US2850638A - Ion producing mechanism - Google Patents

Description

Sept. 2, 1958 K. R. MacKi-:NZIE

ION PRODUCING MECHANISM 2 Sheets-Sheet 1 Filed Jan 4 1946 ,isirr 11:

I N VEN TOR. Kenne/; Macke/7]@ BY Sepft. 2, 1958 K. R. MaGKENZlE v 2,850,638

10N PRonUcING MECHANISM Filed Jan. 4, 194e 2 sheen-sheet 2 IN VEN TUR. en/7 e/ 1P. Macenj/'e sin United States of America as represented by tutes Atomic Energy Commission l Claims. (Cl. ESQ-MME) This invention relates to ion forming mechanisms and particularly to ion generators of the type sometimes referred to as calutrons There is a disclosure of such a structure in United States Patent No. 2,709,222, issued May 24, 1955, to Ernest O. Lawrence, in which Figures 3 to 5 inclusive, particularly disclose an embodiment of a calutron with which the present invention is especially suited for incorporation.

in the operation of an ion forming mechanism there are a number of factors immediately concerned with the production and maintenance of an electric arc utilized for the execution of the ionizing function. ln a calutron the electric are operates in a magnetic eld and extends between a tilament, serving as a cathode, and an anode disposed away from the cathode in the direction of the magnetic field. Fthe nlament is called upon not only to emit electrons but also to resist bombardment by returning positive particles and also to resist displacing forces due to the fact that the filament carries an electric current while being situated in a magnetic heid. lt also a general requirement in mechanisms of this ytype to minimize as much as feasible the consumption of electrical energy by the ionizing structure and it is therefore desirable that the size of a conductor such as a filament be maintained at a low value. lt is furthermore desirable to provide a iilament in which the return bombardment by positive particles does not cause localized overheating and failure of the filament.

lt is, therefore, an object of the invention to provide an improved lament arrangement for a calutron.

Another object of the invention is to provide a i'ilament that is resistant to deleterious effects produced by return particle bombardment.

An additional object of the 'nlament having the foregoing frugal in the use of electricity.

additional object of the invention is to provide a lament that can readily be mounted in the customary gripping devices and yet will be provided with the special attributes above mentioned.

An additional object of the invention is to provide a iilament of small cross section yet of considerable mechanical strength.

A further object of the invention is in general to improve calutrons.

@ther objects, as well as the foregoing, are attained by the embodiment of the invention described in the following description and illustrated in the accompanying drawings in which:

Figure l is a fragmentary view of a portion of a calutron showing especially the source unit and its appurtenances, portions of the drawing being in cross section on a central vertical plane and other portions being broken away to reduce the size of the ligure;

Fig. 2 is an isometric perspective of a source blocl; as illustrated in Fig. l, portions of the structure being broken away to show the interior arrangement;

invention is to provide a qualities yet one that 1s Patented Sept. 2, 1958 Fig. 3 is an elevation of the mechanism shown in Fig. 2;

Fig. 4 is a plan of the structure shown in Fig. 2, a portion of a top plate being removed; and

Fig. 5 is a fragmentary plan to an enlarged scale of the iilament and adjacent block, portions being broken away to reduce the figure size.

While a calutron is described in considerable detail in the above-identified patent of Lawrence, a brief review of that structure will suiice for an understanding of the present development and is given in connection with Fig. l.

ln a calutron there'is provided a volume 6 permeated by a uniform or homogeneous magnetic field established between the upper pole 7 and the lower pole 8 of an electromagnet. Disposed between the poles 7 and S and situated within the magnetic eld is a tank or vessel 9 enclosing a chamber 1li connected to suitable pumping mechanism such as a ditfusion pump (not shown) effective normally to evacuate the chamber ll to a pressure of approximately l04 mm. of mercury. The tank 9 includes a top wall l2, a bottom wall 13, and a face plate le.

Secured removably to the face plate is an insulator le serving also as a support for a mounting and adjusting mechanism i7 not described in detail herein as its detailed functioning is not of consequence in connection with the present invention. The structure i7, however, acts as a support for a mounting stem 13 of a source block i9. A number of conductors 2l and leads 22 included in the structure l? pass with vacuum tightness from the atmosphere into the interior of the chamber lll. The stem iS is preferably related to the source block 19 by a terminal flange 26 and suitable fastenings 27 so that while some thermal insulation is afforded there is nevertlieless good electrical contact.

The source blocl; il@ is at its inner end provided with a heater cavity 2S closed by a disk 29 at its upper end and receiving through its lower end an electric coil heater 3l mounted on an insulating core 32. The heater coil is connected to a pair of leads 33 and 34 one being joined to one end of the conductor 2.2 and the other being connected to the block or ange 26. Upon the imposition of a suitable potential diderence between the conductors 1S and 22 the heater El is effective to increase the temperature of the block l?. The source block preferably is of metal so that heat from the coil 31 is generally conducted in a uniform fashion to a charge cavity 3e formed within the block i9. rl'ie charge cavity extends nearly through the under side of the block and entirely through the top face 37 thereof.

EstablishinU communication between the cavity 36 and the exterior face 3S of the block i9 is a gas passage 39 delined by a pair of parallel planar walls 4l and l2 so that the passage is a straight one extending from within the block to the outside thereof and thus merging not only with the face 38 but also with the adjacent face 37. When charge material is placed in the cavity 36 it is heated and evolves gas or vapor that travels from the cavity 3o rather uniformly through the passage 39 to the exterior of the block.

To close the cavity 3o and a part of the passage 39 there is provided on the face 37 in abutment therewith a plate i3 fastened to the block 3.9 by suitable screws 44 and edective to seal one end of the cavity and one end of the passage. The plate i3 preferably extends beyond the face .i3 and overhangs the edge of the block 19. The plate is provided, in registry with the passage 39, with an aperture i6 preferably symmetrically disposed with respect to the passage.

More particularly in accordance with the present invention, there is provided above the top plate 43 and substantially overlying the aperture 4.15 therein and also in In accordance withthe ,invent-ion' the iilarnentiscomprised of afpairV of legs Y56 and57,Y respectively, pref- -erably :formed ofY metallic rods circular in crpss section f ows'and-la-p'otential-isestablishedbetweengrippers 48 adapted to be iirmlyfhelcl for mechanical supportrand electrical conductionlwithinthe jawsof the-grippers-Yl and 49. The legs 56 and 57 extend substantially parallel togeach otherandterminateina plane` slightly beyond Y the planefof the passageway 39. The cross section ofthe legs56 and-SVZ-is 'such that with respect to thecurrent kowingtheir-temperature at-novltimeV Yexc'zeedsfand prefierably does vnot even approach, thetemperature at which 'thermo-emission occurs. Y Y Y Y ,Y

'Spanningthepace between,V the'legs'56 and57 and Vsecuredgtothemgfor mechanical support and-electrical connection, is a at emitting-portion` 5S preferably fabricatedofa metallicfribb'on'rectangular in transverse cross section Yand having across sectionalV area somewhat less thanthe crosspsrectional area'rof the legs 56 and 57. The ribbon f58ris preferably secured'to therlegs` by any convenient meansffor example, spot welding, so that there- YsistanceV of theV connection is negligibly low. When fproperly positioned, the ribbon 58 extends transversely of .the direction of the magnetic eld and is situated, inthe direction ofv theeld, in registry with therdisc'zharge` slot i397.; The Ywidth ofV the ribbon158 is ,somewhatY greater Y than the width of the slot and preferably theoverlapV on both sides is substantially the same.

YWhenthe leads S1 and 52 are included in an arc electric circuit, such as a power supply 60, inconnection with theblock19, an arc is struck between the emitting portion VE58 of the iilament 47 and extendsthrough the aperture -46 in VVthe plate 43 and into and'rthroughV the Vslot 39 to the block 19 serving Vas an anode. Y PositiveV particles that travel from the arc towardV theV filament are Vcollirnated for connned by thefrnagneticreld andeby the side walls of .the relatively narrow slot 39 so that/they bombard or irn- .pinge uponthe emittingportion k58 of thelarnent in only gafrestricted;are,a, thus leaving a substantial amount of material in the'` filament available for a thermal transfer A to-equalize thei`11ament `temperature and to avoid local overheating The shape of the 'ribbon filament 58 is such that when a current is being carired thereis atforded producing a stable, long-lived arc and contributes to the general improvement of calutron operation.

l. ln an ion source for a calutron having a magnetic eld, the combination comprising an arc block having an elongated gas ionizing passage open along twoA sides of said block, said passage having apredeterminedwidth measured across said magneticeldand the elongated portion extended parallelto said magneticltield, a filamentV vdisposed transversely of-said magnetic'tield, parallel to one of said two sides Vof -said block, and overlyingsaid passage, said `ilamenthavingV a width greater than-the predetermined width'of saidpassage, means provided to develop a ow of an ionizable gas through Ysaid passage,VY

means connected to saidiilament forrenderingthe same electron emissive, and means forincludingsaid-lament and arc block in an electric arc circuit wherebysaid electric arc ills Ythe-entire passage to maximize the quantity of ions -produ'cedbyrsaid gasowingrthrough saidselectric arc. f

2, The combinationrof claim lwherein said filament is Vfurther Vcharacterized Aby having a thickness substan'- 'Y tially less than the -width thereof. Y

3. The combination of claim V1 wherein said lament vis furtherV characterized as having an electron--emissive portion in the form of a ribbon supportedrat-eitherend Y by apairvof current-carrying rods. Y 4. The combination of claim lwherein said iilarnent -is further characterized as having a ribbonlil e1emissive Yportion supported at either end by apairof currentcarrying rods, Vand a pair'ofadjustable clamps'forsup- Y porting saidv rodsin spaced-apart relation Vwith respectto Veach other and-with respect' to said arc block. j

t Beferences-Citedsin the Atile ofgthispatent Y `UNITED STATES PA'ENTSVl Washburn 4June 26, 199.5V West Sept. 16,1947

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