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 ioni zed gases at low E/N values (E being the electric field and N the back ground gas density). The dominant low energy collisional processes (el astic, inelastic, and superelastic collisions) are properly considered . The influence of the thermal motion of background gas (target not as sumed 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 atomi c (He) and molecular (H2O) gases. Then, the present Monte Carlo method is adapted to the low E/N cases in strongly electronegative gases suc h 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 frequ ency is considered to obtain hydrodynamic electron swarm parameters in SF6 at low E/N.