Global gyrokinetic simulations of electrostatic microturbulent transport using kinetic electrons in LHD stellarator

Drift wave instabilities responsible for the electrostatic turbulence transport in fusion plasma, namely, the ion temperature gradient (ITG) and trapped electron mode (TEM), are studied using gyrokinetic toroidal code (GTC) in the LHD stellarator. The ITG turbulence simulations with kinetic electrons show that the kinetic effects increase the growth rate of the most dominant eigenmode by ~1.5 times and the turbulent transport by ~2.5 times as compared to the case with adiabatic electrons. The zonal flow regulates the ITG turbulence transport by reducing it by almost two-folds and hence acts as a dominant saturation mechanism. The linear TEM simulations show that the electrostatic potential is localized on the low magnetic field region where the curvature is bad, just like ITG turbulence. The nonlinear TEM turbulence simulations show that the main saturation mechanism is not the zonal flow but the inverse cascade of the high poloidal and toroidal harmonics to the low harmonics. The comparison of nonlinear simulations with different pressure profiles indicates that the ITG turbulence is more effective in driving heat conductivity whereas the TEM turbulence is responsible for the particle diffusivity.