# Perpendicular and parallel diffusion coefficients of energetic charged particles in the presence of adiabatic focusing [CL]

Understanding stochastic diffusion of energetic charged particles in non-uniform background magnetic field is one of the major problems in plasmas of space and fusion devices. In this paper by using the improved perturbation method developed by He \& Schlickeiser starting from the modified Fokker-Planck equation of energetic charged particles we derive an isotropic distribution function equation with the infinite self-iteration of anisotropic distribution function $g(\mu)$. And then a new perpendicular and parallel diffusion coefficients are obtained which include the infinite self-iteration effect. It is demonstrated that the form of perpendicular diffusion coefficient is form-invariable for the infinite self-iteration effect, but the parallel diffusion coefficient is modified by it. And for simplification by using the simple pitch-angle diffusion model $D_{\mu\mu}=d$ ($d$ is a constant) we find that the modifying factor to parallel diffusion coefficient coming from the infinite self-iteration effect need to be considered at least for the simple model. We also find that the parallel diffusion coefficient derived in some previous papers is the special case of which is obtained in this paper.

J. Wang and G. Qin
Tue, 13 Feb 18
57/76