Uniform beam distribution by nonlinear focusing forces

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

To achieve ultra-low-fluence large-area uniform irradiation of ion beams for advanced applications in the field of materials sciences and biotechnology, a uniform-beam irradiation system has been developed using multipole magnets at the Japan Atomic Energy Agency (JAEA) cyclotron facility. The system consists of a beam attenuator for the wide-range intensity control, an electrostatic beam chopper for the control of irradiation time, scattering foils for conditioning of the initial beam distribution, octupole magnets for transverse tail-folding, sextupole magnets for the correction of the beam misalignment, and the diagnostic station of the two-dimensional beam profile. In this paper, recent experimental results are described, especially on the formation of a beam with a uniform transverse distribution by the combination of the sextupole and octupole magnets.