Design Study of a 250 MeV Isochronous Cyclotron for Proton Therapy

In this paper, the magnetic field design of a superconducting fixed-frequency isochronous cyclotron with four spiral sectors for proton therapy was performed. The basic parameters of the isochronous cyclotron magnet and its characteristics are described. Several magnet sectors were designed during the iteration process to achieve an isochronous magnetic field. The result of 3-D magnetic field simulation using OPERA-3D and the analysis of the designed magnetic field are presented. A special geometry was introduced into the sector gap to achieve the isochronous condition, and the spiral angle was adjusted to control the vertical focusing parameter. The equilibrium orbits were checked for the designed magnetic field, and a single particle tracking simulation was performed with CYCLONE code.