초록 ▼

A cyclotron for ion acceleration is magnetically shielded during ion acceleration by passing electrical current in the same direction through both the first and second superconducting primary coils. A first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducti

A cyclotron for ion acceleration is magnetically shielded during ion acceleration by passing electrical current in the same direction through both the first and second superconducting primary coils. A first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil, while a second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil. Electrical current is also passed through the magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils and generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils.

대표청구항 ▼

1. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersec

1. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersected perpendicularly by the central axis, wherein the electrical current is passed through the first superconducting primary coil in the same direction as the direction in which electrical current is passed through the second superconducting primary coil;passing electrical current through at least a first and a second magnetic-field-shielding coil, wherein the first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil and beyond the outer radius of the first superconducting primary coil, wherein the second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil, wherein electrical current is passed through the first and second magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils, and wherein passing electrical current through the magnetic-field-shielding coils generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils;releasing an ion from an ion source into the midplane proximate the central axis and accelerating the ion in an orbiting trajectory expanding outward from the central axis via a magnetic field generated at least partially by the superconducting primary coils; andshaping the magnetic field in the midplane using at least a first and a second superconducting magnetic-field-shaping coil, wherein the first and second superconducting magnetic-field-shaping coils are positioned at shorter radii from the central axis than the superconducting primary coils. 2. The method of claim 1, wherein the cyclotron lacks a continuous yoke and pole structure around the superconducting primary coils. 3. The method of claim 2, wherein the magnetic field in the midplane is generated by a magnetic-field-generating structure consisting essentially of the superconducting primary coils, the superconducting magnetic-field-shaping coils, and the magnetic-field-shielding coils. 4. The method of claim 2, further comprising changing the magnetic field generated in the midplane while maintaining magnetic shielding by changing the amount of current passed through the superconducting primary coils and through the magnetic-field-shielding coils and maintaining the magnetic field profile in the midplane by proportionally changing the electrical currents in the superconducting primary coils, in the superconducting field-shaping coils, and in the magnetic-field-shielding coils so that the amplitude of the magnetic field changes but the normalized gradient of the magnetic field remains constant. 5. The method of claim 4, further comprising extracting the ion from the cyclotron with a final energy, wherein the final energy of the extracted ion changes as the magnetic field is changed. 6. The method of claim 5, wherein a plurality of ions are accelerated by the cyclotron to produce an ion beam, the method further comprising scanning the ion beam through living tissue while varying the energy of the ion beam over time. 7. The cyclotron of claim 1, wherein the cyclotron has a mass less than 5,000 kg. 8. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersected perpendicularly by the central axis, wherein the electrical current is passed through the first superconducting primary coil in the same direction as the direction in which electrical current is passed through the second superconducting primary coil;passing electrical current through at least a first and a second magnetic-field-shielding coil, wherein the first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil and beyond the outer radius of the first superconducting primary coil, wherein the second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil, wherein electrical current is passed through the first and second magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils, and wherein passing electrical current through the magnetic-field-shielding coils generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils; andreleasing an ion from an ion source into the midplane proximate the central axis and accelerating the ion in an orbiting trajectory expanding outward from the central axis via a magnetic field generated at least partially by the superconducting primary coils,wherein the magnetic field generated in the midplane at radii less than the inner radius of the superconducting primary coils is greater than 5 Tesla. 9. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersected perpendicularly by the central axis, wherein the electrical current is passed through the first superconducting primary coil in the same direction as the direction in which electrical current is passed through the second superconducting primary coil;passing electrical current through at least a first and a second magnetic-field-shielding coil, wherein the first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil and beyond the outer radius of the first superconducting primary coil, wherein the second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil, wherein electrical current is passed through the first and second magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils, and wherein passing electrical current through the magnetic-field-shielding coils generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils; andreleasing an ion from an ion source into the midplane proximate the central axis and accelerating the ion in an orbiting trajectory expanding outward from the central axis via a magnetic field generated at least partially by the superconducting primary coils,wherein the magnetic field generated at radii greater than 1 meter beyond the outer radius of the superconducting primary coils is reduced to less than 0.001 Tesla by the magnetic-field-shielding coils. 10. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersected perpendicularly by the central axis, wherein the electrical current is passed through the first superconducting primary coil in the same direction as the direction in which electrical current is passed through the second superconducting primary coil;passing electrical current through at least a first and a second magnetic-field-shielding coil, wherein the first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil and beyond the outer radius of the first superconducting primary coil, wherein the second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil, wherein electrical current is passed through the first and second magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils, and wherein passing electrical current through the magnetic-field-shielding coils generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils;releasing ions from an ion source into the midplane proximate the central axis and accelerating the ions in an orbiting trajectory expanding outward from the central axis via magnetic fields generated at least partially by the superconducting primary coils, wherein different ions having different masses are accelerated in the cyclotron, and magnetic fields of different magnitudes are generated for the different ions. 11. The method of claim 10, further comprising replacing a beam-acceleration module including the ion source, radiofrequency electrodes, a beam chamber and a beam-extraction system between accelerations of the different ions. 12. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersected perpendicularly by the central axis, wherein the electrical current is passed through the first superconducting primary coil in the same direction as the direction in which electrical current is passed through the second superconducting primary coil;passing electrical current through at least a first and a second magnetic-field-shielding coil, wherein the first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil and beyond the outer radius of the first superconducting primary coil, wherein the second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil, wherein electrical current is passed through the first and second magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils, and wherein passing electrical current through the magnetic-field-shielding coils generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils; andreleasing an ion from an ion source into the midplane proximate the central axis and accelerating the ion in an orbiting trajectory expanding outward from the central axis via a magnetic field generated at least partially by the superconducting primary coils,wherein at least some of the superconducting magnetic-field-shielding coils are positioned at a radius from the central axis more than 1.5 times the radius of the superconducting primary coils. 13. A method for magnetically shielding a cyclotron during ion acceleration, comprising: passing electrical current through first and second superconducting primary coils, wherein each superconducting primary coil is centered symmetrically about a central axis, one on each side of a midplane intersected perpendicularly by the central axis, wherein the electrical current is passed through the first superconducting primary coil in the same direction as the direction in which electrical current is passed through the second superconducting primary coil;passing electrical current through at least a first and a second magnetic-field-shielding coil, wherein the first magnetic-field-shielding coil is on the same side of the mid plane as the first superconducting primary coil and beyond the outer radius of the first superconducting primary coil, wherein the second magnetic-field-shielding coil is on the same side of the midplane as the second superconducting primary coil and beyond the outer radius of the second superconducting primary coil, wherein electrical current is passed through the first and second magnetic-field-shielding coils in a direction opposite to the direction in which electrical current is passed through the superconducting primary coils, and wherein passing electrical current through the magnetic-field-shielding coils generates a canceling magnetic field that reduces the magnetic field generated at radii from the central axis beyond the magnetic-field-shielding coils; andreleasing an ion from an ion source into the midplane proximate the central axis and accelerating the ion in an orbiting trajectory expanding outward from the central axis via a magnetic field generated at least partially by the superconducting primary coils,wherein shielding of magnetic fields generated by the primary coils at radii from the central axis beyond the superconducting primary coils is provided by a magnetic-field-shielding structure consisting essentially of the magnetic-field-shielding coils. 14. The method of claim 13, wherein the magnetic-field-shielding coils are superconducting. 15. The method of claim 13, further comprising shaping the magnetic field in the midplane using at least a first and a second superconducting magnetic-field-shaping coil, wherein the first and second superconducting magnetic-field-shaping coils are positioned at shorter radii from the central axis than the superconducting primary coils. 16. A magnetically shielded, compact cyclotron, comprising: first and second superconducting primary coils, wherein each superconducting primary coil is centered about a central axis, one on each side of a midplane intersected perpendicularly by the central axis;a current source electrically coupled with the first and second superconducting primary coils and configured to direct electrical current through the first and second superconducting primary coils in the same direction;at least a first and a second magnetic-field-shielding coil centered about the central axis and at radii from the central axis beyond the superconducting primary coils, wherein the first magnetic-field-shielding coil is positioned on the same side of the midplane as the first superconducting primary coil, wherein the second magnetic-field-shielding coil is positioned on the same side of the midplane as the second superconducting primary coil, wherein the current source is electrically coupled with the first and second magnetic-field-shielding coils and configured to direct electrical current through the first and second magnetic-field-shielding coils in a direction that is opposite to the direction in which the electrical current is passing through the superconducting primary coils;an ion source positioned to release an ion in the midplane for an outwardly orbiting acceleration; andat least a first and a second superconducting magnetic-field-shaping coil, wherein the first and second superconducting magnetic-field-shaping coils are positioned at shorter radii from the central axis than the superconducting primary coils. 17. The cyclotron of claim 16, wherein the cyclotron is a synchrocyclotron. 18. The cyclotron of claim 17, wherein the synchrocyclotron includes a magnetic-field-generating structure consisting essentially of the superconducting primary coils, the superconducting magnetic-field-shaping coils and the magnetic-field-shielding coils. 19. The cyclotron of claim 16, wherein the cyclotron is an isochronous cyclotron that generates an azimuthally fixed magnetic field and an azimuthally varying magnetic field. 20. The cyclotron of claim 19, wherein the isochronous cyclotron includes a magnetic-field-generating structure for generating the azimuthally fixed magnetic field that consists essentially of the superconducting primary coils, the superconducting magnetic-field-shaping coils and the superconducting magnetic-field-shielding coils. 21. The cyclotron of claim 20, wherein the isochronous cyclotron includes a magnetic-field-generating structure for generating the azimuthally variable magnetic field that consists essentially of sectors of spiral conductive coil windings. 22. The cyclotron of claim 20, wherein the isochronous cyclotron includes a magnetic-field-generating structure comprising iron for generating the azimuthally variable magnetic field. 23. The cyclotron of claim 16, wherein the magnetic-field-shielding coils are superconducting. 24. The cyclotron of claim 16, further comprising: a radiofrequency accelerator system positioned and configured to generate a radiofrequency alternating electromagnetic field in the midplane for accelerating an orbiting ion in the cyclotron; andan extraction system positioned and configured to extract the orbiting ion from the cyclotron.