On the Probability distribution function of particle density at the edge of fusion devices

The Probability Distribution Function (PDF) Pn(n) of the particle density at the edge of several magnetic fusion devices, including tokamaks, stellarators, and linear devices, is known to be strongly non-gaussian. In this paper we present experimental results from RFX Reversed Field Pinch [G. Rostagni, Fus. Eng. Design 25, 301 (1995)], confirming the universal shape of Pn also for RFP's. An explanation for the form of Pn is attempted, on the basis of simple conservation equations. The model result is shown to fitted fairly well empirical data in a few different experimental scenarios.