Statistical model for intermittent plasma edge turbulence

The probability distribution function of plasma density fluctuations at the edge of fusion devices is known to be skewed and strongly non-Gaussian. The causes of this peculiar behavior are, up to now, largely unexplored. On the other hand, understanding the origin and the properties of edge turbulence is a key issue in magnetic fusion research. In this paper we show that a stochastic fragmentation model, already successfully applied to fluid turbulence, is able to predict an asymmetric distribution that closely matches experimental data. The asymmetry is found to be a direct consequence of intermittency. A discussion of our results in terms of recently suggested Bramwell-Holdsworth-Pinton universal curve [ S. T. Bramwell, P. C. W. Holdsworth and J.-F. Pinton Nature (London) 396 552 (1998)], that should hold for strongly correlated and critical systems, is also proposed.