Synchrocyclotron for extracting beams of various energies

Patent metadata

Field	Value
Publication number	US-11160159-B2
Application number	US-202117193997-A
Country	US
Kind code	B2
Filing date	Mar 5, 2021
Priority date	Mar 6, 2020
Publication date	Oct 26, 2021
Grant date	Oct 26, 2021

Abstract

A synchrocyclotron for extracting charged particles accelerated to an extraction energy includes a magnetic unit comprising N valley sectors and N hill sectors, and configured for creating z-component of a main magnetic characterized by a radial tune of the successive orbits. The synchrocyclotron includes a first instability coil unit and a second instability coil unit configured for creating a field bump of amplitude increasing radially. The amplitude of the field bump may be varied to reach the value of the offset amplitude at the average instability onset radius. The offset amplitude may be the minimal amplitude of the field bump at the average instability onset radius required for sufficiently offsetting the center of the orbit of average instability onset radius to generate a resonance instability to extract the beam of charged particle at the average instability onset radius.

First claim

The invention claimed is:

1. A synchrocyclotron for extracting charged particles accelerated to an extraction energy comprised between a low energy and a high energy, the synchrocyclotron comprising:
a first main coil and second main coil centered on a common central axis and arranged parallel to one another on either side of a median plane normal to the central axis and defining a symmetry plane of the cyclotron, the first and second main coils being configured for generating a main magnetic field when activated by a source of electric power;
a dee configured for creating an RF-oscillating electric field of varying frequencies for accelerating the charged particles;
a first field shaping unit and second field shaping unit for shaping the main magnetic field and guiding the charged particles along successive orbits of increasing average radii centered on the central axis, the first and second field shaping units being arranged within the first and second main coils on either side of the median plane and separated from one another by a gap, wherein the first and second field shaping units comprise hill sectors and valley sectors alternatively distributed around the central axis with a symmetry of at least three for shaping the main magnetic field;
a first instability coil unit and a second instability coil unit arranged on either side of the median plane, the first and second instability coil units each comprising a coil configured for creating a field bump localized in a z-component of the main magnetic field; and
a controlling unit configured for adjusting the amplitude of the field bump at various levels such that, for all values of an average instability onset radius between a low radius and a high radius, a value of the amplitude of the field bump at the average instability onset radius is equal to a value of an offset amplitude at the average instability onset radius, and lower than the values of the offset amplitude for all values of the average radius smaller than the average instability onset radius; wherein
the z-component of the main magnetic field is controlled such that the radial tune of the successive orbits is not equal to 1 and is comprised within 1±0.1 for all values of an average radius between the low radius and the high radius, the low radius corresponding to average radial positions of the charged particles at the low energy and the high radius corresponding to average radial positions of the charged particles at the high energy;
the first and second instability coil units are configured for creating the field bump within an azimuthal sector of azimuthal angle, with an amplitude increasing radially between a first field bump amplitude value at the low radius and a second field bump amplitude value at the high radius; and
the offset amplitude is a minimal amplitude of the field bump at the average instability onset radius required for sufficiently offsetting the center of an orbit of an average instability onset radius along which the charged particles are guided, such that a combination of an amplitude of the harmonic 2 and a radial gradient of the amplitude of the harmonic 2 on the orbit is produced by the main magnetic field of symmetry on an offset orbit, and the offset amplitude is large enough to generate a resonance instability of the successive orbits of average radius greater than R≥Ri.

2. The synchrocyclotron according to claim 1 , wherein the first instability coil unit and the second instability coil unit are located within an area defined circumferentially by an azimuthal sector having an azimuthal angle smaller than π/3, and radially between the low radius and the high radius.

3. The synchrocyclotron according to claim 2 , wherein the azimuthal angle is smaller than π/4.

4. The synchrocyclotron according to claim 2 , wherein the azimuthal angle is smaller than π/6.

5. The synchrocyclotron according to claim 2 , wherein the first instability coil unit and the second instability coil unit are in the form of a pair of trapezoidal or triangular coils of dimensions fitting the azimuthal sector and of length at least equal to a difference of the high radius and the low radius in the radial direction, wherein a distance separating the first instability coil unit and the second instability coil unit decrease radially so that a field bump amplitude at the low radius is smaller than a field bump amplitude at the high radius.

6. The synchrocyclotron according to claim 3 , wherein the distance separating the first instability coil unit and the second instability coil unit decreases linearly along the radial direction, and wherein the first instability coil unit and the second instability coil unit form an angle with the median plane between 5 and 30 degrees.

7. The synchrocyclotron according to claim 6 , wherein the first instability coil unit and the second instability coil unit form an angle with the median plane between 10 and 25 degrees.

8. The synchrocyclotron according to claim 2 , wherein the first instability coil unit and the second instability coil unit are formed by a series of two or more pairs of coils radially aligned within the azimuthal sector, each pair of coils being configured for generating a field bump having an amplitude higher than an adjacent pair of coils located closer to the central axis, or generating a field bump having an amplitude lower than an adjacent pair of coils located further away from the central axis.

9. The synchrocyclotron according to claim 1 , wherein for all values of the average instability onset radius between the low radius and the high radius, the offset amplitude at the average instability onset radius is defined such that the offset amplitude is between 0.001% and 1% of an average value of the z-component of the main magnetic field at the average instability onset radius.

10. The synchrocyclotron according to claim 9 , wherein the offset amplitude is between 0.005% and 0.05% of the average value of the z-component of the main magnetic field.

11. The synchrocyclotron according to claim 1 , wherein the synchrocyclotron has a nominal energy of extraction, the low energy is between 20% and 75% of the nominal energy, and the high energy is between 80% and 100% of the nominal energy.

12. The synchrocyclotron according to claim 11 , wherein the low energy is between 30% and 50% of the nominal energy.

13. The synchrocyclotron according to claim 11 , wherein the high energy is between 90% and 99% of the nominal energy.

14. The synchrocyclotron according to claim 1 , wherein the symmetry is an odd number.

15. They synchrocyclotron according to claim 14 , wherein the symmetry is 3.

16. The synchrocyclotron according to claim 1 , wherein the radial tune of successive orbits is comprised within 1±0.025.

17. The synchrocyclotron according to claim 1 , wherein the radial tune of successive orbits is greater than 1.002 and less than 1.015.

18. A method for extracting charged particles out of a synchrocyclotron at an extraction energy between a low energy and a high energy, the method comprising the steps of:
providing a synchrocyclotron configured such that the charged particles reach the extraction energy at a corresponding average instability onset radius of an orbit between a low radius and a high radius, the average instability onset radius corresponding to respective average radial positions relative to a central axis of the charged particles at the low and high energies, wherein a radial tune of successive orbits is not equal to 1 and is within 1±0.1 for all values of an average radius between the low radi

Assignees

• Ion Beam Appl Sa

Inventors

• Mandrillon Jérôme
• Kleeven Willem
• Van De Walle Jarno

Classifications

• H05H13/02 Primary

  Synchrocyclotrons, i.e. frequency modulated cyclotrons · CPC title

• H05H7/10

  Arrangements for ejecting particles from orbits · CPC title

• H05H2007/002

  for modifying beam trajectory, e.g. gantries · CPC title

• H05H7/001

  Arrangements for beam delivery or irradiation (irradiation systems per se G21K5/00) · CPC title

• H05H2007/045

  for beam bending · CPC title