Realization of a phase bunching effect for minimization of beam phase width in a central region of an AVF cyclotron

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

A phase bunching effect has been achieved for the first time using a rising slope of the dee voltage waveform produced at the first acceleration gap between the RF shielding cover of the inflector and the puller in the new central region of the JAEA AVF cyclotron. The feasibility of the phase bunching effect in the central region for a two-dee system with a span angle of 86 in three acceleration harmonic modes was assessed by a simple geometrical analysis of particle trajectories and a three-dimensional beam orbit simulation. The simulation indicated that the initial beam phase width of 40 RF degrees is compressed to 11 RF degrees in the second harmonic mode. A phase width of 1.5 RF degrees FWHM for a 260 MeV Ne beam accelerated in the second harmonic mode was reduced by the bunching effect, compared with the beam phase width of 7.3 RF degrees FWHM in the same harmonic mode for a 10 MeV H beam accelerated in the original central region.