Gil Shohet, Stanford University

Photo of Gil Shohet

Meteoroids and dust routinely bombard objects in space, such as spacecraft and small solar system bodies, and orbital debris also threaten spacecraft in Earth orbit. Such impacts are termed hypervelocity because they occur at velocities greater than the material acoustic speeds, resulting in hydrodynamic behavior. Strong shock waves compress and heat the projectile and target materials, converting kinetic energy to internal and thermal energy and leading to fracturing, melting, vaporization, ionization and cratering. As the partially ionized gas and condensed phase debris expand into the vacuum, plasma oscillations and instabilities produce electromagnetic emissions that threaten spacecraft electronics. Charge attachment to the condensed phase may lead to electron depletion, charge separation, long-range fields, and dusty plasma effects. The research presented examines dust charging in hypervelocity impact plasmas using a combination of experimental observations and dust simulations. First, experimental data from a 2019 light gas gun impact campaign are used to compute the particle size distribution of impact debris and provide evidence of dust charging. Second, we extend orbital motion limited (OML) theory to develop a dust charging and dynamics framework for high energy density (HED) environments. Third, we combine experimental data with the dust evolution model to probe interactions between dust and the impact environment, paying particular attention to quantifying and propagating measurement and model uncertainties. Simulations suggest significant charge depletion occurs in the debris plume shortly after impact. Dust charging depends strongly on initial and environmental conditions, such as the neutral background present in many ground-based facilities. The model predicts transit times and dust charge consistent with plasma measurements. Thermionic emission from impact debris likely explains observations of positively charged debris in light gas gun experiments. This work serves as a starting point for analyzing dust charging in impact plasmas and analogous HED environments, such as laser ablation plasmas.

Abstract Author(s): Gil Shohet, Sigrid Close