Studies of the particle diffusion coefficient in the fluctuating magnetic field by the direct-interaction approximation

Abstract

The particle diffusion in a stochastic magnetic field is investigated by using the functional integral method. With the ensemble average of a functional representation to a kinetic equation over the fluctuating magnetic field and the random variables modeling the Coulomb collisions. a closed set of equations for an ensemble-averaged distribution function and a response function to an infinitesimal external perturbation is derived within the framework of the direct-interaction approximation (DIA). By using the Markovian approximation to the equation for the response function, the cross-field diffusion coefficients are found to be obtained from nonlinear ordinary differential equations. Explicitly calculated diffusion coefficients for various parameters are also shown in the shearless and sheared configurations.