The influence of gas flow rate on breakdown properties and stability of pulsed dielectric barrier discharges (DBDs) in a single filament arrangement using a gas mixture of 0.1 vol. % O2 in N2 at atmospheric pressure was investigated by means of electrical and optical diagnostics, accompanied by fluid dynamics and electrostatics simulations. A higher flow rate perpendicular to the electrode symmetry axis resulted in an increased breakdown voltage and DBD current maximum, a higher discharge inception jitter, and a larger emission diameter of the discharge channel. In addition, a shift of the filament position for low gas flow rates with respect to the electrode symmetry axis was observed. These effects can be explained by the change of the residence time of charge carriers in the discharge region—i.e., the volume pre-ionization—for changed flow conditions due to the convective transport of particles out of the center of the gap.

A planar volume dielectric barrier discharge (DBD) in pure carbon dioxide (CO₂) for the formation of carbon monoxide (CO) is examined by combined electrical and CO density measurements. The influence of the type of electrode, the barrier material, the barrier thickness, and the discharge gap on the plasma power and the CO formation is analyzed systematically. The electrical characterization by means of charge-voltage plots is based on the simplest equivalent circuit model of DBDs, extended by the so-called partial surface discharge effect and the presence of parallel parasitic capacitances. The stackable discharge arrangement in this study enables one to elucidate the influence of parasitic capacitances, which can be overlooked in the application of such plasma sources. The determination of the discharge voltage from charge-voltage plots and the validity of the so-called Manley power equation are revised by taking into account non-uniform coverage as well as parasitic capacitances. The energy yield ($EY$) of CO is analyzed and compared with the literature. No correlations of $EY$ with the mean reduced electric field strength or the geometric parameters of the DBD arrangement are observed.

A non-thermal plasma source based on a surface dielectric barrier discharge (DBD) is developed for purification of recirculating air in operating theatres in hospitals. This is a challenging application due to high flow rates, short treatment times and the low threshold for ozone in the ventilated air. Therefore, the surface DBD was enhanced in order to generate an ionic wind, which can deflect and thus, filter out airborne microorganisms. Electrical and gas diagnostics as well as microbiological experiments were performed in a downscaled plasma source under variation of various electrical parameters, but application-oriented airflow velocity and humidity. The dependence of electrical power and ozone concentration as well as charged particles in the plasma treated air on frequency, voltage and relative humidity is presented and discussed. The presence of humidity causes a more conductive dielectric surface and thus a weaker plasma formation, especially at low frequency. The airborne test bacteria, Escherichia coli , showed significant effect to plasma treatment (up to 20% reduction) and to plasma with ionic wind (up to 90% removal); especially a configuration with 70% removal and an accompanying ozone concentration of only 360 ppb is promising for future application.

The effects of nitrous oxide (N $$_2$$2 O) in nitrogen (N $$_2$$2 ) on the development and morphology of sine-driven dielectric barrier discharges in a single-filament arrangement were studied. Detailed insight in the characteristics of the discharge and its development were obtained from electrical measurements combined with ICCD and streak camera recordings as well as numerical modelling. A miniaturised atmospheric pressure Townsend discharge (APTD) could be generated for admixtures up to 5 vol% N $$_2$$2 O in N $$_2$$2 although N $$_2$$2 O is an efficient collisional quencher of metastable nitrogen molecules. Increasing the high voltage amplitude led to a transition into a hybrid mode with the generation of an intermediate filament in addition to the diffuse, non-constricted APTD. A time-dependent, spatially one-dimensional fluid model was applied in order to study the underlying mechanisms causing the diffuse discharge characteristics. It was found that even for small N $$_2$$2 O admixtures, the associative ionisation of atomic nitrogen and oxygen (O + N( $$^2$$2 P) $$\rightarrow $$→ NO $$^+$$+ + e) is the major electron source sustaining the volume memory effect and is therefore the reason for the formation of a diffuse APTD. Graphical

Experimental studies of single-filament dielectric barrier discharges (DBDs) in a 0.1 vol% O ₂ in N ₂ gas mixture were performed with high spatial and temporal resolution. For the first time, the axial and radial dynamics and electrical characteristics of the DBDs were recorded by high-resolution imaging of the discharge emission combined with synchronised, fast electrical measurements. The axial propagation of the positive streamer and the radial expansion of the discharge channel were studied and correlated to each other. The analysis of the radial dynamics allowed the separation of the streamer propagation and the transient glow phase during channel formation. It was found that the discharge channel widens when the streamer hits the cathode surface and that both the diameter and the radial expansion velocities of the streamer increase with increasing axial propagation velocity. The synchronised quantification of the axial and radial streamer dynamics allowed the estimation of the electric field in the streamer head. Additionally, the time-resolved current density was determined by combining current measurements with fast imaging of the radial discharge development during streamer and glow phase.