Theory and Simulation of Toroidal Momentum Transport

By constructing a radial flux of toroidal angular momentum from the ``energy conserving'' nonlinear gyrokinetic equation in toroidal geometry [1], we can readily identify a diffusive flux and a non-diffusive flux. For the diffusive flux from ITG turbulence, it has been shown that $\chi_{\phi} \sim \chi_{i}$ [2] in rough agreement with observations from NBI-heated plasmas. We've investigated possible physical mechanisms behind the nondiffusive flux, and found that: Mean ${\bf E \times B}$ shear can induce a net momentum flux by breaking the quasi- translational invariance of the ballooning eigenfunctions. Results from the FULL code demonstrate such modifications of eigenmodes. However, ${\bf E \times B}$ shear suppression makes resulting parallel flow weak. New nonlinear simulation results from GTC code including plasma shaping will be reported [3]. \newline \newline [1] T.S. Hahm, Phys. Fluids {\bf 31}, 2670 (1988). \newline [2] N. Mattor and P.H. Diamond, Phys. Fluids {\bf 31}, 1180 (1988). \newline [3] W.X. Wang {\it et al.,} Submitted to Phys. Plasmas (2006).