Comparison of ITG and TEM Microturbulence in DIII–D Tokamak

Microturbulence excited by ion temperature gradient (ITG)-dominant and trapped electron mode (TEM)-dominant instabilities is compared in the fusion plasmas using gyrokinetic simulations based on the realistic equilibrium data from DIII–D discharges. Collisions make a difference between two plasmas and give rise to similar results to those found in previous research experiments Chin. Phys. Lett. 35 (2018) 105201. The mode structures and frequency spectrum of the most unstable modes characterized by the ITG-dominant and TEM-dominant instabilities are excited in the lower and higher T_\rm e plasmas in the linear simulations. In the nonlinear simulations, contour plots of the perturbed potential are shown in the saturated stage, with the radial correlation lengths being microscopic on the order of the ion thermal gyroradius \rho_\rm i in both the ITG and the TEM microturbulences. The dominant mode wavelengths of the perturbed potential increase when evolving from linear to nonlinear stages in both simulations, with the fluctuation energy spreading from the linearly dominant modes to the nonlinearly dominant modes. The radial correlation lengths are about 4\rho_\rm i and the electron density fluctuation intensities are about 0.85% in the nonlinear saturated stage, which are in agreement with the experimental results.