Investigations on pulsed, dielectric barrier discharges in multi-filament arrangements

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Dielectric barrier discharges (DBDs) are a common method to generate non-thermal atmospheric pressure plasmas, which are used e.g. for chemical processing. The DBDs in molecular gas mixtures, such as nitrogen oxygen mixtures, are filamentary, i.e. they form individual and transient discharge channels. It was shown in various studies that the generation of reactive species is more efficient for pulsed operation than for classical sine-driven operation. Preliminary investigations of the applicant concerning pulsed-driven DBDs in a single-filament arrangement have demonstrated that the breakdown and the discharge development can be directly controlled by the HV pulse width (pre-ionisation). In particular, new, up to now unknown DBD breakdown regimes were reported for the first time.Having in mind that the plasma-chemical reactions are triggered by the physical processes within single filaments, there is the possibility to influence the plasma parameters in a way to initiate more selective and effective plasma chemical processes. In DBD arrangements which are used in practice, many filaments occur, but it is not known if the results obtained for a single filament can be transferred to multi-filament arrangements. Therefore, open questions not only concern the electrical breakdown in the gap, but also the interacting impact of volume and surface processes in multi-filament arrangements. The goal of this project is to address and resolve these issues.Therefore, the stepwise transition from a single-filament to a multi-filament arrangement will be performed. For this purpose, novel and special, spatially fixed and free multi-filament arrangements will be developed using our expertise concerning the design of DBD configurations. There will be a systematic study on the behaviour of a single filament in multi-filament arrangements in N2-O2 gas mixtures at atmospheric pressure. The comparison of both single- and multi-filament operation will allow statements concerning the existence of general mechanisms to control the breakdown and the dynamics of DBDs. Furthermore, the interaction of single discharge channels in the volume and on the dielectric surface will be investigated. The aim is to clarify if the dominating effect of volume pre-ionisation for single-filament arrangements occurs also in multi-filament arrangements. For these investigations, fast imaging and spectroscopical diagnostics will be used, which were established during the applicant’s preliminary work and are available at the INP Greifswald. Simultaneously, temporally resolved gas analysis methods will be applied to study the dynamics of plasma-chemical processes. In combination with the DBD characterisation, a correlation of discharge physics and plasma chemistry will be worked out. The experimental investigations will be accompanied by plasma modelling, which includes the simulation of the spatio-temporal discharge development, plasma parameters and plasma chemistry.