Electron losses in hypersonic flows

Abstract

The first comprehensive study of electron gains and losses in hypersonic air flows including the full coupling between non-neutral plasma sheaths and quasi-neutral plasma flows is presented here. This is made possible by the use of advanced numerical methods that overcome the stiffness associated with plasma sheaths. The coupling between the sheaths, the electron temperature in non-equilibrium, and the ambipolar diffusion within quasi-neutral plasma flows is found to be critical to accurately predict electron losses and, thus, the plasma density around hypersonic vehicles. This is because electron cooling arising from the non-neutral sheaths significantly affects the electron temperature everywhere in the plasma and, therefore, the electron temperature-dependent loss processes of ambipolar diffusion and dissociative recombination. The results obtained show that electron loss to the surface due to catalyticity dominates over electron loss within the plasma due to dissociative recombination either (i) at high altitudes where the dynamic pressure is low, (ii) at low Mach number, or (iii) when the vehicle has a sharp leading edge.