Richard June Espino Abrantes

Resolving radiation transport fields subject to opacity profiles with strong, oscillatory line structure while potentially falling under intermediate optical depth conditions presents a numerical challenge in radiation transport modeling. The Young measure-based homogenization technique formulated by Haut et al. (2017) was investigated as a candidate method for resolving radiation fields under such conditions more accurately. The method was compared against frequently-utilized mean opacity methods as the Rosseland and Planck formulations. In this work, all methods were tested through radiation slab calculations separately comprised of aluminum, copper, and krypton, each for different thermodynamic conditions. Following these offline radiation slab calculations, demonstrations shifted towards the SCEPTRE radiation transport code and, subsequently, the multiphysics ALEGRA code for approximately-coupled radiation-material simulations. Throughout all the simulations shown in this study, for a fixed computational cost, the homogenized method was observed to be more accurate than any of the solutions determined through traditional mean opacity approaches.

Collisional rate calculations which account for relative multifluid streaming were implemented in a collisional-radiative model that is applicable for a generalized set of atomic elements. The rate modifications for multifluid streaming were derived in two recent studies for electron-impact excitation, de-excitation, ionization, and recombination [H. P. Le and J.-L. Cambier, Phys. Plasmas 22, 093512 (2015); 23, 063505 (2016)]. This study follows from the previous studies by extending the derivations to radiative recombination. However, the memory intensive aspect of expanding the collisional rate tabulations to temperature and multifluid effects can become a numerical obstacle for large-scale plasma simulations. The main objective of this study is to explore reduced-order modeling approaches for collisional-radiative systems that may adopt collisional rate accounting for multifluid streaming. The ionization test case simulated in this work uses the quasi-steady-state solution and two Boltzmann grouping approaches, one of which is the ionic excitation concept and the other being a relatively finer selection of Boltzmann groups. The reduced-order models captured the general trend of the detailed model, providing a foundation from which to improve or perform coupled plasma simulations in the future.