electrode rendered electron emissive by said rst named means to bombard the other of said electrodes to heat said other electrode for sustaining the emission of both of said electrodes by mutual electron bombardment thereof on alternate half cycles of said alternating voltage and independently of said rst named means, means for producing an arc discharge between one of said electrodes and said anode and means for introducing into the region of said arc discharge a vapor of the material to be ionized.

2. The combination dened by claim 1 above characterized further by the addition thereto of means for controlling the thermionic emission of said electrodes relative to each other comprising means for controlling the magnitude of said alternating voltage and means for selecting the point in the half cycle of said alternating voltage that the electrons emitted by said first one of said electrodes are made to bombard the second one of said electrodes, while maintaining throughout the complete other half cycle of a1- ternating voltage the bombardment of said rst electrode by the electrons emitted by said second electrode.

3. An electric discharge device comprising a main hollow cathode, an auxiliary cathode lnsulatingly supported within the main electrode,

a gaseous medium disposed adjacent said main cathode, means including a iilametary element surrounding said main andl auxiliary cathode for rendering said main cathodes electron emissive, said auxiliary cathode being shielded from said iilamentary element by the main cathode means including a source of alternating voltage connected between said cathodes for producing an electric discharge running from said main to said auxiliary cathode to heat said auxiliary cathode to an electron emissive temperature, whereby the emission of said main cathode will be maintained by the bombardment of electrons from said auxiliary cathode on alternate half cycles of said alternating current independently of said lainentary means, and means for directing electrons emitted from said main cathode into said medium, whereby to ionize said medium.

4. The combination defined in claim 3 above characterized further by the addition thereto of means in circuit with said auxiliary cathode for selecting the portion of the alternating voltage cycle that the electrons of said main cathode bombard said auxiliary cathode while maintaining the bombardment of said main cathode by the electrons of said auxiliary cathode throughout said half cycle of said alternating voltage that the main cathode is positive relative to said auxiliary cathode.

5. An electric discharge device comprising a first cathode, an anode, a second cathode disposed intermediate said first cathode and said anode, means for rendering one of said cathodes electron emissive, means for applying an alterhating voltage between said first cathode and said second cathode whereby electrons emitted `from the cathode rendered electron emissive bombard the other of said cathodes to raise said other cathode to an electron emissive temperature, means for producing a vapor of the material to be ionized in the region disposed between said second cathode and said anode and means for producing an arc discharge between said second cathode and said anode through said vapor containing region to ionize said vapor.

6. A11 electric discharge device comprising an evacuated sealed chamber, means for introducing a gaseous medium to a region within said chamber, a hollow main cathode supported adjacent said region, an auxiliary cathode completely contained within said hollow cathode to be shielded thereby from said gaseous medium, means for initially rendering one of said cathodes electron emissive, alternating current means for sustaining said electron emission of both said cathodes independently of said first named means by the mutual electron bombardment thereof, and means for directing into said region electrons emitted by said main cathode whereby gas in said region is ionized.

7. The combination deiined in claim 6 above characterized further by the addition thereto of means for controlling the electron bombardment of said cathodes relative to each other to control the degree of heating thereof.

8. An electric discharge device comprising an evacuated sealed chamber, means for introducing a gaseous medium into a region within said chamber, a hollow rod arc cathode, an auxiliary rod cathode disposed therein, a iilamentary cathode spaced radially from and surrounding said hollow rod cathode, means including a source of electric power for raising the temperature of said lamentary cathode to render it electron emissve, Ameans including a `voltage source for bombarding 'said' hollow'rodcathode with elec- 'trons emitted 'from `sai`d "lamentary cathode, 'whereby said hollowV rod cathode is rendered electron emissive, vmeans including a source of alter- 'nating voltage connected between said hollow rod arc cathode and said'auxiliary rod cathode for producing an electrcdischarge from said arccathode to said`auxiliary cathode whereby vsaid'auxiliary catho'deis' rendered electron emissive'for sustaining the 'electron emission of both 'said .arc cathode and auxiliary cathode independently of said`la'ment` by the mutual electron` bombardment thereof on alternate half cycles of saidalt'ernating voltage, and means 'for directing electrons'emitte'd by said arc cathode into said region to ionze 'said gaseous medium. 9. An electric .discharge device comprising a .pair of'thermionically emissive'electrodes, means ttor-initiating thermionic emission'from at least "one ofsaidelectrodes, means including a source 'of alternating voltage between said electro'desor 'causing the'electrons emitted by one electrode to bombard`the other of said electrodes to heat saidotherelectrode and sustain by mutual electron bombardment' the emission of both of said electrodes. and a grid`controlled gaseous electric ldischarge'fdeviceseries connected between one of said' lelectrodes' and said 'source for controlling the portion of the half cycle ofelectron bombardmentof one' of saidelectrodes, whereby the power inputto' said one of said electrodes may be con- `trolled`independently of said other electrode.

10. AIn an are sourceorjproducing ions, an

electronic'discharge device comprising first and 1 secondele'ctrodes, means forinitiating' thermionic "emission vfrom'at least'one of said electrodes 'and `means for "sustaining the emission thereof by mutual electron' bombardment' of said. electrodes,

lf2 "meanssupporting' one .of' saidelectro'desrendered -electron emissive within a, 'region 'containing ya gaseous medium, means for 'directing electrons from one'said electrodeintosaidregion whereby said gas insaid' region is ionized,Y and means-for controlling :the electron bombardment of :said electrodes relative' to "each 'other Nto' control the degree of heating thereof.

' 11. 'An electronic discharge 'device-'comprising a "pair "of thermionic'ally "emissive electrodes, "a gaseous "medium disposed Aadjacent 4one "of said electrodesfmeans including :a'source of^ alternating'voltage connectedV betwen saidpelectro'des'for rendering `said electrodes electronic lemiss'rva meansfor'directingelectrons emitted by saidone electrode into 'saidgaseousmedium whereby'said "gas is ionized, "and :means Jforwzontrolling uthe 'lthermionic "emission 'temperature of 'said electrodes relative tov each other.

'12. An `ion generating "device comprising "a .sealed chamber, a relatively massive cathode 'withinsaidnhambenan auxiliary vcathode with- ;"in said'main cathode and completely 'shielded "thereby,"'means'for initiallyrendering oneof said cathodes electron `emissive, alternating 'current means connectedto said cathodes for sustaining said electroniemissionindependently of' saidvrst :means 'by` the -mutual n'electronic bombardment w thereof an anodespaced'ffrom 'saidmain catho'del andmea'ns forstrikln'g an arcf"discharge"be 'tween said' arc `cathode and' `saicl'anode.

13. Thestructure Lofclaim 12 including means "forintroducing a materialto'be'vaporzed and ionizedwithin said sealed chamber and said anode beingv in'the form of a" platform positioned to 'shield' said'man cathode'from said materiales "it' 'vap'orizes 'Norreferencescited

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