Global gyrokinetic simulations of electrostatic microturbulent transport in LHD stellarator with boron impurity

Global gyrokinetic simulations of electrostatic microturbulent transport for discharge # 166256 of the LHD stellarator are carried out in the presence of boron impurity using the gyrokinetic toroidal code (GTC). The simulations show the co-existence of the ion temperature gradient (ITG) turbulence and trapped electron mode (TEM) turbulence before and during boron powder injection. ITG turbulence dominates in the core, whereas TEM dominates near the edge, consistent with the experimental observations. Linear TEM frequency increases from ∼ 80 kHz to ∼ 100 kHz during boron injection, and the ITG linear frequency decreases from ∼ 20 kHz to ∼ 13 kHz, consistent with the experiments. The poloidal wave number spectrum is broad for both ITG: 0 − 0.5 mm⁻¹ and TEM: 0 − 0.25 mm⁻¹ . The nonlinear simulations with boron impurity show a reduction in the turbulent transport compared to the case without boron. The comparison of the nonlinear transport shows that the ion heat transport is substantially reduced in the region where the TEM is dominant. However, the average electron heat transport throughout the radial domain and the average ion heat transport in the region where the ITG is dominant are similar. The simulations with boron show the effective heat conductivity values qualitatively agree with the estimate obtained from the experiment.