Hypervelocity impacts generate transient, non-equilibrium plasmas whose ionization degree and energy distribution are critical for understanding micrometeoroid impacts and for engineering applications in space exploration. Previous numerical models have often assumed single-temperature equilibrium or embedded simplified ionization schemes directly into hydrodynamics, limiting their ability to capture the early non-equilibrium plasma state. Here, we employ a radiation-hydrodynamics framework that treats electron and ion temperatures separately and incorporates plasma-specific processes, such as thermal conduction, radiation transport, and electron–ion temperature exchange, directly into the governing equations. Ionization is then evaluated in a dedicated post-processing step with a Thomas–Fermi-based model applied to the realistic non-equilibrium plasma conditions produced by the simulation. The model successfully reproduces experimental trends in charge yield and ion temperature distributions across 20–45 km s−1 impacts of iron projectiles on rhodium targets. The velocity scaling shows excellent consistency, differing by only 1% and 0.5% from Ratcliff et al. Int. J. Impact Eng. 20, 663 (1997) and Burchell et al. Meas. Sci. Technol. 10, 41 (1999), respectively. These results demonstrate, for the first time, that the velocity dependence of impact-induced ionization can be quantitatively reproduced within a physically consistent two-temperature framework. By explicitly resolving non-equilibrium plasma physics and incorporating geometric effects, our approach achieves what earlier local thermal equilibrium-based or simplified equation of state models could not: a predictive and physically grounded description of impact ionization. This establishes a new modeling framework for interpreting measurable impact signatures in laboratory experiments and for extrapolating hypervelocity impact phenomena to space environments.
Nakazawa et al. (Wed,) studied this question.