Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsh23a..01l&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #SH23A-01
Physics
2104 Cosmic Rays, 2149 Mhd Waves And Turbulence (2752, 6050, 7836), 7839 Nonlinear Phenomena (4400, 6944), 7859 Transport Processes, 7867 Wave/Particle Interactions (2483, 6984)
Scientific paper
With the aid of particle simulations it was discovered that standard quasi-linear theory (QLT) cannot adequately describe the parallel and perpendicular diffusion of cosmic rays in 3D MHD solar wind turbulence, when the turbulence is modeled to a first approximation as a static combination of a dominant 2D component and a minor slab component. Recent non-linear theories based on a Taylor-Green-Kubo (TGK) formalism, such as the non- linear guiding center (NLGC) theory, and the weakly non-linear theory (WNLT) that uses assumptions consistent with extended QLT, proved to be much more successful because it takes into account the transverse diffusive motion of the particle guiding center as it follows a random field with a strong 2D component transverse to the mean field. Instead, we follow a BGK- Boltzmann approach (extended QLT) to investigate the non-linear diffusive transport of cosmic rays in combined 2D and slab MHD turbulence. Going beyond current NLGC theory and WNLT in scope, we derived a complete cosmic-ray transport theory that includes not only non-linear coupled expressions for parallel and perpendicular diffusion, but also drift, convection, adiabatic energy change and momentum diffusion transport coefficients. The BGK-Boltzmann approach enables one to derive tractable yet complicated expressions for all transport coefficients in both the weak and strong particle scattering limits. It will be shown that the WNLT for coupled parallel and perpendicular diffusion can be recovered by combining these two limits in such a way that there is weak particle scattering along the field but strong particle scattering across the magnetic field. The complexity of the WNLT expressions can be reduced to simple analytical expressions of parallel and perpendicular diffusion that reproduces well the rigidity dependence of particle simulations at low to medium rigidities. These expressions also prove to be consistent with well-known expressions for perpendicular diffusion in the literature. It is also discussed how large-scale gradient and curvature drifts get modified by turbulence and how stochastic particle acceleration changes when 2D turbulence is dominant.
le Roux Jakobus A.
Webb Gary M.
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