US2852686A - Calutron receivers - Google Patents

Description

Sept. 16, 1958 K. R. M KENZIE CALUTRON RECEIVERS 3 Sheets-Sheet 1 Filed Sept. 4, 1945 INVENTOR. KEN/vim A. MAC Af/VZ/E BY and accelerating devices.

United States Patent CALUTRON RECEIVERS Kenneth R. MacKenzie, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Application September 4, 1945, Serial No. 614,407 6' Claims. or. 250-419 The general subject of this invention involves the separation, based on difference in mass, of minute particles, such as atoms, and especially the separation of isotopes of an element, or the separation of portions of an element enriched with respect to particular isotopes on a scale yielding commercially useful quantities of the collected material.

The type of means or mechanism to which the invention relates is known as a calutron, and correspondingly the method or process is known as a calutron method or process. In its presently preferred form, a calutron comprises an evacuated chamber mounted in a substantially homogeneous magnetic field and containing apparatus for ionizing a polyisotope to be treated, apparatus for projecting a beam of ionized particles of the polyisotope along paths determined by the masses of the respective ions, and a target apparatus for deionizing the particles of the beam and for retaining at least one selected isotope component in a separated region from which it can be recovered.

The evacuated chamber or tank is placed between the poles of an electromagnet so that the space within the tank is pervaded with a substantially uniform magnetic field of high flux density. Within the tank there is provided a source unit that includes means for supplying the polyisotope as a vapor or gas to an ionizing region, ionizing apparatus for producing positively ionized particles from the vapor, and an accelerating device maintained at a high negative electrical potential with respect to the ionizing apparatus for withdrawing the positive ions and imparting to each of them a predetermined en- .ergy in the form of substantially uniform velocities along paths generally normal to the direction of the magnetic field toward a beam defining slit in the accelerating device disposed generally parallel to the direction of the magnetic field.

The accelerated ions move transversely to the magnetic field and are constrained to travel along arcuate ipaths .having radii that vary with the masses of the particle.

.By "virtue of the accelerating slit construction the paths for the ions of a given mass diverge from a median path to an extent determined by the geometry of theionizing This divergence of the .paths of travel of the ions of a given mass continues through the first 90 of arcuate travel, and then the paths converge during the next 90 and cross each other in a re- .gion of focus approximately 180 from the source innit.

focus at approximately 180 from the accelerating apparatus. .Being composed of ions of different masses,

the streams of ions of different :isotopes have .radii of curvature that differ by an amount dependent solely upon the mass difference of their respective constituent r 2,85Z,fi8 1C6 Patented Sep 1958 ions. As a result, the centers of the foci of the streams of different isotopes are spaced apart by an amount approximately equal to the difference in the diameters of their respective median paths. .In the case of the heavier elements, such as uranium, the diiierence in mass between the isotopes is not sutficient for accomplishing complete separation of the streams in which the ions of the different isotopes respectively travel, while employing a practical minimum divergence of the beam at the beam definingslit, and a plurality of overlapping streams having overlapping regions of focus are created.

A receiver is disposed within the vacuum tank adjacent the foci of the isotope ions to be separated, for deionizing them and for separately collecting one or all of them as may be desired. Because of the necessary overlapping of the streams at their foci, it is impractical in one operation to separate completely the isotopes of the heavier elements, and, in practice, the separated quantities of material collected at the receiver are merely enriched with respect to a particular isotope.

The degree of isotopic enrichment that may be achieved in practice is also limited by a phenomenon known as scattering. Probably as a result of collisions between ions, or between ions and neutral gas particles, a certain number of ions of one mass that'should reach the receiver entirely outside the region of focus of the ions of a lesser mass, lose energy during their travel. After losing energy these ions of greater mass are caused to continue along arcuate paths of increased curvature, and some of them arrive at the receiver within the portion of the beam richest in a lighter'component, thus increasing the contamination of the lighter component by the'heavier component.

In the case of the heavier elements, the close proximity of the centers of the 180 foci of different isotope components of the beam presents still another complication affecting the isotopic enrichment obtainable in practice. The particles reaching the receiver are traveling at high speeds and tend to rebound from the surfaces they first strike. Because the particles do not necessarily rebound from a surface at an angle therewith equal to the angle of collision, scattered material is showered in many diof operation, reference is made to the copending application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9 1944, for Methods of and Apparatus for Separating Materials, now Patent No. 2,709,222 granted May 24, 1955. Only such parts of a calutron will be described herein as are necessary to an understanding of the present invention.

The present invention relates to that part of a calutron referred to as the receiver and the illustrated embodiment is designed particularly for separating two portions of uranium: one portion enriched with respect to the U isotope and the other portion enriched with respect to the U isotope. Throughout the following description, the U isotope will be ignored, as it comprises too small a proportion of normal uranium to be of any importance as a contaminant of the product separated by the particular receiver illustrated.

An object of the invention is to provide a calutron receiver adapted separately to collect and retain a maximum percentage of the ions traveling in two selected portions of an ion beam.

Another object of the invention is to provide a calm- A material entering either receptacle cannot readily scatter therefrom into the other receptacle. 7

Anothe object of the invention is to provide a calutron receiver of the type described having one recep tacle designed to receive a maximum percentage of the matrial traveling in one selected portion of an ion beam without interfering with the reception by a second receptacle of a substantial portion of the material traveling in a second closely adjacent portion of the ion beam.

Another object of the invention is to provide a novel structure for defining the portions of a calutron ion beam to be admitted into a pair of ion receptacles, which structure includes readily replaceable beam defining edges,

Still further objects of the invention will appear from the following description of a preferred embodiment thereof and from the accompanying drawings in which:

Figure 1 is a horizontal sectional view of a calutron tank, showing the arrangement of the source and receiver within the tank and the relation of the tank to the magnet, certain parts being shown somewhat schematically for simplicity;

Fig. 2 is a horizontal sectional view on an enlarged scale of the receiver shown in Fig. 1, the plane of the section being indicated by the line 2-2 in Fig. 4;

Fig. 3 is a vertical sectional view of the receiver shown in Fig. 1, the plane of the section being indicated by the line 33 in Fig. 4;

Fig. 4 is a vertical sectional view of the receiver shown in Fig. l, the plane of the section being indicated by the line 4-4 in Fig. 2;

Fig. 5 is an elevational view of the receiver showing the face plate of the receiver detached from a tank liner to which it is secured in use, as illustrated in Fig. 1, part of the face plate being broken away to show a beam defining structure secured to the back side thereof.

Referring to the drawings, Fig. '1 illustrates a calutron of the general character disclosed in the Lawrence application, mentioned above, but embodying certain modifications including, among other features, a receiver constructed in accordance with the present invention. The calutron comprises a C-shaped tank that is supported midway between a pair of horizontally disposed, vertically spaced apart, pole faces 11 (only one being shown) of a calutron magnet, whereby a substantially uniform magnetic field may be created throughout the interior of the tank with the flux paths passing upwardly therethrough. The tank 10 is adapted to be evacuated through a pumpout conduit 12 to reduce the interior pressure, in a manner disclosed in the Lawrence application.

A source unit, generally designated 13 and-illustrated schematically in Fig. 1, is mounted within the'tank 10 at one end thereof on a set of insulators 14 supported on one of a pair of removable end walls 15, the source unit being adapted to produce, from a polyisotopic charge material, a beam of singly ionized positive ions traveling along arcuate paths to regions of focus approximately 180 along said paths toward the opposite end of the tank.

As hereinbefore indicated, the source unit may be designed to project the ions along paths that are initially divergent to either side of a median path by various angles between predetermined maxima and that later converge toward and diverge beyond a region of focus at angles on either side of a median path equal to their respective initial angular divergences. This beam is schematically and somewhat ideally illustrated in Fig. 1

by two sets of three lines each, one set representing a median path 16 and two extreme paths 17 and 18 of a stream of ions of one isotope, and the other set representing a median path 19 and two extreme paths 20 and 21 of a stream of ions of another heavier isotope. The stream of ions represented by the first-mentioned set of lines 16, 1'7, and 18 converges toward and diverges beyond a region of focus 22 located approximately from the source unit 13 toward the opposite end of the tank 10; and, similarly, the stream of ions represented by the second-mentioned set of lines 19, 20, and 21 converges toward and diverges beyond a second region of focus 23 that is laterally spaced from the region of focus 22 of the ions of a lesser mass. A source unit capable of producing such an ion beam is disclosed in detail in the Lawrence application mentioned above.

As explained previously herein, it is impractical from a production standpoint to obtain a beam in which adjacent foci of two isotope ion streams are completely separated, when dealing with the heavy elements such as uranium, and the unattainable ideal beam illustrated has been shown only in order to disclose more clearly the relationships between the trajectories of ionscomprising a polyisotopic beam.

A receiver, generally designated 25, is mounted on a removable end wall 15 of the C-shaped tank 10, at the opposite end thereof from the source unit 13, for collecting and deionizing the ions arriving at the regions of focus 22 and 23, and for separately trapping the ions reaching the two regions of focus in such a manner that they can be separately removed from the calutron.

The receiver 25 is mounted on a tube 26 that serves both as a housing for the receiver and as a support therefor and that projects outwardly through an aperture (not shown) in the adjacent end wall 15 of the tank 10. The tube 26 is mounted on theadjacent end wall 15 and is insulated therefrom in any desired manner, as by a cylindrical insulator support 27 secured to the adjacent end wall 15 and surrounding the tubular support 26.

A liner 28 is mounted in the tank 19 on insulators (not shown) and is shaped to form an envelope enclosing the beam substantially from one end thereof to the other. The liner 28 is made of electrically conducting material and is maintained at the same electrical potential as the accelerating device 13a of the source unit 13 and the body of the receiver 25. As shown in Fig. 1, an end plate 29 at one end of the liner is provided with an opening 30 through which the beam may pass on leaving the accelerating device of the source unit, and an end plate 31 at the opposite end of the liner is provided with an opening 32 through which the beam may pass to the receiver 25. The function of such a liner is to provide a uniform electric field surrounding the beam, where the potential of the accelerating device (and, consequently, the potential of the beam) is different from that of the calutron tank. Several suitable liner constructions for performing this function are disclosed in the above-mentioned Lawrence application.

The receiver 25 includes a face plate 35 of rectangular configuration that is secured in any suitable manner to a flange 33 surrounding one end of the tubular housing 26, as with bolts 34, to close that end of the housing except for an opening 36 through which the portions of the beam to be collected may pass to a beam delimiting structure 37. The beam delimiting structure 37 is preferably formed of a number of separable elements that are secured to the back surface of the face plate 35 by means of a backing plate 38, that is in turn secured to the face plate by fastening means 38a, the several elements of the beam delimiting structure being arranged to define a pair of elongated rectangular openings 39 and 40 for respectively passing to the interior of the receiver delimiting portions of the beam respectively enriched with the two desired isotope components thereof.

As' best shown in Fig. 5, the beam defining structure may comprise two laterally spaced apart graphite plates 41 and 42, an intermediate graphite strip 43, and four graphite spacer elements 44 that serve to hold the other three members in proper spaced apart relation to define beam delimiting slots of the desired size and shape. These graphite members 41, 42, 43, and 44 are firmly clamped in place between the face plate 35 and seats 45 formed in the backing plate 38 along opposite sides of an elongated rectangular aperture 46 therein, the aperture 46 being somewhat larger than the aperture 36 in the face plate 35 and being aligned therewith. With this arrangement, eroded beam defining members may readily be replaced without necessitating the substitution of an entire new receiver face plate.

An inner frame 47, comprising four plates secured together to form an elongated chamber having open ends and a rectangular cross section, is secured to the back surface of the backing plate 38 by flanges 48 and fastening elements 49, with the open ends of the chamber aligned with the apertures 36 and 46 in the face plate 35 and backing plate 38, respectively. An ion receptacle or pocket 50 is mounted within the inner frame 47 on a side wall therof in electrically insulated relation thereto by means of a number of fastening elements 51 and cooperating insulator assemblies 52. As best shown in Figs. 2 and 4, the ion receiving pocket 50 may comprise a frame 53 open at one end and along the side thereof adjacent the front or face of the receiver, and a liner 54, preferably formed of molybdenum, is adapted to be slipped into the frame 53 in snug contact with the entire inner surface thereof. The liner 54 is closed on all sides except for a single, elongated, rectangular opening 55 therein that is somewhat larger than and is aligned with one of the anterior beam delimiting slots 39 in the beam defining structure 37, whereby substantially all of the ions entering the receiver through this beam delimiting slot will pass unimpeded into the interior of the pocket 50 and be trapped therein. The pocket 50 is substantially wider than the opening 55 therein, and the forward portion of the liner 54 is tapered in widthin the direction of the face plate to reduce the width of the pocket adjacent the opening 55 therein in order to provide space for a second ion receptacle (described below) for receiving ions entering the receiver through the other beam delimiting slot 40. This reduction in width is accomplished by inclining the forward portion 56 of one side wall of the liner 54 inwardly toward the opposite side wall thereof.

To prevent any substantial proportion of the ions entering the receiver through the last-mentioned beam delimiting slot 46 from finding its way into the pocket 50, a deflecting plate 58 is disposed close to and parallel with the forward inclined portion 56 of the pocket 50, within a thin edge 55 of the plate disposed just behind the intermediate beam defining strip 43 and extending parallel therewith. The deflecting plate 58 is provided with an angularly related extension 60 that is adapted to be secured to a seond plate 61 in surface to surface contact therewith, the second plate 61 being disposed parallel to the general direction of travel of the beam adjacent the receiver, whereby the two plates 58 and61 form an ion trap or pocket 62 having rearwardly converging side walls. A shielding member 63, preferably formed of sheet metal, is secured to the forward edge of the second plate 61 in any suitable manner and projects generally toward the thin edge 59 of the deflecting plate 58, but terminates short thereof, to define one side of a gap 64 between the shielding member and the deflecting plate, the gap being somewhat wider than the beam delimiting slots in the beam defining structure 37. A target plate 65, preferably formed of molybdenum, is suitably secured over that part of the surface of the deflecting plate 58 that would be most heavily bombarded by ions passing into the trap 62 through the gap 64.

The trap 62 is mounted on a side wall of the inner frame 47 .in electrically insulated relation thereto by means of a number of fastening elements 66 and cooperating insulator assemblies 67, and is so disposed that the gap 64 is closely adjacent and aligned with the beam delimiting slot 40 in the beam defining structure 37 for admitting into the trap 62 substantially all of the ions passing through the aligned beam delimiting slot. Ions entering the trap 62 through the gap 64 impinge upon the target plate 65, and, after being deionized, are scattered or sputtered therefrom toward the inner surfaces of the second plate 61 of the pocket 62 or the shielding member 63 secured thereto. Practically all of the material so deflected will finally lodge within the trap 62 or will fall or scatter out either end of the trap and finally come to rest within the inner frame 47, which thus serves as a collecting chamber for this material. Obviously, if desired, the ends of the trap 62 may be suitably closed to retain therein substantially all of the material entering the trap through the gap 64.

It will be noted that the two adjacent pockets 50 and 62 have adjacent side walls that are so inclined with respect to the general direction of travel of the beam at the receiver that the pocketSti is disposed partially behind the pocket 62. It will also be noted that each pocket is substantially Wider along its front wall than the ion entrance slot or gap therein. This arrangement permits designing the configurations of both pockets so that sub stantially all of the ions entering the pockets will first strike interior surfaces thereof at acute angles to minimize the loss of received material by scattering or sputtering from the bombarded walls outwardly through the entrance passages of the pockets. In addition to increasing the retention efliciencies of the ion receiving pockets,

such non-reflecting walls reducethe embedding of collected material therein, thus facilitating subsequent removal of the material, and enlarge the areas subjected to direct ion bombardment, thereby minimizing the development of hot spots in the pocket walls.

In order to cool the parts of the receiver most heavily bombarded by the ion beam, a cooling fluid line 70 is brought into the tubular housing 26 from outside the calutron tank, through appropriate vacuum seals (not shown), and is run along the back side of the face plate 35 in heat conducting relation thereto substantially completely around the inner frame 48 and thence out of the calutron tank again through the tubular housing 26, whereby a suitable cooling fluid may be circulated through the tube during a run to cool the face plate and the other parts carried thereby. A second cooling fluid line 71 is brought into the tubular housing 26 from outside the calutron tank, through appropriate vacuum seals (not shown), and into the interior of the inner frame 48 in heat conducting relation to a supporting plate 72 that is secured to an extension of the plate 61 of the second ion receiving pocket by fastening elements 73 and thence out of the calutron tank again through the tubular housing 26, whereby a suitable cooling fluid may be circulated through the cooling fluid line 71 for conducting heat away from the ion trap 62.

The useof an electrically nonconducting cooling fluid, such as distilled'water, permits the cooling fluid line 71 to serve as an electrical lead for measuring the quantity of ions striking the interior walls of the second ion receiving pocket 62.

When the receiver 25 is employed to collect in the pocket 56 uranium enriched with, the U isotope, the intensity of the stream of ions entering the pocket 50 is not generally sufiiciently great to require that this pocket be cooled in the above-described manner. For the purpose of measuring the quantity of ions received by the pocket 56, a suitably insulated electrical lead 74 may be attached to the bottom of the pocket by means of a screw 75 and may be brought out of the tank 10 through 7 the tubular support 26 in the same manner as the cooling fluid lines 70 and 71.

In general, the mode of operation of this receiver will be apparent from the foregoing detailed description of the structure and function of its component parts. After a reception run has been concluded, access to the receiver for recovering the collected material is accomplished by raising the interior pressure of the tank to atmospheric pressure and removing the tank end wall on which the receiver is mounted. By removing the fastening elements 49 that hold the inner frame 47 to the face plate structure and the fastening elements 73 by which the supporting plate 72 for the cooling fluid line 71 is atached to the ion receiving pocket, the entire inner frame 47 may be removed from the receiver. The ion receiving pocket 50 can then be removed from the inner frame 47 in an obvious manner, and the liner 54 may be withdrawn therefrom for recovery of the material deposited therein, which material will include substantially all of the deionized beam components that entered the receiver through the beam delimiting slot 39. The material that entered the receiver through the beam delimiting slot 40 may then be separately recovered from the surfaces of the ion receiving pocket 62 and from the inner surfaces of the inner frame 47.

While I have described in detail a specific embodiment of my invention, it is to be understood that'this has been done for illustrative purposes and that the scope of my invention is not limited thereby except as required by the appended claims.

What is claimed is:

1. In a calutron having means for establishing an ion beam and for causing divergence of beam components of different mass toward respective regions of focus, an ion receiver comprising a pair of pockets disposed closely adjacent each other, each pocket being provided with an opening in a front wall thereof for admitting a selected of different mass toward respective regions of focus, an

3. In a calutron having means for establishing an ion beam and for causing divergence of beam components of different mass toward respective regions of focus, an ion receiver comprising a pair of pockets disposed closely adjacent each other, each pocket being provided with an opening in a front wall thereof for admitting a selected portion of the ion beam, one of said pockets having an inclined side wall that extends from between said openings generally rearwardly and toward an opposite side wall thereof, and the other of said pockets having a side wall that is disposed closely adjacent and behind said inclined-side wall, said pockets being electrically insulated from each other.

' 4. In a calutron having means for establishing an ion beam and for causing divergence of beam components of different mass toward respective regions of focus, an ion receiver comprisng means disposed in the path of the beam for passing only selected delimited portions thereof, a pair of pockets disposed closely adjacent each other behind said means with respect to the approaching beam, each pocket being provided with an opening in a front wall thereof for admitting part of the delimited portions of the beam passed by said means, one of said pockets having an inclined side wall that extends from between said openings generally rearwardly and toward an opposite side wall thereof, and the other of said pockets having a side wall that is disposed closely adjacent and behind said inclined side wall.

5. In a calutron comprising a vacuum envelope and means for producing a beam of ions within said envelope, an ion receiver removably secured within said envelope and comprising an outer shell having means for admitting into the shell selected delimited portions of said beam, a pair of pockets disposed closely adjacent each other within said outer shell, one of said pockets being provided with an opening for admitting a delimited portion of said beam entering said outer shell, and the other of said pockets having an opening for admitting another delimited portion of said beam entering said outer shell, each of said pockets being disposed with one wall forming an acute angle with respect to said delimited portion of said beam for interception thereof.

6. In a calutron comprising a vacuum envelope and means for producing a beam of ions within said envelope, an ion receiver comprising a face plate disposed in the path of said beam and having an opening therein through which a portion of the beam may pass, a backing plate associated with said face plate and having an opening therein aligned with the opening in said face plate, and a plurality of beam delimiting members secured between said face plate and said backing plate on opposite sides of said openings for restricting the effective width thereof, each of said members having an edge defining the restricted portions of said openings.

References Cited in the file of this patent UNITED STATES PATENTS 1,690,297 Hoge Nov. 6, 1928 1,856,195 Sindeband et al. May 3, 1932 1,952,695 Webb et al Mar. 27, 1934 2,202,588 Knieppamp May 28, 1940 2,331,189 Hipple Oct. 5, 1943 2,341,551 Hoover Feb. 15, 1944 2,378,962 Washburn June 26, 1945 FOREIGN PATENTS 493,534 Great Britain 1938 OTHER REFERENCES Hogness et al.: Physical Review, vol. 26, 1925, pp. 44-46.

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