The Fokker-Planck description in the context of the quasilinear theory

The assumptions underlying the Fokker-Planck description are reviewed. The usual computation of the Fokker-Planck coefficients is shown to be incorrect in the case where the random force statistical properties strongly deviate from Gaussian. The consequences concerning the statistical description of charged particles moving in a fluctuating electric field are described in the context of the quasilinear theory. (orig.)