Analysis of phase bunching in the central region of the JAEA AVF cyclotron

Miyawaki, Nobumasa; Kashiwagi, Hirotsugu; Kurashima, Satoshi; Okumura, Susumu; Fukuda, Mitsuhiro*

Phase bunching generated in the central region of an AVF cyclotron was analysed by a simplified geometric trajectory model for particles travelling from the first to the second acceleration gap. At the JAEA AVF cyclotron, phase bunching was realized for the acceleration harmonic number (h) 2 and 3. The geometric conditions of phase bunching for h = 1 were unrealistic for the case of the JAEA AVF cyclotron with an 86 degree dee electrode. The phase difference at the second acceleration gap for an initial particle phase width of 40 RF degrees, estimated by the geometric trajectory analysis, was reduced to 8.9 RF degrees for h = 2 and 27.7 RF degrees for h = 3, but expanded to 43.7 RF degrees for h = 1. The reduction of the phase width was consistent with the results obtained by orbit simulations. The practical phase bunching was demonstrated by the phase width measurement for an internal beam of the JAEA AVF cyclotron.