Highfield synchrocyclotron
First Claim
1. A synchrocyclotron magnet structure including a magnetic yoke comprising a pair of poles that define an acceleration chamber including a median acceleration plane and a central axis orthogonal to the median acceleration plane,wherein the magnetic yoke defines passages about the acceleration chamber and on opposite sides of the median acceleration plane for mounting a pair of magnetic coils,wherein the poles are joined at a perimeter and separated to form a pole gap of at least 3.8 cm across and throughout the acceleration chamber,wherein each pole has an inner surface that is tapered to produce a perimeter pole wing distal from the central axis and proximate the passages for the coils, a central pole tip proximate the central axis and distal from the passages for the coils, and a peak pole gap at an intermediate distance between the central pole tips and the perimeter pole wings, the peak pole gap being at least triple the pole gap between the central pole tips and at least triple the pole gap between the perimeter pole wings at all radial angles about the central axis, andwherein the poles are tapered to shape a combined magnetic field jointly produced by the magnetic yoke and by magnetic coils in the passages so that, when the magnetic coils directly generate a central magnetic field in the median acceleration plane of at least 5 Tesla and fully magnetize the magnetic yoke, the combined magnetic field across the median acceleration plane decreases with increasing radius and a weakfocusing field index parameter, n, is in the range from 0 to 1 from the central pole tips to the perimeter pole wings, where n=−
 (r/B)(dB/dr), and where B is the magnetic field, and r is the radius from the central axis.
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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 “coildominated,” 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.
129 Citations
27 Claims

1. A synchrocyclotron magnet structure including a magnetic yoke comprising a pair of poles that define an acceleration chamber including a median acceleration plane and a central axis orthogonal to the median acceleration plane,
wherein the magnetic yoke defines passages about the acceleration chamber and on opposite sides of the median acceleration plane for mounting a pair of magnetic coils, wherein the poles are joined at a perimeter and separated to form a pole gap of at least 3.8 cm across and throughout the acceleration chamber, wherein each pole has an inner surface that is tapered to produce a perimeter pole wing distal from the central axis and proximate the passages for the coils, a central pole tip proximate the central axis and distal from the passages for the coils, and a peak pole gap at an intermediate distance between the central pole tips and the perimeter pole wings, the peak pole gap being at least triple the pole gap between the central pole tips and at least triple the pole gap between the perimeter pole wings at all radial angles about the central axis, and wherein the poles are tapered to shape a combined magnetic field jointly produced by the magnetic yoke and by magnetic coils in the passages so that, when the magnetic coils directly generate a central magnetic field in the median acceleration plane of at least 5 Tesla and fully magnetize the magnetic yoke, the combined magnetic field across the median acceleration plane decreases with increasing radius and a weakfocusing field index parameter, n, is in the range from 0 to 1 from the central pole tips to the perimeter pole wings, where n=−  (r/B)(dB/dr), and where B is the magnetic field, and r is the radius from the central axis.
 View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)

22. A method for shaping a magnetic field for ion acceleration in a synchrocyclotron, the method comprising:

providing a magnet structure including; a magnetic yoke comprising a pair of poles that define an acceleration chamber including a median acceleration plane and a central axis orthogonal to the median acceleration plane, wherein the magnetic yoke defines passages about the acceleration chamber and on opposite sides of the median acceleration plane, wherein the poles are joined at a perimeter and separated to form a pole gap across the acceleration chamber, and wherein each pole has an inner surface that is tapered to produce a perimeter pole wing distal from the central axis and proximate the passages for the coils, a central pole tip proximate the central axis and distal from the passages, and a peak pole gap at an intermediate distance between the central pole tips and the perimeter pole wings, the peak pole gap being at least triple the pole gap between the central pole tips and at least triple the pole gap between the perimeter pole wings; a pair of magnetic coils mounted in the passages defined by the magnetic yoke on opposite sides of the median acceleration plane; and at least one pair of radiofrequency accelerator electrodes mounted between the poles; passing electric current through the coils to generate a magneticfield component in the median acceleration plane and to magnetize the magnetic yoke, the magnetized magnetic yoke generating another magneticfield component in the median acceleration plane, wherein the coilgenerated and magneticyokegenerated magneticfield components jointly produce a combined magnetic field of at least 6.65 Tesla in the median acceleration plane, the combined magnetic field decreasing across the median acceleration plane with increasing radius and a weakfocusing field index parameter, n, being in the range from 0 to 1 from the central pole tips to the perimeter pole wings, where n=−
(r/B)(dB/dr), and where B is the magnetic field, and r is the radius from the central axis;injecting an ion into the magnetic field in the acceleration chamber; generating an electric field with the radiofrequency accelerator electrodes to accelerate the ion in an outward spiral trajectory across the median acceleration plane and reducing the frequency of the electric field as the ion accelerates outward; and
thenextracting the accelerated ion from the acceleration chamber.  View Dependent Claims (23, 24, 25, 26, 27)

1 Specification