静磁turbulence中的俯仰角散射。II。分析考虑和俯仰角各向同性
Pitch-angle scattering in magnetostatic turbulence. II. Analytical considerations and pitch-angle isotropization
摘要：
目标。俯仰角各向同性的过程对于从扩散激波加速到大尺度宇宙射线输运的许多应用都很重要。在这里，基本的分析描述的基础上重新审视最近的模拟结果。方法.对俯仰角散射的Fokker-Planck方程进行了分析和数值研究。附加的测试粒子模拟得到的帮助下，蒙特卡洛代码被用来验证的结论。结果结果表明，通常通过均方位移定义的俯仰角福克-普朗克系数是有缺陷的。其原因可以追溯到时间均匀性的假设，这不适用于俯仰角散射。结论.通过Fokker-Planck系数计算平均自由程经常被证明可以给出准确的描述。因此，为了数值的目的，必须将定义交换为有利于俯仰角关联函数。
英文摘要：
Aims. The process of pitch-angle isotropization is important for many applications ranging from diffusive shock acceleration to large-scale cosmic-ray transport. Here, the basic analytical description is revisited on the basis of recent simulation results. Methods. Both an analytical and a numerical investigation were undertaken of the Fokker-Planck equation for pitch-angle scattering. Additional test-particle simulations obtained with the help of a Monte-Carlo code were used to verify the conclusions. Results. It is shown that the usual definition of the pitch-angle Fokker-Planck coefficient via the mean-square displacement is flawed. The reason can be traced back to the assumption of homogeneity in time which does not hold for pitch-angle scattering. Conclusions. Calculating the mean free path via the Fokker-Planck coefficient has often proven to give an accurate description. For numerical purposes, accordingly, it is the definition that has to be exchanged in favor of the pitch-angle correlation function.
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