Particle beam accelerator, and a method of operation

• US 5,783,914 A
• Filed: 09/17/1997
• Issued: 07/21/1998
• Est. Priority Date: 03/17/1994
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Sakurabata, Hiroaki, Tadokoro, Masahiro, Hiramoto, Kazuo, Hirota, Junichi
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): DAY, MICHAEL HENRY
• Application Number:
  US08/931,840
• Time in Patent Office: 307 Days
• Field of Search: 315/504, 315/500, 315/507, 313/62, 250/492.3, 250/398, 378/64, 378/65
• US Class Current: 315/504
• CPC Class Codes: A61N 2005/1087 Ions; Protons
• CPC Class Codes: H05H 7/10 Arrangements for ejecting particles from orbits

Abstract

The present invention provides apparatus for acceleration of a charged particle beam which includes energy means for altering the energy of a circulating beam circulating in the apparatus and means for extracting output beams from the apparatus. Control means are arranged to be operable to alter the energy of the circulating beam using the energy means so as to be able to extract output beams of at least two energies from the apparatus using the means for extracting. Thus there is provided an accelerator, and an extraction method therefor, which is capable of extracting a small diameter beam having a varying energy level. This facilitates improved medical irradiation treatment using the beam.

Claims

1. Apparatus for acceleration of a charged particle beam, the apparatus having:

a circulation chamber, for circulation of a charged particle beam,

bending magnets for generating bending magnetic fields for bending a circulating beam circulating in said circulation chamber,

a multipole magnet for generating a multipole magnetic field for specifying a stability limit of resonance of said circulating beam,

energy means for altering the energy of said circulating beam,

extraction means for extracting output beams from the apparatus, and

control means arranged for altering the energy of said circulating beam using said energy means in the extraction of said output beams so as to alter the energy of the output beam and for maintaining substantially constant a stability limit of a resonance of the betatron oscillation of said circulating beam by using bending and multipole magnets while the output beams are being extracted.

2. Apparatus according to claim 1 wherein said control means are arranged to be operable to extract said output beams sequentially using said extraction means so that said output beams are joined to form a continuous beam.

3. Apparatus according to claim 1 wherein said control means are arranged to be operable to alter the energy of said circulating beam using said energy means at the same time as extracting said output beams using said extraction means.

4. Apparatus according to claim 1 wherein said extraction means include means for increasing an amplitude of a betatron oscillation of said circulating beam to exceed said stability limit, and said control means are operable to increase said amplitude in the extraction of said output beams by said extraction means.

5. Apparatus according to claim 4 wherein said means for increasing an amplitude of a betatron oscillation include means for applying a first electromagnetic field to said circulating beam in a direction transverse to the progressing direction of said circulating beam, and said control means are arranged to be operable to adjust said first electromagnetic field in the extraction of said output beams by said extraction means.

6. Apparatus according to claim 5 wherein said control means are arranged to be operable to alter the frequency of at least one component of said first electromagnetic field according to the variance of the energy of said circulating beam while the output beam is being extracted.

7. Apparatus according to claim 1 wherein said energy means include means for applying an electromagnetic field to said circulating beam in a direction along the progressing direction of said circulating beam, said control means being arranged to be operable to maintain the values of bending and multipole magnetic fields produced by bending and multipole magnets respectively in a substantially constant ratio in the extraction of said output beams by said extraction means.

8. Apparatus according to claim 1 including transportation means for transporting said output beams extracted from the circulation chamber, and an electromagnet for controlling said output beams in the transportation means, said control means being arranged to alter the magnetic field produced by said electromagnet in accordance with the energy of said output beams.

9. A method of operating a circular accelerator for a charged particle beam, the method including the steps of

(i) maintaining a circulating beam circulating in a circulation chamber of said circular accelerator,

(ii) maintaining substantially constant a stability limit of a resonance of betatron oscillation of said circulating beam,

(iii) changing the energy of said circulating beam during step (i), and

(iv) extracting an output beam from said circulation chamber while the energy of said output beam is being altered, wherein steps (ii), (iii) and (iv) are carried out substantially simultaneously.

10. A method according to claim 9 wherein the energy of at least one of said output beams varies while said output beams are extracted from said circulation chamber.

11. A method according to claim 9 wherein said output beams are joined to form a continuous beam.

12. A method according to claim 11 wherein the energy of said continuous beam varies while said continuous beam is extracted from said circulation chamber.

13. A method according to claim 9 wherein said step of extracting output beams includes the step of increasing an amplitude of a betatron oscillation of said circulating beam to exceed said stability limit.

14. A method according to claim 13 wherein the circular accelerator includes bending and multipole magnets for producing bending and multipole magnetic fields respectively, and the values of said bending and multipole magnetic fields remain substantially constant ratio in the step of increasing said amplitude of the betatron oscillation.

15. A method according to claim 13 wherein said amplitude of the betatron oscillation is increased by applying a first electromagnetic field to the circulating beam in a direction transverse to the progressing direction of said circulating beam.

16. A method according to claim 15 wherein said first electromagnetic field includes a plurality of radio frequency components at different frequencies.

17. A method according to claim 15 wherein the frequency of at least one component of said first electromagnetic field is altered in the step of increasing said amplitude of the betatron oscillation.

18. A method according to claim 9 wherein said step of changing the energy of said circulating beam includes the steps of:

applying an electromagnetic field to said circulating beam in a direction along the progressing direction of said circulating beam so as to alter the energy of the output beam while the output beam is extracted from said circulation chamber; and

adjusting bending and multipole magnetic fields produced by bending and multipole magnets respectively, wherein the values of said bending and multipole magnetic fields are maintained in a substantially constant ratio while the output beam is being extracted.

19. A method of varying the energy of an output charged particle beam over a predetermined range in an extraction process in which said output charged particle beam is extracted, the method including the step of:

substantially simultaneously adjusting the operation of the following elements of a circular charged particle beam acceleration apparatus;

(i) accelerating means for altering the energy of a circulating beam circulating in the apparatus;

(ii) extraction means for extracting said output charged particle beam from the apparatus;

(iii) a bending magnet and a multipole magnet for controlling a path of said circulating beam and maintaining substantially constant a stability limit of a resonance of betatron oscillation of said circulating beam; and

(iv) a transport magnet for controlling said output charged particle beam.

20. Apparatus for acceleration of a charged particle beam, the apparatus having:

a circulation chamber for circulation of a charged particle beam,

energy means for altering the energy of a circulating beam circulating in the apparatus,

means for extracting output beams from the apparatus;

means for increasing an amplitude of a betatron oscillation of said circulating beam to exceed the stability limit of a resonance of said circulating beam which include means for applying a first electromagnetic field to said circulating beam in a direction transverse to the progressing direction of said circulating beam in the extraction of said output beams by said extracting beams;

wherein said energy means include means for applying a second electromagnetic field to said circulating beam in a direction along the progressing direction of said circulating beam in the extraction of said output beams so as to alter the energy of said output beams while the output beams are being extracted,

and the apparatus further includes bending and multipole magnets for producing bending and multipole magnetic fields respectively to control the orbital path of the circulating beam, and a controller which is adapted to be operable to simultaneously control the energy of said circulating beam and said first electromagnetic field, whilst maintaining the values of said bending and multipole magnetic fields in a substantially constant ratio in the extraction of said output beams by said extraction means.

21. An accelerator having electromagnets for orbiting a charged particle beam, and an extractor for extracting the beam, the accelerator comprising:

bending electromagnets for generating a bending magnetic field for bending said charged particle beam;

a multipole electromagnet for generating a multipole magnetic field for specifying a stability limit of resonance of said charged particle beam;

radio frequency applying means for increasing an amplitude of a betatron oscillation of said charged particle beam within said stability limit by applying a first electromagnetic field;

accelerating means for providing an energy thereto by applying a second electromagnetic field so as to accelerate said charged particle beam; and

a control device for controlling the intensities of said bending and multipole magnetic fields so as to maintain the values of said bending and multipole magnetic fields in a substantially constant ratio while the output beam is extracted, and for controlling a frequency of said first electromagnetic field and a frequency of said second electromagnetic field so as to achieve a required change in energy of said charged particle beam while the output beam is extracted.

22. The accelerator according to claim 21 wherein said control device controls a ratio of an intensity of the multipole magnetic field versus a momentum of the beam so as to maintain said ratio approximately constant.

23. An apparatus for acceleration of a charged particle beam, comprising:

a circulation chamber for circulation of a charged particle beam;

bending electromagnets for generating bending magnetic fields for bending said charged particle beam;

a multipole electromagnet for generating a multipole magnetic field for specifying a stability limit of resonance of said charged particle beam;

power sources for altering the energy of a circulating beam circulating in said circulation chamber;

an extractor for extracting output beams from the apparatus; and

a control device connected to said power sources for altering the energy of said circulating beam using said power sources in the extraction of said output beams in order to alter an energy level of the output beams, and for controlling the intensities of said bending and multipole magnetic fields so as to maintain the values of said bending and multipole magnetic fields in a substantially constant ratio while the output beams are being extracted.

24. An accelerator having electromagnets for orbiting a charged particle beam, and an extractor for extracting the beam, the accelerator comprising:

a radio frequency accelerating cavity for accelerating said charged particle beam by providing an energy thereto;

bending electromagnets for generating magnetic fields for bending said charged particle beam;

a multipole electromagnet for generating a multipole magnetic field for specifying a stability limit of resonance of said charged particle beam;

a radio frequency applying device for increasing an amplitude of a betatron oscillation of said charged particle beam within said stability limit; and

a control device for controlling the intensities of said bending and multipole magnetic fields so as to maintain substantially constant a stability limit of a resonance of the betatron oscillation of said circulating beam, and for controlling a frequency of a first electromagnetic field generated by said radio frequency applying means and a frequency of a second electromagnetic field generated by said accelerating means so as to achieve a required change in energy of said charged particle beam while the output beams are being extracted.