The Nonlinear Guiding Center Theory

Abstract

In the previous chapter, it has been demonstrated that, in most cases, a quasilin- ear description of cosmic ray transport is not accurate and is invalid for at least some parameter regimes or turbulence models. In this chapter, previous nonlinear transport theories are discussed. As a representative of the theories that have been developed in the 1970s of the previous century, we discuss the nonlinear closure approximation that has been derived to describe 90ý-scattering and to solve the problem of perpendicular transport. Also the Bieber and Matthaeus model is dis- cussed that has been developed to describe perpendicular diffusion and drifts of charged particles. More recently, the so-called nonlinear guiding center theory has been formulated to describe perpendicular diffusion, in agreement with test-particle simulations. After discussing the basic assumption of this advanced diffusion the- ory, we consider a comparison with computer simulations and we discuss analytical forms of the perpendicular mean free path.