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.
