In the present research, the magnetic system of an 11 MeV baby cyclotron isdesigned based on the Siemens cyclotron. In this way, the optimized structureof the magnetic system, the synchronicity condition, and the beam focusing arestudied. The magnetic field and the beam dynamics are simulated by the Operaand the Opal codes, respectively. The poles of magnets consist of four valleysand hills and the particles rotate over square-shaped paths. To maintain thesynchronicity condition, we add the magnetic shims on the edges of the hills.So, imposing the magnetic field 1.2 T with the RF frequency 72MHz, the negative hydrogen ions become accelerated up to 11MeV. Keywords: Cyclotron, Magnetic system, Synchronicity condition, Beamdynamics
