US2624020A - Apparatus for accelerating electrically charged particles - Google Patents

Apparatus for accelerating electrically charged particles Download PDF

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Publication number
US2624020A
US2624020A US214471A US21447151A US2624020A US 2624020 A US2624020 A US 2624020A US 214471 A US214471 A US 214471A US 21447151 A US21447151 A US 21447151A US 2624020 A US2624020 A US 2624020A
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anode
circle
electrons
equilibrium
charged particles
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US214471A
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English (en)
Inventor
Wideroe Rolf
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BBC Brown Boveri AG Germany
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Bbc Brown Boveri & Cie
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H11/00—Magnetic induction accelerators, e.g. betatrons

Definitions

  • This invention relates to accelerators for electrically charged particles such as electrons wherein the particles are forced to'travel an orbital path of substantially constant radius while at the same time being constantly accelerated along the path, and is a continuation-in-part of my application Serial No. 198,547 filed December 1, 1950, and now abandoned.
  • One type of accelerator known generally as a. betatron or ray transformer," to which the present invention can be applied, is comprised of an evacuated annular tube into which electrons are introduced from an electron emissive' cathode, and a magnetic system which produces a magnetic field varying with time having a spatial distribution such that the injected electrons are accelerated along a substantially circular orbit within the tube by magnetic induction effects.
  • the magnetic field divides into two components. duction field is responsible for acceleration of the electrons around the orbit, and the other component known as the control field produces an increasing centripetal force upon the electrons which is designed to match the increasing centrifugal forces of the electrons as the latter increases in velocity thus maintaining the electrons on a circular path of substantially constant radius.
  • the electrons reach enormously high energy levels as a result of their acceleration and at the end of the acceleration phase can be diverted from the orbit and caused to impinge upon an anode to produce X-rays or used for other purposes.
  • the betatron type of accelerator usually incorporates a stabilizing device for restoring to the prescribed circular orbit those electrons which deviate from it.
  • a stabilizing device for restoring to the prescribed circular orbit those electrons which deviate from it.
  • Such stabilization can be achieved for example by establishing a gradient in the control field such that the strength of field decreases outwardly with increasing radius of the electron path, and a full discussion of the apertaim'ng theory can be found in U. S. Patent No. 2,103,303, issued December 28,1937, to Max Steenbeck.
  • the stabilization attributable to the decrease in field strength is effective only within a limited vicinity of the precalculated circular orbit for electron travel, known generally as the circle of equilibrium, but within the effective area provides both radial and axial stabilizing force components for any electrons which leave the precalculated orbit.
  • the stabilizing force In the plane of the equilibrium circle, the stabilizing force has two maxima, which lie on circles located radially inward and outward respectively from the circle of,
  • the general objective of this invention is' to provide an improved arrangement for the anode within the annular tube that will assure a maximum yield of accelerated electrons available for impingement against the anode and such objective is achieved by employing a support there-- for extremely thin in the dimension perpen dicular to the plane of the circle of equilibrium and which locates the anode in the plane of the equilibrium circle at a point between the limits of one half and four fifths of the distance to the equilibrium circle from either the inner or outer limit circles of maximum stabilizing force.
  • Fig. l is a view in central vertical section of an accelerator for electrically charged particles known as a betatron, wherein electrons are accelerated by 'magnetic inductive efiects exclusively, to which the invention has been applied.
  • Fig. 2 is a view partly in horizontal section and partly in plan of the accelerator shown in Fig. 1;
  • Fig. 3 is a curve used in explaining the invention.
  • Figs. 4 and 5 are views in top plan and side elevation of the anode and its supporting ture drawn to-an enlarged scale;
  • Figs. 6 and 7 are views similar to Figs. 4 and 5 illustrating a somewhat modified supporting structure for the anode.
  • the electron induction accelerator which is symmetrical about a vertical axis a-a, is comprised of a magnetic structure l made up from steel laminations of appropriate contour and includes a pair of confronting cylindrical induction poles ll
  • the confronting faces of the control poles are preferably tapered in such manner that the air gap I 4'increases' as measured in the radially outward direction from axis a a, thus effecting a corresponding decrease in strength of the control field.
  • Yokernembers [5 complete the magnetic circuit for'the time varied magnetic field set up in the control and induction poles.
  • a winding pref erably split into” two annular coil sectionslfi, l6 surrounding the upper and lower control poles 13 3" respectively and wound in the same direcutn are connected in series for energizanon from a source of alternating current of suitable frequency such as for example 100 cycles/see,
  • An annular evacuated tube It preferably of glass, is disposed symmetrically in the air gap [4 between the control poles l3l3'.
  • the timevaried current in energizing coils lfi-IS' produces the time-varied magnetic field previously mentioned.
  • the induction component of this field responsible for electron acceleration passes through induction poles l [-4 l across air'gap I2, and the control component responsible for maintaining the electrons on a circular path of cons'tant ra'dius' passes through poles l3l3 across air gap ['4.
  • the circular path or circle of "equilibrium is designated k and its radius hidicated by Re, the plane containing the equilibrium circle Ic being perpendicular to axis aa.
  • the stabilizing force P risesluniformly in one direction reaching a'maxirnal time an outer limit circle m' of radius Re.
  • thestabilizing force P rises uniformly in the other direction reaching a maximal along' an in-' ner limit circle n of radius R1.
  • the cathode 2U constituting the source of the The 4 ing limit circle n.
  • a very thin plate 22 whose dimension in a direction perpendicular to the plane of the circle of equilibrium is at most one-tenth of a millimeter projects laterally from housing 2
  • the plate 22 which may be made from platinum or a platinum-iridium alloy preferably is wider at its point of attachment to housing 2
  • the support plate 22 In the plane perpendicular to the plane of the equilibrium circle is, the support plate 22 therefore presents only a very small areaand constitutes, during a small, initial fraction of the acceleration period during which the electrons still deviate appreciably from the equilibrium circle, only a very small obstacle to elec-' tron travel within the total area of stabilization.
  • the anode 23 which preferably consists of platinum, a somewhat larger dimension in the direction perpendicular to the plane of the equilibrium circle is than is given the support plate 22-, as seen more clearly in the enlarged Figs. 4 and-5, so that the face of the anode ofiers to the incoming accelerated beam of electrons an area of about 0.25, or 0.5, or at most LOsquare millimeter; This area is much smaller than the area of plate 22 in the same plane, the length of the plate being about fifteen millimeters.
  • the diniension of the anode 23 and plate 22 in the direction parallel with the plane of the equilibrium circle I k in the experimental model was about 2 millimeters, and the cathode was located approximately the same distance from the inner limit circle n as the anode 23.
  • - I-he necessary control circuits by which the cathode 20 is energized periodically in timed relation with the variation in the magnetic field to inject a stream of electrons into the tube at the beginning of each cycle or half cycle of the alterating magnetic field have not been illustrated since; various arrangements are already well known and moreover are not considered essen an understanding of this invention which concerns only the placement of the anode and cathode elements within the tube, and the support for the anode.
  • meansmiist be provided for stream from the orbit Ic acceleration period so as against the anode 23.
  • the induction poles ll-l I would thus each include a portion Ila, Il'a of restricted area so as to effect a partial magnetic saturation in these poles as the induction field reaches a predetermined magnitude. Thereafter the centripetal forces attributable to the control field would exceed the centrifugal forces of the electrons thus driving the electrons radially inward from the orbit k.
  • the cathode and its housing may be located radially outward from the outer stabilizing limit circle m in which case the anode would be disposed at a corresponding position between the outer limit circle m and the equilibrium orbit it.
  • Such an arrangement would of course require the electron stream to be diverted radially outward from the orbit is for impingement against the anodes and could be effected by producing a partial magnetic saturation effect in the control poles.
  • Figs. 6 and 7 show an arrangement wherein the anode support is constituted by a U-shaped stirrup 28 whose two ends are secured to the cathode housing 21.
  • the anode 28 is secured at the outer end of the stirrup, and like plate 22, the dimension of the stirrup in the direction perpendicular to the plane of the equilibrium circle is would be very small, that is, of the order of .1 millimeter or less so as to present as small an obstacle as possible to the run of the electrons around the orbit.
  • a device for accelerating charged particles comprising a magnetic structure including a pair of axially aligned circular control poles the faces of which are arranged in confronting relation to establish a gap therebetween, an annular tube disposed in the gap between said control poles providing therein an orbital path for acceleration of the particles, means for producing a time varied magnetic field across said gap between said control poles to confine the particles to a substantially circular path coincident with a circle of equilibrium during the acceleration phase, said pole faces being divergent in a radially outward direction whereby the strength of said field decreases in a direction radially outward from the axis of said control poles to establish a stabilizing force for the particles having in the plane of said equilibrium circle two maximals lying respectively on limit circles located radially inward and outward of said equilibrium circle, an anode in said tube disposed in the plane of said equilibrium circle and spaced from the latter by at least half but not exceeding four fifths the distance to the said equilibrium circle from one of said limit circles, and a support within said tube for
  • a device for accelerating charged particles 5.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)
  • Electron Sources, Ion Sources (AREA)
US214471A 1949-12-01 1951-03-08 Apparatus for accelerating electrically charged particles Expired - Lifetime US2624020A (en)

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CH2624020X 1949-12-01

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CH (1) CH280963A (en(2012))
DE (1) DE856340C (en(2012))
NL (1) NL73020C (en(2012))

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2665392A (en) * 1949-10-31 1954-01-05 Gund Konrad Magnetic induction accelerator
US2812463A (en) * 1951-10-05 1957-11-05 Lee C Teng Magnetic regenerative deflector for cyclotrons

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2335014A (en) * 1942-01-13 1943-11-23 Gen Electric Magnetic induction accelerator
US2484549A (en) * 1947-07-30 1949-10-11 Gen Electric Electron injection apparatus
US2550212A (en) * 1945-02-17 1951-04-24 Bbc Brown Boveri & Cie Magnetic induction accelerator
US2553312A (en) * 1946-01-05 1951-05-15 Gen Electric Apparatus for imparting high energy to charged particles
US2558597A (en) * 1945-09-15 1951-06-26 Gen Electric Field correction in magnetic induction accelerators

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2335014A (en) * 1942-01-13 1943-11-23 Gen Electric Magnetic induction accelerator
US2550212A (en) * 1945-02-17 1951-04-24 Bbc Brown Boveri & Cie Magnetic induction accelerator
US2558597A (en) * 1945-09-15 1951-06-26 Gen Electric Field correction in magnetic induction accelerators
US2553312A (en) * 1946-01-05 1951-05-15 Gen Electric Apparatus for imparting high energy to charged particles
US2484549A (en) * 1947-07-30 1949-10-11 Gen Electric Electron injection apparatus

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2665392A (en) * 1949-10-31 1954-01-05 Gund Konrad Magnetic induction accelerator
US2812463A (en) * 1951-10-05 1957-11-05 Lee C Teng Magnetic regenerative deflector for cyclotrons

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CH280963A (de) 1952-02-15
NL73020C (en(2012))
DE856340C (de) 1952-11-20

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