The stochastic diffusion process in reversed-field pinch

The stochastic diffusion process has been carefully analysed for the Reverse Field Pinch (RFP) equilibrium configuration. Three different approaches to the problem have been used, i.e, the direct calculation of the stochastic diffusion coefficient (D-st) from the radial evolution of an ensemble of field lines, an indirect determination using a Gaussian-fit to the field line probability distribution function and finally the relationship of D-st with the maximum Lyapunov exponent of the system. Different perturbation spectra have been also considered and compared and the quasi-linear approximation has been tested.