Various regimes of cosmic ray diffusion in turbulent magnetic fields

Abstract

Charged particle transport in magnetized plasmas is one of the most important issues of plasma physics with a specific emphasis for magnetic confinement fusion, space physics and astrophysics. In Tokamak research, the understanding and the assessment of confinement performances have been hindered by the turbulence which induces complicated way of transporting the plasma energy to the machine walls. In cosmic ray research, turbulence plays also a major role for understanding transport and acceleration across galaxies and the heliosphere. In Tokamaks and cosmic ray physics, the transport induced by turbulent electric and magnetic fluctuations has been investigated by using theoretical works, numerical simulations and measurements. Between the two domains, cross fertilization examples are frequent. In the last decades, the diffusion induced by stationary magnetic fluctuations in a collisional plasma has been extensively studied as an exciting theoretical challenge as well as for fulfilling experimental needs. The results revealed a large variety of regimes with rather unexpected behaviors. This tutorial paper gives an elementary description of the identified mechanisms and tries to assess their interest for cosmic ray transport understanding.