Abstract: The reduction of neoclassical transport in the W7-X stellarator
thanks to its quasi-isodynamic design and the finding of an optimized
operation regime in the LHD stellarator have shifted research interest from
neoclassical to turbulent transport. Over the past few years, some progress
has been made toward gyrokinetic simulations of microturbulence in
stellarators. Global simulations are necessary to include the effects of
the 3D magnetic field such as the secular radial drift of helically-trapped
particles. In this work, we present recent global non-linear gyrokinetic
simulations with kinetic electrons of ITG and TEM turbulence using the
gyrokinetic toroidal code (GTC). ITG and TEM in LHD show similar
characteristics as Tokamaks. Both instabilities are excited in the outer
midplane. However, a new trapped electron mode caused by the
helically-trapped particles is observed in W7-X at the toroidal section
with a weak magnetic field on the inner side of the torus.