Large-area uniform ion beams formed by nonlinear focusing with multipole magnets at the JAEA AVF cyclotron facility

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

We have recently realized a large-area beam with a uniform transverse intensity distribution using protons and various heavy ions for advanced research and future industrial applications at the JAEA AVF cyclotron. The principle of the uniform-beam formation is based on folding the tail of a Gaussian-like beam distribution into the inside by the nonlinear focusing force of multipole magnets. Following techniques have been developed to form the uniform beam efficiently and to evaluate characteristics of the beam precisely: (1) The formation of a prerequisite Gaussian-like beam distribution by multiple scattering, (2) the tuning procedure of the beam optics with multipole magnets, (3) a real-time tuning method of the two-dimensional intensity distribution using phosphor screens, and (4) an evaluation method of the distribution using Gafchromic films. Consequently, the large-area (over 100 cm) uniform beams of H, He, C, Ar, and Xe ions have been so far achieved with a typical uniformity below 10%. In the presentation, we will explain these technical developments, experimental results of the uniform-beam formation, and examples of the beam utilization.