US2713640A - Electron control apparatus - Google Patents

Description

July 19, 1955 H. w. SAVAGE ELECTRON CONTROL APPARATUS Filed Aug. 8, 1945 IN V EN T 0R. fioward VJ aa'age.

July 19, 1955 H. w. SAVAGE 2,713,640

ELECTRON CONTROL APPARATUS Filed Aug. 8, 1945 2 Sheets-Sheet 2 INVENTOR. fyoward WJ'ava e.

United States Patent Ofiice Z7136? Patented July 19, 1955 2,713,640 ELECTRON CONTROL APPARATUS Howard W. Savage, Oak Ridge, Tenn., ass'ignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application August 8, 1945, Serial No. 609,661 8 Claims. (Cl. 25041.9)

This invention relates to means and methods for suppressing or controlling oscillating electrons and ions liberated thereby in the vicinity of high potential electrical apparatus, and more particularly, neutralizing the electrons and ions in regions where their presence is undesirable, or as this procedure is commonly described, dumping them. This problem of undesirable electrical disturbances in electronic equipment, particularly equipment of the type operating in high vacuum, that is the problem of removing, isolating or suppressing the disturbances, is frequently extremely critical. The disturbances are often the by-product of ionization processes and can, if permitted to continue, magnify themselves so as to cause excessive and ruinous heating of the equipment, excessive electrical drain current from the equipment, and/or excessive outgassing and loss of vacuum, any or all of which are likely to result in shut down of the equipment.

The particular type of electrical disturbances which my invention is primarily concerned with controlling are the electron oscillations and ionization induced thereby which arise in high voltage equipment operating in a vacuum and under the influence of a strong magnetic field. The conditions necessary to set up electron oscillations are always present when a body at high positive potential is placed within a body or region of lower potential and the entire equipment subjected to the action of a magnetic field. My invention has a particular use, therefore, in the electromagnetic type of isotope separating apparatus disclosed in detail in the application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9, 1944. In this type of apparatus there is involved an ionizing process which is carried out in a vacuum and a relatively strong magnetic field so that the conditions described above which bring about undesirable electron oscillations are present. A primary object of my invention, therefore, is to provide means for controlling or suppressing undesirable electrical disturbances, particularly in the form of electron oscillations.

Another object of my invention is to provide a means for suppressing electron oscillations by providing a shield of lower potential around the higher potential body, the shield and body being so constructed and arranged that the electrical field therebetween is in such a direction that the resultant of the electric and magnetic field acting on electrons exerts a force on them in a direction towards the high potential body so that the electron will be dumped thereon, and the relative conformation of the shield and body being such that an electron travelling along any line of magnetic flux is confronted by a high potential surface.

Another object of my invention is to provide means as in the foregoing object wherein the electric field shaping means in part are in the form of ribs on the hot body and disposed at an angle to the magnetic field, that is neither parallel nor perpendicular thereto.

Another object of my invention is to provide means as in the preceding objects wherein the electric field shaping means are in the form of ribs on the high potential body and interleaving bafiles forming part of the shield interleaving between the ribs, the ribs and bafiles being arranged at an angle to the direction of the magnetic field, that is, neither parallel nor perpendicular to the magnetic field.

Another object of the invention is to provide means as in the three preceding objects wherein the ribs and interleaving baflies have a V or chevron shape.

Another object is to reduce the likelihood of ionization and electron oscillation by providing a structure wherein the pressure can be kept low by being open for ready evacuation but having a tortuous passage for electrons, thereby tending to inhibit loss of vacuum in the drain system.

The manner in which the objectives of my invention are achieved and numerous further objects and advantages of the invention will become apparent from the following detailed description and annexed drawings wherein:

Fig. 1 is a diagrammatic perspective view of an isotope separating apparatus in which my invention may be practiced in connection with the ion source thereof.

Fig. 2 is a diagrammatic perspective view partly broken away of an ion source having my invention associated therewith which may be used in the isotope separating apparatus of Fig. 1.

Fig. 3 is a detail view of the manner of support of certain of the parts of Fig. 2.

Fig. 4 is an end view showing diagrammatically a fin or rib and a shield or shroud in a position normal to a magnetic field and illustrating the resultant efiect of the magnetic and electric fields on an electron.

Fig. 5 is a diagrammatic view of the rib and shroud or shield of Fig. 4 with the rib and shroud moved to a position at an angle to the magnetic field.

Fig. 6 is a diagrammatic plan view of the arrangement of Fig. 5, with the upper part of the shroud cut away.

Fig. 7 is an end view of the structure of Fig. 6.

Referring to Fig. 1 of the drawings, there is shown schematically the way in which an isotope separating apparatus may be set up and in connection with which an ion source is utilized which may very advantageously make use of my invention. In Fig. 1 numeral 10 designates a rectilinear evacuated tank in which the process is carried out. The tank has an outlet 11 at the back connected by pipe 12 to difiusion pump 13 which in turn is connected by pipe 14 to rotary mechanical pump 15. By means of the pumps, the tank is evacuated to a very low pressure. On opposite sides of the tank 10 are laminated iron cores or pole pieces as designated at 16 and wound around these pole pieces are electrical windings 17. The cores and windings produce a relatively intense magnetic field which is in a direction perpendicular, that is, transverse to the tank 10. Within the tank 10 is a liner structure 18 having the general shape and configuration as shown in Fig. .1, and the interior of the liner is evacuated as well as the remainder of the interior of the tank 10. The tank 10 has a relatively large main face plate 20 at the front which is attached to the tank in a manner to form a seal between the tank and the face plate, and it supports the liner structure 18 within the tank. Numerals 21 and 22 designate sub-face plates attachable to the main face plate in a sealing manner and cooperating with the lower and upper portion of the liner structure 18. The lower sub-face plate 21 in this apparatus carries or supports the ion source unit of the apparatus or the transmitter, as it is sometimes called, and the subface plate 22 supports the receiving structure, the transmitter being operable to project a beam of ions into the liner which are bent into arcs of a circle under the influence of the magnetic field to be collected in the receiver structure carried by the plate 22.

Referring to Fig. 2, the sub-face plate 21 is shown with the ion source or transmitter structure attached thereto, the structure having the electron dumping means of my invention associated therewith. In Fig. 2, numeral 25 designates a steel cylinder or tube which extends inwardly from the face plate 21, and it supports the ion generating or transmitter structure. This structure involves a rectilinear chamber or housing 26 which is supported from the tube or cylinder 25 by a large insulator 27 as is shown in Fig. 3. Within the chamber or housing 26 is a container 28 for a charge of solid material to be ionized. The container 28 has an elongated opening or slit 29 having a baffie 30 associated therewith inside the container 28, and the chamber or housing 26 has two elongated openings or slits 32 and 33 parallel to slit 29, all of the slits being parallel to the direction of the magnetic field indicated by the arrow F. Within the container 28 is an electric heating element 35 which heats and vaporizes the material therein, the vapor passing out through the slits 29 and 32 and 33. Adjacent the ends of the slits 32 and 33 there are filamentary cathodes, one of which may be seen at 36; the cathode 36 is operable to emit a stream of electrons through a collimating slot in a plate 37 supported from a bracket 38 and through an opening in the housing 26 into and along the stream of vapor being emitted from the slot 33. These electrons bombard the vapor and cause it to be ionized as will be presently described. The cathode 36 is supported and insulated from an upright stem 42 which attaches to the tube 25, and the leads to the cathode 36 designated 43 and 44, which may be in the form of water tubes for cooling purposes, extend out through the face plate 21. The upper part of stem 42 and bracket 38 associated with slit 32 are shown broken away.

Numeral 46 designates an element forming an accelerating electrode for accelerating positive ions, that is, for withdrawing them from the ionizing region in the vicinity of slits 32 and 33. The member 46 has slits 47 and 48 parallel to and aligned with slits 32 and 33, the member 46 being supported from a cross-member 49 near the end of tube 25 and vertical insulators as shown at 50. As pointed out, the member 46 constitutes a means for withdrawing the ions from the ionizing region and assisting in projecting them into the magnetic field region so that they can be acted upon as previously described.

The face plate 21 and structure not insulated therefrom is grounded as shown, and the ion source itself, that is, the generator, is maintained at a relatively high positive potential V as shown. A potential V1 is across the leads to the cathode 36 and a potential V2 is connected between the negative cathode lead and the ion source unit or generator. In operation thus there is a potential dilference between the cathode 36 and the ion source unit itself, that is, the structure in the vicinity of the slits 32 and 33, and under the influence of this voltage an arc is struck in the ionizing region adjacent the slits 32 and 33, the positive ions being withdrawn under the influence of the electrode member 46 as described, the member 46 being maintained at a negative potential V3 by a conductor which may be led in through an insulator bushing as shown at 51.

Covering three sides of the ion generator unit, that is, the top, the back, and the bottom, is a shield 55. This shield is supported from the tube 25 by means of a bracket 56 and an upright 57 which is attached to the shield and to the bracket 56 by screw 58. (See Fig. 3.) The shield is thus at ground potential. The shield has openings therein as shown to facilitate evacuation from between the shield and the unit. The chamber or housing 26 has upstanding fins or ribs as shown at 60 and these ribs may have a V or chevron configuration as shown in Fig. 2. Both parts of the ribs are disposed at an angle to the direction of the magnetic field, that is, they are not perpendicular to the field, and they are not parallel 4 to the direction of the field. The top part of the shield has downwardly extending baffie members 61 which are disposed or interleaved between the ribs 60. By means of this structure undesirable electrical disturbances in the vicinity of the generator unit, that is, electron oscillations, are controlled or suppressed. During the operation of the ion generator unit large numbers of free electrons will be produced in the vicinity of the ionizing region which will be free in the region of the slits and which will be acted upon by the magnetic field and the electric fields to travel in a generally counterclockwise direction looking at Fig. 2 with reference to the structure shown, this being in accordance with the well-known law of physics that the electrons when under the influence of initially perpendicular magnetic and electric fields will travel in a direction at right angles to both fields. As described above, these free electrons are capable of producing more free electrons by ionizing collision with other particles and therefore magnifying and increasing the deleterious effect. These oscillating electrons may produce an undue amount of heating which is very destructive of the apparatus and they may result in relatively high and undesirable current drains from the high potential body, such as the ion generating unit itself and the accelerating electrode member 46. The purpose of my invention is to control and suppress these oscillations and this is accomplished by the shield 55, the ribs and the bafile members 61. It will be seen that electrons travelling in a counterclockwise direction relative to the structure between the shield 55 and the high potential body, that is, the ion generator, in order to traverse the depth of the generator structure would have to follow a tortuous pathway in rising up over the ribs 60 and then down to the bottom of the bafiies 61 before proceeding past the next rib. The arrangement of the. structure is such that the electrons will be dumped before they can achieve any great degree of progress, whereby to increase the electron oscillations by further ionization. The manner in which the dumping is achieved may be understood by reference to Figs. 4, 5, 6, and 7. In Fig. 4 there is shown a rib or fin 65 having a shroud 66 over it which forms a baffie on each side of the rib corresponding to the structure of Figure 2. The rib and shroud in Fig. 4 are shown in cross-section and in a position with the rib and shroud at right angles to the magnetic field F. In Fig. 4 the electric field is indicated by the arrows E directed inwardly towards the rib 65 from the shroud 66, the rib 65 of course being at high potential and the shroud 66 being at a relatively lower potential. Considering an electron at point A, it will be influenced by the force of the magnetic field F and by the electric field illustrated by the vector AB. The vector AE has two components AE1 and B1B. The component AE1 is parallel to the magnetic field F and thus its only effect is to tend to move the electron in the direction of the component, that is, parallel to the magnetic field F or along the line AB. Points A and B lie on a line of equipotential represented by the curve CD midway between fin 65 and shroud 66. The effect of the component EiE which is at right angles to the magnetic field F is to cause the electrons to move at right angles to both fields, which would be in a direction into the paper in Fig. 4 as indicated by the small circle at A,

1 thus the total resultant effect on an electron at point A is that it will oscillate between points A and B (points of equipotential) and move along the rib at the same level without being dumped on the rib. The effect therefore is that an electron rising up between the rib and the shroud would reach point A and then oscillate between points A and B without being dumped.

Referring now to Fig. 5, there is shown a view of the structure of Fig. 4 with the structure disposed at an angle to the magnetic field F, that is, neither parallel nor perpendicular to the magnetic field. In this posi- AE1E is that of rotating it out of the paper and around line AE1. Vector ErE is perpendicular to the magnetic field F as in Fig. 4, but the resultant of B1B and F, that is, the direction followed by an electron travelling perpendicular to both, is represented by H which has a direction into the paper and downwardly. Vector AE1 tends to cause electrons to follow along the magnetic field as before and this motion combined with that occasioned by H causes the electrons to dump on fin 65. The effect on electrons at point B tending to cause them to dump is similar but having an upward direction (and out of the paper) as indicated at J, the combined effect of H and I being generally a helix-like motion along the fin as shown on the Figures 5, 6 and 7, the motion appearing elliptical in the end view, Fig. 7. Thus the forces acting on electrons between fin 65 and shroud 66 are such as to cause them to move toward the fin and eventually dump. In the case of an electron relatively near the top of the shroud 66, one or more collisions with gas particles may be necessary to drop the electron and its helical path closer to the fin 65 so that it will be intercepted by the fin.

In this process ions and additional electrons will be liberated. The ions being of heavy mass will go directly to the shroud while the additional electrons will pursue helical paths of their ow Thus to avoid a considerable number of collisions and additional electrons, the highest degree of evacuation in the shroud is desirable. The present invention inhibits the entrance of gas to the fin and shroud region by its tortuous nature, but at the same time is open at the ends and along the top of the shroud for good evacuation.

The embodiment of my invention disclosed herein is representative of its preferred form. The disclosure is to be interpreted in an illustrative rather than a limiting sense, the scope of the invention being determined in accordance with the claims appended hereto.

I claim:

1. Oscillation suppressing means for high potential bodies disposed in a magnetic field comprising a shield adjacent the body and electrically negative relative to the body, said body and shield having relative conformations such that the electric field therebetween has direc" tional components at an angle between and 90 to the direction of the magnetic field and so that the resultant of the effect of the magnetic field and said components of the electric field on electrons has a direction toward the high potential body causing electrons to dump thereon, the said conformations being such as to physically inhibit the travel of electrons between the body and shield.

2. Oscillation suppressing means for high potential bodies disposed in a magnetic field comprising a shield adjacent the body and electrically negative relative to the body, said body and shield having relative conformations such that the electric field therebetween has directional components at an angle between 0 and 90 to the direction of the magnetic field so that the resultant of the effect of the magnetic field and said components of the electric field on electrons has a direction toward the high potential body, the said conformations being such as to necessitate that electrons travel a tortuous pathway betwen the high potential body and shield until dumped.

3. Oscillation suppressing means for high potential bodies disposed in a magnetic field comprising a shield adjacent the body and electrically negative relative to the body, said body and shield having relative conformations such that the electric field therebetween has directional components so that the resultant of the elfect of the magnetic field and said components of the electric field on electrons has a direction toward the high potential body, the said conformations comprising ribs on said body and members extending from the shield adjacent the ribs, said ribs and said members being disposed at an oblique angle to the magnetic field.

4. In a device for suppressing electrical disturbances, a high potential body disposed in a magnetic field, said body having ribs arranged transverse of the magnetic field and at an oblique angle thereto, and means forming a shield having relatively negative potential and having baffle members interleaved between said ribs whereby an electron travelling along any line of magnetic force is confronted by a high potential surface, the electric field between the shield and body having directional components such that electrons travelling at right angles to both the magnetic field and said components move toward said body.

5, In a device for suppressing electrical disturbances, a high potential body disposed in a magnetic field, said body having ribs arranged transverse of the magnetic field and at an oblique angle thereto and having the shape and arrangement of chevrons, and means forming a shield having relatively negative potential and having bafile members interleaved between said ribs whereby an electron travelling along any line of magnetic force is confronted by a high potential surface, the electric field between the shield and body having directional components such that electrons travelling at right angles to both the magnetic field and said components move toward said body.

6. An electron dump for use with a high potential body disposed in a magnetic field comprising a rib member on said body disposed at an oblique angle to the directlon of the magnetic field, and a shield having negative potential adjacent said body and having extending portions adjacent and parallel to said rib on opposite sides of the rib.

7. An electron dump for use with a high potential body disposed in a magnetic field comprising a chevron shaped rib member on said body disposed at an oblique angle to the direction of the magnetic field, and a shield having negative potential adjacent said body and having chevron shaped extending portions adjacent and parallel to said rib on opposite sides of the rib.

8. An electron dump for high potential bodies disposed in a magnetic field comprising ribs on the body disposed at an oblique angle to the magnetic field, and a shield having relatively negative potential adjacent the body and having electric field shaping means comprising baflie members adjacent and parallel to the ribs.

No references cited.

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