In several astrophysical applications one needs analytical forms of cosmic-ray diffusion parameters. Some examples are studies of diffusive shock acceleration and solar modulation. In the current article we explore perpendicular diffusion based on the unified nonlinear transport theory. While we focused on magnetostatic turbulence in Paper I, we included the effect of dynamical turbulence in Paper II of the series. In the latter paper we assumed that the temporal correlation time does not depend on the wavenumber. More realistic models have been proposed in the past, such as the so-called damping model of dynamical turbulence. In the present paper we derive analytical forms for the perpendicular diffusion coefficient of energetic particles in two-component turbulence for this type of time-dependent turbulence. We present new formulas for the perpendicular diffusion coefficient and we derive a condition for which the magnetostatic result is recovered.

No abstract

No abstract

We explore analytically and numerically the motion of energetic particles such as electrons and protons through space. The electrically charged particles interact with a large scale or mean field B 0  and a turbulent component B d  leading to a complicated stochastic motion. This type of physical scenario is important in plasma physics as well as particle astrophysics. Years ago a quasi-linear theory for particle transport was developed and applied in hundreds of research papers. Whereas it became clear that quasi-linear theory does not work for the transport of energetic particles across a large scale field, it is still unclear for which parameter regimes the theory works if diffusion along that field is explored. In the current paper, we therefore combine quasi-linear theory with dynamical isotropic turbulence and different turbulence spectra. The obtained results are then compared with test-particle simulations. We show that in the general case, quasi-linear theory does not provide an accurate description of parallel transport for isotropic turbulence even if dynamical turbulence effects are included.

No abstract