Characterising the transport dynamics in the Scrape-Off Layer (SOL) of tokamaks is especially important, since localised and transient outbursts may strongly modify both the recycling properties and the lifetime of plasma facing components. In this paper, turbulent transport is investigated in the SOL by means of a two-dimensional (flute modes) electrostatic code for interchange instability. With the assumption of constant electron temperature and cold ions, the code solves the continuity and charge conservation equations, involving the density and the electric potential. A particle source injects free energy into the system, which then relaxes with intermittent long range transport events called avalanches.
The transport intermittency is characterised by the probability distribution function (PDF) of the turbulent flux, which is skewed toward large outbursts and exhibits exponential tails. The PDF of density fluctuations, given the constraint of positive total density, can be fitted by a log-normal plot. Conversely, radial and poloidal E×B drifts have an almost symmetric PDF with a Gaussian shape. These statistical results are in good agreement with experimental observations in several tokamaks. Zonal flows (ZF) are found to reduce the intermittency in regulating the magnitude of avalanche-like events. Bursts then appear to be more frequent but smaller. The overall transverse turbulent transport significantly decreases in the presence of ZF, provided the parallel connection lengths L_// are large enough. Indeed, due to Bohm-like parallel boundary conditions in the SOL, such a parameter governs the magnitude of electric potential fluctuations.

This complex dynamics leads to an exponential fall-off of the mean density profile. Intensive numerical simulations suggest the e-folding length scales like : λ∼L_//^2/3. This scaling departs from both a diffusion (λ∼L_//^1/2) and a convective transport (λ∼L_//). A simple analysis of this profile in terms of diffusion-convection coefficients would however suggest a convective dominated transport. A transport barrier can be generated by imposing a poloidal (or toroidal) ring of bias potential localised radially. The induced poloidal velocity shear as well as the radial width of the ring appear to control the magnitude and the strength of the barrier. The latter can be quantified by generating large avalanches with a transient and poloidally localised source. Such a biasing would provide a mean to screen the wall of the main chamber from long range transport events.