Fluctuations and Correlations in tokamak plasmas

The relation between stationary fluctuations of equilibrium states and irreversible processes is described. The wave-number dependence of spatial correlations in homogeneous systems is obtained from Einstein distribution, and the mean square of fluctuations is then calculated. Using the fluctuation-dissipation theorem and a convective diffusion equation, the power spectrum and auto-correlation function are computed. The results are compared with the observed plasma density fluctuations in tokamak experiments.