US2874295A

US2874295A - Mass separators

Info

Publication number: US2874295A
Application number: US645465A
Authority: US
Inventors: Oppenheimer Frank; James W Bell
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-02-04
Filing date: 1946-02-04
Publication date: 1959-02-17
Anticipated expiration: 1976-02-17

Description

' Feb. 17, 1959 F. OPPENHEVIMER ET A 2,374,295

' ,MASS SEPARATORS 8 Sheets-Sheet 1 Filed Feb. 4, 1946 FIEI J Feb. 17, 1959 QPPENHEIMER ETAL 2,874,295

MASS SEPARATORS s Sheets- -Sheet 2 Filed Feb. 4, 1946 FIE E .50 K V, Pan/er Supp/y Vacuum Z'nye/ope7 IN V EN TOR.5 frank 0,0,0 e/vfi e/rner James IAK 5e// Y Arce/ero 1 lEi Z3 Feb. 17, 1959 F. QPPENHEIMER AL 2,874,295

MASS SEPARATORS 8 Sheets-Sheet 3 I Filed Feb., 4, 1946 m-v m hwnl mn QQ mm Jam es W Bell Feb. 17, 1959 F. OPPENHEIMER L 2,874,295

MASS SEPARATORS Filed Feb. 4. 1946 8 Sheets-Sheet 4 v INVENTORS Frank OpperI/Ie/Mer Byjames M52 Feb. 17, 1959 F, OPPENHEIMER 'ET'AL 2,874,295

MASS SEPARATORS' Filed Feb. 4, 1946 s Sheets-Sheet, s

k3 INVENTORS Feb. 17, 1959 F. OPPENHEIMER ErAL 2, 4,

MASS SEPARATQRS 8 Sheets-Sheet 6 Filed Feb. 4, i946.

h m hh INVENTORS Fran-i Oppenfie/rner- James M 5e// NNQ , F. OPPENHEIMER Ei'AL 2,874,295

Feb. 17, 1959 MASS SEPARATORS 8 Sheets-Sheet 7 Filed Feb.. 4, 1946 f'r-arz OppenAe/nver pyJamgs 1415a Feb; 17, 1959 OPPENHEIMER ETAL 2,874,295

IL I I Y I I, I I I I 1 I I I I I I I I I I I I I I I l I I INVENTORS Fran/ Oppen/e/fnr BY/am as M 52 Ernest 0. Lawrence.

United States Pate MASS SEPARATORS Frank Oppenheimer and James W. Bell, Berkeley, Calif.,

assignors to the United States'of America as represented by the United States Atomic Energy Commission Application February 4, 1946, Serial No. 645,465

15 Claims. (Cl. 25041.9)

This invention relates to calutrons and more particularly to an ion source for mass separators, which source is adapted to project a beam of high-velocity ions into a magnetic field.

Calutrons of the general type referred to are described in U. S. Patent No. 2,709,222, issued May 24, 1955, to

These devices are adapted to separate commercial quantities of materials that differ from each other in certain properties, particularly where the materials differ in mass. In practice, the materials are reduced to a very small size such as molecular or atomic particles, are ionized preferably with like charges, and projected into a magnetic field. If the energies of the two particles are substantially equal, the heavier particles will describe a circular path of greater radius than the lighter particles, and if suitable collectors are interposed in the circular paths, the ions may be collected, deionized, and a quantity of the material realized that is considerably separated from material of different mass as compared to the original heterogeneous charge. These mass separators are particularly useful for separating isotopes of a given element, and in practice have been employed to separate isotopes of uranium, particularly the isotope U from the isotope U The most general technique of operation of these calutrons is substantially embodied in the design and mode of operation of the present ion source. The desired metallic element is converted to a salt which may be vaporized at a convenient temperature, and when the isotopes of uranium are to be separated, it is preferable to change the metal element into chloride or fluoride salts path according to the strength of the magnetic field. The ions, being positively charged particles, are attracted toward the negatively charged electrode and pass through the aperture therein to describe the circular path just referred to. The heavier U ions have substantially the same energy as the lighter U ions, resulting in the heavier ions describing the arc of greater radius. In practice, a divergent beam is used which appears to originate substantially at a point close to the ion exit, and because of the effect of magnetic focusing upon such a divergent beam, the greatest distance of separation is realized at the 180 point of travel in the circular path of the ions. Collectors are accordingly disposed at the 180 point, the U ions being received in a collector that is separate from that for the U ions. When it is possible to obtain an 'ion beam wherein the initial paths of the ions are parallel to each other, the collection of course takes place at the 90 point of travel.

The general mode of operation just described is somewhat modified by certain improvements that are embodied in the present invention but which form no part thereof. One ofthese improvements is the use of a decelerating electrode as Well as an accelerating electrode. The accelerating electrode ofsuch a structure is held at a negative potential which would result in a circular ion path of much greater radius than desired, and accordingly an apertured decelerating electrode is placed closely adjacent to the accelerating electrode so as to reduce the energy of the ion particles passing therethrough, causing the ions to take a path of the desired radius.

. The purpose of this increased accelerating voltage is to to realize a much lower vaporizing temperature than that p of the metal. The desired salt of the element is placed in a container which is inserted in a reservoir or furnace chamber of the ion source. The entire ion source mechanism is then placed Within a vacuum envelope which is positioned within a magnetic field. When a suitable vacuum is obtained in the vacuum envelope, such as a pressure of 10- to 10- mm. of mercury, heater elements of the reservoir are operated, vaporizing the salt, which vapor is directed into an ionizing chamber. The ionizing medium is an arc aligned with the magnetic field and the vapor'must pass through the are before it can reach the exit opening of the ionizing or are chamber. The are is not diflicult to strike because of the fact that the charge vapor present raises the pressure of the arc chamber considerably above that of the vacuum tank pressure just mentioned. The electron stream of the arc bombards the molecules of metal salt, breaking them into parts, and in the case of uranium chlorides, a negative chlorine ion is formed and a positive uranium ion is formed, the majority of the uranium ions being singly charged.

An apertured accelerating electrode is placed outside of the ion exit opening and is held at a high negative potential, which will cause the positive ions to be accelerated and thereafter they describe a suitable circular obtain a greater number of ions from the arc chamber, since the number of ions withdrawn is dependent upon the negative voltage of the accelerating electrode. Thus, the use of accelerating and decelerating electrodes in an ion source results in a much larger ion beam having the same radius, or a smaller radius for the same size ion beam than had been produced prior to this improvement.

A structural feature of considerable importance is also embodied in the present invention and in connection with which certain aspects of the invention find employment. This feature is the use of an ion generator (including the arc block) that is insulated from the supporting structure of the vacuum envelope, and the operation of the ion generator at a positive potential with respect thereto. In considering this feature it will be realized that an ion source is preferably operated in a vacuum tank that is maintained at ground potential, since this insures the greatest safety for the operators of the equipment. The ion generator which is attached to the inside of the tank may be operated at the same potential as the tank itself,

in which case the accelerating electrode must be negative withrespect to the tank and the ion generator so as to create an accelerating electric field for the ions. In such a structure, however, there'will be an electric field from the electrode structure to the tank, and after the ions pass through the apertured accelerating electrode they will encounter this electric field which will now be in the opposite sense and cause deceleration of the ions. This undesired result is eliminated by enclosing the area traversedby the ions in a metal tube held at the same potential as the last electrode in the electrode structure.

The collector is also maintained at a similar potential. The ions in such a case travel along a path that is completely free of electric fields, the electric fields then being established between the path-enclosing tube and the vacuum tank.

between this electrode and the tank to perturb the paths of travel of the ions. When this last accelerating electrode is at ground potential, the ion generator must necessarily be at a potential that is positive with respect thereto so that there will be a negative electric field to withdraw the ions from the arc block and accelerate them. When accelerating and decelerating electrodes are used, the ion generator is held at a potential positive with respect to ground, the accelerating electrode is held at a potential negative with respect to ground, and the decelerating electrode is held at ground potential since it is the last, or exit, electrode.

In the past, the use of ion generators at a positive potential with respect to the grounded tank, which are referred to as hot ion generators, has resulted in severe problems of electron bombardment of the various parts of the entire source unit, and particularly the insulators supporting the ion generator. These electrons come from several places about the ion source, for example stray electrons that may be knocked out of the arc chamber by heavier particles, electrons from gas that may be ionized in the vacuum tank by the travel of the ions, and by secondary emission from the accelerating and decelerating electrodes after bombardment by the ion beam or the side bands thereof, such as doubly-charged or triply-charged uranium ions or positive chlorine ions. Upon being released, these electrons are subjected to an electric field about the ion source that is caused by the fact that the top and bottom walls of the vacuum envelope are at ground and the ion generator is at a positive potential with respect thereto. The electrons, being negatively charged, are attracted toward the ion generator, but since the entire ion source is in a strong magnetic field they are confined substantially to the lines of magnetic flux in their travel. They therefore continue to be accelerated along the magnetic field until they pass the center of this electric field as they near the ion generator. The electrons are then decelerated as they approach the top or bottom of the tank, assuming the magnetic field to be vertical, since these are negative with respect to the ion source. They are stopped at some intermediate point, depending upon the initial strength of the electric field in which the electron is generated, and begin a reverse travel along the magnetic field, due to the fact that the field now accelerates them that had previously decelerated them after arriving with some energy.

The electrons thus oscillate up and down in the magnetic field at a rate believed to be several thousand times per second. Due to the usual forces involved in a magnetic field, the electrons, while oscillating vigorously, will begin a slow migration in a clockwise manner about the hot ion source as viewed from above, when the south pole of the magnet is the upper pole. They thus migrate completely around the ion generator and strike any insulators that are transverse to the magnetic field. In this connection it is noted that prior to the present invention, the common practice was to support hot ion generators by insulators that were transverse to the magnetic field. The oscillating electrons in such cases struck the insulator, and since the electrons contained considerable energy, caused the insulator to become heated at very localized points; namely, the nearest edge to the clockwise travel of the electrons. This local heating of the insulator caused it to crack and thereupon become useless.

This insulator cracking problem is so severe as to seriously limit the use of hot ion generators, and accordingly very elaborate shielding has been devised for the protection of these insulators that are transverse to the magnetic field. The present inventiomhowever, avoids the useof any such insulator shielding by a novel insulating structure that avoids the effects of electron oscillation, thus prolonging the life of ion source units and also resulting in much cheaper production costs. Structures which avoid the use of insulator protecting shielding are employed at two points in the present invention, one in the support of the ion generator, and the other in the introduction of the hot (i. e., positive) leads that are brought through the vacuum envelope to the ion generator.

As indicated heretofore, the general structure in which the invention will be embodied in an ion source for a calutron, wherein the ion source is held at a high positive potential, for example 35 kv., the accelerating electrode is held at a negative potential, for example 15 kv., and a decelerating electrode is employed which is held at ground potential. The entire source unit is supported by the vacuum envelope through the medium of a bracket secured to a removable face plate of the vacuum envelope, which bracket forms a supporting platform that is generally transverse to the magnetic field. The ion generator is mounted on a pedestal-type insulator supported on the bracket, and the hot leads are brought into the vacuum envelope through a tubular elbow connected to the vacuum envelope, having the axis of its outer opening aligned with the magnetic field at which point a bushing-type insulator is employed.

A general object of the invention is to provide a simple and reliable ion source mechanism for a mass separator.

It is another object of the invention to provide an ion source having a simple and rugged mounting.

Another object of the invention is to provide an ion source having an insulated ion generator at a positive potential with respect to the, enclosing vacuum tank, that is free from the problem of electron bombardment of the insulator.

Still another object of the invention is to provide an ion source having an ion generator at a positive potential that has the electrical leads therefor brought through the vacuum tank by a construction that protects the insulator therefor from electron oscillation.

A feature of the invention is the provision of the ion generator with a novel type of heating and temperature control apparatus.

Other'objects, features and advantages of the invention will be apparent in the following description and claims.

The invention will be described with reference to the accompanying drawings, in which:

Figure l is an isometric view of the complete source, including the removable face-plate of the vacuum envelope;

Figure 2 is a schematic view of the principal electrical components of the source, wherein the applied voltages are indicated by different types of lines outlining the components;

Figure 3 is an isometric view, partially exploded, of the apertured accelerating electrode and its supporting and adjusting structure;

Figure 4 is a plan view in full section of the ion generator, the accelerating, and the decelerating structure of the source, taken along the line 44 of Figure 5;

Figure 5 is an elevation view in full section of the ion source along the line 55 of Figure 9, as viewed from its right side, assuming that the forward end of the source is the ion exit end;

Figure 6 is an elevation view of the complete source as viewed from its left side, the view being similar to that of Figure 2;

Figure 7 is an elevational view of the complete ion source from the right-hand side, partly in section and with portions broken away, but with the grounded shielding removed;

Figure 8 is a sectional view of the electrical lead assembly to the high positive ion generator, taken along the line 88 of Figure 7.

Figure 9 is a plan view of the part of the source inside the vacuum envelope including the removable face plate, supporting bracket, ion generator, and accelerating and decelerating structure, except that the plate on the top of the ion generator has been broken away in part; and

Figure is an isomeric view of the oil heat transfer tubes for the reservoir and mixing chamber.

The ion source unit is shown in its completely assembled condition in Figure 1. There is illustrated a removable face plate for the vacuum envelope, to which is secured a supporting bracket 16. The bracket 16 is preferably cast and provides a supporting platform for the ion generator, and the accelerating and decelerating electrodes and that is generally transverse to the magnetic field, which is vertical with respect to Figure 1. As a general measure of the size of this particular embodiment of the invention, it is noted that in one operative embodiment the bracket 16 is roughly about three feet in length and a foot and a half wide. Supported by bracket 16 is an ion generator unit 17 that is held at a high positive potential with respect to the face plate 15 and the supporting bracket 16, which are at ground potential. The ion generator 17 is surrounded about its sides by spaced shielding 18, held at ground potential and therefore referred to as grounded or cold shielding. Potential is supplied to the ion generator 17 by hot leads 24 which pass through an aperture 23 in the face plate 15 and through an aperture in the grounded shielding 18. A tubular portion of the grounded shielding 18 projects into the aperture 23 and surrounds the hot leads 24. The accelerating electrode is not visible in Figure 1; however, a decelerating electrode 19 does appear in this view. This decelerating electrode 19 is heated electrically, one terminal for the heater supply being a strip 22 Se cured to the forward end of bracket 16, the other end being grounded to the decelerating electrode 19, which is at ground potential. by a water tube 21 of copper or other suitable material, laid about its inside edges. All parts of the ion source are preferably of a nonmagnetic material to prevent local disturbances of the magnetic field passing therethrough.

The electrical construction and operation of the entire The supporting bracket 16 is cooled source unit is shown in Figure 2, wherein are shown bottom and

top walls

26 and 27 of a vacuum envelope, as Well as the face plate 15 that completes the vacuum enclosure. The various parts of the ion source unit which are at ground potential are indicated by solid lines, the various insulators are indicated by stippled surfaces, the parts of the ion source at a high positive potential are indicated by dash-dot lines, and the parts of the ion source at negative potential are indicated by broken lina. A schematic power supply 43 is shown which may be of any suitable capacity, such as 50 kv. A resistor 44 connects the output terminals and at any desired point this resistor may be connected to ground, as by a lead 48, so that one end of the power supply 43 is negative with respect to ground and the other end positive.

The ion generator 17 is supported on an insulator 28 of the pedestal type by means of a T-shaped bracket 29. There is thus provided a physical clearance between the ion generator 17 and all other parts of the ion source. The ion generator 17 is held at a high positive potential, as indicated by the dash-dot lines, by a lead 34 connected thereto and passing through the face plate 15 into a tubular elbow 36 which 'has a bushing-type insulator 37 secured to its lower end. The lower end of the bushing insulator 37 is closed by a plate 38, to which a positive lead 47 from the power supply 43 is connected. A cathode assembly 33 is also shown in dot-dash lines, inasmuch as this structure varies from the potential of the ion generator 17 by only a few hundred volts, and the leads are similarly brought through the elbow tube 36. Also shown in Figure 2 is an accelerating electrode 31 which is suitably apertured as indicated in Figure 3, so that the ions from the generator 17 may pass therethrough. This accelerating electrode is supported on two post insulators 32 by an adjustable mechanism more clearly illustrated in 'Figure 3. A lead 39 for the accelerating electrode passes through the face plate 15 by means of a transformer-type insulator 41, supported on a tubular collar 42 secured 6 to the face plate 15. A lead 46 connects the outer end of insulator 41 with the negative terminal of the power supply 43. The decelerating electrode 19 is at ground potential, as indicated by the solid lines, and needs no electrical lead because it is mechanically fastened to the grounded bracket 16, which in turn is secured to the grounded face plate 15.

In operation, positive ions are formed in generator 17 and are accelerated outwardly therefrom by the negative potential on accelerator 31. Thereafter, they pass through the apertured decelerating electrode 19 and, still possessing considerable energy, pass into the magnetic field, there to describe their circular paths as previously mentioned. Suitable collectors may be disposed in these paths, the ions deionized, and material collected. It will be noted that the ion generator mounting bracket 29 covers one end of the pedestal-type insulator 28, the other end of which is secured to the bracket 16. There is thus a simple electric field between opposite ends of the insulator 28 that are aligned with the magnetic field, which field does not induce electron oscillation. As will be described in more detail later, there are no parts of the bushing insulator 37 that are not similarly capped by a high potential at one end and a different potential at the other with respect to the magnetic field, thus avoiding electric fields that induce electron oscillation.

The detailed structure of the accelerating electrode 31 will be described with reference to Figure 3 before proceeding further with the general description of the ion source as a whole. The post insulators 32 (one of which is shown in Figure 3) support a metallic strip 51 having a rectangular groove 52 cut therein. Fitted within the groove 52 is a right-angle strip 53 having two elongated holes 54 therethrough into which are placed screws 56 that are threaded into the strip 51 to secure the two strips together. Slots 57 are formed through the other leg of the angle strip 53, through which screws 58 pass to thread into a flatted end 61 of a supporting arm 62 for the accelerating electrode 31. Three screws 59 are threaded into the strip 53 to contact the face of the fiatted portion 61 to adjust the position of the support arm 62 in any plane of movement. The

screws

59 and 58 are covered by a cap 64 of sheet metal, secured by screws 66, thus protecting the screw heads from the effects of corrosion by the un-ionized vapor that issues from the ion generator 17. The supporting arm 62 is spliced to a shank 63 of the electrode 31, which has an aperture 49 therethrough. The apertured electrode 31, together with its shank 63, is preferably milled from a single piece of carbon, since this material resists corrosion and bombardment more successfully than most metals. The adjusting structure just described permits adjustment of the accelerating electrode in all three dimensions in space and in any plane of rotation.

The general description of the ion source is continued with reference to Figures 4 and 5. There it will be noted that the ion generator 17 includes a reservoir 71 which is suitably heated, and into which a charge container 72 may be inserted. When a cap 73 of the charge bottle is removed and the charge heated, vapor flows through a nipple 74 into a mixing chamber 76, where it is distributed somewhat confined by a double knife-edge bafile plate 77. Thereafter, it passes into an arc chamber 78 where it is bombarded by the electron stream of an are initiated by an electron emissive filament 79. The ions and tin-ionized vapor thereafter issue through the arc slit opening 81, the positive ions being accelerated by the high negative potential upon the accelerating electrode 31. After passing through the apertured electrode 31, the ions are subjected to a decelerating electric field defined by an apertured plate 82 having rounded aperture edges and mounted in the decelerating electrode structure 19. A decelerating electric field is present due to the fact that the decelerating electrode 19 is held at ground potential, which is positive with respect to the accelerating electrode 31. Typical voltages that may be applied to the electrode structure are a positive 35' kv. on the ion generator 17 with respect to ground, a negative kv. on the accelerating electrode 31 with respect to ground, resulting in a total accelerating field of 50 kv., and a decelerating potential at ground resulting in a decelerating field of 15 kv., giving the beam a net energy as though accelerated by a single electrode of kv.

Having now described the principal components and the general mode of operation of the source unit embodying the invention, a detailed description will now be given referring again to Figures 4 and 5. Passing through the bottom of the supporting bracket 16 are screws 67, which secure the pedestal-type insulator 23, as well as a lower shallow cup 68 that accurately defines the electric field about the lower end of the insulator. Placed on the top of the insulator 28 are two spacer plates 69, the larger of which is cooled by a water tube 83. The T-shaped bracket 29 is secured to the insulator by bolts 84 passing therethrough and through the spacers 69. The ion generator 17 is secured to the T-shaped bracket 29 by bolts that secure a U-shaped sheet metal portion 86 of the ion generator, the top of which remains open. The bottom of the U member 86 is closed by a readily removable plate 87 which gives access to the reservoir 71 after removal of a reservoir bottom plate S ll. Secured to the forward end of the U member is a casting 38 in which are formed the mixing chamber 76 and the arc chamber 73. The mixing chamber 76 is lined by a suitable corrosion-resisting material 89, such as stainless steel. The entire arc chamber and the arc slit geometry is formed of a single piece of carbon 91, this material being chosen because of its corrosion-resisting properties. The are chamber carbon-911 is secured to the casting 88 by two side strips 92, pressing against shoulders therein. The ion exit or are slit opening is defined by a beveled edge 93 and two stepped grooves 94 on each side. The operation of the ion exit opening lil is assisted by maintaining the arc slit edges at a high temperature. This is accomplished by cutting a deep groove 96 in the outer face of the carbon back toward the are chamber '78. This groove prevents the conduction of heat from the arc slit opening, which heat is derived from the are itself, thus maintaining the slits at a high temperature which prevents condensation of vapor thereon, resulting in a clean structure at all times.

The heating system for the reservoir 71 and the mixing chamber '75 is also illustrated in Figures 4 and 5, as Well as in Figure 10. This system consists of tubing appropriately disposed about the reservoir and mixing chamber and through which a heated liquid may be circulatcd, such as oil. Since this tubing is an integral part of the ion generator, it must be held at the same positive potential, and the tubing is therefore brought through the tubular elbow 36 and in fact forms the electrical lead also for the ion generator. Referring to Figures 4, 5, and 10, the inner end of the tube through the tubular elbow is capped by an angle block 97 to which is connected a length of square tubing 93, formed in a helix to surround the tubular metal piece forming the reservoir 71. A lower end of the helix is led forwardly and then upwardly to the top of the arc and mixing chamber casting 88, which has grooves 99 formed in either side thereof. This end of the tube 98 is there connected to a header 161 having three tubes 1922 connected thereto, and which fit in the grooves 99. A lower header 103 is cross-connected to a similarheader 104 on the opposite side of casting 38 by a connecting tube 106. Three tubes .197 lead from this lower header to an upper header 138, from whence the return conduit 1'99 leads to a junction block 111 (Figure 9) and thence out the tubular elbow 36.

This type of heating system is particularly suitable for uranium isotope mass separators wherein uranium hexare supported by insulated clamps.

. 8 achloride is used as a charge material. This material vaporizes at the operating pressure at about 90 C., making feasible the use of hot oil. Heating the charge container 72 also melts a thermoplastic seal about the ferrous cover 73 thereof, whereupon the magnetic field causes the cover 73 to assume a vertical position permitting the exit of vapor. The

tubes

152 and 107 that lie against the arc and mixing chamber casting 88, which may be cast of copper, serve not only to beat this chamber to a desired temperature but also to maintain the temperature fairly constant. These tubes may even withdraw heat from this casting 88 when an external source of heat, such as the arc, raises the casting to a temperature greater than that desired. Temperatures higher than the operating temperature may result in the decomposition of uranium hexachloride vapor to uranium tetrachloride, which has a distinctly higher vaporizing temperature and would therefore accumulate as a solid in an undesired manner.

The cathode structure for the ion generator is best illustrated in Figures 5 and 9. Two cathode leads 1.1.2 and 113 pass through the tubular elbow 36 and terminate in cathode clamp blocks 114 and 116, respectively, separated by a strip of mica 115. A difference of potential of one to ten volts is maintained between these

leads

112 and 113 to pass current through the U-shaped filament 7? clamped in blocks 114 and 116. Inasmuch as considerable heat is evolved when the filament 79 is raised to electron-emissive temperatures by the conductive current, the

leads

112 and 113 are preferably squirt tubes; that is, each includes concentric tubing through which cooling water may be introduced and which is exhausted in the space between the two tubes, the inner tube ending a short distance from the end of the outer tube. In this manner the

electrical leads

112 and 113 act as water cooling tubes also, keeping the clamp blocks 114 and 116 cooled. The filament leads 1.12 and 113 Referring to Figure 5, a block 117 is secured by a screw to the back of the casting 86 and two short post insulators 118 are secured thereto, the upper ends of which support securing blocks 119. A screw fastens each securing block 119 to its respective cathode clamp block. A similar insulated supporting mechanism for the cathode leads is provided at the back wall of the U-shaped ion generator member 86, and is generally referred to as the insulator assembly 120. Placed over the filament 79 is a tungsten plate 121 connected to clamp block 114, which is preferably the negative of the two blocks. This plate creates an electric field that is negative with respect to-thc electron emission from the filament, preventing a iiow of electrons to the upper cover of the ion generator which would occur in the absence of such a plate.

Referring still to Figtu'e 5, the upper end of the arc chamber '78 includes an apertured plate 122, which aperture admits only the most intense and steady electron emission from the filament The entire carbon arc block structure is electrically positive with respect to the filament, and acceleration of the bombarding electrons takes place between the filament 79 and the apertured plate 122. The electrons enter the arc chamber, ionize the vapor emanating from the charge bottle 72, and create an are which enhances the ionizing action of the electron stream. An electron bombardment plate 123 is provided in the bottom of the arc chamber and acts to stop the electrons of the arc discharge. This plate 123 is preferably inserted in slots in structure defining the ion exit 81.

The details of construction of the decelerating electrode are best shown in Figures 1, 4, 5, and 7. Secured to the support bracket 16 is a pair of upright supports 124. The decelerating electrode 19, which is preferably cast of copper or similar nonmagnetic material, is mounted therein byscrews 126. The principal electric field of the electrode is defined by an apertured plate 82* fittedin a slot in casting 19, and may be' formed of carbon.

Cast into the decelerating electrode, 19 is a pair of resistance heaters 127 of the Calrod type, which comprise an inner rod of resistance material insulated from an outer tube by a non-conductor such as magnesium oxide. Current is supplied to the heaters by the strip 22, which is at 80 to 115 volts above ground, and the inner ends of the heaters are grounded to the decelerating electrode structure. A lead 128 passing through the face plate 15 connects the strip 22 with a suitable source of supply.

The details of the structure for introducing the hot leads inside the vacuum envelope are shown best in Figures 7 and 8. Referring to Figure 7, it will be noted that the vacuum envelope is placed between magnetic pole pieces 129 of a magnet, which is preferably an electromagnet having an iron core. Although the principal magnetic field is through the ion generator and the nearby structure, there is also an intense fringing magnetic field through the tubular elbow 36. The tubular elbow 36 is secured to the face plate 15 by studs passing through an integral flange 131. The elbow 36 turns through the desired angle, in this case 90, to align the axis of the outer opening with the magnetic field. A flange 132 is secured to this outer end and an insulator supporting ring is secured thereto which is spaced from the bushing-type insulator 37. Melted sulfur is poured into the space between these two members, and upon cooling expands to form a tight joint securingthe bushing insulator to the flange 132. Suitable seals 133 are provided to make the 'joint of the insulator 37 with the flange 132 airtight. The cover plate'38'is secured to the lower end of the bushing insulator 37 in a similar manner The two ends of the insulator cooling tubing 83 pass through the-cover'plate 38 by means of a suitable vacuum seal, and oil heating tubes 134 also pass therethroughand are suitably sealed against air leak. The

cathode squirt tubes

112 and 113 also pass therethrough but are suitably insulated from the cover plate 38 and from each other by an insulator seal 136. The assembly of all three tubes is shown in Figure 8, where it will be noted that the oil heating tubes 134 and the filament squirt tubes 112'and 113 are enclosed by a.

two-piece housing 137, secured together by screws. The insulatoncooling tube ends 83 have a separate housing 138;

Referring now to Figure 7, it will be noted that the housing 137 about the hot leads that pass through the elbow 36. is at a high positive potential with respect to the grounded elbow 36, and that a strong magnetic field traverses both elements. Electrons that find their way into this elbow are therefore caused to oscillate as mentioned previously along themagnetic field, due to the electric field set up. These electrons tend to migrate toward the outer end of the tube while still maintaining their oscillating condition. In the present structure, however, as the electrons migrate past the turn in the tube they are exposed to the positive potential of the coverpla te 38, as well as that of the hot lead housing 137, with the grounded elbow wall intermediate the two. This electric field, a negative member between two positive members, does not permit electron oscillation, and the electrons will discharge to the nearest positive member. Thus the electrons discharge to the housing 137 or the, plate 38, both of which are made of thick metal and therefore able to withstand local heating. It will be noted that the bushing-type insulator 37 is'entirely protected from bombardmentby these electrons because it is within the confines of the flange'132 and the plate 38, and since the electrons cannot leave their paths as determined by the magnetic field, there is no possibility that they will strike this insulaton For this reason, the defects of prior insulator construction, namely local heating'due tobombardmenbtare completely eliminated, and

electrons.

reliable service as well as long life result from this com s'truction.

.The accelerating electrode bushing passing through the face plate 15 is best shown in Figures 6 and 9. The flanged collar 42 is fastened to the face plate .15, and the insulator 41 of the transformer type is inserted through a hole in the face plate and rests upon the flanged collar 42. A split clamping ring 139 mechanically secures the insulator 41 to the collar 42. The accelerating electrode lead 39 is connected to the inner end of the insulator 41 and the power supply lead 46 is connected to the outer end, which end is tight against air leaks in accordance with standard manufacturing technique. I

As mentioned in connection with the description of Figure 1, the entire ion generator 17 is surrounded by a grounded shield 18. The purpose of this shielding is to define the limits of the electric field between the grounded portions of the ion source and the hot portions, the object being to provide as little volume as possible in which the electrons may oscillate, inasmuch as the oscillating electrons ionize ambient gas and produce additional electrons. A series of fins and blisters have been devised for such shielding, the fins projecting outwardly into this oscillating volume to further limit the volume in local regions and limit the amplitude of the oscillating The fins are necessarily complemented by protruding blisters in the grounded shielding so as to maintain the physical clearance necessary to prevent electrical breakdown. Thus there is shown in Figure 7 a forward fin 141, an intermediate dumping fin 142, and a generally circular rear fin 143. These fins are complemented by blisters in the grounded shielding, as shown in Figure 1; namely, the

blisters

144, 146, and 147, respectively. This combination of grounded shielding and fin and blister substantially reduces the deleterious efiects of oscillating electrons. .Inasmuch as this structure forms no part of the invention, the operation is not described in any great detail in the present specification.

It will be noted, however, with reference to Figures 5 and 7, that the pedestal-type insulator 28 is surrounded by a generally cylindrical skirt 148 connected indirectly to the T-shaped bracket 29. This skirt insures that there will be no electrical fields in the region of the insulator that will in any way tend to give rise to electron oscillation that could damage the insulator. The skirt 148 is provided with apertures 150 which aid in the outgassing or pumping down operation of the entire vacuum envelope. As explained previously, this skirt is not necessary and all that is required is a plate that intercepts the magnetic field that permeates the insulator.

Referring still to Figure 5, it will be noted that there is an opening 149 in the casting 16 under the reservoir and are chamber regions of the ion source. This opening permits access to the ion generator, for example to permit loading of the charge bottle 72 into the reservoir 71, and is normally covered by a metal sheet 151. The upper surface of the ion generator is covered by a plate 152 which aids in keeping out the un-ionized vapor that might otherwise condense upon the various parts thereof. A small block 153 is placed in front of the filament between the arc block and the cover plate 152 to eliminate the electric field of the accelerating electrode from the filament region, which might otherwise result in sparking.

In explaining the detailed operation of the ion source, reference is first made to Figures 4, 5, and 7. The source unit is charged when it is outside of the vacuum envelope.

In removing the source, the volts securing the face plate 15 are unscrewed from the remainder of the vacuum envelope including the top and

bottom plates

27 and 26, and removed bodily together with the entire source unit. The entire source unit is then readily accessible for the charging operation and any other operations to be performed thereon. In charging, the cover plate 151 garages is then removed from the bottom of the supporting bracket 16 and the bottom plate 87 on the reservoir 71 is also removed. The plate 90 is next unscrewed, which permits the charge container 72 to drop bodily out of the reservoir 71. A new charge container 72 is then inserted which may be filled with a suitable charge, such as uranium hexachloride, and properly sealed against moisture, as noted previously, by the thermoplastic seal about the magnetically removable cover 73. The

plates

90, 87, and 151 are next replaced, and the unit is ready for operation.

The face plate 15 is next secured to the vacuum envelope and vacuum pumps (not illustrated) are operated to reduce the pressure within the envelope to a suitable value such as 10* or 10- mm. of mercury. The high positive voltage is next applied to the ion generator 17 and the high negative voltage applied to the accelerator electrode 31, the decelerating electrode 19 remaining at ground potential. Hot oil is next circulated through the oil leads 134 into the tubing 98 surrounding the reservoir chamber 71. The heat from the oil vaporizes the charge, which action occurs at about 90 C. when the charge is uranium hexachloride. The heat from the oil also melts the thermoplastic seal about the cover 73, and thereafter the magnetic field causes the body of the cover to be aligned therewith, opening the charge container 72. Vapor then flows through the reservoir outlet 74 into the mixing chamber 76, and thereafter the vapor is metered past the baffie 77 to enter the arc chamber 78 at a substantially uniform rate along its entire length.

When the vapor is flowing into the arc chamber 78, a suitable potential such as 200 volts is applied to the cathode leads 112 and 113 with respect to the rest of the ion generator 17. At the same time, a difference of potential is impressed across the cathode leads 112 and 113 which may be of the order of two to ten volts to drive a current through the tungsten filament 79, which is heated to a white heat and becomes electron emissive. The electrons therefrom are accelerated toward the collimating plate 122 in the top of the are chamber 78, and passing through the opening therein strike an arc in the arc chamber 78. The arc thus formed enhances the ionizing properties of the electron discharge, producing a large number of ions due to bombardment of the vapor, the pressure in the arc chamber 78 being somewhat higher than that of the vacuum tank in general, so that an arc is not difficult to strike.

The arc plasma fills the entire arc chamber 78, and the positive ions on the surface of the arc plasma in the region of the ion exit opening 81 are accelerated toward the accelerating electrode 31 by the electric field impressed between the electrode 31 and the arc chamber housing 91. The positive ions thereupon attain considerable energy and pass through the aperture 49 in the electrode 31, and upon reaching the extreme exit edge thereof encounter the decelerating electric field induced by the ground potential on the decelerating electrode 19. This field is defined by the aperture plate 82 in the electrode 19. Thus, the electrode structure draws out a large number of ions from the arc plasma in the arc chamber 78, due to the high voltage on the accelerating electrode 31, the difference of voltage between the arc chamber housing 91 and the electrode 31 being of the order of 50 kv. Inasmuch as ions of this energy would describe too large a radius within the magnetic field, the decelerating electrode 19 is employed to reduce the energy of the ions, causing them to describe a circular path of the desired radius.

The ionizing and accelerating actions of the ion source give rise to numerous electrons outside of the arc chamber housing 91. These electrons encounter the electric field. created by the grounded bracket 16, the grounded vacuum envelope top 27, and the highly positive. ion generator 17. The electrons in attempting to discharge on 12 the highly positive ion generator 17 are attracted thereto but are confined by the strong magnetic field permeating the ion source to paths aligned with the magnetic field. They are thus accelerated to an intermediate point between the two grounded members, whereafter they are decelerated as they approach the relatively negative vacuum envelope portion 27 or the relatively negative support brackets 16. They are then stopped at some intermediate point and accelerated in an opposite direction by the field mentioned, resulting in a very rapid oscillation of the electrons about the ion source 17. This electron oscillation is very undesirable, inasmuch as the electrons possess considerable energy, and upon striking any object within their path will heat it, either melting it or cracking it when it is a nonmetal such as an insulator. The oscillating electrons are preferably confined to as small volume as possible, inasmuch as they ionize the ambient gas within the vacuum envelope, and produce additional electrons which also assume the deleterious oscillations previously mentioned. This oscillating volume is confined by grounded shielding 18, as shown best in Figures 1, 4, and 5. In this connection it will be noted that the insulator 28 is so disposed, relative to the magnetic field, that it is entirely outside of the paths that any oscillating electrons may take. This results from the fact that there is a high positive potential on the upper end of the insulator 28 and a relatively negative field on the other end of the insulator 28, resulting in a simple electric field between the opposite ends thereof. Inasmuch as a simple electric field will not result in electron oscillation, none occurs in this region.

The oscillating electrons migrate rearwardly from the right side of the source and upon reaching the positive lead assembly, strike a split oscillating field. Some will continue about the ion generator 17, and will therefore strike and discharge upon the lead housing 137; others of the oscillating electrons make their way through the aperture 20 in the rear wall of the grounded housing 18, and continue to oscillate rearwardly along the high positive lead assembly 24 and inside of the tubular elbow 36, as best shown in Figure 7. These electrons continue to oscillate because of the oscillation-inducing field set up as previously mentioned; namely, a positive element 137 between the grounded upper and lower wall portions of the elbow 36, as aligned with the magnetic field. These electrons continue their slow migration rearwardly until they come to the turn in the elbow 36, whereupon they are faced with a reversed electric field; namely, a positive lead assembly 137 and the positive cover plate 38 and the intermediate grounded wall member 36 and its attached flange 132. This electric field stops all oscillations, the electrons discharging to the plate 38 or the lead assembly 137, whichever is closer. It will be noticed from this construction and from the paths taken by the electrons that the bushing-type insulator 37 is completely out of the paths of the oscillating electrons, and is never struck by them. This avoids the difficulties of prior constructions, wherein insulators were directly in the path of oscillating electrons, resulting in local portions becoming heated which thereupon cracked the insulators and rendered them useless as a vacuum seal and weakened them mechanically so that they were unfit to support insulator members.

This description has been made with reference to a particular embodiment thereof, but the invention is not limited to this embodiment nor otherwise except by the terms of the following claims.

What is claimed is:

1. In a calutron having a vacuum envelope having a removable wall portion, the combination comprising a bracket secured to the inner face of the removable wall portion and providing a supporting platform generally perpendicular to the removable wall, and an element of '13 an ion beam forming mechanism securcd to andflsupported by the bracket. I d

2. In a calutron having means for establishing a magnetic field and a vacuum envelope positioned therein, the combination comprising an insulator attached to the inside of the vacuum envelope, and an ion generator attached to the insulator for operation at a potentialpositive with respect to the vacuum envelope, the point of attachment of said ion generator being positioned with respect to the point of attachment of the insulator to the vacuum envelope in a direction along the magnetic field so that the ends of the insulator along the magnetic field are subject to difierent electrical potentials.

3. In a calutron having means establishing a magnetic field and a vacuum envelope positioned therein, the combination comprising a tube connected to the outside of the envelope and communicating with the interior thereof and having an outer opening with an axis aligned with the magnetic field, a bushing type insulator secured to the outer end of the tube and having its axis aligned with the magnetic field, a cover plate on the unsecured end of the bushing insulator, an element insulatedly mounted inside the vacuum envelope, and leads secured to the cover plate and passing through the bushing insulator and the tube for supplying electrical potential to the element inside the vacuum envelope.

4. In a calutron having means establishing a magnetic field and a vacuum envelope positioned therein and having a removable portion, the combination comprising a bracket secured to the inner face of the removable wall portion and providing a supporting platform generally perpendicular to the removable portion, an insulator secured to the bracket, and an ion generator attached to the insulator for operation at a potential positive with respect to the vacuum envelope, the point of attachment of said ion generator being positioned along the magnetic field with respect to the point of attachment of the insulator to the supporting bracket, so that the ends of the insulator along the magnetic field are subject to different electrical potentials.

5. In a calutron having means for establishing a magnetic field and a vacuum envelope positioned therein, the combination comprising an insulator attached to the inside of the vacuum envelope, an ion generator attached to the insulator for operation at a potential positive with respect to the vacuum envelope, said ion generator attached thereto along the magnetic field with respect to the point of attachment of the insulator to the vacuum envelope, a tube connected to the outside of the envelope and communicating with the interior thereof and having an outer opening with an axis aligned with the magnetic field, a bushing type insulator secured to the outer end of the tube and having its axis aligned with the magnetic field, a cover plate on the unsecured end of the bushing insulator, and leads secured to the cover plate and passing through the bushing insulator and the tube and connected to the ion generator for supplying electrical potential to the ion generator inside the vacuum envelope.

6. In a calutron having means establishing a magnetic field and a vacuum envelope positioned therein and having a removable wall portion, the combination comprising a bracket secured to the inner face of the removable wall portion and providing a supporting platform generally perpendicular to the removable wall, an ion generator insulatedly secured to the bracket, -a tube connected to the outside of the removable wall portion and communicating with the interior of the vacuum envelope and having an outer opening with an axis aligned with the magnetic field, a bushing type insulator secured to the outer end of the tube and having its axis aligned with the magnetic field, a cover plate on the unsecured end of the bushing insulator, and leads secured to the cover plate and passing through the bushing insulator and the tube for supplying electrical potential to the ion generator inside the vacuum envelope.

'7. In a calutron having means establishing a magnetic field and a vacuum envelope positioned therein having a removable wall portion, the combination comprising a bracket secured to the inner face of the removable wall portion and providing a supporting platform, an insulator attached to the bracket, an ion generator attached to the insulator for operation at a potential positive with respect to the bracket and the vacuum envelope, said ion generator disposed along the magnetic field with respect to the point of attachment of the insulator to the support ing bracket so that the ends of the insulator along the magnetic field are subject to difierent electrical potentials, a tube connected to the outside of the removable wall portion and communicating with the interior of the vacuum envelope and having an outer opening with an axis aligned with the magnetic field, a bushing type insulator secured to the outer end of the tube and having its axis aligned with the magnetic field, a cover plate on the Iunsecuredend of the bushing insulator, and leads secured to the cover, plate and passing through the bushing insulator and the tube for supplying electrical potential to the ion generator inside the vacuum envelope.

8. In a calutron having means establishing a magnetic field and a vacuum envelope disposed therein having a removable plate portion that is aligned with the magnetic field, the combination comprising a bracket secured to the inside face of the plate and providing a supporting platform that is generally perpendicular to the magnetic field, and an ion beam forming mechanism secured to and supportedby the bracket.

9. In a calutron having means establishing a magnetic field and a vacuum envelope positioned therein having a removable plate portion that is aligned with the magnetic field, the combination comprising a bracket attached to the inner face of the plate and forming a supporting platform that is generally transverse to the magnetic field, an insulator attached to the bracket, an ion generator attached to the insulator and having its point of attachment to the insulator disposed along a magnetic field with respect to the point of attachment of the insulator to the bracket, an elbow tube secured to the outer face of the plate and communicating with the interior of the vacuum envelope and having the axis of its outer opening aligned with the magnetic field, a bushing type insulator secured to the outer end of the elbow and having its axis aligned with the magnetic field, a cover plate on the outer end of the insulator, and leads secured to the cover plate and passing through the bushing type insulator and the elbow and connected to the ion generator.

10. In a calutron having means for establishing a magnetic field and a vacuum envelope disposed therein, the combination comprising an insulator secured to the inside of the envelope, a metal member secured to the insulator and disposed along the magnetic field with respect to the point of attachment of the insulator to the vacuum envelope, and intersecting all the magnetic field that passes through the insulator, and an ion generator secured to the member for operation at an electrical potential difierent from that of the vacuum envelope, the arrangement of the member with respect to the insulator creating a simple electric field about the insulator that eliminates the oscillation of charged particles near the insulator.

11. In a calutron having means establishing a magnetic field and a vacuum envelope positioned therein, the combination comprising a tube connected to the outside of the envelope and communicating with the interior thereof and having an outer opening with an axis aligned with the magnetic field, a bushing type insulator secured to the outer end of the tube, the inner dimension of the insulator being at least as great as the inner dimension of the tube outer opening, a cover plate on the unsecured end of the bushing type insulator, and leads secured to the cover plate and passing through the insulator and tube and adapted to be at an electrical potential different from that of the vacuum envelope.

12. In an ion source, the combination comprising an electrode comprising an insulated support, a right angled member secured to the support with a connection that is adjustable along one of its legs, a flatted shank secured to the other end of the member in overlapping and spaced relationship with a connection that is adjustable along the other leg, three screws threaded in the member and contacting the flat of the shank for adjusting the flat in any plane relative to the right angle member, and an electrode secured to the shank.

13. In an ion source, the combination comprising an ion generator reservoir comprising a cylindrical tube, and a helix of smaller tubing wrapped around the cylindrical tube, so that a charge bottle may be inserted in the cylindrical tube and a hot fluid circulated in the helical tube to heat the charge bottle.

14. In an ion generator, the combination comprising means defining a reservoir chamber, means defining a mixing chamber communicating therewith, means defining an arc chamber adjacent to the, mixing chamber and wherein an arc discharge is adapted to occur, a tube in heat transfer relationship on the walls of the mixing chamber, and a tube positioned around the reservoir chamber and connected to the mixing chamber tube, so that a fluid of predetermined temperature may be introduced therein to heat the reservoir, which fluid may be exhausted through the mixing chamber tube to hold the mixing chamber at a desired temperature.

15. In an ion source, the combination comprising means defining an arc chamber having a Wall with an ion exit opening therethrough, means for striking an arc therein, and heat insulating means about the exit opening comprising a slot cut into the wall adjacent the exit opening, so that the heat imparted to the opening edges is not readily conducted away by the wall and the temperature of the opening edges is maintained.

No references cited.