Research on the Design of Scanning Magnets for Proton Therapy Nozzle

Pencil beam scanning nozzle as a key component in superconducting proton therapy facility, which Iaterally extends proton beam with a pair of scanning magnets so that the irradiation field can be consistent with the tumor section. The paper first introduce the nozzle layout principle. Second, based on the deflection theory and geometrical relationship about proton beam within magnetic field to figure out the mapping relation between scanning of magnetic field intensity and irradiation field (deflection distance), and preliminarily predicts about the $\displaystyle \max $ field intensity of scanning magnets X (SMX) and Y (SMY). Then designs the outline of the scanning magnet, modifies the scanning magnetic field by using a trapezoidal shim. The poles of the SMX have a taper to accommodate the deflection envelope of the SMY. The calculation results indicate that the integral fields' uniformity of SMX and SMY is below $2\times 10^{-3},$ which can well guarantee the deflection precision of the proton beam.