宇宙プラズマ中の荷電粒子の「超」拡散

*羽田 亨[1]

九州大学大学院総合理工学研究院[1]

Super-diffusion of energetic particles in a space plasma

*Tohru Hada[1]
E.S.S.T., Kyushu University[1]

Diffusive transport of charged particles in a collisionless plasma is one of the central issues in space plasma research. Most of the conventional arguments are based on a classical diffusion model, a second order linear diffusion equation with a prescribed diffusion coefficient. However, recent progress in spacecraft observations as well as numerical simulation studies imply that several essential modifications are necessary to the model. In particular, the use of the Levy statistics appears to be indispensable, in which the transport properties have explicit dependence to relevant spatial and temporal scales. This is a direct consequence of that (1) the observed MHD turbulence in space has large amplitude and (2) the MHD waves have finite phase coherence.

After a brief introduction of the Levy statistics, we will introduce the so-called fractional Fokker-Planck equation to describe time evolution of the ensemble of particles, and then we will show some numerical examples to relate the model to numerical simulation studies of various transport phenomena.