Ionization of Hypervelocity Impact Iron Plasmas via a Monte Carlo Collision Model

Hypervelocity impacts (HVI) are impacts from objects in the space environment (e.g. orbital debris or mi-crometeoroids) that strike a target with a velocity greater than the speed of sound of the material. These impactors can be as small as a micron, have velocities between 11–72 km/s, and have kinetic energy high enough to ablate material upon impact, forming plasma. Understanding the physics behind this phe-nomenon is important in being able to prevent electrical damage on spacecraft. Unfortunately, the chem-istry and reactions governing plasma production are not well understood. Previous computational studies utilized smoothed-particle hydrodynamics to model the multiphysics nature of this phenomenon (A. Fletcher, S. Close, D. Mathias, “Simulating plasma production from hypervelocity impacts,” Phys. Plas-mas, 2015). However, the model treats plasma as a singular fluid, neglecting the dynamics of individual species (positively-charged ions and electrons) and is unable to investigate individual reaction mechanisms. This work aims to investigate the mechanisms behind iron plasma production from HVI femtoseconds after impact using a OD3V Monte Carlo Collision (MCC) null-collision algorithm. This efficiently samples a subset of macroparticles and calculates their probability of undergoing a certain reaction, such as electron-impact ionization and elastic scattering (V. Vahedi and M. Surendra, “A Monte Carlo collision model for the particle-in-cell method: applications to argon and oxygen discharges,” Comput. Phys. Commun., 1995).