2次元磁場ゆらぎ中での高エネルギー荷電粒子の非古典拡散

Abstract

Non-classical diffusion of energetic particles is studied using a simple 2-d cross field diffusion model. Important parameter is ratio of typical particle Larmor radius (rho) to the field correlation length (L). In the model, when rho/L is infinitesimally small, the particles essentially gradient-B drift along equi-contour lines of the magnetic field strength, and thus the diffusion in this parameter regime can essentially be understood by analyzing statistics of magnetic field islands composed of these equi-contour lines. The statistics of field islands such as probability density function of mean radius and fractal dimension of field islands are numerically evaluated, depending on power-law index of the magnetic field turbulence. In the model, both super-diffusion (for finite time scale) and sub-diffusion can take place. The scaling law of the diffusion coefficient is found numerically and analytically using the parameters obtained by field islands statistics.