Ion composition of expanding microdischarges in dielectric barrier discharges

The properties of the filamentary microdischarges found in dielectric barrier discharges depend on the manner of charging of the dielectric. The charging of the dielectric removes voltage from the gap thereby reducing E/N and producing a transition from an avalanching discharge to a recombination or attachment dominated discharge. In this article, we report on a computational investigation of these processes using a one-dimensional plasma chemistry model. We find that the expansion and ultimate stalling of the microdischarge is largely determined by charging of the dielectric at larger radii than the core of the microdischarge. The lowering of E/N in the core of the microdischarge in attaching gases can quickly consume electrons. This transition produces a discharge consisting of an expanding shell having a high electron density and an inner core dominated by negative ions. In extreme cases where the gas mixture contains thermal electron attaching gases, the core of the microdischarge is essentially a negative ion-positive ion plasma. Using square wave voltage pulses, the residual charge on the dielectric after the microdischarge, which contributes to the gap voltage on the next voltage pulse, is largely determined by the attachment rate in the core of the microdischarge. Rapid attachment reduces the plasma conductivity and leaves residual charge on the dielectric. © 1998 American Institute of Physics. @S0021-8979~98!00212-6#