High-field superconducting synchrocyclotron

• US 7,541,905 B2
• Filed: 01/19/2007
• Issued: 06/02/2009
• Est. Priority Date: 01/19/2006
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Antaya, Timothy A.
• Primary Examiner(s): Enad; Elvin G
• Assistant Examiner(s): Talpalatskiy; Alexander
• Application Number:
  US11/624,769
• Publication Number:
  US 20070171015A1
• Time in Patent Office: 865 Days
• Field of Search: 335/216, 313/62
• US Class Current: 335/216
• CPC Class Codes: H05H 13/00 Magnetic resonance accelerators; Cyclotrons strophotrons, turbine tubes H01J25/62
• CPC Class Codes: H05H 13/02 Synchrocyclotrons, i.e. frequency modulated cyclotrons
• CPC Class Codes: H05H 7/04 Magnet systems , e.g. undulators, wigglers free-electron laser H01S3/0903; Energisation thereof
• CPC Class Codes: Y10S 505/806 Niobium base, Nb
• CPC Class Codes: Y10S 505/924 Making superconductive magnet or coil
• CPC Class Codes: Y10T 29/49014 Superconductor

Abstract

The magnetic field in an acceleration chamber defined by a magnet structure is shaped by shaping the poles of a magnetic yoke and/or by providing additional magnetic coils to produce a magnetic field in the median acceleration plane that decreases with increasing radial distance from a central axis. The magnet structure is thereby rendered suitable for the acceleration of charged particles in a synchrocyclotron. The magnetic field in the median acceleration plane is “coil-dominated,” meaning that a strong majority of the magnetic field in the median acceleration plane is directly generated by a pair of primary magnetic coils (e.g., superconducting coils) positioned about the acceleration chamber, and the magnet structure is structured to provide both weak focusing and phase stability in the acceleration chamber. The magnet structure can be very compact and can produce particularly high magnetic fields.

Claims

1. A magnet structure including a magnetic yoke comprising a pair of poles that define an acceleration chamber with a median acceleration plane,

wherein the poles are joined at a perimeter and separated to form a pole gap in a central region with a peak gap of at least 37 cm between the poles,

wherein each of the poles includes a pole wing that converges beyond the peak gap to produce a gap between the poles that is less than one-third the peak gap,

wherein each pole is structured to shape a magnetic field in the median acceleration plane so that the magnetic field decreases with increasing radius in the median acceleration plane from an inner radius for ion introduction to an outer radius for ion extraction when the magnetic yoke is fully magnetized by a pair of magnetic coils positioned about the acceleration chamber and when a central magnetic field of at least 5 Tesla is directly generated in the median acceleration plane by the magnetic coils, and

wherein the magnetic yoke further comprises localized magnetic tips positioned circumferentially on the upper and lower pole wings.

2. The magnet structure of claim 1, wherein the magnetic yoke has an outer radius, measured from the central axis parallel to the median acceleration plane, of no more than 114 cm.

3. The magnet structure of claim 1, wherein the magnetic yoke has an outer radius, measured from the central axis parallel to the median acceleration plane, of no more than 89 cm.

4. The magnet structure of claim 1, wherein the separation between the poles across and throughout the acceleration chamber is at least 6 cm.

5. The magnet structure of claim 1, wherein the separation between the poles across and throughout the acceleration chamber is at least 3.8 cm.

6. The magnet structure of claim 1, wherein the magnetic yoke contains a resonator structure including electrodes between the poles for generating a particle-acceleration voltage in the acceleration chamber.

7. The magnet structure of claim 6, wherein the resonator structure is coupled with a radiofrequency voltage source.

8. The magnet structure of claim 1, wherein each of the poles includes a pole wing that converges beyond the peak gap to produce a gap between the pole wings that is less than 20% of the peak gap.

9. The magnet structure of claim 8, wherein the pole wings have inner surfaces that slope toward the median acceleration plane at an angle of between 80 and 90°

with the median acceleration plane.

10. The magnet structure of claim 8, wherein the pole wings have inner surfaces that slope toward the median acceleration plane at an angle from 82.5°

to 87.5°

with the median acceleration plane.

11. The magnet structure of claim 1, wherein the magnetic yoke defines the passages for the magnetic coils.

12. The magnet structure of claim 11, further comprising magnetic coils in the passages defined in the magnetic yoke.

13. The magnet structure of claim 12, wherein the pole wings shield the acceleration chamber from the magnetic field generated by the magnetic coils.

14. The magnet structure of claim 1, wherein the localized magnetic tips are discontinuous.

15. The magnet structure of claim 1, wherein the poles are tapered to shape a magnetic field in the median acceleration plane that decreases with increasing radius from a central magnetic field of at least 8.9 Tesla.

16. The magnet structure of claim 1, wherein the poles are tapered to shape a magnetic field in the median acceleration plane that decreases with increasing radius from a central magnetic field of at least 9.5 Tesla.

17. The magnet structure of claim 1, wherein the poles are tapered to shape a magnetic field in the median acceleration plane that decreases with increasing radius from a central magnetic field of at least 10 Tesla.

18. The magnet structure of claim 1, wherein the poles are tapered to shape a magnetic field in the median acceleration plane that decreases with increasing radius from a central magnetic field between 7 and 13 Tesla.

19. The magnet structure of claim 1, wherein the poles are tapered to shape a magnetic field in the median acceleration plane that decreases with increasing radius from a central magnetic field of at least 13 Tesla.

20. The magnet structure of claim 1, wherein the magnetic yoke is structured to contribute from 1.6 to 2.4 Tesla of additional magnetic field in the median acceleration plane when the magnetic yoke is fully magnetized.

21. The magnet structure of claim 1, wherein the magnetic yoke is structured to contribute no more than 3 Tesla to the median acceleration plane when the magnetic yoke is fully magnetized.

22. The magnet structure of claim 1, wherein the magnetic yoke comprises gadolinium.

23. The magnet structure of claim 1, wherein the weak-focusing field index parameter, n, is in the range from 0 to 1 across substantially all of the median acceleration plane.

24. The magnet structure of claim 1, wherein the pole gap expands over an inner stage as the distance from the central axis increases, and wherein the pole gap decreases over an outer stage as the distance from the central axis further increases.

25. The magnet structure of claim 1, wherein the magnetic yoke has a height, measured orthogonal to the median acceleration plane, less than 100 cm.

26. The magnet structure of claim 1, wherein the magnetic yoke has a mass less than about 23,000 kg.

27. The magnet structure of claim 1, further comprising a pair of primary magnetic coils positioned about the acceleration chamber.

28. The magnet structure of claim 27, further comprising additional magnetic coils for shaping the field generated by the primary magnetic coils, wherein the additional magnetic coils circumscribe the central axis.

29. The magnet structure of claim 28, wherein the primary magnetic coils and the additional magnetic coils are coupled with at least one voltage source.

30. The magnet structure of claim 29, wherein at least one of the additional magnetic coils is coupled with the voltage source to conduct electrical current in a first direction through the additional magnetic coil, wherein the primary magnetic coils are coupled with the voltage source to conduct electrical current in a second direction through the primary magnetic coils, and wherein the second direction is opposite to the first direction such that the magnetic field generated by the additional magnetic coil will at least partially cancel the magnetic field generated by the primary magnetic coils over a region of the median acceleration plane.

31. The magnet structure of claim 29, wherein the additional magnetic coils comprise a material that is superconducting at a temperature of at least 4.5K.

32. The magnet structure of claim 27, wherein the primary magnetic coils comprise a material that is superconducting at a temperature of at least 4.5K.

33. The magnet structure of claim 32, wherein the primary magnetic coils comprise Nb₃Sn or NbTi.

34. The magnet structure of claim 1, wherein the magnetic yoke defines a passage along the central axis for injection of ions into the acceleration chamber.

35. The magnet structure of claim 1, wherein each pole is tapered along its inner surface to produce a magnetic field in the median acceleration plane that decreases with increasing radial distance from the central axis.

36. The magnet structure of claim 1, wherein the poles include changes in composition, wherein the compositions have different magnetic properties, to shape the magnetic field in the median acceleration plane.

37. The magnetic structure of claim 1 wherein the inner surfaces of the poles are substantially circularly symmetrical about the central axis.