Development of the central region for control of a beam phase width at the JAEA AVF cyclotron

Miyawaki, Nobumasa; Okumura, Susumu; Kurashima, Satoshi; Kashiwagi, Hirotsugu; Yoshida, Kenichi; Ishibori, Ikuo; Yuri, Yosuke; Nara, Takayuki; Agematsu, Takashi; Fukuda, Mitsuhiro*

The central region of the JAEA AVF cyclotron has been modified to solve the problem of the beam instability caused by the electric discharge between the dee electrode and the RF shielding cover attached to the inflector electrode and to control a beam phase width for microbeam production. The beam stability has been improved by separating the inflector electrode and its RF shielding cover. The beam phase width, controlled with phase slits, has been 4.5 rf degrees FW for acceleration harmonic mode 1 (H=1) and 3.6 rf degrees FW for H=2 to fulfil the requirement for the microbeam production.