Gyrokinetic particle simulation of electrostatic drift wave turbulence in W7-X and LHD stellarators

We report gyrokinetic particle simulation of ion temperature gradient (ITG) instabilities in Wendelstein7-X (W7-X) and Large Helical Device (LHD) stellarators by using Gyrokinetic Toroidal Code (GTC). The ITG instabilities have been studied in both full torus and partial torus geometries. The linear toroidal coupling effects due to the 3D magnetic fields are kept in partial torus simulation of toroidal domain with minimal length by taking advantage of the toroidal periodicity of stellarators. The mode structure in W7-X is more localized in the toroidal direction, and LHD is more extended in the toroidal direction and tokamak-like. GTC simulation results of linear frequency, growth, and mode structures are in good agreement with EUTERPE simulation results. Initial nonlinear simulation results of ITG instability saturation and turbulent transports in stellarators are presented, which support the view that turbulence-driven fluctuating zonal flows can suppress turbulent transport.