Formation of a uniform beam profile using multipole magnets

Large-area uniform irradiation is one of essential techniques for charged-particle beam applications. Recently, the nonlinear focusing method using multipole magnets has been widely receiving attention as an alternative uniform irradiation technique. Here, we have experimentally studied uniform beam formation using multipole magnets. A beam line was improved for uniform-beam formation using sextupole and octupole magnets at an accelerator complex of the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA), Japan Atomic Energy Agency (JAEA). The transverse profile of the beam extracted from the JAEA azimuthally-varying-field (AVF) cyclotron was transformed into a uniform one by means of octupole nonlinear focusing. We have demonstrated the uniformization of an off-axis beam applying a sextupole force in addition to an octupole force. The characteristics of its method as a uniform-irradiation technique are also discussed, compared to the raster scanning method. (author)