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

A uniform ion-beam formation/irradiation system has been developed at the accelerator complex TIARA in Japan Atomic Energy Agency (JAEA). In this system, a large-area beam with a uniform intensity distribution can be formed on the target by the nonlinear beam optics including octupole magnets. Therefore, the whole of a large-area sample can be irradiated uniformly at a constant fluence rate unlike a conventional scanning method and, thus, this uniform beam is suitable for short-time, low-fluence and/or low-fluence-rate irradiations. Recently, a versatile target chamber has been installed in order to conduct various beam studies and users' experiments efficiently. The ion-irradiation response of Gafchromic radiochromic films has been investigated for the evaluation of the transverse intensity distribution of the uniform beams. For several species of heavy ions, beam characteristics are explored toward realization of a heavy-ion uniform beam. We have, so far, obtained the uniform intensity distribution of 9 cm square with an rms uniformity of 5% for a 10-MeV proton beam. Such a large-area uniform beam has been used for the radiation degradation test of space solar cells. (author)