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An isochronous cyclotron includes at least two superconducting coils, a magnetic yoke surrounding the coils and containing at least a portion of a beam chamber, a plurality of superconducting flutter coils on each side of the median acceleration plane, a non-magnetic reinforcement structure filling

An isochronous cyclotron includes at least two superconducting coils, a magnetic yoke surrounding the coils and containing at least a portion of a beam chamber, a plurality of superconducting flutter coils on each side of the median acceleration plane, a non-magnetic reinforcement structure filling the valleys between the superconducting flutter coils so as to maintain the positioning of the superconducting flutter coils, internal reinforcement structures mounted inside the superconducting flutter coils, and a cryogenic refrigerator thermally coupled with the superconducting coils and with the magnetic yoke.

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1. An isochronous cyclotron, comprising: at least two superconducting primary coils that are substantially symmetric about a central axis, wherein the superconducting primary coils are on opposite sides of a median acceleration plane;a magnetic yoke surrounding the superconducting primary coils and

1. An isochronous cyclotron, comprising: at least two superconducting primary coils that are substantially symmetric about a central axis, wherein the superconducting primary coils are on opposite sides of a median acceleration plane;a magnetic yoke surrounding the superconducting primary coils and containing at least a portion of a beam chamber, wherein the median acceleration plane extends through the beam chamber;a plurality of superconducting flutter coils on each side of the median acceleration plane, wherein each superconducting flutter coil or pair of superconducting flutter coils serves as a sector pole tip with valleys between the sector pole tips on each side of the median acceleration plane, and wherein the sector pole tips are radially separated across the median acceleration plane by a gap that is narrower than a non-magnetic gap that separates the valleys across the median acceleration plane;a non-magnetic external reinforcement structure filling the valleys between the superconducting flutter coils so as to maintain the positioning of the superconducting flutter coils;internal reinforcement structures mounted inside the superconducting flutter coils; andat least one cryogenic refrigerator thermally coupled with the superconducting primary coils, with the superconducting flutter coils, and with the magnetic yoke. 2. The isochronous cyclotron of claim 1, wherein the non-magnetic external reinforcement structure comprises aluminum. 3. The isochronous cyclotron of claim 1, wherein a first cryostat contains a first of the superconducting primary coils, a first of the superconducting flutter coils, and a first non-magnetic external reinforcement structure; and wherein a second cryostat contains a second of the superconducting primary coils, a second of the superconducting flutter coils, and a second non-magnetic external reinforcement structure. 4. The isochronous cyclotron of claim 3, further comprising an integral maintenance boot assembly that separates the cryogenic refrigerator from the primary coil(s) to which it is thermally coupled and that is configured to preserve a vacuum in the cryostats if the cryogenic refrigerator is removed. 5. The isochronous cyclotron of claim 1, wherein the non-magnetic external reinforcement structure defines a plurality of apertures through which current leads to electrode dees can pass. 6. The isochronous cyclotron of claim 1, wherein the superconducting flutter coils have a spiral shape in a plane parallel to the median acceleration plane. 7. The isochronous cyclotron of claim 1, wherein the internal reinforcement structures contract less with decreasing temperature than does the superconducting flutter coils, and wherein the superconducting flutter coils contract less with decreasing temperature than does the non-magnetic external reinforcement structure. 8. The isochronous cyclotron of claim 1, wherein a gap exists between an inner surface of each of the superconducting flutter coils and its respective internal reinforcement structure and between an outer surface of each of the superconducting flutter coils and the non-magnetic external reinforcement structure at temperatures between 200-300K. 9. The isochronous cyclotron of claim 1, wherein the internal reinforcement structures comprises at least one metal selected from copper and stainless steel. 10. The isochronous cyclotron of claim 1, wherein the superconducting flutter coils are in only a three-sector configuration about the central axis. 11. The isochronous cyclotron of claim 10, wherein just 3 or 6 superconducting flutter coils are included in the isochronous cyclotron. 12. The isochronous cyclotron of claim 1, wherein the superconducting flutter coils are in a four-sector-or-higher configuration about the central axis. 13. The isochronous cyclotron of claim 1, wherein the isochronous cyclotron has a mass less than 35 tons. 14. The isochronous cyclotron of claim 1, wherein each cryogenic refrigerator includes a head, and wherein the coupling of each cryogenic refrigerator with the primary coil(s) is oriented and configured to place the head of each cryogenic refrigerator at a distance from the median acceleration plane that is beyond the magnetic yoke. 15. The isochronous cyclotron of claim 1, wherein the isochronous cyclotron includes 3 or 4 superconducting flutter coils, and wherein each superconducting flutter coil serves as a sector pole tip. 16. The isochronous cyclotron of claim 1, wherein the isochronous cyclotron includes 6 or 8 superconducting flutter coils, and wherein each pair of superconducting flutter coils serves as a sector pole tip, and wherein the superconducting flutter coils are coupled with a voltage source to generate alternating electric current flow direction in the respective superconducting flutter coils of each pair of superconducting flutter coils. 17. A method for isochronous ion acceleration, comprising: employing an isochronous cyclotron comprising:a) at least two superconducting primary coils that are substantially symmetric about a central axis, wherein the superconducting primary coils are on opposite sides of a median acceleration plane;b) a magnetic yoke surrounding the superconducting primary coils and containing at least a portion of a beam chamber, wherein the median acceleration plane extends through the beam chamber;c) a plurality of superconducting flutter coils on each side of the median acceleration plane, wherein each superconducting flutter coil or pair of superconducting flutter coils serves as a sector pole tip with valleys between the sector pole tips on each side of the median acceleration plane, and wherein the sector pole tips are radially separated across the median acceleration plane by a gap that is narrower than a non-magnetic gap that separates the valleys across the median acceleration plane;d) an external reinforcement structure filling the valleys so as to maintain the positioning of the superconducting flutter coils;e) internal reinforcement structures mounted inside the superconducting flutter coils;f) at least one cryogenic refrigerator thermally coupled with the superconducting primary and flutter coils and with the magnetic yoke; andg) a plurality of electrodes coupled with a radiofrequency voltage source and mounted in the beam chamber;introducing an ion into the median acceleration plane at an inner radius;providing a voltage from the radiofrequency voltage source to the electrodes to accelerate the ion at a fixed frequency in an expanding orbit across the median acceleration plane;cooling the superconducting primary coils and the superconducting flutter coils with the cryogenic refrigerator, wherein the superconducting primary and flutter coils are cooled to a temperature no greater than their superconducting transition temperature;providing a voltage to the cooled superconducting primary coils to generate a superconducting current in the superconducting primary coils that produces a radially increasing magnetic field in the median acceleration plane from the superconducting coils and from the magnetic yoke;providing a voltage to the cooled superconducting flutter coils to generate a superconducting current in the superconducting flutter coils; andextracting the accelerated ion from beam chamber at an outer radius. 18. The method of claim 17, wherein accelerated ions reach an energy of 10-250 MeV. 19. The method of claim 17, wherein the magnetic yoke is maintained at a temperature over 200 K as the ion is accelerated. 20. The method of claim 17, wherein the isochronous cyclotron includes as many electrodes as superconducting flutter coils, and wherein the electrodes are positioned at angles between the superconducting flutter coils about the central axis. 21. The method of claim 17, further comprising directing the extracted ion at a tumor in a human patient. 22. The method of claim 21, wherein a beam of extracted ions are scanned across the tumor via pencil beam scanning. 23. The method of claim 22, wherein the pencil beam scanning process is completed in no more than 10 seconds. 24. The method of claim 22, wherein the pencil beam scanning process is completed in no more than 5 seconds. 25. The method of claim 17, wherein the ion is introduced into the median acceleration plane by injecting the ion from an external electron cyclotron resonance ion source. 26. The method of claim 17, wherein the extracted ion is a proton with an energy of at least 220 MeV. 27. The method of claim 17, wherein the isochronous cyclotron generates a central magnetic field in the median acceleration plane greater than 3.5 T. 28. The method of claim 17, wherein the isochronous cyclotron includes 6 or 8 superconducting flutter coils, and wherein each pair of superconducting flutter coils serves as a sector pole tip, and wherein the voltage provided to the superconducting flutter coils generates alternating electric current flow direction in the respective superconducting flutter coils of each pair of superconducting flutter coils.