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

Global gyrokinetic simulations of ion temperature gradient (ITG) and trapped electron mode (TEM) in the LHD stellarator are carried out using the gyrokinetic toroidal code (GTC) with kinetic electrons. ITG simulations show that kinetic electron effects increase the growth rate by more than 50% and more than double the turbulent transport levels compared with simulations using adiabatic electrons. Zonal flow dominates the saturation mechanism in the ITG turbulence. Nonlinear simulations of the TEM turbulence show that the main saturation mechanism is not the zonal flow but the inverse cascade of high to low toroidal harmonics. Further nonlinear simulations with various pressure profiles indicate that the ITG turbulence is more effective in driving heat conductivity whereas the TEM turbulence is more effective for particle diffusivity.

Automated summary

In this study, global gyrokinetic simulations are conducted to investigate the ion temperature gradient (ITG) and trapped electron mode (TEM) in the LHD stellarator. The simulations reveal that kinetic electron effects significantly enhance the growth rate and turbulent transport levels. Zonal flow is found to dominate the saturation mechanism in ITG turbulence, while the inverse cascade of toroidal harmonics plays a crucial role in the saturation of TEM turbulence. Furthermore, the simulations indicate that ITG turbulence is more effective in driving heat conductivity, while TEM turbulence is more efficient for particle diffusivity.