Magnetic field measurements and experimental verification of 0.5-MeV permanent-magnet electron-beam-spread system

In this work, a permanent-magnet electron-beam-spread system for irradiation has been developed and constructed, and its performance was experimentally measured with a beam. This work is helpful to counter beam-tail sweep issues (resulting in excessive doses at the ends of each sweep). Using the beam’s optical transmission matrix and beam dynamics simulations, we analyzed the impact of the individual parameters of a special quadrupole magnet and a special octupole magnet on the beam spread, and we determined the optimal parameters for irradiation production. To meet the design requirements of the magnetic field, the yoke structure was optimized, and permanent magnets with very similar degrees of magnetization and small magnetic declinations were used. The permanent-magnet electron-beam-spread system was applied to an actual 0.5-MeV electron irradiation accelerator, and the engineering feasibility of the permanent magnet electron beam spread system was fully verified by measuring the uniformity of the beam after the spread.