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A. M. Dimits, B. I. Cohen, N. Mattor,
W. M. Nevins, D. E. Shumaker
Lawrence Livermore National Laboratory, Livermore, CA 94551 USA
S. E. Parker, C. Kim
University of Colorado, Boulder, CO 80309 USA
Abstract. Results are presented from nonlinear gyrokinetic simulations of
toroidal ion temperature gradient (ITG) turbulence and transport. The ion
thermal fluxes are found to have an offset linear dependence on the
temperature gradient and are significantly lower than gyrofluid or
IFS-PPPL-model predictions. A new phenomenon of nonlinear effective critical
gradients larger than the linear instability threshold gradients is observed,
and is associated with undamped flux-surface-averaged shear flows. The
nonlinear gyrokinetic codes have passed extensive tests which include
comparison against independent linear calculations, a series of nonlinear
convergence tests, and a comparison between two independent nonlinear
gyrokinetic codes. Our most realistic simulations to date used actual
reconstructed equilibria from experiments and a model for dilution by impurity
and beam ions. These simulations highlight the importance of both
self-generated and external
E×B flow shear as well as the need for
still more physics to be included.
IAEA 2001
