US2945972A

US2945972A - Ion source

Info

Publication number: US2945972A
Application number: US838009A
Authority: US
Inventors: Clarence W Blue; John S Luce
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-09-03
Filing date: 1959-09-03
Publication date: 1960-07-19
Anticipated expiration: 1977-07-19

Description

July 19, 1960 oN'souRcE Filed Sept. 3, 1959 2 Sheets-Sheet 1- Q 2 i Ef.

I m u 03 1 9 1 f `00 ifo i Lof r l g l l P5 m C) I Il I Q l |l| K* I I 7" s.. Il' l' k n "l .`f N* E LL r2 H --F f |l I N. ll i N '5 i o 0: 334-- 9::- E t t` 3 g 1 x 'n lIII o l, I I l@ lo I w E INVENTORS. H John S. Luce and ,l I BY Clarence W. Blue July 19, 1960 c. w. BLUE ET AL 2,945,972

10N SOURCE v Filed Sept. 3, 1959 2 Sheets-Sheet 2 INVENTORS. John S. Luce and BY Clarence W. Blue MAJ/.IM

ATTORNEY Patented July 1,9,v 196g Figure 1 is a cross-sectional View of the iron source utilizing; a cylindrical arc discharge, 2,945,972 Figure. 2y is an enlarged cross-stctional view of the cylindrical arc discharge. structure o Figure 1, and ION SOURCE 5 Figure 3 isan enlargedl cross-sectional view'of a small Clarence W. Blue, Knoxville, and John S. Luce, Oak Soiid efe discharge Which may be substituted 'foi' eyiiiiv Ridge, Tenn., assignors to the United States of America drical arc discharge of Figure 1. asV represented by the United States Atomic Energy The above objects have been accomplished in the pres- Commission l ent invention by establishing an arc discharge parallel to the direction of and inside a magnetic field, surrounding Filed Sept 3 1959 ser' No' 838009 vsubstantially all the discharge with an yaccelerating elec- 8 Claims. (Cl. 313-53) trode, except for an ion exit aperture, and establishing an electric lield between that electrode and the arc, the

electric field being oriented at an acute angle to the mag- This invention relates to ion sources, and more particuiietic iieid- I011s are drawn thrOiigh'eXit aliertiires in the lady to a novel method of and. Ingang for generating ions accelerating electrode in a direction substantially diverexternal t0 01- Within a magnetic. field and withdrawing gentto. the direction of the magnetic iield and so will ions at an acute angle to that field. l travelj in a spiral orbit along the magnetic field. Thus, Ion Sources are used to furnish ions for particle acion` motion is directed away from the source so that the celerators. They are used also in experimental thermoid nS'Wiii net Strike the source at any Point in their Orbit nuclear research, and in thermonucle'ar fusion devices. Within the iieid When the 1011s from the nhOVe Source The latter devices produce energetic neutrons which are 'ereiiilected 'nite a inagiietie rnlri'cr iieid, the Source 1S useful in bombarding materials, for example, in studies POSltlOhed in the magnetic InirrOr field near One end and of radiation interaction with matten the ions are then injected into a pulsed, time-rising lmag- One ofl the problems encountered in the development netic icid 'This time-rising magnetic iieid is required t0 of successful thermonuclear devices involves generating, PreVent the i0nS, after being reflected by the llnlrrOrieid injecting, and retaining ions in a magnetic mirror field. iii the other end 0i the device, f rOni returning and striking When ions are accelerated from an ion source perpenthesource. The 10u lnjectlqn 1S continued Until the rhag dicularly into a uniform magnetic eld, they are bent netlc held has increased .With tline t0 e predetermined into a circular orbit. The ions then return and strike Yniiie after Which the inleetien 1S StOPPed- Duringv the the source on their inst tum in the Ymagnetic field, and miectwa, an energetic piasmais formed and iS magneti;- thus are 10st to the System' -If the ons are given Sum. cally contained between `the mirror regions. Thus, 1t can cient angular displacement in the direction along the be Seen that theioii source diseidsed herein is ilsefiii ,as field, they will travel away from the source in a spiral a ineens fer initiaiiy establishing an .energetic Plasma in orbit. If injected between .magnetic mirrors, they will an enegetic neutron Producing device 01' a. thermmu return after their first reflection and strike theV source, Cie-ei eXPeriinentei device regardless of their original angle of entry into the mag- The soiii'ee is additionaiiy Useful in PiOViding ien/S in netic field' a magnetic tield for measuring the charge exchange and it is desirabie to inject ions into the magnetic nel@ ,of Scattering Cross-Sections 0f 1011s 0f a Particuii materiel'- a controlled thermonuclear machine in such `a direction 40 Also, a Very importent Property, the t0n diffusion feite; that the path ef the ions diverges Substantiaiiy from the may. be determined for any particular type of injected direction of the magnetic field and yet ionsv willnot re- 1011s.- Iii addition, the ion Source of this invention ,may turn to strike the ion source. It `is also desirable, to inbeused as 'an initial Source 0f ioiis 'foi' e Particle accelerject ions having orbits orientedl at a large angle tothe eter. The ions, after spiraling a certain distance Within yaxis of the machine in order tominimize the loss` ofv ions a iiiiitferm magnetic iieid', can he fed into the Particle '39? through the magnetic mirrors. For example, it has been ceiefeior Wiiefethe ioiis are giV-eii a further aceeieretidnshown that the minimum (critical) angle, 0c, `between Figiiiegl illustrates one embodiment in which thcprin magnetic field yand ionA entrance path at which ions will @Pies tot this'iiiieiitioiimvay be Carried out In this, ein' be retained in the mirror region is obtained from the hedirrieiit, aii the components 'aresiiPPQrted fronte-coinexpression; hlilcdtT-,Shapcd insulating support and vacuum connection Connection 1 may` be constructed from Pyrex,

Sini 00:3@ for example, Closing' one side o f` the T connectoris a B1 supportv iiange Zand associatedequipment attached there- Where: to. Closingia portion of they opposite side-of the T con- Hector is a'groundiiange 3, The bottom of the con- Bq`=magn1tude of the uniform iix between the mirrors; nec/[01. is mixed` to vcuum une (riot-shown); andh Bi=max1mum Value of the mirror uxi top is either capped or connected to vacuurr'if.` Y' t l' 'i where B0/B1=1/4, for example, 00:302 Attached tothe support flange 2 is ya hollow, stainless With a knowledge of the problem of retaining ions in Steel, SUPPOIt tribe 4 Whichy extends through the T con,- a magnetic field because of their-returningvto strike the nectOI 1 andgrcnnd Hang@ 3 'toward the electrode endpf source, it is a primary object of this invention to vprovide the seriirce essielnhiyf `Sillillnrt ,tube 4 iS fOrIiiedDfn a method for injecting ions from an ion source into a indefiniti @Outer Stube, siiPPiied With cooling W-tcrithere.- magnetic field such that the ions will be retained and will between-i A hOiiPWj'eStniniesS Steel, SOnrce-tLl-he. 5 is. CQ.- not return* to strike the source. Y a'Xi-allyfaligned Within support tube 4 and extends .through It is another object of this invention to provide 'an @5 the support ange 2 into the atmosphere. Sourcepube ion source wherein ions are injected in sucha direction 5, is .provided Vvvithrneaiis 6 for limparting rotational adthat-their direction of motion is highly divergent vfrom justnentito tube s witli respect to tuberi. Meansfis the direction of the magnetic field. i aiiixed vto 'supportflange 2 and provides torgaxial adjust'- These and other objects and advantages of this` invenment of :tube 5 with respect to tube i4, Attached toi-the tion will become apparent from a considerationof the opposite endet source tube v5` is a tantalurn,` ion .source following detailed description and4 the accompanying drawings wherein:

tiefes evergreen eevli'rigrlines8'nand nsf-feed tbe`9 extend through source tube 5 nd head 7. Comi pression type seals, not shown, are used as vacuum seals around the lines within source tube 5, and an O-ring seal is used between source tube 5 and support tube 4.

A perforated, stainless steel, ground shield 11 is supported from the ground flange 3 and extends perpendicularly in both directions therefrom. Shield 11 has blisters l2 to co-act with drain fins 13 positioned upon support tube 4 and source head 7 for elect-ron dumping I Also supported from ground flange 3 is a perforated, cylindrical, stainless steel, accelerating electrode support tube 14, Enclosing tube 14 is a glass tube 22. Tube 14 and flange 3 are connected to ground by a member 20 and lead 21.

Positioned within the extremity of source head 7 are appropriate source components. These consist of a generally circular filament 15 backed with a shield 16, a cylindrically apertured defining electrode 17, and au insulated reflector or .terminal electrode 18. Gas is fed to the aperture of electrode 17 through ga's feed tube 9 from a source of gas, not shown. A radially perforated accelerating electrode 19, supported from the electrode support tube 14, encompasses the terminal electrode 18. The openings in accelerating electrode `19 and in electrode 17 are three radial slits with narrow bridges between them. The three bridges of each electrode are spaced 120 apart, and the slits in electrode 19 are aligned with those in electrode 17. The region between the defining electrode and the terminal electrode `forms the arc chamber from which ions are withdrawn by the accelerating potential. As can be more clearly seen from Figure 2, the radial openings in accelerating electrode 19 are slightly off-set with respect to the opening between

electrodes

17 and 18 so that a strong electrostatic field is impressed on the arc on one side and a weaker field on the other. This results in bowing of the arc meniscus, as shown. Since ions leave at a right angle to the arc meniscus, they are injected at an angle into a magnetic field H and are caused to spiral by the magnetic field and thus miss the source on the first and subsequent revolutions. The eld H is provided yby electromagnets, not shown.

Glass tube 22 enclosing the device may be mounted in one end of a neutron producer or a thermonuclear device such as disclosed in the application of Albert Simon, Serial No. 732,770, filed April 28, 1958, or the application of P. R. Bell et al., Serial No. 753,846, filed August 7, 1958, for initially `forming an energetic plasma. The ion source may be positioned in the magnetic mirror region in the one end of the device such that ions accelerated om the source are injected at a traverse angle, as discussed above, and spiral within a time rising containing magnetic field between the mirror regions. After the energetic plasma is formed, the ion source is removed and the plasma may then be sustained by means such as set forth in the co-pending application Serial No. 814,939, filed May 21, 1959, of Bell et al.

Glass tube 22 may also be mounted in one end of an evacuated enclosure, not shown, which is provided with a containing magnetic field. 'Ihe charge exchange crosssection, scattering and ion diffusion properties of the ions injected from Ithe source may then be determined.

Tube 22 may also be mounted in one end of an evacuated enclosure, not shown, which is provided with a uniform magnetic field. A particle accelerator, not shown, may be located at the other end of the enclosure in such a position that ions, injected into ythe uniform magnetic field from the source, will spiral through the field and enter the particle accelerator where they are further accelerated.

In operation, the device of Figure 1 is connected to vacuum pump through connection 1. The pressure in the device is lowered to a value of about 10-5 mm. Hg. The magnetic field H is established at a value depending on'the device in which the ion source is used.` 'I'hefield strength may be in the range from 6 to 105 kilogauss.

The filament 15 is made of tantalum and is heated by a direct current of 350 amperes by means, not shown. The filament support clamps are of copper and are water cooled with water supplied through tubes 8. The source head 7 is also water cooled by water supplied through tubes 8.

A potential gradient of about volts is established by a conventional power supply between lament 15 and defining electrode 17. Electrons are drawn from the lainent by this potential gradient. Gas, such as hydrogen, deuterium, or a mixture of deuterium and tritium, is admitted to the slot in electrode 17 and is ionized by the electrons drawn from the filament. Primary electrons are reflected back into the arc 23 Aby reflector 18 since the reflector 18 assumes a negative potential, with respect to the defining electrode 17, and is equal to that of the filament 1.5. vThe ion accelerating voltage is applied between the defining electrode 17 and the accelerating electrde 19 so as to draw ions from the arc in a traverse direction as discussed above.

It may be desirable to substitute a small solid arc discharge for the cylindrical larc discharge of Figure 1. Such a solid arc discharge is shown in Figure 3. A solid arc 23 is established between a filament 15' and terminal electrode or reflector 18. The defining electrode 17' is appropriately apertured for a solid arc, and gas is fed `from aline 9' into the aperture in electrode 17. A cup-shaped accelerating electrode 19 is provided with radial openings that are slightly off-set with respect to the radial openings in reflector electrode 18'. As in Figure 1 discussed above, electrons are drawn from filament 15 by a potential gradient between filament 15' and defining electrode 17'. Gas, such as used in Figure l, is fed through tube 9' and into the defining aperture of electrode 17', where it is ionized by the electrons to form an arc discharge 23 which reuxes between filament 15 and reflector electrode 18' in a manner similar to that for Figure 1. A potential gradient between electrode 17 and accelerating electrode 19 and the off-set relationship between the radial openings in electrodes 18 and 19', will cause ions to be accelerated through said openings in such a direction that they will spiral into the magnetic field H and will not return to strike the source when the source s yused in a magnetic mirror device such as discussed above for Figure l.

The ion source of Figure l, when operated in a mag netic field of 6000 gauss, produced an arc current of about 0.250 ampere, or a density of about 0.750 ampere/ in.2 of arc area. On the other hand, the ion source of Figure 3, when operated in a magnetic field of 6000 gauss, produced an arc current of 0.175 ampere, or a density of about 2.0 amperes/in.2 of arc area.

Thus, itv can be seen that we have provided an ion source which can be used to inject ions into a mirror-type machine at a large angle with respect to the axis of the machine and still prevent the ions from returning and striking the source.

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

What is claimed is:

l. An improved ion source comprising a support flange, a ground flange, a T-shaped insulating support and vacuum connection affixed to and disposed between said flanges, a support `tube afiixed to said support flange and extending through said ground flange in spaced relation thereto, a source tube disposed within and spaced from said support tube, an ion source head affixed to said source tube, means disposed within said source head for initiating a gas-fed reuxing arc discharge therewithin, comprising a heated filament electrode, an electrically oating anode disposed in spaced relation to said filament electrode, an apertured arc defining electrode disposed between said filament electrode and said anode in spaced relation thereto, means for .connecting a potential gradient between said filament electrode and said are defining electrode, a cup-shaped accelerating electrode disposed around said anode and provided with a pl-urality of radial openings, means connecting said accelerating electrode to ground, a source of gas, a gas feed tube, means for feeding gas from said source and through said gas feed tube into the aperture of said arc defining electrode, said gas being ionized by electrons drawn from said filament electrode by said potential gradient to thus form a refluxing arc discharge through said arc defining electrode and between said filament electrode `and said anode, means for establishing a magnetic field parallel to said discharge, said radial openings in said accelerating electrode being slightly off-set with respect to the spacing .between said defining electrode and said anode, whereby ions are accelerated out of said arc discharge by said accelerating electrode and at .a traverse angle with respect to the direction of said magnetic field such that said ions will spiral into said field and .away from said discharge and will not return to strike said discharge.

2. The ion source set forth in claim 1, wherein said support tube and said source head are enclosed within a cylindrical, grounded, perforated shield member, said shield member being provided with a plurality of blisters, a plurality of drain fins mounted on said support tube and said source head, one each of said fins being disposed in one each of said blisters to thus form a plurality of electron dumps.

3. The ion source set forth in claim 1, wherein the filament electrode is in the shape of a ring, and the arc discharge formed between said filament electrode and said anode through said arc defining electrode is cylindrical.

4. The ion source set forth in claim 1, wherein the filament electrode is a small solid plate, and the arc dis charge formed between said filament electrode and said anode through said arc defining electrode is a small solid arc.

5. The ion source set forth in claim l, including means for cooling said source head, said support tube, and said filament electrode.

6. An improved ion source comprising a source head, means for supporting said head, means disposed within said source head for initiating a gas-fed refluxing arc discharge therewithin, comprising a heated filament elec trode, an electrically floating reflector electrode in axial alignment with said filament electrode, an apertured arc defining electrode disposed between said filament electrode and said reflector electrode in spaced relation thereto, a source of gas, means connected to the aperture within said arc dem'ng electrode for feeding gas thereto from said source, means for connecting a potential gradient between said filament electrode and said arc defining electrode, a cup-shaped accelerating electrode disposed around said anode and provided with a plurality of radial openings, means connected to said accelerating electrode for providing an accelerating potential between said are defining electrode and said accelerating electrode, said gas within the aperture of said arc defining electrode being ionized by electrons drawn from said filament electrode by said potential gradient to thus form a refluxing arc discharge between said filament electrode and said reflector electrode through said arc dening electrode, means for establishing a magnetic field parallel to the direction of said discharge, said radial openings in said accelerating electrode being slightly off-set with respect to the spacing between said dening electrode and said refiector electrode such that ions are accelerated out of said arc discharge by said accelerating potential and at a traverse angle with respect to the direction of said field, said ions spiraling into said field and away from said discharge so as not to return to strike References Cited in the file of this patent UNITED STATES PATENTS 2,901,628 Lamb Aug. 25, 1959