Influence of the RF magnetic field on beam dynamics in SC200 cyclotron

Abstract

Abstract The SC200 superconducting cyclotron is developed by the collaboration between ASIPP (Hefei, China) and JINR (Dubna, Russia). The SC200 cyclotron will deliver 200 MeV beam for proton therapy and research. The influence of the time-dependent magnetic field created by the acceleration system of SC200 should be taken into account in beam dynamics simulations and during the shimming procedure, as two conditions are present together: first — due to the spiral shape of the accelerating cavities, there is no vertical plane of symmetry through the middle of the dee; and second — second harmonic mode of acceleration in four-sector magnet structure imposes that the RF phase shift from beam entrance of the dee to its exit is not 180 degrees. Particle tracking was performed with 3D maps of electromagnetic fields obtained from computer modelling of the magnet system and the accelerating RF cavities using CST Studio Suite. We have calculated particle dynamics taking into account RF magnetic field and have estimated a value of additional mean field needed for the compensation of beam phase lag induced by RF magnetic field. And finally, we designed a shim that should form the required additional field.