Monte Carlo simulation of electron swarms at low reduced electric fields

A Monte Carlo method, based on the classical null collision technique, is developed and applied for electron swarm simulation in weakly ionized gases at low E/N values (E being the electric field and N the background gas density). The dominant low energy collisional processes (elastic, inelastic, and superelastic collisions) are properly considered. The influence of the thermal motion of background gas (target not assumed at rest) on electron kinetics, which can play an important role at very low E/N, is also taken into account. At zero field and low E/N conditions, the influence of low energy collision processes on space and time evolution of electron swarm parameters is emphasized in atomic (He) and molecular (H₂O) gases. Then, the present Monte Carlo method is adapted to the low E/N cases in strongly electronegative gases such as SF₆ to overcome the problem of the vanishing of seed electrons by attachment processes which can stop the simulation. In that case, an additional fictitious ionization process with constant collision frequency is considered to obtain hydrodynamic electron swarm parameters in SF₆ at low E/N.