Optimization of the flattop acceleration voltage for the JAERI AVF cyclotron

Miyawaki, Nobumasa; Fukuda, Mitsuhiro; Kurashima, Satoshi; Okumura, Susumu; Nara, Takayuki; Agematsu, Takashi; Ishibori, Ikuo; Yoshida, Kenichi; Kashiwagi, Hirotsugu; Yokota, Wataru; Arakawa, Kazuo; Nakamura, Yoshiteru

The flat-top acceleration system with the fifth-harmonic of the fundamental frequency has been designed to minimize energy spread for the microbeam production in the JAERI AVF cyclotron. In principle, the amplitude of the fifth-harmonic voltage is of fundamental one to obtain a uniform energy gain distribution, but in reality the voltage ratio for the optimum flat-top acceleration doesn't correspond to , because an accelerating voltage distribution depends on a radial position and the dee angle. The optimum voltage ratio has been investigated for every accelerating condition by shifting a magnet field from isochronism. The energy spread of 210 can be achieved even in non-isochronous condition by changing an initial beam phase and an outermost trim coil field.