US3005931A

US3005931A - Ion gun

Info

Publication number: US3005931A
Application number: US18461A
Authority: US
Inventors: Raphael A Dandl
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-03-29
Filing date: 1960-03-29
Publication date: 1961-10-24
Anticipated expiration: 1978-10-24
Also published as: GB916854A; NL260940A

Description

R. A. DANDL Oct. 24, 1961 'ION GUN 2 Sheets-Sheet I Filed March 29, 1960 INVENTOR.

Raphael A. Dond/ ATTORNEY R. A. DANDL oct. 24, 1961 ION GUN 2 Sheets-Sheet 2 Filed March 29. 1960 mumDOw ZO INVENTOR. Raphael A. Dand/ mmnow 2@ ATTORNEY United i States Patent O 10N GUN Raphael A. Dandl, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Mar. 29, 1960, Ser. No. 18,461 6 Claims. (Cl. 315-111) This invention relates to apparatus for the production of an electrically neutral ionized plasma. Such a plasma may be used in a variety of accelerators, mass spectrometers, high temperattnechetniealreactors, and other electrical devices.

In conventional practice, a plasma is usually accompanied by an energetic electron beam, and the plasma is commonly contaminated with varying amounts, of neutral gas particles. Collision processes of the neutral gas particles and other attendant phenomenon seriously alter the behavior of the plasma and :may render such a plasma uniit for various uses. In conventional practice a plasma may be generated by electron bombardment of gas molecules as in an arc discharge such as disclosed in the application of John S. Luce, Serial No. 833,897, iiled August 14, 1959, now Patent No. 2,956,195, issued October 11, 1960. However, the discharge of this application and other similar discharges are not free of objectionable neutral gas particles. Still another characteristic of these prior discharges is that the voltage applied between widely spaced electrodes to produce the discharges causes contaminants :from the electrodes to be introduced into the .ICC

Y the annulus. The 'gas fed to the manifold is withdrawn therefrom into the annulus between the anode and cathode by the pressure differential thereacross and is substantially ionized by the arc discharge across the annulus. It has been determined that the plasmay produced by the apparatus of this invention will attain a reasonable density and stability when the immediate electrode is aligned with the annulus, 'for any given rate of -gas feed andmagnetic field strength. The existence'and positioningof the intermediate electrode isV a critical feature of the present invention. Little, if any, plasma is produced when this i electrode is o mitted. Furthermore, when this electrode extends into the oteradia) portion 'of tire manner" TW rf-** that the annulus between the cathode and anode is not shadowed, the resultant plasma is small and extremely unstable. Thus, a satisfactory plasma can be obtained only when the intermediate electrode is essentially aligned with the annulus or is recessed into the inner portion of the manifold. The thus formed plasma is withdrawnfrom the annulus by thecombined effects of -thepressure differential and the magnetic iield.

The ion gun of this invention is considered suitable for providing a plasma toV be utilized in Va variety of devices characteristically similar in that a plasma, i.e., an electrlcally neutral mixture of ions and electrons, is employed therein for sundry purposes. Electrically neutral plasmas are of interest in-the thermonuclear iields and for experimental purposes; while charged ion beams, which may be produced by charge separation and/or charged particle acceleration treatment of neutral plasdischarges and also causes electric iields within the dismas, 'may be @56d ill Cllalged Particle aclel'als, maSS charges, particularly along the discharge, thus--resalting-inw.SQGCIGDJGCIS and the llli-V certain instabilities therein. In addition, xuse Vof Widely spaced electrodes in these prior discharges resulted in the necessity for providing very special baiiles and differential pumping means to insure stability of the discharges,

With a knowledge of the limitations of prior devices in the production of a plasma, it is a primary object of this invention to provide an ion gun for productionof a well defined, relatively uncontaminated plasma.

It is another object of this invention to provide an ion gun for production of a plasma that is characterized by very little extraneous electrical fields, particularly longitudinal electric vfields along the plasma. y It is still another object of this invention to provide an ion gun for production .of a plasma that requires no special baliles ordiierential pumping means, and in which very little electrode material is introduced into the plasma during operation of the ion gun.

These and other objects and advantages of this inven- 5 tion will become apparent upon consideration of the' following detailed speciiication and the accompanying drawings wherein: y Y

FIG. 1 is a cross sectional view of a preferred embodiment of the-inventicnandsn- FIG. 2 is a cross sectional view of chine utilizing the device of FIG. l.

The above objects have been accomplished in the present invention by providing an evacuated system in which f there is contained an ion gun for producing a plasma and a region where the plasma isto be utilized. The ion gun comprises an anode and a cathode mounted in concentric relationship with a narrow annulus therebetween. The facing surfaces of the rear portions of the anode and cathode are recessed to form an annular manifold. Positioned within this manifold is an annular intermediate electrode aligned with the annulus between the anode and cathode. Gas is fed to the manifold and an arc discharge is established between the anode and cathode. A pressure differential is established along theV annulus by the evacuated system anda uniform magnetic iield is established so that the -eld lines traverse and are parallel to a mirror type mau It is one aspect of this invention to utilize the ion gun Y 1n a magnetic mirror type thermonuclear machine. When so used, the ion gun is positioned at about center of one of the magnetic -mirror regions` to assure as uniform a magnetic iield as possible in the manifold and annulus regions of the ion gun. The resultant hollow plasma will follow the field lines and will terminate against some form of bathe placed in or near theV second magnetic mirror region. This plasma may then be used as a means for lthe breakup of molecular ions causing atomic ions to be formed and magneticallyl trapped within the Ihollow plasma, the plasma wall acting as a shield for the trapped atomic ions against the instreaming of neutral particles from the iwalls of the machine, in a manner similar to that set forth in the application of lohn S. Luce, Serial No.- 833,897, iiledrAlugust 14,1959, entitled, Hollow Carbon Arc Discharge, now Patent No. 2,956,195, issued October 11,Y 1960.

In FIG. l, one embodiment of the subject'device is shown. An anode electrode 1 and a cathode electrode 2 are mounted in concentric relationship with a narrow annuluskS therebetween. The anode 1 is mounted on a conducting electrode support 4 which, in turn, is mounted supported in one end wall of the housing 20. Cathode 2 is mounted directly uponv the end of a second support tube 6 which, in turn, is insulatingly supported in the one end wall of housing 20.- 'I'he facing surfaces of the rear portionsnof the anode and cathode are recessed to form an annular manifold 7. Positioned within this manifold 7 is an intermediate cylindrical electrode 8 which is mountedon a conducting electrode support 9. This support 9, in turn, is mounted upon the end of a third 'support tube 10. This tube 10 is insulatingly supported in the one end wall of housing 20. An exact spacing of this intermediate electrode 8 with respect to the anode 1 and cathode 2 is accomplished bythe insertion of an annular rinsulator 11 between support tube 10 and support tube ,5, andthe concentric annular insulator 12f between support tube 6 and the electrode support 9, A vgas-tight `seal between these components is provided by the insertion of Q-rmgs or similar seals 13 therebetween. The manner in which the electrodes are supported, as discussed above, 1s not lrnnted to the specific means set forth since any other conventional means may be employed fiar this purpose.

Electrode support 4 is provided with an axial passageway 1n whlch a tube 14 is disposed. This passageway communicates with an axial passageway 15 in anode 1. Passageway 15, in turn, communicates with radial passageways 16 m anode 1. Feed gas, such as hydrogen or deuterlum, for example, is fed from a gas supply 21 through tube 14,

passageways

15 and 16 into the manifold 7.

The housing 20 forms' a chamber 29 which is evacuated by means of a vacuum pump, not shown, connected to a member 22 communicating with the chamber 29. Tube 6, which supports cathode 2,` is connected by an electrical lead 28 to the negative terminal of a variable D.C. supply 27. Tube 5, which is electrically connected -to anode 1, is connected by lead 24, switch 2 5, and lead y26 to the positive terminal of supply 27. Thenegative terminal of the supply 27 is grounded, as shown.

A uniform magnetic lield is provided by a concentric electromagnetic coil 2.3 disposed around the housing Coil 23 is energized by a source of D.C. potential, not shown. The magnetic field lines provided by this electro.- magnet are in axial alignment -withthe annulus 3 b etween the cathode 2 and anode 1.

A baille 17 is disposed in confronting relation to the electrodes of the ion gun and is mounted on the other end of housing 20 by an insulator 18. Battle 17 may be grounded by a lead 19, and a switch 76, if desired.

Some of the dimensions and materials of construction of the device of FIG. l are given below, by way of examples. The length of the anode andv cathode is 21/2 in.; diameter of anode is 11A in.; thickness of annulus 3 is Af; in.; effective length of anode and cathode is l in.; outside diameter of cathode is 2 in.; effective length of intermediate electrode 8 is 1% in.; thickness of intermediate electrode is 1/15 in.; inside diameter of manifold 7 is 3:4; in.; and outside diameter of manifold 7 is 1% in. The electrodes 1, 2 and 8 are machined from graphite stock, and the electrode supports and support tubes are copper. Steatite is used as the insulating material-for `

members

11 and 12. The outside diameter of the inter-- mediate electrode 8 is 1% in., so that the outer surface thereof is aligned with the inner surface of the annulus 3.

The above dimensions and materials of construction, with the exception of the position of the intermediate eltrode, are not critical to the operation of the device of FIG. l. For example, the electrodes may be constructed vfrom stainless steel, the insulating members may be constructed from any of conventional inert insulating materials, and the dimensions of the electrodes and the annulus therebetween may be made larger or smaller with substantially the same-operating results if operating parameters are modified accordingly. v

In a normal operation of the device of FIG. 1, the ion gun is aligned in a uniform magnetic eld, for example 3000 gauss, so that iield lines traverse and are parallel to, the annulus 3. The region external Vto the ion gun in the chamber Z9 is evacuated to about 8 X10-5 mm. Hg or less. r[he pressure in the manifold 7 is at a higher value than in chamber 29 during the time the device is producing a plasma. Gas is admitted to the manifold 7 vfrom gas supply 21 through

passageways

14, 15, 16. With the intermediate electrode 8 electrically heating, a voltage is applied between the anode 1 and cathode 2 by means of supply 27, and when this voltage reaches about 800 volts, a gas discharge is struck between these electrodes. The discharge can be initiated at lower voltages when the magnetic eld is higher. The voltage is then raised to an operating value of about 1800 volts. The current flow between the anode and cathode is then about 0.2 ampere for the spacing and pressure cited above.

Immediately upon striking the discharge, an ion plasma is formed along the magnetic field lines within and external to the ion gun. There is a pressure differential across the annulus 3 by virtue of the difference in pressures between the manifold 7 and the chamber 29. The gas drawn through this annulus by this pressure differential is substantially ionized by the arc discharge between the anode and cathode. The plasma thus emerging from the ion gun is relatively uncontaminated by neutral particles. The plasma will follow the field lines until it strikes the electrode or baille 17. The baie 17 may be used as a reflecting electrode for the plasma which strikes it when the switch 76 is opened, or alternately it may be used as a collector electrode for the plasma when the switch 76 is closed. With a magnetic iield strength of 3000 gauss and a voltage of 1800 volts between the anode and cath- Vode, a plasma of about 3 1011 particles/cc. is obtained. With a fixed rate of gas feed and a fixed applied voltage, this plasma density has been shown to vary nearly proportionally to the square of the magnetic field strength.

The` plasma of ions produced in the operation of the above-described device doesnot haveany applied axial potential gradient therealong. The absence of such an applied potential gradient substantially eliminates extraneous electrical iields, particularly longitudinal fields. Thus, it can be seen that the plasma of ions produced by the device described above does not have certain of the objectionable electrical liields which are characteristic of conventional gas-fed are discharges of the prior art. By positioning all the electrodes at one end of the device, less electrode material gets into the plasma as contaminant, and such positioning materially reduces baffling and differential pumping problems that are characteristic of prior art arc discharges.

It should be noted here that with the small current of .0.2 ampere between the electrodes that there will be u minimum of electrode heating and at this small current flow there with be less problem of the electrodes disintegrating because of a lack of heat due to the small current flow between the electrodes. The device of this invention may be operated at higher voltages and currents, and when so operated, cooling means for the elec-V trodes may be required. `When required, cooling coils would be mounted on the -electrode supports.

It should -be noted here, in the event the plasma generator is used i-n an apparatus such as an accelerator or the like, that the housing 20 may be eliminated and an evacuated region of such apparatus may provide the hereinbefore-mentioned means providing an evacuated system.

The principles of the ion gun discussed above may be used in a mirror type machine such as disclosed in the embodiment of FIG. 2. A similar type of mirror machine is described in U. S. Patent No. 2,920,234, issued January 5, 1960, to John S. Luce, entitled, Device and Method for Producing a High Intensity Arc Discharge. In FIG. 2 of said patent the ion gun is positionedin one of the magnetic mirror regions such that the magnetic Ifield lines traverse the annulus between the anode and cathode and are substantially parallel with this annulus. The mirror machine of FIG. 2 of the present application comprises an inner chamber 59 and two

end chambers

60 and 61. The inner chamber 59 is connected through an opening 63 to a .vacuum pump, not shown. The inner chamber 59 is enclosed by means of a liner 65. The liner .65 may be constructed from stainless steel or Inconel, for example. The inner chamber 59 is enclosed with an outer enclosure 30. Enclosure 30 is provided with an opening 62 in communication with one of the end charnbers 60, and is provided with an opening 64 in communication with the other end chamber 61.

Openings

62, 64 are connected to separate vacuum pumps, not shown, for evacuating chambers 60 and 6&1, respectively. Disposed in one end of enclosure 30 is an ion gun assembly consisting of an anode 31, and a cathode 32, defining an annulus 33 therebetween. Cathode -32 is supported by an annular tubular member 36. The anode 31 is supported by the annular tubular member 35. Disposed within a manifold 37 between the anode and cathode is an intermediate electrode 3S. This electrode 38 is connected to a concentric tubular member 4i). Disposed about the tubular member 36 of the -ion gun assembly is an annular section of insulating material 73 which supports the concentric tubular members of the gun assembly and entends through the one end of the enclosure 3i).

Gas is supplied to the manifold 37 of the ion gun from a gas source 51, through a tube 44, and then through passageways in the anode 31. The members 35, 4t) and 36 are disposed in concentric relation with respect to each other and are held in a suitable spaced relation with respect to each other by insulating means in the same manner as in the device of FIG. 1. Member 36, which is electricdly connected to the cathode 32, is connected to a source of D.C. supply v5'2" by a lead 5S. The other side of DC. supply 57 is connected by a lead 56 to the member 35, which is in electrical contact with the anode 31. rIlle D.C. supply 57 is a Variable D C. supply for supplying operating voltage between the cathode and anode. The anode, cathode, and intermediate electrode of the ion gun are positioned in the center of a magnetic mirror region provided byA an annular electromagnetic' coil 66.

Disposed between coil 66 and the ion gun assembly are a plurality of bai 67 disposed about the ion gun assembly. These baies 67 are insulatingly mounted on a portion of the inner chamber wall 65. A second annularV electromagnetic mirror coil 66 is provided iat the other end `of the device and is mounted in concentric relation to a baflie or plate 47. This plate 47 is grounded through a plate support member 74, lead 49, and switch 75. The

coils

66 and 66 are energized by a source of D.C. potential, not shown. The member 74 is encompassed or surrounded with an insulating material 43 which extends through the other end of the enclosure 30. Disposed between the annular electromagnetic coil 66 and the plate 47 are a plurality of annular baies 68. These baffles 68 are insulatingly mounted on an extension of the inner' liner 65.

In the operation of the device of FIG. 2, the arc discharge is established in an identical manner to that described above for lFIG. l. After the arc discharge has been established between the anode 3i and cathode 32, the pressure diiferential across the annulus 33 between the manifold 37 and the innerachambcriris Such 35.10...

cause the gas within the manifold 37 to ow through the annulus 33 and thus through the arc discharge. The collimating effect of the magnetic iield lines within the annulus 33 plus the pressuredifterential across the annulus 33 will cause a plasma of relative uncontaminated ions to be ejected from the ion gun in the form of a hollow beam 72. This beam 72 will follow the magnetic iield lines provided by the mirror coils 66 and 66', and any other coils that may be provided therebetween. 'This beam 72 will follow the magnetic field lines until it strikes the plate 47. As in the device of FIG. 1, the magnetic iield strength is about 3000 gaussfthe voltage aQIlQSSJhS e160- trode at operating value is about 1800 volts, and a plasma of about 3X1()11 particles/cc. is obtainable. As in the device of FIG. 1, the plasma beam 72 of FIG. 2 is substantially free of neutral gas particles because of the fact that the gas is substantially ionized by the arc discharge in the annulus 33 before it leaves the ion gun.

This plasma beam 72 may be used as a dissociating mechanism in the same manner as seti-forth in theaforementioned Patent No. 2,956,195. When the plasma as shown in FIG. 2 is used as a dissociating mechanism, a.Y

stream 71 of molecular ions yare injected from an ion source through an accelerator 70 into the inside wall of the plasma 72 in an operating zone between the mirror coils. A portion of the molecular ions 71, when they come in contact with the plasma beam 72, are dissociated by this plasma beam into atomic ions and neutrals. 'The n atomic ions will be magnetically trapped due to the effect of the coniining magnetic field and will form a ring of atomic ions. This trapping principle is -fully set forth in the co-pending -application of John S. Luce, Serial No. 728,754, tiled April 15, 1958. The portion of the rnc'-A lecular ions that are not dissociated by the plasma beam 72 will continue to move in the same trajectory they had before contacting the beam 72. The neutrals formed in the dissociating process will ow off at a tangent to the points of dissociation and are lost to the system. These neutrals, however, may be used as an input to a particle accelerator, if desired. It should be noted that all electrical potentials for the device of FIG. 2 are applied in.n

a zone removed from the operatingzone of the plasma between the mirror coils, thus preventing formation of ay longitudinal electrical iield along the plasma beam 72.' Absence of this field will insure better stability of the plasma beam.

The plasma beam 72 of FIG. 2 is considered to be superior to the hollow car on arc discharge of the aforementioned Patent No. 2,956,195, for the reason lthat the plasma 72 isessentially lfree of neutral gas particles, and therefore, when used as a dissociating mechanism, will not introduce extraneous matter or neutral particles into the plasma of atomic ions formed in thetdissociating process. As discussed above for the device of FIG. 1, the device of FIG. 2 will-produce -a plasma with Vless contaminants from'electrode materials than plasmas produced by prior arc discharges. Also, there are less baffling and diiferentialV pumping problems withV the device of FIG. 2 than there are for prior arc discharges. In addition, there are less electric fields produced in FIG. 2 4than in prior arc discharges. As pointed out above, the plasma beam 72 will serve as -a means for preventing the instreaming of neutral particles from the walls of the machine, in a manner similar to that set forth in the aforementioned Patent No. 2,956,195.

The gas supplied to the ion gun of FIG. 2 may be hydrogen, for example, deuterium, tritium, or mixtures thereof. 'Ihe pressure in chamber 59 is maintained `at a value of about 3 1O5.rnm. Hg, and the pressure in the end chambers and 61 is maintained at a value of about 1x10-4 mm. Hg, for example. For some applications, lower pressures may be desirable.

The accelerator tube 7), referred to above, is energized by a suitable/high Voltage generator. The beam 71 of Wmolulanions mayihellqb or Dj, for egiample, 'andiale injected from the source 69 and through the accelerator 70 with an energy of about 600 kev.

Essentially all low energy neutral particles that strike the plasma beam 72 are immediately ionized by the plasma and are pumped out of the system along the plasma beam and through the space between either the baies 67 -and the ion gun or between the baffles 68 vand bafe 47 into the end chambers.

The plasmas supplied by the ion gun of both FIG. 1 and FIG. 2 -are dierent from conventional yarc'discharges V in that they are relatively quiescent and stable under their normal operationY conditimrfrnrventionatgas-are discharges may be and are usually highly contaminated by neutral gas particles fed to the arc discharge. This is a disadvantage when they are used as dissociating mechanisms, for the reason that these neutral particles will interfere with the build up of, a suiciently dense plasma of atomic ions to the necessary density to provide a ther- V monuclear plasma. It should thus be seen that the plasma beam of FIG. 2 is amore eiicient'dissociating mechv anism because of its characteristic of being relatively free from objectionable neutral gas particles and electrode contaminants therein.

This invention has been described by way of illustration rather than limitation, and it should be apparent that the invention is equally applicable in elds other than those described.

What is claimed is: I

l. An improved ion gun comprising a container, an ion gun assembly disposed in one end of said container, said ion gun assembly comprising an anode and -a cathode mounted in concentric relationship with a narrow annulus therebetween, an anode support member connected to said anode and mounted in one end of said container, a cathode support member mounted to said cathode and disposed in said one end of said container, the rear portions of said anode and cathode being recessed to form an annular manifold, an intermediate electrode positioned within said manifold, a support member connected to said intermediate electrode and extending into said one end of said container, means for insulatingly supporting said support members in concentric relation with respect to each other, means for insulating said support members from said one end of said container, a source of gas supply, a gas supply feed tube connected to said gas source and extending through said member supporting said anode, -an axial passageway within said anode connccted to radial passageways within said anode, said radial passageway communicating with said manifold, said gas feed tube being in communication with the said axial passageway within said anode, a source of variable D.C. voltage, means for connecting said D.C. source between said anodeV and said cathode, means connected to and in communication with said container for evacuating said container, a baille mounted to the other end of said enclosure in confronting relation -with the `face of said ion gun assembly, an electromagnetic coil disposed in concentric relation around said enclosure, said electromagnetic coil supplying a magnetic iield, the magnetic ield lines of said coil being substantially parallel to and in alignment with the annulus between said cathode and said anode, said coil extending from an area adjacent to the electrodes of said ion gun assembly to an area encompassing said baie, said intermediate electrode within said manifold being aligned with the annulus between said anode and Vsaid cathode, Ithe pressure within said container providing a pressure differential across said annulus, whereby the larc discharge established between Said anodeand said cathode by said variable D.C. supply substantially ionizes `the gas owing through said annulus by virtue of said pressure'differential to provide a plasma beam substantially yfree of neutral gas particles.

Y 2. The ion gun set forth in claim l, wherein the magnetic eld strength is about 3000 gauss, the region adjacent to the face of the electrodes of the ion gun is evacuated to about 8 l0r5 mm. Hg, the gas supplied to said manifold from said gas source is hydrogen, the voltage applied between the anode and cathode is about 1800 volts, said intermediate electrode being electrically oating, and the current ow between the anode and cathode being about 0.2 ampere, whereby said plasma beam provided by said ion gun has a density of about 3 X 1011 particles/ cc. Y

3. An improved ion gun comprising a container, means connected to said container for evacuating said container, an ion gun assembly disposed in one end of said container, said ion gun assembly comprising an anode and a. concentricallydisposed cathode deiining an annulus between said anode and said cathode, the rear portions of said anode and said cathode defining a recessed manifold, an intermediate electrode positioned within said manifold and aligned with said annulus, a source of feed gas, means for feeding gas from said source into the interior of said manifold at a controlled rate, means connected to said anode, said cathode, and said intermediate electrode for supporting them, said supporting means being mounted within one end of said container, Vmeans for providing a containing magnetic field within said container to provide magnetic eld lines that are parallel to and in alignment with the annulus between said anode and said cathode, a source of variable D.C. supply, means for connecting said D.C. supply Vacross said anode and said cathode to supply operating voltage thereto, the pressure within said container providing a pressure dif# ferential across said annulus, whereby the arc discharge established across said anode and said cathode by said D.C. supply will substantially ionize the gas supplied to said annulus from said manifold, said gas being directed to said annulus by virtue of said pressure differential across said annulus, said ion gun assembly thereby providing a substantially ionized plasma which is collimated by said magnetic iield to supply a substantially cylindrical hollow plasma to the evacuated region of said container.

4. The device set forth in claim 3 wherein the container is provided with a central chamber and two end chambers, said ion gun assembly electrodes being positioned in one end of said central chamber, a baille disposed in the other end of the central chamber, said magnetic eld being provided by a pair of electromagnetic mirror coils, one of said mirror coils being disposed in concentric relation to the electrodes of said ion gun assembly, the other mirror coil being disposed in concentric relation to said baffle, said evacuating means being connected to each of said respective central chamber and said end chambers.

5. The device set forth in claim 4 wherein the central chamber is evacuated to a pressure of about 3 l05 mm. Hg, the voltage across said anode and said cathode is about 1800 volts, the gas fed to the said manifoldis hydrogen, the magnetic iield strength supplied by said magnetic mirror coils is about 3000 gauss, said end chambers being maintained at a pressure of about 1x10-4 mm. Hg, whereby the plasma ejected from said ion gun assembly is substantially free from neutral gas particles, said plasma following the magnetic held lines provided by said mirror coils until said plasma contacts said baille.

6. The device set forth in claim 5 and further including a source of molecular ions, means for accelerating a beam of molecular ions from said ion source into the inside wall region of said plasma at an angle substantially perpendicular to said plasma, said plasma partially dissociating said beam of molecular ions into atomic ions, neutral particles, and electrons, said atomic ions being magnetically trapped within the area defined by said plasma, and said neutrals being ejected away from said plasma.

References Cited in the tile of this patent UNITED STATES PATENTS Luce Ian. 5, 1960 v corrected below.

UNITED 'sTL-Aii'lij"'P'T EN'ITOFFIQE CERTU?IGME 0F CORRECTION--- Patent Nm1 3,005,931 i v october 24, 19er Raphael. A. Dandl It is hereby certified that error appears in the above numbered patent requiring correction and 'that the said Letters Patent should read as Column 7, line 56,l rfor '"xloll" made-e '3x1o-ll-- Signed and sealed this 15th day of May 1962e EAL) ttest:

ERNEST W. SWIDER DAVID L. LADD Y. Attesting Officer v ACommissioner of Patent UNITED STTEPTENT@-oEEIEH i y CERTIFICATE 0F C@ERECTION-v`l` ,e

Patent No. 31,005,931 October 24; 1.961

RaphaellLA. Dandl It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

column 7, line 56 for "SXIVU" read-#-3XI01l-.-

Signed and sealed this 15th day of May 1962,

EAL) Hest:

ERNEST W. SWIDER DAVID L. LADD Y Attesting Officer e .Commissioner of Patents