Structural Optimization of Fast Scanning Magnets for Proton Therapy Device

A new proton therapy facility is under construction in Huazhong University of Science and Technology. Scanning magnets play an important role in this device. They can form an arbitrary two-dimensional radiation shape conformal with the tumor. In the pencil beam scanning system, the magnetic fields are excited by time-varying currents and the maximum repetition is up to 50 Hz. Therefore, the temperature rises of two magnets caused by eddy currents should be considered. In this paper, the coupling analysis of Multiphysics was carried out by COMSOL electromagnetic thermal module to optimize the magnetic pole structure of the scanning magnet. The tapered air gap of the downstream magnet X was designed to match the deflection envelope of the proton beam after the upstream magnet Y. The pole of the magnet SMX was optimized to meet the requirement of the local and integral fields. The module of natural convection and surface heat radiation were used to replace the empirical heat transfer coefficient in the thermal analysis so that the simulation agrees better with reality. The results show that the accuracy of the heat transfer coefficient should be further validated by comparison with the simulation that is more realistic.