Systematic Investigation Of The Pulsed Barrier Discharges In Flowing And Stationary Gas: From Differences To Similarities

Pulsed dielectric barrier discharges in flowing and stationary helium at atmospheric pressure are comparatively studied. The discharges are generated in plane-parallel configuration and driven by positive voltage pulses. The intensified charge coupled device imaging and electrical measurements are used for temporally, spatially, and spectrally resolved discharge emission. The populations of excited states are investigated by optical emission and absorption spectroscopy. The discharge operating in flowing helium is characterized by a single current pulse per each voltage flank and a "residual current peak." In stationary helium or in flowing helium with low velocity (<10cm/s), multiple current pulses are observed. The appearance of the subsequent current pulse(s) is related to the disappearance of the "residual current peak." Besides these differences between the two discharge regimes, some similarities are also registered. The maximum emission intensity is reached at the cathode, even for the subsequent current pulses formed in stationary helium, confirming the generation of the glow and multi-glow discharges. Also, the most important similarities between the discharges working in stationary helium and in flowing gas mixture, in relation to flowing helium mode, are discussed. Finally, the subsequent current pulses formed in multi-glow discharges are due to re-ignition of the discharge dominantly by direct electronic excitation and ionization processes, not by Penning ionization, because of the decrease in metastable atoms density and their lifetime. In addition, the metastable lifetime reaches a critical value, for which the discharge transits from glow to multi-glow mode, when the gas velocity or its composition changes.