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

概要

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We study non-classical diffusion of energetic particles using a simple 2-d cross field diffusion model. Important parameters are ratio of typical particle Larmor radius ρ to the field correlation length L. In our model, when ρ/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. We numerically evaluate the statistics of field islands such as probability density function of mean radius and fractal dimension of field islands, depending on power-law index of field turbulence spectrum. In our model, both super-diffusion (for finite time scale) and sub-diffusion can take place. We find numerically and analytically the scaling law of the diffusion coefficient using the parameters obtained by field islands statistics.
九州大学の論文