Investigations of Turbulent Transport Channels in Gyrokinetic Simulations

Magnetic-field stochasticity arises due to microtearing perturbations, which can be driven linearly [1] or nonlinearly (in cases where they are linearly stable [2]), even at very modest values of the plasma beta. The resulting magnetic-flutter contribution may [1] or may not [2] be a significant component of the overall electron (particle and thermal) transport. Investigations of the effect of ExB flow shear on electron-drift magnetic-flutter diffusion coefficient $D_{edr}(r$,v$_{\vert \vert })$ using perturbed magnetic fields from simulations, using the GYRO code [3], of ITG turbulence show a significant effect for electrons with parallel velocities v$_{\vert \vert }$ surprisingly far from the resonant velocity. We further examine changes in the radial dependence of this diffusion coefficient vs. v$_{\vert \vert }$ and which resonant magnetic-field perturbations are important to the values and radial structure of $D_{edr}$. The resulting electron transport fluxes are compared with the simulation results. Improvements over [2] in treating the ambipolar field in the relationship between the magnetic (or drift) diffusion coefficients and the transport have been made in these comparisons. \\[4pt] [1] W. Guttenfelder, et al., Phys. Plasmas \textbf{19}, 056119 (2012).\\[0pt] [2] E. Wang, et al., Phys. Plasmas \textbf{18}, 056111 (2011).\\[0pt] [3] J. Candy and R. E. Waltz, J. Comput. Phys. \textbf{186}, 545 (2003).