Numerical simulation of neutral gas release experiments in the ionosphere

A two-and-one-half-dimensional electrostatic particle simulation model has been developed to study neutral gas release experiments into the ionosphere. The electrons are assumed guiding center particles, while the full dynamics of the ions (with real masses) are followed in time and space. Ionization processes of the neutral gas by charge exchange and electron impact are included by means of the Monte Carlo technique. It is shown that the model can be used to simulate the neutral gas interaction, with the ionosphere using realistic experimental parameters. The model was applied to study the critical ionization velocity (CIV) tests recently conducted as part of the ATLAS-1 [Geophys. Res. Lett. 20, 499 (1993)] xenon gas releases from the space shuttle. The simulation results show suprathermal electrons produced by an ion beam-driven lower hybrid instability, create a xenon ion population much more rapidly than the production by classical processes, indicating the prevalence of a CIV-type mechanism