Density fluctuation in Tokamaks

Explaining the features of turbulent fluctuation spectra from fundamental theory is a very difficult task at present. Linear theory is useful when the instability sets in, but present experiments are not designed to investigate the transition to turbulence, but simply to study the properties of the turbulent state itself. Therefore, it is generally difficult to state which instabilities are responsible of the observed state. More over the theory of saturated turbulence seems itself not enough developped to give quantitative answers. In this work a phenomenological approach is pointed out. An attempt is to describe fluctuations around the observed (average) state by means of some equation for the fluctuating part of the density n(r,t). More precisely, essentially the power law behavior of correlation functions at large frequency and wavenumber is considered