Impact of Ion Mobility on Electron Density and Temperature in Hypersonic Flows

Abstract: This study provides the first comprehensive analysis of how ion mobility affects electron density and temperature in hypersonic flows. We compare two ion mobility models: one derived from Gupta-Yos cross-sections, and the other from swarm drift velocity experiments. The ion mobility model significantly alters the plasma density around a hypersonic waverider, with increases of more than twofold observed at low dynamic pressures and high Mach numbers. This is partly due to electron loss through surface catalysis, which depends on ambipolar diffusion scaling with ion mobility. We also derive novel scaling laws that highlight the strong dependence of electron cooling on ion mobility both within the quasi-neutral regions and the non-neutral plasma sheaths. Electron cooling influences the electron temperature across the plasma, leading to a previously unrecognized impact of ion mobility on plasma bulk temperature. This in turn affects plasma density via electron-ion recombination rates which are temperature-dependent. Accurately modeling ion mobility is critical for predicting hypersonic plasma behavior, with important implications for optimizing magnetohydrodynamic technologies and mitigating or exploiting plasma-induced interference with electromagnetic waves.