Beta scaling of transport in microturbulence simulations

A systematic study of the beta (beta) scaling and spatial structure of thermal and particle transport in gyrokinetic turbulence simulations is presented. Here, beta is the ratio of the plasma kinetic pressure to the magnetic pressure. Results show that the nonlinear self-consistent temperature profiles exhibit a (statistically) time-stationary flattening in the vicinity of rational surfaces with a concomitant drop in the electrostatic components of the thermal diffusivity. Simultaneously, the increased magnetic fluctuation amplitude at these surfaces enhances the steady-state electromagnetic (flutter) component of the electron thermal diffusivity. The electromagnetic components of the ion transport coefficients remain close to zero, as expected on theoretical grounds. Only a weak dependence of ion energy transport on beta is observed, consistent with recent tokamak experiments [C. C. Petty , Phys. Plasmas 11, 2514 (2004)]. (C) 2005 American Institute of Physics.