Large-area uniform ion beam formed by the nonlinear beam optics at the JAEA TIARA cyclotron

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

A nonlinear focusing method has been studied to form an ion beam with a large-area uniform transverse intensity distribution using octupole magnets at the TIARA cyclotron facility for use in materials and biological sciences. The uniform intensity distribution can be formed on the target by folding the tail of a Gaussian distribution with the nonlinear focusing force of octupole magnets in this method. Therefore, the whole of a large-area sample can be irradiated uniformly at a constant fluence rate. The recent progress will be reported on the uniform beam formation in this presentation. Commissioning of the heavy-ion beam transport has been performed to explore beam characteristics and optimize operation parameters. The uniform intensity distribution with a root-mean-square uniformity of 5% has been obtained in 9 cm square using 10-MeV proton beams, so far. Such a large-area proton uniform beam has been used for the radiation degradation test of space solar cells.