  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.
