Multiple microdischarge dynamics in dielectric barrier discharges

Dielectric barrier discharges (DBDs) are pulsed atmospheric pressure devices in which the plasma forms as an array of microdischarges having diameters expanding from 10 to 100's mu m and area densities of 10 to 100's cm(-2). The microdischarges are <10's ns in duration and are terminated by charging of the dielectric barrier which removes voltage from the gap. If microdischarges are spaced sufficiently close together they may interact during their expansion. In this article, we discuss results from a two-dimensional plasma hydrodynamics model for microdischarge development in DBDs with the goal of investigating the interaction between closely spaced microdischarges. We find that the efficiency of ionization is only moderately affected by microdischarges which expand into physical contact. The residual charge left on the dielectric following a current pulse can, however, significantly impact the spatial extent of the subsequent microdischarges. During expansion the underlying dielectric charges to progressively larger radii as the microdischarge expands. This leads to voltage collapse in the center of the microdischarge prior to the outer radius. In attaching gas mixtures larger rates of attachment relative to ionization at the lower values of the electric field/number density produce cores which are highly electronegative, surrounded by shells of higher electron density. (C) 1998 American Institute of Physics. [S0021-8979(98)07620-8].