对高能粒子扩散理论NLGC-E的系数研究

A Study of the Coefficient a^2 in the Extended Nonlinear Guiding Center Theory

带电粒子的扩散机制一直被认为是天体物理学的一个很重要的问题.最近,Matthaeus等人在2003年得出了带电粒子垂直扩散的非线性引导中心理论(NLGC),该理论采用平行扩散系数作为一个输入,这个NLGC理论与数值模拟结果符合得比较好.另外,Qin在2007年得到了非线性的平行扩散理论(NLPA),这个理论如果与NLGC理论联立可以得到扩展的非线性引导中心理论(NLGC-E),该理论是两个积分方程的形式并且可以用来同时求出平行和垂直扩散系数.NLGC理论中有一个系数a^2,通过与数值模拟结果比较选定最佳值为1/3.尝试改变NLGC-E中的系数a^2,确定与模拟结果吻合最好的系数值.

The diffusion mechanism of charged particles is one of the very important problems in astrophysics. Recently, Matthaeus et al. （2003） developed a nonlinear guiding center theory （NLGC） of the perpendicular diffusion of charged energetic particles with the parallel diffusion coefficient as an input. This theory agrees with the numerical simulations very well. In addition, Qin （2007） developed a nonlinear parallel diffusion theory （NLPA） following the idea of NLGC. Combined the NLGC with the NLPA, a new theory, NLGC-E is developed to solve the parallel and perpendicular diffusion coefficients simultaneously. In the NLGC, there is a coefficient a2 taken as 1/3 to best agree with the numerical simulations. In this work we have tried different values of a2 to obtain the best one for the NLGC-E to agree with the numerical simulations.