Conception design of helium ion FFAG accelerator with induction accelerating cavity

In the recent decades of particle accelerator R&D area, 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, FFAG accelerator is adopted to accelerate 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 FFAG accelerator and exploring the possibility of developing high power FFAG accelerators. The conventional period focusing unit of 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 helium ion FFAG accelerator, which avoids the potential breakdown of acceleration field caused by 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({\Delta}T) caused by accelerating voltage drop of flat top and energy deviation. The particle longitudinal motion in two waveforms is simulated.