Parallel and Perpendicular Diffusion Coefficients of Energetic Charged Particles with Adiabatic Focusing

It is very important to understand stochastic diffusion of energetic charged particles in the nonuniform background magnetic field in plasmas of astrophysics and fusion devices. Using different methods considering an along-field adiabatic focusing effect, various authors derived a parallel diffusion coefficient kappa(parallel to) and its correction T to kappa(parallel to 0), where kappa(parallel to 0) is the parallel diffusion coefficient without an adiabatic focusing effect. In this paper, using the improved perturbation method developed by He & Schlickeiser and iteration process, we obtain a new correction T' to kappa(parallel to 0). Furthermore, by employing the isotropic pitch-angle scattering model D-mu mu( =) D(1-mu(2)), we find that T' has a different sign from that of T. In this paper, the spatial perpendicular diffusion coefficient kappa(perpendicular to) with the adiabatic focusing effect is also obtained.