Comparisons of Nonlinear Toroidal Turbulence Simulations with Experiment Comparisons of Nonlinear Toroidal Turbulence Simulations with Experiment

The anomalously large thermal transport observed in tokamak experiments is the outstanding physics-based obstacle in the path to a commercially viable fusion reactor. Although decades of experimental and theoretical work indicate that anomalous transport and collective instabilities in the gyrokinetic regime are linked, no widely accepted description of this transport yet exists. Here, detailed comparisons of rst-principles gyroouid and gyrokinetic simulations of tokamak microinstabilities with experimental data are presented. With no adjustable parameters, more than 50 TFTR L-mode discharges have been simulated with encouraging success. Given the local plasma parameters and the temperatures at r=a ' 0:8, the simulations typically predict T i (r) and T e (r) within 25% throughout the core and connnement zones. In these zones, the predicted thermal dif-fusivity increases with minor radius robustly. For parameters typical of r=a > 0:8, toroidal stability studies connrm the importance of impurity density gradients as a source of free energy potentially strong enough to explain the large edge thermal diiusivity, as rst emphasized by Coppi, et al. Advanced connnement discharges have also been simulated. The dramatic increase of T i (0) observed in Supershots (from 5 keV to 30 keV) is recovered by our model for dozens of simulated experiments. Finally, simulations of VH and PEP mode-like plasmas show that velocity-shear stabilization of toroidal microinstabilities is quantitatively signiicant for realistic experimental parameters.