Scaling laws of stochastic E x B plasma transport

Two distinct regimes of cross-field test particle diffusion due to electrostatic turbulence are discussed. In the quasi-linear regime, which takes place for small amplitude φo of the potential perturbation, the local turbulent diffusion coefficient scales as Dτ∝φo2. For the turbulence amplitude exceeding the mixing length level, the E x B drift of particles is sensitive to the topology of contours of constant potential φ(x, t) due to longer correlations of drift orbits. In this regime, the percolation theory is used to describe the long flights of particles along the critical level contours. The percolation scaling for the diffusivity Dτ∝φo7/10 is then derived and applied to edge tokamak transport. (author)