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

The probability distribution function P-n(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 experimental results from RFX reversed field pinch (RFP) [G. Rostagni, Fusion Eng. Des. 25, 301 (1995)] are presented, confirming the universal shape of P-n also for RFP's. An explanation for the form of P-n is attempted, on the basis of simple conservation equations. The model result is shown to fit fairly well empirical data in a few different experimental scenarios. (C) 2004 American Institute of Physics.