The Fokker-Planck operator as an asymptotic limit in anisotropic media

We derive the Fokker-Planck operator describing a highly forward-peaked scattering process in the linear transport equation, in anisotropic media, as a formal asymptotic limit of the exact integral operator. The resulting operator, being both convective and diffusive in angle and energy variables, reduces the degenerate nature of the Fokker-Planck system compared to the isotropic media case where the corresponding limit is only convective in energy and diffusive in angle.