Three temperature plasma shock solutions with gray radiation diffusion

TL;DR

This paper investigates plasma shock structures influenced by gray radiation diffusion, revealing different temperature regimes and coupling behaviors, and validates steady-state solutions as effective tests for multi-physics simulations.

Contribution

It introduces a comprehensive analysis of plasma shock solutions with gray radiation diffusion, including three-temperature and two-temperature regimes, and demonstrates their use in verifying multi-physics numerical algorithms.

Findings

Three-temperature plasma shock solutions in optically thin conditions.

Two-temperature behavior when radiation flux is significant but pressure is negligible.

Strong coupling of all components when radiation pressure dominates.

Abstract

The effects of radiation on the structure of shocks in a fully-ionized plasma are investigated by solving the steady-state fluid equations for ions, electrons, and radiation. The electrons and ions are assumed to have the same bulk velocity but separate temperatures, and the radiation is modeled with the gray-diffusion approximation. Both electron and ion conduction are included, as well as ion viscosity. When the material is optically thin, three-temperature behavior occurs. When the diffusive flux of radiation is important but radiation pressure is not, two-temperature behavior occurs, with the electrons strongly coupled to the radiation. Since the radiation heats the electrons on length scales that are much longer than the electron-ion Coulomb coupling length scale, these solutions resemble radiative shock solutions rather than plasma shock solutions that neglect radiation. When radiation pressure is important, all three components are strongly coupled. Results with constant values for the transport and coupling coefficients are compared to a full numerical simulation with a good match between the two, demonstrating that steady shock solutions constitute a straightforward and comprehensive verification test methodology for multi-physics numerical algorithms.