Ionizing Shocks in Argon. Part 1: Collisional-Radiative Model and Steady-State Structure (Preprint)

摘要

A detailed collisional-radiative model is developed and coupled with a single-fluid, two-temperature convection model for the transport of shock- heated argon. The model is used in a systematic approach to examine the effects of the collision cross sections on the shock structure, including the relaxation layer and subsequent radiative-cooling regime. We present a comparison with previous experimental results obtained at the University of Toronto and the Australian National University, which serve as benchmarks to the model. It is shown that ionization proceeds via the ladder-climbing mechanism and is dominant from the upper levels as compared to the metastable states. Taking this into account, the present model is able to accurately reproduce the metastable populations in the relaxation zone measured in previous experiments, which is not possible with a two-step model. Numerical results of the radiative-cooling region are in close agreement with experiments and have been obtained without having to consider radiative transport. In particular, spontaneous free-bound emission to the upper levels together with Bremsstrahlung emission account for nearly all radiative losses; all other significant radiative processes, resulting in a transition into the groundstate, are mostly self-absorbed and have a lesser impact.