In the recent decades of particle accelerator R＆D area, the fixed field alternating gradient （FFAG） accelerator has become a highlight for some advantages of its higher beam intensity and lower cost, although there are still some technical challenges. In this paper, the FFAG accelerator is adopted to accelerate a helium ion beam on the one hand for the study of helium embrittlement on fusion reactor envelope material and on the other hand for promoting the conception research and design of the FFAG accelerator and exploring the possibility of developing high power FFAG accelerators. The conventional period focusing unit of the helium ion FFAG accelerator and three- dimensional model of the large aperture combinatorial magnet by OPERA-TOSCA are given. For low energy and low revolution frequency, induction acceleration is proposed to replace conventional radio frequency （RF） acceleration for the helium ion FFAG accelerator, which avoids the potential breakdown of the acceleration field caused by the wake field and improves the acceleration repetition frequency to gain higher beam intensity. The main parameters and three-dimensional model of induction cavity are given. Two special constraint waveforms are proposed to refrain from particle accelerating time slip （AT） caused by accelerating voltage drop of flat top and energy deviation. The particle longitudinal motion in two waveforms is simulated.
The linac to the transmuter beam transport line （LTBT） connecting the end of the linac to the spallation target is a critical sub-system in the accelerator driven system （ADS）. It has the function of transporting the accel-erated high power proton beam to the target with a beam footprint satisfying the special requirements of the minor actinide （MA） transmuter. In this paper, a preliminary conceptual design of the hurling magnet to transmuter beam transport section （HTBT）, as a part of the LTBT, for the China ADS （C-ADS） system is proposed and developed. In this design, a novel hurling magnet with a two dimensional amplitude modulation （AM） of 1 kHz and scanning of more than 10 kHz at 360 in transverse directions is used to realize a 300 mm diameter uniform distribution of beam on target. The preliminary beam optics design of C-ADS HTBT optimized to minimize the beam loss on the vacuum chamber and the radiation damage caused by back-scattering neutrons will be reported.
