Circular accelerator and operating method therefor

• US 8,525,448 B2
• Filed: 02/08/2012
• Issued: 09/03/2013
• Est. Priority Date: 02/28/2011
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Tanaka, Hirofumi, Yamamoto, Kazuo, Pu, Yuehu, Shinkawa, Kanji, Haruna, Nobuyuki, Kashima, Takayuki
• Primary Examiner(s): Cavallari, Daniel
• Assistant Examiner(s): Sathiraju, Srinivas
• Application Number:
  US13/368,435
• Publication Number:
  US 20120217903A1
• Time in Patent Office: 573 Days
• Field of Search: 315500-507, 335/216, 335/299, 250/396.ML, 250/298, 250/400, 250/492, 328/233, 328/235, 328228-230, 313/62
• US Class Current: 315/502
• CPC Class Codes: H05H 13/005 Cyclotrons
• CPC Class Codes: H05H 13/02 Synchrocyclotrons, i.e. frequency modulated cyclotrons
• CPC Class Codes: H05H 7/12 Arrangements for varying final energy of beam

Abstract

The circular accelerator comprises: a bending electromagnet that generates a bending magnetic field; a radio-frequency power source that generates a radio-frequency electric field in accordance with an orbital frequency of charged particles; a radio-frequency electromagnetic field coupling part connected to the radio-frequency power source; an acceleration electrode connected to the radio-frequency electromagnetic field coupling part; and an acceleration-electrode-opposing ground plate provided to form an acceleration gap between the plate itself and the acceleration electrode, for generating the radio-frequency electromagnetic field in an orbiting direction of the charged particles; wherein the bending electromagnet generates the bending magnetic field varying in such a way that the orbital frequency of the charged particles varies in a variation range of 0.7% to 24.7% with respect to an orbital frequency at the charged-particles'"'"' extraction portion, during a time of injection to extraction of the particles.

Claims

1. A circular accelerator that accelerates charged particles injected into the center thereof by a radio-frequency electric field while making the particles orbit along a spiral orbit by a bending magnetic field, the circular accelerator comprising:

a bending electromagnet that is excited by an exciting coil and thereby generates the bending magnetic field, the bending electromagnet including an electromagnet hill for forming a narrow magnetic pole gap and an electromagnet valley for forming a wide magnetic pole gap alternately disposed in an orbiting direction of the charged particles;

a radio-frequency power source that generates the radio-frequency electric field in accordance with an orbital frequency of the charged particles;

a radio-frequency electromagnetic field coupling part connected to the radio-frequency power source;

an acceleration electrode connected to the radio-frequency electromagnetic field coupling part; and

an acceleration-electrode-opposing ground plate provided to form an acceleration gap between the plate itself and the acceleration electrode, for generating the radio-frequency electromagnetic field in the orbing direction of the charged particles;

wherein

the bending electromagnet generates the bending magnetic field varying in such a way that the orbital frequency of the charged particles varies in a variation range of 0.7% to 24.7% with respect to an orbital frequency at the charged-particles'"'"' extraction portion, during a time of injection to extraction of the particles.

2. A circular accelerator according to claim 1, wherein average magnetic flux density B(r) in the orbiting direction of the charged particles and total energy of the particles E(r) in a position with a radius r can be expressed using average magnetic flux density B_O at a radius corresponding to an extraction position of the charged particles and energy E_O of the particles in the extraction position as follows:

B(r)=(B_O/E_O^x)×

E(r)^x

in which relationship, the bending electromagnet generates magnetic flux density distribution with x being a constant excluding 1.

3. A circular accelerator according to claim 2, wherein the above x is −

0.2<

x<

0.97.

4. A circular accelerator according to claim 1, wherein a frequency of a radio-frequency wave supplied from the radio-frequency power source is varied in accordance with variation in the orbital frequency of the charged particles.

5. A circular accelerator according to claim 4, wherein a Q-factor in resonant characteristics of an acceleration electrode portion, which is resonant characteristics of an entire load viewed from an input end of the radio-frequency electromagnetic field coupling part, is less than 100.

6. A circular accelerator according to claim 5, wherein the variation in the orbital frequency of the charged particles is within half-power bandwidth of the resonant characteristics of the acceleration electrode portion.

7. A circular accelerator according to claim 1, further comprising a unit that changes a resonant frequency of an acceleration electrode portion, which is a resonant frequency of the entire load viewed from an input end of the radio-frequency electromagnetic field coupling part.

8. A circular accelerator according to claim 7, wherein the radio-frequency electromagnetic field coupling part includes a unit that changes inductance or capacitance.

9. A circular accelerator according to claim 1, further comprising a unit that modifies radial magnetic flux density distribution of the bending magnetic field.

10. A circular accelerator according to claim 9, further comprising a plurality of coils for modifying a magnetic field that is disposed radially and modifies the radial magnetic flux density distribution of the bending magnetic field.

11. A circular accelerator according to claim 10, wherein the plurality of coils for modifying a magnetic field is provided in a position of the electromagnet hill.

12. A circular accelerator according to claim 9, wherein a coil for modifying a magnetic field, that modifies the radial magnetic flux density distribution of the bending magnetic field is provided in the same radial position as the exciting coil.

13. A circular accelerator according to claim 1, wherein the acceleration electrode is disposed in a position corresponding to the electromagnet valley.

14. A method of operating a circular accelerator according claim 9, wherein the radial magnetic flux density distribution of the bending magnetic field is modified while a radio-frequency wave is not supplied from the radio-frequency power source, and in addition, a resonant frequency of the acceleration electrode position, which is a resonant frequency of an entire load viewed from an input end of the radio-frequency electromagnetic field coupling part, is changed.

15. A method of operating the circular accelerator according to claim 14, wherein the resonant frequency of the acceleration electrode portion is changed by changing inductance or capacitance of the radio-frequency electromagnetic field coupling part.

16. A circular accelerator according to claim 1, wherein the electromagnetic valleys are comprised of an electromagnet that is thinner than an electromagnet of the electromagnetic hills.

17. A circular accelerator that accelerates charged particles injected into the center thereof by a radio-frequency electric field while making the particles orbit along a spiral orbit by a bending magnetic field, the circular accelerator comprising:

a bending electromagnet that is excited by an exciting coil and thereby generates the bending magnetic field, the bending electromagnet including an electromagnet hill for forming a narrow magnetic pole gap and an electromagnet valley for forming a wide magnetic pole gap alternately disposed in an orbiting directing of the charged particles;

a radio-frequency power source that generates the radio-frequency electric field in accordance with an orbital frequency of the charged particles;

a radio-frequency electromagnetic field coupling part connected to the radio-frequency power source;

an acceleration electrode connected to the radio-frequency electromagnetic field coupling part; and

an acceleration-electrode-opposing ground plate provided to form an acceleration gap between the plate itself and the acceleration electrode, for generating the radio-frequency electromagnetic field in the orbiting direction of the charged particles;

wherein

average magnetic flux density B(r) in the orbiting direction of the charged particles and total energy of the particles E(r) in a position with a radius r can be expressed using average magnetic flux density B_O at a radius corresponding to an extraction position of the charged particles and energy E_O of the particles in the extraction position as follows;

B(r)=(B_O/E_O^x)×

E(r)^x

in which relationship, the bending electromagnet generates magnetic flux density distribution with x being a constant excluding 1.

18. A circular accelerator according to claim 17, wherein the electromagnetic valleys are comprised of an electromagnet that is thinner than an electromagnet of the electromagnetic hills.

19. A circular accelerator according to claim 17, wherein the x is −

0.2<

x<

0.97.