Study Of The Cosmic Ray Energetic Particles’ Diffusion Coefficient

Solar energetic particles’ diffusion mechanism in interplanetary is one of the veryimportant problems in the astrophysics, but also require in-depth understanding of knowledgein space weather research. Parker was first introduced in1965, focusing equation to study theproblem of the propagation of solar energetic particles. In general, use the analytical approachfor solving the propagation equation of charged particles is very difficult, we generally takethe numerical solution of particle propagation equation. Jokipii proposed the classicquasi-linear theory, that perpendicular diffusion coefficient often much smaller than paralleldiffusion coefficient, therefore, in the line of propagation in the interstellar previous studies ofsolar energetic particles, often the perpendicular diffusion coefficient can be ignored.However, recent studies show that perpendicular diffusion can be compared with paralleldiffusion. And taking into account the nonlinear effect of magnetic field fluctuations cancause large perpendicular diffusion. Especially, Matthaeus et al.(ApJ2003) developed anonlinear guiding center theory (NLGC) of perpendicular diffusion of charged energeticparticles with parallel diffusion coefficient as an input, which agrees with numericalsimulations. In addition, Qin (ApJ2007) developed a nonlinear parallel diffusion theory(NLPA) which if combined with NLGC could be used to solve parallel and perpendiculardiffusion simultaneously. However, both of the NLGC and NLPA are in the forms of integralequation and not easy to be adopted in cosmic ray transport models.The first part of this thesis is regarding in the NLGC there is a coefficient a2to be takenas1/3to best agree with numerical simulations. In this work we try different value of a2totest the best one for the NLGC-E to best agree with numerical simulations.The second part of this thesis that Zank et al.(JGR2004) provided an approximatesolution of NLGC. The solution agrees with the exact solution of the NLGC results very well.In this work we will adopt the similar method from Zank et al.(2004) to approximatelysolve the NLPA (Qin2007) so that the solution of both parallel and perpendicular nonlinear diffusion coefficients can be included in numerical codes for cosmic rays transportsimultaneously.