A low-temperature plasma collisional framework for quadrature-based moment methods

Abstract

The mathematical framework for elastic and inelastic collisions for quadrature-based moment methods (QBMM) is developed and validated for low-temperature collisional plasma physics problems represented by the Boltzmann equation. QBMM are more computationally expedient than direct Eulerian solvers and are able to provide a noise-free solution to the Boltzmann equation, as well as capture non-equilibrium velocity distribution functions (VDF). Closure for QBMM is provided by considering that the VDF is a sum of weighted kernel functions placed at discrete velocity abscissas. For all plasma particles (electrons, ions, and neutrals), expressions for the reaction integrals within the QBMM framework are derived and generalized to an arbitrary moment order for elastic collisions represented by a BGK operator and inelastic collisions (ionization and excitation) represented by a Boltzmann operator. The accuracy of different QBMM to compute reaction integrals is discussed, and numerical solutions of the moment model are presented for multiple low-temperature plasma physics problems that feature both elastic and inelastic collisions. It is shown that the Extended Quadrature Method of Moments, which uses a sum of weighted continuous Gaussian kernels, is most advantageous to compute reaction integrals. Good agreement with results from the literature is obtained for the evolution of the VDF and integrated moments, thus demonstrating that the QBMM collisional framework adequately captures the underlying physics of low-temperature plasmas.