An S 2 Nonlinear Acceleration Scheme for Particle Transport Calculations

We present a nonlinear acceleration scheme, S2NA, for particle transport calculations. The approach is conceptually similar to the coarse-mesh finite difference method, in which a nonlinear current correction factor is applied to a low-order equation. However, instead of using the diffusion equation, S2NA employs a low-order S2 discrete ordinates formulation. In this framework, the correction factor is computed independently for each ordinate, enabling improved consistency with the high-order transport solution. Fourier analysis and numerical experiments confirm that the scheme is unconditionally stable and exhibits rapid convergence across the full range of optical thicknesses, making it a robust and efficient acceleration technique for particle transport problems.