Development of a uniform beam irradiation system by the nonlinear focusing method

Yuri, Yosuke; Yuyama, Takahiro; Ishizaka, Tomohisa; Ishibori, Ikuo; Okumura, Susumu

A research and development study has been in progress on the formation and irradiation of a uniform ion beam using multipole magnets at TIARA of JAEA. The uniform beam irradiation system is based on the nonlinear focusing method, which enables us to make the beam's Gaussian distribution uniform and irradiate any position on a large-area sample at a constant particle fluence rate. In this paper, several measurement techniques have been investigated to tune the beam in real time and evaluate characteristics of a large-area uniform beam. By measuring the 2D relative distribution using radiochromic films, we have confirmed that a uniform proton beam of 6 cm square with 6 % uniformity is formed. Features of the uniform irradiation by means of the nonlinear focusing method are also discussed.