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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Diffusion of energetic particles in focusing fields
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Diffusion of energetic particles in focusing fields

机译：高能粒子在聚焦场中的扩散

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We address the modification of the effective spatial diffusive coefficient of energetic charged particles in magnetic field configurations where the divergence of the field lines and the consequent weakening of the field strength lead to adiabatic focusing. Particles propagating along the magnetic field lines and undergoing pitch angle scattering and adiabatic focusing are considered. In the presence of significant focusing the conditions for the applicability of a diffusive description are not strictly valid, thus focusing modifies the effective parallel diffusion coefficient kappa(parallel to). We calculate the appropriate spatial diffusion coefficients from a method based on the use of adjoint Green functions. The correspondence between this method and the method based on the velocity correlation function < v(i) (0) v(j) (t) > developed by Kubo [1957] is discussed. We target the modulation of galactic and anomalous cosmic rays, which can be best approximated by the assumption of a constant, or slowly varying, spatial gradients, for which the method of adjoint Green functions is most suitable. We show that this assumption leads to an effective kappa(parallel to) identical to that derived by Bieber and Burger [1990] from a Born approximation. The derivation also results in a nonsteady analytical solution to the Fokker-Planck equation, which describes a distribution of constant spatial gradient moving at a constant speed. We also discuss the case of hemispherical scattering, when scattering is effective within each of the mu < 0 and mu > 0 hemispheres (where mu is the cosine of pitch angle) but is restricted between the two hemispheres. A refinement to the hemispherical equation of Isenberg [1997] and Schwadron [1998] is suggested. [References: 28]
机译：我们讨论了磁场配置中高能带电粒子的有效空间扩散系数的修改，其中磁力线的发散和随之而来的场强减弱导致绝热聚焦。考虑沿着磁场线传播并经历俯仰角散射和绝热聚焦的粒子。在存在显着聚焦的情况下，扩散描述的适用条件并非严格有效，因此聚焦会修改有效的平行扩散系数kappa（平行于）。我们根据一种基于伴随格林函数的方法来计算适当的空间扩散系数。讨论了该方法与Kubo [1957]开发的基于速度相关函数的方法之间的对应关系。我们以银河系和反常宇宙射线的调制为目标，这可以通过假设恒定或缓慢变化的空间梯度来最佳地近似，对于这种梯度，最适合使用格林函数的方法。我们表明，这种假设导致有效的kappa（平行）与Bieber和Burger [1990]从Born近似推导的结果相同。该推导还导致了Fokker-Planck方程的非稳态解析解，该方程描述了以恒定速度运动的恒定空间梯度的分布。我们还讨论了半球散射的情况，当散射在mu <0和mu> 0半球（其中mu是俯仰角的余弦值）中的每个半球内有效但被限制在两个半球之间时。提出了对Isenberg [1997]和Schwadron [1998]的半球方程的改进。 [参考：28]

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