  The basic physics properties and simplified model descriptions of the
paradigmatic "percolation" transport in low-frequency, electrostatic
(anisotropic magnetic) turbulence are theoretically analyzed. The key problem
being addressed is the scaling of the turbulent diffusion coefficient with the
fluctuation strength in the limit of slow fluctuation frequencies (large Kubo
numbers). In this limit, the transport is found to exhibit pseudochaotic,
rather than simply chaotic, properties associated with the vanishing
Kolmogorov-Sinai entropy and anomalously slow mixing of phase space
trajectories. Based on a simple random walk model, we find the low-frequency,
percolation scaling of the turbulent diffusion coefficient to be given by
$D/\omega\propto Q^{2/3}$ (here $Q\gg 1$ is the Kubo number and $\omega$ is the
characteristic fluctuation frequency). When the pseudochaotic property is
relaxed the percolation scaling is shown to cross over to Bohm scaling. The
features of turbulent transport in the pseudochaotic regime are described
statistically in terms of a time fractional diffusion equation with the
fractional derivative in the Caputo sense. Additional physics effects
associated with finite particle inertia are considered.
