An Angular Multigrid Acceleration Technique for S_n Equations with Highly Forward-Peaked Scattering

An angular multigrid method for the S_n equations has been developed that is much more effective for highly forward-peaked scattering than the diffusion synthetic acceleration (DSA) method. Only one-dimensional slab geometry is considered in this study, but it appears that this method can be generalized to curvilinear and multidimensional geometries. The new method is derived, theoretically analyzed, and computationally tested. The angular multigrid method costs only about twice as much as the DSA method, but it gives a spectral radius of 0.6 in the asymptotic forward-peaked Fokker-Planck scattering limit, whereas the diffusion synthetic method gives a spectral radius of unity.