US2599188A - Magnetic peeler for proton synchrotron - Google Patents

Description

3 Sheets-Sheet l INVENTOR.

M. STANLEY LIVINGSTON 3 Sheets-Sheet 2 .3 g. 3. we H 2: J3" my ndE INVENTOR. MSTANLEY LIVINGSTON June 3, 9 M. s. LIVINGSTON 2,599,188

MAGNETIC-PEELER FOR PROTON SYNCHROTRON Filed Feb. 21. 1950 3 Sheets-Sheet 3 INVENTOR.

msumev LIVINGSTON Patented June 3, 1952 MAGNETIC PEELER FOR PROTON SYNCHROTRON Milton Stanley Livingston, Belmont, Mass, assignor to the United States of America as represented by the United States Atomic Energy Commission Application February 21, 1950, Serial No. 145,401

Claims. (Cl. 313-62) The present invention relates to a method and apparatus for deflecting accelerated high energy charged particles from curved orbits in a particle accelerator such as a synchrotron, a betatron or others which confine the path-oi the accelerating particles to a generally circular one.

Ion accelerators, of the type which confine particle motion to a generally circular path, employ a magnetic field which increases in strength as the ion velocity increases to maintain motion in a circular path of approximately constant radius. When the accelerated ions have attained a desired energy or velocity some means must be provided to cause the ions to be deflected from their confined paths in a controlled manner and to be thus removed from the accelerator.

It is accordingly an object of the present invention to provide a novel method and apparatus for deflecting ions from a generally circular orbit in a particle accelerator.

It is another object of the present invention to provide a method and apparatus for deflecting ions. from a generally circular orbit which apparatus is operated automatically responsive to the generation of energy in said accelerator.

Other objects and advantages will be in part obvious and in part pointed out hereinafter.

In one of its broader aspects the method of the present invention comprises changing the magnetic properties of the path-restricting magnet in a region along a relatively short segment adjacent the path to which the ions are confined during their acceleration and changing the radius of curvature of said particles in the apparatus to bring them into the region of changedmagnetic properties. An apparatus which has been found particularly suitable for carrying out the method of the present. invention comprises means for changing the magnetic flux of a short segment adjacent. the closed curvilinear path about which said particles are being accelerated and means for moving said flux changing means toward and away from the ion path.

The present invention will be described with reference to a. proton synchrotron although it will be understood that the method and apparatus such as is described in this embodiment is applicable with slight modification to the removal of accelerated ions from other particle accelerators employing a magnetic field which increases with time to restrict the ion motion to a closed curvilinear path.

It is believed that clarity of the explanation of the present invention will be aided by reference to the drawings wherein:

Figure 1 represents a top plan view of a synchrotron in conjunction with which the present application may be employed.

Figure 2 represents a sectional view of thesyn chrotron taken along angulated line 2! of Figure 1.

Figure 3 represents a vertical section taken along the line 33 of Fig. 4 of one embodiment of the apparatus of the present invention shown in position with respect to a channel in which acceleration of particles is carried out.

Figure 4 is a front elevational view of Figure 3 taken along a line 4-4 of Figure 3.

Figure 5 is a detailed view of a magnetic deflector channel which has been found satisfactory for use according to the present method.

Figure 6 is a top plan view in part in section of the apparatus of Figures 3 and 4.

Referring to Figure 1 and 2 a pulse of protons is injected into an evacuated generally ring shaped chamber 98 by means of an electrostatic generator Hit of the Van der Graaf type. Vacuum is maintained in the chamber by continuously withdrawing gas through the conduits 82 which connect the chamber 98 to the pumps 80. In traveling between the electro-static generator I and the chamber 98 the charged particles pass through conduit I82. On their arrival in the evacuated chamber 98 particles are deflected into th generally ring-shaped path, defined within the chamber 98, by a suitable charge on the electrostatic deflector plates I04 located at the open ing where the conduit I82 joins the chamber 98. The charge is supplied to the deflector plates I04 through the electrical connections I05 from a suitable power source I81. As the particles travel along the path within the chamber 98 they pass through and are caused to curve along a generally ring-shaped region or core 99 centrally lo cated in the chamber by the action of a magnetic field permeating the curved portions of the chamher. The magnetic field is set up to permeate the curved portions of the chamber between the jaws of four magnet quadrants [86, H0, H4 and H8, these magnet quadrants having a generally 6- shaped cross section (best seen in Figure 3).

The power used in generating the magnetic field in the magnet quadrants is supplied from the dynamo motor assembly 92 through the conductor 9! which passes through the innermost portions of the jaw openings in the C-shaped quadrants I86, H8, H4 and H8. The dynamo motor assembly 92 consists of a pair of rotatable electric machines or dynamos 98 which may be operated asv either generators or motors and are mechanically coupled to a pair of fly wheels 88, the dynamos being electrically connectable through the switch: 89 to the conductors 9| or a source of electric power (not shown) through the conductors 8 The energy to be used in building up the mag:-

netic flux in the-jaws of the magnet quadrants isdelivered from the dynamos 99 to the quadrants through the conductors 9 I. A very large amount of electrical energy must be delivered within a relatively short time in order to build up the desired flux density across the jaws of the magnet quadrants. By connecting the dynamos 90 through the switch 89 to a source of electric power through the conductors 81 the dynamos are made to act as motors and store the necessary energy in the rotating fly-wheels 88. When the flywheels have reached a desired velocity the switch 89 is thrown thereby connecting the dynamo 90 to the conductors ill. The energy stored in the fly-wheels is converted to electrical energy by the rotation of the dynamos, Which in thi connection act as generators to generate the electricity necessary to energize the magnet quadrants I96, III], H4 and I18. As the particles pass between the quadrants they describe a relatively straight path and therefore, those portions I08, H2, H6 and I20 of the wall of the chamber 98 are straight.

The acceleration of the ions is achieved by imparting an accelerating energy thereto as they pass through the ring member I24 enveloping a short section of the straight portion H6 of the chamber 98. The energy is applied at predetermined intervals from the pulse generator I40,

, the frequency mixer I42, and the voltage genervated by the trigger detector mechanism I48 also described in the Blewett application. By maintaining a balance between the acceleration of the particles and the increasing magnetic field permeating the curved portions of the chamber 98, particles are caused to continuously rotate within the chamber 98 in relatively stable orbits.

As the ions are accelerated in phase with the increasing magnetic field between the jaws 94 and 96 of the magnet quadrants, they tend to be confined to stable orbit paths which are centrally located in the annular core 99 of the chamber 98. During the initial portion of the acceleration period the ion paths are not confined to the core 99 but fill a substantial volume of the chamber 98 due to both vertical and radial oscillation from the core 99. During this portion of the acceleration period, when the ion paths are not confined to the center of the chamber 98, it is necessary to keep the portions of the chamber through which the ion paths deviate free from any article which would be struck by the ions or which would cause the ions to be deflected from their paths of travel within the chamber.

By the method of the present invention ions are deflected from an evacuated ring chamber after having been accelerated to a desired velocity by changing the phase relation of the accelerator so as to cause the ions traveling in the central portion of the chamber to be deflected toward the radially outermost portions thereof and by providing a region of reduced magnetic flux density along a segment of the outermost portions of the chamber.

Referring to Figures 3, 4 and 6, an apparatus suitable for carrying out the objects of the present invention is shown in place in a modified form of the apparatus of Figures 1 and 2 and consists essentially of the following. The magnetic field which is generated in the "0 magnet having pole faces I95 and I98 is augmented in this modified illustration of the example by the electrical windings 29 (seen best in Figure 3) located atthe outer extremity of the pole faces. These windings 29 are held in place by the brackets 22. The ions are deflected from their orbits in the evacuated chamber I98 (having in this modification a rectangular cross section) by means of a peeler unit I9. For the proton synchrotron. a preferred location of the peeler unit is the section of a magnetic quadrant preceding a straight section of the chamber I98 with reference to the direction of travel of the ions. However it may be located at any desired point within the magnetic field of the magnet quadrants. The peeler comprises an axially movable rod member 28 which is hermetically sealed through the chamber wall, threaded along its externally extending portion, and supporting at its internal end a channel bar 284. The bar 284 is provided with a channel 292 which is aligned with the path of flight of the ions. Thev rod 28 is slidably supported ina bearing tube 29 and prevented from turning by the action of a key 44 extending from the rod 28 into a key way 45 in the internal bearing tube wall. The rod is urged to its greatest external extension by a spring 38 concentric to the rod, and compressed between the outer end of the bearing rod 26 and a nut 38 threaded on to the rod. The compression on spring 38 may be adjusted by axial movement of the nut 36 along the rod 29. The spring rests against shoulders 48 and 42 provided on the bearing tube 26 and nut 36 respectively. A hermetic seal is provided at the portion of the chamber wall through which the rod 28 passes in the form of a packing material 32 compressed between the internally threaded flange cup 34 and the nut 35 threaded therein. The flange 31 of cup 34 is sealed to the flange 39 of the recessed portion I2 of chamber I98. All of the metallic parts of the peeler I 0 are preferably composed of non-magnetic material except for the channel bar 294.

With reference to Figures 3, 1 and 6 the operation of the peeler may be described as follows. When the protons are intially introduced into the chamber I98 from a Van de Graaf accelerator they tend to oscillate vertically and radially about the core I99 of the chamber I98. During the initial acceleration period while the oscillations are at a maximum, the channel bar 204 (shown in phantom as 284 is held in the recessed portion I2 of the chamber I98 by the action of spring 38. As the oscillations of the ions are damped, the ion paths become confined to the core I99 of the chamber I98 and the magnetic field between the pole faces I94 and I96 increases. Increase in the magnetic field strength is necessary in order to maintain ion motion in a circular path of approximately constant radius and confine them to the chamber I98. According to a preferred embodiment, the compression on the spring 39 is adjusted by movement of the nut 38 along the rod 28 to allow the magnetic pull of the C magnet on the channel bar 204 to overcome the spring pressure on the rod 28 after the ions have been confined to the core I99 of the chamber #98, but before the ions have been accelerated to their desired energies. The channel bar 294 is thus brought into the chamber I98 after the ion oscillations have been damped. Its presence does not interfere with the initial acceleration of the ions in the chamber because while the ion paths fill a substantial portion of the chamber the channel bar is recessed in the projecting portion I2 of the chamber I98. The channel bar 294 is present, however, when the ions have been accelerated to a desired velocity and thus is available for their removal.

Referring again to Figure 1 accelerated ions may be removed from chamber 98 along the path indicated by the arrows by introducing a channel bar 209 similar to that illustrated in Figure 5 into the chamber as part of a peeler unit l0. As pointed out below the means for urging the channel bar 200 into the chamber may be any conventional means of effecting a precisely timed rapid movement of a member. Such means is represented by the unit 9 to which the peeler unit I0 is operatively connected. Once the channel bar is in place in the chamber the frequency of application of the accelerating voltage to the induction accelerator I24 is increased without increasing the magnetic flux between the pole faces sufficiently to restrict the ion paths to the core 99 and thereby cause the ions to be confined to the core 99. Rather the ions expand their orbits in the chamber 98 and are thus brought within the influence of the reduced magnetic field in the channel of bar 294. The eifect of ions passing through the region of reduced magnetic field within the channel 202 of bar 204 is to change their path of flight from a generally circularly curved path due to the influence of the magnetic field between the pole faces 94 and 96, to a relatively straight or tangential path. As a result, when the ions reach the straight portion I08 of the channel 98, their direction of travel carries them through the port I09 from the channel 98 or to any apparatus aligned with this port along the path of ion flight. The length of the bar 204 is determined by the angle of deflection desired, the field reduction obtainable in the groove, and the curvature of the orbit. For a 50% reduction in the field strength between the magnetic poles to occur within the channel 202, the length of the channel bar should be such as to subtend an arc of the orbit having an angular value equal to twice that of the deflection desired.

In operation, the magnetic peeler described therefore provides an eflective means for removing ions which have been accelerated to desired energies from the proton synchrotron or similar apparatus at a desired point of the apparatus and with a high degree of control. In the operation of the proton synchrotron described in the Blewett application referred to above, assuming the period of acceleration to be approximately one second and the lateral oscillations of the ions causing them to fill the entire horizontal extent of the tube to last for approximately one-tenth of a second, approximately nine-tenths of a second remains for the channel bar 204 to be brought into position in the chamber 98 to effect the removal of the ions. Alternative methods are contemplated according to the present invention for introducing the channel bar 204 into position during this period. For example, an electronic solenoid powered by external circuits which are pulsed at appropriate times may be used. Similarly a hydraulic ram in which a piston is driven by fluid or gas pressure operated by valves, or a mechanical system driven by cams or levers may be substituted for the above-described scheme for utilizing the varying magnetic field of the magnet quadrants of the synchrotron for automatically moving the peeler channel rod into place. Conventional means for activating the valves or levers in time with the changing magnetic field in the quadrants may be employed. One such activating apparatus, a peaking strip, is described in the copending application of J. P. Blewett referred to above.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described, it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense.

I claim:

1. An apparatus for changing the trajectory of high energy ions moving in a curvilinear path in a magnetic field in order to eject said ions from said field in a controlled member which comprises an elongated magnetic metal member having a longitudinal channel therein, means for moving said channel in said magnetic field toward and away from said curvilinear path and for keeping said channel aligned with said path.

2. An apparatus for changing the trajectory of high energy ions moving in a curvilinear path in a magnetic field in order to eject said ions from said field in a controlled manner which comprises an elongated ferromagnetic member having a longitudinal channel therein, means for moving said channel in said magnetic field toward and away from said ion paths and for keeping said channel aligned with said paths.

3. In a synchrotron for'accelerating ions to very high energies a channel bar member the channel of which is aligned with and confronts the path of travel of ions in said sychrotron, said bar being movable in said magnetic field toward and away from said ion paths responsive to the change in magnetic flux through which said ions move whereby the trajectory of said ions in said magnetic field may be changed as said ions pass through the channel of said member.

4. In a synchrotron for accelerating ions to very high energies including an evacuated ring chamber in which said ions are confined by a magnetic field permeating said chamber, an apparatus for removing said ions from said chamber which comprises a rod hermetically sealed through the chamber wall in sliding relation, a channel bar affixed to the internal end of said rod, the channel of said bar being aligned with and confronting the path of travel of ions in said chamber and external means for moving said rod toward and away from the path of flight of said ions in said chamber.

5. In a synchrotron for accelerating ions to very high energies including an evacuated ring chamber in which said ions are confined by a magnetic field permeating said chamber, an apparatus for removing said ions from said chamber which comprises a rod hermetically sealed through the chamber wall in sliding relation, said rod supporting at its internal end a channel bar, the channel of which is aligned with and confronts the path of travel of said ions in said chamber and spring means operatively associated with the externally projecting portion of said rod for urging said rod to its greatest external extension.

M. STANLEY LIVINGSTON.

REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name Date 2,142,857 McArthur Jan. 3, 1939 2,215,979 Schuchmann Sept. 24, 1940 2,372,422 Hillier Mar. 27, 1945 2,394,070 Kerst Feb. 5, 1946

Images