Guiding center diffusion induced by stochastic ∇B and curvature drifts

Turbulent processes occurring in the plasma seem to be the origin of the anomalous transport observed in tokamaks. The transport induced by stochastic fluctuation has been studied by consideration of the diffusion of guiding centers due to the stochastic electric drift or the motion of the centers along fluctuating magnetic lines. However the diffusion induced by the stochastic ∇B and curvature drifts has not received special attention because it is believed that these diffusive processes are too weak in comparison with other processes. The treatment of stochastic ∇B and curvature drifts requires the development of a formalism to treat fluctuation with both time and space dependence. In a recent paper a mathematical approach to deal with these type of fluctuations has been presented, and here we apply these results to a model for the magnetic field turbulence and evaluate the diffusion of guiding centers due to these drifts. (author) 3 refs