Flat-top acceleration system for the variable-energy multiparticle AVF cyclotron

Fukuda, Mitsuhiro; Kurashima, Satoshi; Okumura, Susumu; Miyawaki, Nobumasa; Agematsu, Takashi; Nakamura, Yoshiteru; Nara, Takayuki; Ishibori, Ikuo; Yoshida, Kenichi; Yokota, Wataru; Arakawa, Kazuo; Kumata, Yukio*; Fukumoto, Yasushi*; Saito, Katsuhiko*

A combination of the fundamental- and the fifth-harmonic voltages is ideally suited for flat-top acceleration in a variable-energy multi-particle cyclotron for energy-spread minimization. The flat-topping of the energy gain distribution using the fifth-harmonics has the advantages of minimizing an amplifier power, reducing power dissipation in a resonator and increasing the energy gain per turn. The flat-top acceleration system of the JAERI AVF cyclotron was designed to reduce the energy spread to 0.02 , required for microbeam production. Tolerable fluctuations of acceleration voltages and the magnetic excitation were 2.010 for the fundamental voltage, 1.010 for the fifth-harmonic voltage, and 1.910 for the magnetic field. In order to enhance compactness of the flat-topping cavity and to make a substantial saving of the amplifier power, optimum geometric parameters of the flat-topping cavity were determined by a cold model test and a calculation using the MAFIA code.