Effects of stochastic drifts and time variation on particle diffusion in magnetic turbulence

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Abstract
The effect on the guiding center trajectories of the stochastic drifts due to the curvature of the stochastic magnetic lines is studied in the first part of this paper. It is shown that the subdiffusive √t behavior of the mean square displacement of the particles cannot exist in a realistic magnetic configuration. The particles undergo a diffusive process even in the absence of the perpendicular collisional diffusion. The anomalous diffusion coefficient is estimated. The second part of this work deals with time-dependent stochastic perturbations of the confining magnetic field. It is shown that the time variation has a strong effect of decorrelating the particles from the magnetic lines. The diffusion coefficient is determined as a function of the correlation time of the stochastic field. The influence of a cross field collisional diffusion on the results of the two problems presented here is also estimated. © 1996 The American Physical Society.