Characteristics Of Distribution Function in a Time-Dependent Velocity Diffusion Process

The time-dependency of the particle velocity diffusion m plasma turbulence has been discussed by various theoretical models and shown in the test-particle computer simulations [1]-[4]. The non-Markovian effects are responsible for the time-dependent nature of the diffusion coefficient that deviates far from the quasilinear value at a moderately strong turbulence level in Langmuir turbulence [5]. Under the assumption of Gaussian turbulent fields, the non-Markovian effects were discussed by treating the particle velocity as a Wiener process. The memory property appears in the spatial increment of particle trajectory as well as in the term of retarded effective turbulent friction in the generalized Langevin equation [5]. We further study such a non-Markovian behavior in velocity diffusion by introducing the non-Gaussian nature in turbulent fields. This modification leads to a deviation of probability distribution function of particle velocity from the Gaussian distribution. The effect of non-Gaussian turbulent fields on the particle diffusion coefficient is discussed in detail.