US3328708A - Method and apparatus for accelerating ions of any mass - Google Patents

Description

June 27, 1967 B. 1-1. SMITH ETAL 3,328,708

METHOD AND APPARATUS FOR ACCELERATING IONS OF ANY MASS Filed March 4, 1965 2 Sheetssheet 1 1 SYNCHROTRON 62 MAGNET POWER SUPPLY a [4 If 12-1 /13-2 STORAGE RING 24 MAGNET POWER /63 14 SUPPLY 22 I36/ RADIO FREQUENCY SYSTEM INVENTORS 3 BOB H. 311111111 FREQUENCY /64 ROBERT M. MAIN CONTROL ALBERT GH/ORSO ma-W ATTORNEY June 9 B. H. SMITH ETAL 3,323,703

METHOD AND APPARATUS FOR ACCELERATING IONS OF ANY MASS Filed March 4, 1965 2 Sheets-Sheet 2 INVENTORS 808 H. SMITH ROBERT M. MAIN ALBERT GHIORSO ATTORNEY United States Patent 3,328,708 METHOD AND APPARATUS FOR ACCELERATING IONS OF ANY MASS Bob H. Smith, Berkeley, Robert M. Main, Oakland, and Albert Ghiorso, Berkeley, Caliii, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Mar. 4, 1965, Ser. No. 437,332 16 Claims. (Cl. 328-235) This invention relates to the acceleration of charged particles to high energies in synchrotrons and more particularly to a method and apparatus for accelerating particles having very different masses including particles which are much heavier than those heretofore accelerated by such means. The invention provides techniques for producing a beam of ions of any desired element within a synchrotron.

It is increasingly evident that beams of high energy heavy particles have particular physical properties which are of great interest in many new fields of biological inquiry at virtually every level. The interaction of heavy particles with biological tissue is related to the highlinear-energy-transfer properties of the heavy particles. With a high-linear-energy-transfer, a quantitatively differentmode of both excitation and ionization seems to occur in matter; as a result it is found that the effects of heavy particles on crystals, organic molecules, proteins, and living cells involve different molecular mechanisms than do the effects of lightly ionizing rays.

It has become apparent, for example, that the production of high energy beams of heavier ions will be of very great interest in connection with cancer research. Studies at existing accelerators have shown that such a beam can be used to irradiate an aifected region with little deleterious effect on the healthy tissue through which the beam must pass to reach the affected region, owing to the Bragg peak. Lesions without scarring may be produced in a laminar plane by a penetrating sheath of heavy particles, the lesion running parallel to the surface of the tissue at a predetermined depth. The availability of a source of heavy ions is also of great importance to many other phases of basic bio-medical research and in space medicine studies.

Heavy ions can be accelerated by many of the various conventional types of particle accelerator, however, each has certain disadvantages when used for this purpose. For instance, with electrostatic accelerators such as the Cockcroft-Walton type, the maximum obtainable energy is severely limited. To a lesser degree, the maximum practical energy which can be obtained for heavy ions in a cyclotron is also limited. A linear accelerator can be used to obtain a high energy for a particular heavy particle, but for all lighter particles of similar charge the maximum attainable energy from a specific linear accelerator is correspondingly less. Thus the weight range of particles which may be effectively accelerated in a given linear accelerator is very limited. Also, the extreme length, and therefore the cost, of a linear accelerator for the heavier particles is a practical obstacle to the use of such means. A linear accelerator is ordinarily utilized to inject particles into a synchrotron and therefore the limitations of the linear accelerator are imposed upon the synchrotron. If heavy particles are injected into a synchrotron from a cyclotron, the cost is again very great; while if heavy particles are injected into a conventionally operated synchrotron from an electrostatic generator, the maximum obtainable output energy is limited by the low injection energy.

In the present invention a synchrotron is utilized in a novel manner to overcome the above-mentioned difficulties. The synchrotron as employed in the present inven- "ice tion is conventional insofar as ions are accelerated to a higher speed during each revolution around the synchrotron by a radio-frequency potential, the frequency of which is increased in step with the increase in the energy of the accelerated particles. In each stage of particle acceleration, the magnetic field intensity of the synchrotron is swept from a minimum to a maximum so that the ions remain in an orbit of nearly constant radius.

In this invention, particles are injected into the synchrotron by an electrostatic accelerator. Ordinarily, atoms of an element of high atomic weight can only be initially ionized to a relatively loW charge-to-mass ratio, i.e., only a few of the orbital electrons can be removed. Any ion will be accelerated by an electrostatic accelerator, but the amount of acceleration is proportional to the chargeto-mass ratio. Thus, the heavier nuclei such as uranium, for example, which are initially ionized with a very low charge-to-mass ratio, must necessarily be injected into the synchrotron at a relatively low velocity.

While the charge-to-mass ratio of the ions can be raised by passing the ions through an electron stripper such as a thin metallic foil, such stripping can be satisfactorily accomplished only after the ions have been accelerated to a much higher velocity than is obtainable in the electrostatic injector accelerator. However, as mentioned previously, the maximum energy which may be imparted to the ions in a single acceleration stage of a synchrotron is limited by the charge-to-mass ratio of the particle and by the maximum magnetic field obtainable.

Thus the basic problem in connection with accelerating heavier ions in a synchrotron is that the ions cannot, initially be given the degree of charge that would be required to allow the synchrotron to accelerate the ions to the desired high energy. While the ions can be given the needed high charge by stripping, after some acceleration in the synchrotron, the magnetic field thereof cannot be abruptly changed in the middle of a cycle to adjust to a sudden radical change in the charge of ions which are circulating therein.

To overcome these problems, in the present invention, ions of relatively loW charge are accelerated to the maximum velocity obtainable in a single cycle and then are extracted from the synchrotron. The ions are then passed through an electron stripper wherein several or all the remaining orbital electrons are removed. These stripped highly charged ions are then injected into a storage ring. While the magnetic field of the synchrotron is being decreased back to a minimum value in preparation for a second stage of acceleration, the ions circulate in the storage ring in a steady state magnetic field. At the beginning of the next synchrotron cycle the ions are then re-injected into the synchrotron and, taking advantage of the higher charge-to-mass ratio obtained by removal of electrons in the stripper, the ions are further accelerated to a very high energy. Alterna-tely, the ions may be stored in the initial charge state and stripped just prior to re-injection into the synchrotron. After the second stage of acceleration, the ions may be extracted and used to bombard a target; or may be further stripped of electrons, stored, re-injected into the synchrotron and accelerated still more in a third stage of acceleration.

This accelerator system has been designated as an Oinnitron in view of its capability of accelerating ions of any atomic weight to all energies within the minimum and maximum design range.

It is an object of this invention to increase the versatility of charged particle accelerating installations.

It is an object of the present invention to provide a method and apparatus suitable for accelerating particles of any atomic weight to high energies.

It is another object of the present invention to provide techniques by which the peak output energy of ions from accelerators of the synchrotron type can be efilciently increased.

It is another object of the present invention to provide a method and apparatus for accelerating heavy ions in a synchrotron from a low initial injection energy to a very high output energy.

It is another object of the invention to provide a highly versatile synchrotron system having a very low energy spread obtainable over a wide, continuously variable energy range.

it is still another object of the invention to provide for the repetitive staged acceleration of ions to successively higher energies within a single accelerator of the synchrotron class.

It is a further object of the invention to facilitate the study and treatment of biological conditions by providing for the generation of high energy beams of a wide variety of heavy charged particles.

The invention will be better understood by reference to the accompanying drawing of which:

FIGURE 1 is a diagrammatic plan view of a synchrotron storage ring and appurtenances in accordance with the invention,

FIGURE 2 is an enlarged more detailed view of the segment of the synchrotron of FIGURE 1 which is enclosed by dashed line 2 thereon, and

FIGURE 3 is a greatly enlarged and more detailed cross-sectional view taken at line 33 on FIGURE 2 and showing the magnet and gap structure of the synchrotron.

Referring now to FIGURE 1 there is shown a synchrotron 11 having eight major beam-guiding magnet sectors 12 for containing and directing the ion beam in an annular orbit, the sections being separated by eight orbit straight sections 13. In order to refer separately to individual straight sections 13 and curved magnet sections 12, the reference numbers will be followed by a number designating an individual sector or section, proceeding clockwise around the synchrotron, for example 131 to 13-8 for the straight sections. Four conventional radio-frequency accelerating resonators 14 are provided in alternate straight sections 13-2, 13-4, 13-6 and 138, while various pulsed beam-bending magnets are disposed in the remaining straight sections for receiving and extracting an ion beam as will be described later. Except as will be herein described, the structural detail and components of the synchrotron 11 may be of customary design as understood by those skilled in the art.

The ions are first created and formed in a low energy beam in a Cockcroft-Walton accelerator 16 or the like and directed into a beam infiector 17 at one of the straight sections 134.7, which guides the ions into the synchrotron beam orbit. The beam then circulates through a long annular vacuum pipe 15 Which extends around the synchrotron and encloses the beam orbit thereof. In FIGURE 1, arrows are provided along vacuum pipe 15 to indicate the direction of the ion beam.

A constant orbit radius is maintained inasmuch as the ions are accelerated concurrently with the increase in magnetic field intensity. When the maximum available magnetic field is obtained and the particle reaches maximum energy, the ion beam is extracted inwardly by a beam extractor 31 at one of the straight sections 135 and is guided through a series of beam-bending magnets 18 and 19. The resonators 14 are energized from one or more conventional synchrotron radio-frequency systems 61 while the synchrotron and storage ring magnets are energized from direct current power supplies 62 and 63. A frequency control 64- is operated as in a conventional synchrotron, the control correlating the frequency provided by the radio-frequency systems 61 with the magnetic field intensity so that the path of the charged particles in the synchrotron is maintained near the center of the vacuum pipe 15. Such control also provides for synchronizing and correlating the operation of the various elements of the omnitron as will be described.

An electron stripper foil 24 is disposed between the bending magnets 13 and 19 to increase the charge on the ions after extraction from the synchrotron 11. Foil 24- removes one or more electrons from the ions, the number removed depending mainly upon atomic number and velocity of the ion, and to some extent upon foil thickness.

A beam storage ring 21 is disposed within the area enclosed by synchrotron 11 and is comprised of four curved beam-guiding magnet sections 22 mutually separated by four straight sections 23. The accelerated ion beam from synchrotron 11 is directed into the storage ring 21 at one of the straight sections 234 thereof at a beam inflector 32. The magnetic field intensity in the beam guide magnet sections 22 of storage ring 21 is steady state and the ion beam circulates around the storage ring without change in energy. In the meantime, the magnetic fields in the synchrotron guide magnets 12 are recycled to the necessary low value for re-injection of the stored particles into the synchrotron 11. The stored ion beam is then extracted from the storage ring 21 by the beam extractor 33 at one of the straight sections 23-1 thereof, the ions being guided by two beam-bending magnets 26 and 27 for re-entry into the synchrotron 11 by beam inflector 34 at one of the straight sections 13-3.

The ion beam is then again accelerated in the synchrotron 11 as before, however, since the injection velocity of the ions is much higher than in the first acceleration state, a higher harmonic of the radio-frequency signal is utilized for accelerating the ions, as discussed later.

After the second cycle of acceleration of the ions in synchrotron 11, the ion beam can again be directed back through the stripper foil 24 to the storage ring 21, in preparation for a third acceleration. Ultimately, however, the ions are extracted from either the storage ring 21 or syn chrotron 11 for bombarding a target, for the treatment of a medical patient, or for any of the other uses for which charged particle beams are employed.

If a well-defined brief pulse of ions is to bombard a target 28, the ion, beam can be extracted at straight section 13-1 by beam extractor 36 of synchrontron 11 and directed toward the target. If, on the other hand, the ions are to strike an alternate target 29 at a more constant rate over an extended time interval, then the beam may be extracted from the storage ring 21 by beam extractor 37 at straight section 232 and directed to the target.

More details of the synchrotron structure are shown in FIGURE 2, which is an enlarged view of straight section 135 with the adjoining potrions of guide magnet sectors 125 and 12-6. Many individual guide magent sections 41 form each magent sector 12, a greatly enlarged cross-section view of the structure of magnet sections 41 being shown in FIGURE 3. Subjacent each magnet section 41 is an adjustable positioning means 42, disposed on a concrete foundation 43, which is provided to facilitate the alignment of each guide magnet 41. Each such magnet section further includes a C-shaped iron core 44 with pole tips 46 suitably shaped to provide an alternating gradient field, as described in detail in Physical Review 88, 1190 (1952), by Courant et al. The vacuum pipe 15 through which the ions pass extends between the pole tips 4-6. The beam-guiding magnetic field is produced by magnet coils 48 and 49 disposed around each of the pole tips 46.

With reference again to FIGURE 2, each major sector 12 of the synchrotron magnet is comprised of many of the magnet sections 41 disposed along the beam orbit 15 with successive ones of the sections facing in opposite directions to produce the alternating gradient effect. To correct any tendency of the ions to deviate widely from the optimum orbit, supplementary focussing means are disposed at intervals therearound. Thus in the straight section 135 the ion beam orbit passes through two conventional quadrupole magnetic focussing lenses 51 and 52. In the beam extractor 31, a pair of ferrite core pulsed magnets 53 and 54 for deflecting the ion beam out of the synchrotron are disposed in the straight section 135.

The straight sections 131, 13-3 and 13-7 of synchrotron 1'1 utilize other beam extracting or beam inflecting means 36, 34 and 17 similar to that described with respect to FIGURES 2 and 3.

The magnet sectors 22 and the straight sections 23 of the storage ring 21 may have a detailed construction essentially similar to that of the synchrotron-11 as described with reference to FIGURES 2 and 3.

While the design of an accelerator system for practicing the present invention may be varied in very many respects, an example of specifications for a particular embodiment of the invention is as follows:

Injection system Cockcroft-Walton injection potential rnegavolts 2 Synchrotron 11 6 Energy (a) Greater than 400 million electron-volts (mev.) per nucleon for all ions having an atomic weight equal or less than 40 (b) Greater than 300 million electron volts (mev.) per nucleon for all ions having an atom weight equal to or less than 238 (Uranium) (c) Energy spread does not exceed 0.2%.

Beam intensity (a) Number of alpha particles should be greater than 4 10 particles per second at 100-400 mev. per'nucleon (b) Number of xenon particles should be greater than 1'10 particles per second up to 15 mev. per nucleon.

This synchrotron provides 60 acceleration stages per second. Therefore, if two-stage acceleration is used, the beam output rate is 30 pulses per second.

Ions are created with only the outer few electrons removed. With progressively heavier nuclei, the e/m (charge-to-mass) ratio of ions available in quantity from existing ion sources decreases. For uranium, for example, it is only 0.02. Acceleration by the Cockcroft-Walter in- Magnet: 25 jector 16 is proportional to the charge-to-mass ratio so I I 2 Mean 0rb1t diameter feet 93 the amount of acceleration of the heavier ions decreases Maximum guide field kilogauss 10 with increasing mass number. The relatively slow speed Useful aperture inches 1% x 2% of these particles requires a very low orbit frequency in Number of magnets 64 the synchrotron at injection, the orbit frequency being Length of magnets inches 28 30 defined as the reciprocal of the orbit period around the Number of straight sections 8 accelerator. Length of straight sections feet 12 In Table I there is shown a tabulation of orbit frequen- Weight of steel tons 77 cies, harmonic numbers and radio-frequency data. The. Weight of copper do 13 harmonic number may be defined as the number of radio- Stored energy kilojoules 212 frequency cycles occurring at a particular resonator 14 Input power, AC kilowatts.. 134 forone revolution around the synchrotron of a particular Input power, DC do 268 particle.

TABLE I Orbit freq. (megacycles) Orbit period (500.) Freq.ofRF (megacycles) Elm Harmgnie V Max Min. Min. Max. Hum er Max. Min.

Accelerqfion system Thus as indicated above, for particles with e/m==0.02, Maximum frequency mc /Sec 33 the orbit frequently is only 0.0311814 mc., while the Minimum frequency 1 6 highest orbit frequency (corresponding to lighter particles Energy gain per tum 'i with em=0.5) is 2.556498 me. The ratio of these freeg of gg kg n u 4 quencies is 82/1. If the radio-frequency system of the synchrotron had to cover this range, the task would be Storage ring 21 6 formidable. However, if the harmonic number is varied Mean orbit diameter feet 54 inversely with the c/m ratio, the dynamics of the syn- Guide field 'ig g 10 chrotron are independent of e/m, thus the frequency Useful apertur; l 1 2% range is essentially constant for all particles, and the neces- Number of g u 40 sary range of the radio-frequency system is approxi- Length of magnets inches 28 ii Number of Straight Sections 4 e pm 16m of qq l h phase relatwnshlp 3 Length of Strainht Sections feet 12 tween the several cavlties 1s cons1derably reduced by dr1v- Wei ht of steel 48 ing all the radio-frequency resonators 14 in-phase and Weight of Co 8 selecting only harmonic numbers which are integrals of Inpugt power Pp ig g 370 the number of resonators. For an accelerator with the above-described configuration, a radio-frequency system covering the range from 1.6 to 33 mc. is required. This frequency range can be accommodated by including two cavities in each of the resonators 1 4. The first cavity tunes from 1.6-to 7.5 mc., the second from 7 to 33 me. The

portion of the available frequency range actually utilized in any particular acceleraing stage depends upon the e/m ratio of the particular ions being accelerated. Such a system is described in detail in the report, The RF System for Princeton-Penn Accelerator, Princeton University Report PPAD408E, 1961, by J. Reidel et .al.

The number of bunches of particles in a synchrotron is equal to the harmonic number of the radio-frequency. For uranium with an e/m ratio of 0.02 there are 192 bunches, each spaced only 18 inches apart. For lower harmonic numbers the bunch spacing increases.

At full field the transit time of the particles around the described synchrotron orbit varies from 6.4 microseconds for e/m=0.02, to 0.391 microseconds for e/m=0.5 particles. Because of the choice of harmonic number, the time between particle bunches is approximately the same for all beams0.030 microseconds.

Obviously, many variations may be made in the design of the invention, for instance; the storage ring 21 is not necessarily disposed within the synchrotron, the number of straight sections may be altered; and electrostatic beam inflection and extraction may be utilized rather than the magnetic components as herein described, suitable detailed structures for either type being known to those skilled in the art.

Therefore, while the invention has been disclosed with respect to a specific embodiment, it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

1. In a method for producing high energy beams of heavy ions in a synchrotron, which synchrotron is of the class having a cyclically varying magnetic field defining a particle orbit and a cyclically varying electrical field thereat for accelerating ions therearound, the steps comprising generating said ions with a first charge-to-mass ratio, accelerating said ions at said orbit of said synchrotron to a first energy level during a first cycle of said magnetic field thereof, raising the charge-to-mass ratio of said ions to a second higher value, and further accelerating said ions at said orbit in said synchrotron to a second higher energy level during a subsequent cycle of said magentic field, said further acceleration of said ions being phased with a higher harmonic of said electrical field than the initial acceleration thereof.

2. A method for producing high energy beams of heavy ions as described in claim 1 and comprising the further step of changing the frequency range of said electrical field between the initial acceleration of said ions and the further acceleration thereof to compensate for the changed charge and energy of said ions.

3. A method for producing a high energy beam of particles in a synchrotron comprising the steps of initially ionizing said particles to a low charge-to-rnass ratio, accelerating said particles in said synchrotron during a first operating cycle thereof, storing the accelerated particles outside said synchrotron, raising the charge-to-mass ratio of said particles during the storage period, and further accelerating said particles in said synchrotron during a subsequent operating cycle thereof.

4-. A period for imparting high energy to atomic nuclei which may be of any atomic weight comprising the steps of removing a portion of the orbital electrons from said nuclei, injecting said nuclei into a charged particle accelerator at the start of a first acceleration stage thereof, removing said nuclei from said accelerator at the end of said first acceleration stage, storing said nuclei until the start of a subsequent acceleration stage of said accelerator, removing additional orbital electrons from said nuclei following said first acceleration stage, and re-injecting said nuclei into said accelerator at the start of a subsequent acceleration stage for further acceleration therein.

5. A method for producing a high energy beam of multiply charged praticles from atoms which may be of any atomic weight in a synchrotron of the class having a cyclical magnetic field defining a particle orbit and a cyclical frequency modulated electrical field thereat for accelerating ions therearound, comprising the steps of removing a portion of the orbital electrons from said atoms to produce ions, injecting said ions into said synchrotron, accelerating said ions in said synchrotron during a first cycle of said magnetic field, removing said accelerated ions from said synchrotron and storing said ions until a subsequent cycle of said magnetic field and a subsequent sweep of said frequency modulated electrical field, stripping additional orbital electrons from said ions during the interval between accelerating stages to increase the charge thereof, re-injecting said ions into said orbit of said synchrotron, and further accelerating said ions during said subsequent cycle of said magnetic field in phase with a higher harmonic of said electrical field.

6. In apparatus for generating high energy ion beams, the combination comprising a charged particle accelerator, an ion source coupled thereto for injecting ions into said accelerator at a first charge-to-mass ratio whereby said ions are accelerated to a first energy level, an ion beam storage device, an ion extractor connecting said accelerator with said storage device whereby said ions may be transformed thereto following acceleration to said first energy level, means connecting said storage device with said accelerator for returning said ions thereto following storage for further acceleration therein, and an ion stripping element disposed in the path of said ions between said accelerator and said storage device whereby the charge-to-mass ratio of said ions is raised to a second higher value prior to said further acceleration thereof.

7. In apparatus for accelerating multiply charged ions to high energies, the combination comprising a charged particle accelerator of the class having a cyclical magnetic field defining an ion orbit and having a cyclical frequency modulated electrical field thereat for accelerating ions therearound, an ion source coupled to said accelerator for injecting ions having a first charge-to-mass ratio into said orbit for acceleration during a first cycle of said magnetic field of said accelerator, an ion beam storage ring of the class having a magnetic field defining an ion beam orbit, first beam guiding means connecting said accelerator orbit and said storage ring orbit for transferring said ions to said storage ring following said first cycle of acceleration, second beam guiding means connecting said storage ring orbit and said accelerator orbit for returning said ions thereto during a second subsequent cycle of said magnetic field of said accelerator for further acceleration thereby, and an ion stripping element disposed in the path of said ions between said accelerator orbit and said storage ring orbit for raising the charge-to-mass ratio of said ions to a second higher value prior to said further acceleration.

8. In apparatus for accelerating multiply charged ions to high energies as described in claim 7, the further combination comprising a frequency control circuit coupled to said accelerator for changing the frequency range of said electrical field thereof between the first and sec ond acceleration periods of said ions to adjust for change in charge-to-mass ratio and changed energy thereof.

9. In apparatus for accelerating multiply charged ions to high energies as described in claim 7, the further combination comprising a control circuit coupled to said accelerator, said ion source and said first and second beam guiding means and sequentially activating said source and said first and second beam guiding means in a predetermined timed relationship with respect to the magnetic field cycle of said accelerator.

10. In apparatus for bombarding a target with charged particles, the combination comprising a source of said charged particles, a synchrotron of the class having a cyclically varying magnetic field forming a closed particle orbit and having a cyclically varying frequency modula-ted electrical field thereat for accelerating successive pulses of said particles, a charged particle beam storage ring, a first particle injector coupling said source to said synchrotron for injecting said charged particles from said source into said orbit of said synchrotron during a first acceleration cycle thereof, a first particle extractor disposed at said synchrotron orbit to remove said charged particles from said synchrotron following said initial acceleration thereof, a second particle injector disposed at said storage ring and coupled to said first extractor for receiving said charged particles from said first extractor and adapted to inject said particles into said storage ring, a second particle extractor disposed at said storage ring and adapted to remove said charged particles from said storage ring during a second subsequent acceleration cycle of said synchrotron, a third particle injector disposed =at said synchrotron and coupled to said second particle extractor for receiving said charged particles from said second extractor and adapted to re-inject said particles into said synchrotron for a further stage of acceleration, an electron stripper disposed in the path of said charged particles between said synchrotron orbit and said storage ring to increase the charge of said particles between said acceleration stages, and means for directing said charged particles from said synchrotron to said target following said further acceleration thereof.

11. Apparatus for bombarding a target with charged particles as described in claim 10, wherein said synchrotron is provided with a circuit controlling the frequency of said electrical field, said circuit producing a high frequency charged particle accelerating potential variable over a range of frequencies, the frequency of said accelerating potential having a harmonic the number of which is equal to the number of high frequency cycles through which said electrical field passes during the time required for said charged particles to complete one revolution around said synchrotron, said harmonic number being of a progressively lower order during successive ones .of said acceleration stages.

12. In apparatus for bombarding a target with heavy ions which may be of any selected atomic weight, the combination comprising an ion source, an electrostatic accelerator coupled thereto for accelerating said ions from said source, a synchrotron having an ion input coupled to said electrostatic accelerator for receiving said ions from said electrostatic accelerator, said synchrotron having a beam guiding magnet structure defining a closed orbit with a field capable of being varied across a range of intensities, said synchrotron having resonators spaced around said orbit accelerating ions, said synchrotron further having radio-frequency power producing means coupled to said resonators, a first extractor at said orbit for removing said ions from said synchrotron, a storage ring receiving said ions from said first extractor, a second extractor for removing said ions from said storage ring and re-directing said ions into said synchrotron orbit, means disposed in the path of said ions and outside said synchrotron orbit for stripping additional electrons from said ions between successive acceleration stages, a control circuit in said synchrotron correlating a first selected harmonic of the frequency of said radio-frequency power with the intensity of said magnetic field whereby said ions are maintained in said orbit, said control circuit being adapted to correlate a second selected harmonic of said radio-frequency power with magnetic fieldintensity for maintaining an orbit of fixed radius for said ions that are returned to said synchrotron orbit from said storage ring, said second selected harmonic being of a lower order than said first selected harmonic, and a third extractor disposed at said synchrotron orbit for directing said ions from said synchrotron to said target.

13. Apparatus for bombarding a target with heavy ions as described in claim 12, wherein said electrostatic accelerator is of the Cockcroft-Walton type.

14. Apparatus for bombarding a target with heavy ions as described in claim 12, wherein said stripping means is a thin sheet of metallic foil disposed transversely in the path of said ions between said first extractor and said storage ring.

15. Apparatus for accelerating heavy ions comprising an ion source, an electrostatic accelerator coupled to said source and accelerating ions therefrom, a synchrotron having an ion input connected to said electrostatic accelerator for further accelerating said ions, said synchrotron further having a plurality of curved spaced-apart magnet sectors forming a closed ion orbit in which a plurality of straight orbit sections separate adjacent pairs of curved orbits sectors, an ion beam storage ring having a plurality of curved spaced-apart magnet sectors each separated by straight sections, a first ion extractor disposed at a first of said stratight sections in said synchrotron orbit, =a first ion injector disposed at a firs-t straight section in said storage ring positions to receive ions from said first extraction, an electron stripping foil disposed in the path of said accelerated ions between said first straight section of said synchrotron and said first straight section of said storage ring, a second ion extractor disposed at said storage ring for removing stored ions from a second straight section of said storage ring, a second ion injector disposed at said synchrotron and positioned to receive ions from said second extractor for re-injection into a second straight section of said synchrotron, and means disposed at said synchrotron for directing fully accelerated ions to a target.

16. Apparatus for accelerating heavy ions as described in claim 15, further characterized in that said storage ring is disposed within said synchrotron.

References Cited UNITED STATES PATENTS 2,473,477 '6/ 1949 Smith 31362 2,789,221 4/ 1957 Tobias 328--233 3,227,597 1/1966 Feldm-ann 328234 JAMES W. LAWRENCE, Primary Examiner.

V. LA FRANCHI, Assistant Examiner,

Claims (1)

1. IN A METHOD FOR PRODUCING HIGH ENERGY BEAMS OF HEAVY IONS IN A SYNCHROTON, WHICH SYNCHROTON IS OF A CLASS HAVING A CYCLICALLY VARYING MAGNETIC FIELD DEFINING A PARTICLE ORBIT AND A CYCLICALLY VARYING ELECTRICAL FIELD THEREAT FOR ACCELERATING IONS THEREAROUND, THE STEPS COMPRISING GENERATING SAID IONS WITH A FIRST CHARGE-TO-MASS RATIO, ACCELERATING SAID IONS AT SAID ORBIT OF SAID SYNCHROTRON TO A FIRST ENERGY LEVEL DURING A FIRST CYCLE OF SAID MAGNETIC FIELD THEREOF, RAISING THE CHARGE-TO-MASS RATIO OF SAID IONS TO A SECOND HIGHER VALUE, AND FURTHER ACCELERATING SAID IONS AT SAID ORBIT IN SAID SYNCHROTON TO A SECOND HIGHER ENERGY LEVEL DURING A SUBSEQUENT CYCLE OF SAID MAGNETIC FIELD, SAID FURTHER ACCELERATION OF SAID IONS BEING PHASED WITH A HIGHE HARMONIC OF SAID ELECTRICAL FIELD THAN THE INITIAL ACCELERATION THEREOF.

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