US2922061A - Particle accelerator - Google Patents

Description

Jan. 19, 1960 LEE c. TENG PARTICLE ACCELERATOR 2 Sheets-Sheet 1 Filed Jan. 31, 1957 Source Jan. 19, 1960 LEE c. TENG 2,922,061

PARTICLE ACCELERATOR Filed Jan. 31, 1957 2 Sheets-Sheet 2 F E INVENTOR. 54'

Lee C. Tai q BY United States atenr 2,922,051 Patented Jan. 19, 1969 PARTICLE ACCELERATOR Lee C. Teng, Chicago, 111., assignor to the United States of America as represented by the United States Atomic Energy Commission Application January 31, 1957, Serial No. 637,595

7 Claims. (Cl. 313-62) The present invention relates generally to particle accelerators, and more particularly to devices for transferring particles from one accelerator to another.

Circular accelerators have proved to be a useful tool in producing high energy particles. In such machines, charged particles, such as protons and deuterons, are introduced into an orbit and revolve about the axis of the accelerator gaining energy with each revolution. The radius of the orbit of the charged particle is a function of the energy of the particle and the magnetic field traversing the orbit. As a result, the orbit radius of the particle increases with increased energy, the magnetic field being held constant, or the radius of the orbit may be held constant by increasing the magnetic field as the energy of the charged particle increases. In most ring accelerators of fixed magnetic field designed for high energy, the magnetic field increases from a minimum adjacent to the axis of the machine to a maximum at the periphery thereof, so that the radius of the orbit of the charged particles increases only slightly with increased energy. In the case of cyclotrons, the charged particles are introduced at substantially zero energy approximately on the axis of the machine, and the cyclotron accelerates these particles causing them to move out toward the periphery of the machine to a maximum energy. In most ring accelerators, the particles are introduced into an orbit located on the inner boundary of the machine at a substantial energy, and the increased energy of the particles due to acceleration causes the particles to move only slightly toward the outer periphery of the machine due to the greatly increased magnetic flux in this region.

Acceleration of the particles within the accelerator is achieved by synchronizing an alternating electrical field with the position of a group of particles in the accelerator. At low energies, the electrical field may operate at a constant frequency, however, as the particles are accelerated to higher energies, the frequency of the accelerating potentials changes.

The maximum energy obtainable with any given circular accelerator is limited by the maximum magnetic field which is attainable. As a practical matter, the maximum magnetic field attainable is limited by the saturation density of the magnet. Since iron is universally employed in the magnets of' accelerators at the present time, it is considered that the maximum magnetic field attainable is approximately 20 kilogauss. As a result, very high energy particles can only be achieved with a large radius for the final accelerating orbit. On the other hand, it has not been possible to inject particles of high energy into the inner orbits of an accelerator, thus re quiring a single accelerator to cover a wide energy range. Heretofore, particles could be injected into an accelerator at energies of only approximately 50 mev., or less. This fact efiectively limits the diameter of a ring accelerator. Further, the minimum magnetic field which may be employed in an accelerator is of the order of 50 gauss, because of the effects of terrestrial and stray magnetism. As a result, the low energy particles must be injected into a substantial. magnetic field, thus resulting in a relatively small diameter orbit.

It is one of the objects of the present invention to provide a device for injecting charged particles into an accelerator which may be employed regardless of the energy of the particles. In this manner, particles of high energy may be injected into an accelerator, such as a ring accelerator, and further accelerated to a much higher energy than has heretofore been possible. The high energy accelerator may be a ring accelerator of much larger diameter than any that has heretofore been possible. Since the accelerator need not handle the range of energies previously required, substantial amounts of iron or other magnetic metal may be eliminated from the magnet of the accelerator.

It is a further object of the present invention to provide a device for accelerating charged particles which includes at least two cascaded accelerators. As a result, the energy of the particles injected into the low energy orbit of the higher energy accelerator Will be very much greater than the energy of the particles previously injected into an accelerator, resulting in simplification of the design of the higher energy accelerator. The particles may be raised in the initial accelerator to any desired energy, depending principally upon the complications in the design of the initial accelerator which are to be undertaken.

The design of the high energy accelerator is greatly simplified when the energy of the particles injected into the accelerator is high. Since the energy range handled by the higher energy accelerator is reduced by this fact, it is not necessary to frequency modulate the accelerating potentials over as wide a frequency range as is required with accelerators in which low energy particles are injected. it is much easier and economical to build a high potential radio frequency generator which is frequency modulated over a narrow range than it is to construct such a generator which is frequency modulated over a wide range. In addition, substantial quantities of magnet material are no longer required, since it is unnecessary to accelerate the particles over the range of radii required when the energy of injection of the particles is low. Further, the emerging high energy beam from the accelerator may be obtained at greater intensity than has been previously possible at high energies.

These and additional advantages of the present invention will become readily apparent to those skilled in the art from a further reading of this disclosure, particularly when viewed in the light of the drawings, in which:

Figure 1 is a sectional view of a particle accelerator employing a synchrocyclotron and fixed field alternating gradient ring accelerator disposed in cascade according to the teachings of the present invention;

Figure 2 is a sectional view taken along the line 2-2 of Figure l; C

Figure 3 is a top elevational view of the particle accelerator illustrated in Figure l, partly schematic;

Figure 4 is a sectional view taken along the line 4-4 of Figure 3; and

Figure 5 is a sectional view taken along the view 55 of Figure 3.

Charged particles may be accelerated according to the teachings of the present invention by cascading accelerators. The outer orbit of the first accelerator is introduced into the low energy orbit of the second accelerator by a transfer device. The transfer device includes a deflector in the first accelerator to displace the outer high energy orbit outwardly from its normal path to pass through a slit in the first accelerator and into the second accelerator. Within the second accelerator, an infiector is positioned to change the orbit of these particles (now the magnetic circuit of the electromagnet.

J synchrocyclotron '10 through the aperture 32.

low energy particles) in the'high energy accelerator to cause them to rotate about the axis of the accelerator.

The applicants device for transferring particles from one accelerator to another may be employed with any.

type of circulariaccelerator and is not limited in the energy of the particles being transferred. It is, of course, most likely that the second accelerator will be a ringtype accelerator, since substantial energy is being injected into the accelerator and there is no reason to provide the very low energy orbits which are characteristic of cyclotrons. It is also likely that the low energy accelerator will be of the cyclotron-type, since a cyclotron is capable of accelerating particles from essentially zero energy on up to the maximum energy obtainable in the particular machine. However, the present invention may also be practiced by cascading cyclotrons, or ring accelerators. For illustrative purposes, the figures illustrate the low energy accelerator as a synchrocyclotron 10, and the high energy 'accelerator as a fixed field alternating gradient ring-type accelerator 12.

The synchrocyclotron has an air impermeable housing 14 of generally cylindrical shape. One portion 16 of the housing 14 protrudes outwardly from the cylindricalremainder thereof. The peripheral portions of the housing, designated 20, also protrude outwardly from the other in Figure 4. The housing 14 isconstructed of nonmag- 4 r 1 54 has a rectangular cross section, as'illus'trated in Fig. 5, and is provided with an inwardly. protruding portion 56 which merges with and is sealed to the outwardly extending portion 16 of the housing 14. Particles passing through the aperture 32 in the lip 30 of the coil 22 pass 7 directly into the orbit chamber 54 of the ring accelerator The ring accelerator 12 is provided with a magnetic field which traverses the orbit chamber 54 in a direction 62 and across the :side of the yoke 62 opposite the channormal to the .planeof thering. This magnetic field nel 64, as illustrated in Figure 5.

One or more cavity resonators 68 are disposed between a pair of adjacent electromagnets 60-to accelerate the particles revolving in the orbit chamber 54. The resonator 68 is in the form of an electrically conducting plate.

netic material and is evacuated in a conventional manner."

The protruding portion 20 of the housing 14 contains a generallyannular coil 22 which is electrically insulated from the housing and forms the coil of an electromagnet. A core 24 of the electromagnet comprises a pair ofbars 26a and 26b which are disposed on opposite sides of the housing 14 in contact with each other. The confronting surfaces of the bars 26a and 26b arev contoured to The resonator 68 extends through the wall of the orbit chamber 54 and is provided with an aperture'70 which permits the particles within the orbit chamber 54 to pass through the resonator. The resonator 68 is connected to a pulse source 72 which places a potential on the resonator to accelerate the particles. The pulse source 72' is synchronized with the source 42, so that the pulses from the source 72 occur at the proper time.

' An inflector 74 is disposed within theorbit chamber 54 confronting the lip 30 of thecoil'22. The inflector form pole pieces 27 fitting the shape of the region defined by the coi1'22, hence placing the portion of the housing 147between the protruding portion 20 in the gap of the The coil 22 is in the form of a copper strip, and, ex-

cept for the portion 16 of the housing, it is spaced from posed in the half of the housing 14 opposite to the lip 30.

A folded D 38 is disposed between the D 36 and the coil 22, and a transmission line 40 extends from the Ds 36 and 38 out of the housing 14. The transmission line 40 is connected to a source 42 of frequency modulated radio frequency excitation. In like manner, a source 44 of direct current is connected to the coil 22,

A deflector 46 is positioned downstream from the lip 30 of the coil 22 and is disposed adjacent to the coil 22. The deflector 46 consists of two magnetic members 48 and 50, the members 48 and 50 being secured to opposite sides of the housing 14 and having protruding ridges 52 in spaced confronting relationship generally aligned parallel to the outer orbit. The deflector 46 intensifies the magnetic field between the ridges 52 to displace the outer orbit of the cyclotron 10 and direct it through the aperture 3 2.

The ring accelerator 12 surrounds the cyclotron 10, and abuts the protruding portion 28 of the coil 22 of the cyclotron 10. The ring accelerator 12 is disposed generally tangent to the synchrocyclotron 10. The ring accelerator 12 has a circular orbit chamber 54 which is evacuated in a conventional manner. The orbit chamber- 74 is disposed adjacent to the inner edge of the magnet 60. and consists of a pair of magnetic members identical synchrocylotron 10, and the: location and strength of the inflector 74 in the ring accelerator 12 must be carefully selected relative to the .distance from the lip 30. The deflector 46 should be positioned at a distance from the axis of the cyclotron 10 slightly greater than the 7 last equilibrium orbit thereof, and should be positioned downstream from the lip 30 by an angle -between the radius of the lip 30 and the radius of the deflector 46 given by the following equation:

' sink a,

where P is the strength of the deflector element given by the expression betatron oscillations, per revolution of the particles. S is the azimuthal width of the, deflector element, H is the strength of the magnetic field in the magnet, and'R is the radius of the machine. Also, i

is the frequency of the ions, and w /1 n)w, where 5 E H dR e is defined by the expression:

cosh a cos 2vrw sin 21m,

The deflector in the low energy accelerator and the inflector in the high energy accelerator both operate to increase the field at their respective areas, thereby creating a magnetic bump which shifts the orbit from its normal direction. In the case ofthe deflector 46, the magnetic bump pushes the orbit inwardly from the equilibrium orbit, causing the charged particles to pass through the lip. In the case of the inflector 74, the magnetic bump pulls the charged particles to displace their orbit into the high energy accelerator, thereby preventing the charged particles from striking a portion of the wall of the accelerator rather than following the orbit chamber 54. Therefore, the equation above defines the location not only of the deflector 46, but also of the inflector 74,- provided the ring accelerator 12 operates as a nonaltere nating gradient accelerator. However, when the high energy ring accelerator 12 is an alternating gradient type machine, as here disclosed, the angle (15' between thelip 30 and the inflector 74 relative to the axis of the ring accelerator 12 is given by the expression:

7/ is the number of radial betatron oscillations per revolution of the particles in the accelerator, and P is the strength of the inflector, as defined above. 6,, and a are parameters yielding a measure of the scallop in the orbit of the particles and specifying the type of accelerator. In the special case of nonalternating gradient accelerators, such as the 'synchrocyclotron set forth above, =w and 6 :0, thus producing the special form equation set forth for the synchrocyclotron above. In the case of an alternating gradient ring accelerator, ,u and 6 assume values in the orderof to 100, which represent design criteria for the accelerator.

Throughout this disclosure, the deflector and inflector have been illustrated as single assemblies of confronting magnetic elements. However, it is to be understood that the inflector and deflector may be constructed with a plurality of assemblies of confronting elements also. For example, in the deflector 46 it may be desirable to place an assembly of elements on the upstream side of lip 30 in order to restore the orbits within the accelerator to their proper position relative to the axis of the accelerator. Also, it may be desirable under some circumstances to place an assembly of elements which operate to decrease the intensity of the magnetic field on the upstream side of the lip 39.

The transfer mechanism for cascading accelerators is effective to transfer particles continuously or in pulses depending upon the method of operation of the low energy accelerator, here the synchrocyclotron 10. Further, the transfer mechanism may be employed to transfer particles of any energy from one machine to another.

From the foregoing disclosure, those skilled in the art will readily devise many modifications and additions to the structure here disclosed. It is therefore intended that the scope of the present invention be not limited by the foregoing disclosure, butrather only by the appended claims.

What is claimed is: a

1. A device for accelerating charged particles comprising, n om ina ion, a firs c rcular ac er a nd la a e er te: ha-Y ega port qnthe po ed essentially tangentially to the'first circular accelerator, and means for transferring particles from the first accelerator to the second accelerator including a magnetic deflector in the first accelerator, a magnetic shield disposed between the accelerators, anda magnetic inflector in the second accelerator. i

2. A device for accelerating charged particles comprising, in combination, a cyclotron, a ring accelerator having a portion disposed tangentially to the cyclotron, and means to transfer particles from the cyclotron to the ring accelerator including a magnetic deflector disposed Within the cyclotron, a magnetic shield disposed between the ring accelerator and the cyclotron, and a magnetic inflector disposed within thering accelerator.

3. A device for accelerating charged particles comprising, combination, a cyclotron having an annular accelcrating cavity with an outwardly protruding portion terminating in a radial lip, ,a ring accelerator having an annular orbit chamber with an inwardly protruding portion terminating in a radial lip, the ring accelerator being disposed essentially tangential to the. cyclotron with the radial lip of the cyclotron confronting the radial lip of the ring accelerator, a radialmagnetic shield disposed between the cyclotron and ring accelerator having an aperture for the passage of particles from the cyclotron to the ring accelerator, a deflectordisposed on the downstream side of the shield within the magnetic field of the cyclotron and radially outwardly from the outermost orbit thereof, and an inflector disposed radially inwardly from the innermost orbit and within the magnetic field of the ring accelerator at the dgwnstream side of the magnetic shield.

4. A device for accelerating charged particles comprising, in combination, a cyclotron having an annular accelerating cavity with an outwardly protruding portion terminating in a radial lip, 21 ring accelerator having an annular orbit chamber with an inwardly protruding portion terminating in a radial lip, the ring accelerator being disposed essentially tangential to the cyclotron with the radial lip of the cyclotron confronting the radial lip of the ring accelerator, a radial magnetic shield disposed between the cyclotron and ring accelerator having an aperture for the passage of particles from the cyclotron to the ring acceleratorQa deflector disposedon the downstream side of the shield within the magnetic field of the cyclotron at a distance slightly greater than the diameter of the outermost orbit thereof and spaced from the shield by an angle g5 relative to the axis of the cyclotron given by the expression: tan l sin 21rw,+(l-OOS 210:

Where (e is the number of radial betatron oscillations per revolution of particles in the cyclotron, 03; is defined by the expression:

and P is the strength of the deflector,

H being the magnetic field intensity, R being the radial distance of the deflector from the center of the cyclotron, and S being the azimuthal width of the deflector, and an inflector disposed radially inwardly from the innermost orbit and within the magnetic field of the ring accelerator at the downstream side of the magnetic shield by an :7 angle relative to the center of the ring accelerator given by the expression: ,7

Q,(1+co's 21rv,,') '-sin- 2arv,]ll

where 11,, is the number of radial betatron os :illa tions' per revolution of the particles in the ring accelerator and" Q isequalto' 1 '7 iP seco- F: i z

-P being defined'for the inflcctor as hereinbefore for the deflector, ,u and being accelerator constants that' assume values in the order of to 100.

5. A device for accelerating charged particles com-j prising, in combination, a first circular accelerator, a second circular accelerator having a portion thereof disposed essentially tangenti ally'to the first circular accelerator, and means for transferring particles from the first accelerator to the second accelerator including a magnetic deflector in the first accelerator, a magnetic shield disposed between the accelerators, and a magnetic inflcctor, in the second accelerator, the deflector being disposed on the downstream side of the magnetic shield by an angle relative to the axis of the first accelerator given by the expression:

tan (Ka b-i x) cos 27 1 +SiIl 271' 1 where 11,, is the number of radial betatron oscillations" perrevolutionof the particles and Q is equal to i sec 1 2p, on: P being the strength of the deflector, s

' 5& s 2RH R s H being the magnetic field intensity, R being the radial distance of the deflector from the center of the first accelerator, S being the azimuthal width of the deflector, 11. and 0 being accelerator constants, and the inflcctor being disposed in the second accelerator on the downstream side of the magnetic shield byan angle relative ,to the axis of the second accelerator'given' by the above expression. y

6. A-device for accelerating charged particles comprising, in combination, a cyclotron having a cavity and erator is a fixed field alternating gradient accelerator.

an annular strip of electricallyconducting material with an outwardly protruding portion and a radial lip extending therefrom, said lip having an aperture for passing particles and forming a magnetic shield, a ring accelerator disposed essentially tangentially to the cyclotron, said accelerator having anaannular. orbit chamber with: an inwardly protruding portion confronting the radial lip; of the cyclotron, a deflector disposed on the downstream side of the shield within the magnetic field of the cyclotron radially outwardly from the outermost orbit thereof at a distancejlightly greaterthan the diameter of the outermost orbit thereof and spaced from the shield by" an angle 5 relative to the axis of the cyclotron given by the expression:

wherel'w is the number of radial betatron oscillations per revolution of thelparticles in the cyclotron, a3, is defined'by the expression:

cosh c cos 21rw,+ sin 2m, P is the strength of the deflector,

where 11,; is thenumber of radial betatron oscillations per revolution of the particles in'the ring accelerator,

Q is equal to sec v,

P being defined as hereinbefore, and ,u; and 03, being accelerator constants that assume values in the order of 10 to 100. i t

A device for accelerating charged particles com--' prising the'elementsof-"claim 2 wherein the ring accel- References Cite'din the file of this patent PATENTS l 2,473,477 Smith M514, 1949: 2,658,999 Farly 4--. Nov. "10, 1953

Images