Transition from Townsend Toglow Modes in Atmospheric Dielectric-Barrier Discharges

Summary form only given. Atmospheric pressure glow discharges (APGD) have a homogeneous and diffuse appearance over a large range of the discharge current density. This is sometimes translated into a perception that plasma properties of APGD are very similar regardless their operation conditions, particularly the plasma power density and discharge current. Recently we have established that there exists at least two glow modes in radio-frequency APGD, namely the alpha mode and gamma mode of contrasting current-voltage characteristics. Secondary electron emission is found to be unimportant when the current density is below a critical value. In this contribution we consider different modes and their transition in a helium atmospheric glow discharge produced between two parallel and dielectrically insulated electrodes. Our approach is based on a hybrid APGD model with which electrons are treated kinetically and heavy particles are treated hydrodynamically. Our numerical study suggests that different modes indeed exist in helium atmospheric dielectric-barrier discharges and their current-voltage characteristics change markedly when they evolve from the Townsend mode to glow mode. Different from radio-frequency APGD, secondary electron emission is found significant throughout the entire range of the discharge current density from the low-current Townsend mode to the high-current end of the glow mode. Discussion is presented to unravel mechanisms in mode transition in atmospheric dielectric-barrier discharges and possible reasons responsible for the difference in their mode structure from that of RF APGD