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Updated: Aug 19, 2026

The Diffusion of Passive Tracers in Laminar Shear Flow
Published on: May 1, 2018
Nondiffusive transport in plasma turbulence: a fractional diffusion approach
D del-Castillo-Negrete1, B A Carreras, V E Lynch
1Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6169, USA. decastillod@ornl.gov
Abstract:
Numerical evidence of nondiffusive transport in three-dimensional, resistive pressure-gradient-driven plasma turbulence is presented. It is shown that the probability density function (pdf) of tracer particles' radial displacements is strongly non-Gaussian and exhibits algebraic decaying tails. To model these results we propose a macroscopic transport model for the pdf based on the use of fractional derivatives in space and time that incorporate in a unified way space-time nonlocality (non-Fickian transport), non-Gaussianity, and nondiffusive scaling. The fractional diffusion model reproduces the shape and space-time scaling of the non-Gaussian pdf of turbulent transport calculations. The model also reproduces the observed superdiffusive scaling.
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