The development of dielectric barrier discharges in gas gaps andon surfaces

Abstract

Dielectric barrier discharges (DBDs) occur in configurations whichare characterized by a dielectric layer between conducting electrodes. Twobasic configurations can be distinguished: a volume discharge (VD)arrangement with a gas gap; and a surface discharge (SD) arrangement withsurface electrode(s) on a dielectric layer and an extensive counter electrodeon its reverse side. At atmospheric pressure the DBD consists of numerousmicrodischarges (VD) and discharge steps (SD), respectively, their numberbeing proportional to the amplitude of the voltage. These events have a shortduration in the range of some 10 ns transferring a certain amount of chargewithin the discharge region. The total transferred charge determines thecurrent and hence the volt-ampere characteristic of each arrangement. Themicrodischarges (discharge steps) have a complicated spatial structure. Thedischarge patterns on the dielectric surface depend on the polarity and amplitudeof the applied voltage as well as on the specific capacity of the dielectric.Experimental findings on DBDs in air and oxygen are presented and discussed.On the basis of a self-consistent two-dimensional modelling the temporal andspatial development of a microdischarge and discharge step are investigatednumerically. The results lead to an understanding of the dynamics of DBDs.Although in VD arrangements cathode-directed streamers appear especially inelectronegative gases, their appearance is rather unlikely in SD arrangements.The application of DBDs for plasma-chemical reactions is determined by theproductivity, with which the energy of the electric field can be converted intointernal states of atoms and/or molecules. Depending on the desired product itcould be both the generation of internal electronic states of molecules oratoms and dissociation products of molecules. The discharge current andcurrent density of DBDs in both the SD and VD arrangements as well as the energyrelease and energy density distribution in the discharge region are presented.As an example the effectiveness of the energy conversion into ozone productionis detailed. Some peculiarities of the discharge parameters, for instance thecorrelation between discharge patterns (microdischarges or discharge steps)and surface charge density, are discussed.