Mixed-hybrid discretization methods for the linear Boltzmann transport equation

The linear Boltzmann transport equation is discretized using a finite element technique for the spatial variable and a spherical harmonic technique for the angular variable. With the angular flux decomposed into even- and odd-angular parity components, mixed-hybrid methods are developed that combine the advantages of mixed (simultaneous approximation of even- and odd-parity fluxes) and hybrid (use of Lagrange multipliers to enforce interface regularity conditions) methods. An existence and uniqueness theorem is proved for the resulting problems. Beside the well-known primal/dual distinction induced by the spatial variable, the angular variable leads to an even/odd distinction for the spherical harmonic expansion order.