Electron and ion kinetics in a DC microplasma at atmospheric pressure

The results of a particle-in-cell Monte Carlo collision (PIC-MCC) simulation of a direct current (dc) helium microplasma that operates at atmospheric pressure are presented. Electron and ion kinetic information that is not available from previous fluid studies is reported. Despite the high collisionality at atmospheric pressure, electrons are found to be in nonequilibrium. Similar to large-scale low-pressure dc discharges, the electron energy probability function (EEPF) in the bulk plasma presents three temperatures near the cathode, and it evolves into a bi-Maxwellian distribution as electrons approach the anode. The bi-Maxwellian character of the EEPF in the elastic energy region is not accounted for in fluid models, and as a result, PIC-MCC simulations predict a lower electron temperature than fluid models. The mean energy of ions that are impinging on the cathode is found to be significantly lower than in low-pressure discharges due to the large collisionality of the sheaths.